Industrial Minerals of Mozambique

Cilek: Front page

Contents Page of the Book

Industrial Minerals of Mozambique

by Dr. Václav Cílek

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Cilek: Front page

View from Isla Mozambique photo by Dr. Václav Cílek (250 kB)

BOOK REVIEW (2 kB)

1. INTRODUCTION (6 kB)

2. GEOLOGICAL REVIEW of Mozambique (61 kB)

3. DEPOSITS of INDUSTRIAL MINERALS

3.1 Andalusite, kyanite, and sillimanite (20 kB)

3.2 Asbestos (23 kB)

3.3 Beryllium minerals (13 kB)


Cilek: Front page

3.4 Feldspar (44 kB)

3.5 Fluorite (30 kB)

3.6 Graphite (25 kB)

3.7 Lithium minerals (15 kB)

3.8 Magnesite (9 kB)

3.9 Mica (20 kB)

3.10 Rare-earth minerals (41 kB)

3.11 Talc and soapstone (7 kB)

3.12 Titanium and zirconium minerals (46 kB)

3.13 Zeolites (9 kB)

4. DEPOSITS of INDUSTRIAL ROCKS

4.1 Bauxite and aluminum laterite (42 kB)

4.2 Bentonite - smectites (28 kB)

4.3 Clays (45 kB)

4.4 Decorative stones (29 kB)

4.5 Diatomite (18 kB)

4.6 Glass sands and foundry sands (20kB)

4.7 Gypsum and anhydrite (20kB)

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Cilek: Front page

4.9 Limestone and dolomitic limestone (52 kB)

4.10 Mineral pigments (6 kB)

4.11 Nephetine syenite (27 kB)

4.12 Perlite (14 kB)

4.13 Phosphates and apatite (34 kB)

4.14 Quartz raw materials (14 kB)

4.15 Salt (8 kB)

5. DEPOSITS and INDUSTRIAL USE of building raw materials (4 kB)

5.1 Raw materials for cement and lime production (10 kB)

5.2 Raw materials for brick production (6 kB)

5.3 Resources and production of building stone (7 kB)

5.4 Resources of sand and gravel (11 kB)

6. CERAMIC and GLASS INDUSTRY; REFRACTORIES

6.1 Ceramic industry (6 kB)

6.2 Glass industry (6 kB)

6.3 Refractories (9 kB)

7. PROSPECTIVE and POTENTIAL industrial minerals and their uses (7 kB)

8. Minerogenetic provinces and epochs (6 kB)


Cilek: Front page

9. SELECTED REFERENCES (16 kB)

© Václav Cílek 1989


Cilek: Bookreview

Industrial Minerals of Mozambique

By Václav Cílek, Prague: Czech Geological Office, 1989 Originally Paperback, 250 mm * 174 mm, 326 p. ISBN 80-7075-027-8 Not for sale

This is a most important landmark book on Mozambique coming at a time of improving outlook for the country. The disruptive 15-year civil war between Frelimo government and the Renamo guerrillas has meant that numerous industrial mineral deposits and prospects have lain dormant and so Dr. Cilek's review of the industrial minerals sector provides a useful plank for the launch of renewed interest in exploration and development.

Surprisingly, the Geological Survey of Czechoslovakia opted for publication in English in preference to Portuguese, the official language of Mozambique. Furthermore, in view of the country's tiny output of industrial minerals, another surprise is the massive size of the publication - 326 pages. Whereas English language and completeness are very helpful many passages of text are poorly edited and detract from the overall presentation.

The order of presenting the principal information adopts the conventional A-Z format, first for industrial minerals (andalusite to zeolite) then for industrial rocks (bauxite to salt). In the final sections the author discusses construction materials, manufacturing applications and future prospects. Each commodity is introduced with background information and a general overview followed by a detailed description of all known deposits and occurrences within Mozambique and presentation of all the available data. These commodity sections finish up with appropriate conclusions and summary comments.

The material assembled provides an up-to-date record of the current knowledge about Mozambique industrial minerals and should be of considerable interest to those in the mining industry contemplating ventures into this underdeveloped and under-explored region.

Book review: D. Nichol, Minerals Industry International, March 1991, p. 19.

The idea of electronic version of the book started when I had read the book with great interest and then later met Dr. Vaclav Cilek two times. His positive reaction and permission about copyright made it all possible. The electronic version of the book started intensively in winter 2001/2002 when all the text pages were scanned at VTT with the generous help of Mr. Eero Hietalahti. During the spring and summer 2002 all the figures were scanned and editing work was started by Prof. Veikko Komppa,

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Cilek: Bookreview

originator of the project. Digitizing a printed book is not so straightforward business because technical and chemical text is full of errors after scanning. Also the tables do not scan properly. Tables and bad pages were mainly corrected by myself or by Ms. Mervi Efraimsson.

The purpose of this e-version was, and it still is, to be used as a basic reference and training book when World Bank's Mozambique Project will start in the area of the Industrial Minerals. The e-version will be improved gradually but due to minimal resources allocated at the moment for the work, nothing fancy will be produced.

Father of the e-version:

August 2002, Prof. Veikko Komppa, VTT Processes


Cilek: 1. Introduction

1. INTRODUCTION

Mozambican resources of industrial minerals and rocks are large enough to cover most of the requirements of the national industry and to contribute also to the export. The most recent data on more than forty industrial raw materials of Mozambique will help the geologist, the mining engineer, the planners and decision-makers in the government to find the best solution for the present and future industrial development. This first book on Mozambican resources of industrial minerals and rocks intends to present basic data on non-metallics which are of great importance in the development of a number of common industrial branches. Economic recovery and development cannot take place without a progress in the building and silicate industry, chemistry, agriculture and environmental protection. And just industrial raw materials - known also as non-metallics - are the main basis for this development. Being bulk materials they must be extracted and utilized locally because are cheap materials and cannot be imported. Besides the bulk materials, modern industrial minerals include also several valuable raw materials mined in small quantities and which after the beneficiation can become the most important in our era of the new technical revolution.

The primitive man started to utilize nonmetallic materials in the production of stone axes or spears with stone points, or clay in the pottery production. In the Bronze Age, and later the Iron Age, stone implements were replaced by metallic ones and this started the industrial revolution which led to a heavy abuse of mineral resources, to economic tremors of the present days. The new technological revolution returns to a utilization of industrial minerals and rocks, naturally on much higher level than during the Stone Age. The new technical revolution is the new era of non-metallics. This era substitutes expensive copper by common silica, special metallic alloys by ceramic masses in the space industry, metallic engines by the construction of ceramic engines that are better than the metallic ones, microelectronics use structural properties of cheep silicate materials, miniaturization is based on the use of rare earth elements and new composite materials display extra ordinary properties by combining metallic and nonmetallic materials. But even the common products of the modern silicate industry, when using nontraditional processes, can attain special properties - special cements can be used for the production of hulls of ships, ultra fine ground limestone can substitute kaolin in paper and save about 30% of synthetic material when used as a filler, besides an improvement of physical and mechanical properties, smectites (bentonites) and other absorbing materials can save up to 70% of fertilizers in sandy soils which otherwise could be washed away etc. Most of these materials are present in Mozambique, but have not yet been investigated. One of the weakest points of the utilization of Mozambican mineral raw materials is the low degree of technological research both in the field of "progressive" materials, and in the production of such common products as bricks and tiles, leaving alone the white ceramic production, refractory materials etc.

Abundant industrial mineral resources are kaolin, materials for refractories, high quality graphites, metallurgical grade fluorite, large reserves of nepheline syenites, rare-earth minerals, zirconium and lithium minerals, large reserves of gypsum and anhydrite (also for sulphuric acid production), glass sand, limestone and diatomite. Also building materials are ubiquitous.


Cilek: 1. Introduction

Missing or in small quantity or of a low quality are white ceramic clays (ball and bonding clays), industrial salts, asbestos, magnesite and dolomite, vermiculite, of the chemical materials these are sodium carbonate and sulphate, borates, bromine, iodine and nitrates; phosphates (apatite) are abundant but of low quality.

The volume is introduced by a brief review of the Mozambican geology and mining.While the knowledge of the Archean and Precambrian regions in the W a NW is good and adequate to the needs of a mineral exploration, the situation in the NE comprising the provinces Niassa, Nampula and Cabo Delgado is somehow obscure in spite of the fact, that a new geological map, scale 1 :1,000 000, has just been published. This region needs a detailed geological mapping and further exploration work for graphite, marble, nepheline syenite, ultrabasic rocks, kimberlites and pegmatites must be supported.

The raw materials are divided in three parts in alphabetic order: * deposits of industrial minerals * deposits of industrial rocks * building materials.

The last part of our short review deals with the production of cement and lime, brick industry and a survey of resources of building stone, sand and gravel. This is followed by a chapter on ceramic and glass industries and some proposals for a future production of refractories.

The book is concluded by a short review of prospective materials and minerogenetic provinces and epochs.

The selected literature contains just fundament publications and reports.

Several paragraphs dealing with particular raw materials are complemented by conclusion and recommendation expressing the author's opinion on the subject. It is hoped that some of these conclusions will be changed in the future hand in hand with an increasing knowledge of the geology of non-metallics and a subsequent industrial development.

Mozambique can supply the neighboring countries of SADEC (Southern Africa Development and Economic Cooperation) with a number of industrial materials - kaolin, feldspar, diatomite, glass sand, products of nepheline syenite beneficiation, talc, bentonite and materials for refractories. Of the group of building materials, the country can export cement and lime of the highest quality. It is also hoped, that sulphuric acid could be produced on the basis of anhydrite utilization in addition to a substantial quantity of fertilizers.



Cilek: 2. Geological Review of Mozambique

2. GEOLOGICAL REVIEW OF MOZAMBIQUE

Mozambique - Republica Popular de Moçambique - covers an area of 799,380 km2 and extends from 10°27' northern latitude at the mouth of the river Rovuma to 26°52' southern latitude at Ponta d'Ouro. It is bordered in the N by Tanzania, in the W by Malawi, Zambia and Zimbabwe and the SW by the Republic of South Africa and the Kingdom of Swaziland. It has 12,130 000 inhabitants (1980 consensus) with an average density of 15 inhabitants per km2 and is divided into ten provinces.

Geomorfological division: this is based on a series of belts in decreasing altitude from the interior to the Indian Ocean coast. Mozambique covers mainly the coastal belt fronting on the sea; its important ports serve the interior African states. There are four principal belts: 1. Interior belt above 1,000 m altitude with several mountains above 2,000 m near the Zimbabwe border-Precambrian 2. Alto Planalto belt, 1,000 to 600 m altitude, with an escarpment on the NE - Precambrian-Karroo 3. Medio Planalto belt, 600 to 200 m, Lebombo Mts. altitude 600 m 4. Planicie -belt of lowlands with elevations between 200 and 0 m savanna landscape, dunes, marshes, lagoons. Good information on Mozambican geomorphology is available from the map "Carta Geomorfologica", scale 1:2,000 000, elaborated by S. Bondyrev in 1983.

The main rivers, from N to S: Rovuma river fronting on Tanzania in the N, opening in a delta (deposit of heavy minerals at Msimbati - Cilek 1976); the Lurio river with a small delta; the Zambezi river, length 850 km. It enters Mozambique at Zumbo, narrows to enter an artificial lake at Cabora Bassa, than narrows again past the town of Tete to enter the Lupata Gorge. Then it crosses the East African graben which is traversed from N-S by the younger Urema-Chire graben which served, originally, for a deviation of the flow of the Zambezi along the Cheringoma escarpment to the present port of Beira; the Save river with a small delta and, in the south, the rivers Limpopo and Incomati. The capital is Maputo, former Lourenço Marques, an important port in the south with railway links to RSA, Swaziland and Zimbabwe. In the centre of the country, port Beira serves the transport to Zimbabwe and interior regions with the town of Manica (former Macequece), an old mining centre with gold production and a geological museum, further the town Tete in the Zambezi valley with important coal mines at Moatize, with links to Malawi. On the NE side of the Zambezi delta the port Quelimane handles exports of the Zambezi Province (tea, copra, lobster and sugar). The main port of N- Mozambique is Nacala with railway links to Malawi and the lake Niassa. The division of Mozambique into the provinces is shown in Fig. 2.1.

The geological situation of Mozambique has been described in various comprehensive publications. The first book on this subject with simple geological map, was published by Andrade (1929); Borges made the similar compilation in 1940 and 1949, Freitas in 1957. The last geological maps of the Mozambican territory were made by Oberholzer (1966,1968-Carta geologica 1:2,000 000) and Alfonso (1978).

Fig.2.1 Administrative Divisions of Mozambique (189 kB)

After the independence in 1975 most of the country was almost unknown except for the main deposits found by prospectors and hunters such as pegmatites of the Alto Ligonha district, graphite at Angonia and Nampula, coal at Moatize, gold at Manica and many small deposits of semiprecious and precious stones. According to Jourdan (1986) 66% of systematic geological work was done between 1975 and 1983 by experts from

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Jugoslavia, USSR, GDR, Sweden, UK, France, Italy, Bulgaria, Czechoslovakia, UN-agencies and, of course, by local Mozambican geological brigades. After 1983, most of the field activities was hampered by the actions of antigovernmental forces, but despite this, the geological evaluation programme was started and several basic geological works originated or were in preparation: Hunting Geology and Geophysics Ltd. edited an comprehensive report (1984) about the central and southern part (Tete, Sofala, Manica Provinces), ENH - Empresa Nacional de Hidrocarbonetos de Moçambique (1986) concluded the evaluation of sedimentary basins and finally BRGM published a geological map, scale 1 : 1,000 000, with explanations (1986). These three latter publications were used as a basis of the present geological review.

The development of the Mozambican Precambrian was depending on the geological evolution of E-Africa and on the origin and the separation of the Gondwana continent. The continental fit is presented in Fig. 2.2. The old Gondwana in the E-African region was built by the continental nuclei - the cratons of Dodoma, Congo, Bangweulu, Zimbabwe and Transvaal of the Archean, to the Middle Proterozoic (3,800 - 2,500 m. y.); around their passive continental margins was deposited the flyshoid facies during the ifumide orogeny (1,800 - 1,300 m. y.). This flyshoid deposits can be traced over a distance of 5,000 km and are known as Group Muva in Zambia and Group Rushinga in Mozambique, followed by the development of a volcanic arc of the Sasare type and completed by strong granitization around 1,300 m. y. ago. The structural development of the Mozambique belt within the Gondwana continent was complicated further during the Mozambique orogenic phase and by the Pan-African orogenic phase along the craton margin as seen in the Group Zambue in the NW corner of Mozambique. The central Gondwana in the area of today's Mozambique was "cut" across by two distinctive tectonic belts, probably collision zones, which were reactivated during 1,100 - 900 m. y. and represented in the W by the Mid-Zambezi graben -the Mylonite Zone of Hunting (1984) see Fig. 4. 4. 2, and by the Lurio belt in the E. These zones of ENE - WSW direction, which are in fact a continuation of Damarides of Zimbabwe and Botswana, are at present interrupted in the middle by the East-African rift valley of N - S direction. This prominent rift is the original structural element of the Pan-African orogeny (500 ± 100 m. y.) which is represented in Mozambique by the deposition of the Group Cobue in the extreme NW. On the border with Tanzania it continues to Malawi and Tanzania and is accompanied by several parallel zones both W and E. The present and still active East-African rift represents a modern separation of the continental plate, a specific African phenomenon.

Fig.2.2 The continental fit of the old Gondwana continent according to Smith and Hallam (1979) (363 kB)

The Mozambican Precambrian was divided into three provinces: * the Mid-Zambezi Province * the Niassa Province * the Mozambique Province. The same division was accepted by BRGM (P. Pinna, 1986), in the description in "Explanations to the new geological map" * the southern region, S of the Mid-Zambezi Graben and along Zimbabwe * the northwestern region, N of the Mid-Zambezi and W of the East-African rift * the northeastern region, E of the East-African rift (see Fig. 2.3.).

Fig.2.3. Structural scheme of Mozambique and surroundings (BRGM, 1987) Part 1 (1182 kB)



Part 2 (254 kB)

Structurally, the Precambrian can be divided into four big main units: 1. Archean-Proterozoic Inferior, 3,800-2,500 m. y., covering the border zone with Zimbabwe; it is a prolongation.of the Zimbabwean "greenstone" belts and younger "granitic-gneiss" Complex of Archean and part of Proterozoic terrain of cratons margin (Group Gairezi) 2. Precambrian B, 1,800 m. y., the Group Umkondo, metasediments and volcanics resting with unconformity on the craton, the Umkondo cover is almost not folded 3. Precambrian B, beginning of PrecambrianA, 1,300-900 m. y., the regions with strong orogeny can be divided into two principal cycles:

a) continuation of the irumidian belt of Zambia (Supergroup Muva) into the NW corner of Mozambique (Group Zambue etc.) and reworking of this belt by subsequent orogenies along the craton's margin during Precambrian B with orogenic phase at about 1,300 m. y. b) the Mozambican belt which covers the largest part of the Precambrian; as a Mozambican orogenic cycle, it can be divided into three episodes: 1) the depositional epoch called "pre-Mozambican" aged 1,800? - 1,000 m. y. corresponds with the Kibarian epoch with deposition of supracrustal sediments in connection with a stretching of the continent - the Supergroup Chiure in the Mozambique Province was deposited as a volcanic-sedimentary sequence on the crust and Group Mecuburi with deposits of an active continental margin (see later) 2) the convergence epoch (1,100 - 900 m.y.) with intense origin of igneous material in two zones as: Granulitic Complex with transformation (from W to E) of all igneous rocks of charnockite composition s. 1. to alkaline and tholeiite rocks and granulites, with examples of the Luia Group at Angonia in the Niassa Province and the Unango Group and Supergroup Lurio in the Mozambique Province (see the granulitic Mozambican axis on the structural map Fig 2. 3); as Migmatitic Complex of Supergroup Nampula (see structural map) with migmatites, granitoids, migmatoids of calc-alkaline composition 3) the crustal separation epoch according to Pinna (1986) with thrusting accompanied by metamorphosis of Supergroup Lurio and Chiure over the Nampula Supergroup over a distance of several hundred kilometres both N and S of the Lurio belt. The complexes are granulitic and supposed allochthonic with an upper part of gneisses and mylonites of supracrustal origin. In my opinion, such orogenic events with "nappes" known for example from Alpides are hardly to be expected to occur in the Mozambican belt. An overthrusting is, of course, common and connected with the zones of collision or with doming along the massifs. In neighbouring Tanzania the corresponding Usagaran System to Lurio and Chire Supergroups is generally divided in two-level units, the lower one with granulites and granites overlain by metasediments of upper unit. The upper part of the Supergroup Lurio consists of gneisses and ultramylonites of supracrustal origin of an ancient hiatus of oceanic deposition and, in my opinion, corresponds with the upper metasedimentary level of Usagaran in Tanzania. The "allochthonous" members-the Supergroups Lurio and Chiure are therefore probably erosion remnants of the upper-level member resting on the Nampula Super group. The process of convergence and crustal separation is accompanied by intense granitization. 4) Pan-African cycle represented by: a) deposits of the Katangan age discordantly overlying the Mozambican granulites in extreme NW (750-500 m. y.) of Groups of Geci and Cobue. They are of periglacial and glacial origin, post-Mozambican and correspond with the Katangan Supergroup of Zaire and Zambia b) intense tectonic activity on the Mozambican basement with fold axis ENE-WSW and NNE-SSW direction with intrusive "stocks". The main mobile structures of this cycle are the Zambezi and Lurio belts. Several



granitoid synkynematic massifs developed in the NW, and ring structures in the Lurio belt (500 ± 100 m. y.).

Description of Precambrian provinces

A. Mid-Zambezi Province is divided into two geological groups-the Archean craton with its margin and Precambrian complexes developed between the Craton, Mid-Zambezi graben or the Mylonite Zone of Hunting (1984) and Phanerozoic deposits in the E. The Mylonite Zone as a main structural line divides the southern province from the northern Niassa Province which is composed largely of granite, while the southern province consists more of metasediments. The Archean Zimbabwean craton comprises the Manica belt-group Manica as a prolongation of the Zimbabwean Umtali belt near the town of Manica. The Manica group is divided into the Macequece Formation composed of serpentinites, ultrabasic rocks, tremolitic schists and quartzites and the M'Beza-Vengo Formation consisting of conglomerates, sericite-chlorite schists and marbles. South of Manica the greenstone belt corresponds with the Cronley belt of Zimbabwe. Small relicts of the greenstone belt are known to occur E of the craton in the Barue Formation, e. g., at Honde with iron deposits or at Mavita with asbestos and talc deposits. Among younger members of the Archean are granitoids and orthogneisses either of an oriented or nonoriented structure. The Archean terrain is known for its gold mineralization in quartzites, banded ironstones and veins, asbestos and talc and copper. The marginal formations include the Gairezi and Fronteira Groups and the Group Umkondo. The Gairezi and Fronteira Groups consist predominantly of orthoquartzites and pelitic and semi-pelitic schists with a widespread occurrence of kyanite and staurolite together with andalusite and sillimanite. Both groups are folded and tectonically disrupted. The Umkondo Group occurs S of Manica overlying the craton in a tabular arrangement, and S of the Limpopo belt. It is composed of calc-silicate sediments, gray-wackes, red beds, quartzites and overlain by andesitic lavas. The age corresponds with the Roan beds of Zambia and, together with the Gairezi Group, the Umkondo is part of Irumides (1,800-1,300 m. y.).

The Middle-Upper Proterozoic is represented by irumide orogeny along the margin of the craton, with deposition of the Groups Rushinga and Gairezi as an equivalent of the Supergroup Muva of Zambia dated to before 1,350 m. y. by the main orogenic phase - Mozambican aged 1,100 - 900 m. y., accompanied also by the longest depositional phase. Two main groups are developed: 1. Group Rushinga 2. Group Barue The Rushinga Group is composed of metasediments mainly with manganese mineralization represented by the minerals of spessartite, rhodonite, rhodochrosite and by gneisses and migmatites of a late Mozambican aqe (850 ± 40 m.y. ) The Barue Complex is a prominent belt in S-Mozambique with typical metaintrusions of calcium-alkaline composition accompanied by crustal granitoids. Most of the sequence is probably of Mozambican age (1,100 - 800 m. y.), part could be pre-Mozambican (1,800 -1,100 m. y.). The Complex Barue is further divided into five groups: Group Matamba of gneisses, probably a lateral equivalent of the Rushinga Group Group Changara, charnockites and amphibole gneisses Group Madzuire with gneisses, granitoid rocks and anatexites: in the E there are typical marbles and quartzites at Metotola, in the W, alumina-gneisses with sillimanite Group Canxixe with orthogneisses and migmatites



Group Nhamatanda with gneisses, micaschists, talcschists and sericite schists with andalusite, metabasites and iron-quartzites probably of Archean age?

B. The Niassa Province or NW region is delimited by the grabens of Chire and Zambezi which originated along the old Precambrian lines and were filled up later by Phanerozoic sediments. Rocks of the Mozambican belt underwent polycyclic and multistructural development during Precambrian B and A. All three orogenic cycles are traceable: cycle of irumide with deposition of the Fingoe Group and a small part of metasediments of the Group Zambue including metamorphosis, tectogenesis and intrusions of Pre-Fingoe granites; in most parts of the region the Mozambican cycle shows a high grade regional metamorphosis and intense granitization within the groups of Zambue, Luia, Angonia together with intrusive massifs of anorthosites, charnockites, granodiorites and granites; the katangan cycle is marked by a discordance inside the Group Fingoe and other similar units and is terminated by a polyphase tectogenesis and granitization of Pan-African orogeny. The region is composed of five different groups: 1. Zambue, probably Precambrian B 2. Luia and Tete gabbro-anorthosite Complex 3. Angonia 4. Pre-Fingoe granites 5. Fingoe cycle The Group Zambue covers the NW part of the country and is composed of gneisses and migmatites with several layers of marbles and quartzites. The age of some migmatites is 940 ± 60 m. y. Micaschists with sillimanite are known from contact zones of metadiorites with ironstones at lower levels. Younger Post-Fingoe granitic massifs extend along the NE-SW axis and are of katangan age. The group originated during the irumide cycle and the deposits are passive margin sediments which later were substituted by volcano-sedimentary rocks of an active margin eventually in the zone of subduction at about 1,300 m.y. ago. The Group Luia is divided into three different lithological units: the Group Luia with highly metamorphosed gneisses, migmatites, garanulites, cataclasites and blastomylonites is further divided into the Chacocoma Formation and the Chidua Formation which represent the floor of gabbro-anorthosites of the Tete Complex. The Chidue Formation with distinct marbles and ironstones contains W, Cu, Ni and Co. Of importance is the gabbro-anorthosite Complex of Tete with gabbros, norites, anorthosites and pyroxenites with magnetite and ilmenite with vanadium. Its age is 940 ± 175 m. y., but the main magmatic episode falls into the early Mozambican cycle of (1,100 - 1,000 m. y.). The last unit is composed of old charnockites and granitoids aged about 1,050 +20 / -10 m.y. (orthogneiss of the Chipera Complex). To it belongs also brown granites consisting of enderbites, mangerites, leucocharnockites etc. The Group Angónia situated in the NW of the country fronting on Zambia and Malawi, is composed of gneisses, metabasites, meta-anorthosites, mangerites and granitoids. The structural pattern is N-S and NW-SE (area of Domue and Zobue) with the large granitic massif of Desaranhama. In the Ulongué belt of NW-SE direction the known deposits of graphite and limestone have been exploited. Also asbestos is present. The Pre-Fingoé granites are of crustal origin composed of damelites and granodiorites, aged 940 ± 60 m.y. They have been encountered in the groups Luia, Angónia and Zambue. The Fingóe cycle is composed of supracrustal groups of Fingóe, Mualadzi and Mchinje. The Group Fingóe is a belt extending in ENE-WSW direction about 150 km long, from Monte Atchiza to the E of town of Fingóe. In the SW end is the Monte Atchiza complex with ultrabasic rocks of peridotites, serpentinites, pyroxenites,



gabbros and norites intruded in Fingóe metasediments and metavolcanics, and both are intruded by Post-Fingóe granites. The Fingóe Group is a typical of cipolinos (marbles and metadolomites), talc, schists and amphibolites, quartzites and metaconglomerates with skarn deposits in contact zones of gold and copper. The Group Mualadzi continues into Zambia as the Mwani Formation of a similar composition to that of the Fingóe Group. The Mchinje Group covers the batholite of Desaranhama with schists, gneisses and quartzites.

C. The Mozambique Province or NE region is the biggest of all Precambrian provinces. In the W, it borders the East-African rift valley - the Chiré and Niassa graben, in the N the river Rovuma; its remaining eastern boundary is formed by a coastal strip along the Indian Ocean. Generally, two structural units can be distinguished: 1. NW region along the eastern shore of Lake Niassa represented by extensive granulites and charnockites of Mozambican age, 1,100 - 900 m.y., reworked on the western margin during the Pan-African orogeny, 500 ± 100 m.y. The Mozambican granulites originated from a separation of the mantle from the crust. The main representative is the Group Unango composed of granulitic othogneisses of either an alkaline or tholeiites composition. 2. Mid- and E region in ENE-WSW direction, divided into two parts by the Lúrio belt. On both the northern and southern sides, two structural crustal levels can be distinguished: an upper granulitic level represented by the Supergroup Lúrio (allochthonous according to B. R. G. M., 1986) of the subduction zone the Supergroup Chiure of supracrustal origin and the lower granitoid and migmatic Supergroup Nampula on the SE. The tectonic contact zone between these two structural levels represents a crustal coupling. According to a new concept suggested by the B. R. G. M. (1986) with regard to a structural development of this region and, in fact, of the whole Mozambican belt, the E-W trending Lurio belt is an important collision zone of the Central Gondwana, along which a subduction of the plate occurred with a partial melting of the mantle. During a separation of the crust, large crustal and supracrustal units were thrown over large distances. However, all this will have to be confirmed by reliable evidence. The Supergroup Nampula in the SE part of N - Mozambique has a special structural position as a nucleus of antiform outcropping from overlying folded Pan-African units. It appears to be an old crustal remnant of the continent which had later been rejuvenated. It could be interpreted as an island arc or an active continental margin nowadays made up of calc-alkaline igneous rocks of the melted mantle aged 1,100 - 1,030 m. y., calc-alkaline-potassium igneous rocks aged 1,050 - 950 m. y. of crustal contamination and of synkinematic granites and leucogranites of the same composition as previous ones aged 1,020 - 950 m.y. Some granitoids are probably of cratonic origin of the Archean or lower Precambrian age. Typical of the whole Nampula Supergroup is the absence of alkaline and tholeiitic rocks. The Mozambican orogeny is the main event of 1,100 - 950 m.y. age which represents a crustal convergence followed by a denudation phase up to 750 m.y. Between 800-and 450 m. y., the Mozambican structures were reworked with a folds in N-S and NE-SW direction. The structurally important Lurio belt has been active since the time of the Mozambican orogeny, with a subsequent fold overthrusting with vergence direction towards SSE (B. R. G. M., 1986 - Monapo structure as tectonic remnant on Nampula Supergroup with transport of 150 km?) and new movements with vergence direction towards the NW during the Pan-African cycle, terminated by the origin of the Pan-African granites and Alto Ligonha pegmatites at 500 ± 100 m.y. The whole Mozambican province is divided into a western structural region and an eastern structural region. a) The western structural region on the northern side of Lake Niassa is composed of: Group Meponda of highly metamorphosed supracrustal units with a late -magmatic mineralization of Monte Naumar (nepheline syenite, hyperalcaline essexites, carbonatites with U, Nb, RE, Ta in the fracture zone) Group Unango of charnockites with mineralization of U, Nb, RE apatite in nepheline syenite and carbonatite at Lucuisse N of Lichinga -1,070 - 1,020 m.y. Ultramylonites of different age Groups Geci and Colue of katangan



metasediments (marble at Malulo) b) The eastern structural region is typical of granulitic complexes overlying migmatitic and granulitic units ("nappes" of B. R. G. M., 1986) and divided by the mobile Lurio belt in southern and northern sectors. i) The southern - Nampula-sector consists mainly of granitoids and migmatites with over 50% in the Nampula Group, nodular sillimanitic rocks in the Mecuburi Group and later synkinematic granitoids in "nappes" of several other groups. The Supergroup Lúrio, of a granulitic metamorphic grade, is represented by synform structures of Monapo (with apatite deposit of Evate) and Mugeba with several lithological units overlying with disconformity the older Nampula group. Overlying groups contain typical metasediments of supracrustal origin such as cipolinos, graywackes, schists, quartzites together with metabasites, metagranites, granulites and mylonites of a tectonic "melange" composition. ii) The northern region, N of the Lúrio Group along the river Lúrio, has a similar composition to that of the southern sector. It is divided into basement migmaties and granitoids which can be compared with the Nampula Group. They are present as erosional remnants within the synforms in the Group Marrupa. The Marrupa Group originated during several phases; first between 1,550 and 1,250 m. y. ago with a deposition of original sediments, followed by quartz-diorites and monzonites (1,050 ± 100 m.y.), potassium granites and syenites (750 ± 150 m.y.) and alkaline granites (500 ± 100 m.y.). There are other groups of different composition.

The superstructural units are composed of mylolites and magmatic rocks in several folds represented at present by synforms such as at Montepuez with marble deposits or by antiforms at Marrupa or Meluco. They include also the Supergroups Chiúre and Lúrio of a regional extension as probable erosional remnants of one original superunit, the pre-Mozambican supracrustal zone of granulites. The Group Lúrio s. s. extending from the mouth of the river Lúrio in the E to the village of Tepere in the W is made up of gralunites and mylonitic gneisses. The Pan-African plutonic rocks of the Mozambican belt occur at Mocubela NE of Quelimane as elipsoidal massifs of monzonitic granites and leucocratic granites of 490 ± 21 m.y., in the area of Luleia as noritic gabbros, leucogranites and syenites within the Lurio belt and at Candulo near the river Rovuma of 480 m.y. Of the same age may be also rich pegmatites of the Alto Ligonha district.

The Karroo Supergroup

The Precambrian basement rocks are overlain by sediments and lavas of the Karroo Supergroup. The coal seams in the lower part of the sequence are among the biggest and most important mineral resources of Mozambique. The Supergroup is also the oldest sedimentary substratum common to the two main sedimentary basins in Mozambique: i. e., the S-Mozambique basin and the N-Rovuma basin. In Southern Africa, the Karroo is subdivided into: Stormberg series - volcanics and sandstones Beaufort series - sandstones and shales Ecca series - shales, coal seams, silt and sandstones Dwyka series - tillites and shales The age of Karroo Supergroup is the Late Carboniferous to the Jurassic, but the lower Karroo - Dwyka, is not represented in Mozambique. The oldest Karroo sediments are of the middle Ecca age, followed by upper Ecca, Beaufort and Stormberg series. In Mozambique Karroo outcropping areas occur in five regions: 1. NE of Lake Niassa, from Metangula to the river Rovuma - Maniamba basin



2. scattered outcrops along the Lugenda valley towards the river Rovuma 3. Mid-Zambezi graben, from Zumbo on the Zambian border towards Tete; E of it Karroo is covered by younger sediments up to the Indian Ocean 4. narrow strip between the Lupata Group and the Gorongosa massif and between the rivers Buzi and Save 5. the Lebombo Mts. extending from Pafuri in the N to Swaziland in the S.

The history of the development of the Mozambican basins, which started already by a deposition of Karroo sediments, is typical of the evolution of passive continental margins In Mozambique, the development is dominated by rifting and flexural subsidence associated with a continental break-up and a separation of parts of the continent in this case the Madagascar plate (S. Lawrence in ENH report, 1986). During the first "Karroo" phase, a break-up of the early Gondwana continent started between the Late Paleozoic to the Early-Mid Jurassic, followed by second phase up to the Mid-Cretaceous during which the separation of Madagascar occurred by sea-floor spreading and the earliest creation of the oceanic crust. On the continental margin originated the so-called sag basins, while several tectonically bounded fracture basins developed in the interior-the original East African rift valley system with network of a tri-radial basin pattern. In Mozambique, the small Maniamba basin developed as an arm of the greater Karroo basin of Songea in Tanzania, but the main sedimentation occurred in the Zambezi graben, which is a part of Great Karroo basin of South Africa extending over the sag basins into Antarctica and Madagascar plates. To conclude this presentation of plate tectonic history it should be mentioned that during the third phase lasting from the late Cretaceous to the present the progressive opening of the Indian Ocean continues. On the continent, a system of rift basins has been established across East Africa, some following the fracture zones of earlier Karroo basins, some cutting across these grabens such as, for example, the Lake Niassa basin with an interior fracture basin formation, with a spreading of the floor, a thermal flexual subsidence and an injection of mantle material. Karroo in the Maniamba basin is an equivalent of the Beaufort and Ecca series - the lower part of the Songea Series of Tanzania with coal seams, shales and sandstones in Mozambique known as the Lunho series. The Lunho Series is about 300 m thick composed of a lower shale section, a middle limestone section and upper sandstones. The base is covered with a conglomerate, surrounding the western part of the basin. Karroo of the Lugenda valley represents erosional remnants of sandstones of the upper Ecca to the lower Beaufort series. The main Karroo basin is the Mid-Zambezi rift with Karroo sediments over 1 000 m thick split up into several smaller basins such as Moatize and Condezi near Tete or the Mucanha - Vuzi sector on the north shore of Lake Cabora Bassa. Karroo is represented by the middle and upper Ecca with several coal seams exploited at Moatize followed by Tete sandstones of the Beaufort Series overlain by Mpiusa siliceous shales. The Stormberg series is made up of sandstones (Quengene, Batonga, Forest sandstones) overlain by Batoka basalts about 300 m thick. Towards the E, in the area of Lupata Gorge the Stormberg basalts are again overlain by a conglomerate, sandstones and rhyolites of the Post-Karroo age (see Fig. 2. 4.). The economically most important part of the Karroo Supergroup is the Productive Series of lower Karroo of lower Ecca. In the Moatize basin it is about 400 m thick, with six coal complexes of which the second lowest is mined. Coal measures consist of interbedded coal seams and mudstones with thickness of 40 - 1.5 m in ascending order. The Condesi basin contains a 450 m thick sequence with five coal measures.

Fig.2.4. Stratigraphic Section of the Lupata Group at Lupata Gorge on the river Zambezi (ENH, 1986) (316 kB)



The narrow belt of Karroo outcrops from S of the river Zambezi towards the rivers Buzi and Save consists of Ecca and Stormberg Series, of about 200 m of sediments and 200 m of basalts, and partly rhyolites, dipping eastwards below Cretaceous and younger sediments. The belt terminates in Mozambique just on river Save where it rests on the Umkondo System of slightly folded low grade metamorphosed Precambrian metasediments. The same belt enters again the Mozambican territory at Pafuri and continues for about 800 km to the S along the frontier building one of the most prominent geomorphological and geological feature of the whole of South Africa - the Lebombo Range, 20 - 30 km wide and of about 600 m elevation. The Karroo rocks of the Lebombo Mts. form a monoclinal structure dipping at 10-20°/E; its bottom consists of Cave and Bushweld sandstones of the Stormberg series followed by limburgites and basalts. The generalized section is (from top to bottom): upper basalt (Movene) -137 m. y. early Cretaceous rhyolites of Pequenos Lebombos basalts and Goba sandstones rhyolites and tuffs of the Lebombo Range lower basalts -167 m. y. - Lias (early Jurassic) Cave Sandstone In Mozambique, the Movene basalt is overlain ununiformly by Lower Cretaceous Maputo sandstone. The Lebombo Mts. originated along the "rift" fracture zone from eastwards outpouring lavas. Deep boreholes E of Lebombo Mts. indicate (ENH, 1986), that the Karroo lavas continue under the sedimentary cover; however they do not form a continuous sheet of effusives, but rather a series of parallel, meridionally trending fractures issueing ever younger magma from W to E.

The Karroo Intrusive rocks are related to the younger post- Karroo (Cretaceous) large alkaline ring complexes and carbonatite intrusions situated along the rift valleys, not evident in the overlying Cretaceous sediments. These rocks are often found very far from the rift zones within the Basement Complex, for example, they are widespread at Manica in the Archean greenstone belt. Their age span is from Stormberg (Lower Jurassic) to Cretaceous (Hunting, 1984). Prevailing are swarms of dolerite dykes, porphyry and felsite. In Karroo sediments, both in outcrops and in the boreholes, sills and small stocks of microgabbro have been observed.

The Post-Karroo

The stratigraphy of Post-Karroo formations is presented on the generalized stratigraphic column (ENH, 1986). The sedimentary thickness attains 10 km, the bottom is well marked by the Liassic stage marking an unconformity between the top of the Karroo and generally the Albian -Aptian transgression. The Post-Karroo strata produce generally a wedge of minimum thickness over the exposed Precambrian; their thickness increases eastwards towards the Indian Ocean. The ENH (1986) model consists of three phases, each with its own litho-tectonic character: 1. Intratectonic basin fill-deposition of Karroo 2. Rift Valley fill of volcanics and sediments, over the Karroo deposits a deposition of continental sediments with intercalations of marine sediments in places in communication with the sea (Jurassic? and Lower Cretaceous) 3. Break-up basin fill and post break-up transgression and progradation (Upper Cretaceous-Tertiary). As it is common to passive continental margin zones these phases are separated by unconformities, sediments



are of shallow marine-littoral or paralic origin on the onshore and more on the marine offshore. Features typical of lagoonal and marine deposition of evaporites and subsequent salt diapirs known from Tanzania have not been found in Mozambique despite some indications that salt diapirs may have been present in the Rovuma basin. However, the Miocene Temane Formation of evaporites (gypsum and anhydrite) in the Mozambique basin is proof of a similar marine influence. In the Mozambique basin, the oldest post-Karroo deposits are of Jurassic age (post-Liassic). They are known from the Lupata Gorge on the Zambezi river (see Fig 2.4) and are composed of continental sediments and volcanics. S of the Save river "red beds" of continental origin that could be ascribed to the Jurassic (Middle?) were encountered in several boreholes. During the Cretaceous, three main transgressions occurred with three cycles of deposition, ranging from Aptian to Albian, from Cenomanian to Turonian and from Senonian to Eocene. Again in the E, open marine sedimentation conditions prevailed followed by neritic and finally paralic and littoral sedimentation in the W (see Fig. 2. 5).

Fig.2.5. Stratigraphic Column Karroo-Recent (ENH, 1986) (371 kB)

The Lower Cretaceous is known as the Maputo Formation of marine origin of sandstones with glauconite and tuffaceous material exposed in the Maputo river valley. This formation is overlain by a Cenomanian and Domo Formation of sandstones. The Lower to Middle Cretaceous is represented by the continental Sena Formation overlying with unconformity Jurassic rhyolites. The formation was built by one or more igneous members (phonolites) and sandy members. The facies equivalent to the Sena Formation is the Lower Domo shale (ENH, 1986) overlain by prominent Domo sandstone with gas shows and an upper member of the Upper Domo shale. The marine Grudja Formation of Upper Cretaceous-Lower Eocene age consists of Lower and Upper Grudja of glauconitic sandstones and claystones with a rich fauna. The Grudia sandstone of the Paleocene is the main gas reservoir of the Pande gas field and others. In South Africa, the Grudja is known as the Santa Lucia Formation of Zululand. In outcrops in the area of tributaries of the Limpopo river the Upper Cretaceous was described as Elefantes continental Formation, Singuedzi transitional Formation and Uanetze shallow marine Formation. The last formation shows the presence of evaporites. During the Tertiary, the stretching of the continental margin was almost complete but the development of rift basins on the continent, and partly on the shelf, continued. The filling of these rift basins was accelerated by their deepening, and different facies originated from thick delta cones up to reefoidal development. The sea transgression culminated in the uppermost Eocene and during the Oligocene and Lower Miocene the regressive stage prevailed (ENH, 1986). While the transgressive stage was characterized by the development of the marine Cheringoma Formation of reefoidal limestones, the regressive stage is typical of evaporites of the Temane Formation. Upper Grudja and Cheringoma Formations of the Paleocene - Eocene age (60 ± m.y. of glauconite, ENH, 1986) were observed in many oil boreholes, but just Cheringoma limestones are about 70 m thick and rest unconformably on the underlying Grudja (see cross section Fig. 2.6). A deposition of Salamanga limestones occurs in the S.

Fig.2.6. Diagrammatic cross-section from the Gorongosa Massif to Inhaminga (ENH, 1986) (347 kB)

The Oligocene starts with a general regresion throughout East Africa. In Mozambique Oligocene onshore is



absent, but it is thick in deltaic sediments of the rivers Zambezi and Limpopo (paleodelta of Zambezi and Limpopo - Cilek, 1985); sediments continued to the deposited during the Miocene and Pliocene. Between the Oligocene and the Miocene there is a slight disconformity and a deposition of Inharrime sandy limestones. In the area S layers of gypsum, clay anhydrite and dolomite of lagoonal origin (see Fig. 2.7).

Fig.2.7. Miocene Sedimentary Distribution (ENH, 1986) (442 kB)

The tilting of the continental margin in the Miocene (King, 1983) resulted in a marine deposition of the Jofane Formation outcropping widely along the river Save and S of it. Jofane deposits are sandy limestones, pure organic limestones and sandstones uplifted during the Pliocene. Pliocene and Pleistocene deposits are widespread throughout coastal Mozambique. A representative is the Mazama Formation of sand, sandstones and conglomerates overlying the Cheringoma limestones. Widespread sands, cemented sands, gritty sandstones of the Pliocene - Pleistocene can be correlated with the Kalahari System of SW Africa (Zimbabwe, Botswana); here, they are known as proluvial (decksand) sands (Cilek, 1985), a transitional source of heavy minerals in beach deposits. S of the river Save, sandy lacustrine limestones are found also in some narrow grabens - depressions reactivated during the Pleistocene. Igneous activity of the Post-Karroo is complex and rocks of different chemical composition are accompanied, sometimes, by a mineralization of rare earths, phosphorus, trace elements and others, thus representing valuable mineral resources. They include atractive rocks such as carbonatites, nepheline syenites and gabbros. The magmatic activy during the Phanerozoic has been illustrated as follow (for a detailed description see Chapters 3 and 4):

Age Magmatic features Type of rock with examples

Pleistocene-Paleocene vents, extrusions, intercalations in graben

1. basic-ultrabasic: Mutarara-Sena, Cheringoma, Gorongosa, Balama (augitites, limburgites, nepheline and olivine basalts)

2. alkaline: Canxixe, Gorongosa, Nhamatanda, W of Maputo

Upper to Lower Cretaceous

lava flows and volcanic vents, explosive centers, intrusive domes

1. phonolites-trachytes: Area of Lupata-Doa tuffs, pyroclastics

2. lavas, trachytes, carbonatite agglomerates: Area of Lupata, river Chicongola



3. Vents of alkaline syenites: Salambidua, Morrumbala, Milange

4. Alkaline granites: Morrumbala

5. Phonolites, Limburgite: Chandawa, Buzimuana

6. Carbonatites: Mt. Muambe, Cone Negose, Mts. uchene (Lupata), Xiluvo, Cabo Delgado 12°S, 39° E (R. Muirite), Milange, Chiperone, Derre

7. Nepheline syenite: Morrumbala, Mt. Tumbine, Zanga, Mandimba, Chandava, Chuare, Buzimuana

Lower Cretaceous-Upper Jurassic

extrussive rocks intrusions 1. basalts: Angoche-llha Mozambique (120-177 ± m. y.)

2. kimberlites: in Karroo basin of Maniamba

3. gabbros and norites, hyperites, olivine gabbro, olivine hyperite: Lichinga (syenites, monzonites etc.), Gorongosa massif

Karroo volcanics of Jurassic-Upper Karroo age:

rhyolites and ingimbrites of Lupata-Doa basalts, trachytes and rhyolites of Rio Luia rhyolites and basalts of Lupata and Canxixe acid lavas and basalts of river Buzi volcanics of Lebombo Range

The Post Karroo of the Rovuma basin

The Jurassic is not known in this border basin, but some beds near Nacala may be of Kimmeridgian-Tithonian



age (ENH, 1986). The Lower Cretaceous is developed as a thick sequence of sandstones first described by Bornhart (1900) as Makonde beds from Tanzania from Makonde Plateau. They are of Aptian age and about 450 m thick (see Fig. 2.8). Near Pemba, coarse sandstones are outcropping with overlying pelagic beds with Megatrigonia schwarzi of Neocomian age. S of Pemba there are Aptian - Albian strata, while NE Seonian beds lie directly on Neocomian beds.

Fig.2.8. Section of Rovuma basin sediments of Mozambique (ENH, 1986) (272 kB)

Makonde beds are represent a well-known transgression of the Lower Cretaceous over the Precambrian basement. The Upper Cretaceous occurs in outcrops near the W margin of the basin in the form of Globotruncana marls, with limey concretions and Gypsum flakes on the S end of the Pemba bay. These marls are of Maestrichtian age. A large part of the Upper Cretaceous, i. e., Cenomanian, Turonian and Senonian, is missing. The Tertiary-Quaternary is represented by some outcrops of Paleocene and Eocene sediments with sandy limestones as an equivalent of the Cheringoma Formation followed by deltaic sediments. Overlying Mikindani beds of Mio-Pliocene age are about 100 m thick. Quaternary sediments of coastal Mozambique are of considerable extent and thickness. They developed under unstable conditions of glacial and interglacial periods. A description is given of a thick sequence of sands, cemented sandstones, clays of marshes and mangroves, beach sands and dune sands, located of different elavations above the present sea level. The width of Quaternary deposits in the area of the Limpopo paleodelta is over 80 km, with eolian sands sheets reaching sometimes the foot of the Lebombo Mts. Important placer deposits with heavy minerals were found here (Cilek, 1985). These deposits are the only -living1' deposits in the country, being permanently moved and replenished when ever destroyed.

The mineral resources or Mozambique can cover almost all needs of the country, but just a few can be used for export. In the past, the two resources of importance were coal and minerals of pegmatites, i. e., mainly columbo-tantatite. The mining industry was small in comparison with other S-African countries such as Zimbabwe, Zambia, Republic of South Africa, Botswana and Angola. This was because, during the partition of Africa, the mineral-rich highlands of SE-Africa convenient to European settlers, became part of the English or German empire, while Portugal a small country had to make do with its coastal part. In 1983, the mining sector of Mozambique participated with 2% only in the national export earnings and its futher development was retarded by internal security problems. The mineral production illustrated in Table 1 shows that concentrates of microlite, pollucite and tantalite together with coal are the main contributors. The development of the local industry and the utilization of some minerals is shown in Table 2. Just a few minerals are used in the home industry and, besides a small amount of coal, all are industrial minerals. The original colonial character of the country's economy, i. e., a low degree of utilization of local mineral resources still prevails. During the last few years, many new resources have been investigated and reserves of different degree of verification secured, showing clearly the big potential of diversified mineral raw materials. Basing on data from different sources, the reserves are these:

Apatite 128 Mt Heavy minerals 138.00 Mt



Asbestos 0.50 Mt Iron ore 64.00 Mt

Bauxite 0.37 Mt Kaolin 2.00 Mt

Bentonite 2.45 Mt Limestone 38.80 Mt

Coal 7,577.52 Mt Marble 29.80 Mm3

Copper 0.10 Mt Mica 0.07 Mt

Diatomite 3.03 Mt Natural gas 120.00 Gm3

Feldspar 1.00 Mt Nepheline syenite 4.30 Gt

Fluorite 1.50 Mt Perlite 0.95 Mt

Gold 47 t Red clay 11.90 Mt

Graphite 40.00 Mt Silica sand 11.50 Mt

Guano 0.76 Mt Tantalum pentoxide 0.007 Mt

White clay 6.40 Mt

The main mineral resources which are being exploited or can play an important rote in the country's economy are fuels, both coal with several billion tons of resources but a higher ash content and low coking properties, and gas discovered already at Pande, Temane and other localities with an expected discovery of oil in the offshore partof the Mozambique basin. The next deposits are heavy minerals in beach and dune sands along the coast containing big reserves of world-wide importance apart from a number of valuable minerals-ilmenite, rutile, zircon, monazite and others. Next are the pegmatite bodies which have been mined for many years in the Alto Ligonha district for tantalum, niobium, lithium, rare earths, precious stones and, as a byproduct of kaolin, feldspar, mica, quartz and others. Recent investigations revealed big resources of flake graphite of high quality, fluorite in substantial quantities and metallurgical grade and diatomite of filtration grade. The reserves of other minerals and mineral raw materials can ensure both industrial development and export requirements. There is no doubt that the former underdeveloped mining industry of Mozambique may turn into a major contributor to the national income on the basis of its present reserves of mineral resources.

Table 1

1981: 50 t pollucite 1984: 89 t pollucite

Mineral Production (data Ministry of Mineral Resources)

Material unit 1978 1979 1980 1981 1982 1983 1984 1985 1986

microlite conc.

ton 42 35 25 43 30 23 10 6 2

tantalite conc. ton 40 24 26 34 22 14 7 4 3

mica scrap ton 105 101 226 300 148 39 126 - -



bismutite ton 5 8 6 4 4 1 1 - 0.08

monazite ton 6 7 9 4 3 4 2 0.16 0.1

beryl indust. ton 16 28 6 7 8 6 7 3 1.4

aquamarine cut

kg - - 5 3 2 2 3 0.6 0.8

morganite cut kg - - 2 6 4 4 11 17 4

emerald cut kg 18 0.6 0.6 0.7 2 0.03 - - -

tourmaline cut

kg 12 5 8 3 20 2 0.5 7 1.2

aquamarine pique

kg 0.5 13 4 3 0.9 0.01 - 7 1.2

morganite pique

kg - 11 0.9 2 1 - - 0.6 3.4

emerald pique

kg 3 0.5 0.7 293 94 22 - - -

tourmaline pique

ton 4 0.7 7 0.2 0.4 0.01 - 3 1

quartz rose pique

ton - - 12 12 8 5 2 - -

garnet cut ton 2 1 2 2 2 1 1 - -

garnet pique ton 7 9 8 11 9 10 5 - -

feldspar ton 682 585 921 775 696 317 185 67 -

kaolin ton 179 139 216 297 310 292 256 152 -

marble m3 60 304 299 167 561 406 577 715 1137

copper conc. ton 557 1125 691 880 1065 1189 1240 590 1303

asbestos ton 37 789 94 1425 852 - 145 56 -

bentonite ton 1976 1656 848 716 1455 250 413 361 1112

obsidiane ton 78 30

coal natural ton 236,177 319,608 408,543 534,546 66,577 58,713 66,855 20,400 -

coal dressed ton 148,916 197,458 207,263 329,621 200,863 58,122 39,917 39,466 -

External trade

M US$

1.98 6.27 6.56 7.46 1.83 2.24 2.23 5.81

value in pounds

M £ 35 31 23 24

*) Meticals - 486 m3 marble

Table 2 Internal trade of mineral raw materials

Name unit 1978 1979 1980 1981 1982 1983 1984 1985

Coal coking ton - - - - 32172 15277 1562 368



Coal steam ton - - - - 51580 21986 7178 9633

Coal total ton 81939 123128 76128 123287 83752 37263 8740 10019

Bentonite ton 200 252 205 632 595 506 830 589

Kaolin ton 200 220 280 377 270 289 210 -

Feldspar ton 400 565 1272 440 858 150 133 122

Asbestos ton - - - 14 136 - 92 7

Marble m3 211 240 223 17 266 243 - 106

Ornamental stones

million meticals

64 204 214 300 70 91 115 50

*) 1 US $ = 40 Meticals

Data supplied by the Ministry of Mineral Resources



Cilek: 3.1 Andalysite, kyanite, sillimanite

3. DEPOSITS OF INDUSTRIAL MINERALS

3. 1. Andalusite, kyanite, sillimanite

The chemical composition of the main sillimanite minerals andalusite, kyanite and sillimanite is equivalent to the formula Al2O3 · SiO2, with 62.93% of alumina and 37.07% of silica. Three other minerals topaz [Al2Si4O (OH, F)2 ], dumortierite 8 Al2O3 · B203 · 6 SiO2 · H2O and pinite (a mixture of sericite, chlorite and serpentine) are also included in this group. The presence of fluorine in topaz, and boron in dumortierite has in some countries prevented their use due to environmental problems. Topaz has a typical composition of 55-57% of alumina, 33% of silica and 16-18% of fluorine, while dumortierite as a basic aluminium borosilicate has about 64 to 69% of alumina, 28-32% of silica and 5% of B2O3. The most important property of sillimanite minerals is their refractoriness, which depends on the alumina content. It was discovered that the presence of sillimanite, andalusite and kyanite in ceramic materials improves their mechanical resistance and insulating power, but also their refractory properties. All three minerals when fused are converted to mullite of the formula 3 Al2O3 · 2 SiO2, a fibrous mineral similar to sillimanite. And just mullite is the material sought after by the refractory industry whereby sillimanite minerals, topaz and dumortierite, are merely acting as "mullite" ore. Mullite is extremely refractory, has a low coefficient of expansion, resists abrasion and slag erosion. Calcination of these minerals results in a change to a mixture of mullite and silica (88% of mullite and 12% of cristobalite) at a temperature of complete decomposition: 1,410°C for kyanite, 1,500°C for andalusite and 1,625°C for sillimanite. Dumortierite breaks down at a temperature of 1,250°C and topaz at 1,480°C, giving rise to about 95% of mullite. According to a commercial grading of sillimanite minerals, these have to contain a minimum of 54 to 56% Al2O3, 42% SiO2, 1.0-1.8% Fe2O3, 0.5% TiO2, 0.1% CaO 0.1-0.2% MgO, 0.4% K2O and 0.4-0.6% Na2O. Of mullite refractories, 90% are used chiefly in the metallurgical, glass, ceramic, and cement industries, being classified as midway between acid silica and basic magnesia refractories with 47 to 90% of alumina content. The remaining 10% are used as abrasives, in chemical and electrical industries, as part of glazes and non-slip flooring. The most modern uses are in ceramic mixtures for the production of special ceramics and composite materials in such industrial branches as spacecrafts, atomic industry and as substitutes of metals in engineering. Mullite can be by-produced synthetically by mixing, for example, kaolin and bauxite to reach an alumina content close to the mullite theoretical value of 71.8%. Minerals of the sillimanite group are found in deposits and accumulations of a different origin. Typical is their occurrence in aluminous metamorphic rocks in some of the metamorphic zones. These zones could be characterized by index minerals within the progressive regional metamorphism in which sillimanite, kyanite and staurolite represent the highest grade in descending order. Physical conditions of metamorphism may appear to be less important in the development of each mineral than the chemical composition of the rock. The main world deposits of sillimanite minerals



originated during the regional metamorphism of aluminous sedimentary rocks. Andalusite is most commonly found in aluminous shales in contact-metamorphic zones around granitic or gabbroic intrusions. It is mainly a mineral of thermal metamorphism. Kyanite occurs generally in metamorphic zones of high pressure and lower temperature in mica schists, gneisses and quartzites and could be associated with corundum, garnet and staurolite. Sillimanite, the most similar to the natural mullite, forms normally in the highest grades in regional metamorphism, at a raised temperature and a dynamic metamorphism combined with processes of metasomatism. It is usually found in metamorphic zones of granulite and amphibole facies in mica-gneisses, quartz-mica-sillimanite schists and cordierite gneisses. Sillimanite deposits have its origin also in alumina-rich rocks, but can develop in rocks of a low alumina content such as quartzites. It was proved that metasomatic processes with alumina-rich fluids play a prominent role. But it is clear that economic deposits could develop from very pure bauxitic or kaolinitic clays or clay-rich sands and silts.

The following types of sillimanite group mineral deposits are known: 1. in regionally metamorphosed rocks and contact zones, sillimanite can develop as a dissemmation or massive concentration of prismatic or fibrous aggregates this process normally beginns with the development of quartz-sillimanite-nodules (QSN) and can reach the stage of massive sillimanite in layers and lenses 2. deposits in contact-metamorphosed argillaceous rocks with the development of hornfels mainly with andalusite but also corundum, dumortierite, pyrophyllite and sillimanite 3. occurrences of kyanite in bladed disseminated crystals or massive aggregates in quartzites, mica schists and quartz veins of contact zones, hydrothermal veins and pegmatites 4. deposites of miscellaneous origin: andalusite, kyanite and dumortierite in secondary quartzites under the influence of hydrothermal and metasomatic solutions, kyanite-sillimanite deposits in mica-gneisses with graphite or staurolite of metasedimentary origin, typical quartz veins etc. 5. placers of different origin from fluviatile to beach sand deposits and dunes.

In Mozambique no economic deposits of sillimanite minerals, dumortierite and topaz have been discovered as yet. The reason for this is not their absence in Mozambique but the little attention given to these minerals in the past. Their occurrence, either mineralogical or in zones and localities which could be traced during a geological mapping is known from many places (see Fig. 3.1.1.).

Fig.3.1.1. Occurence of andalusite, kyanite, sillimanite, magnesite (336 kB)

Five main areas could be indicated: 1. occurrence of argillaceous rocks in contact-metamorphosed zones with andalusite, sillimanite and staurolite 2. occurrence of QSN, fibrous and prismatic sillimanite in high-grade metamorphic zones 3. occurrence of kyanite in NW Mozambique 4. occurrence of dumortierite in secondary quartzite 5. placers



1. Occurrence of Archean and Proterozoic Age in the Manica Province

The oldest occurrence of andalusite is known from the greenstone belt of the Manica Formation of Zimbabwe craton. Andatusite is present in the metasediments of the "Formacao do Vengo", in beds of black argillitic and sericitic schists, argillites and conglomerates. The base of the metasediments consists of granodiorites, adametlites and tonalites which are younger and crop out about 1 km northward. Andalusite is a typical contact-metamorphic mineral. It occurs at about 10 km N the town of Manica in the Serra Vengo range. In the vicinity of a Mavita asbestos occurrence, increased content was discovered: kyanite (0.5-1.0 kg/m3) and sillimanite together with kyanite (150 g/m3) was present in alluvial deposits. Another and more extensive occurrence of sillimanite minerals is known for a long time from the Proterozoic "Formacao de Fronteira", which consists of metasediments of mica-schists, banded ironstones and quartzites resting with disconformity on granitic rocks of the Zimbabwe craton and granitic gneisses of the Barue Formation. Slightly regionally metamorphosed sediments of the Fronteira Formation arranged in narrow S-N ridges, mark the eastern margin of the Archean craton. Ideal conditions for thermal metamorphosis exist in all contact zones made up of argillaceous sediments. Three main localities are known in the vicinity of Catandica (former Vila Gouveia) stretching from there northwards to Senga-Senga over a distance of about 50 km (see Fig. 3.1.2.)

Fig.3.1.2. Geological map of Catandica area (729 kB)

Serra Choa with kyanite in long-bladed crystals Barauro with andalusite and kyanite, the latter producing rich eluvial deposits from the decomposition of micaschists Senga-Senga with presence of schists with kyanite, staurolite and garnets. The content of kyanite in the rock is about 10%. Several other sites of sillimanite occurrences are marked in the geological map No 1833 (1 : 250,000) S of Catandica towards Nova Vanduzi. Some localities are within micaschists, some in narrow belts of orthoquartzites, some even in biotite-amphibole gneisses of the Barue Formation. No analyses and no industrial test are available in spite of the fact, that geological conditions for a development of economic deposits are most favourable.

2. Occurrence within the zones of high-grade metamorphism

During the geological mapping of the whole Mozambique belt, sillimanite minerals have been encountered in many places. Generally, every zone of high metamorphism, i. e., the zones of granulite and amphibole facies both in crustal and supracrustal deposits, are suitable for the origin of sillimanite minerals and corundum. From the genetic point of view, the most interesting site of occurrence is that near Montepuez in the Cabo Delgado Province. The highly metamorphosed Precambrian rocks produced two different lithotogical and structural units: the older Nampula group composed mainly of migmatites of two orogenic cycles 1,100-1,300 m. y. and 750-800 m. y. and the younger Lurio group (850-1,000 m. y.) with migmatites, biotite gneisses, leptinites and crystalline limestones.



Near the town of Namapa, in the proximity of the contact with the Lurio group, several zones of leptinites and leptinitic gneisses with biotite and garnet contain QSN (quartz-sillimanite-nodules), which, in my opinion is the first stage of a concentration of sillimanite into the massive type. Here, the sillimanite is typically fibrolithic and, together with quartz, displays a "pseudoconglomeratic" texture. Similar QSN were described also from the Mecuburi Formation in the vicinity of Ribaue and Meconta. In the area of Nacala-Memba in the coastal zone, sillimanite-plagioclase gneisses (besides quartz and biotite) are often present. Sillimanite is accompanied by kyanite, and both minerals may replace biotite. Sillimanite is found in finer prismatic crystals and kyanite in elongated crystal forms. Within the Lurio group in Chiure and the Morrola subgroup, there is a distinctive zone of quartzites with alumina minerals with sillimanite, biotite and muscovite. Around the mouth of the river Lurio, E and S of Alua, sillimanite often occurs together with garnet and graphite, located in the central zones of anticlinal structures. Close to the Monapo structure - a brachysynclinal "ring" structure with apatite, iron and graphite, which is of the same age as the Lurio group-granulites with sillimanite and granitic gneisses contain sillimanite. All these rocks are apparently of a sedimentary origin. A promising content of sillimanite and kyanite was found specially in sillimanitic-zoned quartzites of the following composition: quartz 39-80%, sillimanite 7-54% kyanite 6-7%, rutile < 1%, mica-muscovite 1%, kaolin 1-4% and Fe-hydroxides 2%. Quartzites and, in some places, also quartzitic gneisses with sillimanite and kyanite occur in the form of prominent horizons throughout the Monapo group, with kyanite anomalies up to 5 g/m3 especially in the NW part of the group and within the Ramiane Formation. Sillimanite is mostly prismatic, in grains up to 5 mm long and without fissures Sillimanite rocks were found in the eastern part of the Monapo group particulary in the Ramiane Formation and in part of the Evate Formation. There, near Netia, the content of sillimanite ranges from 10 to 500 g/m3. in the zone between Metocheria and the Evate Forma ion, NW of Naculue the content of sillimanite was higher than 50 g/m3. All zones with sillimanite are somewhat connected with quartzites. Generally, the high degree of metamorphism in the northern part of Mozambique is characteristic of sillimanite, which could also be a good indication of graphite deposits. In NW Mozambique, within the Barue Formation, reports are available of several localities with quartz veins with kyanite, and also of sillimanite in gneisses from the Gairezi Formation.

3. Occurrence of kyanite in NW Mozambique

In area of Muvudzi, about 40 km NNW of Tete severa1 pegmatite bodies and quartz dykes were discovered in the past. The mineralized bodies are situated within the Tete massif and the locality Mavudzi is known as a now exhausted source of radioactive minaral davidite. Kyanite is present in the veins of quartz in massive aggregates several kg in weight with bladed dark grey sligthly greenish crystals. Apparently its concentration was brought fort under the influence of hydrothermal solutions and thermal metamorphism. Around the northern margin of the Tete massif, the development of a contact zone with metasediments of the Fingoe Formation - schists and crystalline limestones - coincided probably with the development of andalusite and kyanite. It is of interest that a massive kyanite deposit is being mined in Malawi alonq the border with



Mozambique (NE-part of the Tete province), and that disseminated kyanite schists are present in the district Ncheu, at Kapiridimba, just at 1.5 km NE of the border (of beacon 22). Malawi rocks (gneisses and granulites) belong to the Mozambican Angonia Formation, and kyanite-bearing rock is present at Tsangano on the Mozambican side. In the Satambidwe Hill (Necungas)-a ring structure of syenite intrusion surrounded by Karroo sediments -a contact zone with hornfels was discovered just at the border with Malawi. About 30% of the rock is made up of andalusite in short, idiomorphic, prismatic crystals, accompanied by graphite derived from clay-marl sediments of the Karroo. Andalusite occurs in intergrowth with plagioclase.

4. Dumortierite in secondary quartzite

One locality of dumortierite only is known from Mozambique; it is situated on the southern side of the Cabora Bassa dam along the road Chicoa-Estima. The dumortierite quartzite is a very distinctive rock of cobalt-blue colour, sometimes greyish, hard and massive, occuring in fragments, 10 to 20 cm long, scattered on the surface. It is commonly used as an ornamental stone. Dumortierite is developed in small crystals of prismatic shape and in aggregates of radial structure in fine grained quartzites. The quartzite forms apparently lenses and irregular bodies along the fault zones between Karroo sediments and Precambrian rocks of granulites, pegmatites and porphyrites. Results of the chemical analysis (in %):

SiO2 61.48 CaO 1.75 P2O5 0.01 SiO2 0.71

Al2O3 16.60 Na2O 0.05 TiO2 0.37 B 0.38

Fe2O3+FeO 17.20 K2O 0.08

Reserves were not calculated and the primary deposit under the eluvium is not known.

5. Placers

During the geochemical prospecting of the country, andalusite, sillimanite and kyanite were found to be common minerals of heavy mineral concentrates. Higher weight percentages are known, for example, for river deposits in the Manica province. Owing to the river transport, these minerals are now common constituents of marine placer deposits. In these deposits, they may represent a valuable byproduct. In Mozambique, a higher content of andalusite in heavy mineral suite was observed at the mouth of the river Limpopo (5.3%), at Praia Massano and Chidenguele (1.3 and 1.2%), at Ponta Zavora, Guinguane-Jangamo and Praia Tofo Miramar (3.8, 1.9, 2.5%), Praia Wor'rungulo and Pomene (3.0, 1.7%) and the Paradise Islands (2.4%). All these beach sand localities are situated within the Limpopo paleodelta and the sediments supplied to the sea originate in Transvaal craton, Limpopo zone and Zimbabwe craton with its platform deposits. The increased amount of andalusite indicates clearly a contact-metamorphic origin of the deposits. Between Beira and the Zambezi delta, one beach sample contained 4.8% of kyanite. The central section of the seashore between the river Zambezi and Mozambique Island is characteristic



of a prevailing presence of kyanite: Gorai, Idugo, Pebane, Melai, Moebase, Moma, Larde, Angoche, Congolone, Quinga (1.7, 1.2, 1.1, 2.3, 3.4, 1.4, 2.8, 1.3, 2.6, 1.5 % of total heavy minerals). Andalusite in larger quantities is known to occur at Ilha Olinda near the opening of the Zambezi river (1.8%), Pebane (2.1%) and Larde (1.8%). The source rocks are within the Mozambique belt. Higher content of kyanite was discovered in scattered sand bodies in the northern section of the Mozambican seashore (1.4-3.0%) with identical source-rocks in the Mozambique belt to those within the central part. Kyanite forms mostly elongated tabular grains which are transparent or faintly bluish in colour, the grains of andalusite are mostly isometric in form and yellow to yellowish brown in colour; transparent grains are less frequent. Graphitic pigmentation is common to both minerals. Andalusite is rarely developed in the form of chiastolite. Grain size of about 70 to 80% is 0.1 mm, about 2.0 to 15.0% are below 0.1 mm. The reserves of the sillimanite-group minerals in beach and dune was estimated to about 2 million tons.

Conclusions: Except the beach and dune deposits with a small content of andalusite and kyanite, very little is known of the sillimanite-group minerals in primary deposits. Certainly the most promising area is the extensive N-S trending zone between the Mozambique belt of the Baru6 Formation and the Zimbabwean craton with contact-metamorphic deposits in overlying metasediment of the Fronteira Formation. The contact zone and the aureole of pegmatitic and quartzitic dykes around the Tete massif may provide kyanite accumulations. The sillimanite deposits should be investigated within the high-grade metamorphic zones, especially in northern Mozambique, in the provinces Nampula and Cabo Delgado, in areas of graphite deposits, similarly to that ones in Angonia N of Tete.



Cilek: 3.10. Rare-earth minerals

3.10. Rare-earth minerals RE-minerals are a source of sixteen elements which play the increasing role in modern industry. Without these the present technical revolution would not be possible. From a modest beginning of utilization in the production of gas mantels and flint stones RE-elements found their application in every branch of industry. The rare-earths group is divided in two subgroups - cerium or light subgroup and yttrium or heavy subgroup.

Cerium subgroup: Yttrium subgroup:

Lanthanum La Yttrium Y

Cerium Ce Terbium Tb

Praseodymium Pr Dysprosium Dy

Neodymium Nd Holmium Ho

Promethium Pm Erbium Er

Samarium Sm Thulium Tm

Europium Eu Ytterbium Yb

Gadolinium Gd Lutetium Lu

included is also Thorium Th included is also Scandium Sc

The cerium subgroup is represented mainly by two minerals - bastnaesite and monazite, while the yttrium subgroup is concentrated in xenotime. These three minerals are, in fact, the only commercial sources of RE. RE-minerals have generally a complex formula because of geochemical affinity. The important RE-minerals:

bastnaesite (Ce,La) (CO3) F

monazite CePO4

xenotime Y PO4

euxenite (Y, Ca, Ce, U, Th) (Nb, Ta, Ti)2 O6

gadolinite Be2 Fe Y2 Si2 O10

cerite Ca Ce6 Si O13

Monazite is of a more complex composition, i. e. (Ce, La, Y, Th) PO4 and for RE, the ratio of Ce/La is 1:1 (about 30%) and the content of ThO2 up to 12%. Therefore monazite is also an important source of thorium. Yttrium occurs in small quantities only. The content of RE is 50-60%. In bastnaesite, the content of the main two cations is 1:1,36% each. All three main RE-minerals are concentrated in endmembers of magmatic rocks, i. e., in granitic and mainly pegmatitic deposits of acid composition, and in alkaline end members such as nepheline syenites and pegmatites. At a temperature of 800°C, the monazite crystallizes from magma with prevailing Ce, at 700°C, at an onset of separation of pegmatitic material, the monazite crystallizes together with oxides of Ti, Nb, Ta and RE, with prevailing Y and Ce. Around 500°C, the last RE mainly as Ce and Y, are separated in apatites. All RE-minerals of RE accumulate in primary rocks in carbonatites only, which represent a special geochemical cycle. Exceptional are primary vein deposits of bastnaesite and monazite. Accumulations of monazite in placers - fluviatile or marine origin represent the main RE source. A new production of bastnaesite as a byproduct of iron-ore mining was started in China. In the Soviet Union, RE are recovered by a processing of apatite from the Kola peninsula. Composition of RE-ores (Kuzvart, 1984-Harben-Bates, 1984) (248 kB) The mining of monazite and xenotime is closely related to placer deposits mining, where they are found in commercial quantities (about 1% of total heavy minerals) as a byproduct of titanium and zirconium extraction. As a result, the production level of monazite (xenotime is quite rare in placers) is dependent mainly on the market demands for titanium minerals. In fact, the content



of monazite is low, but it is present in many placer deposits and the large volumes of sand treated secure a constant supply and often oversupply of monazite on the world market. Bastnaesite in just one commercial deposit at the Mountain Pass area of the San Bernardino County in carbonatite, averages 5-15% of the carbonate rock. Another exception is the monazite deposit of the vein type Van Rhynsdorp in the Republic of South Africa which produces an RE-concentrate of 50-80% purity with 2-10% ThO2. In the Soviet Union, an important source of RE are apatites with an RE-content of 0.6-0.8%. The production of a RE-concentrate from crude ore and ore mining are cheap in comparison with a separation of RE (such as chlorides, Ce-RE carbonates and La-RE carbonates) from the concentrate which could be 1000 times more expensive. Two technological processes are used in the treatment of RE concentrate-monazite: 1. acid-using H2SO4 up to 180-200°C (1.5 t of sulphuric acid for 1 t of concentrate) 2. alkali-explained by the equation: (RE)PO4 + 3 NaOH ===> RE(OH)3 + Na3PO4 (1.5 kg NaOH on 1 kg of monazite). The result is RE as sulphate or hydroxide and separated Th. Then follows a separation of each RE-element by liquid-liquid solvent extraction and ion exchange. Few countries only export a natural concentrate of RE, most produce intermediate products such as RE-chloride and only a few REO of 99.9% purity. From RE-chloride, the so-called mish-metal is produced, i. e., an intermediate product of this composition: 51-53% Ce, 15-17% Nd, 3-4% Pr, 22-25% La, 2-3% Sm, 3% Tb, 3% Y and about 5% iron. Mish-metal is a compound representing the first utilization of an RE-mixed alloy used in the production of flints for lighters, later in that of docile iron and, nowadays, HSLA (high strength - low alloy) steels. It is necessary to stress that 0.01% of mish metal substantially increases the steel quality and can substitute several expensive alloying metals. Mish metal found other uses in the production of strong permanent magnets substituting expensive samarium. Cerium plays an important role in the polishing of glass, lenses, mirrors, TV-screens, but also as a colouring agent for TV-tubes and in a decolourization of glass. In electronics, RE are used in computers for memory films in GGG (galium-gadolinium-garnet), in the production of special ceramics. Yttrium is essential in the production of YAG (yttrium-aluminium-garnet) for magnetic information storage, in an imitation of diamonds and crystals in lasers. In the atomic industry, yttrium secures the production of special stainless steels, gadolinium and europium in active zones of reactors as neutron absorbents. Main uses of REO: 40% as catalysts, 35% in the iron and steel industry, 18% in glass and ceramics and others. In the last group, the greatest future development is expected in control rods in atomic powerstations, phosphors and luminophors, super-alloys, magnets, catalysts, military applications and fiber optics. Mozambique is one of the few African countries where RE were extracted and exported. A unique deposit is the Guilherme pegmatite near Ribaue from where euxenite ore was transported to a dressing plant at the Boa Esperanca mine. Euxenite was exported to England for some years, but owing to unfavourable market conditions, production was discontinued sometimes in 1966. In Mozambique sites of RE occurrence are numerous and cover all genetic types of known deposits: 1. deposits in pegmatites and granitic rocks 2. deposits in alkaline rocks 3. deposits in carbonatites 4. accumulations in apatites 5. placer deposits. Of all these five genetic types, the placer deposits in beach and dune deposits in the coastal zone are the most important and economically most feasible ones (see Fig. 3.6.1).

1. Pegmatite deposits RE are concentrated within the group of rare earths and radioactive minerals-pegmatites arranged in certain zones generally of NW-SE direction, crossing the zones of pegmatites with rare metals in NE-SW direction.

Fig. 3.10.1 Alto Ligonha pegmatite district (Zambezi Province, Aquater, 1983). (63 kB)

Minerals with RE: fergusonite Y, Er, Ce, U, ... (Nb, Ta) O4 samarskite Fe, Ca, UO2 • Ce, Y (Nb, Ta)6 euxenite -niobite and titanite of Y, Er, Ce, U polycrase - niobite and titanite of Y, Er, Ce, U



betafite - hydrous titanite and columbate of Ca, U, Y, Er, Ce monazite-(Ce, La, Nd) PO4 xenotime-Y2O3 • P2O5 rabdophanite - hydrated phosphate of Y, Ce pollucite- H2O • 2CS2O • 2Al2O3 • 9SiO2 According to Barros-Vicente (1963) fergusonite was discovered in pegmatites of Enluma I. and Jlodo, in the shape of small spindles, 1 to 5 cm long, associated with quartz and zircon. On the surface, the crystals are covered by a yellowish alteration zone. Samarskite -is present in the area of Ribaue, in the mine Boa Esperanca, at Macotaia, Ingelo, Nahia and elsewhere. It is associated with muscovite, rarely with columbite. The crystals of samarskite are often arranged fanlike, of a distinctive violet-blue colour covered with a yellow layer, probably from uranium alteration. The aggregates are big, 25 cm length, over 2 kg. Samarskite from pegmatite Nahia: %

SiO2 1.24 ThO2 1.94

SnO2 1.48 Ce2O3 2.62

PbO 0.47 Y2O3 12.16

TiO2 1.59 U3O8 10.04

Ta2O5 + Nb2O5 52.43 CaO 2.20

Fe2O3 9.72 MgO traces

MnO 0.90 H2O 2.16

Al2O3 1.54

Many other sites of samarskite occurrence had been discovered in the past. Bulgargeomin (1983) found a pegmatite in the area at the mouth of the river Lurio 5 km NW of Taquinha, with beryl, quartz, tourmaline and another pegmatite of small dimension (5 m · 0.5 m) 32 km SW of Taquinha with samarskite. It was also reported from pegmatites of Serra Meluli near Nipepe, in about 10 cm long masses (Geol. Inst. Beograd, 1984). Euxenite is well-known from several pegmatites of the Alto Ligonha district s. l. Often, it was found at Nauela and Ile, Mucharro, Nampoca, Nahavarra etc. It was mined at Guilherme and Muetia (Nauela region) and concentrated at the Boa Esperanca mine at Ribaue. Two samples were analysed by de Ledoux Co. (Barros-Vicente, 1963):

% Guilherme Mucharro % Guilherme Mucharro

TiO2 27.89 23.36 Pr6O11 0.06 0.24

ZrO2 1.53 1.35 Nd2O3 0.30 0.85

Fe2O3 3.42 4.18 Sm2O3 0.29 0.53

U3O8 11.99 9.58 Eu2O3 0.01 0.02

Nb2O5 26.87 24.13 Gd2O3 0.037 0.84

Ta2O5 4.53 4.08 Tb4O7 0.01 0.02

P2O5 0.33 1.48 Dy2O3 0.72 1.32

Al2O3 1.05 1.05 Ho2O3 0.015 0.27

CaO 0.76 0.87 Er2O3 0.61 1.02

PbO 1.18 0.96 Tu2O3 0.13 1.90

SiO2 1.23 2.08 Yb2O3 1.03 1.90

BaO 0.07 0.04 Lu2O3 0.15 0.27

MgO 0.02 0.15 Sc2O3 0.01 0.02

MnO 0.07 0.15 ThO2 2.52 2.56

SnO2 0.16 0.04 S 0.005 0.008

Y2O3 5.30 10.72 C 0.072 0.064



La2O3 0.04 0.18 L. i. 6.68 4.09

CeO2 0.07 1.23

Euxenite is associated with columbite in tubular crystals, often altered. Polycrase or euxenite-polycrase occurs in pegmatites of Boa Esperanca and Giline. It is quite rare and generally covered with a yellow alteration zone similarly to euxenite and samarskite. Betafite is present just at the Boa Esperanca mine, in small massive aggregates of black-greenish colour. Moçambiquite was introduced as a new mineral by J. M. Cotelo Neiva and J. M. Correia Neves on the international Geological Congress (1960) at Copenhagen (Barros - Vicente, 1963). It is a mineral composed mainly of thorium occurring in one locality only - the mine Muiane, where forms octahedrons of yellow-brownish colour and specific gravity 5.24. Spectrographic analysis: Th-dominant; Si, U, Zr, Y abundant; Pb, Er, Cd, Sa, Mn in traces. Chemical analysis of Mocambiquite from the Muiane mine (University of Coimbra by Neiva-Neves) (in %):

SiO2 11.00

ThO2 58.80

U3O8 6.04

CaO 0.59

Fe2O3 0.22

Al2O3 4.40

RE 8.60

H2O

Monazite is frequent in pegmatites of Alto Ligonha and surroundings and is the mineral that occurs not only in RE-radioactive minerals-pegmatites but often also in the group of rare metals pegmatites. Its crystals are generally tabular or elongate and in aggregates of prismatic crystals usually about 1 cm long. Some crystals are even 5 cm long, and aggregates may attain a weight of more than 2 kg. The colour of the mineral depends on the thorium content, when strongly radioactive (20% of ThO) it is greenish (areas of Ingela, Naquissupa, Namacotche), when weakly radioactive it is of brownish-green colour. Main pegmatite localities with monazite are the mine Morrua and an area of Ribaue. Apart from the Alto Ligonha district, monazite occurs in many other localities throughout the Mozambican belt in connection with granitic pegmatites. Two chemical analyses are known (de Ledoux Co.):

% Muetia Guilherme

P2O5 32.80 31.42

Ce2O3 23.80 22.45

ThO2 7.1 7.8

Y2O3 etc. 35.0 36.25

Xenotime Barros-Vicente (1963) reported it from one locality only - pegmatite Namivo - where it is in intergrowth with zircon. Later, the author visited the mine Boa Esperanca (1980) and learned that xenotime was produced and processed in the Ribaue area. The concentrate was exported to England in this composition (minimum 53% RE) (in %):

CeO2 11.2 Sm2O3 2 Ho2O3 < 1

Y2O3 46.3 Eu2O3 < 1 Er2O3 6

La2O3 5 Gd2O3 3 Tm2O3 1



Pr6O11 1 Tb4O7 1 Yb2O3 8

Ne12O3 6 Dy2O3 7 Lu2O3 < 1

Rabdophanite - reported from Nuaparra, in close intergrowth with thorite. Pollucite, a mineral of cesium, occurs in several, especially zoned pegmatites, in the zone of lithium minerals, commonly with petalite at Namacotche, Nahora, Muiane, Morrua etc. Its main producer was the pegmatite mine Namacotche, in a quality of Cs 33.45%, Rb 0.48%. RE minerals are concentrated in zoned pegmatites in the internal zone, within the zone of big feldspars. Monazite, euxenite, samarskite and xenotime are the main RE-minerals. In the central and SW part of the Alto Ligonha pegmatite field, there occur both mineralization of RE with rare metals. Some pegmatites of a microcline variety display a simple zoning with vein-type pegmatite bodies up to a length of 250 m. Mineralization is represented by beryl, columbite-tantalite, bismute, monazite, euxenite, zircon and xenotime. Another known area of its occurrence lies 10 km NE of Alto Molucue, with the group of pegmatites of Guilherme, Muetia and Conua. Veins are about 150 m long, 15 m wide and almost subvertical. They occur in granitized host rocks with a simple zoning of quartz core, block microcline and external homogeneous pegmatite. Mineral assemblage is represented by euxenite, monazite, bismutite, beryl within the zones of albitization. The Boa Esperanca mine near Ribaue is not known only for its kaolin and feldspar production, but also for the presence of a number of other minerals - samarskite, zircon, monazite, xenotime and others. The pegmatite with a quartz nucleus has a zonal structure with oligoclase-microcline block pegmatite, muscovite and a homogeneous external zone. Perhaps the best example of RE-pegmatites is present in the Zambezia Province, between Mocuba and Gurue, and its NE extension to Alto Ligonha towards Nacala. Host rocks are biolite-amphibole and pyroxene-biotite gneisses, rarely granitoid massifs. The pegmatites can be classified as microcline with a zonal structure. Mineralization occurs with monazite, euxenite, samarskite, ilmenite, magnetite, columbo-tantalite and beryl. One of the most important areas is that at Moala, on the right bank of Lurio river, 47 km NE of Gurue. The veins are 500 m long or more, 3-5 m wide. Zonal structure is well developed. Mineralization occurs in the form of veins and disseminations with samarskite, monazite, itmenite, magnetite, and a minor content of columbite, tantalite and zircon. Spectroscopic analyses disclosed significant quantities of Nb, U, Sc. Other pegmatites of this area contain thorite, davidite and uraninites. Total extension of RE-pegmatites is about 400 km2. Numerous pegmatites are known to occur near the port of Nacala. Generally, they exhibit a simple zoning and are about 8-10 m wide. There are two main areas - one 9 km SW of Nacala (Tulua, Equesa, Namiope), the other around Vila Cabo-Comane. The Tulua vein, at present the main supplier of feldspar and amazonite, is 250 m long, 10-15 m wide, dipping 50-55°SE. It is of zonal structure with a quartz nucleus, a sodalithic zone, a microcline zone and a quartz-microcline zone. Mineralogical assemblage: samarskite, monazite, zircon, garnet, microlite, tantalite, cassiterite, bismutite and uraninite. The Equesa and Namiope veins are 100 m long, 10 m wide, dipping 40-50°. Zonal structure is similar to that of Tulua, mineralization is represented by black, green and pink tourmaline, monazite, xenotime, zircon, ilmenite, garnet and rarely columbite, microlite, bismutite and cassiterite. At Vila Cabo-Comane, the small pegmatite is of the microcline variety with a quartz nucleus. Minerals present are tourmaline, monazite, zircon, xenotime, rutile, ilmenite, magnetite and garnet. Three RE-minerals of pegmatites were produced in Mozambique (Barros-Vicente, 1963): euxenite, samarskite and monazite. Their production started in 1937, with 17.5 t of samarskite, dropping to 0.4-0.06 t (except for 1.25 t 1948) and stopped in 1953 due to unfavourable market conditions. Euxenite was produced in a small quantity only (total 1944-1960: 1.66 t). Monazite started to be produced in 1937 with 13.04 t, dropping to 250 kg and ceasing in 1961 with 243 kg (Barros-Vicente, 1963). Pollucite was also produced; in 1961, 5 t were exported to the USA. The only mineral still produced and exported is monazite-2.1 t produced in 1974, 12 t in 1975, 9 t in 1980 going down to 0.16 t in 1985, from three pegmatite-producing mines, Morrua, Marropino and Muiane. 2. Deposits in alkaline rocks Several nepheline syenites and alkaline syenites bodies known to occur in Mozambique have been investigated for different minerals. Some of these contained RE. In the massif Conguene at the southern end of-Malawi, on the E side of the Niassa rift valley, nepheline syenites with biotite are developed. RE were found within the type of alkaline metasomes-fenites. They concentrate in the contact zone of the non-nephelinic syenites with nepheline syenites, with Rb2O (300 g/t), Nb2O5 (400-2,000 g/t) and Ta2O5 (100-400 g/t). Trace elements (VAMI, Leningrad, 1981) (in g/t):



Sample Ga Rb2O V2O5 Li2O Ta2O5 Nb2O5 Tr2O3 Zr Cr2O3 TiO2 Cl F Sr Ba

B-1 33 230 30 20 12 240 68 835 tr. 1,200 120 360 370 700

B-2 32 130 10 10 5 108 118 263 30 3,400 280 490 900 -

Both samples have an interestingly increased content of gallium and rubidium, both are of high value and could be economically recovered as byproducts, thus improving overall economic parametres of syenites, which could be used in the alumina production (see chapter alkaline rocks). Besides the reserves of alumina raw materials, possible reserves of niobium pentaoxide were calculated in the order of 25,000 t, content 0.1%. Similar reserves of rubidium oxide can be estimated in the order of 30,000 t. In the northern part of Mozambique, in the Province Niassa in the vicinity of Unango (N of Lichinga), over a area of about 5,000 km2 several alkaline complexes were discovered during geochemical prospecting, with mineralizations of uranium, niobium, tantalum and RE connected with anomalies of phosphorus. In the same province, just near the bank of lake Niassa, around Meponda in Precambrian gneisses, several intrusions of granites, monzonites, syenites and alkaline syenites were discovered. On Monte Tchonde (Geol. Institute, Beograd -1984) a circular structure composed of these rocks is cut by several dykes of rhyolite. Several radioactive anomalies were detected, with three types of mineralization: a) in relation with red granites and quartzitic monzonites of Mt. Tchonde b) in rhyolitic dykes c) in alkaline rocks The first two anomalies are characterized by a high content of K, U, Th, their value is small. The third type contained an increased quantity of V, Th, Ta, Nb and RE. These accumulations are regarded as promising. Some preliminary work deliniated the anomalies which extend for about 8 km, 100-200 m width, in altered alkaline syenites, subalkaline metadiorites and nepheline syenites. Trenching revealed that several lenses of highly altered rocks of this belt, measuring 10 to 1 000 m in length and several m width, contain U -0.05% to 0.16%, thorium up to 1.3% with niobium, tantalum and RE.

3. Deposits in carbonatites Generally, all carbonatites display a higher amount of phosphorus and RE. All carbonatites of Mozambique are connected with deep-seated fractures of rift valley systems. The main localities of volcanic vents with carbonatite are: Monte Xiluvo in the S, Monte Muamba on the N near Tete and Cone Negose near the Zambeze river in the W. Other bodies, originally supposed to be carbonatites such as Salambidwe at the Malawian border or Serra Morrumbala E of the Niassa rift valley, are syenite intrusions without a carbonatite vent. Monte Xiluvo has not yet been explored substantially; Monte Muambe is an important fluorite deposit (see chapter-fluorites) with an increased amount of niobium and RE, the latter being included most probably in monazite and partly in pyrochlore (?). A spectroscopic analysis of carbonatite revealed the presence of Y, Ce, Nb and Sr. Cone Negose is a carbonatite intrusion close to the N boundary fault system of the mid-Zambezi trough. The country rocks to the N of the main fault are metasediments of the Fingoe Formation intruded by granites and cut by porphyry and dolerite dykes (Hunting, 1984). Karroo sediments occur S of the fault. Cone Negose is situated N of the main fault; all other small satellite Cretaceous intrusions occur to the S in the Karroo area. Cone Negose consists of a central core of carbonatite surrounded by a ring of trachytic and carbonate breccia or vent agglomerate. All satellite stocks and plugs to the S consist of similar trachytic vent agglomerates. Carbonatites are developed in various successive stages (Carvalho, 1977): A. grey carbonatite with pyrochlore and monazite (RE) B. red veins and buff carbonatite with bastnaesite and baryte (RE) C. phosphatic carbonatite with brookite and barytes D. silicified carbonatite with fluorapatite, pyrochlore and baryte F. fluorapatite Buff carbonatite is characterized by an increased content of baryte and a high content of bastnaesite with RE; red vein stage has high content of niobium bearing TiO2. Carbonatites of Cone Negose are of the magnesium type i. e. "rauhaugites". New discoveries of RE in carbonatites were made in the northern part of Mozambique. The site is called Luicuisse after the river Luicuisse; it lies in the Province Niassa, near the settlement Navago, about 240 km NE of Lichinga. In Precambrian rocks, several alkaline intrusions of nepheline syenites and syenites were discovered with fracture zones filled up



by mineralized carbonatites with RE, U and Th and apatite. The superficial zone of weathering is 7-8 m thick, its mineral content is increased. The Luicuisse finding is, in fact, a large circular structure with complex mineralization. In the weathering zone in many pits, columbite, pyrochlore, apatite, monazite and magnetite were determined. Over an area of 0.66 km2, an eluvial deposit of 30 m thickness was delineated; it contained columbite and zircon (in 90% of samples), pyrochlore (78% of samples) and apatite (in 33.8% of samples). RE, Nb, Ta, Cs, La, Y, Zr are ten-times higher than their clarke. The content of P2O5 averages 2.34%, in some samples 6.77%.

4. Accumulations in apatites Apatite deposit in crystalline limestones of the Mozambican belt at Evate in the Province Nampula contains partly also fluorapatite Ca5 (F (PO4)3), rarely hydroxyde apatite (Ca5 (PO4)3 (OH)) with an increased amount of SrO (0.25%) and RE (0.59% max.). RE are represented by Ce predominant over La and a minor Y and Yb. The content of almost 0.6% RE in some sections of the deposits, with an average of 0.3%, is very similar to the average content of apatite from the Kola peninsula in the Soviet Union (0.6 - 0.8 % RE). The technological process of recovering RE from Kola apatite has been known for many years and apatite is an important source of RE. If the Evate apatite were to be mined also RE could be recovered as a byproduct.

5. Placer deposits Heavy mineral accumulations are known to occur along the whole Mozambican seashore. They are both in beach-and dune deposits with heavy minerals (HM) represented by ilmenite, rutile, zircon, monazite, kyanite and andalusite. The main accumulations of HM are in Mid-Mozambique, in a section of the seashore between Beira and Quinga. In southern Mozambique, huge beach- and dune deposits developed during the Quaternary with an inland extension of about 80 km from present seashore. The HM assemblage consists of economic HM (see above) and waste silicate minerals. In N- Mozambique from Mozambique Island to the Rovuma river, just few and small sand bodies with HM were found on the coralline seashore. The content of monazite in an assemblage of economic HM is usually less than 1%. Within the whole HM assemblage, a minimum content of 0.5% of monazite is regarded as an economic accumulation. List of localities:

Marracuene - 1.0%fossil placer on an old beach hurried under eolian sands and eroded on the bank of river Incomati

Inhambane Bay - 0.5% old dunes on the W side of the peninsula bordering the E side of the bay

Beira - 1.5%, beaches NE of Beria towards the delta of the river Zambezi, transgressive sands

Deia - 5.8%beach sand on Deia deposit with altered HM near Quelimane, samples of Nöldeke (1978)

Deia - 0.5% beach sand -Deia deposit, modern beach with silicate HM

Raraga - 1.8% beach sand from retention ridge with economic minerals

Gorai - 0.5% beach sand, 3 km long beach with high concentration of HM

Idugo - 0.8% beach and dunes, deposits of old concession

Pebane - 0.6% beach with high content of HM concentrate produced contained 3% monazite

Melai - 0.5% beach, part of Pebane deposit

Moebase - 0.7% beach, 50 km long seashore, surveyed beach 13 km, HM also in dunes

Moma - 1.7% beach, 15 km long, beach and dune ridges

Angoche - 1.7% beach NE of town with several ridges

Congolone - 1.2% huge dune deposit NE of Angoche, dune Congolone is complex dune

Quinga - 0.9% last stretch of beach and dune deposits of middle Mozambique

Palma - 0.7% thin layer of sand over coral platform

Monazite forms usually round oval grains of yellow-brown colour. Also a small amount of xenotime was found, but it could not be separated.



Monazite contains elements of the cerium group - mainly La, Ce, Nd and Sm. The average of REO is usually 50-60% and 2-10% Th. Mozambican monazite has about 38-45% of RE with prevailing La, Ce, Nd 36-43%, but even the Sm content is interesting. Average U and Th content is above 5%; the mineral can indeed be classified as a strategic one (see Table 5). Table 5. Instrumental neutron activation analysis of Monazite made at IMRM-Czechoslovakia: (in %) (262 kB) Estimated reserves of monazite in selected beach - and dune deposits represented about 500,000 t. The world annual production is about 25,000 t/y, a production unit needs about 5,000 t of monazite annually and this amount could be extracted just from a few deposits. An example of a possible future source of monazite is the Congolone-dune deposit from which about 1,500 t of monazite could be recovered as a byproduct at an annual production of about 100,000 t of ilmenite. Conclusions: Mozambican rare-earths resources are both big and diversified. Again, the well-known pegmatite district of Alto Ligonha proved its extraordinary properties in that not only columbite-tantalite ores are extracted at present but in the also commercial quantities of RE-minerals euxenite, samarskite and monazite. There are large possibilities to produce monazite as a byproduct of rare-metals mining and to start a new production of RE and radioactive materials from several promising pegmatites both in the Alto Ligonha district s. l. or outside it. Futher resources in alkaline rocks-nepheline syenites are feasible as soon as these are put into production either for ceramics or the alumina industry. The content of rubidium is promising. A similar situation can be envisaged with the production of apatite which contains, for example at the Evate deposit, a maximum of 0.6% RE. The most feasible are deposits of monazite from beach - and dune sands known to be present in many places on the seashore. Several thousand tons could be recovered annualy and processed directly in Mozambique either as a chloride or a mishmetal, which finally could be used locally in the production of special alloys and high-strength steel.



Cilek: 3.11. Talc and soapstone

3.11. Talc and soapstone Talc is a hydrous magnesium silicate Mg3(Si4O10) (OH), originating as secondary mineral from an alteration of magnesium silicates such as olivine, pyroxenes or amphiboles. Commonly it is white or green, in pearly foliated masses. The massive variety is called steatite. Talc is very soft; number 1 on the Mohs hardness scale, greasy, with a perfect basal cleavage, often in foliated structure. Admixtures with some elements give talc a special colour: chromium deep green with violet spots in serpentinites, nickel or Fe2+ - apple-green, copper-bluish green. In deposits, talc is accompanied by several minerals such as serpentine, dolomite, magnesite, tremolite, anthophyllite, quartz and others. Commercial-grade talc is rock composed predominantly of talc (from 60 to 98%), calcite (1-12%), tremolite (30-40%) and anthophyllite (5%). Rock composed of at least 35% talc and 25% of the mentioned minerals, is called soapstone. Chemical and physical properties of talc and steatite are used in many industrial branches. Talc is a mineral used with still increasing intensity for the softness of its powder, its high coating ability, high melting point, low electric conductivity, high absorption capacity and white colour. Talc found its use in the textile industry, production of soap, tooth-paste, in the cosmetic and the rubber industry, in chemistry in catalysis. Other applications are in the pharmaceutical industry, as a lubricant, oil absorbent, filler in paint (important in white-pigment TiO, dispersion), plastics and paper. Electroceramic talc must contain less than 0.7% Fe2O3 and also steatite can be used as refractory material. Mixed with 25-40% of clay it is used in the production of earthenware. It can replace kaolin as a paper-coating product and several materials in refractory products. Soapstone can be cut in quarries into structural units for the use as refractory bricks in metallurgical, glass and cement furnaces. Its oldest and still popular use is in soapstone carvings. Two genetic types of deposits are known: 1. in ultrabasic rocks and serpentinites 2. hydrothermal deposits in dolomitic and silicate rocks 1. Deposits developed similarly to deposits of asbestos. Talc rock can replace whole bodies of serpentinite, but more commonly forms a rind around serpentinite with asbestos. Often, several zones are developed: unaltered serpentinite - zone of talc - carbonate serpentinite - talc zone - actinolite and chlorite zone - granitic rock. Talc is an alteration of serpentinite by hydrothermal solutions with SiO, and CO, during regional or contact metamorphism according to the equations (Kuzvart, 1984): H4Mg2Si2O9 (serpentinite) + 2SiO2 ===>H2Mg3Si4O12 + H2O (talc or steatite) 2 H4 (Mg, Fe)3 Si2O9 + 3CO2 ===> H2Mg3Si4O12 + (Mg, Fe) CO3 + 3 H2O (soapstone) 2. Deposits of talc in magnesites, dolomites and dolomitic limestones are formed by hydrothermal influence of nearby intrusions according to the equations (Kuzvart, 1984): 3 MgCO3 + 4SiO2 + H2O ===> H2Mg3Si4O12 + 3 CO2 3 MgCa (CO3)2 + 4SiO2 + H20 ===> H2Mg3Si4O12 + 3 CaCO3 + 3 CO2 In both cases, SiO2 is supplied by granitic intrusions. In Mozambique, talc is not being produced, despite the fact that several deposits of talc may be present in mined asbestos deposits (see chapter "asbestos"). Knowledge is available just of deposits of the first type in ultrabasites and serpentinites, while an absence of dolomites and a scarcity of dolomitic


Cilek: 3.11. Talc and soapstone

limestones prevented a development of the second type of deposit (see Fig. 3.2.1). a) The Serra Mangota asbestos deposit also contains talc and talc schists. In the W- part originated the carbonate-talc zone of serpentinite while in the E- part prevail talc schists. Because good quality asbestos is connected mainly with carbonate serpentinite, talc deposits, presumably best-developed in the E part of the ridge, should be explored and mined here. b) Small findings of reworked greenstone belts of the Mozambican belt include a continuation of "Cronley greenstones" from Zimbabwe to Mozambique with a possible occurrence of talc in areas of Maravia near Fingoe and the ultrabasic complex of Monte Atchiza. In the latter, an alteration of peridotites and pyroxenites into serpentinite and further into actinolite and anthophyllite is common. The presence of talc may be possible. c) The asbestos deposit Mavita is the best example of a first-type deposit with the development of a different zone between the unaltered serpentinite and intrusive rocks. The rind structure of talc, talc-schists and chlorite and mica schists around the serpentinite and asbestos was observed on many partial asbestos deposits. Talc-schists are apple-green, mainly steatite-schists, pearly and greasy. They form belts ranging from several to several tens of m width, with reserves estimated to more than several million t. No tests for talc materials were made despite the fact, that this material could improved substantially the mining for asbestos. d) The Mulatala deposit is a large zone of altered ultrabasic rocks, with a presence of talc in harzburgitic serpentinites. The rock of asbestos is composed of talc, vermiculite, anthophyllite, chlorite and probably quartz. Other localities with talc, tremolite, actinolite and chloritic rocks were discovered by Bulgargeomin (1983) in ultrabasites at Monte Nicuculo, 50 km W of Pemba and 7 km S of M. Nicuculo.

Conclusions: Promising talc deposits are connected with ultrabasic mainly serpentinite bodies containing asbestos. No talc tests were made. Two deposits should be explored for talc in Mozambique: Serra Mangota near Manica and anthophyllite deposits at Mavita S of Chimoio. A utilization of talc and soapstone could be beneficial mainly to the local industry: as refractory material in glass, cement and future metallurgical industry, in several other industrial branches such as the production of earthenware-porcelain and tiles, in textiles, tooth-paste, soap, rubber and as a filler.



Cilek: 3.12. Titanium and zirconium minerals

3.12. Titanium and zirconium minerals Common titanium minerals are ilmenite, rutile, anatase, brookite, leucoxene. Among the oxides, the most abundant is rutile with a content of 89.5 to 99% TiO2, followed by anatase (98.4-99.8 % TiO2), brookite, ilmenite-rutile, tantalum-rutile and ulvospinel. Other mineral groups include ilmenite FeTiO3 and titanite CaTiSiO5. The content of TiO2 in ilmenite varies between 48.6 and 57.3%. A higher content of iron is caused by an intergrowth of hematite or magnetite. Some ilmenites possess a higher content of TiO2 than theoretically acceptable, i. e. 52.7%, because of the presence of fine pheno crystallites of rutile or spinel. V, Nb, Cr and Ta are present as impurities. The TiO2 content in a commercial product should not fall below 50%, the maximum content of vanadium 0.5%, that of chromium 0.1%, manganese 0.5%, niobium 0.5% and copper 0.1%. In rutile, a minimum content of TiO2 of 92% is acceptable. Zirconium minerals include zircon and baddeleyite. Zircon is silicate ZrSiO4 and baddeleyite oxide ZrO2. Zircon supplies 98% of world demand for zirconium and contains 67% ZrO2 and about 2% of hafnium. Baddeleyite is almost pure zirconium oxide with 96.5-98.9% ZrO2 and is mined in primary deposits in a few places only. The most important of titanium minerals is ilmenite which accounts for almost 85% of the minerals used in titanium products. Leucoxene called "altered ilmenite" is an accompanying mineral in placer deposits, in which a minimal content of at least 68% TiO2, had been upgraded by oxidation and partial removal of iron. Rutile is the most important of Ti-oxides. The most important of all zirconium minerals, is zircon, followed by quite rare baddeleyite. In both minerals, common impurities include thorium, uranium, rare earths and yttrium, calcium, magnesium, iron and hafnium. Hafnium is very similar to zirconium in chemical and physical properties, but must be removed in certain applications of zirconium. More than 90% of titanium minerals are used in the production of titanium dioxide, TiO2, a pigment known as white pigment, used also in plastics, paper, rubber, additive in frits, glazes and titanium ceramics mixtures. The remaining 10% are used mainly as titanium metal, which is light, strong and anticorrosive and finds increasing use in the aircraft industry, rocket and satellite construction, atomic industry, in submarines, special machinery for chemical, textile and metallurgical industries and also in medical appliances. Two methods are used in a production of titanium dioxide-the older, nowadays seldom used sulfate route and the modern chloride route. The sulfate route requires either simple ilmenite with 45-55% of TiO2 or titanium slag with 70-80% TiO2. This material is dissolved in sulphuric acid and titania is then precipitated by hydrolysis, filtered, washed and calcined to produce TiO2. A problem arises from waste disposal (ferrous-sulfate) harmful to the environment. In Czechoslovakia, ferrous-sulfate is used partly in the pigment industry. The chloride route is more complicated, more expensive, requires a feedstock with a higher TiO2 content, but is environmentally harmless. The material is usually made-up of rutile or, nowadays, different products of upgraded ilmenite-synthetic rutile or titanium slags with 85% TiO2 or more, chlorinated at 850-950°C in the presence of petroleum coke to produce TiCl4. This is oxidised to produce TiO2. Titanium tetrachloride is the basic material for the production of metal using a reduction process with metallic magnesium. Zircon displays high mechanical strength, it is refractory and resistant to corrosion and has a low neutron absorption. Thus, over 90% are consumed in special refractories and ceramics to produce refractory bricks, refractory sand and foundry sand. Zirconia ZrO2 is produced by reacting zircon and dolomite resulting in still higher refractory products, melting point 2,700°C (200°C higher than that of zircon). Zirconium is applied also as casings of atomic fuel rods, in ferroalloys, as abrasives, in the chemical industry, enamels and glazes. As a part of alloys it is used in special steels and as zirconium boride, melting point 3,300°C. Zircon is admixed with hafnium, which is difficult to separate from zirconium. The presence of Hf is harmful in an utilization of zirconium in the atomic industry because it diminishes the permeability of Zr for neutrons. Titanium minerals are concentrated in magmatic rocks and their derivates. The most important are basic magmatic rocks with ilmenite mainly. In most cases, ilmenite is not separated, but developed as titanium-magnetite. This type of deposits bound on anorthosites, gabbros, pyroxenites and amphibolites are residual liquid segregation deposits usually injected in zones of weakness. The most important in an economic utilization of titanium-magnetites is the degree of separation of ilmenite and magnetite. At a temperature of 800°C, a mixing of magnetite and ilmenite is continuous, at 700-600°C the



isomorphic mixture disintegrates and an intergrowth of crystals of ilmenite and magnetite originates. The degree of separation of ilmenite crystals is decisive for a treatment of iron ore. Two types of deposits of Ti-magnetite occur - one with a high content of Ti (over 20%) connected with anorthosites and gabbros, the other with 5-8% TiO2 bound to pyroxenites and peridotites. By contrast, rutile minerals are concentrated in acid magmas, as accessories in pegmatites, in contact deposits and vein deposits of the alpine type. Zirconium minerals with a hafnium admixture are quite common minerals to almost all types of rocks but, substantially, occur as accessories in granitic rocks and their pegmatites, in some granodiorites and badeleyite especially in syenites with a high alkali content. Both titanium and zirconium minerals are hard, with a specific gravity of 4 or more and can easily accumulate as heavy minerals in placer deposits. Placers are first fluviatile and finally marine either in beach or dune accumulations. A heavy minerals assemblage on the seashore normally includes ilmenite, rutile, magnetite, zircon, monazite and many others such as andalusite, kyanite, garnets, leucoxene. The assemblage composition varies according to the extension of mineralogical provinces of the hinterland. The presence of some minerals depends also on the cyclic development of a sand body, while a polycyclic development can eliminate less resistant heavy minerals such as magnetite or, during a temporary deposition and subsequent transport, the iron in titanium-magnetite may be removed leaving ilmenite only. There are several developmental stages of heavy minerals accumulations in economic beach and dune deposits: suitable parent rock containing heavy minerals a period of long and deep weathering and the origin of a weathering profile uplift and destruction of weathered land surface stream transport of resistant heavy minerals deposition on the seashore in one or rather more cycles sufficient sea-energy, energy of currents and waves on an emergent seashore. A deposition of sand with heavy minerals on beaches occurs generally in narrow strips, sometimes at a high concentration; these may be carried by wind action to form subsequently large dune deposits thereby decreasing frequently the original higher concentration of heavy minerals. All placer deposits are mined in the same manner i. e. as an extraction of building sand using front-end loaders, excavators or dredges. Big floating dredges are used on beach - and dune deposits and heavy minerals are concentrated on the board using gravity methods - spirals, shaking tables, magnetic and high-intensity electromagnetic separation of magnetic and non-magnetic and low and high conductive minerals. These placers are mined for an extraction of ilmenite and rutile, zircon is a byproduct. The mining of primary titanium minerals is confined to a few large deposits in the world: titania-ferrous magnetite (ilmenite in anorthosite) gabbro body in Quebec, Canada, ilmenite deposits in anorthosites in Norway and ilmenite-magnetite and titanomagnetite in the Ural, Soviet Union. A special method, known as QIT process has been developed by Quebec Iron and Titanium to produce titanium slag and pig iron in electric furnaces. The same process is used for low quality S-African ilmenite at Richard's Bay. Baddeleyite in primary deposits is mined on the Kola peninsula from ultrabasic igneous complex and from Palabora, an igneous complex in Transvaal. Very pure concentrates of zirconia are obtained (96-99% ZrO2). In Mozambique there are present both primary and secondary titanium deposits. Descriptions are available of many zircon localities both in primary and placer deposits. Types of titanium mineral deposits (see Fig. 3.2.1): 1. Primary deposits of ilmenite: a) titanium-magnetite deposits in gabbro-anorthosites b) ilmenite, magnetite, rutile in pyroxenite and alkaline rocks in Precambrian c) ilmenite-rutile in pegmatites 2. Primary deposits of rutile: a) in quartz veins or pegmatites b) in metasomatic deposits 3. Primary zirconium: in pegmatites and alkaline rocks 4. Secondary deposits:



in placer of fluviatile and marine origin.

la) Primary deposits of magmatic origin of Upper Precambrian rocks are connected with the Tete gabbro-anorthosite Complex (see Fig. 3.12.1) which extends for almost 120 km in an irregularly E-W trending massif N of the town of Tete. According to Hunting (1984) it is a large sheet or monolith between 10 to 20 km thick composed of basic igneous rocks. It consists of gabbro, norite and anorthosite with minor ultrabasic rock types. It also contains plenty of opaque minerals (ilmenite, magnetite, sulphides) enriched in titanium and vanadium, impoverished in chromium and cobalt when compared to those of layered intrusions such as the Bushveld Complex. It is a rigid body which resisted deformation and could be compared with the Allard Lake in Canada, the Adirondacks area in the U. S. A. or the Tellnes deposit in Norway.

Fig. 3.12.1 Schematic cross section of the Tete Complex (Hunting, 1984) (295 kB)

Gabbro-anorthosites are associated with titanium-magnetite deposits, which result from a magmatic segregation and later injection into the zones of weakness. These ilmenite-magnetite segregations are widespread in the form of individually small very irregular dykes, sheets and lenses. Sometimes, they contain base metals-copper, nickel and cobalt. The Tete gabbro-anorthosite Complex covers an area of about 6,000 km2 and is of Upper Precambrian age. The mineralogical assemblage is composed of magnetite and ilmenite intergrown with subordinate minerals of titanospinel, ulvospinel, anatase, pyrite, chalcopyrite and pyrrhotite. Titanomagnetite deposits stretch over 140 km in NW-SE direction along the N- bank of the river Zambezi. The main deposits, from NW to SE, are these: Massamba Inhantipissa (Singere) Txizita Machedua Antigo Caldas Xavier Lupata The average composition of titanomagnetites is: 20% TiO2, 50% Fe2O3, 18% FeO, 0.60% V2O5. The maximum content of TiO2 - 32.9% was discovered in the deposit Txizita. Also rutile is often present in magnetites. Mineralogically, the ore contains 20% ilmenite, 30% magnetite and 50% hematite. Ilmenite occurs in grains of about 0.2 mm in size, exceptionally 0.6-2 mm in diameter, in some places in laminae and needles intergrown with magnetite and hematite.

Ore composition (in %):

Locality TiO2 Fe V2O5

Deposit Machedua 14.40 - 18.50 49.07 - 50.89 0.51 - 0.71

Mt. Txizita 32.76 44.98 -

Mawili 9.75 - 13.29 50.86 - 52.10 - Mg 0.90 - 2.0

Pilot tests performed with Tete titanomagnetite showed that the content of TiO2 was low and Ti-slag, as a byproduct of iron, of a low grade.

1b) Titanium minerals in pyroxenites and alkaline rocks of the Precambrian Two localities were found in metamorphic rocks of the Mozambican belt: Ulongue in the Tete Province and the deposit Mazua near Memba in the Nampula Province. The Ulongue ilmenite prospect was discovered by a UN project (1982) as a small hill 8 km SE of the village. The deposit is located in the Ulongue metallogenic zone of NW-SE direction containing graphite, iron ore, ilmenite, asbestos, vanadium minerals and limestone. The zone is underlain mostly by paragneisses, migmatites and granulites, which are intruded by basic, acid and alkaline rocks.



Three ilmenite localities coincide with the eastern graphite-bearing zone, two at Chiziro with three ilmenite dykes, 200 m long and 0.75 to 2.5 m wide with 53% TiO2, one at the river Mepassadoze about 1,800 m NW of Chiziro with an ilmenite dyke in a wide zone of kaolinized granulite, 600 m long and 2.5 to 3.0 m thick. The deposit Flazua is situated 40 km NW of Memba in the Nampula Province and was discovered by Geol. Institute - Beograd during an exploration for asbestos. The ilmenite body is 10 km long, average width 20 m, and reserves of ilmenite calculated up to a depth of 5 m are 2,700 000 t. The ore body is part of the pyroxenite-amphibolite zone and contains also rutile. It needs further exploration. The deposit appears to be promising, and probably of the intrusive type connected with as yet unknown anorthosite-gabbro bodies.

1c) Ilmenite (rutile) in pegmatites Ilmenite together with magnetite is found very often in pegmatites of the Alto Ligonha district s. l. In zonal pegmatites in the areas of Mocuba, Nauela and Morrua ilmenite is concentrated in external zones and especially in the contact zone with andalusite, rutile, beryl, hornblende etc. and in the zones of homogeneous and "book" mica. Ilmenite and rutile are absent in the internal zone, but rutile could again be found in the contact zone between the quarzitic nucleus and the quartz-mica zone. Ilmenite occurs normally in grains, without a crystalographic habitus, in fragments up to 7.4 cm (Barros-Vicente, 1963). Ilmenite-rutile (estruverite) is rare in pegmatites of Nampoca and Morrua. Rutile, generally in quartz crystals, occurs in pegmatites of Muiane and Nahora. At Morrua, it is grained and found often in the inner zone with microlite.

2a) Rutile in quartz veins and pegmatites In the Tete Province, NW of the town and around the river Zambezi, several rutile locaties were discovered in the past. Along the road Tete-Estima, on the river M'Tetadzi, there are outcrops of quartzitic gneisses with several veins of quartz and pegmatite with abundant rutile. Rutile in quartz builds remnants of up to 5 cm in diameter and some loose crystals in alluvial deposits may attain 8 cm length (Real, 1959 in Godinho, 1970). The zone with rutile is 4 km long. Another large site of its occurrence lies on the river Mulato in quartz veins and pegmatites and in eluvial deposits. Near river Zambezi, in quarries of Boroma, rutile can be encountered in pegmatites within the contact zone of gneiss and gabbro.

2b) Rutile in metasomatic deposits In the same area as 2a, rutile was found at Zumbo on the Zambian border, in crystalline limestones with inclusions of pyroxene, mica, graphite. In the locality Cacame near the road Tete-Furancungo, a metasomatic deposit with abundant rutile developed in limestone near its contact with diorite. The content of rutile averages 60.42%, with 1.05% iron and 2.85% ilmenite; small amount of chalcopyrite and pyrite is present.

3. Primary zirconium occurrence Zircon is represented in several pegmatites of the Alto Ligonha district s. l., for example at Boa Esperanca, Namecuna, Nuaparra, Nampoca, Macochaia, Namacotche, Muiane, Muhano, Namirrapo etc. (Barros-Vicente, 1963). Some crystals of zircon are 2 cm long with one exception measuring 6.5 x 3.5 x 3.5 cm (at Namecuna). The mineral is generally radioactive. Zircon is associated with quartz, bismuthite and columbo-tantalite in the inner zone, in some pegmatites as an intergrowth with xenotime or microlite. The variety naegite -zircon with yttrium, niobium-tantalum, thorium and uranium associated with quartz, bismuthite, thorite, rhabdophanite and metatorbernite, was found in Nuaparra pegmatite. Another variety cirtolite with uranium, thorium, RE was found at Morrua. Some zircons have a greatly increased HfO2 content of 32% at Namacotche. Altered zircon of the brownish vitreous variety known as malaconite was found in the area of Ribaue. Chemical analysis from pegmatite Namecuna: %

SiO2 28.91

ZrO2 + HfO2 66.21

TiO2 0.14



Fe2O3 0.64

Al2O3 1.02

MnO Tr.

U3O8 0.97

ThO2 + REO 0.55

CaO 1.22

MgO 0.23

L. i. 0.27

residue 0.64

Total 100.80

In the Niassa Province, within the sedimentary basins of the rivers Lunho and Fugue, several bodies of kimbertitic rocks were discovered in 1982-83. Kimberlites and its breccia form several dykes with a typical mineralogical assemblage of ilmenite, zircon and rutile; they are developed in the Maniamba graben.

4. Secondary deposits-placers The description of localities of a primary occurence of Ti-Zr minerals was intended to point out possible primary resources-parent rocks of these mineral in the hinterland of the seashore, where the most important and economic deposits of these minerals occur. Naturally, some of these primary deposits may gain in economic importance if the concentrated minerals were present in large quantity and in good quality, but these cases are an exception. However, for a development of secondary accumulations, minerals of a rock-forming nature or accessory minerals in igneous and sedimentary formations are more important. An example of small-scale accumulations heavy minerals (HM) are alluvial deposits, for example those of the river Zambezi basin, with a concentration of ilmenite, rutile, or zircon. These placers represent, in fact the direct source for marine accumulations around the mouth of the Zambezi river. Similar situation exists around the estuaries and deltas of other big Mozambican rivers as the Limpopo, Save, Ligonha, Lurio and Rovuma. The origin of-HM accumulations is a complicated process which passes through several stages. A sorting of HM occurs gradually along with a destruction of resistant minerals, and the longer this process (weathering-transport-sorting) the higher the degree of sorting and the higher the content of HM remnants within the mineralogical assemblage. The parent rocks of HM in Mozambique are present in various Precambrian formations: with regard to the catchment areas of big rivers they are far inside the African continent. Along the Mozambican coast HM accumulations could be found either on beaches or in dunes. In the past, titanium minerals were mined at Pebane (1959), and several other deposits were explored. The main useful minerals were: ilmenite, leucoxene, rutile, zircon, monazite, kyanite, andalusite and magnetite. The titanium group is the most useful and predominant one. The main mineral is ilmenite, FeTiO3 of 48.6 - 57.3% TiO2 with the presence of MgO and up to 6% Fe2O3. Leucoxenized ilmenite is typical of all Mozambican deposits. Unaltered ilmenite grains hardly ever occur. The process of leucoxenization represents a removal of some iron and the recrystallization to an anatase - rutile mixture: it leads to an increase in TiO2 over the theoretical content. On the other hand, ilmenite does not reach even this level in some deposits. This might be due to the fact that there are some magnetite inclusions which change the Ti: Fe ratio in favour of Fe. The results show, that the TiO2 content is below 50% in the whole area, from South African border to Xai-Xai up to the river Save, to an area which is called the Limpopo paleodelta. In some places, is the content of Cr2O3 higher, up to 1%. Deposits NE of the mouth of the river Zambezi also contain low-grade ilmenite. At Pebane the TiO2 content is high, but the content of impurities is increased. The commercial product from Pebane contains 0.15% Cr2O3 and 53% TiO2. A spinel was discovered to contain about 25% of Cr. Good-quality ilmenite can be found in Angoche and the Quinga area, but also at Gorai, Idugo, Moma and Moebase. It is believed that "old concentrates" of multi-cycle origin contain a higher-quality ilmenite. The reason could be a prolonged weathering process and a partial removal of iron.



Rutile TiO2 is the best titanium mineral, with a TiO2 content between 89.5 and 99.0%. Zircon Zr SiO4 is a byproduct of ilmenite mining. Chemical analyses show a ZrO2 content from 46 to 60%. HM deposits in coastal Mozambique (from south to the north): Ponta d'Ouro-Maputo Marracuene Around Limpopo river mouth Xai-Xai Ponta Zavora-Jangamo Praia Morrungulo Inhassoro Beira Deia Ilha Olinda Zalala Pebane (Idugo, Gorai, Raraga) Moebase Moma Angoche Congolone Quinga small local incidence N of Ilha Moçambique. The most promising deposits are those between Quelimane and Quinga. The deposits of southern Mozambique are not well-known, but widely extended beach- and dune deposits of the Quaternary in an 80 km wide belt and an occurence of HM on modern beaches suggest a large potential of these low-grade deposits. In 1983, Aquater of Italy made a detailed exploration in the Quelimane area and its estimate of reserves was 24.9 Mt of HM sand i.e. 2.5 Mt of HM, of which 2 million t was ilmenite. The quality of ilmenite was 48.5-50% TiO2 (its content in mineral sand 9.61%), 65.5% ZrO2 for zircon with reserves of about 200,000 t. At Angoche, the Jugoslav Team explored the biggest dune in Mozambique called Congolone and surroundings and discovered over 14 Mt of HM in the area. The Congolone dune contained 2.2 Mt of HM in grade over 8% in the sand and 2.8 Mt of HM 4-8% HM in sand. Ilmenite represents over 81%, leucoxene 1.3%, zircon 5.2%, rutile 2.8% and monazite 1.2% of HM suite. Chemical analyses of ilmenite: %

Area TiO2 FeO Fe2O3 Cr2O3 P2O5 V

Ponta d'Ouro 49.67 35.96 13.05 0.22 0.042 0.04

Marracuene 51.16 27.62 17.99 1.04 0.033 0.12

Limpopo 47.60 31.99 18.75 tr. 0.054 0.075

Xai-Xai 47.13 32.71 17.55 0.41 0.061 0.11

Zavora 48.83 33.86 15.72 tr. 0.036 0.093

Morrungulo 49.93 31.97 15.29 tr. 0.023 0.099

Inhassoro 49.70 27.97 20.12 0.93 0.037 0.13

Zalala 46.13 27.91 21.79 0.80 0.34 0.098

Pebane 52.76 22.15 20.27 0.21 0.120 0.073

Moebase 53.75 20.14 23.86 0.26 0.042 0.081

Angoche 54.41 22.47 23.09 0.23 0.078 0.063

Congolone 55.36 16.34 25.71 0.18 0.072 0.063



Quinga 56.80 14.43 25.06 0.17 0.120 0.052

The quality of ilmenite is low in most localities, but may be improved by treatment. Clearly, the best-quality ilmenite is found in the NE part of Mid- Mozambique between Pebane and Quinga. Chemical analyses of rutile: %

Area Cr V Fe2O3 TiO2

Ponta d'Ouro 0.076 0.226 0.67 99.0

Xai-Xai 0.210 0.093 1.36 08.3

Macuse 0.101 0.211 0.77 98.9

Idugo 0.118 0.223 0.82 98.8

Pebane 0.104 0.236 1.32 98.3

Angoche 0.102 0.204 1.40 98.3

Quinga 0.074 0.225 0.70 99.0

A true picture of mineral assemblage in a HM concentrate of Mozambican beach sands, from which several economic minerals mentioned above are being recovered is shown by the following analysis: Praia Zalala - beach concentrate, analysis by Geoindustria, Prague: g/m3

Magnetite* 5.5 spinel black tr.

Scheelite tr. spinel green tr.

Gold 1 grain garnet 50

Titanite 1.5 rutile 5.50

Tourmaline upto 1 brookite tr.

Andalusite tr. anatase upto 1

Kyanite 1.5 limonite tr.

Monazite tr. leucoxene upto 1

Sillimanite 1.5 martite tr.

Staurolite 1.5 apatite upto 1

Zircon 1.5 zoisite tr.

Epidote 5.50 carbonates (org.) tr.

Pyroxene tr.

Ilmenite tr.

Remark: Magnetite including titanomagnetite and chromite.

On the deposit Quelimane three control analyses of HM concentrate were made in 1987 in U. S. A. at Rice University and the University of Georgia. First the size analysis and sink/float analysis were performed with these results:

Sample + 14 mesh - 14 mesh floating - 14 mesh sinking

1. 0.7 86.3 13.0

2. 1.3 82.9 15.8



3. 0.2 83.6 16.2

The -14 mesh sink fraction represents the HM suite, which in this case is composed of different heavy minerals, in Mozambique divided into two groups: economic HM and waste silicate (non-economic) HM. The Quelimane deposit therefore represents a mineralogical suite rich in non-economic HM which is common to fluviatile sediments, here sediments transported by the river Zambezi and deposited on the beach in very short distances. Analysis of sink fraction:

Sample 1 2 3

Rice U U of GA Avg Rice U U of GA Avg Rice U U of GA Avg

- Ilmenite 24.3 30.3 27.3 23.6 30.6 27.1 34.0 34.3 34.2

Economic HM

Rutile 0.8 0.7 0.7 3.1 1.0 2.0 1.9 0.7 1.3

Zircon 1.7 1.2 1.5 0.4 1.9 1.1 5.1 3.1 4.1

Monazite 0.4 0.4 0.4 0.4 0.4 0.4 N.D. 0.4 0.2

- Iron oxide 10.1 1.3 5.7 9.8 2.5 6.2 12.2 2.5 7.4

- Amphibole 18.6 32.2 25.4 30.1 37.0 33.5 19.1 31.4 25.2

Garnet 10.9 0.3 5.6 16.4 1.8 9.1 14.5 6.5 10.5

Pyroxene 8.6 3.4 6.0 8.6 3.6 6.1 5.8 4.3 5.0

Non- economic HM

Sphene 3.5 4.1 3.8 2.1 4.2 3.2 2.3 2.5 2.4

Apatite 2.0 1.1 1.6 2.3 1.6 2.0 0.8 2.1 1.5

Spinel 1.2 N.D. 0.6 N.D. N.D. N.D. 0.7 N.D. 0.4

Al-Sil 1.8 1.9 1.8 0.9 2.4 1.7 0.8 N.D. 0.4

Feldspar 4.2 1.1 2.6 0.4 0.4 0.4 N.D. N.D. N.D.

Biotite N.D. N.D. N.D. 0.2 N.D. 0.1 0.5 N.D. 0.2

Quartz 11.9 7.7 9.8 1.7 0.9 1.3 2.3 1.0 1.7

Iron silicates N.D. 14.3 7.2 N.D. 11.3 5.6 N.D. 10.8 5.4

- Chromite N.D. N.D. N.D. N.D. 0.4 0.2 N.D. 0.4 0.2

Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0

The table shows, that ilmenite represents just about 30 to 55% of total HM i. e. its actual content in sand is 3.9 to 5.5%. Because the commercial product of ilmenite requires a minimum of 45% TiO2, but normally about 60% TiO2, the quality of ilmenite was this:

Sample1 2 3

Rice U U of GA Avg Rice U U of GA Avg Rice U U of GA Avg

TiO2 content % Distribution of grains

< 45 % 45-50% 50-55% >50%

3.6 41.1 30.4 25.0

20.7 44.4 19.8 15.1

12.1 42.8 25.1 20.0

1.8 30.4 57.1 10.7

13.8 38.4 28.5 19.3

7.8 34.4 42.8 15.0

2.3 37.2 38.4 22.1

9.3 35.8 29.9 25.0

5.8 36.5 34.1 23.6

No. of grains counted

300 300 - 300 300 - 300 300 -



Avg TiO2 content (wt % in ilmenite)

52.0 49.0 50.5 51.7 50.5 51.1 52.0 49.0 50.5

No. of grains for avg TiO2 content

56 63 - 56 68 - 86 77 -

Conclusion: The above data indicate that the maximum TiO2 content that could be produced as an ilmenite product from the three (3) samples examined will be 49-50% TiO2 assuming standard extraction techniques and recovery factors. The estimated reserves of HM in dune- and beach deposits are substantial in Mozambique - over 120 Mt, of which about 95 Mt is ilmenite, 3.6 Mt futile and 6 Mt zircon. Futher HM reserves, of an order of about 60 Mt, were discovered on the shelf in the Zambezi delta by the research vessel Valdivia (1971). Conclusions: Primary deposits of titanium minerals are present in the Tete gabbro-anorthosite Complex in the form of titanomagnetites, with about 20% of TiO2. The treatment of this ore yields low-quality titania slag. More promising are some sites of ilmenite occurrence in Precambrian basic rocks, especially at Mazua near Memba in the Nampula Province. Such deposit should be worth further exploration. Long before an exploitation of all possible primary deposits of titanium and zirconium minerals, huge reserves in beach and dune deposits should be utilized. These deposits place Mozambique in the position of a potential world producer of ilmenite, rutile, zircon and monazite.



Cilek: 3.13. Zeolites

3.13. Zeolites Comprise a large group of related minerals, usually well-crystallized and found in cavernes of lavas, mainly basalts. They are hydrated aluminium silicates of alkaline elements with the structure of an open aluminosilicate framework composed of (Si, Al)O4 tetrahedra. Wide channels inside the structure contain molecules of water and cations of Na K and Ca which balance the negative charge of the framework. The name zeolite-boiling-stone - is due to their intumescence (bubbling) when heated. The water is released continuously in increasing temperatures and dehydrated zeolites can absorb other liquids without disrupting the strong bonded framework structure. Zeolites with different framework topologies are found in nature (about 30 varieties) and are also produced synthetically (about 150). Economically important natural zeolites:

analcime Na16 [(AlO2)16 (SiO2)32] • 16H2O

clinoptiolite Na6 [(AlO2)6 (SiO2)30] • 24H2O

chabasite Ca2 [(AlO2)4 (SiO2)8] • 13H2O

mordenite Na8 [(AlO2)8 (SiO2)40] • 24H2O

phillipsite (K, Na)10 [(AlO2) (SiO2)22] • 20H2O

laumontite Ca4 [(AlO2)8 (SiO2)46] • 16H2O

erionite 4.5(Ca, Mg, K2, Na2)4.5 [(AlO2)9 (SiO2)27] • 27H2O

natrolite Na16 [(AlO2)16 (SiO2)24] • 16H2O

The zeolite structure is used in the industry for its special properties: a) adsorption b) molecular sieve c) ion-exchange The first two properties are used when water is removed by heating and the zeolite can then adsorb other molecules. The channel diameter range from 2 to 7 Å therefore selected molecules only are accepted. This property is used in a separation of hydrocarbons, adsorption of H2S, CO2, SO2, cleaning radioactive waste of Cs, Sr. The ion exchange property is used in agriculture in a similar way to bentonite, to bind fertilizer elements and release them slowly, in animals aid nutrition and as a carrier of herbicides, pesticides and fungicides. Natural zeolites are used in hydraulic cement productions, as a filler in the paper industry, as a polishing agent, a catalyst and others. Knowledge of zeolite deposits is fairly recent, just about twenty years, but they are widespread and found in different types of deposits of saline alkaline lakes, deep sea sediments, in volcanic glass altered by meteoric water, hydrothermal deposits and initial metamorphic stages. Generally zeolites originate from a reaction of pore water with other materials such as volcanic glass, clay or silica. They alter further by a reaction of pore water. Clinoptiolite is altered to analcime, which may be replaced by laumontite etc. and this results in a



reduction of a number of zeolite varieties in older rocks (no zeolites occur in the Early Precambrian). The process of zeolite genesis - zeolitization - is rapid, they originate from basaltic or rhyolitic glasses in a few days or years. Zeolite deposits may attain several tens to hundreds of meters and, in many deposits, especially those developed in open hydrologic systems they occur together with smectites (upper zone); the lower zones have a higher pH and contain dissolved solids. Important deposits are present in places of hydrothermal alteration of volcanic rocks by intrusive massifs and under the effect of fossil or modern geothermal water. Generally, zeolite deposits may be expected in areas of volcanic activity owing to an alteration of volcanic glasses, tuffs and tuffites by the action of hot waters or meteoric waters and in connection with smectites.

In Mozambique, an occurrence of zeolites, well-developed crystals in cavity, was described by Carvalho (1944) from Mossurize in Karroo basalts. In 1969, zeolites from Corumana Mountain in the Lebombo Range (NW of Maputo at the town of Sabie) were described by Neves and Nunes from the contact zone of rhyolites and basalts. Big crystals of quartz, stilbite, laumontite, scolecite and natrolite measuring 10 x 30 cm, are found in cavities. Stilbite occurs in typical larger-sized sheaf-like aggregates, white or light reddish in colour, in a thin tabular habit. The theoretical formula is 4 • [Ca (Al2Si7O18) • 7H2O] which differs in a substitution of Na Al - Si and Ca Al2 - Si2.

Chemical composition (in %) Cell content

SiO2 56.18 Si 26.19

Al2O3 15.26 Al 8.39

Fe2O3 0.80 Fe 0.27

CaO 8.32 Ca 4.14

Na2O 0.70 Na 0.61

K2O 0.05 - -

H2O 18.64 H 57.77

total 99.95 O 98.75

Laumontite occurs in two phases - fully hydrated laumontite and the less hydrated leonhardite. The mineral is milky white and occurs both in a prismatic habit over stilbite, and in veins. Comparing the cell content with a theoretical value corresponding to formula 4 [Ca (AlSi2O6)2 • 4H2O] a good fit exists except for a lower value of hydrogen. Natrolite and scolecite of a light reddish colour are developed either in veins of a fibrous habit or in close associated parallel layers. The chemical analysis revealed: SiO2 - 46.94%, Al2O3 - 26.11%, CaO - 4.07%, Na2O - 12.60%, K2O - 0.01% and H2O - 10.50%. Aggregates are made up of about 23 to 35% scolecite and 76 to 63% natrolite. The paragenesis of minerals at Corumana in cavities of basalt begins with saccharoid quartz, then white stilbite in crystals and finally laumontite. Fibrous zeolites - natrolite and scolecite - are intimately



associated and crystallized simultaneously. Zeolites in crystals in cavities and veins in Karroo basalts of a late-hydrothermal origin will probably be more widely distributed than described for the above mentioned two localities. Microcrystalline zeolites, of economic importance in the country, can be expected in thick layers of rhyolitic and basaltic ash-tuffs and tuffites altered either directly in shallow basins during or shortly after the deposition or by underwater action. The zeolites could be found below the bentonite layers or in the zones of higher tectonic movements influenced by hydrothermal or meteoric waters. The importance of zeolites discovery for the Mozambican agriculture and industry is not in need to be stressed. A potential source of zeolites are Karroo volcanics from the Lebombo Mts. range to the area of Chibabava of Karroo volcanics in the Tete Province.



Cilek: 3.2. Asbestos

3.2. Asbestos The term asbestos is generally used for the group of minerals which consist of flexible fibers - closely packed crystals, or fibrils that can be spun or are resistant to heat andchemical attack. The longer fibers "spinning" - blended with cotton, rayon or other fibers are used in yarn or cloth; "nonspinning" fibers are valuable for different types of fireproofing and insulation materials. Asbestos minerals fall into two groups: i) serpentine, which is represented by chrysotile - Mg6[(OH)4Si2O5]2 ii) amphibole,which is represented by anthophyllite - (Mg, Fe2+)7 (Si8O22) (OH, F)2, amosite, crocidolite. The asbestos minerals are products of metamorphism and occur as "cross fibers" ex-tending from wall to wall, "slip fibers" roughly parallel to the vein walls and "mass" fibers as an aggregate of non-oriented fibers. Asbestos deposits originated by alteration processes in four types of rocks: 1. ultramafic rocks of alpine-type with chrysotile mainly 2. ultramafic rocks-stratiform deposits with chrysotile mainly 3. banded ironstones with amosite, crocidolite, anthophyllite 4. dolomitic limestones-contact deposits with chrysolite About 95% of the world production is chrysotile or "white asbestos", fusion point 1,521°C. Chrysotile is found in fillings of veinlets in serpentine producing largely a complex stockwork. The rock is mined in bulk, crushed and asbestos is separated in the mill. Amphibole asbestos varies greatly in its chemical composition, with several impurities and chemical substitution. Crocidolite known as "blue asbestos", has generally a good development of long fibres, low fusion point 1,193°C, but a high resistance to acids and alkalies. Amosite "brown asbestos" is of coarse texture and resistant to acids and alkalies and also heat. Anthophyllite is well-resistant both to heat (melting point 1,468°C) and chemicals, but has short harsh fibres of poor flexibility. Its present economic utilization is negligible. The most abundant are asbestos deposits with chrysotile in serpentinites. They originate by the process of serpentinization (autometamorphic) of ultrabasic rocks which probably represent the rocks of the upper mantle. The majority of chrysotile is formed,most probably, after serpentinization by the action of solutions associated with granitoid intrusions. According to the temperature and pressure in different zones, these minerals developed:

650°C - biotite zone near the granites

550-600°C - amphibole zone (anthophyllite)

500°C - talc zone

450°C - antigorite zone

400°C - chrysotile zone ultrabasic rock



Autometamorphic serpentinization may have affected 40-80% of rock such as peridotite or pyroxenite; serpentinite could further be altered by hydrothermal solutions associated with granitic veins and massifs intruding the body of mafic rocks already fractured during the orogenesis. Asbestos minerals are used mainly in the manufacture of asbestos-cement products(sheet, pipe), in flooring products and in friction products (brake linings etc.). Their utilization in asbestos textiles, paints production, insulation and as filler is small. Asbestos mining, treatment and end uses represent health hazards such as lung disease, cancer of the lung etc. Therefore, there is a considerable pressure for a replacement of asbestos fibre. This results in a year by year reduction in the consumption of asbestos and at present the quantity of asbestos fibre available exceeds world demands. In Mozambique, two genetic types of asbestos could be found in four areas (see Fig.3.2.1): 1. chrysotile asbestos in serpentinite body originating from a metamorphosis of Archean greenstones of the Zimbabwe craton - deposit Serra Mangota near Manica 2. small chrysotile asbestos bodies as clusters of reworked old greenstone belts within the Mozambican belt - Manica, Sofala, Upper Zambezi provinces 3. anthophyllite asbestos originating from a serpentinization by the action of solutions associated with granitic intrusions-mixed type of stratiform ultramafic intrusion and partly probably of banded ironstone type - deposit Mavita S of Manica 4. anthophyllite asbestos in glimmerites of ultrabasic rocks of the Mulatela - Nampula Province.

Fig.3.2.1 Occurences of asbestos, beryl, talc and soapstone, titanium minerals, rutile, zircon (471 kB) 1. Serra Mangota In 1930, a small exploitation of chrysotile asbestos was in progress at Serra Mangota about 10 km NNE of Manica. In 1951, mining was not reported. Serra Mangota is a ridge of E-W extension composed of serpentinite and schists. It is a part of Archaic rocks - greenstones belt of the Upper zone of the Zimbabwe craton. In Mozambique, just accross the border with Zimbabwe, these archaic metasedimentary and volcanic rocks of the Manica (Macequece) Formation produced an E-W trending belt resting on granitic rocks. They are composed mainly of serpentinites with subordinary inclusions of metasediments. Serpentinites build extensive bodies within the Manica Formation and also outside it resting on the surrounding granitic shield. They are supposed to be either metamorphosed lavas or intrusive rocks with intercalations of talc schists, chloritic and sericitic schists and banded ironstones (see Fig. 3.2.2). The Manica Formation is famous for its gold mineralization.

Fig. 3.2.2 Geological map of Serra Mangota (Obretenov, 1984) (629 kB)

The Serra Mangota s. s. is a steeply dipping serpentinite body with two petrological varieties: a hard, green serpentinite and lighter green carbonated one. The hard green variety forms the highest parts of the ridge, while the softer, carbonated serpentinite forms the levelled plateaus. Furthermore are present talc



schists, young intrusives of microgranites and dolerites, ferruginous quartzites and metasediments. Several faults of NE-SW direction traverse the range. Separated asbestos outcrops are present over a strike of about 5 km. Eastwards, the amout of carbonated serpentinite decreases and talc schists become apparent. Towards the west, carbonated serpentinite with short good-quality fibers is predominant. In the east, two areas were exploited before World War 2 (with long fibres). Long, rich fibers were not of great interest, because they occurred invery small serpentine lenses surrounded by talc schists. The mining area was in thewestern part mainly, with carbonate serpentinite with good amount of fiber over a dis-tance of 1,200 m and width of the zone 200 m, dipping steeply (see Fig. 3.2.3) The favourable host rock of chrysotile is a carbonate serpentinite variety with a fiber content arround 2 %. Asbestos extracted from open pits was of good quality but small in quantity (some samples can still be seen in the museum in Manica). Mining was abandoned before 1940 and later prospection revealed that the bulk of serpentinized bodies have the oreexhausted. Only some ore with more than 1% of fiber remained. No talc evaluation was made.

Fig. 3.2.3 Cross-section of Serra Mangota asbestos-talc deposit (311 kB) 2. Small occurrence or chrysolite asbestos Many small sites of occurrence of asbestos were observed in Manica, Sofala and theUpper Zambezia provinces. They developed within clusters of reworked old greenstonesbelts in many parts of the Mozambican belt. The greenstones are represented by serpen-finite bodies surrounded by metasediments and included in gneisses, migmatites andgranitic rocks at quite a big distance eastwards from the eastern margin of the Zimbabwecraton. Within the Zimbabwe craton, in the area of the rivers Bonde and Zonue, "Cronleygreenstones" were observed by Hunting (1984); they extended from Zimbabwe, with sev-eral tenses of serpentinites and banded ironstones with possible asbestos occurrences(see Mavita deposit). Chrysotile was found in the Maravia area near Fingoe and in the Monte Atchiza area.Especially Monte Atchiza with its ultrabasic complex and chrysolite occurrence has beenin the centre of interest for a long time. It consists of bodies of serpentinites, gabbros andnorites, with minor peridotites and pyroxenites. This ultrabasic complex intruded themetasedimentary Fingoe Formation and later was intruded itself by post-Fingoe granites. Monte Atchiza complex was regarded as the northern extension of the Great Dyke ofZimbabwe, but it is younger and differs from it mainly in a dominance of olivine over orto-pyroxene in peridotites and pyroxenites. It seems, that ultrabasic rocks are in a stratiformarrangement with serpentinites with patches of chrysolite. Peridotites and pyroxeniteshave also partly been altered into serpentine, actinolite, anthofyllite and opaque minerals. No significant mineralization of chromium, nickel, platinum as that of the Great Dyke and the Bushveldt Complex, was observed there (Hunting, 1984). Some inextensiveoccurrences were found of chromite and asbestos only. According to Real (1960) the as-bestos at Monte Atchiza occurs in two different varieties - in veins and veinlets (in thenortheastern part) of picrolite and antigorite associated with accumulations of garnierite(Atchiza-Nhantreze) and highly silicified in hard- and long fibres - amphibole asbestos (up to 50 cm long) (N of Mt. Atchiza) within the metamorphic rocks of the Formation Fingoe. Results of analyses of two samples of serpentinites of Monte Atchiza (in %):



SiO2 38.40 40.25

Al2O3 2.09 2.61

FeO 1.69 1.46

Fe2O3 5.32 4.36

Fe2O3 + FeO (7.01) (5.82)

MgO 38.87 38.85

CaO 0.45 -

Na2O 0.14 0.18

K2O 0.24 0.16

TiO2 0.05 -

P2O5 - 0.08

Cr2O3 0.34 0.35

MnO 0.12 0.02

NiO 0.57 0.08

Near the Malawi border, about 120 km N of Tete and 1.5 km W of the village of Tzangano, an ultrabasic body, partly serpentinized was encountered. The body is some 2.4 km long and 200-400 m wide. Tough, initially, only tremolite and actinolite were found, also long fibre-asbestos was present in lenses and veins. The lenses of asbestos are 20-40cm wide, that of long fibre-anthophyllite attain a thickness of 2.6 m. Magnetite is ubiquitous, in the ultrabasic body. The enclosing rocks are biotite gneisses. No analyses of asbestos were made, only one sample of serpentinite was analyzed for the presence of metals: 80 ppm Co, 15 ppm Cu, 30 ppm Pt, 0.26% Cr and 0.81% Ni. On the footwall there is a outcrop of grey-green talcose mica schists. River Ualadze asbestos Hunting (1984) reports a small occurrence of asbestos on the river Ualadze near Chicoa at the Cabora Bassa dam. The asbestos is associated with a pair of basaltic dykes which intruded coarse, mesocratic, unfoliated granite with feldspar phenocrysts in a groundmass of hornblende, quartz and biotite. The dykes are cut by a sub-horizontal shear plane along which the asbestos occurs. It can be inferred from the occurrence of thicker sheets of asbestos where the shear plane cut the earlier dykes, that asbestos developed probably during shearing and hydration of the basaltic dyke rock. The bodies of asbestos appear to have been very small and are of no economic interest. 3. Deposit Mavita The first research work performed during 1943-46 in the Mavita area, about 60 kmSSE of Manica, revealed small scattered deposits of anthophyllite. Exploitation started in the sixties. The following data are available on production: 1967 - 507 t



1968 - 120 t 1972 - 600 t 1973 - 624 t The deposit was the property of Minas Gerais de Moçambique Lda. In 1973, the production was interrupted and a rehabilitation program was started in 1978 with the assistance of the German Democratic Republic. Small production was obtained from a pilot plant of anthophyllite of about 25,000 t of ore up to the end of 1980. No futher mining continued. The Mavita deposit area, similarly to the Serra Mangota deposit, is situated within the greenstones belt of Archean age-Zimbabwean craton. Asbestos occurs in serpentinized ultrabasic rocks or in association with these. The rocks belong to the Manica Formation, but here they display a general structural NNE-SSW trend. Serpentinites, probably of the"alpine-type", were tectonically injected and later reworked. Metasediments include sericitic and chloritic schists, quartzites and iron-banded formation. Metavolcanics are represented by the greenstones group (see Fig. 3.2.4). Associated with serpentinites are talc, talc-schists and mica-schists. Intrusive rocks include granites, pegmatites and basic dykes. Migmatization is ubiquitous. Asbestos occurs over an area of about 300 km2, with some 160 asbestos bodies acknowleged so far. The reserves are: 325,000 t proved and 237,000 t probable Geophysical exploration of 48 km2 by the GDR in 1978 and 1980, and some drilling revealed about 36,000 t of reserves. Anthophyllite is found in lenses of a 2 x 3 m range, few are 10 m long, with a maximum length of 45 m. Asbestos is associated with talc-schist lenses within the granitic rocks and migmatites, or gneiss, with a biotite-enriched zone at the contact. The content of asbestos in the rock is about 30%. Anthophyllite is usually of the long fiber type, hard and is not amendable to fiber separation which is also due to the widespread phenomenon of silicification. Weathering affects greatly the migmatites and lowers the quality of the fibres. Talc and talc-schists with tremolite are common in the deposit zone, but their quality is not known. Mavita's anthophyllite is unsuitable for asbestos-cement products and for making woven material. It can be used in the production of insulation bars, seals, acid-resistant filtres (results of the Laboratory Dresden, GDR, 1980). According to Eternit S. A. of Switzerland, the mineral cannot be used in their products. 4. Deposit of Mulatala Within the whole Mozambique belt, small massifs of ultrabasic rocks with asbestos are found in many places. Some are serpentinites with small veins and pockets of asbestos and layers of talc schists, some simply just slightly altered ultrabasic rocks. They are generally of small economic importance. One of these deposits in the Province Cabo Delgado was described by the Belgrade Geological Institute (1984). It is situated between the rivers Mulatala and Nacala in the coastal zone near the port of Nacala. Most of the area is made up of biotite gneiss with gneiss-granite building intrusions up to 30 m thick The zone with asbestos is 6 km long and 70 to 100 m wide, with the old pegmatite mine of Gerais Minas in its central part.



Ultrabasic rocks originated along the fracture zone 60-240°, 2 to 100 m thick. It consisted of brecciated greenish altered serpentinite, which is, in fact, completely silicified consisting of harzburgite, enstatite and dunite. The original rock was rich in olivine and enstatite-pendotites which underwent serpentinization, carbonitization, talcozation and silicification. This resulted in an almost complete serpentinization with few relics of enstatite and chromite. The zone is composed at random of talcized harburgitic serpentinites, enstatite-duniteserpentinites and dunitic serpentinites. The original ultrabasic rocks were altered meta-somatically during the hydrothermal phase which is in connection with the origin of granitoid rocks nearby. The zone contains also metagabbro in veins, gedriric schists, cumingtonite schists and mainly beds of glimmerites. And precisely within the glimmerite are the bodies of asbestos. The asbestos zone is composed of anthophyllite, vermiculite, chlorite, quartz and talc. The cumulative content of asbestos is (Geol. Inst. Beograd -1984):

+1mm +0.5 mm +0.2 mm +0.1 mm

0.76 % 8.30 % 8.68 % 2.74 %

The chemical analysis of asbestos and asbestos rock (talc, vermiculite, anthophyllite, chlorite, quartz?) in %:

SiO2 58.88 60.51

Al2O3 1.59 1.27

Fe2O3 5.39 3.50

FeO 2.54 2.70

CaO 3.35 3.65

MgO 22.92 22.83

MnO 0.21 0.14

TiO2 0.08 0.07

Na2O 0.28 0.33

K2O 0.15 0.09

Cr2O3 0.152 0.143

NiO 0.122 0.122

A physico-mechanical test revealed these properties of asbestos rock: * loose dyke mass 0.410 g/cm3 * compact dyke mass 0.732 g/cm3 * specific mass of asbestos 2.94 g/cm3 Other small anthophyllite bodies were found also in enstatite-dunite serpentinites.



Generally, asbestos bodies are very irregular in shape, often oval, along the foliation planes, as a result of tectonic movement. The content of asbestos is a complex fiber aggregate mainly of variable quality with a small proportion of elongate fiber (fiber length below 1 mm). Large bodies of asbestos were not found. Conclusions: Only areas of greenstones belt of the eastern extension of the Zimbabwe craton into Mozambique can be envisaged as promising for a future exploration of asbestos. A possible extraction of asbestos should be accompanied by the utilization of other mineral products, mainly talc. Other asbestos occurrences within the Mozambique belt, similar to other East-African countries, are generally small and of low economic importance. At present, two units produce asbestos-cement in the country - Beira and Maputo. They use annually about 4000 t of asbestos fibres, which are imported, but could be produced locally. The formely mined Mavita anthophyllite, could have been used locally as a filler,coating material and in acid-alkali resistant products.



Cilek: 3.3. Beryllium minerals

3.3. Beryllium minerals The content of beryllium in earth crust ranges from 1 to 3.5 ppm and about 40 minerals contain a substancial quantity of beryllium. A major portion of beryllium minerals are binded on granite pegmatites, especially on the type of albite-pegmatite, albite-microcline pegmatite, less microline and albite-spodumene pegmatites (about 20 minerals). A smaller part, about 11 minerals, are known from alkali pegmatites, followed by hydrothermal-pneumatolytic deposits, skarns, metasomatic deposits etc. Two minerals only bear economic significance - beryl and bertrandite. The list below contains the main beryllium minerals (the last three minerals occur in Mozambique: they are of little importance):

Mineral Formula % BeO Remarks

Beryl Be3 Al2 (Si6 O18) 14.0 - gem varieties: emerald, aquamarine, morganite, heliodor

Bertrandite Be4 Si2 O4 (OH)2 42.0 - the only commercial source: USA - Utah

Chrysoberyl Be Al2 O4 19.8 - in pegmatites, with Fe, Cr, - gem variety alexandrite

Phenakite Be2 Si O4 45.0 - in quartz veins

Helvite 3 (Mn, Fe) Be SiO4 · MnS 11-14 - in ore veins and skarns

Barylite Ba Be2 Si2O7 16

Euclase H Be Al SiO5 in pegmatites and veins

Gadolinite Be2 Fe Y2 Si2O10 in granite pegmatites

Herderite Ca Be (F, OH) PO4 in pegmatites

Beryllium is an element of a rapidly increasing importance in our modern technological age. About 75% of total consumption is used in special alloys Be-Cu, Be-Al, Be-Ni, Be-Co which are hard, elastic, refractory, have nonsparking properties, thermal and electrical conductivity and they are used in aircraft, missiles, spacecraft industries, solid rocket fuels, computer parts etc. About 15% of total consumption is used in the form of beryllium oxide (BeO) with a melting point of 2,750 °C in specialty refractory ceramics as sparking plugs, aircraft engine parts, high frequency insulators, together with beryllium carbide (BeC). The beryllium metal production uses about 10% of the total annual output; the metal is used in the atomic industry, as neutron deflector etc. A small admixture of a few 0.X % even improves substantially the properties of steel for special purposes as noncorrosive, high-heat resistant, for special surgical instruments etc. An increased industrial consumption is impeded by limited resources. The traditional source of beryllium is beryl, with typical content of 12 - 13.5% of BeO (theoretical 14.0%). A lower content of BeO is accounted to impurities and substitutions such as Na, Li, Cs, Rb, K (maximum 1%), and minor amounts of Ca, Mg, Mn, Fe, Cr, H2O and CO2 (carbonate). Chemically pure beryl is colourless, but in nature it is blue or greenish-blue (aquamarine), yellow (heliodor) in a mixture with Fe, emerald green with Cr or V. Morganite is pink because it contains Li and Cs. The BeO content varies between 10 and 15%. Beryl crystals occuring mainly in pegmatites may attain a spectacular size with crystals weighting of several tons. Beryllium-bearing pegmatites are principally of Precambrian age (50%) or of Paleozoic age (37%). In pegmatites, beryl is concentrated usually near the quartz core. The actual ore grades contain about 3-4% BeO with crystals of about a few cm to a few mm long, but some deposits of beryl, with a content of 0.3-1.0% of mineral, could also be mined economically. In Mozambique, all beryllium resources occur in pegmatite deposits. Apart from coal Mozambican pegmatites are the most significant mineral resources of the country and, within the pegmatite deposits, beryllium minerals and columbo-tantalite ores are the most important ones (see Fig. 3.2.1.) at present. Pegmatites developed practically in all areas of the Precambrian in connection with granites of two orogenies-an older less important one of 1,100-800 m. y. -Mozambican and Pan-African orogeny of 500 - 450 m. y. Pegmatites can develop on granitic plutons without any visible connection, but, generally, are connected with certain types of metasediments in old lineaments.



The known pegmatite areas are these (see Fig. 3.3.1): * Alto Ligonha, Zambeze Province * Monapo-Nacala, Nampula Province * Ribaue - Malema - Nipepe in Nampula - Niassa provinces * Balama-Montepuez-Mueda-Rio Rovuma in the Cabo Delgado Province * Zumbo-Zambue in the Tete Province and others. Pegmatites are economically important in an extraction of rare-metals, rare-earths, radioactive minerals, in semiprecious and precious stones and industrial minerals. The group of industrial minerals comprises beryllium and lithium minerals, mica, feldspar, kaolin, quartz and others.

Fig.3.3.1 Pegmatites of the Alto Ligonha district Zambézia (Barros-Vicente, 1963) (554 kB)

Pegmatite group 5 A - Pegmatite field of Alto Ligonha (Murropoce, Nuaparra, Muhano, Marige, Muiane, Tarupe, Naquissupa (Namuaca), Ingela, Piteia, Nahia, Mirrucue, Merrapane, Macula B - Pegmatite field of Alto Molócué (Namacotche, Mutala, Namarrela, Mecossa) C - Pegmatite field of Gilé (Famalicão, Nahora, Namivo, Nampoça) D - Pegmatite field of Meleta (Morrua, Melela, Namarripo, Marropino) E - Pegmatite field of Mucubela (Ginamo, Ilodo)

Pegmatite group 6 A - Pegmatite field of Ribaue (Boa Esperança) B - Pegmatite field of Nauela (Guilherme, Muetia, Comua) C - Pegmatite field of Erego (Ile) D - Pegmatite field of Mugeba (Mugema, Bere, Minhote, Maria, Nigule) E - Pegmatite field of Naburi (Nalume) F - Pegmatite field of Murrupula (Mtomoti, Mocotaia)

Pegmatite group 7 A - Pegmatite field of Mocuba (Namagoa, Munhamade, Licungo, Munhiba)

Beryllium minerals were mined in pegmatites of the Alto Ligonha area. It was started in 1936; the first prospecting for gold and mica in the area dates back to the year 1930. First data on beryl recovery are from 1938 (see also Table 3.).

Table 3 Minerals and concentrates of pegmatites extracted in the Alto Ligonha 1957-1963 (377 kB)

The known beryllium minerals are these: Beryl industrial, in gem-quality: aquamarine, heliodor, morganite, emerald, gadolinite, euclase, herderite.

Beryllium minerals were mined on a small scale in many pegmatite bodies; only a few bigger pegmatite mines produced beryl in larger quantity: the mines Morrua, Muiane, Ilodo, Naipa, Namivo, Murropoce and Nuaparra. In the last years, the sole producers were Muiane, Morrua and Nuaparra. In the production of industrial beryl Mozambique always ranked among the principal world producers. Here are some figures



on beryl production (examples for certain years only):

1938 5,000 kg 1947 61,000 kg 1960 1,495 634 kg

1942 9,200 kg 1949 135,547 kg 1961 973,067 kg

1943 15,000 kg 1953 218,474 kg 1963 556,362 kg

1945 3,608 kg 1954 909,140 kg 1973 6,000 kg

1946 28,000 kg 1957 1,696 723 kg 1978 16,000 kg

In 1979, after the independence beryl production reached the top with 28,000 kg; it decreased to 3,000 kg in 1985. Since then, the production ceased. Beryl is encountered in pegmatites within the zones of big feldspars and lithium minerals, in connection with albite. Smaller quantities are to be found also in the inner zone of mica-quartz and near the quartz core. Beryl differs in colour, volume and shape. Minimum grain size is slightly above 0.5 cm, the mineral is handpicked. Some crystals produce perfect hexagonal forms in a prism with rare pyramidal faces. Some attain a spectacular size such as the crystal from Muiane weighting 14 tons and measuring 1 x 4 m, that from Nihir with 22 tons and Munhamala I - with 50 tons. Crystals of 400 kg weight are not infrequent. The colour is white, green, blue, brown and black -the latter a speciality of Mozambique. Black beryl is found in pegmatites of Moneia, Munhamala, Muiane, Muhano and Naipa. It is worth knowing, that this variety has been zoned. The content of BeO generally is >10.5 %, often surpassing 13.0 %. BeO content (average of 114 samples) in a commercial product (1963): maximum 13.32 %, minimum 9.10 %, average 11.76 %. Impurities include quite commonly quartz, microcline and muscovite; rarely tourmaline, zircon, chromite, tremolite, garnet. Some crystals display a zonation with white beryl surrounded by green beryl, rarely vice versa. Beryl in gem quality is often found in the form of aquamarine, in irregular bands within industrial beryl crystals. At Muiane, a piece of aquamarine measured 40 x 20 cm, a piece of morganite from Marropino measured 25 x 13 cm. Chemical analyses of beryl:

1. Alto Ligonha (Campos J.-1948) % 2. Muiane (Barros-Vicente, 1963) %

SiO2 64.26 62.99

Al2O3 20.69 18.65

Fe2O3 0.36 4.29

BeO 12.45 13.02

MnO2 tr. -

CaO 0.12 0.10

MgO 0.00 tr.

Na2O + K2O 0.66 0.30

Li 1.46 0.59

P2O5 - 0.05

Total 100.00 99.99

Chrysoberyl was found at Muiane, but appears to be very rare in general. Gadolinite is known from two localities - Muiane and Macotaia.



Chemical composition: %

SiO2 30.03 MgO 1.10

(Er,Y)2O3 38.94 Fe2O3 0.65

(Ce, La, Di)2O3 2.82 FeO 13.35

ThO2 0.76 H2O 0.60

BeO 10.98 rest. 0.29

CaO 0.48 100.0

Density: 4.470 Euctase occurs in pegmatites of Muiane and Nahora in the form of small prismatic crystals only.

Chemical composition: Muiane %

SiO2 41.10 H2O- 0.09

Al2O3 35.00 99.94

BeO 17.25 Ga2O 0.013

H2O+ 6.40 GeO2 0.026

Herderite is more frequent in the area of Alto Ligonha and was identified in the Muiane mine. It has the form of crystalline aggregates of greenish-blue colour.

Conclusions: Beryl is the only beryllium mineral of Mozambique that bears economic importance. It is found in pegmatites together with columbo-tantalite, microlite and lithium minerals for example at Nuaparra, Muiane, Morrua and Ribaue within the Alto Ligonha area. Outside this area, occurs in Tulua pegmatite near Nacala, Nacala-Mamba and near the Tanzanian border. Futher localities favourable for beryl development could be the tectonically active zones with pegmatite, and intrusive massifs of granitic and syenitic rocks at the Morrola shear zones, in the vicinity of Montepuéz and Muéda, Cabo Delgado Province and elsewhere. The present importance of beryllium and its limited natural resources place Mozambique in very favourable world position. Small-scale mining operations for beryl look upon a very long and successful history in Mozambique and this experience could be renewed.



Cilek: 3.4. Feldspar

3.4. Feldspar Feldspars contsitute one of the most important groups of rock-forming minerals. All are aluminum silicates and move over a range of potassium sodium and calcium contents (rarely barium). Feldspars are divided in two subgroups: a) potash feldspars-orthoclase, microcline, sanidine, adularia b) sodium calcium feldspars or plagioclase series albite, oligoclase, andesine, labradorite, bytownite, anorthite. Orthoclase K(AlSi308) is monoclinic and often associated with quartz and mica. Often it is found as twinned crystals (Carlsbad-, Baveno, Manebach twins). When potassium is replaced by sodium the high-temperature polymorph of sanidine originates (50% Na). Varieties of orthoclase, adularia, sanidine or albite with a bluish opalescent display of colours are called moonstone. Orthoclase commonly changes to kaolinite or sericite. Microcline K(Al Si308) is triclinic and occurs frequently in pegmatites in the form of large crystals and cleavable masses. It grades often into albite Na(Al Si3O8) through a microscopic intergrowth termed perthite. Perthite also displays a coarse perthitic structure. Microcline is the only bright green feldspar which is called amazonite or amazonstone. Both orthoclase and microcline are used in ceramics, ceramic glazes and glass. Amazonite is used as a ornamental stone and in jewellry. The Plagioclase Series starts from sodium rich end member of albite to calcium rich end member of anorthite.

% of albite

Albite Na (Al Si3 O8) 100 - 90

Oligoclase a 90 - 70

Andesine continuous 70 - 50

Labradorite change 50 - 30

Bytownite to 30 - 10

Anorthite Ca (Al2 Si2 O8) 10 - 0

Labradorite is marked by an iridescent colour display of blue and green; aventurine is either an albite, oligoclase or labradorite with a golden sparkle due to hematite inclusions. Plagioclase feldspars alter into sericite, kaolinite and calcite. Commercially used feldspars are potash-feldspars (orthoclase, microcline), albite as soda feldspar and their grades perthite-albite-oligoclase. More than 90% are used in the glass and ceramic industries, the rest serves as fillers in plastics, paint, rubber, and as mild abrasives in grinding wheels and powder. In the glass production feldspar preferably natrium feldspar introduces aluminium (1-3%, <15%), which increases the viscosity of glass and its thermal stability, and decreases a tendency of crystallization. The alkalies required are Na2O (6%) and K2O (<1%) with a low content of Fe2O3 < 0.4%. In ceramics, feldspars are valued as flux because of their content of alkalies. When heated, feldspar dissolves all ceramic components to solidify in a white glassy mass-a porcelain when sintered or faience when porous. The ceramic industry prefers generally potash feldspars which melt gradually during a long temperature interval, which allows the escape of gases. Small deformations occur during the firing only. By contrast soda feldspars are melted bulk and the gases cannot escape which leads often to a deformation of the product. Nowadays, plagioclase feldspars are preferred because they need a lower firing temperature and thus are energy-saving.



Potash feldspars, even at a higher cost of energy, produce ceramic ware of lower porosity, a better electric resistivity and strength. Porcelain ware is coated with a glassy glaze, in which K-feldspar of highest quality is used. The amount used is twice that of its content in the ceramic body. Feldspars are divided into several groups in different countries according to their quality and the mode of use. The best quality feldspar is K-feldspar with 85% of feldspar mass, at a ratio of K2O/(K2O + Na2O) 0.75 to 1.0% and with contents of Fe2O3 <0.15% and TiO2 <0.1%. The lowest grade is feldspar low in sodium with 40-55% of feldspar mass, ratio K2O /alkalies 0.0-0.4%, content of Fe2O3 1.0% and TiO2 <0.2%. The different feldspar grades are called glaze grade feldspar, feldspar, pegmatite glaze grade, feldspar pegmatite and pegmatite. The group of feldspars includes also "Cornish Stone" or pegraph, which is, in fact, a partly weathered kaolinized granite with feldspar particles used in the manufacture of bone china. Several rock types are mined a feldspathic materials-substitutes of feldspars-and used both in ceramic mass and glass production: aplite, alaskite, phonolite and rhyolite. Other ceramic mixtures include kaolin, feldspar and quartz in alluvial and eluvial deposits, in partly decomposed rocks and sands with a feldspar grain content. During the field explorations for feldspar deposits, three main criteria are used for an evaluation of its grade: 1. feldspar content calculated from chemical analysis: Na2O • 8.458 = content of soda spar K2O • 5.905 = content of potash spar CaO • 4.961 = content of calcium spar 2. ratio of alkalies - potassium contra sodium+potassium K2O /(K2O + Na2O) or K2O/ Na2O 3. content of Fe2O3 and TiO2 Genetic types of feldspar deposits include granite pegmatites of sodalic and potassic composition, feldspar-bearing intrusive rocks and sedimentary deposits of feldspar gravel and sand. The oldest industrial type are pegmatites, the resources of which are nowadays exhausted in many countries. The development of large feldspar crystals and masses enabled a mining by handsorting and this resulted in a very pure industrial product. The second type of intrusive rocks is used more and not only because pegmatites are mined out, but because the bodies of these rocks are very large and enable the introduction of automated processes. This concerns the following rocks: ataskites (45% oligoclase, 20% microcline), albitites, aplites, felsite and dacite porphyries, nepheline syenites (see chapter 4.12, nepheline 20%, albite 60%, microcline 15%) and miaskites. Partly decomposed rocks with kaolin, feldspar, mica etc. are also used in the ceramic industry. An alteration of feldspar-rich rocks is due to weathering (see the development of the kaolin profile) or by hydrothermal alteration (on some ore deposits or stratiform deposits with dacite, rhyolite). Sedimentary deposits consist of sand and gravel with some content of feldspar particles in alluvial deposits, in beach and dune sands or in eluvial layers. In Mozambique, the mining of feldspar is of a recent date; in 1955-59 the extraction of 296 t of feldspar was reported from the pegmatite mine Boa Esperanca near Ribaue (Barros-Vicente, 1963). Since then, the production continued till 1984; the present production of a few hundred tons a year is covered by the Tulua pegmatite mine near Nacala. In Mozambique, these potential sources of feldspar can be considered (see Fig. 6.2): Pegmatites of all types, zonal or homogeneous, of soda-or potash-feldspar type Intrusive rocks nepheline syenites, aplites, mica granites, syenitic granites, rhyolites, phonolites of Precambrian to Cretaceous Age. Sedimentary deposits mainly alluvial and eluvial deposits of weathered feldspar rich rocks of Tertiary and recent times. Traditionally, the main mineral resources of the country are pegmatites with a production of columbo-tantalite, microlite, beryl, lithium-minerals and semiprecious and precious stones. In the past, around 70% of



mineral income was derived from pegmatites. Pegmatites are innumerous, and hundreds or perhaps thousands of these have not been explored as yet. A typical feature of most of the bigger pegmatite bodies is deep superficial weathering in some pegmatites up to a depth of 50 m which alters feldspars and the whole parent rock into kaolin and unaltered remnants of feldspar, quartz and mica with economic minerals, which could be easily extracted. However this is not favourable for the production of feldspar and most of the kaolin and feldspar is lost as waste during the separation of valuable economic minerals by washing and screening. That the production of these "waste" materials is possible shows the mine Boa Esperanca at Ribaue. The pegmatite extending from N-S, is about 130 m long and 60 to 70 m wide, with a core of quartz about 90 m long and 30 m wide. Along this core are zones of feldspar with mica, beryl, amazonite, with economic minerals of euxenite, samarskite, tourmaline and bismutite (see Fig. 3.4.1).

Fig. 3.4.1. Cross-section of Ribaue pegmatite (Geol.Institute, Beograd, 1984) (435 kB)

The most of feldspar is altered to kaolin with feldspar in relics only. The deposit was originally mined for beryl, mica, amazonite and rare-earth minerals. A small beneficiation plant treated the kaolinized pegmatite to produce washed kaolin (10-20% of material) and another dressing unit produced the feldspar. In 1982, for example, the annual production was 1,790 t of raw kaolin, 310 t of washed kaolin, 7,420 t of raw feldspar and 635 t of ground feldspar. The deposit is almost exhausted; a team of the Geological Institute of Belgrade (1984) calculated about 23,400 t of raw kaolin and 820 t of feldspar. Unfortunatelly the reserves of 390 kt of kaolinized pegmatite were not evaluated. The feldspar is orthoclase-microcline, very pure, in lenses near quartz core. The chemical analyses show this composition (in %):

Sample No. 110038 110038 110039

SiO2 61.05 62.98 63.67

TiO2 0.03 - 0.25

Al2O3 22.47 19.83 20.40

Fe2O3 3.19 0.41 0.28

FeO 0.07 - -

MgO - 0.02 0.06

CaO 0.84 0.42 0.35

Na2O 0.39 0.46 0.68

K2O 8.00 13.25 12.88

LOI 3.00 2.42 1.30

The grain size of processed feldspar is 0.8 mm and it is sold in two grades-white and pink. Part of it is exported, part is used locally. The iron content is somehow increased, the potassium content is high. The feldspar is used in the ceramic industry. Nuaparra pegmatite in the pegmatite district of Alto Ligonha is an example of an unaltered pegmatite body with very well preserved feldspars of high quality. The quarry is connected by a dirt track of about 33 km with the mine Muiane, the most important one producing rare metals. In the vicinity of the Nuaparra mine, which produced originally beryl-aquamarine and later mica, are numerous other pegmatites (see Fig. 3.4.2.). Generally,



these pegmatites are different from the pegmatites of the Alto Ligonha district s. s., they are poor in columbo-tantalite and gemstones contents, but rich in mica, which has been mined here over 20 years. Big crystals of beryl are found near the quartz core. The pegmatite is mined from both sides of Namiroe river in four small quarries. The Nuaparra pegmatite and its vicinity was surveyed by Intergeo-Praque (Duda et al., 1986) and this resulted in an estimate of reserves: 1,373 kt of feldspar, of which 540 kt corresponds to rich potassium-sodium feldspar with 65-85% of feldspar mass, 0.6 to 0.75 of ratio of alkalies, <0.4% of Fe2O3, suitable for the production of glazes with simple dressing, 833 kt of feldspar of high-grade glaze directly useable with 77.78% of feldspar mass. Apart from this 55 kt of mica of inferior quality was calculated and 504 kt, i. e., about 26% of parent pegmatite-rock with a number of economic minerals such as coloured quartz, beryl, topaz, tourmaline, bismutine and columbo-tantalite.

Fig. 3.4.2 Nuaparra pegmatite area (Duda, 1986) (341 kB)

Regional rock types belonging to the Precambrian can be subdivided into two major groups. The Lurio Group (-950 - 970 m. y.) found more northwards, and the Nampula Group, approximately 1,000 - 1,300 m. y. old. The latter group can be subdivided into seven series, the oldest of which is the Nampula Series. The oldest rocks are of charnockitic composition overlain by granitoid migmatitic rocks. The youngest rocks consist of metasediments. The older ones underwent high-grade metamorphism, and although the charnockites were dated to 1,000 - 1,300 m. y. they are probably much older (2,000 m. y.). The degree of metamorphism gradually diminishes higher up in the stratigraphic sequence. Younger granites and pegmatites intruded the older rocks. These intrusions are probably linked with the Pan-African orogeny. Granites and pegmatites in the area were dated to 403 ± 20 m. y., 437 ± 50 m. y. and 883 ± 28 m. y. Regional fold systems have a NE-SW trend and the faults bear a NW-SE direction. Thus, the terrain is divided into large blocks of which the Alto Ligonha pegmatite field is an integral part. The field forms an elongated ellipse and covers basically the area between Nampula, Gile, Mocuba, Cuamba and Ribaue. This is one of the richest rare-metal pegmatite regions in the world. The pegmatites also contain precious and semiprecious stones as well as rare-earth minerals. According to the type of mineralization, the pegmatite field can be subdivided into six subareas of which the central Alto Ligonha and the Rio Melela areas are the most important. The Nuaparra pegmatites belong to the Alto Ligonha subarea. These pegmatites are distinguished from the other types by a lesser developed K-zonation. Principal minerals are feldspar, beryl and mica. Numerous outcrops of pegmatites are found in the study area and most of these cut discordantly through the surrounding country rocks. In the NW part of the area, rocks consist of schistose amphibole, gneisses, biotite gneisses, and sericite gneisses. Pegmatites have a general 120°-140° trend and are widest close to the Namiroe river. In the NE sector granitoid gneisses occur. Pegmatites are small and their number decreases towards the NE. Their orientation varies from 120° close to the Namiroe river to 175° in the N part. The area S of the Namiroe river is completely different from the two other areas. Pegmatites, instead of being lenticular, form dikes with general strikes of 140° to 160°. Country rocks consist of gneisses and schistose gneisses. The NW area appears to be the most promising for the fact that the country rocks (schistose gneisses) are enriched by mineralization. Compared to pegmatites exploited in other areas such as Muiane, Morrua and Marropino, pegmatites of the Nuaparra area have poorly developed albitised zones, no lithic zones and low Nb-Ta contents. On the other



hand, they are characterized by a low degree of kaolinization of feldspar, although Na is never completely absent. Zonation in Nuaparra 1/1 pegmatite (Fig. 3.4.3): 1. Marginal pegmatite zone 2. Small block zone 3. Large block zone 4. Metasomatic zone

Fig. 3.4.3. Cross-section of Nuaparra pegmatite (Duda, 1986) (283 kB) Result of analyses of feldspar samples from Nuaparra:

Jung 1978 Obretenov 1978 Ivanicka et al. 1981

I. A I. B I. A I. B I. A I. B

sample weight kg

20 20 2000 20 5 5

% SiO2 65.5 64.4 65.5 65.0 64.96 65.40

Al2O3 18.4 19.2 18.5 18.7 17.82 18.73

Fe2O3 0.12 0.10 0.10 0.06 0.04 0.02

TiO2 0.005 0.01 0.06 0.01 0.02 0.01

CaO 0.07 0.07 0.07 0.09 0.01 0.01

MgO 0.09 0.09 0.22 0.06 0.04 0.02

MnO - - - - 0.01 0.001

P2O5 - - - - 0.085 0.090

K2O 13.1 13.2 13.2 13.6 12.50 10.80

Na2O 1.8 2.5 2.2 2.1 2.24 3.56

H2O - - - - 0.60 0.06

L. I. 0.7 0.4 0.3 - 1.36 1.13

Content of feldspar mass

92.6 99.1 96.6 98.1 92.8 93.9

K2O/(K2O + Na2O) 0.88 0.84 0.86 0.87 0.85 0.75

colour after firing

pure white

pure white

pure white

pure white

white greyish

white

Temperature of firing °C

1,4651,465

without1,465

fissures and1,320 rests

1,250 1,250

volume weight kg/cm3

- - - - 2.512 2.495

Nuaparra feldspar belongs to the very rich potassium natrium grade and can be used in the porcelain mass. Its whitness at 1,410 °C is 71.88%, tensile strength 808 kp/cm , good transparency; all this indicated its suitability in fine ceramic ware, sanitary ware and glazes. Duda et al. (1986) describe different types of feldspars, of which the main variety was potassium feldspar with a



variable component of Na due to the presence of perthitic albite. The content of Fe was below 0.1%, if higher it is due to weathering. Four samples were analysed (in %): Sample

No. SiO2 Al2O3 K2O Na2O MgO CaO MnOFe2O3 -FeO

P2O5 L.I. Total

39 64.12 18.17 13.58 1.76 0.11 0.01 0.04 0.18 0.03 1.20 99.20

43 64.40 18.40 13.28 2.25 0.02 0.03 0.01 0.08 0.01 0.74 99.20

46 64.47 18.48 14.09 0.52 0.02 0.05 0.02 0.05 0.08 1.80 99.54

64 64.47 18.56 13.06 2.88 0.03 0.04 0.02 0.08 0.03 0.65 99.64

The plagioclase group is represented by albite - oligoclase, which originated from the albitisation process similar to albite-cleavelandite and albite-perthite. Spectral analysis of cleavelandite: content of elements >10% - Al, Si, | 10-1% - Na |1-0.1% - Ca, Fe, B, Bi, K, Mg, Ti | 0.1-0.01% - Ba, Be, Cr, Li, Mn, Nb, Zr | < 0.01% - Ag, Co, Cu, Ga, Ni, Pb, Sn, Sr, V. The mineralogical composition of feldspars and other minerals shows that pegmatite of Nuaparra represents an intermediate type between feldspathic - muscovitic pegmatites with a low mineralization of Be (Ta, Nb) and microclinic pegmatite with a mineralization of rare metals in microcline zone. The latter zone is represented by green beryl, columbo-tantaline and sometines by the development of a complex of quartz-albite-lepidolite. The Nuaparra pegmatite probably originated in the granitic massif Muacomuane nearby. As to a zonal chemical composition and structural features of feldspars, two main zones can be distinguished: 1. pegmatite of the large block zone 2. Pegmatite of the small block zone Feldspar in big blocks is an industrial material of high quality which consists of feldspatic material 75-85% and a low content of coloured oxides (often above 0.15%). Major elements of feldspar: (in %)

Sample Na2O K2O Fe2O3 TiO2 CaO

A section 2.16 11.98 0.14 0.01 0.03

B section 1.00 12.82 0.15 0.01 0.02

Borehole F-4 3.5-34.7 m 1.80 11.56 0.25 0.01 0.04

Borehole F-4 38.4-43.9 m 9.91 0.39 0.20 0.01 0.22

Average 1.57 12.01 0.16 0.01 0.03

SiO2 average 58.82%, Al2O3 19.84%, FeO 0.06%, MgO 0.003%, Li2O 0.008%, BeO 0.0012%, Bi2O3 0.004%, Nb 0.0002%.

Feldspar of the small block zone is generally low in content, irregularly developed and of medium quality.The recovery ratio is 49.8% only with 75% of potassium feldspar, 12% of plagioclase and 4% of calcite, mica and kaolin. Chemical composition: Na2O 4.18%, K2O 6.13%, Fe2O3 0.28%, TiO2 0.03%, CaO 0.26%. The content of coloured oxides is 0.17 - 0.40% (maximum 0.60%), SiO2 63.48%, Al2O3 18.88%, MgO 0.007%,



Li2O 0.006%, BeO 0.0032%, Bi2O3 0.003% and Nb 0.0006%. Besides the main pegmatite body at Nuaparra (1/1), with reserves of about 1,072 kt in the large block zone and 860 kt in the small block zone in category C-2, five other pegmatite areas N outside Nuaparra (1/4) were explored which disclosed these reserves in D-2 category: 1/3 ........... 1,200 kt 1/4 ........... 1,080 kt 1/5 ........... 1,117 kt 1/6 ........... 2,331 kt 1/7 ........... 1,010 kt total ......... 5,700 kt The Nuaparra deposits and pegmatites in the vicinity represent very high quality feldspars suitable for export and easily marketable. The reserves could be augmented. Pegmatites of the Alto Ligonha district, with vast reserves of feldspars, can be divided in four types: A. Natrium pegmatites zonal, with beryl, columbo-tantalite, microlite, tourmaline, lithium-minerals, cassiterite etc. Typical examples are Mocuba, Muiane, Marige, Naipa, Nahira, Murropoa, Nauro, Morrua, Moneia. This type is not the best for the recovery of feldspars which are mainly albites or other feldspars in several small zones. An example of such zonal pegmatite was described by GDR geologists from Marropino (1983): 1. zone of quartz nucleus, thickness 0-15 m 2. zone of lithium minerals with albite of medium to very big size 0-35 m 3. zone almost without lithium minerals, with albite-pegmatite of medium size, 0-30 m 4. pegmatite with quartz-muscovite 5. homogeneous pegmatite of saccharoid texture, with albite and muscovite, 0-20 m 6. greisen with lepidolite, 0-1 m 7. greisen with phlogopite, 0-0.07 m 8. albite-microcline pegmatite with muscovite, 0-10 m 9. microcline-pegmatite with or without muscovite, 0-3 m 10. granitoid pegmatite with muscovite and biotite, 0-3 m; granite migmatitic, 0-2 m parent rock of granite, syenitic to monzonitic B. Potassium pegmatites zonal, with an ill-developed potash zone. The principal minerals are K-feldspar, beryl and mica. Examples are Nuaparra, Mugeba, Nauro, Igaro. These pegmatites are the best source of feldspars (see Nuaparra). C. Potassium pegmatites zonal, rich in radioactive minerals and rare-earths; for example at Boa Esperanca and Gurrue. They are suitable for feldspar recovery with valuable byproducts. D. Heterogeneous pegmatites with amazonite and tourmaline, e. g. the Monapo structure.

The main potash-feldspar is microcline, often perthitic, which is probably the original feldspar of most pegmatites of the area. It is found mainly within the zone of grand feldspars in big masses often altered. A close connection with other economic minerals such as beryl and columbo-tantalite is common. Microcline can also be found in external zones. Usually, crystal forms are not developed and, in few localities only, the Carlsbad and Baveno twins were found (Muiane, Naipa, Munhamola). The amazonite variety occurs outside the Alto Ligonha district. Orthoclase is less frequent than microcline and often replaced by albite. It is more common in external zones (Muiane), less in the zone of grand feldspars. Orthoclase originated under conditions of higher temperature and pressure and its remnants are found in microcline. Albite is most common to the group of plagioclase. Generally, it occurs within the lithium-minerals zone with



lepidolite and spodumene. It is indicative of mineralization of niobium-tantalum and beryllium. Cleavelandite, its lamellar variety, is known, for example, from Nahia, Namacotche and Munhamola. Albite is commonly altered and in intergrowth with tantalite and gem-tourmaline (Muiane, Morrua). Oligoclase is bound to the homogeneous zone of pegmatites and, in some places, is the first mineral to crystalize. It is quite frequent in pegmatites of Muiane, Naipa, Moneia and Namiro. The distribution and description of feldspar in different pegmatite mines (Barros et Vicente, 1963) see above, is of historical value. Feldspar is produced in four pegmatite mines at present: Muiane, Morrua, Marropino and Nuaparra. At the Muiane mine, a big body of pegmatite is mined for recovery of columbo-tantalite, beryl, mica and precious stones. The pegmatite is almost completely kaolinized and small amount of feldspar remnants persist within the inner zones mainly the lithium zone. Feldspar grains together with kaolin represent the waste material which is deposited in a nearby depression. Reserves of kaolin are substantial, but so far not used in industry. An estimate of feldspar reserves was made by Zuberec et al. (1981) at a range of 80,000 t, with additional reserves of 200,000 t in pegmatite deposits. No analyses were made of feldspar. At the Morrua mine, the most important in columbo-tantalite production, the situation is simitar to that at Muiane. All altered pegmatitic materials of kaolin and feldspar are regarded as a waste and dumped without futher use. Zuberec et al. (1981) analyzed chemically sample of feldspar from the quarry and obtained these results.

SiO2 64.71 P2O5 0.072

Fe2O3 0.02 MnO 0.001

Al2O3 16.99 Na2O 3.24

CaO 0.56 K2O 9.40

MgO 0.02 H2O 0.40

TiO2 0.08 L. I. 4.39

The content of feldspathic mass:

82.9 % Ratio K2O/(K2O+Na2O) 0.74

Colour after firing at 1,250 °C: white with small rests. It is a sodium - potassium feldspar which could be used in the ceramic industry. It is supposed that about 5,000 t of feldspar per year could be extracted from Morrua. However, at present, the project cannot be realized for a very poor conditions of the roads. At the Marropino mine, no feldspar samples were analysed. The mine produced tantalite, microlite, lepidolite, bismutite, but feldspars of the potassium - sodium type within the zone of grand feldspars have never been utilized, because of their almost total alteration to kaolin. Since 1984, all feldspar production has come from the Tutua deposit 30 km SW of the port of Nacala. Opencast manual mining started in mid-1984. Due to the security situation it has not been possible to survey the deposit. In 1985,66.7 tons of crushed feldspar were produced for the glass industry. The projected milling capacity is 2,500 t/year. The Tulua pegmatite is composed of quartz and perthitic microcline, which are the ceramic materials of the deposit. In addition, amazonite, mica, beryl and transparent tourmaline are found in the vicinity. Other feldspar-pegmatite localities were described in the provinces of Nampula, Niassa and Cabo Delgado. The Yugoslav team (1984) studied several localities NW of Ribaue, in the vicinity of the villages of Nipepe and



Metarica. Pegmatite with amazonite was found in Serra Nhoto about 5 km SW od Munjaveni: dominant is microcline with smaller lenses of quartz, zones of mica and tourmaline. The pegmatite is 155 m long and up to 13 m wide and during colonial times, was exploited for amazonite, occurring in irregular zones and lenses of light green to dark green colour with white microcline. The reserves of ornamental amazonite are estimated to about 15 m3. Samarskite in 10 cm masses is also present. Another pegmatite, 160 m long and up to 60 m wide, is located 4 km N of Metarica. Again microcline is dominant with light green amazonite in lenses of dcm to 0.5 m thickness. Arithmetic mean of 30 samples of Serra Meluli feldspar (in %):

SiO2 66.60 MgO 0.23

FeO 0.17 Na2O 1.44

Fe2O3 2.02 K2O 7.94

Al2O3 19.72 TiO2 0.04

CaO 0.64 L. I. 4.24

Potassium feldspar is dominant, but a hight iron content, probably due to weathering, renders these feldspars uneconomic. In the vicinity of Ribaue, a small pegmatite body 100-150 m long was explored (1 km SW of the Boa Esperanca mine). The feldspars of pegmatite show a high content of iron, silica and a low content of alkalies. It is an example of uneconomic pegmatite. Two analyses were made (in %):

SiO2 72.18 73.84 CaO 1.82 0.70

Al2O3 16.10 16.87 MgO tr. tr.

Fe2O3 3.19 3.40 K2O 3.73 2.64

FeO 0.29 0.22 Na2O 1.71 0.33

TiO2 0.05 0.50 L.i. 0.73 1.56

In the past, kaolinized granite, 6 km NE of the railway station Japala near Nampula, was used for the production of ceramic ware in Nampula. Weathered granite forms about 10 m high outrops of reddish colour representing the lower kaolin zone. The reserves of this material are big, the estimate is 4-5 million t. Weathered kaolinized granite has a high alumina content (average 21%), an iron and titanium content of up to 5.76% and is unsuitable for the commercial use. One sample No. 110 005 is presented here (in %):

SiO2 69.08 CaO 0.79

Al203 17.76 MgO 0.08

Fe2O3 3.89 K20 5.83

FeO 0.22 Na2O 0.32

TiO2 0.15 L. i. 4.24

Halfway between Nampula and Ribaue, near the Namina railway station, one pegmatite body, about 3.5 m thick,



was discovered. It is potassium feldspar with a relatively high alkali content, but with an increased iron content. Chemical analyses (in %):

SiO2 58.46 58.33 CaO 0.80 0.56

Al2O3 24.20 24.63 K2O 8.50 8.79

Fe2O3 1.68 1.20 Na2O 0.96 0.48

FeO 0.24 0.07 L. i. 4.72 5.49

TiO2 0.10 -

Also other pegmatite bodies have been described from between Nacala-Memba, with a homogeneous zone and a zone of grand feldspars, and at Bacia de Msauize, with pegmatites of the C-type. Information on the quality of feldspars in pegmatite from other areas such as Inchope Doeroi in the Manica Province or Zambue in the Tete Province, is not available.

Eluvial and alluvial deposits with feldspar are known from the vicinity of Nacala port. Zuberec et al (1981) described kaolinitic sands with a considerable content of feldspar grains i.e. 48% of feldspar within the fraction 0.208 - 2.0 mm and about 21% of feldspar within the fraction 0.053 - 0.208 mm. These sands are the result of weathering of some granites and pegmatites, with a subsequent transport over a short distance. Gula (1981) describes typical sedimentary deposits of sand with 7% of orthoclase and albite from Maconde beds. These beds are of Cretaceous age (Neocomian-Aptian), fairly large in extension, overlying Precambrian rocks in an about 400 m thick sequence, from the estuary of the river Lurio to the Tanzanian border. They build up the margin of the Rovuma basin and, generally, are cemented into quartzitic-feldspathic sandstone, finely to coarsely grained with conglomerate intercalations. No technological tests have been made. The feldspar content of these deposits is to low to be of economic value but a utilization of quartz could make it profitable. During the exploration of beach and dune sands along the coast, no feldspar accumulations were found in the quartzitic, generally well sorted, sands.

Conclusions: Mozambique, with regard to feldspar resources, has not yet reached the stage of a developing country. The production and internal consumption of feldspar is more than marginal. The famous Alto Ligonha district and many other less known pegmatite fields offer huge possibilities for a future mining of pegmatites just for feldspar or as a byproduct of mining for other minerals. Pegmatites could provide first-grade feldspar concentrates both for export and the local market. Also other feldspar resources such as aplites, some granitic rocks, rocks with feldspathoids and sedimentary deposits could be mined, but not for the reason of a shortage of first-grade material, but from an economic point of view, i.e., because of transport difficulties or a cheaper substitute material on the local market. An example could be the use of rhyolites, phonolites or nepheline syenites, close to the site of production.



Cilek: 3.5. Fluorite (fluorspar)

3.5. Fluorite (fluorspar) The element fluorine is widespread within the crust and its minerals originated in range from high temperature magmatic minerals to minerals of low temperature in sedimentary deposits. One of the first minerals which crystalizes from the magma is fluorapatite Ca5(PO4)3 F. The content of fluorine is 3.78%, but the content of apatite, especially in alkaline rocks, is low, about 2-3%, and rarely could build economic accumulations. The main mass of fluorine during the magma crystallization is concentrated in ore veins and pegmatites. Here, fluorine is found in independent minerals or as an isomorphic admixture in many silicate minerals, owing to a strong affinity between fluorine and many elements. The ionic radius of fluorine (1.33 Å) corresponds practically with that of hydroxyl (1.33,1.40 Å) and oxygen (1.36 Å). Therefore, fluorine is found in a combined form, or as a substitute for other ions. During the magma derivation the main part of fluorine migrated into various deposits, i. e., hydrothermal, hypothermal, mesothermal and epithermal. All these deposits represent also the main economic accumulations. Selected fluorine-bearing minerals: Fluorite CaF2 - ore veins and metasomatic deposits below 300 °C, rarely in pegmatites below 400 °C, in sediments at low temperature Cryolite Na3 Al F6 - in pegmatites of alkali magma, a sole economic deposit at Ivigtut which ceased mining Villiaumite NaF - in miarolitic cavities of nepheline syenites Sellaite Mg F2 - ore veins, fumaroles, salt paragenesis Topaz Al2 SiO4 (F, OH) - prominent mineral of granite pegmatites Chondrodide 2 Mg2 SiO4 • Mg (F, OH)2 - contact-zone mineral, in crystalline limestones Fluorapatite Ca3 (PO4)3 • (F, Cl) - pegmatites, ore veins, alkaline rocks, metamorphic rocks. The most common and also the most important is fluorite. Theoretically, it contains 51.1% calcium and 48.9 fluorine. The colour ranges from colourless, white, yellow, green, purple to deep blue and violet. Originally, fluorite crystals were used as ornamental stones for carving pearls, cups, vases and slabs and in China and Korea of today, they are used for statuttes and different complicatelly carved ornamental utensils. Fluorite of commercial value is called fluorspar. According to Harben-Bates (1984) flourspar is produced in three grades: acid, ceramic and metallurgical. 1. Acid - grade fluorspar is of highest quality; it is used in the chemical industry (more than 60% of total consumption and should contain 95-97% CaF2, maximum 1% SiO2, 0.03 to 0.10% sulphur and 0.00x % Ba, Pb etc.). Other limitations are, for example, the content of CaC03 which should not be higher than 1%, moisture and grain size. Fluorite is used in the production of hydrofluoric acid (HF-aqueous), the starting point in the production of various organic and inorganic fluoride chemicals, elemental fluorine and synthetic cryolite. The acid is used as an etching agent on glass, sulphur hexafluoride as a gaseous insulator in high-voltage installations, elemental flourine as the most important fluorating agent in organic synthesis. In nuclear industry fluorine is applied in separation of 235 U from abundant 238 U, as refrigerant aerosol propellent and solvent. Very important is the production of synthetic cryolite which is prepared from HF, Na2CO3 and Al(OH)3 ===> AlF3 • 3 NaF. Synthetic cryolite is a molten electrolyte used in the Hall-Heroult process of aluminum production, and about 55 kg are required for the production of 1 t of Al. Other uses are: part of high-octane petrol, production of Teflon, glass polishing, enamel stripping, electroplating etc. 2. Ceramic grade fluorspar includes several grades with about 95% CaF2 maximum 1% CaCO3, 3.0% SiO2 and 0.15% Fe2O3. This grade is used in the production of flint and opal glasses, enamels as coatings of steel parts, for example, of refrigerators, cooking ware etc. Lower grades are nowadays used in the glass-fiber production for insulating and building purposes, in cement production (minimum 50% CaF,) where it decreases the temperature of clinker from 1,250 °C to 800 °C, in the plastic industry and in different building materials. 3. Metallurgical grade fluorspar in the manufacture of steel is used to lower the melting point, improve the fluidity of stag and absorb impurities such as S and P from the iron ore. In open-hearth furnaces, electric furnaces and oxygen converters, the minimum content of CaF2, is 75%, with maximally 10% of SiO2 and 6% BaSO4. The grain size must be above 3 mm (the prevalent grain size 30 mm), without presence of Pb and Zn. A minimum of 60 effective percent of fluorspar is required (= SiO2 % x 2.5 substracted from CaF2 %). The amount of fluorspar needed for producing 1 t of steel is 1.6 to 6.0 kg.



Fluorite is found in a wide range of ore deposits: in greisen within the roof zone of granitic intrusions, in skarn within the contact zone of limestone, quartz-fluorite veins with Cu-Pb-Zn mineralization, in nepheline syenites with RE and uranium minerals, in fluorite-barite-quartz veins, in stockworks and impregnation deposits, filling of brecciated zones, in residual fragmentary deposits and small accumulations in pegmatites. Important concentrations coincide with regions of low gravity and high heat flow such as the rift valley continental zones accompanied, in the vicinity, by igneous activity of alkalic or carbonatite composition and hydrothermal postorogenic effects. The deep-seated fault zones of regional structure are the main pathways for a liberation of fluorine from the upper mantle. Fluorine then reacts with surrounding rocks: with limestone to produce CaF2 and different silicates. Replacement deposits occur in carbonates, they are stratabound and ought to be associated with adjacent structural breaks. Fluorite is also common in contact deposits, in alkalic rock complexes and in carbonatites. In Mozambique, fluorite mineralization is associated with Mesozoic magmatism, with deep-seated faults connected with the East-African rift valley, with hydrothermal solutions. Two large genetic groups of fluorite deposits can be distinguished (see Fig. 3.1.1): 1. hydrothermal deposits on fracture zones in veins and fissures 2. hydrothermal deposits of the metasomatic type with the stages hypothermal, mesothermal to epithermal, connected with magmatic rocks (alkaline and carbonate). The first type of deposits is represented by massive fluorite of a crystalline arrangement, with concretions in parallel layers and of a radial structure, of greenish and violet colour; in small pockets disseminated with brecciated quartz and chalcedony. The second type of deposits connected with alkaline rocks and carbonatites is represented either by irregular aggregates of radial arrangement of yellow colour or as impregnation of ftuorite of a blue colour. From the regional point of view of distribution, all main deposits are found either on the E or W side of the East-African rift valey (Niassa rift), of N-S extension or along the Mid-Zambezi rift valley branching from the main rift westwards along the river Zambezi. On the E side of the Niassa rift, there are several nepheline syenite massifs of Cretaceous age, with fluorite mineralization, e. g., at Morrumbala, Tumbine and Mauzo; a presence of other fluorite was indicated in trachytic lavas of Lupata bordering on the NW the Cretaceous sediments of the Zambeze depression. There, fluorite is developed as a dissemination, in small cavities inside the lavas and as a cementation agent in porous trachytic breccia. On the W side of the Niassa rift, all known carbonatite intrusions display a certain content of fluorite: Monte Xiluvo on the southern end, Monte Muambe near the river Zambeze and Monte Salambidwe with syenite in the outer ring and with inner carbonatite on the Malawi side. Some of these localities are richer in apatite and rare earths. The best known and recently explored fluorite deposit is Monte Muambe (Geol. Institute, Beograd 1984). An extract of the report was published in "Summary of World Congress of non-metallic minerals" (1985). Mt. Muambe is a ring-shaped hill (see Fig. 3.5.1) situated on the southern margin of the Tete Complex, in a depression filled with Mesozoic sediments and volcanics of Karroo. The ring consists of Upper Karroo arcositic sandstones, the diameter of the external ring is 6 km with a crater about 200 m lower. The floor of the crater is of highly dissected carbonatite, which is strongly karstified and covered with laterite. Carbonatites-carbonatite s. s., agglomerate tuff, feldspathic rocks and basic dykes cover about 40% of the caldera. The typical carbonatite is a hard, compact rock, grey or brown in colour, with knots of silicified material. Prevalent are calcitic carbonatites-sovites, less abundant are sideritic carbonatites. According to texture, these types of carbonatite can be distinquished: hypidiomorphic granular medium grained fine grained pseudoporphyric trachytic.

Fig.3.5.1. Geological map of Monte Muambe (Geol.Institute, Beograd, 1981) (538 kB) Pure carbonatite may contain over 80% CaCO3, 0.2-6.15% dolomite; carbonate-silicate rock contains about 40% CaCO3. Carbonatite fills the vent and is also injected into adjacent rocks and then altered. Chemical composition of carbonatite (1 = mean chem. content, 2 = minimum and 3 = maximum content (in %).



1 2 3

SiO2 - 0.8 5.48 Carbonatite occurs often

TiO2 0.29 - 0.44 in veins and postvolcanic

Al2O3 1.54 0.12 6.37 dykes some as hydrothermal

Fe2O3 5.87 1.08 10.83 flurite solutions with

FeO 0.08 0.01 0.12 an increased content of

MnO 0.84 - 2.28 rare earths such as Y, La,

MgO 0.42 - 0.95 Ce.

CaO 49.29 42.05 54.70

Na2O 0.11 0.02 0.31

K2O 0.23 0.02 0.75

P2O5 0.64 0.01 2.73

H2O- 0.16 - 0.54

H2O+ 0.09 - 0.13

CO2 38.37 31.29 41.65

Spectrochemical analysis (ppm-arithmetic mean):

Cu Ti Mo Y La Ce V Be Nb Sr CaF2

5.65 21.21 2.73 85.15 263.73 380.30 19.33 94.24 47.27 2898.40 4.29

Surroundind carbonatites on the outer side build-up a ring of rocks very rich in alkaline feldspars. These rocks are products of fenitization, a process typical of changes in adjacent country rocks during syenite alkaline melt intrusions. Chemical analyses of samples of syenite-fenite: 90% of K-feldspar, accessory minerals 1 - 10% (apatite, zircon, pyrite, martite, potash feldspar-sanidine, monazite) - texture: hypidiomorphic granular

% 1 2 3

SiO2 41.21 44.32 45.35

TiO2 0.36 0.39 0.35

Al2O3 18.80 15.39 17.07

Fe2O3 6.57 15.50 8.45

FeO 1.55 0.01 0.01

MnO 0.46 1.47 0.99

MgO 0.61 1.82 0.81

CaO 8.41 3.65 8.41

Na2O 0.40 0.48 0.95

K2O 13.70 12.05 12.68

P2O5 0.98 0.52 0.43

H2O 0.10 0.36 0.14

CO2 5.32 4.70 4.79

Fluorite mineralization was formed by postvolcanic activity, i. e., after the emplacement of carbonatite. Mineralization is found in permeable and fractures zones One such zone is the contact betwen fenites and carbonatite. In the field, fluorite was observed on the W and S margins of the carbonatite intrusion. Electrical prospecting revealed a resistivity anomaly near the



eastern part that could be linked to fluorite mineralization. The whole contact length of 9 km should be investigated in detail to determine the extent of the mineralized area. Although the primary dissemination halo of fluorite veins within the carbonatite is small, i.e. seldom more than 1 cm, it can be as wide as 50 metres in fenite. Fractured zones related to a collapse of the central part of the caldera, are sometimes mineralized and fluorite occurs as a crust around brecciated fragments and as a fracture filling of smaller "en echelon" fractures. Two types of fluorite mineralizations are found: a) Blue fluorite, composed of fine-grained aggregates of hypidiomorphic-idiomorphic cubic crystals. Inclusions (gas, fluid, calcite) are often present. Metallic minerals constitute an average of 6-10% by volume, sometimes 20%. An analysis of a typical sample is given below. Blue fluorite is rich in beryllium, strontium, yttrium and lathanum. Be concentration was recorded to be as high as 10,000 ppm. b) Yellow fluorite consists of two types: (i) Massive yellowish-white fluorite (ii) Transparent yellow fluorite, often occurring in "kidney shaped" structures. Inclusions are far less common to this variety. Concentrations of Be, Y, La and Nb are lower, while the concentration of Sr is higher than that in blue fluorite.

Analysis (in %) Yellow Fluorite Blue Fluorite

SiO2 2.06 1.86

Fe2O3 8.80 15.95

Al2O3 1.10 2.67

TiO2 0.21 0.65

MnO 0.006 0.010

CaCO3 1.16 2.11

CaF2 85.11 74.49

MgCO3 0.86 1.53

Na2O 0.05 0.12

K2O 0.08 0.10

S 0.02 0.01

Pb 0.03 0.03

Zn 0.05 0.08

Sb 0.016 0.004

Cu - -

Ba 0.05 0.08

Sr 0.23 0.27

L. i. 1.22 0.02

(Analyses of two representative fluorite samples). The reserves are substantial and it is necessary to stress that in some trenches, massive fluorite of a thickness of about 20 m has been encountered. The average width of veins is 10-20 m, length 100-250 m, reserves are calculated to 50 m depth with specific gravity 2.7. It ought to be remembered, that just a small part of the Muambe deposit was explored. Following reserves are calculated:

Prospective: 699,849 t of fluorite ore with 81% of fluorite 567,457 t pure fluorite



Possible: 723,057 t of fluorite ore with 75% of fluorite 552,631 t pure fluorite

Total: 1,422,906 t of fluorite ore 79% of fluorite 1,120,088 t pure fluorite

Apart from caldera, residual deposits contain 1,510,375 t of martite without TiO2, with an increased value of Ba, Nb, Sr and probably RE. The deposit covers about 200 ha, its average thickness is 0.8 m. Fenites can serve as potash-rich rocks, for example, in the ceramic or glass industry and part of the carbonatites in cement or lime production (with a low phosphorus content). Preliminary dressing tests indicate that fluorspar of the metallurgical grade can be obtained (partly even without dressing) with CaF2 74-85%, SiO2 2%, Fe2O3 9-15%, and acid fluorspar with CaF2 92-98% prepared by flotation for use in the chemical industry. The Muambe fluorite deposit is of extreme economic value and future exploration will increase the reserves. Mineralization and ore emplacement are the results of post-volcanic hydrothermal activity. South-west of the river Zambeze, and appreciably remote from the deep-seated faults of the East-African rift are two important areas with fluorite mineralization: 1. the zone of Macossa-Maringoe-Canxixe 2. the zone of Djanguire-Monte Domba

1. This zone is about 100 km long and 20 km wide, with several veins of fluorite along the contact-line between the Precambrian Barue Formation and sedimentary and volcanic rocks of the Karroo and Cretaceous. The boundary is tectonic, as common to a development of Karroo troughts, it represents the tectonic margin of the Mid-Zambeze rift which deviates here from a N-S to a NW direction. Fluorite mineralization is bound to faults in N-S (15 °E or W) direction, richer deposits developed in sites of an intersection with NW-SE fractures. Alves (1961-64) recognized ten areas of fluorite veins:

Rio Nhamafunda thickness 0.02 m

Djalira Sul 0.6 - 5.1 m, inclination 50° to vertical

Rio Nhanzamba 0.01 - 16.5 m, vertical

Djalira-Rio M'Bahate 6.15 - 7.00 m, 65° to vertical

Djalira Norte 0.10 - 1.60 m, 30° to vertical

Sambza Sul 0.10 - 1.35 m, 40° to vertical

Entre os rios Samba e Nhatsapo small mineralizations

Monte Geramo brecciated quartz veins

Povoacao de Joni 2.70 m

Monte Chizumba -

Some of the deposits have been known for quite a long time; about 2,000 t of fluorite were extracted from the surface to a depth of 25 m from deposit Geramo. In the whole area, fluorite is closely connected with chalcedony-quartz in veins which are concordant to the general foliation of surrounding metamorphic rocks. The length of veins is about 20 to 600 m, with a thickness of 1-3 m. Some veins may attain a length of 2-4 km and thickness of 10-15 m. The inclination of veins is from steep to vertical. Drilling disclosed fluorite up to the depth of 80 m. In the southern part, the veins can be followed for about 40 km; the width of the zone is about 2-4 km, exceptionally 10 km. About forty interrupted veins are present. Fluorite developed either in a disseminated or massive form. The disseminated type forms inclusions and amygdaloidal fillings in strongly fractured quartz, or as a cemented material in breccias. Massive fluorite occurs in veins and lenses up to 8 m thick. The colour of fluorite is violet and green, seldom yellow, with an ore content averaging 24.0-38.9% CaF2. Technological tests made with Djalira (Maringue) fluorite confirmed that metallurgical fluorspar can be produced with a CaF2 content of 85%, and acid fluorspar with 97% CaF2. Fluorite from Geramo (Canxixe) was tested by the Mitsubishi Shoji



Kaisha Company (1972), and the concentrate of 97% CaF2 was produced. According to new tests (1982) two types of fluorite can be produced from the original concentrate of 82-84% CaF2: acid fluorspar with 96% CaF2, with 16% recovery metallurgical fluorspar with 92% CaF2, with 5-6% recovery. The reserves of the Maringue deposit are estimated to 43,000 t, those of Canxixe to 160,000 t of fluorite in three veins. Other fluorite veins represent estimated reserves of 500,000 t.

2. The deposit Djanguire is situated at 154 km from the town of Tete on the Tete-Changara road. It was first examined in 1963/64. It is composed of zones with different degree of fluorite mineralization of which the zone "Inter Luia" is the most important one. This zone is about 2,000 m long with a maximum width of 750 m. The thickness of the veins is 0.10 to 3.0m. Composition of some veins of the Djanguire deposit:

Name of vein CaF2 SiO2 CaCO3 BaSO4 F S

Inter-Luia F.1 22.7-82.8 13.74-57.28 0.51-1.92 0 0.34-1.4 0.01

Inter-Luia F.2 71.8-83.8 14.81-27.33 0.79-0.95 0 0.47-0.68 0.01

Inter-Luia F.3 65.9 28.92 0.61 0 0.36 0.01

Mt. Nhambadula F.8 80.8 14.08 0.69 0 0.58 0.01

The reserves of fluorite in the Djanguire area (Alves, 1961-64): 70,000 t proved 110,000 t probable 600,000 t possible total 780,000 t The Monte Domba deposit is situated near Changara and fluorite with quartz in veins of NW-SE direction developed in a number of veins with two types of mineralization - disseminated and massive. The length of one vein is about 70 m with thickness between 1.70 and 2.25 m, the others are shorter and less thick. Fluorite is incrusted on quartz and, sometimes, of a cockade texture. Baryte is present, but rare. Alves (1961-64) described the genesis of the deposit: phase of crustal fracturing with a development of oriented fractures filling up of fractures by massive milky quartz new phase of fracturing resulting in crushing of massive quartz deposition of fluorite and chalcedony formation of crust of hialine and euhedral quartz. Fluorite occurs generally in small crystals of green colour, sometimes banded. The genesis is in connection with faults of the rift-valley, but also with a post-volcanic activity and the origin of ring structures of alkaline rocks. Especially Monte Domba originated on fault lines connected with a regional fault system known here as the Metangua Rift. The age of mineralization is Jurassic or Cretaceous. Further to the NW, within the E-W section of the Mid-Zambeze rift valley, and on the northern bank of the Cabora Bassa dam, is the prominent area of Cone Negose with a carbonatite intrusion and a complex mineralization with apatite, fluorite, rare earths and metals. In some places the content of fluorite is 20%, but generally is low and of no economic interest.

Conclusions: The most important fluorite deposit is that of hydrothermal and metasomatic origin on the Monte Muambe carbonatite intrusion. Untreated fluorspar is of metallurgical grade, acid fluorspar can be obtained by flotation. Reserves are big and could be increased by futher exploration. Together with fluorite some reserves of rare earths, beryllium, niobium and strontium can be expected. The weathering crust on the caldera carbonatite deposit offers some reserves of good-quality martite. Classical deposits of fluorite are connected with deep-seated faults of the Niassa and Mid-Zambeze rift and are developed mainly on the western or southern side of the rift-valley, in the area of Djanguire-Mt. Domba and Macossa-Maringoe-Canxixe. The deposits are fluorite-chalcedony-quartz veins on fractures within the Precambrian rocks but close to the troughs of Karroo or



Cretaceous filling. They are of Jurassic-Cretaceous age. Some accumulations of fluorite are to be found also on the eastern side of the rift valley, in intrusive carbonatite or alkaline rocks and over an extensive area Lupata alkaline lavas of Karroo. It is almost certain that future exploration will substantially increase these reserves together with reserves of other elements and rare earths. In this field, Mozambique has indeed a bright future.



Cilek: 3.6. Graphite

3.6. Graphite Graphite is a mineral of a hexagonal modification of carbon, black to steel-gray in colour, hardness 1 to 2, specific gravity 2.1 to 2.3. In nature, it is found in igneous, sedimentary and mainly metamorphic rocks. Graphite in igneous rocks is primary crystallized carbon in veins or bands; in metamorphic rocks, it is the result of organic matter transformation. Graphite is plastic due to a perfect basal cleavage with weakly bond layers allowing them to slide over one another. The plasticity of graphite is responsible for easy tectonic movements on fault planes. Graphite is also a good heat conductor, it has a metallic lustre and it is resistant to weathering. According to its structure, graphite is divided into "flake graphite" or crystalline graphite (flakes 0.1-X mm in size), microcrystalline or massive (crystals 0.001-0.1 mm) and cryptocrystalline or amorphous (crystals below 0.001 mm). The term amorphous refers to the soft black earthy appearance of graphite in metamorphic rocks, while crystalline graphite displays metallic luster. The minimum content of crystalline graphite in rock should be at least 3% of carbon for massive graphite about 10% C in rock is needed for economic mining. The three largest industries are steelmaking, foundries and refractories. A mixture of clay and graphite is used for refractory crucibles and retorts for melting nonferrous metals and alloys. The last innovation of use of flake graphite is in the production of magnesite carbon refractory bricks. For smelting crucibles, amorphous or flake graphite can be used. A minimum 95% C graphite is required for use as a lubricant, which is applied, for example, in textile machines or in places with an increased temperature. Specifically, it is used as moderator in atomic reactors, rocket components, turbines, military machines etc. Other uses include dry-cell batteries, carbon brushes in electrical motors, in paints and pigments and, of course, in pencils. Many small uses are in carbon paper, chinese ink, lining of foundry moulds, in shoe polishes and rubber. The quality requirements of graphite differ in each country and in fact, in each factoty, although some general norms have been accepted internationally. For casting: ash content 18 - 25%, moisture up to 1.5%, important is the fineness of ground material: +0.25 mm < 5%, -0.053 mm maximum to 25% For ceramic crucible: ash content 8.5 - 11.0%, volatile matter at 300°C up to 2%, moisture up to 1% and Fe2O3 up to 1.7% Galvanic elements and basic accumulators: ash content 10-14%, volatile matter up to 1%, moisture up to 1%, Cu maximum 0.05%, total Co Ni Pb As in traces, fineness of ground material +0.16 mm up to 10%, - 0.063 mm minimum 45% Electrodes: crystalline graphite with ash content up to 20% for anthracite electrodes and 6-10% for coke electrode, volatile matter not measured, moisture up to 1% and fineness of ground material - 0.063 mm up to 20% Pencils: ash content up to 3%, or to 5%, volatile matter up to 1%, moisture up to 1%, fineness of ground material - 0.063 mm up to 1% Lubricants: ash content up to 7-9%, moisture up to 1%, volatile matter up to 1% pH neutral, sulphur up to 0.2%, fineness 100% up to 0.2 mm.

The origin of graphite is still a controversial issue. However most graphite deposits are of metamorphic origin. All types of organic matter such as dispersed carbonaceous matter, hydrocarbons, anthracite, anthraxolite and slightly metamorphosed coal sedimentary layers may be converted to graphite by contact and mainly regional metamorphism. The carbonaceous material changes from amorphous graphite to crystalline graphite with regard to the grade of metamorphic processes, reaching the amphibolite facies of ultrametamorphic stage with well-developed graphite crystals. The degree of graphitization depends mainly on temperature, pressure conditions are less important. It is believed that graphite needs a minimum of 400°C for its origin. This metamorphic process is valid for most Phanerozoic deposits with either disseminated graphite in metasedimentary formations or in concentrated graphite layers on foliation on schistose planes. Controversal is the origin of secondary-epigenetic graphite. This graphite is common to Precambrian schists and gneisses of medium but mainly high-grade metamorphism. Graphite occurs in veins, fracture fillings, replacement and seggregation concentrations. It is clear that part of the graphite can crystallize in situ from the present organic matter, but part of it must be redeposited. Harben et Bates (1984) suggest (viz Weis et al., 1981) that epigenetic graphite is derived from syngenetic graphite or carbonaceous detritus by a process that converts carbon to a fluid. It is a reaction of superheated water vapour and carbonaceous compounds (but not carbonates!) at 700-900°C:



C + H2O ===> CO + H2

which produces the only mobile carbon compound. Under geological conditions the precipitation of carbon starts at about 600-750°C:

CO + CO ===> C + CO2

A basic condition for this process is the presence of the original organic matter in a sedimentary sequence. Where this matter does not exist, graphite accumulations can not develop. Genetic types of graphite deposits according to Kužvart (1984). 1. Early magmatic graphite develops during an intrusion of alkali rocks-granites, syenites, into a metasedimentary formation. Graphite crystallizes synchronously with the intrusive rocks in the form of stocks and nests. Its quality is high, but deposits of this type are rare. 2. Contact-metasomatic (skarn) deposits develop at the contact of carbonate rocks with plutonic magmatites such as pegmatites and aplites causing a crystallization of organic carbon. The graphite is flaky in the form of stockwork and veins. 3. Vein deposits formed from postmagmatic solutions with graphite in veins and lenses of few mm to 2-5 m. This development occurs in crystalline rocks with pure graphite of 80-98% C, coarsely flaky (see previous discussion on epigenetic graphite) in veins stockworks, pockets, cavity fillings in Precambrian gneisses, granulites, quartzites etc. 4. Metamorphogenic deposits formed by a concentration and crystallization of organic matter during predominantly regional metamorphism. Kužvart (1984) divides these deposits into: a) metamorphic graphite deposits in layers and lenses in crystalline rocks with disseminated graphite flakes, with a graphite content in the rock between 1 and 15% in series about 15-210 m thick b) metamorphosed graphite deposits are generated by contact or regional metamorphism from sediments rich in organic matter such as coal etc. Metamorphosed coal seams attain several m in thickness with graphite of the massive type (80-85% C) on the contact with granitic rocks. Regionally metamorphosed shales, sandstones and limestones with organic matter are transferred to gneisses, marbles and quartzites with crystalline or amorphous graphite, often with sulphur, vanadium and phosphorus (biogenic origin). Later tectonic stresses can change the disseminated graphite in stringers, swelled lenses and bizarrely scaled structures of higher purity graphite. Into this group fall the biggest world deposits. Weathering-resistant graphite is often mined in superficial deposits of wholly or partly decomposed parent rocks with a low graphite content of 3-5%, enriched in residual deposits to about 10-15% (see Madagascar deposits). In Mozambique, the mining of graphite started as early as 1911 in the Tete Province - Angónia and, in 1927, after the discovery of the Itotone deposits near Nacala by Europeans. Nunes (1952) mentions that graphite from the latter locality called "itoto" by the local population, was known several centuries ago and used for ornamental painting of pots known as "muapas". Beside the Itotone deposit, other deposits nearby a Metocheria and Jagaia, Otaco-Ancone and Evate were also exploited. This graphite was exported from the port of Nacala; was never treated mechanically, but just handpicked. Fereira da Silva (1953) presents some mining data and states that about 2,500 t of graphite with a C content of 70-74% was exported from Itotone in 1953. Sometimes, it contained even more than 80% C. At that time, also the mine Otaco-Ancone was in production, the deposit Nacoto (Netia) was explored and big bed of disseminated graphite with a content of 18% C was discovered (see Fig. 3.6.1). On the Evate deposit, mining started in 1951, and soon the mine reached an annual production of 300 t. The quality of exported graphite as given by Nunes (1952):

% C volatile C graphite Ash

Otaco-Ancone 1.40 49.00 47.82

Itotone 1.87 91.79 6.18

Angónia 5.84 80.72 12.60

The second historical area of graphite exploitation is at Angónia in the Tete Province near the Malawian border. First, graphite occurrence was reported in 1912, although actual mining had started in 1911. In 1944, about 50 t of graphite had been exported



from the port of Beira. Mining operations ceased in 1955. The quality of graphite is mentioned above. The mines in operation were situated in the zone NW-SE of Ulongue towards the Malawian border: Metengo-Balama, Chiziro (Satemua) and the nearby mine Maue. Other sites of graphite occurence were discovered in the Niassa province at Juluti (Mogovolas) and Catur near Lichinga; Balame near Montepuez, between Chiure and the river Lúrio, near Macondes, Muecate and Ancuabe near Pemba in the Cabo Delgado Province. In the Manica and Sofala provinces, a small occurrence of graphite was found at Barue, Gorongosa, Mossurize, Mombane and in the Province Zambezia at Serra Chiperone and Morrumbala (Nunes, 1952). Mozambican graphite deposits can be divided into these main areas (see Fig. 3.6.1): a) Angónia b) Monapo structural unit c) Lúrio belt d) Morrola structural unit

Fig. 3.6.1. Occurence of graphite, mica, rare-earth minerals (328 kB) The dominant genetical type of graphite deposits is represented by metamorphosed deposits in zones of high grade metamorphism of amphibole or granulite facies in metasedimentary graphitic rocks. Quite common is a secondary enrichment of graphite in veins, fractures and fillings due to a regional ultrametamorphism, or in contact zones. Rare is an occurence of epigenetic graphite and graphite of magmatic origin. Lächelt (1985) divides graphite deposits into five groups: 1. disseminated graphite in graphitic gneisses, biotite-amphibole and amphibole-pyroxene gneisses 2. graphite along the zones and boundaries of migmatization and inside the migmatites 3. graphite (fuchsite) in crystalline limestones and other metasediments near the zones of graphitic rocks 4. graphite in stockworks, veins etc. of epigenetic origin (often in magmatic but also in gneissic rocks); this includes also graphite in a kaolinized cover of basic magmaticrocks as, for example, anorthosites of Angónia 5. Graphite in the weathering crust of primary deposits.

a) Angónia The Angónia Formation is composed of different rocks of the Precambrian Mozambique belt, mainly metasediments - paragneisses, crystalline limestones and quartzites. The general structural trends is NW - SE and the graphitic zone follows this direction from Vila Coutinho Velha through Ulongoe to Metengo Balama in the SE of the Malawian border. The graphitic zone is highly metamorphosed in granulitic-charnockitic facies with several areas with an incereased content of both primary and epigenetic graphite (see Fig. 3.6.2.)

Fig. 3.6.2. Geological map of the Ulongue zone - Angónia (Huntington, 1984 - Geol.Intitute, Beograd, 1982) (435 kB)

Primary graphite in metasediments is of metamorphogenic origin, normally disseminated within leucocratic gneisses, amphibole-pyroxene gneisses, garnet gneisses, quartzites and crystalline limestones with apatite and pyrhotine. Graphite accumulations follow the plane of foliation with an inclination of above 45°/NE. According to Lächelt (1985), also the margins of vast areas of migmatitization are richer in graphite content but always in gneisses and not in migmatites. Epigenetic graphite present in stockworks and veins of hydrothermal origin, developed in crystals well known in this area which attain up to 15 cm. Graphite occurs within massifs of metaanorthosites, seldom syenites, which intrude the metasediments. Some graphite is found in gneisses. The veins of graphite are well preserved in the superficial, partly kaolinized zone on meta anorthosites. Deposits within the graphitic zone (from NW to SE): 1. Vila Coutinho Velha (Ulongoe Velha) - graphite in gneisses and lateritic deposits 2. Nhankar - graphite in two layers in gneisses and also in crystalline limestone 3. Rio Maue and Chiziro, grapite in stockwork and veins in anorthosite and kaolin 4. Satemua (Mouzinho), graphite in gneisses and laterites 5. Metengo Balama, graphite in stockwork and veins in anorthosite.



The occurence of graphite at Vila Coutinho Velha is of small importance. Graphite is present in gneisses rich in biotite, which are enclosed in migmatites and granulites with almandine, partly is in lateritic crust. Nhankar deposit, situated about 14 km NW of Ulongoe, is of dissimenated type, in biotite-amphibole gneisses following the zone of granulites. Mineralized graphite developed in two layers separated by the zone of migmatites. Also here crystalline limestone is developed. An estimate of reserves in steep dipping strata, made in 1950, suggested 234,000 t of rock with 17,200 t of extractable graphite. The most important and best known deposit is Satemua. In 1983, the deposit was investigated by the Geological Institute of Beograd. It is situated about 10 km SE of Ulongoe. Graphite is disseminated in laminae and veins of different thickness. The deposit is about 1,200 m long, with an average thickness of 40 m and an incline of 40-60° to the NE. It consists of two mineralized zones of graphitic gneisses surrounded by migmatites and granulites. Also crystalline limestones and carbonatic rocks contain graphite. The reserves were calculated in different levels: at 20 m depth with 6% C - 67,000 t of graphite at 30 m, with 6% C - 338,000 t graphite at 100 m - 650,000 t of graphite. The technological test using flotation indicated that crystalline graphite of the flakey type, with 94% C, 1% of moisture and 5% of ash can be obtained. Opencast mining is feasible. Some parts of deposits contain about 10% of graphite, part of it in lateritic deposits and an increased content of V2O5 0.10-0.54% bound in mineral essentially muscovite-roscoelite. The deposits of Rio Maue-Chiziro and Metengo Balama are of the stockwork and vein type, with pure graphite in cm thickness, which was mined in the past. They are mineralogically attractive, with big graphite crystals but of small economic importance. The geologists of the Beograd Geological Institute collected several samples from Angónia graphite deposits: their content of carbon varied between 10.03-11.12%, SiO2 43.03-48.32% and ash content 78.74-85.94%. Two main types of graphite zones can be distinguished: disseminated in flakes in gneisses and massive in veins and lenses in granulites. Some laminae are 0.5 to 3.0 mm thick. The flotation product is of the metallurgical grade and can have many other uses, except in the pencil manufacture. Results of chemical tests: Sample No.: 1. Rio Maue-epigenetic graphite 2. Satemua-primary graphite 3. Nhanhar Zone I-primary graphite 4. Nhanhar Zone II-primary graphite

% sample 1. 2. 3. 4.SiO2 43.3 46.34 48.32 48.11TiO2 0.47 1.20 0.95 1.20

Al2O3 22.62 18.23 17.40 18.46Fe2O3 6.93 10.67 9.56 9.28MgO 3.09 3.80 4.67 2.19CaO 3.08 4.77 3.91 4.03

Na2O 1.50 1.15 1.10 1.41K2O 1.40 1.45 1.80 2.75

S 0.09 0.17 0.26 0.14V2O5 0.04 0.10 0.10 0.08

C 11.12 10.22 10.21 10.03Ash 85.55 78.74 83.29 85.94

Moisture 2.47 3.01 2.99 2.71

b) The Monapo structural unit



is situated in the Nampula Province between the towns of Nampula and Nacala. It is interpreted as an "overthrust", a tectonic unit thrust from the northern Lúrio belt to above the older Nampula Formation. Another interpretation is that of a synclinal structure, ringshaped, lying with discomformity on the older Precambrian. In my opinion, this is the upper part of the Precambrian known in Tanzania as Usagaran; its upper unit which is mainly metasedimentary is represented as an erosional remnant. The grade of metamorphism corresponds to that of the Lúrio belt; most of the rocks are metamorphosed to granulite facies or even ultrametamorphosed. Dominant are granite gneisses, granite-migmatites, paragneisses, amphibolites, carbonatic metasediments with intrusive basic and acidic rocks. Within the Monapo structure are several old graphite mines of which the oldest and also best known is the mine itotone. The Geological Institute Beograd (1984) explored the whole area of Monapo. The average C content of the itotone deposit was 70-74%, of the Evate-Utoca deposit 68% (with 3,000 t of graphite extracted), and 18% only in the mine Nacota with "black" graphite. Around the itotone mine there are several other graphite deposits. The graphite occurrence is associated with fillings of fractures in granite gneiss, coarse-grained granite and also pegmatites few cm thick or in small nest-like clots. Granite seems to have been injected migmatically into the gneisses. Veins of graphite are very steep in NE-SW direction. It was determined microscopically that graphite occurs in veins and veinlets or impregranations with 25-95% content, its thickness ranges between several mm and several cm. A thickness of 25 cm is known from an older report. Generally it is thought, that the graphite content in the graphite zone is about 1%. Of the analyses of graphite from Itotone made, here are three control analyses (in %):

Sample 3. 14. 26.SiO2 38.83 28.45 35.24

Al2O3 9.67 7.24 7.87Fe2O3 1.51 3.85 2.82CaO 0.33 0.23 0.44MgO 0.09 0.16 0.67TiO2 0.35 0.27 0.86P2O5 0.07 0.27 0.34MnO 0.008 0.023 0.056Na2O 0.81 0.21 1.86K2O 3.85 2.10 3.10

V ppm 30 30 30

S 0.05 0.05 0.05 H2O 0.27 0.43 0.77L.i. 44.04 56.69 45.69

Content of carbon is expressed by the loss of ignition. Several general rules in the development of vein-type graphite deposits have been determined at the Monapo structural unit: graphite is connected with very high degree of metamorphic rocks of granulite facies with typical mineral of sillimanite. There exist two types of mineralization - first with graphite in granite-gneisses disseminated or as impregnations or in pockets with average 25%; secondly in typically vein or swarm of veins within fractures, locally of pegmatitic origin, accompanied by quartz and siliceous impregnations. The content of graphite could attain even 94% of flaky crystalline variety.

c) Lúrio belt forms the northern boundary of the so-called Nampula block, and is composed of several different formations. Lächelt (1985) suggests that it is of geosynclinal origin with regard to its present degree of metamorphism of amphibole and granulite facies. The most distinctive feature of the belt is its structural development. Within the generally trending Mozambican belt in N-S direction, the Lúrio belt proceeds generally E-W or ENE-WSW along the river Lúrio. Some rocks are metasediments



composed of garnet gneisses, graphitic gneisses and crystalline limestones with intrusive rocks of granodioritic to syenitic composition. Within the Lúrio belt, the occurrence of metamorphic graphite has been known for a long time (Noticia Explicativa, 1974) from Nipepe, Nicomissore and Mequice located in the central part of this belt, from Nipepe to the S. However, no data are available on these sites as yet. At the E-end of the Lúrio belt, just near the boundary between Precambrian rocks and the coastal sedimentary basin, an occurrence of graphite at Mazeze was observed long ago. The entire crystalline area around the mouth of the Lúrio river was explored by Bulgar Geomin in 1983. They discovered several tens of graphite deposits and regarded this area as one of the most promising graphite districts of Southern Africa. The main deposits extend from the N of river to the SW, close to the port of Pemba. The advantage of the area is its close proximity of the port and good tarmac roads, with concentrations of deposits over an area of about 5,000 km2. Of about thirty deposits, the more important are these: 1. Rio Uanapula, at about 12 km S of the road Pemba-Montepuez. The graphite zone is 8 km long, its thickness ranges from 20-70 m, with massive graphite with C content of 15-22%. About 1.2 million t of graphite can be extracted to the depth of 20 m in opencast. 2. Taquinha, at 9 km NE of the river Megaruma. The graphite zone consists of gneisses of the Metoro Formation, 3 km long, 50-70 m thick, trending E-W, inclination 25-30°C, massive flaky graphite with a C content of 15-20%. The reserves, up to a depth of 20 m, have been estimated to 6,490 000 t of graphite ore. 3. Rio Megaruma, at 10 km N of Mazeze, is an important graphite deposit. It is part of the subformation Matasse, with massive, large-flake graphite. This is the original deposit Mazeze, which had been mined intermittently in the past. The graphitic zone of E-W direction with 30° inclination is 9-10 km long, 10-20 m thick with a C content of 10-17%. The reserves, up to a depth of 20 m, have been estimated to 3,870 000 t of graphite ore. 4. Mazeze, 13 km E of Mazeze and N of the main road Mazeze-Pemba; the deposit was discovered in the 1970ties by BRGM searching for uranium. The deposit is very promising, with a graphitic zone of the subformation Namiropa, about 3 km long, thickness of graphitic gneisses from 15-20 m to 50-60 m, C content 15-20%. The massive graphite is of the large-flake variety. Estimated reserves, up to a depth of 20m, are 3,600 000 t of graphite ore. 5. Monte Nipacue represents a zone of 3-5 km length, thickness 15-60 m, C content 17.15%. The reserves up to a depth of 10 m, are estimated to 10,750 000 t of graphite ore. 6. Rio Muaguide - Ivanca, at 17 km NE of Metoro and near the road Pemba-Ancuabe. Graphitic gneisses of the subformation Namiropa form a zone 3,000 m long 40-60 m wide, C content 15-20%. The zone trends NW-SE with inclination of 5°. The reserves estimated to a depth of 20 m, are 5,160 000 t of graphite ore. 7. Monte Jocolo, is situated W of a mountain of the same name (695.8 m above sea level), and 5 km E of the deposit Rio Uanapula. The zone is 4 km long, 10-20 m wide, 110° strike and 35° inclination, C content 10%. The estimated reserves of graphite ore are 1,720 000 t. 8. The Ancuabe deposit near the road Pemba-Montepuez with graphite content 3-10% of the large-flake variety. For the whole district, the estimate of graphite ore reserves is about 35 million t. Bulgargeomin collected several bulk samples of graphite ore from which they obtained pure concentrates of high quality flake graphite. Pilot tests as well as a processing unit are being prepared. Graphite deposits around the mouth of the river Lúrio are certainly of greatest importance in Mozambique and will add further reserves.

d) Morrola structural unit is part of the Lichinga block, the most northern part of Mozambique. It is interpreted as a sinform structure with structural trends from N-S to NE-SW. It is named after a small village SW of Montepuez. The only known site of graphite occurrence is at Montepuez (in Map of Deposits No. 125, 1974), in graphitic shists closely connected with well-known crystalline limestones deposits-marbles of Montepuez. Graphite with fuchsite is part of the marble sequence. The Morrola Formation consists of paragneisses, carbonatic rocks and quartzites with ilmenite, garnets and epidote. Graphitic gneisses are common. The metamorphic sequence with magmatic rocks, mainly pyroxenites, is metamorphosed to granulite facies. No exploration work has been performed as yet.

Conclusions: Mozambique has an old tradition in graphite mining. The quality of exported graphite from Angónia and Monapo areas was derived, in the past from an extraction of best-quality graphite without any treatment. Despite this setback, the quality of Mozambican graphite was high, of metallurgical type. New discoveries around the mouth of the river Lúrio place Mozambican graphite deposits, with regard the reserves and quality, among the potential and biggest producers of this mineral in the world.





Cilek: 3.7. Lithium minerals

3. 7. Lithium minerals Lithium is a white soft metal, and one of the lightest of all metals, atomic weight 6.938. Its average content in the earth crust is 20 ppm, and it had been concentrating mainly in residual magma during magma crystallization. Granite pegmatites are the main lithium source together with beryllium, tantalum, tin, cesium, rubidium and others. Within zonal pegmatites, lithium minerals belong to a later phase of crystallization during which commence metasomatic processes of albitization. Therefore, lithium zones are best developed in sodalitic-albite-spodumene pegmatites. Besides granitic pegmatites, the main source of lithium are lithium-rich brines. Although lithium occurs in substabtial amount in some 20 minerals, just three of these are of commercial value. Spodumene LiAl (SiO3)2 composed of 64.6% SiO2, 27.4% Al2O3 and 8.0% Li2O. The average Li20 content is usually 4 to 7.5% (from 2.91 to 7.66%) due to a substitution of lithium by natrium or potassium. In pegmatites spodumene is often developed in big crystals which can easily alternate in a mixture of eucryptite LiAl SiO4 and albite NaAl Si3O8. Spodumene is the most important source of lithium for direct use in the glass industry but its Fe2O3 content should not be higher than 0.1%, and Li2O about 6-7%. A lower Li2O content indicates an intergrowth with quartz. Transparent spodumene is of gem quality: greenish-hiddenite, yellow-triphanite and pinkish-kunzite. Petatite LiAl (Si2O5)2, is composed of 78.4% SiO2, 16.7% Al2O3 and 4.9% Li2O. The actual range of Li2O is 3.0 to 4.9%. The mineral is mostly massive, colourless and friable. It is accompanied in pegmatites by spodumene, lepidolite, eucryptite and tourmaline. Its industrial use is similar to that of spodumene, i. e., mainly in the glass industry. Lepidolite (OH, F)2 KLi Al2Si3O10 is a monoclinic mica of varying composition due to isomorphic mixing. Its chemical and structural properties change according to the lithium content. Lepidolite occurs in the form of small crystals and blades, but mainly as a massive flake-grained variety. It is of purplish colour. Its theoretical Li2O content is 7.74%, but the range of the ore is mainly 3.0-4.7%. Lepidolite is commonly enriched by rubidium (0.91-3.80 Rb2O) and cesium (0.16-1.90 Cs2O). Fluorine and rubidium contents (sometimes up to 4%) render the ore more suitable for melting which is favourable for use in the glass industry and enamel production. Since fluorine content is environmentally harmful, lepidolite is substituted nowadays by other materials. Two other important lithium bearing pegmatite minerals are eucryptite and amblygonite. Eucryptite LiAl SiO4, is a mineral of the nepheline group and its theoretical Li2O content is 11.88%. It occurs commonly in pegamtites where its crystals are often enclosed in albite. It originates from an alteration of spodumene by the action of sodium-rich solutions. Eucryptite is a rare mineral and could be mined as a byproduct only. The only commercial world deposit is Bikita in Zimbabwe. Amblygonite LiAl (PO4) (F, OH), the only lithium non-silicate mineral, represents the last member of the group with high fluorine content. It forms big crystals or is massive, with high Li2O content of 10.2%. The ore grades usually have 7.5-9.0% Li2O, but the mineral is rare. Deposits of lithium minerals can be divided into: 1. Lithium granites 2. Granite-pegmatites 3. Pneumatolytic deposits



4. Hydrothermal deposits 5. Lithium-rich sediments 6. Evaporites 7. Brines, mineral waters, sea water

Of all these types, just types 2 and 7 are of commercial interest at the present. Pegmatites with lithium minerals are either zonal or homogeneous, unzoned, mainly of the albite-spodumene type. They range from early-stage minerals like iron-rich spodumene of green colour through the intermediate stage with spodumene-petalite-lepidolite-amblygonite to the last stage of hydrothermal alteration with eucryptite, cookeite and bikitaite. The minimum content of lithium minerals to be economically extractable is about 1% in hard rocks and about 0.03% in brines. Natural ore of spodumene and petalite is used in the ceramic industry, glass-ceramics, enamels, frits and lithium salts production. Lepidolite is used mainly in the glass production, amblygonite as raw material in lithium-chemicals. Lithium represents an excellent flux in glass batch, because it lowers viscosity and melting point, improves chemical resistivity, surface strength etc. Its main use is in the production of TV tubes and glass-ceramics and also in special whire ceramics and refractories. In the chemical industry, lithium compounds are used as special lubricants (greases in motor-cars, military), lithium hydroxide as an absorbent of carbon dioxide in submarines and spacecrafts, buthylene-lithium in the production of synthetic rubber and polymers. Large quantities are used in aluminium and metal industry for the production of batteries in civil and military fields. Future applications include new technologies in glass products using minor amounts of 0.075 to 0.15% of Li2O, better quality glass of some borosilicate glasses, production of aluminium-lithium alloys for aerospace industry (1.5-3.0% of Li2O) and moilten carbonate fuel cells. Its main future use is envisaged in the atomic industry in thermo-nuclear reactors where lithium can serve as an atomic combustion and cooling agent. In thermonuclear reactors, the energy source will be a mixture of deuterium-tritium, part will be produced inside the reactor by the bombardment of isotope Li-6 by neutrons released during the reaction: see the equation - 6Li (n, alpha) T. Another future use is in batteries for the storage of electrical energy produced for example from solar energy or wind energy, which is very important for many developing countries. These batteries should serve also as a source of electricity in future automobiles. From these points, lithium resource may constitute, in the near future, a bigger source of energy than present solid and liquid fuels. In every country lithium resources require special attention and a careful evaluation of reverves. World production in 1973 was 6,400 t of contained lithium. In 1986 it increased to 8,400 t. Two major applications for lithium during these years concern additions of lithium carbonate to aluminium potlines and its use as a constituent in glass and ceramics. In Mozambique,three lithium-bearing minerals have been produced: lepidolite, amblygonite and petalite. All of these are pegmatite minerals, obtained generall as byproducts in columbo-tantalite



mining. Lithium minerals are concentrated in zonal pegmatites in the lithium zone near the quartz core with albite, locally with spodumene and always with lepidolite (see Fig. 3.7.1.). In some pegmatites such as Marropino, another lithium zone has been developed with lepidolite-greisen of a small thickness. Lithium minerals are concentrated in peqmatites of the sodium-lithium type with beryl, columbo-tantalite, microlite and typically with tourmaline. The zones differ in thickness from 1 to 40 m. Fig. 3.7.1. Structural scheme of the zonal pegmatite of Zambezia (Barros-Vicente, 1963) (314 kB) Lepidolite is a typical mineral of sodium-pegmatites and, in Mozambique, it develops often in aggregates of columnar shape with a spherical top and a diameter about 15-20 cm. The spheroidal columns are usually 30-40 cm long with pink mica flakes on the surface, inside with massive radial aggregates. Besides in these typical columns, lepidolite is found in massive medium-grained layers commonly mixed with quartz. The columnar shape is characteristic of the lithium zone near the quartz-core, the massive form often of greisen zones. Owing to a deep weathering of pegmatites of Alto Ligonha area, the lepidolite in different aggregates is easily released from the kaolinitic groundmass. The colour of lepidolite is lilac or pink not depending on the lithium content but on the presence of manganese and iron. The Li-content varies between 1.82 and 4.92% (Marropino). Generally, the content of lithium in Alto Ligonha area is lower than expected and this could be the result of a mining of lepodolite with muscovite and quartz. In the past, a major portion of lepidolite was unsalable because of its low Li-content. The content of rubidium in Alto Ligonha area is 0.23-0.35% Rb2O, that of cesium 0.78-1.68% Ce2O. Lepidolite is connected with the development of tourmalines of gem quality, with verdelite and rubelite. In addition, lepidolite is associated with microlite and with some radioactive minerals - mainly monazite or zircon as it is known from mines of Morrua, Muiane, Marige, Namivo and Ilovo. Cookeite is a product of alteration of spodumene and this lithium-mica occurs in the form of small aggregates at Muiane, Marige, Morrua and Marropino. Spodumene is found in all sodium-lithium pegmatites with lepidolite and albite usually in big massive forms, always altered and difficult to identify. Prismatic crystals occur together with albite and quartz in irregular bands in pegmatites of Morrua, Moneia, Muiane, Namivo, Nahora and Maipa. Some of these crystals are 5-50 cm long, 2-10 cm in diameter and fibrous. When altered, they are commonly of a reddish colour. In some mines such as Morrua, Marropino and Nahora, the gem variety of violet kunzite is extracted; hiddenite of yellow to greenish colour was mined at Namacotche, Munhamola I., Muiane and Nahora. Chemical analysis of spodumene (pegmatite Ilodo, Barros-Vicente 1963) in %

SiO2 61.12

Al2O3 + Fe2O3 30.00

CaO 0.24

MgO 0.07

P2O5 tr.

Li2O 5.0



Petallite has been reported from the lithium-zone of a few pegmatite mines only: Morrua, Marropino, Ginamo, Nahora and Moneia. Usually, it is in close connection with lepidolite in those parts of the lithium-zone, in which spodumene is less developed. Eucryptite is a rare mineral usually in intergrowth with albite, and derived probably from spodumene. It was found at Morrua and Marropino. Amblygonite is common to the lithium-zone of many pegmatites such as Nanro Napa, Namacotche, Moneia, Nahora, Morrua, Marropino, Ginamo and Ilodo. It is present in blocks of different shape and small veins which cut accross the lepidolite, its colour is white, sometimes greyish. Chemical analysis-pegmatite Nanro; Barros-Vicente 1963: %

SiO2 1.00 Li2O 5.91

P2O5 47.33 Na2O 1.39

Al2O3 34.98 K2O 0.45

Fe2O3 0.52 F 1.07

CaO 0.48 L. i. 8.00

101.13

Pollucite is a cesium mineral, formula H2O • 2Cs20 • 2 Al2O3 • 9 SiO2. It is mentioned here because of its intimate connection with petalite within the lithium zone of some pegmatites such as those from Namacotche, Nahora, Muiane, Moneia, Morrua and others.

In Mozambique the production of lithium minerals started after World War 2. The first figures on production were given in 1949, about 510 t of Li-minerals, 1951 - 278 t, 1952 1,000 t, 1953 - 1,462 t, 1956 - 1,002 t, 1959 - 90 t, 1963 - 104 t. Lepidolite was often of poor quality and some tonnages were not salable. According to Barros-Vicente (1963), the average composition is 4.15 % Li2O (3,9 - 4.92 %) and 0.99 % Fe2O3 (0.15-2.23 %). Lepidolite was exported from 1957 - 50 t with maximum of 274 t in 1962. At present Li minerals are stockpiled for a shortage of markets, - pollucite stockpile is about 55.9 t (P. Jourdan, 1986). Petallite was produced in small quantities (in 1956 - 25 t and amblygonite 35-40 t ?). From the port of Beira, petallite (minimum 3.8% Li2O), lepidolite (min. 7.5% Li2O), spodumene (3.8% Li2O) and ambligonite (min. 7.5% Li2O) were exported (Barros-Vicente, 1963). Conclusions: Lithium minerals, despite of present lack of market, will become very important potential resources in the near future. A complex utilization of pegmatitic material could improve also the quality of each lithium mineral to a marketable product. With the development of glass, ceramic and alumina industry in Mozambique big internal market for lithium could be established.



Cilek: 3.8. Magnesite

3.8. Magnesite Magnesite, magnesium carbonate, MgCO3 (47.8% MgO, 52.2% CO2) is the end member of an isomorphous series of carbonates. The complete substitutional series extends up to siderite FeCO3 as a result of a substitution of ferrous iron by magnesium. Manganese, calcium, cobalt, Al2O3 and SiO2 may substitute magnesium or are common admixtures. Magnesite is the most important magnesium mineral. It occurs in two physical forms: cryptocrystalline or amorphous in dull white compact porcelain-like masses with a conchoidal fracture, and crystalline, which is softer of higher specific gravity, coarse, cleavable and marble-like masses. Magnesite is found as: 1. infiltration deposits of amorphous magnesite originating from an alteration of magnesium-rich rocks such as serpentine, dunite, peridotite-by the action of waters carrying carbon dioxide 2. hydrotermal deposits of amorphous magnesite in ultrabasic rocks due to the leaching of magnesium from serpentine by hydrothermal solutions 3. replacement hydrothermal-metasomatic deposits of crystalline magnesite of dolomite, limestone, shales by magnesium-bearing solutions 4. sedimentary deposits of massive magnesite developed in salt lakes, around hot springs and in lagoons; magnesite forms with high concentration of MgSO4 in an alkalic environment. Coarse, cleavable masses of magnesite are of metamorphic origin and commonly associated with talc, chlorite and mica schists. Two main commercial grades of magnesia are produced from crude magnesite: caustic magnesite clinker-calcined magnesia produced at 700-1,000°C from both crystalline and amorphous magnesite; deadburnt magnesia produced at 1,450 - 1,750°C from crystalline magnesite only. The latter is the main refractory grade with mineral periclase as main constituent, and other minerals such as forsterite, spinellides and monticellite. The higher the content of periclase, the higher the quality of the product. Magnesia - MgO produced from magnesite is inert and has a high melting point; therefore it is used as refractory in steel fournaces. Production increased substantially with an introduction of an oxygen furnace, which needs a basic-refractory lining such as magnesite. Other uses are in nonferrous metal-processing units, cement kilns and sulphuric acid manufacture. About four fifhts of magnesite goes into the production of refractories. The remaining part is used in fertilizers, special oxychloride cement, as a source of carbon dioxide, production of magnesium compounds and magnesium metal, and in medicine. Two thirds of commercial supplies are derived from magnesite and, at present, an increasing volume is produced from seawater. The introduction of new refractory products based on magnesia and flake graphite (magnesia-carbon or mag-carbon refractories) changed the situation in the consumption of magnesite. Mag-carbon refractories originally developed for use in electric-arc steelmaking, are used in an increasing rate as linings in basic oxygen steel production. The use of deadburned magnesia requires a higher-quality material: over 97% MgO, low iron and boron content, lime and silica ratio 2:1, bulk density 3.4 g/cc or above, crystallite size over 100 microns. It means that supply is restricted to the seawater product and to a few top-quality magnesite deposits. Caustic grade magnesia of medium and lower grade is less used, and new methods of beneficiation of natural magnesite have been developed.



In Mozambique, the occurrence of magnesite is limited to a few localities (see Fig. 3.1.1), and these had not been investigated. Of these, the most important is situated at Monte Atchiza, a complex in the Tete Province just on the northern bank of the Cabora Bassa dam. The complex consists of basic and ultrabasic rocks within the drainage basin of the river Mecucoe. It intruded the fold belt of the Fingoe Group after the main deformation of the latter rocks. It itself has been intruded by Post-Fingoe granites. The complex was maped during the 1960ies by Real (1962) and, recently, by Hunting (1984). It consists of serpentinite, gabbro and norite with minor peridotite and pyroxenite. Real (1962) observed big, almost white, veins of magnesite within the black rocks of serpentinite. Some of these veins are 20 to 30 cm thick and traverse the basic rocks. Many concretions of magnesite could be found also in river alluvia. The presence of opal is typical of hydrothermal origin. Hunting reports magnesite float which is plentiful in the eluvium and colluvium overlying and surrounding the serpentinites. Bed rock occurrence found by Real does not appear to represent concentrations of magnesite veins of any significance. According to the above description it could be concluded that amorphous magnesite originating from weathering and a hydrothermal alteration of serpentinites occurs in serpentinites of Monte Atchiza. The presence of CO2-containing water is possible, common are thermal waters on faults bordering the rift valley. The process could be explained as follows: H4 Mg3 Si2 O9 + 2 H2O + 3 CO2 ===> 3 MgCO3 + 4 H2O + 2 SiO2 (opal, chalcedony, quartz). An extension of the Monte Atchiza massif into a combination with fault lines and thermal waters could be very favourable for the development of magnesite deposits. It should be noted that these deposits are developed to the maximum depth of about 200 m and the economic content of magnesite within the rock complex should be minimum 20%. The second site of occurrence of magnesite is connected with serpentinites and asbestos deposits. In Serra Mangota near Manica in an Archean greenstones-belt these are of a similar origin to those at Monte Atchiza. No details are available of this occurrence. A small deposit of magnesite was discovered by Gouveia (1967) in the Cabo Delgado Province near Pemba on Monte Namalasse. Here the ultrabasic rocks-dunites - are developed with fractures filled up by magnesite. On the surface the blocks of 20-50 cm of white magnesite can be found. The magnesite again originated from ultrabasic rocks alteration with amorphous magnesite. Carvalho (1944) presents a description of magnesite occurrence near the railway at Chimoio in the Manica Province. The occurrence is supposed to be big (?) and the magnesite in the rock has a 92% purity. Analysis (in %):

MgO 43.77 SiO2 1.78

Fe2O3 + Al2O3 0.50 CO2 + H2O 51.03

CaO 2.92

Conclusions: In Mozambique, just deposits of the serpentine alteration type are developed. Their occurrence should have an economic importance, if the ultrabasic complexes were larger in extension, the grade of amorphous magnesite high and the content of ore over 20%. From this point of view, the Atchiza complex is promising and should be explored. Otherwise, basic type refractories could be produced from



serpentinites or dolomitic limestones of crystalline origin. The presence of flake graphite in large quantities, together with periclase materials may represent a basis for the production of magnesium-carbon refractories. Lower-grade refractories (up to 1,500°C), could be produced from available dolomitic or serpentinitic raw materials.



Cilek: 3.9. Mica

3.9. Mica Mica represents a group of minerals with common physical properties to those of muscovite, biotite, phlogopite, lepidolite and zinnwaldite. Micas are common rock-forming minerals, but muscovite and phlogopite only, due to their physical properties, and lepidolite and zinnwaldite, as a source of lithium, are economically important. Muscovite K Al2 (Al Si3 O10) (OH)2, specific gravity 2.77-2.88, is called common or white mica, monoclinic; it occurs in small flakes or foliated masses, or large hexagonal crystals known as "mica books" from pegmatites. Muscovite contains isomorphous admixtures of Fe3+ (up to 4%), Fe2+ (up to 1.2%), Mg, Na, Rb, Cs, Ba, Cr. Phlogopite K Mg3 (Al Si3 O10) (OH)2, specific gravity 2.76-2.90 known as bronze mica, is commonly found in hexagonal tapering elongated "mica books", usually in dolomite marbles. It contains iron, fluorine or manganese. If the ratio of Mg : Fe is less than 2 :1, it is called biotite. In the old days muscovite was used as window panes in Moscow, hence its name and exported from Russia to the West. Because it splits readilly into thin, flexible, but tough sheets, muscovite found its application in the electroinsulation industry. It is electricity resistant, mechanically, chemically and thermally stable. The colour is one of the main properties for grading: muscovite with tints of ruby is called ruby mica and is regarded as superior in respect to electrical properties, green mica as superior for optical uses. Muscovite is a primary constituent of acid igneous rocks such as granite or pegmatite, in a variety of metamorphosed rocks and in clastic sedimentary rocks. Much of the commercial muscovite comes from pegmatites as sheet mica or as a byproduct of feldspar mining or kaolin dressing. Sericite - a fine-grained muscovite is used as a cement - binding material. Phlogopite is regarded as inferior to muscovite, but is superior to muscovite in heat resistance (muscovite breaks up at 800°C, phlogopite at 1,000°C). It is associated with crystalline limestones or ultrabasic rocks. High-quality mica, known as sheet mica, is found in "books" in pegmatites and is mined and sorted by hand. After cleaning it of impurities such as quartz, feldspar, it is split into block mica of a minimum dimension of 4 cm2. Quality-sheet mica is divided into eight groups: above 150 cm2 up to 4-6 cm2 with sheets of rectangle of sides 3 :1. The minimum content of mica in pegmatites is about 20 kg/m3, but high-quality mica containing 3-5 kg/m3 can be mined economically. A low content of mica is acceptable also when mica is a byproduct of feldspar or quartz mining. Sheet mica is usefull because of its electrical properties; during World War 2, became a strategic mineral for aircraft and tank engines production. It is used in condensers, as an insulating material, in furnaces windows, as a nonconducting element in electrical appliances, radio and TV, radar, fillers of plastics, in the paper industry, but also in the building industry as an admixture of plaster. About 10% of mined mica only can be used as sheet mica, therefore, the wastes of sheet mica are nowadays cemented together, layer by layer to form a "mica-sandwich" for use in electronics, substituting much of the sheet mica. Ground mica is processed waste mica both from sheet mica waste and flake mica from mining of pegmatite and kaolin as a byproduct. Mica is ground in a dry or wet process and used in plaster-board joint cement, as a dusting agent in roofing and often as lost-circulation material in drilling, and also in paint and rubber industry (less than 40 micron).

Table 4. Mineralization of zonal pegmatites of Zambezia (Barros-Vicente, 1963) (588 kB) In Mozambique, mica mining is restricted to pegmatite mining. No other mica resources have been used as far. Scrap mica could be obtained as a byproduct of columbo-tantalite mining and mining for other economic minerals in pegmatites (see Fig. 3.6.1). Barros-Vicente (1963) published some information on the history of mica mining in the pegmatite district of Alto Ligonha. Around 1934, the interest in mica mining was started by Portuguese settlers; earlier, mica was extracted at Ribaue and at Naipa and Merrapane. During a search for other mica deposits, together with gold rush in this region, important localities of columbo-tantalite, beryl, topaz and semiprecious stones were discovered. Two grades of mica - black spotted and ruby, were exported from pegmatites of Zambezia. Later, also natural mica - scrap mica of a small size, has been produced. There were certain doubts expressed even by Barros-Vicente (1963) whether split - sheet mica of commercial size was produced in Mozambique, as this was common to the former British colonies in the neighbouring Zimbabwe and Tanzania. The production, according to these authors, was as follows:

Year Production (kg) Export (kg)

1956 12,164 233

1957 30,170 1,711

1958 2,074 50

1959 5,518 2,470

1960 1,051 1,297

1961 1,522 1,528

1962 551 -

1963 - -

Total 53,050 7,279kg


Cilek: 3.9. Mica

The main producer of black-spotted mica was the Naipa mine, while Intocha (Intxotxa) produced the bulk of ruby mica. Only a small part of mined mica was of commercial grade (10-15%), a major portion of mica was sold directly at the mining site to different foreign companies at a lower price. This trend in production of scrap mica continued even after independence, when annual production reached the peak of 300 t in 1981. Mica in pegmatites is very common and abundant. In zoned pegmatites, it is concentrated mainly in the external zone, or near the quartz core (see Table 4.). Different types of mica are known to occur in pegmatites: muscovite, sericite, gilbertite, lepidolite, cookeite, biotite, vermiculite and phlogopite. Ruby mica of the Gile district is concentrated in pegmatites of Nahora, Intocha, Mocachaia and Namacala, while black-spotted mica occurs and is mined in the Alto Ligonha district mainly from pegmatites of Murropoce, Muchuloni, Nuaparra, Muiane and Naipa. More favourable for the development of mica are pegmatites either unzoned or of simple zonation, when compared with complicatelly zoned pegmatites of the columbo-tantalite and sodium-lithium type (muscovite of a larger dimension in "books"). Also pegmatites in mica-gneisses, with a well-developed marginal zone, and xenoliths of the surrounding rock, display better-developed mica crystals. In the past, mica was extracted either as a main - or a byproduct (the latter is more common) from these pegmatites:

1. Alto Ligonha district:Murropoce Mucholoni

15°40' S 30°05' E

spotted mica with beryl, morganite, aquamarine, Bi, Ta-Nb

Naquissupa 15°39' S mica with beryl 38°21' E Ta-Nb

Nuaparra15°46' S 38°03' E

scrap mica with beryl, rose qurtz, aquamarine, Ta-Nb, Bi

Merrapane 15°52' S ruby mica with beryl 38°22' E Ta-Nb, Bi, cassiterite

Nahia15°46' S 38°28' E

mica with beryl, Ta-Nb, Bi, monazite

Muiane Naipa

15°45' S 38°15' E

mica with quartz, lepidolite, amblygonite, beryl, Ta-Nb, Bi, kaolin

2. Gile districtNahora Intocha Namacala

15°57' S 38°19' E

spotted mica ruby mica, exported block mica ruby mica (upto 30x50cm) with beryl, monazite, quartz, Ta-Nb, Bi

3. Ribaue districtBoa Esperanca

15°05' S 38°19' E

scrap mica with feldspar, kaolin samarskite, zircon, beryl, monazite, Ta-Nb

4. Mugeba districtEnluma

16°37' S 37°18' E

mica with beryl, Ta-Nb, Bi, monazite

Maria Muagotaia

16°36' S 37°23' E

mica with beryl, Ta-Nb, Bi

5. Mocuba district Munhida16°58' S 36°55' E

mica with beryl, Ta-Nb, Bi

6. Alto Molocue districtNamcotche Munhamola

15°57' S 37°55' E

green splitting mica with beryl, polucite, microlite, tantalite, columbite, monazite, cassiterite, bismutite

The pegmatites outside the Alto Ligonha distriuct s. l. are of less economic importance, the zonation is simple, pegmatites are less differentiated, a typical feature is the presence of rare earths. These pegmatites contain tourmalines, beryl, feldspars and mica as major constituents. Some contain radioactive minerals. These pegmatites are present in the Monapo structural unit, in the area of Nacala-Memba and around the Msauize basin, in the vicinity of Metarica, in the area of Chimoio near Gondola and in many other places within the whole Mozambican belt, in sites with smaller and bigger occurence of pegmatites. In 1978, experts from the GDR-Dresden, investigated the mica occurrence in Mozambique.They visited several localities of previous mining: mines of Merrapane, Namacala and Intocha with ruby mica. A very important deposit of ruby mica was Merrapane from which big quantities of sheet mica were exported as block mica during the World War 2. The deposit Intocha was also in production till 1971 for splitting mica (about 950 t), later just scrap mica was exported from both mines to Great Britain and other countries as a source of mica powder. Although a grinding plant for the production of ground mica for oil-well boreholes had been projected, this plan was not realized. Four samples were investigated: No. 1607 - Nuaparra I, green muscovite, unsuitable as splitting and scrap mica No. 2302 - Namacotcha, green muscovite, to be used as splitting mica (sheet mica) No. 2401 - Munhamola, muscovite, suitable as sheet mica


Cilek: 3.9. Mica

No. 2801 - Intocha, ruby mica, exported as block mica. Other pegmatite mines were also evaluated: Boa Esperance with muscovite unsuitable for sheet-and block mica, Muiane producing mica as a byproduct and useable as ground mica only, Naipa with impurities and unsuitable as block mica, and Murropoce with black-spotted mica. The results obtained from the samples: Desintegration:

Sample Noloss in

calcination %

yields %

volume cm3

thickness micron

g/cm3force rupture

kp/cm

resist. to rupture kp/mm2

Temperature of calcination

1607 2.57 68.8 35.0 53 1.16 0.315 0.167 796°C

2302 2.05 83.6 33.0 44 1.39 0.244 0.119 824°C

2401 3.26 81.9 31.0 42 1.44 0.255 0.112 776°C

2801 2.22 90.9 33.5 41 1.48 0.726 0.302 900°C

For the muscovite, the temperature of breakdown is between 600 and 800 °C; calcination starts at almost 800 °C and is effective at 900°C (Sample No. 2801). Loss of water is normal except for sample 2401. Sample 1607 from Nuaparra: mica of low quality demonstrated by a low yield, large volume, big thickness of the fine product and, therefore, small specific gravity. Samples 2302 and 2401 are almost identical, of good quality, but even here the yield is somewhat low. Sample 2801 from Intocha is the best, with good resistivity to rupture and good material recovery. This mica ranged in grade from "fair stained" to "spotted", but has traces of impurities represented by ilmenite, hematite and magnetite. It can be used as sheet mica up to sheet size of 5 to 20 cm2. The green mica from Nuaparra is suitable as scrap mica only in the production of mica paper. Green micas from Namacotcha and Munhamola can partly be used as sheet mica, while ruby mica from Intocha is suitable both for splitting and electroinsulation purposes. The only approved reserves of mica in Mozambique are those from the mine Muiane. Thieke (1980) calculated 72,000 t of mica reserves (content 1.1% in kaolinized pegmatite in a fraction above 6.35 mm), but no qualitative tests were made. Previous results of GDR experts (1978) indicated that this mica is suitable as ground mica (oil-wells, filler?). In 1986, Duda et al. described the Nuaparra pegmatite deposit. The exploration was aimed at an evaluation of feldspar reserves, but some data on mica properties were also gained. It is necessary to stress, that this deposit, besides some semiprecious stones and a small amount of Ta-Nb and Bi, served as a source of mica. This mica was exported as natural mica without beneficiation. According to Duda (1986), the muscovite of Nuaparra is developed in two types: 1) in the zone of quartz-muscovite with mica in books and 2) in the middle zone with big microcline.

Spectral analyses Content of elements in descending order

1. muscovite Si, Al K, Fe Li, Mg, Mn Ba, B, Cr, Ga, Nb, Pb Ag, Cu

Ca, Bi Na, Ti, Be Sb, Sc, Sn, Sr, W, Zr Mo, Ni, V, Y

2. muscovite Si, Al K, Fe Li, Mg, Mn B, Ba, Be, Ga, Nb, Sn Ag, Cu

Ca Na, Ti, Bi Sr, W, Zn, Zr Mo, Ni, Pb, Cr, V

In both cases, the muscovite is of normal composition with a low content of lithium but an increased content of Be, Ti, Sn, Ga. Quite new is the determination of Bi, Nb, Zr, Mo, Ni. Conclusion: The estimated reserves of mica in Mozambique are 72 kt. Reserves from the pegmatite mine Muiane represent a byproduct of columbo-tantalite mining mixed with kaolin, feldspar and quartz. The quality of mica is low and is suitable for the production of ground mica only. Mozambique has an old history of mica mining in pegmatites, some deposits have been supplying high quality ruby mica, some scrap mica, but better commercial grades of sheet mica were never produced. Local manpower was used for the extraction, but skilled manpower necessary for the splitting and cutting was not introduced. Two ways exist to develop huge mica resources in Mozambique: 1. special mining for mica on less zonal or unzonal pegmatites 2. to utilize mica byproducts in an mining of other minerals and produce scrap and ground mica. The emphasis should be put on high-quality scrap mica-mica without impurities - in small flakes and for different industrial branches. Substantial reserves exist already in the present pegmatite mines.



Cilek: 4.1. Bauxite and aluminum laterite

4. DEPOSITS OF INDUSTRIAL ROCKS 4.1. Bauxite and aluminium laterite Bauxite is a group name for a mixture of hydrous aluminium oxides composed mainly of trihydrate gibbsite Al(OH)3 with 65.35% Al2O3 and 34.65% H2O, and monohydrates AlO(OH) diaspore with 85% Al2O3 and 15% H2O and boehmite with 84.97% Al2O3 and 15.03% H2O and finally of amorphous cliachite Al2O3 • n H2O. Bauxite is a rock name and also a commercial name commonly applied to aluminum ore. Bauxite is generally the endproduct of a complicated alteration process of aluminium-rich rocks undergoing several stages of weathering which include: a) kaolinization in which aluminium-silicate minerals of the parent rocks (plagioclase feldspar is probably the best altered mineral) are transferred to hydrated silicates of alumina, or kaolinite minerals b) lateritization - laterite and aluminum laterite is a mixture of hydroxides of iron and alumina and other residual materials such as alkalies, lime, titania, magnesia and silica. Aluminum laterite is the endproduct towards the last stage of c) bauxitization with prevailing hydrated aluminum oxides, some iron oxides and impurities including remaining silica. In nature, these three-stage products and zones are not allways developed. Bauxite can rest directly on the parent rock, the process can stop at the kaolin zone, the kaolin zone with bauxite zone only is developed or, and this is true in most cases, aluminum laterite is the end product. Bauxite development requires certain chemical, physical and geological conditions: * tropical climate above 20°C * alternating wet and dry seasons * high-porosity rock with high alumina content * vegetation cover with bacterial activity * low topographical relief on higher ground * long periods of stability and weathering. Under these conditions, the chemical leaching is possible, silica is removed and alumina oxides and iron are concentrated. The movement of the water table and porosity of parent rocks make it easier. The result is a bauxite residual deposit. From there eluvial and detrital bauxite deposits are derived. Main genetical types of bauxite and Al-laterites deposits: a) "terra rossa" or limestone bauxite, also called karst bauxite b) lateritic or silicate bauxite, Al-laterites. Karst bauxite deposits occur in sinkholes of a recent surface or a fossil surface. Some of these can be folded and disrupted tectonically. These deposits cannot be regarded as a limestone weathering residue, because some deposits are of the thick blanket-type and, therefore, rewashed or entrapped Al-laterites had to undergone further desilification in an alkaline environment. Evidence of postdepositional changes is a sharp boundary between different bauxite facies. Al-laterites can develop on different parent rocks, from sedimentary to metamorphic ones, and, therefore, the resulting lateritic bauxite is extremely variable. The best deposits developed by lateritization of high alumina and low silica and iron are leucocratic rocks as for example syenites and anorthosites. The quality of the bauxitic horizon can be improved by organic substances made available from an overlying peat horizon, to increase deferrization. On the surface of the profile, a hard iron-rich zone - hardpan develops, followed by a spotted horizon underlain by a kaolin zone. Resulting from a destruction of lateritic or bauxitic profiles, rewashed deposits originate-conglomerate and slope deposits, deposits transported over short distances and deposits in sedimentary formations either as fillings of valley and other depressions, or stratiform deposits. Bauxites and lateritic bauxites contain several admixtures: kaolinite, chlorite, illite, quartz, often a substantial amount of titanium minerals, iron oxides, rare-earths, uranium and thorium and some metals. When metamorphosed they give rise to deposits of the sillimanite-group minerals, corundum and emery. About 95% of all mined bauxite is used in the Bayer process to produce alumina and from this about 90% is then used in metal production. The Bayer process consists of a conversion of bauxite to soluble sodium aluminate by mixing it with soda, the insoluble SiO2, TiO2, and Fe2O3 are then



removed. Alumina trihydrate, after calcination, is prepared for an electrolytic production of Al-metal. The requirements for the quality of bauxite is minimally 40% Al2O3, maximally SiO2 5%. For low-grade bauxite ore the sintering process (LSS method) is used. The use of different processes depends directly on moduli Al2O3/SiO2 and the content of calcium (see following table):

Technology Al2O3 % modulus Al2O3/SiO2 CaO %

Bayer - high grade minimum 40 minimum 10 maximum 3

Bayer minimum 40 - maximum 3

LSS - high grade - minimum 10 over 3

LSS - minimum 3 -

Bauxite for nonmetallic uses, when calcined or fused, requires a specific composition: Al2O3 above 58%, less than 2% Fe2O3, maximum 5% SiO2, 3% TiO2, and 0.2% Na2O + K2O. This material is used in a production of calcined ware with a mixture of mullite and corundum (Al2O3 is 80-90%) or after heating, to produce fused alumina-pure corundum with almost 100% Al2O3. Refractory bricks, crucibles and cement are produced for blast furnaces and cement killns. Futher uses are abrasives in grinding wheels and cements. In chemical industry, the bauxite composition required is this: 56-60% Al2O3, 4-9% SiO2, up to 3.5% TiO2, 3% Fe2O3. Bauxite is also used as an admixture in special cement production. The byproducts of aluminium are cast iron, Fe2O3, V, Cr, Ga recovery, red-mud for manufacturing of cement and pigments and titanium recovery. Owing to a scarcity of high-quality bauxite several countries started to use subtitute-raw materials, such as kaolinic or illitic shales, kaolinic clays, nepheline syenites, alunite, anorthosite etc. The Al2O3 content of these materials is 20 to 30%. During World War 2, kaolinic clays for alumina production were used in Japan, Germany, Poland; the nepheline syenite is still used in Soviet Union, with cement as a byproduct.

In Mozambique, the development of bauxite and Al-laterites is known to occur in a few localities only and, in fact, all these are situated in high attitudes (over 1,600 m above sea level), and originated by an alteration of alkaline rocks (see Fig. 4.1.1).

Fig. 4.1.1. Occurences of bauxite and aluminium laterite; bentonite, perlite. (380 kB) The only deposit in production is Serra de Moriangane, also known as Alumen or Monte Snuta in the Province Manica just on the Zimbabwean border. It was discovered in 1911. Other areas with some bauxite occurence are: Monte Salambidua and others in the Province Tete, Monte Mauzo and others in the Province Zambezia. The deposit Alumen was the property of the former Rhodesian company Wankie Collieries (from 1935) and was and is still mined by John Meikles Co. The production started in 1938 with 382 t, 1940 - 180 t and, during the period 1940-1950, total production was 5,799 t used in refractory bricks and 21,408 t in the production of alumina sulphate by African Explosives Co. Later, the production stabilized on 4,000 t/year and continued with about 2,000 t/year up to the present. Three claims are situated just ENE from the border. In Zimbabwe the bauxite is of low quality (about 40% Al2O3) and also in the E part which was explored by "Companhia de Mozambique" it is of a lower quality with a high content of SiO2 (15-46%) and a low content of Al2O3 (40-45%). The Alumen claims produced bauxite with SiO2 - 11-12%, Al2O3 - 58-60% and Fe2O3 - 2.0% (1940-1950). Analyses of selected samples (in %)-Borges (1950):

1940 - production 1,030 t 1941 - production 1,351 t



humidity 0.68 1.13 0.57 0.073 0.6 0.7 0.87 0.63

SiO2 5.86 10.61 7.86 8.54 10.68 9.52 - -

Al2O3 64.91 64.56 60.32 60.86 59.85 60.81 62.98 59.16

Fe 1.09 1.19 1.11 1.21 0.83 0.78 0.78 0.81

insolubles 8.15 13.15 17.66 16.32 - - - -

Quality of mined bauxite and gibbsite in 1961 was as follows: %

Bauxite Gibbsite

Al2O3 62.36 58.08

SiO2 3.14 12.62

Fe2O3 2.18 1.82

H2O 30.53 26.29

The Alumen deposit represents an alteration zone of about 1 m thick, with bauxite containing nodules of gibbsite and overlaid by a kaolinitic horizon. The mined zone is very irregular, bauxite developed in lenses or pockets with an irregular thickness of overburden. Bauxite originated from an alteration of hornblende syenite which follows a narrow zone of contact betwen gabbroic and gneissic rocks. Reserves (Real, 1963) are small: 85-115,000 t of bauxite, 3,000 t of gibbsite nodules and 600,000 t kaolin, which represents the waste. A low content of iron oxides enables a utilization of bauxite as refractory and chemical materials, the high silica content (over 5%) is unfavourable for metal production. The deposit is small but has established the local market. In the vicinity, new exploration started with the aim to increase the reserves. P. Knup gave this description of the area: "The bauxite ore bodies occur in the N part of the lower Precambrian Odzi-Umtali greenstone belt, close to a contact with the Zimbabwean granite-gneiss complex. N of the deposits is an outcrop of granite-gneisses and talc-schists. SW of these, chlorite-schists and felsites were observed. The ore bodies themselves overlie mainly intrusive rocks of saturated to undersaturated composition such as a gabbro-anorthosite rock sequence, diorites and mafic volcanic rocks. The rock units are folded and regionally epimetamorphosed. Their dips attain 50° to 60°, and they strike in E-NE direction. Moderate faulting with relatively small displacements occurs in some places (Fig. 4.1.2).

Fig 4.1.2. Area of Alumen bauxite mine (Knup, 1987) (385 kB)

The deposits are residual. They occupy predominantly an E- directed escarpment of the watershed where precipitation is much higher than on the W slopes. Deep bauxitization by weathering and leaching developed on slightly inclined, plateau-shaped, old erosion surfaces which are mostly SE oriented. Subsequently, the surfaces became dissected into stream valleys causing erosion along their courses in incised river beds and on the slopes. Therefore, just remnants of different sizes representing the once coherent plateau, are now present and contain ore bodies. These are rare in altitudes below 1,500 m. Four main ore types exist: A. White saprolitic bauxite. It is friable, texturally light and porous, and often retains characteristics of the primary parent rock, notably joints. B. Light brown saprolitic bauxite of similar physical nature to A. C. Brown, ferruginous, saprolitic bauxite. It is mainly fine-textured, friable and rich in iron. D. White kaolinitic clay with concretionary, white bauxite. The contents of gibbsite nodules are very variable and so are their sizes and shapes. Diameters from 1 to tens of cm are observable. Both silex and anothosite nodules are, however,



also present. The clay is sticky when wet, and, on the other hand, extremely fine and friable when dry. There is a conspicuous relationship between bauxite and the parent rock. White bauxites - types A and D - derived from anorthosites, light brown bauxite - type B - derived from diorites and intermediate of the gabbro-anorthosite series, and ferruginous bauxite type C-derived from gabbros and basic volcanic rocks. The variety of source rocks, and their complex interrelationship contributed greatly to a considerable degree of ore grade variation over even very short distances. They are also responsible, together with erosion, for the lens-shaped nature and restricted size of the bauxite ore bodies. These vary in lengths from 100 to a maximum of 500 m, in width from 25 to 150 m. Their thickness varies from a few metres to over 20 metres in some places. Since intensity of weathering and leaching differ locally, the depth of the unaltered bedrock are irregular and often unpredictable. For practical purposes, both white-ore types A and D are regarded as first quality, high grade ore. Type B is regarded as second quality bauxite, whereas type C as third quality (Al2O3 < 45%), and deemed to be waste. White kaolinitic clay, having been liberated from gibbsite nodules by wet screening and /or scrubbing must be considered to be another raw material usable, for instance, in the building industry. At present, however, it is dumped. Reserve estimates for ore types A, B and D, and kaolinitic clay in the Alumen Mine and Morondo areas range between 3 and 5 million tons. Analytical results of representative ore type samples:

Location Ore type (%)

Quarry 3 A

P 39/2-3 Quarry 10

B

P 81/0-1 Quarry 8

C

P 32/3-4 Quarry 7

D

F 21/7-8 Quarry 7

Kaolinitic Clay

Al2O3 58.83 49.65 44.01 57.16 39.60

Fe2O3 1.55 13.81 17.78 0.64 0.91

TiO2 0.27 0.84 3.07 0.00 0.01

SiO2 9.00 9.19 9.92 16.92 43.90

L. i. 28.62 23.96 24.12 24.05 15.00

Na2O 0.04 0.04 0.07 0.11 0.09

K2O 1.65 1.20 0.10 0.58 0.19

CaO 0.02 0.08 0.00 0.03 0.00

MgO 0.27 0.09 0.00 0.00 0.00

P2O5 0.01 0.04 0.21 0.02 0.00

MnO 0.06 0.03 0.07 0.06 0.02

Total 99.92 98.93 99.36 99.57 99.72

In the past (Real, 1963) several other areas were checked in the vicinity of Serra Moriangane: Rio Inhamucarara Monte Vumba Chimanimani - Rotanda Around the tributaries of the Rio Inhamucara, an alteration of granite-gneiss occurred, with the development of 0.4-1.4 m thick horizon of kaolin and bauxite with about 0.3 m of gibbsite. The silicate bauxite contains Al2O3 54%, SiO2 10% and Fe2O3 5.6%. On the Vumba mountain, well-known in Mozambique for its popular mineral water, just a small kaolinized zone was discovered on the contact between gabbro and granite. In the Chimanimani area a few zones with kaolin-bauxite are connected with intrusive dolerite dykes. Other small areas are Serra Zuira with laterites (41.70% Al2O3, 10.60% SiO2, 21.56% Fe2O3) and E of Alumen claims, within the Serra Moriangane (1,823 m) there is a lateritic crust and bauxite. Real (1963) analysed one trench with this profile (in %):



Depth SiO2 Fe2O3 Al2O3

1.8m 6.04 24.53 49.93

2.3m 17.84 3.19 54.95

2.8m 17.78 1.98 58.40

3.0m 17.68 1.21 52.11

Judging from these observations bauxite horizons may have developed in several places under mountainous conditions, if suitable parent rocks were present. Generally speaking, deposits in this area will be inextensive and variable in quality. Most of these may be as inaccessible as the deposit Alumen, accessible just from the Zimbabwean side only. Within the Tete Province, several localities with a possible bauxite occurences had been explored in the past (Real, 1963) and during 1980-81 (Samokhvalov, 1981). They found just laterites with an increased quartz content and an insignificant alumina content (localities near Zobue, Vila Coutinho). The most prominent syenite intrusions of the region are Salambidua NE of Tete on the Malawian border, and Cheneca composed of three massif: Domue, Cheneca and Macangue, NE of Furancungo on the Malawian border. Here the margins consist of gneisses and migmatites, but the central part of syenites with hornblende. The top levels are about 1,300-1,400 m high surrounded by sharp slopes. There are two types of weathering zones: clayey sand zone 2 m thick N of Domue and in the border zone, and a zone of kaolinitic-clays reddish, 4.5 m thick, with about 15-20% of quartz, in S and SE part of the massif. Bauxite was not discovered. The Lupata massif of Cretaceous age developed as a brachysynclinal closure of the Mid-Zambeze basin was also examined. Trachytes, phonolites and amygdoidal effusives are covered with a weathering zone of thickness 1.5 m without laterite. In the Province Zambezia, several localities were checked, but only two of these Mauzo and probably Milange, have better conditions for the development of bauxite horizon, but certainly not of significant economic value. The exploration work provided some valuable data on the development of weathering profiles - mainly lateritic - on different parent rocks and on different elevation levels and is worth to be included here (Samokhvalov et al., 1981). The best known locality is Mauzo. It is situated 40 km N of the town of Milange on the Malawian border. The mountain is composed of nepheline syenites which are of an intermediate composition between foiatites and luiavrites with pyroxene. The main components are: orthoclase-perthite, nepheline, heguirine, heguirine-augite. Accessory components are: hornblende, biotite, albite and sodalite. The height of Mauzo is 1,472 m and the elevation above the surrounding plain composed of biotite-plagioclase gneisses is about 800 m. The top of the mountain is flat, more than 2 km long and more than half a km wide, at level 1,400-1,472 m. About 30% of the plain is occupied by outcrops of syenite or by rock debris. The rest is a lateritic cover, eroded in many places, because it lacks a superficial hard ferruginous horizon. In 1963, Real described this locality and analyzed rocks and bauxite. According to him, the parent rock is nepheline syenite with aegirine-augite (foiatite) of this composition (in %):

SiO2 55.28 CaO 3.78 TiO2 0.69

Al2O3 20.77 Na2O 7.69 P2O5 0.20

Fe2O3 2.22 K2O 7.38 MnO 0.11

FeO 1.45 H2O+ 0.33

MgO 0.29 H2O- 0.25

Real also described the weathering profile: 0.15-0.20 m -horizon of black soil with gibbsite nodules 1.40 m - blocks of kaolinized syenites 1.0 m - blocks of yellowish bauxite At the depth of 1.6 m, he analyzed a sample of bauxite (in %):



H2O 0.68 Fe2O3 7.59 TiO2 1.23

SiO2 4.21 P2O5 0.34 K2O 0.17

Al2O3 56.94 MgO 0.78

Thus, the presence of bauxite with gibbsite was confirmed and futher explored in 1967. From trenches made at that time channel samples (1980) were taken by a Russian team. Established profile: 0.25 m - soil with humus 1.20 m - clay yellowish - reddish with concentrations of gibbsite or kaolinized syenites 2.25 m - clay yellowish - reddish with gibbsite,syenites nepheline highly weathered Five selected samples some of good quality of Mauzo correspond to the composition of bauxite (in %):

Sample Al2O3 SiO2 Fe2O3 TiO2 L. i. Total gibbsite kaolin

Ma - 1 (4.5 m) 50.31 20.28 4.65 1.04 24.00 100.28 63.74 22.19

Ma - 3 (1.5 m) 47.82 14.93 7.58 1.34 28.58 100.25 66.06 13.59

Ma - 5 (2.5 m) 37.82 44.80 7.70 0.68 20.10 100.50 14.60 72.68

Ma - 6 (0.4 m) 44.46 23.08 6.69 0.86 24.88 99.97 40.90 45.56

Ma - 6 (3.0 m) 60.40 1.23 5.99 0.73 32.07 100.42 91.15 2.08

Complete chemical analyses showing a similar composition (USSR, 1981): %

SampleSiO2 quartz

SiO2 bound

Al2O3 Fe2O3 FeO TiO2 CaO MgO P2O5 K2O Na2O SO3 H2O CO2

P-71-1 40.07 0.28 36.06 5.35 0.53 1.03 0.45 0.05 0.117 0.86 0.05 0.09 1.12 0.05

P-71-2 44.01 1.00 34.89 4.85 0.27 0.91 0.38 0.41 0.043 3.09 0.13 0.04 1.13 0.05

P-71-3 32.66 0.12 39.73 6.72 0.72 1.29 0.51 0.05 0.237 0.21 0.05 0.11 0.89 0.06

These analyses of channel samples indicate the presence of Al-laterites. The higher content of alumina and a low content of silica in previous research work was probably due to the selected material. A detailed exploration of Monte Mauzo, may disclose small reserves of bauxite, say in the order of 150-200,000 t with Al content 43-50% with silica modulus 2-3, but hardly an economic deposit. S of Monte Mauzo are the Milange Mts. consisting of Serra de Tumbine (1,524 m) and Monte Tundo (1,274m). The Tumbine massif is composed in its central part, of nepheline syenites (aegirine-biotite), in NE-part of leucocratic syenites, on the margins of quartzitic syenites. The intrusion is surrounded by different gneisses. The top is flat over a small part only and therefore the development of a weathering profile is difficult to assess. Tumbine is a continuation and a small extension of the big massif Milange, which is situated mainly in Malawi with the well-known "planalto" of Lichineya with Al-laterite. The deposit was discovered in 1924 by Dixley and explored in 1939 confirming 60 million t of Al-laterite of this average composition: Al2O3 - 42.73%, SiO2 (quartz) - 15.65%, SiO2 (bound) - 2.22%, Fe2O3 -13.93%, TiO2 - 1,57% and loss of ignition 23.46%. This discovery was the main reason for starting exploration work at Tumbine. According to the first results only the content of alumina reached seldom 40%, with a high content of silica 20 - 40%. Samokhvalov (1981) and his group made several pits to a depth of 8 m and discovered that the lateritic profile is mainly kaolinitic. Gibbsite was developed just locally and usually below 20%, maximum value 26%. These laterites are of no economic interest. Some analyses of laterite Tumbine (USSR, 1981) (in %):



Sample Al2O3 SiO2 Fe2O3 FeO TiO2 L.i. Gibbsite Kaolin

T-3 (0,46 m) 36.92 33.09 8.88 - 1.22 18.91 25.99 51.12

T-3 (4,00 m) 32.87 41.68 1.67 - 0.56 16.07 23.17 45.55

T-17 (1,10 m) 39.49 39.26 4.86 - 0.89 15.60 10.26 84.27

T-17 (3,10 m) 35.10 46.96 4.41 - 0.48 12.48 18.05 59.90

P-2 (0,10-2,00 m) 37.10 33.40 8.90 0.29 - 20.60 - -

P-2 (0,10-2,00 m) 37.38 33.68 8.80 0.63 1.95 16.42 13.69 72.00

P-4 (0,50-3,00 m) 30.80 33.70 9.20 0.65 - 16.10 - -

A complete analysis (USSR, 1981) Tumbine (in %):

Sample SiO2

quartz SiO2

boundAl2O3 Fe2O3 FeO TiO2 CaO MgO

P-3 (1,5-3,2 m) 45.45 0.32 27.47 7.19 1.17 0.82 0.58 0.32

P-3 (3,25 m) 52.00 0.44 21.53 6.77 2.06 1.01 0.67 0.64 Sample P2O5 K2O Na2O SO3 L.i. H2O CO2

P-3 (1,5-3,2 m) 0.149 5.13 1.62 0.05 9.70 0.69 0.05

P-3 (3,25 m) 0.167 6.38 3.39 0.03 5.37 0.45 0.17

The results of these analyses suggest a laterite-kaolin composition. The upper part of the profile with gibbsite and a hardpan-ferruginous crust had probably been removed by erosion. In other nepheline syenites areas two localities only were checked: Monte Derre in Serra Chiperone and Serra Morrumbala in the S near the river Zambezi. In both cases, only kaolinitic profiles with laterites were found. The following analyses (Afonso-Pinto, 1967) show this composition (in %):

Sample L.i. Al2O3 SiO2 Fe2O3 TiO2 Gibbsite etc.

Monte Derre 107/SP (1,0 m) 14.54 35.34 33.56 11.03 0.97 10.55

Monte Derre 104/SP (4,5 m) 13.74 35.03 30.23 7.81 0.56 16.43

Serra Morrumbala R1/RA (1,0 m) 10.50 18.45 22.50 5.40 0.65 -

136SP (3,0 m) 11.08 27.63 30.03 7.50 0.40 3.21

It can generally be said about the bauxite occurrence on nepheline syenites in the Tete and Zambezia provinces, that just the Mauzo hill could yield some bauxite with an Al2O3 content over 40%, an elevated silica content and iron between 4-8%. The large group of nepheline syenites in this area can be utilized in ceramics and in a production of alumina. This problem is discussed in Chapter 4.11. The following description is dealing with an exploration of lateritic profiles and presented here, because little is known of these residual deposits; widespread in tropical countries. An example of lateritic profile development in the Province Zambezia is an area SE of Milange, with parent rocks of migmatites at the level of 660-700 m (Samokhvalov, 1981)-area of Macassania. The weathering profile, common to many other areas of Mozambique, is composed basically of kaolin, oxides and hydroxides of iron, quartz and little gibbsite developed just within the horizon of pisolithic argillite. Interesting is an icreased content of P2O5 (0.28-1.206 %).



Profile established (elements in average %):

Horizon Thickness

m SiO2 Al2O3 Fe2O3 FeO TiO2 L.i.

humus soil 0.3 - - - - - -

agrillite pisolithic cemented 1.4 29.76 21.66 25.60 0.73 3.79 14.77

agrillite reddish with pisoliths 1.2 31.53 20.16 21.90 1.29 2.10 14.90

agrillite reddish with sand 1.0 42.08 25.15 14.3 0.42 2.32 13.58

agrillite dark red 1.4 33.11 22.06 18.39 1.14 1.96 13.31

buff argillite massive 1.1 42.41 20.67 13.86 0.92 1.92 12.22

argillite bedded 1.7 32.26 21.91 20.23 1.57 0.87 13.77

In the past, during an investigation of soil profiles at Gurue, two samples of a clay component were analyzed. They contained: Al2O3 37.92% and 38.87%, SiO2 15.42% and 17.89%. A mineralogical analysis disclosed 38% and 38.5% of gibbsite respectively in these samples. Samokhvalov (1981) examined the weathering profiles over amphibole and biotite gneisses in several trenches in an area 5-12 km WNW of the town of Gurue. The altitude of the area ranges between 670 and 750 m. General profile (average chemical composition in %):

Horizon Thickness

m SiO2 Al2O3 Fe2O3 TiO2 L.i.

humus soil 0.75 - - - - -

argillite pisolithic 1.1 39.18 22.57 17.84 2.87 15.77

argillite reddish sandy 4.4 38.80 35.24 15.04 2.15 13.34

argillite reddish 1.9 38.57 25.45 13.51 3.14 15.89

argillite kaolinitic 3.0 37.90 25.61 14.98 2.09 14.61

argillite kaolinitic bedded 2.7 45.46 20.92 14.61 1.94 13.61

Some samples were washed to remove big grains of quartz, an improvement of Al2O3 content was about 2%. The clay consisted mainly of kaolin with oxides and hydroxides of iron, with a small amout of dispersed gibbsite which cannot be concentrated. In two cases only, the content of gibbsite attained 7-24%. In the Province Nampula, two areas were examined: in the vicinity of Nacala and Angoche, both in the coastal strip. Near Nampula and close to Mossuril, a belt of basalts of Cretaceous - Jurassic age was found and on it a thick alteration cover. The basalts were amygdaloid and porphyric, with up to 20% of opal, chalcedony and quartz. The lateritic zone was more than 10 m thick and consisted, in 70-75% of laterite and ferruginous and kaolinitic material. Iron compounds attained 19-23%, gibbsite was not detected. Only in two cases, layers of allites were found with Al2O3 27.94 and 33.10%, SiO2 16.22 and 24.80%; gibbsite accouned for 18.0 and 21.7%, respectively. General profile (with average chemical composition) (in %):

Horizon Thickness


humus soil 0.4 - - - - - -

argillite sandy with pisoliths 2.7 33.66 24.10 14.70 0.93 1.39 17.18



argillite reddish pisolithic 6.5 36.70 25.79 16.36 0.51 1.15 17.13

argillite kaolinitic 0.95 38.38 19.42 14.06 0.53 1.18 19.78

argillite kaolinitic bedded 1.2 37.65 21.11 13.18 - 1.04 18.72

Also near the village of Boila, 4.5 km NW of Port Angoche, the weathered crust above Cretaceous-Jurassic basalts was examined (Samokhvalov, 1981). The elevation was similar to that at Nacala (30-40 m above s. l.) with groundwater near the surface. At sites of outcropping basalts, a hard crust, 0.5-1.0 m in thickness, with dominant iron pisoliths was developed. In places, where the basalts were covered with Quaternary sediments, the alteration zone is thicker. An example of weathered profile near Angoche:

Horizon Thickness


soil humus 0.5 - - - - - -

sand clayey 5.6 - - - - - -

argillite pisolithic 5.0 36.21 22.7 22.48 0.36 0.90 14.92

argillite kaolinitic 3.2 44.70 16.27 21.30 - 1.44 12.55

argillite kaolinitic bedded 1.5 41.89 24.24 13.81 1.22 1.16 15.50

Here and in other localities kaolinitic-ferruginous lateritic clays only were encountered with kaolin content of 47-64%, iron 27.6-32.5%, silica 3.2-20.3% and gibbsite 1.7%. The superficial cemented crust was composed of oxides and hydroxides of iron (50-58%) and kaolin (26-35%). The composition of argillites with pisoliths was kaolinic-ferric with fragments of not fully dissintegrated rocks. No bauxites were found. In the Province Niassa, two genetically different weathering profiles were studied by Samokhvalov (1981): a) a fossil horizon at the base of Karroo Formation b) recent and subrecent profiles on Precambrian rocks in altitudes between 1100 and 1300 m.

a) In borehole no. 9., in the area Lufutize, basal sediments of the Karroo basin consisted of gabbroic rocks strongly altered in a kaolinic mass; the upper part of the weathered horizon was rich in apatite (10%) and ilmenite-magnetite (20%). Overlying were conglomerates and ateurites of red colour of K-3 horizon. On some outcrops near the river Matonda, crystalline rocks had been deeply weathered in pre-Karroo times, partly transported and mixed with basal Karroo sediments in a transitional zone. b) Lateritic cover of crystalline rocks in the surroundings of Lichinga (70-100 km around), about 1 to 6 m thick, of a lateritic-ferruginous composition with quartz grains. In some places, a lateritic crust with abundant pisoliths was encountered, with underlying sediments of argillitic-pisolithic composition: SiO2 48.6, 57.6%; Al2O3 22.5, 25.3%; Fe2O3 11.0, 11.4%. The presence of bauxites was not detected.

Conclusions: As in many African countries of tropical zone, widespread weathering crusts are developed over the biggest part of the region. A reddish lateritic, mostly kaolinic and partly ferruginous horizon is developed. The content of gibbsite in these lateritic horizons attains even 38%, as in the area of Gurue, but is much lower in other areas of the coastal plain (30 m above s. l.) up to an elevation of over 1,000 m (1.7% at Angoche, 24% at Gurue, 20% at Milange). In some of these lateritic horizons, the content of some trace elements such gallium, yttrium, zirconium and niobium is of interest. Bauxite with content of more than 60% Al2O3, about 2% of Fe2O3 and 3% SiO2 of refractory and chemical grade has been mined near Manica since 1938 and exported by the Zimbabwean company E. C. Meikles Ltd. The annual amount of ore extracted is small, ranging between 2,000 and 3,000 t in the last years. Reserves are small and not fit for big operations. The deposit is accessible from the Zimbabwean side only. Another very small source (about 200kt of reserves) was found on Monte Mauzo, this time on the Malawian borders.



Both deposits developed by an alteration of nepheline syenites at an altitude of about 1,400 m on flat surface, as erosional remnants. Several other sites with nepheline syenite in Mozambique do not contain bauxite despite favourable geological and geomorphological conditions such as at Serra Morrumbala. A refractory-grade bauxite from Manica should be used in the production of refractory bricks for the Mozambican industry. Present exploration programme in the surroundings of Manica revealed promising reserves of 3 to 5 million tons of bauxite ore.



Cilek: 4.10. Mineral pigments

4.10. Mineral pigments Mineral pigments or inorganic pigments are used in paints according the their covering power, suitable colour, sorbing capacity for oil, neutral pH and opacity. The chemical composition is of minor importance. These pigments are used in plaster, cement, mortar, rubber, plastics, in foodstuff, "old" cosmetics, ceramics and glass, floor and wall tiles, linoleum etc. Bateman (1951) divides pigments into three classes: * natural mineral pigments * pigments made by burning or subliming natural pigments * manufactured paints. Natural pigments contain usually iron as the main colouring agent in minerals of limonite, hematite, magnetite with admixture of clay and rarely manganese minerals. These minerals form natural ochres, umbers and siennas of yellow, brown and red colours and have been used by primeval man in decorations and drawnings (rock paintings common to E-Africa). They have been employed in many industrial branches and at home both in the past and the present. Mineral red is composed of hematite which underwent residual weathering. Other iron -bearing minerals produced similar reds. The content of Fe2O3 ranges between 60 and almost 90%, whereby the purest paints are almost pure red hematites. Ochres and bolus (smectite clay with limonite) are neutral in character and widely accepted as a component part of wall paints, in a number of plastic products, oil paints etc. They are mixtures of hematite, limonite and clay of yellow to brown colours. They require fineness (remnants on sieve mesh size 0.09 mm maximally 0.5-2.0%) Fe2O3 in a dry state around 16% to 40% (exceptionally up to 80%), clear colour, consumption of oil 60% etc. Roasted ochres give a reddish brown colour. Manganese oxide (11-25%) in ochre gives a typical brown colour and is known as umber; less manganese oxide and more limonite is known as sienna. Green-coloured materials originate in nature in rocks rich in chlorite, greenstones and glauconite. Ground shales are responsible for the particular colour of the original material - red, black, grey etc. Whites are obtained from kaolin, baryte, talc, white clay and other rocks and minerals. Malachite gives a green colour, azurite a blue, pyrolusite a black colour, etc. Different paints can be produced even from carbon materials - for example oxyhumolites, weathered coals from the outcrops, are used in the production of brown or grey pigments. Manufactured pigments are prepared by roasting ochres using iron ore, copper ore and other compounds of lead, zinc, barium, chromium etc. Various combinations of colour are prepared by mixing different materials. In Mozambique, mineral pigments have been used since the stone age. In the Manica Province, for example at Serra Vumba, very nice rock paintings made of reddish and brown ochres were discovered. In the Nampula-Nacala area, graphite was used (Nupes, 1952) several centuries ago for ornamental paintings of pots known in the region as "muapas". In the area of nepheline syenite massifs (Martins, 1940), the weathered clay cover of a reddish colour-in fact reddish kaolin, was used as paint by the local people.


Cilek: 4.10. Mineral pigments

White paint for ornamental purposes has been used in many villages where limestone was burned in furnaces to produce lime. White skin paint based on kaolin is used by the women of N-coastal Mozambique. There existed certainly in the past many other paints and pigments in different regions of Mozambique. And mineral raw material could have provided a number of mineral pigments both in the past and again at present. Here are several suggestions: Red and brown ochres - in all localities of residual weathering on banded ironstones, iron deposits with hematite and magnetite, on ultrabasic rocks (Tete, Manica, Barue, Niassa) Whites - on kaolin profiles, on bauxite profiles (Manica, Nampula, Cabo Delgado) Pink and red - on weathered kaolin profiles, on lateritic soils and laterites on weathered syenites and anorthosites, on rhyolites and basalts Grey and black - graphites of Angonia, Monapo, Nacala and Lurio, weathered coal outcrops in Karroo in Tete Province and Niassa Province Green - copper mineralization, greenstones of the Archean and Precambrian, glauconite of the Cretaceous Greenish-white - talc of the Manica, Tete and Nampula Provinces Carbon-black - natural gas soot from gas deposits at Buzi, Pande, Temane

Conclusions: No natural pigments are industrially used in Mozambique and therefore, recommendations have been made only for future research on these generally cheap materials. These materials will come into the industrial stream as soon as the country starts to develop industrial minerals and rocks and to economize on imported raw materials. A utilization of these very different materials with low tonnage consumption is a case for small-scale mining enterprises.



Cilek: 4.11. Nepheline syenite

4.11. Nepheline syenite Nepheline syenite is a new modern rock introduced by the U. S. A. and Canada after World War 2 which competes with feldspar and aplite as a source of alumina and alkalies in the production of glass, ceramics, the production of alumina, cement and caustic soda, potassium sulphate, as filler and in the production of chemicals. Nepheline syenite is a silica-deficient, crystalline rock resembling granite in appearance but of a different composition. It consists essentially of feldspar (both albite and microcline), nepheline and varying amounts of mafic and accesory minerals. Nepheline Na3 K (Al4Si4O16) is usually massive or occurs as embedded grains in syenites, phonolites, some basalts and pegmatites. The nepheline content of nepheline syenites is over 20%, no quartz is present and apart from a few % of accessory minerals, the remaining rock is made up of feldspars. The few producers of nepheline syenite in the world are these: in Europe Norway with a deposit on Stjernoy Island, USSR with deposits of apatite on the Kola Peninsula and in America at Blue Mountain in Canada, and the Canaan deposit in Brazil. The production from Stjernoy deposit is a good example of a utilization of the ore in glass, ceramic and filler industries, that of Kola an example of a successful complex utilization of this rock for alumina, alkalies and cement products. The Stjernoy deposit started production in 1961 (Bull-Miksch, 1985). The crude ore contains: 56% of perthite, 34% of nepheline and other minerals such as magnetite, biotite, amphibole, pyroxene, calcite and sphene. Two types of nepheline syenite facies have been identified -a biotite and a hornblende-pyroxene type. The latter is the main commercial source. The deposit in Caledonian crystalline rocks is part of a ring structure with gabbros and carbonatites, lens-shaped about 2 km long and 250 m wide. The ore is crushed, screened, dressed in low- and high- intensity magnetic separators and air classifiers. Three commercial grades are produced: * glass grade * amber grade * ceramic grade of this chemical composition (in %):

Oxide Glass grade Amber grade Ceramic grade

SiO2 57 56.5 57

Al2O3 23.8 22.5 23.8

Fe2O3 0.10 0.4 0.12

Na2O 7.9 7.5 7.8

K2O 9.0 8.2 9.1

CaO 1.3 2.5 1.1

L. i. 1.2 no mention 1.1

Nepheline syenite is valuable mainly for its high alkali and alumina content, high fluxing power of nepheline and perthite and a common hardness and whiteness. The glass industry uses nepheline syenite in the production of glass containers, sheet glass, float glass and fibreglass. The iron content required has to be low and the ratio Fe2O3 : Al2O3 should be 0.0004. The ratio alkalies/silica i. e. Na2O + K2O : SiO2 should be 1 : 3 - 4. Nepheline with the ratio Na2O : SiO2 = 1 : 2 has a high alkaline content when compared, for example, with albite (1 : 6). This means that in flint glass production the melting time is 11 minutes for nepheline and 103 minutes for albite, which is self-explanatory. Glass, which is a mixture of silica (sand), soda ash and limestone mainly, has to be complemented with alumina, which induces high strength and prevents devitrification. The nepheline syenite replaces alumina and part of the expensive soda ash.



The foam and fibreglass production, the popularity of which is rapidly increasing, welcomes the amber grade as a cheap raw material (0.4% of Fe2O3 is acceptable). In the ceramic industry for which the chemical components and fluxing agents of nepheline syenite (i.e., reactivity in the mass, rheology and whiteness after firing) are decisive is used in a production of hotel china, sanitary ware, enamel, electrical and dental appliances. It is used less frequently as a filler and extender for its durability, acid-resistance and low vehicle absorption. Demands for nepheline syenite are expected to increase in the future because the glass industry will be introducing new types of glass containers. Nepheline syenite of the Kola Peninsula is a raw material for the production of alumina, sodium and potassium chemicals and the waste, red mud, is part of the cement clinker. The deposit is, in fact, a source of apatite developed in two zones, the upper one containing 65% apatite, 20% nepheline and 10% aegirine-amphibole, the lower zone with 30% nepheline and 45% apatite. 150 t of nepheline concentrate produces 40 t of alumina and another 30 t of potash and soda. Apart from rare earths, also gallium and rubidium were recovered. Average composition of Kola nepheline syenite for alumina production: 27-29% Al2O3, maximum 17.5% of alkalies, 40-44% SiO2, 1.3-7.5% CaO, 0.4-1.2% Mg, Na2O 11.3-12.8% and iron oxides are almost absent. Moduluses are used in an evaluation of the reserves of syenites:

Alkaline Calcic Silica Alumina

Na2O + K2O CaO SiO2 Al2O3

___________ _____ ______ _________________

Al2O3 Al2O3 Al2O3 Fe2O3 + FeO + MgO

Other ratios like between Na2O and K2O are also important. Exact specifications do not exist, each deposit is evaluated under special specifications. Canadian nepheline syenite (Harben-Bates, 1984) is composed essentially of 20-25% nepheline, 48-54% albite and 18-23% microcline. The accessory minerals totalling 6% include 0.2-0.6% magnetite, 0-4% biotite, 0-3% hastingsite and 0-2% muscovite and aegirine. The Brazilian nepheline syenite is composed of 55% microcline and microcline-perthite, 20% nepheline and 15% albite. In Mozambique, nepheline syenites are concentrated mainly along the East African rift valley, at the border with S-Malawi. These massifs intrude into a Precambrian basement and their age is 116 -138 m.y., i.e. Upper Jurassic-Lower Cretaceous. This determination of age was made for the Chilwa alkaline province in Malawi (Afonso-Pinto, 1967), no data are available for the Mozambican side. Apart from the Chilwa alkaline province (Fig. 4.11.1) syenite was found in many parts of Mozambique: syenites-gabbros without nepheline syenites in the SW part of the Lurio belt, in the Niassa Province, ring structures in the northern continuation of the Lake Chirua graben, Monte Tchonde near Meponda on the bank of Lake Niassa, massifs of Mecula and Lugenda, nepheline gneisses within the ring structures of Monapo and Mocuba, and others. All these sites are situated around or at a certain distance from the rift structures and deliminate in fact these tectonic features.

Fig. 4.11.1. Schematic map of Southern Malawi-Chilva Alkaline Province (Cilek, 1987) (493 kB) The best known sites of syenite and nepheline syenite occurrence in Mozambique are in the Chilwa alkaline province, and represent there the biggest accumulation of these rocks. On the Malawian side, syenitic intrusions are accompanied by carbonatites, which are dominant in many areas. All these intrusions are in close connection with deep-seated fractures of different sections of the East African rift: in the S, the Urema graben, Shire graben and in the N Niassa-Rukwa rift. The genesis of syenite massifs (carbonatites are clearly of explosive origin) is explained by a magma stopping. The massifs are epizonal and many are of a



typical oval shape with sharp boundaries, some are quasi concordant and follow the foliation planes of Precambrian rocks, but all are epizonal stocks and developed as follows (Afonso-Pinto, 1967): a) phase of collapse - destabilization of the magmatic chamber and origin of fractures b) phase of passive magma ascent - the cover of the chamber is fragmented and blocks fall into the magma from surrounding rocks and are melted and absorbed c) phase of consolidation - the upper part of the magma solidifies and its subsidence starts with the development of fractures, ring-dykes and cone-sheets. Generally, the initial phase is triggered by an explosive phase which causes the first magma movement known as "updoming". Erosion will uncover the massif, remove the cone-sheets and flatten the intrusive rocks to a certain geomorphological level here probably to the Pan-African land surface (Tertiary age).

Syenite massifs of Mozambique (from S to N) on the eastern margin of the Rift Valley)-

Monte Mauzo

Serra Tumbine

Serra Chiperone (Conguene, Derre, Pandibue, Muembili)

Serra Morrumbala

Western margin of the Rift Valley:

Salambidua

Cheneca (see fig. 4.11.1)

On the Mozambican side Monte Mauzo is composed of nepheline syenites with aegirine, on the Malawian side, the central part consists of carbonatites feldspathic breccia and agglomerates and syenites. Mauzo (and Tumbine in the S) are of a typical oval shape, in SE-NW direction. According to Afonso-Pinto (1967) this hill is composed of nepheline syenite with foids with a fenitization ring around the syenite, with dykes and intrusions of microgranites and phonolites. Residual deposits of bauxite and Al-laterite are described in Chapter "Bauxites" Chemical analyses: 1. Nepheline syenite-Mozambique (Real, 1965) 2. Foiate with aegirine-augite, Malawi (Dixey, 1955) 3. Phonolite from the Malawian side (Dixey, 1955), which may also serve as glass or ceramic material.

% 1 2 3

SiO2 55.28 54.37 56.83

TiO2 0.69 0.77 0.12

Al2O3 20.77 23.22 20.78

Fe2O3 2.22 1.62 3.57

FeO 1.45 1.32 0.41

MnO 0.11 0.07 0.40

MgO 0.29 0.57 0.02



CaO 3.78 1.60 0.65

Na2O 7.69 8.25 10.73

K2O 7.38 7.35 4.72

P2O5 0.20 0.08 0.001

H2O+ 0.33 0.50 0.32

H2O- 0.25 0.20 0.07

SUM 100.44 99.92 98.621

Another additional analysis: ZrO2 - 0.50%, BaO - 0.01% and SrO - 0.07%. The phonolite contains orthoclase and sodium pyroxene. Nepheline syenite is typical and can be compared with that of Chiperone. Serra Tumbine is almost circular measuring 8 km in diameter. It is a typical intrusion in gneisses and granites of a basement of alkaline syenite and syenite sub-alkaline with dykes of microsyenites and trachyte. Residual deposits of Al-laterites and kaolin are restricted. Alkaline syenites are predominant, they are microperthitic with biotite, amphibole and sphene. Quartz in small quantities was found in the border zone of syenites. Subalkaline syenites are greenish, medium-grained rocks with mirmequilite, perthitic orthoclase, some quartz and apatite. Mafic minerals are represented by aegirine-augite, biotite, sodium amphibole and nuclei of pyroxene. The rocks could be classified as subalkaline syenite, biotitic and amphibolitic, with apatite. Two analyses were: 1. Syenite microperthitic with augite, riebeckite and aegirine-augite (Coelho, 1959) 2. Syenite microperthitic with augite, acnite and riebeckite (Coelho, 1959)

% 1 2 % 1 2

SiO2 60.18 61.18 CaO 2.00 1.34

TiO2 0.68 0.88 Na2O 8.75 6.77

Al2O3 18.50 17.80 K2O 5.99 6.33

Fe2O3 1.18 1.01 P2O5 0.20 0.09

FeO 1.84 2.44 H2O+ 0.23 0.11

MnO 0.03 0.10 H2O- 0.42 0.51

MgO 0.30 1.19

Total 100.30 99.75

Serra Chiperone s.s. is composed of nepheline syenite with some pegmatites of nepheline syenite and some younger dolerite dykes. An oval intrusion penetrates the basement rocks of gneisses, migmatites and granulites. The massif extends in NW-SE direction for 12 km with an elevation of 2,065 m. Serra Chiperone is part of the mountain range, which includes also the morphologically separated hills Derre, Pandilue, Muembili and Congene (Conguene) in SE direction, and the hills Missouge, Missecue, Langoma and Mongoe in W direction. Analyses of syenite microperthitic, nephelinic with biotite (Coelho, 1959): %



SiO2 53.76 54.44 CaO 1.85 1.26

TiO2 0.47 0.33 Na2O 8.29 7.59

Al2O3 23.93 22.05 K2O 6.74 6.92

Fe2O3 2.10 2.91 P2O5 tr. 0.04

FeO 1.91 2.82 H2O+ 0.46 0.33

MnO 0.03 0.10 H2O- 0.26 0.27

MgO - 0.14

Total 99.80 100.15

Nepheline syenites of Serra Chiperone are chemically similar to those of Mauzo and Tumbine. The mountains Derre, Pandibue and Muembili are massifs of nepheline syenite, elongated in NE direction, with axes 9.5 and 5.7 km long and 1.3 and 2.4 km wide. The basement consists of gneisses and migmatites, which underwent a fenitization around the contact zones. The main rock, i. e., nepheline syenite, is medium - to coarse - grained composed of abundant microperthite, microcline, albite, nepheline (some crystals are on margins altered to calcite and cancrinite), very rare quartz, biotite, epidote, magnetite, sphene and alanite. It can be classified as syenite microperthitic nephelinic with biotite. Monte Conguene is the only locality, explored recently by a Russian team as a possible source of alumina (see Barmine-Tveriankine, 1982 and technological research by VAMI - Leningrad, 1981). All data presented here are excerptions of these reports and of a report by Afonso-Pinto, 1967. The massif is composed of two hills, Conguene and Chissindo, covering an area of 14 km2, in elongated oval shape in NE direction. Similar to other syenite massifs, it is a typical intrusion into Precambrian schists and gneisses, of Cretaceous age. The main part consists of nepheline syenite of the miaskite series, which is a potential source of alumina and a subsequent metal production. From the N to the NE and the NW, nepheline syenite borders a belt of alkaline biotite - feldspar syenite which extends in a belt of 200 to 1000 m in width. Nepheline syenites are of leucocratic and mesocratic medium-grained varieties and have a gneiss-like texture. They contain: 55 - 75 % microcline-perthite 15 - 20 % nepheline accessory minerals: biotite, magnetite, ilmenite, titanite, zircon, pyrochlore Non-nepheline syenite occurs in the biotite-hornblende and the biotite-pyroxene-hornblende varieties: there are also hybridic rocks with amphibole-feldspars, with quartz up to 5% presenting another variety of quartzitic syenites. Over 102 samples were collected and analysed. Results of sample analyses:

Content: SiO2 Al2O3 CaO Na2O K2O R2O Fe total R2O/ Al2O3 CaO/ SiO2 SiO2/ Al2O3

minimum 50.08 18.12 0.01 4.65 3.85 8.27 2.21 0.60 0.0001 3.38

maximum 61.50 25.33 2.72 10.80 7.26 14.83 9.69 1.08 0.0555 5.79

average 55.63 22.03 0.73 8.22 5.88 12.08 4.29 0.90 0.0149 4.30

From these 162 samples, 101 samples were selected covering the area of suitable rock for reserves calculation. The results of analyses of 101 samples are as



follows:

Content SiO2 TiO2 Al2O3 Fe2O3 FeO MnO2 MgO CaO Na2O K2O P2O5 R2O Fe2O3

minimum 51.0 0.01 19.51 0.97 0.01 0.01 0.01 3.26 3.13 0.01 0.33 5.32 1.81

maximum 59.3 0.77 27.0 4.45 2.63 0.19 1.18 2.72 10.8 7.26 5.32 14.48 5.96

average 52.23 0.27 22.57 2.57 1.26 0.09 0.15 0.70 8.31 5.99 0.08 12.26 3.97

The moduluses are: R2O/Al2O3 CaO/SiO2 SiO2/Al2O3

0.36 0.0001 3.45

1.08 0.0555 5.16

average 0.90 0.0137 4.16

Two bulk samples were collected for technological tests, using the soviet method for producing alumina, sodium and potassium carbonates and high grade portland cement together with recovery of gallium and rubidium. It was clear from the very beginning that the Mozambican samples (B-1 Conguene, B-2 Chissindo) are different from soviet Kola material in that they have a lower Al content (22%) and a higher Si content (57%). Average chemical composition (in %):

1 (Sample B-1) 2 1 (Sample B-2) 2

Al2O3 25.3 21.9 22.3 22.0

Na2O 7.95 8.4 10.5 9.3

K2O 4.64 5.64 3.75 4.7

CaO 0.35 0.7 2.1 0.8

SiO2 56.9 57.0 54.8 56.6

Fe2O3 1.40 1.9 4.85 1.2

FeO 0.30 1.6 3.57 2.2

MgO 0.08 0.17 0.1 0.15

TiO2 - 0.12 0.24 0.25

MnO 0.05 0.09 0.13 0.13

P2O5 0.05 0.02 0.1 0.07

H2O 0.28 - 0.39 -



L.i. 1.82 0.53 - 0.92

Samples "2" are controlled analyses performed by VAMI. Fluctuation of the major components was considerable: Al2O3 19.2-25.8%, Na2O 8.0-15.3%, K2O 2.5-5.0%, Fe2O3 2.7-6.6%, FeO 1.9-5.0%. In a selected area measuring 1.6 km2, nepheline syenite has a alumina content of 23.6-27.0%, alumina modulus 5.9-6.0, alkaline modulus 0.91 and Na2O/K2O ratio 1.5-1.9. Quantitative mineralogical composition:

B-1 B-2 B-1 B-2

nepheline 18.9 18.0

natrolite - 1.6 orthoclase (microcline) 28.2 26.9

analcite 1.6 - plagioclase 42.5 40.1

liebernite 1.2 2.2 biotite 5.9 8.3

cancrinite - 1.1 apatite - 0.2

sodalite - 0.5 sphene - 0.1

calcite 0.2 0.4 zircon 0.1 -

feldspars total 70.7 67.0 titano-magnetite 1.4 0.6

total 100.0 100.0

Distribution of main chemical components in minerals (% of total content):

MineralsB-1 B-2

Al2O3 Na2O K2O SiO2 Al2O3 Na2O K2O SiO2

nepheline 30.2 40.4 15.0 13.7 28.2 36.7 14.0 13.0

nepheline alteration 3.7 2.2 1.7 2.3 7.9 6.7 4.0 4.2

feldspars 62.3 57.4 75.0 80.5 58.3 56.0 72.0 77.7

mafic and opaque minerals 3.8 - 8.3 3.5 5.6 0.6 10.0 5.1

total 100 100 100 100 100 100 100 100

The main minerals of nepheline syenite are feldspars (microcline, orthoclase, microcline-perthite) of the soda-potash variety and calcium-soda feldspars (placioclase-albite); in sample B-1 28.2 and 42.5%, in sample B-2 26.9 and 40.1%. The quantity of nepheline is below 20%. A favourable feature of Mozambican ore is its high alkaline ratio (0.91-0.93) and its high CaO content which ensure a high yield of potash; a negative feature is its lower alumina content (22%) and its higher silica content (57%) when compared with Kola ore. Generally, this nepheline syenite belongs to the high-alumina type, of miaskites of the Na-K branch. According to VAMI-Leningrad, the specification grade is



to category III and, therefore, it is suitable for a production of alumina sodium and potassium compounds and portland cement. The reserves estimated from the samples are 1,200 000 t (specific gravity 2.5 t/m3), prognostic reserves of the whole nepheline syenite body 290 million t. As a result of alkali metasomatosis and albitization, higher amounts of Nb2O5 with content 0.1%, Ta2O5, Rb20 (100-400 g and 300 g/t respectivelly) have developed with possible reserves. Serra Morrumballa is a huge intrusive massif N of the river Zambezi (see Fig. 4. 11. 2), of irregular oval shape, N-S direction, 15 km in length and about 5 km in width. The structure of the massif is fairly complicated and different from other syenite massifs.

Fig. 4.11.2. Geological map of Serra Morrumbala syenite massif (Geol. Inst. Beograd, 1981) (403 kB) It is a plutonic body intruded in Precambrian gneisses composed of syenites, granites, granulosyenites and rhyolitic lavas and breccias. Alkali granites occupy the NE part, alkali syenites the S part. Several veins of syenitic and granitic composition cut through the massif. They are alkali syenite porphyry, nepheline syenite porphyry, trachyte and solvsbergite, of alkali province. Alkali granite is pink, medium - to coarse - grained, with alkali amphibole (10%), orthoclase-perthite (60%) and quartz (20-30%). Alkali syenite with quartz (3-10%) contains about 10% of mafic minerals and orthoclase-perthite. Alkali syenites of Morrumbala are composed of microperthite and orthoclase, aegirine, augite, sodium amphibole, biotite, sphene and zircon. Syenite alkali: microperthitic with pyroxene, amphibole and rare riebeckite (Coelho 1959):

1 2 1 2

SiO2 57.68 52.04 MgO 1.03 0.75

TiO2 1.03 0.53 CaO 3.61 1.19

Al2O3 18.08 21.07 Na2O 7.22 11.82

Fe2O3 1.48 3.72 P2O5 0.49 0.24

FeO 3.80 1.90 H2O+ 0.19 0.09

MnO 0.07 0.12 H2O- 0.30 0.87

In general, its chemical composition is similar to that of other massifs of the Chilwa Alkaline province, but at Morrumbala the structure of the massif is more complex with migrating centres or different plutonic rocks and a different degree of magma contamination. From an economic point of view, just some vein rocks with a higher alkali content could be of interest, the alumina content is low, the silica content high. Alkaline massifs west of the Rift Valley The W- part of the massif Salambidua is situated in Mozambique. It is composed of hornblende syenites without nepheline; the central part on the Malawian side is made up of carbonatite. The massif is a circular plutonic intrusion (see Fig. 4.11.3). The chemical composition of microperthitic syenite with amphibole and pyroxene (Coelho 1956) is this (in %):

SiO2 58.96 MnO 0.11 P2O5 tr.

TiO2 0.62 MgO 0.83 H2O+ 0.23

Al2O3 17.27 CaO 3.08 H2O- 0.35

Fe2O3 1.93 Na2O 7.47



FeO 3.95 K2O 5.09

Fig. 4.11.3. Geological map of Monte Salambidwe syenite massif (Geol.Inst., Beograd, 1981) (426 kB)

The massif Cheneca, not explored into detail, consists of hornblende-syenites. Minor alkaline intrusions occur also at Monte Buzimuana (Chuare) located between the carbonatite ring structure of Muambe in the S and Salambidua in the N. From these radiate dykes of solvsbergite and other alkaline rocks. The largest Cretaceous intrusion of the whole region is the Serra de Gorongosa, which rises 2,000 m above the surrounding plain. The complex consists of a central core of micropegmatite granite which intruded an earlier gabbroic intrusion comprising tholeiitic gabbros with labradorite and clinopyroxene and some norite and olivine gabbros. These rocks are, naturally, out of use even as substitutes for nepheline syenites, but are of an identical alkaline province. Often, they are accompanied by a swarm of dykes extending from Gorongosa complex over 60 km (Hunting, 1984). Some of these alkaline complexes with phonolites, trachytes and affinite derivates may provide alkalies and alumina for the glass industry in order to substitute soda ash and add alumina to the batch. In many countries, phonolites, trachytes and rhyolites are used in a production of coloured container glass. An example is trachyte of Monte Nharuchonga which belongs to the Xiluvo carbonatite ring structure and lies W of Beira. Composition is this (in %): SiO2 - 50.66, Al2O3 - 17.20, Fe2O3 - 7.19, FeO - 1.60, CaO - 1.75, Na2O - 7.50, K2O - 6.03, P2O5 - 0.09, SO3 - 0.65 and L. i. 3.69%. In 1984, the Geological Institute of Beograd explored a complex of alkaline rocks in central Mozambique. They examined two groups of rocks: Alkaline rocks of the Lupata Series of the Lower Cretaceous, similar rocks to those of the Sena Formation, Mio-Pliocene age. The Lupata series is composed, at its base, by several different alkaline rocks, which form an extensive sickel-shaped outcrop in mid-Zambezi, at the Lupata rapids. Rocks of the Lupata Series are mostly trachytic, they include phonolites, analcite kenyites and blairmorites, with different agglomerates. The lavas are potash-enriched, undersaturated and of alkaline affinity. The age of the rocks spans over 130 to 100 million years (Hunting, 1984). Phonolites of the Lupata Series contain abundant nepheline, alkali-feldspar, clinopyroxene and are of a trachytoid and nephelinoid texture. Overlying unconformly Cretaceous sediments and volcanics the Sena Formation is composed mainly of pebbly calcareous muddy grit and several volcanic vents. The volcanic rocks of the Sena Formation are phonolites, trachytes with nepheline basalts, olivine basalts, augitites and limburgites. Analysis of phonolites samples from the Sena Formation by Geol. Inst. Beograd (1984):

Sample 1 2 3

SiO2 53.99 53.90 53.63

TiO2 0.25 0.17 0.17

Al2O3 19.37 22.52 21.67

Fe2O3 3.02 3.74 1.32

FeO 1.50 0.44 3.07

MnO 0.13 0.08 0.11

MgO 1.56 0.86 0.86

CaO 1.62 0.25 1.35

Na2O 7.20 10.20 10.40



K2O 5.64 4.80 5.32

P2O5 - - 0.02

H2O+ 5.46 3.77 1.77

H2O- 0.49 0.10 0.29

Total 100.23 100.83 99.98

Samples 1, 2 were obtained from a phonolite plug penetrating Precambrian rocks, sample 3 from a volcanic vent into the Sena Formation. Other alkaline rocks occurring in Mozambique are these: nepheline syenites, trachytes and phonolites - ready sources of raw materials needed in the glass and ceramic industry. Pegmatites of nepheline and other types of syenites may represent a source of corrundum, rare metals and earths and other minerals. Apparently, they are to be found along all rift valleys and grabens filled with Karroo and younger sequences or in deep faults and ring structures within the whole Mozambican belt.

Conclusions: There are such quantities of nepheline syenites in Mozambique that, if mined, they could easily surpass the world production of nepheline syenite for glass and ceramic industry. In addition they may represent a resource in a production of alumina, sodium and potassium compouds, rare earths and metals. Nepheline syenites are concentrated in the Chilwa alkaline province covering the East African rift valley in the form of several isolated epizonal plutonic massifs - intrusions mainly of Cretaceous age. Nepheline syenites may serve as a source of nepheline feldspars and, generally, may be a valuable flux -and alumina component of glass and part of ceramic mixtures in porcelain, sanitary ware etc. Although it has not been tested along these lines, several chemical and mineralogical analyses confirmed, that a production of commercial products depended on the dressing method of each petrological type of syenite in question. Technological tests made of nepheline syenite from Monte Conguene proved that it is suitable for alumina production. Reserves were estimated to 290 million t with 1,200 000 t of checked reserves. Considering other nepheline syenite massifs described in the text, estimated reserves suggest several thousands of million tons and are, in fact, inexhaustive.



Cilek: 4.12. Perlite

4.12. Perlite Perlite is a volcanic glass of a typical concentric globular "pearl-like" structure, commonly light grey and of rhyolitic or rhyolite-dacite composition. The "pearl-like" or onion-like structure with macro- and microscopic cracks is the result of shrinkage by cooling of volcanic glass. The commercial product, however, is glass, that at about 760-1,100°C will expand and form a lightweight frothy material. The expanding properties are caused by molecular water and loosely contained water (1-10%). During sintering water in the glass is converted to steam which cannot escape through the viscous walls of glass and thus glassy foam is produced. It is somewhat similar to natural pumice. The volume of the original glass increases 10 to 20 times and its density decreases from about 1.0 to 0.02. In nature, this process is repressed by the weight of overburden or by a quick cooling of the outer parts of lava flows, lava domes or at the contact with the water basin. The composition of expanded perlite is identical to that of the parent rock - about 70% SiO2, 12% Al2O3, 3% coloured oxides and up to 8% of alkalies. The water content varies from 1-10%. Apparently most perlite deposits originate by a hydration of obsidian (< 2% water), which contains magmatic water only. Therefore the presence of meteoric water from groundwater resources decides probably upon the expanding properties of perlite. In the U. S. A., some perlites contain rounded bodies of obsidian nuclei - drops of black glass known as Apache tears (Harben, Bates -1984), confirming the hydratation process in obsidian. Perlite displays significant physical properties - it is light, highly porous and stabile; its thermal and acoustic properties are utilized in lightweight concrete, in insulation in foundries for the transport of ingots, in the transport of liquified natural gas, as a filler in paints, plastics, for filtering water etc. Perlite is usually pretreated at the deposit site, it is crushed and sieved to the required grain size (0.3 to 1.5 mm), and transported to the place of consumption where it is expanded. Competitive material is pumice, which is stronger in concrete and naturally expanded, but it has to be transported in large volumes. Another competitive material is vermiculite with similar or even better properties. In nature, perlite is found in lava domes, lava flows, dikes and sills, in rhyolites, andesites and dacites layers originating from hydrothermal alteration. In the geological past, "old" perlites changed from a vitreous to a crystalline texture, whereby the devitrified or recrystallized material lost its expanding properties. The age of commercial perlites is rarely older than the Oligocene (Harben-Bates, 1984). The minimum-sized economic deposit should contain 100-300,000 t of ore. In Mozambique, perlite (see Fig. 4. 1. 1) was discovered by L. Mallac during the prospection of the Pequenos Lebombos Mts. in 1953-1960. The sites are located S of bentonite deposits and layers of obsidian and perlite in rhyolites are fairly slender. The two major deposits explored were: Muguene South and Muguene North. On Muguene South, proved reserves were 100,000 t, probable reserves 400,000 t, while on deposit Muguene North the reserves of vitrified rhyolite glass achieved 250,000 t of proved and 1 million t of probable reserves. Several other claims in the vicinity - Ali, Lona, Cris, Ursula were laid down. Before 1961 (Mallac, 1962) one furnace for perlite heating was errected there and small amounts of perlite were produced. However not every volcanic glass was suitable for a production of expanded perlite. A sample of perlite was sent to the South African Portland Cement Institute in Johannesburg and tests



were made with the following results: loose bulk density lb/cu. ft. 8.77 - USA perlite 6.84 consolidated bulk density lb/cu. ft. 12.03 -USA perlite 8.46 A low density is essential for the quality of perlite and perlite from Muguene has a bulk weight of aproximately 30% higher than the American sample. The grading analysis gave these results:

BS Sieve No. Muguene sample USA comp. sample

7 99.5 100

14 95.1 87

25 62.7 51.1

52 39.0 28.9

100 25.0 16.0

The Muguene sample has an excess of fine material, when compared with the American product. The material is acceptable for use as a concrete or plaster aggregate, but could be improved by reducing the amount -100 mesh material to about 15%. In 1978-79, the vicinity of Muguene was again explored and 28 boreholes were sunk. The overlying strata are rhyolites of brownish colour and a fluvial structure which are altered and partly bentonized. Below the rhyolite is a layer of bentonized rhyolite (thickness about 3 m) overlying dark grey obsidian (about 2 m thick). This is followed by a layer of greenish perlite, about 1 m thick. The lowest layer above the basalts is fine-grained grey aleurite, about 2 m thick. In places where the obsidian layer is thin, it is completely altered into bentonite (Kouzmine-Akimidze, 1981). Maximum thickness of obsidian in borehole 28 was 3.34 m. Chemical analysis (Laboratories ING):

SiO2 72.90 MgO 1.71

Al2O3 11.47 P2O5 0.025

Fe2O3 2.35 Na2O 5.95

CaO 0.56 K2O 4.55

Reserves were calculated for two sectors: sector A - average thickness of obsidian 1.45 m specific gravity 2.33-2.41 g/m3 reserves 32,370 t. sector B - average thickness of obsidian 2.12 m specific gravity 2.35 g/cm3 reserves 22,090 t. Acceptable are just the reserves of sector A with an overburden of rhyolite of a maximum thickness of 15 m. An interesting observation is an alteration in the texture of perlite, the material is devitrified and



rhyolitic glass is recrystallized; it is composed of a number of oolitic and spheric nuclei with grains of quartz. In 1982, the new exploration stage of the whole area of Pequenos and Grandes Lebombos made by Ivanicka-Sykora resulted in the discovery of a deposit of obsidian close to the town of Ressano Garcia. The deposit extends just N and S of the main road Maputo-South Africa, about 20 km E of Ressano Garcia (Fig. 4.12.1).

Fig. 4.12.1. Geological map of a part of the Lebombo Mts. (Compiled by Ivanicka, 1982) (563 kB) The volcanic complex of the "Grandes Lebombos" forms a 20 km wide chain, oriented from N to S. The rocks belong to the Jurasic Stormberg Series (Upper Karroo), and consist of rhyolites, basalts and doleritic dykes. In the study area, rhyolites are in tectonic contact with younger basalts. They contain intercalations of porphyrites, rhyodacites and volcanic breccias. The thickness of the complex is up to 500 m: volcanic glass is developed in its upper part. The deposit, studied at length, has a N-S trend extending over 600 m, with an average width of 60 m and a depth between 3.5 m and 25.0 m. Volcanic glass is of a rhyodacitic composition, it is dark greyish to black in colour, which changes locally into greenish brown and green. It is compact and strongly recrystallized, and has a perlite texture. This volcanic glass was transformed to bentonite along faulted contact faults. Basalts occupy the low-lying parts and are seldom seen in outcrops. The fresh rock has a dark grey colour and is finely grained. Dolerite sills are prominent in the landscape and are of a dark green, compact variety. Volcanic glass is part of a volcanic sequence composed of rhyolites, rhyodacites and tuffs, all of effusive origin. Part of the lava flow emerged from rhyolite copulas and a substantial cooling of their outher part occurred probably in water environment. The composition of glass corresponds to that of rhyodacite (Fig. 4.12.2).

Fig. 4.12.2. Cross section of volcanic glass occurences at Ressano Garcia (Ivanicka, 1982) (293 kB) Similarly to the Muguene deposit in Pequenos Lebombos, altered rhyolites and tuffs developed in the roof of the obsidian layer. The thickness of bentonized material is 2-3 m, its composition (in %) is this:

A minimum maximum

SiO2 54.86 60.64

Al2O3 14.42 15.11

Fe2O3 5.22 6.91

CaO 0.42 0.86

MgO 0.81 1.99

Na2O 0.92 1.47



K2O 0.98 3.04

TiO2 0.24 0.53

H2O- (105°C) 8.08 14.40

H2O+ (1,100°C) 3.32 6.37

The ion exchange is high: Na+ mval/100g 1.11- 2.72 K+ mval/100g 0.44- 1.52 Ca2+ mval/100g 12.50-30.00 Mg2+ mval/100g 33.71-41.91

The composition of volcanic glass is similar to that of the analyzed bentonitic material which proves that bentonites originated from an alteration of volcanic glass. Apparently the development was this: obsidian ===> hydratation ===> perlite ===> recrystallized and devitrified perlite ===> bentonite. Part of perlite may be absent. Chemical composition of volcanic glass:

mimimum % maximum % minimum % maximum %

SiO2 66.19 67.80 P2O5 0.03 0.06

Al2O3 13.73 14.89 MnO 0.05 0.09

Fe2O3 3.13 4.05 Na2O 2.81 3.85

CaO 0.27 0.34 K2O 2.08 3.32

MgO 0.28 0.36 SO3 0.11 0.41

FeO 0.55 2.90 H2O- (105°C) 1.76 2.62

TiO2 0.13 0.44 H2O+ (1,100°C) 3.17 4.08

The absorption coefficient of most of the samples is lower than 1%, specific weight between 2.38 and 2.75 g/cm3 (more commonly between 2.3 g and 2.45 g/cm3), porosity low, ranging from 0.1% to 2.5%. The Los Angeles test resulted mostly in value exceeding 35%, but below 80%. Compression tests were carried out just with 9 samples and values differed considerably. The minimum value was 335 kg/cm2, the maximum 1,197 kg/cm2. Estimated reserves:

Category C1 585,792 t

Category C2 322,388 t

Total 908,180 t

Overburden is negligible.



The Ressano Garcia deposit was chosen for its favourable location and expansion tests were made of representative samples after drilling. For each of these samples, the fractions 4.75-10.00 mm and 0.20-1.18 mm of crushed rock were heated from 1,000°C through 1,100°C to 1,200°C, but expansion characteristic were not observed at any of these temperatures. Fractions between 0.20-1.18 mm were tested in Czechoslovakia in an expansion oven but no expansion occured. The results indicated that the material could not be used as expanded perlite, although its chemical composition, i.e. a high concentration of H2O+ at 1,100 °C and it as an expandable type. However, it can be used in road construction or concrete production. This exploration of volcanic glass - a possible source of expanded perlite-serves as an example of an underestimation of the importance of technological testing of the investigated material before the start of the main exploration. The result is, that expensive exploration programme was the disclosure of a "deposit" of volcanic glass, which could possibly be utilized as ornamental stone or as a doubtful building material in an area, in which high-quality building stone is plentifull. Other perlite occurence may possibly be found within other areas of Karroo volcanics of Jurassic-Cretaceous age. Their commercial utilization will depend on the degree of subsequent alteration and devitrification.

Conclusions: Perlite is a very useful material for the building industry, as a thermic and acustic insulation, for filtration and as a filler. Perlite deposits in Karroo volcanics of Cretaceous age are either too small - layers of 1.3 m thick, or the degree of alteration, in this case the process of bentonization and devitrification is so high that commercially important deposits could hardly be expected in Mozambique. If the common rule that deposit older than the Otigocene could hardly contain expanded perlite were to be valid throughout the world, the Karroo volcanic glasses in Mozambique would yield only remnants of commercially suitable material even if found in a bigger quantity. In my opinion, other sources of expanded material could be used in the country such as Karroo claystones or other younger clays of the Tertiary age.



Cilek: 4.13. Phosphates and apatite

4.13. Phosphates and apatite Phosphorus is one of the most essential elements for life, and beside nitrogene and potassium, a primary material in fertilizer production. The importance of phosphorus compounds increases directly with an increase in the world population and still higher demands for food, more soil and higher crop yields. Therefore, phosphates are in the centre of attention of all countries, both developed and developing, because it can secure the food supply for the population. More than 90% of phosphates are used in the production of fertilizers. A useful phosphorus mineral of phosphates is apatite, which may be present in magmatic rocks and in sedimentary formations, where the rock is called phosphorite. Apatite is a calcium fluorine-chlorine-hydrozyl phosphate of the formula Ca5(PO4)3 (F, Cl, OH). Apatites in magmatic and metamorphic rocks are crystalline fluorapatite Ca5(PO4)3F and chlorapatite Ca5(PO4)3Cl with a content of P2O5 42.3 and 41.0%. The hydroxy-fluorapatite Ca5(PO4)3 (OH, F) is also the main constituent in most igneous rocks and carbonatites. In sedimentary deposits, apatites are not as structurally stable as are crystalline apatites. Besides Cl and F in a complex anion, the groups OH, O or CO3 are always present and the resulting rock is a mixture of several main components, which is known as francolite or cellophane of an amorphus structure, the essential part of sedimentary apatites of a formula identical to that of fluorapatite Ca5(PO4, CO3, OH) (F, OH). One of the isomorphic component of sedimentary phosphorites is also carbonateapatite Ca10(PO4)6 (CO3). Apatite of igneous origin occurs in typical hexagonal prismatic crystals of greenish, yellow, violet colour or colourless, with a vitreous luster of specific gravity 3.1-3.2; by contrast, sedimentary apatite occurs in granular to dense masses, in colloform or botryoidal crusts, cryptocrystalline (francolite). Besides normal phosphates, also aluminous phosphates can serve as a source of phosphorus. Three minerals in this group are of some importance: wavellite, crandallite and miltisite. Phosphates in sedimentary rocks appear in the form of cement in sandstones and sand, grains in clays, part of fossil shells (content 10-25% P2O5) and in oolites (mm diameter) and concretions. Commercial "phosphate rock" should contain at least 20% of P2O5 despite the fact that some deposits have a P2O5 amount of 5% and are still economic (carbonatites with byproducts of magnetite, pyrochlore, rare earths, monazite, anatase, vermiculite). The content of P2O5 is the main criterium used in quality grading, the P content is rarely used. The old American grades of PBL (bone phosphate of lime) still survive from the time when phosphates were produced from bones. The main use of phosphate is in the fertilizer production. Mainly readily soluble carbonate phosphates are applied after grinding directly to the soil, but most of the phosphates - both crystalline and amorphous need to be beneficiated. First, the impurities such as chert, clay, sand, limestone, dolomite, must be removed, by crushing, sieving, washing and flotation to increase the P2O5 content to about 30%. The phosphate is then treated in a dry or wet process. The first process - production of the so-called thermophosphate, involves heating in an electric furnace to produce elementar P, which is converted to pure phosphoric acid used in chemical and food-grade products. The wet process includes the action of sulphuric acid on beneficiated phosphate to produce superphosphate CaH2 (PO4)2 • H2O + CaSO4 • 2H2O with 16-21% P2O5. In this process, roughly 5 t of impure gypsum is obtained from 1 t of P2O5 and most of it is waste. Superphosphate can further be treated to triple superphosphate with about 45% P2O5, the final member of which is phoshoric acid. This acid or superphosphoric acid is preferred in the industry, because it can easily be transported by tankers. Not all natural phosphates are suitable for fertilizer production, because some cannot be beneficiated. The high content of CaO needs an extra amount of sulphuric acid, also harmful is an increased amount of Fe, Mg and Al. This applies also to Cl and F. The remaining 10% of phosphate (90% fertilizer) are utilized by various industries foodstuff, fodder, detergents, drinks, surface metal treatment etc.



A division of the genetic types of apatite and phosphate deposits is this: 1. crystalline apatite in late magmatic deposits of magnetite-apatite and nepheline-apatite type 2. skarn deposits 3. metasomatic deposits in carbonate rocks 4. carbonatite deposits 5. hydrothermal and mesothermal veins and sills 6. metamorphosed sedimentary deposits Types 1-5 are primary deposits of apatite in relation to igneous rocks of alkaline composition or in carbonatites volcanic bodies. An accumulation of apatite is brought about by magma separation, hot fluids and gases in the way of metasomatic replacement, hydrothermal solutions or simple injection. Sedimentary deposits originate from these primary sources. They constitute about 85% of commercial production of phosphates and can be divided into: 1 sedimentary phosphate deposits of geosynclinal and epicontinental seas originate during biochemical process bringing forth concretionally and oolithic phosphates. The development of these deposits is usually multicyclic process which requires specific structural conditions, chemical system, transport of elements, reworking of deposits, residual enrichment and additional new phosphorus material 2 phosphate gravel or land pebble or river pebble deposits originate by reworking of older deposits 3 residual and infiltration deposits originate from a dissolution of carbonates by phosphate, mainly in karst areas, and a deposition in blanket deposits or in cavities and fissures 4 guano deposits of two types, birds excrements and bats excrements, originate from an interaction with underlying limestone 5 wavellite, a alumina phosphate, may be concentrated in a phosphate deposit The Mozambican phosphate deposits are essentially primary deposits of apatite in 1 crystalline limestones of the Precambrian originated from a replacement and metasomatism together with injection; apatite-carbonate, apatite-magnetite and apatite-silicate types of mineralization occur. The two deposits are: Monte Muande-Monte Fema near Tete and Evate deposit near Nampula 2 Occurence in carbonatites with apatite of a low content, dispersed or in thin hydrothermal veins; three volcanic massifs are known: Monte Xiluvo near Beira, Monte Muamba SE of Tete and Cone Negose on the bank of the Cabora Bassa dam, of Jurrasic -Cretaceous age; small sill bodies of carbonatite at Luicuisse in the Niassa Province. Sedimentary deposits can also be divided into two groups: 3 Phosphorites of hypothetical presence, supposed to be developed in coastal sedimentary basins: in the S-Mozambican basin and in the N-Rovuma basin, of Cretaceous-Tertiary age 4 Deposits of guano of bats in karst cavities of Cheringoma and Jofane limestones of Eocene and Miocene age; the only phosphates used by the local population. The guano is of Quaternary age (Fig. 4.13.1).

Fig. 4.13.1. Occurences of phosphate and apatite (323 kB) The best known magnetite-apatite deposit is Monte Muande. The iron ore mined will be used in the production of sponge iron in the first Mozambican iron and steel factory. Apatite as a byproduct will be concentrated and futher treated. The Monte Muande deposit is situated about 30 km NW of Tete on the N- bank of the river Zambezi and continues as the Monte Fema deposits in SW direction across the river on its S- bank. It is part of hills called Serra Muande which lies in the zone of uranium mineralization of Mavudzi type (davidite). In the past, interest was centered mainly on magnetite deposits, investigated by the Nissho company in 1960 and by the Yugoslav team in 1984 (Fig. 4.13.2).



Fig. 4.13.2. Schematic geological map of Monte Muande (Geol.Inst., Beograd, 1984) (429 kB) The deposit Muande consists of medium grained crystalline marble belonging to the Chidue Group, with abundant bands and crystals of magnetite, and interlayers of gneisses. The marbles overlie biotite and augen gneisses and, in the contact zones, remobilized marbles penetrate in the gneiss in a thin layers (Hunting, 1984). Marbles of the Chidue Group are overlain by igneous rocks of the Tete Complex, mainly gabbro, with some pyroxenites and hornblendites intruding the marbles. All rocks of the region are intruded by late granite, aplite, syenite and pegmatite dykes. Magnetite and apatite concentrations of economic importance located around the top of Monte Muande, occur within the marble massif (4.5 km long) as stratiform bodies concordant with the foliation. While magnetite forms different sills or is disseminated in marbles in very variable concentration, the distribution of apatite is more homogeneous. The ore zones are of NE-SW direction; the mineralization is concentrated in three zones of which the central is the richest. The marble beds could be several 100 m thick and biotite marbles with apatite and none or little magnetite, but with a characteristic presence of flint nodules, alternate with magnetite-mineralized marbles. The main magnetite zone is 3,500 m long and 800 m thick (see Fig. 4.13.3).

Fig. 4.13.3. Cross sections through the central zone of Monte Muande (Geol.Inst., Beograd, 1984) (482 kB) The process of mineralization starts with apatite at a pneumatolytic phase of the Tete igneous complex, with coarse grains and, sometimes, concentrated layers, followed by magnetite ore injection of residual liquids after magma differentiation into an adjacent area of ductile crystalline limestones. The apatite of the pneumatolytic phase is accompanied by rare-earth mineralization, the magnetite injection with ilmenite. Analysis of a composite sample (in %):

Fe (total) 17.68

Fe (sol.) 15.54

P2O5 4.03

SiO2 4.19

Al2O3 1.45

TiO2 1.99

CaO 35.29

MgO 6.24

S 0.30

Mn 0.13

This composition corresponds to the mineralogy of biotite and chlorite 13%, apatite 11 % which contains about 4% P2O5, ratio apatite: carbonate = 1:5.1, difficult to separate; opaque minerals 20% (magnetite, hematite, goethite, pyrite, small pyrrhotite and chalco pyrite). Magnetite easily separable at 0.3 mm .

Average content of total



Fe 3 - 67 %

FeO 2 - 28 %

TiO2 0.8 - 5.6 %

P2O5 0.2 -11.4 % (mainly 4.4 - 5.6 %)

CaO 1.0-46.0 %

The deposit was divided by the Yugoslav team into these primary zones:

1 high-grade Fe deposit- average thickness 5.15 m

Fe 3.59 - 60.08 % - av. 34.52 %

P2O5 0.06 -11.51 % - av. 5.12%

2 moderate - grade Fe deposit - average thickness 8.75 m

Fe 4.05-56.19 %, av. 21. 11%

P2O5 0.45-11.41 %-av. 5.25%

3 low-grade Fe deposit - average thickness 29.0 m

Fe 2.00-28.50 %-av. 9.95%

P2O5 0.89- 7.56 %-av. 4.02%

In addition an eluvial deposit covers the marble area at an average thickness of 2.52 m and an Fe content of 1.55-66.50%-average 45.52%, P2O5 0.25-13.40%, average 5.01%. The eluvial deposits are of a typical residual origin on marbles with karst phenomena. Therefore, reserves were calculated

in eluvial deposit: 2,680 000 t Fe 295,000 t P2O5

in primary deposit: 14,620 000 t Fe 3,855 000 t P2O5

total 17,300 000 t Fe 4,150 000 t P2O5

Reserves were calculated to a depth of 140 m only. Futher reserves may be delineated in the Monte Fema area on the S-bank of the river Zambezi. The Evate deposit within the Monapo structure is situated about 100 km of Nampula and close to the port of Nacala. The deposit was discovered during a geophysical investigation for graphite by the Russian team (1975), later explored by Bulgarian (1983) and finally by Czechoslovakian geologists (1985) (Fig. 4.13.4 eastern part of Evate).

Fig. 4.13.4 Geological map of E - Evate deposit (Bulgargeomin -1983, Intergeo - 1985) (810 kB) Two regional geological units of the area are the older Nampula Group and the younger Lurio Group. The Monapo structure and also the formation are supposed to be an isolated plate of the younger Lurio Group shifted from the N and resting on the older Nampula Group. The shape of the structure is brachysynctinal, oval, with its axis in NNE-SSW direction. It is divided into four units, from the bottom upwards: Namialo, Ramiane, Metocheria and Evate. The deposit of apatite-magnetite within the Evate unit is composed of biotite gneisses, sillimanite- monzonitic- and graphitic gneisses with two different marble horizons.



According to Yourde-Wolf (1974) the age of the Monapo Formation is 970 ± 23 m.y. for granulites in the upper part of the sequence, 1,035 and 1,175 m.y. for leptinites and granulites-charnoquites, 860 m.y. for the phase of anatexis, for the Katangan orogeny 500 m.y., terminating the orogenic activities in the region. The Evate deposit consists of a lens of marbles, about 3 km long and a maximum width of 850 m, which constitutes about 70% of the area, the remaining part are gneisses, 2 to 40 m thick. The mineralized apatite zones are 5-100 m thick. The marbles contain as their main constituents apatite, magnetite, forsterite, phlogopite and graphite, and minor proportion of diopside, amphibole, wollastonite, tremolite, scapolite, serpentine, garnets, spinele, microcline, plagioclase, quartz, rutile, sulphides, zeolites, cancrinite and anhydrite (Intergeo, 1985). In the past, graphite was mined in the Monapo Formation (see Chap. graphite), marble was burned to produce lime and some pegmatites were exploited for amazonite. Magnetite of Evate, similar to that of Muande, developed very irregularly throughout the deposit; its content ranges from 0 to 10% and is quite independent of the distribution of apatite. The central part of the deposit, where magnetite was first discovered, is the richest, with layers of magnetite of a disseminated type. The chemical composition of magnetite is this: Fe2O3 - 67.33%, FeO - 27.95%, TiO2 - 2.24%, MgO - 1.58%, Al2O3 - 0.79%, MnO - 0.0%. Apatite of Evate is of the fluorapatite variety Ca5(PO4)3F , an occurence of hydroxy-apatite Ca5(PO4)3 OH with an increased content of strontium, and RE is fairly rare. The apatite content in marbles is 15-30% with richer and poorer layers; their content increases to 40-50% just in the contact zones with gneisses. In the eluvial part, an enrichment zone of P2O5, 14-18%, represents about one fourth of the reserves. A chemical analysis revealed this composition: 0.05-19.7% P2O5 in marbles, 7-8% only in isolated marbles surrounded by gneisses and 0.00-1.5% in intrusive rocks. Beltchev (1983) analysed two composite samples, one with P2O5 above 8% (sample 1), the second below 8% (sample 2).

% sample 1 sample 2

P2O5 10.96 6.29

Fe2O3 + FeO 7.8 2.86

CaO 46.25 47.17

MgO 4.26 2.90

TiO2 1.63 0.52

SiO2 1.50 0.67

Al2O3 0.70 0.37

Calculation of the reserves (Bulgargeomin, 1983):

Apatite ore

category C2 92 million t

category C1 32 million t of this composition: 9.59% P2O5, 3.80% Fe2O3, 3.59% MgO, 0.53% TiO2, 5.14% Fe2O3 + FeO

Iron ore

category C2 1.25 million t



category C1 3.45 million t of this composition: 0.98% P2O5, 27.86% Fe2O3, 30.71% CaO, 7.76% MgO, 2.58% TiO2

Having regard to all complexities of a dressing of Evate ore, the results of a new stage of this exploration by Intergeo (1985) indicated considerably larger reserves of this composition: 155.413 000 t of apatite ore of 9.32% P2O5, 5.76% Fe, 1.21% TiO2, 47.69% CaO. The reserves were calculated at 100 m above sea level. A geochemical prospection made of the whole Monapo structure revealed very interesting results (Zacek-Duda, 1986). An evaluation of an interaction of each geological field with a display of materials and energies in each section, revealed dislocation zones of a different age. The most important fracture zones are directed from N-S, W-E and NW-SE. These interpreted lines, probably deep-seated fractures, helped to clarify accumulations of some elements and minerals. Apparently fluids with phosphorus and other elements ascended along these zones and processes of metasomatosis together with infiltration-diffusion occurred there. At a contact of silicate and carbonate rocks, metasomatic degradation of carbonates by forsterite, enstatite, apatite and wollastonite took place, and the process of apatite and badeleyite deposition continued during the postmagmatic phase. The authors are of the opinion that further apatite mineralization may be discovered in the Metocheria unit (apatite-martite-silicate mineralization) in connection with basic and ultrabasic intrusive rocks. This type of mineralization is highly promising. An occurence of apatite in carbonatites of Jurassic-Cretaceous age originates in volcanic massifs connected with deep-seated fractures along the rift. Usually, the central part of the crater is filled with carbonatite, while the outer ring is made up of alkaline rocks. This can be seen in the Xiluvo carbonatite massif by a carbonatite centre surrounded by volcanic breccia and accompanied by trachyte volcanic cones. Xiluvo carbonatite is extracted and used as a building stone in three quarries. Chemical composition of some samples of carbonatite (in %):

Sample % SiO2 Al2O3 Fe2O3 FeO CaO Na2O K2O P2O5Xiluvo 1 17.86 2.29 5.00 2.76 35.23 1.23 1.25 3.60Xiluvo 5 28.35 5.35 11.00 1.45 27.69 0.49 6.87 1.39Xiluvo 9 10.5 4.84 2.80 2.76 22.43 0.23 0.01 6.08Xiluvo 10 13.48 5.86 12.28 4.50 24.88 0.32 1.92 2.56

Some of the samples have an increased content of P2O5, but mainly in hydrothermally affected zones. Very little is known about apatite mineralization, or a possible occurrences of fluorite. In my opinion, the best utilization of Xiluvo carbonatite is in agriculture, in the production of lime, in which an increased content of phosphorus should be of advantage (see Fig. 4.13.5).

Fig. 4.13.5. Geological scheme of Monte Xiluvo carbonatite (Hunting, 1984) (287 kB) The next site of carbonatite occurrence is caldera of Monte Muambe (see Chap. fluorite). The carbonatite contains from 0.01 to 2.73% P2O5 (in apatite). A higher phosphorus content may be found in residual deposits of caldera with karst phenomena. Cone Negose carbonatite situated near the Mid- Zambezi rift, is a stock-like intrusion measuring 2 km in diameter, associated with alkaline volcanic activity of Mesozoic age (Middle Jurassic-Upper Cretaceous). The central intrusion is accompanied by a number of small volcanoes situated mainly in the Karroo Formation disrupted by several fault lines (Fig. 4.13. 6). Prior to carbonatite intrusion, intense alkaline metasomatism



occurred around the vent.

Fig. 4.13.6. Geological sketch map of Cone Negose carbonatite and surroundings (Hunting, 1984) (759 kB) Carbonatites were deposited in various succesive stages of dome development (Geol. Inst., Beograd, 1984): grey carbonatite - first stage buff carbonatite - second stage red-vein stage with hematite, baryte, quartz with TiO2 and Nb metasomatically altered carbonatite with grains of apatite silicified carbonatite zones - last stage. Apatite mineralization occurs in metasomatic rocks altered during the final action of fluids, with a phosphorus and silica enrichment. Carvalho (1977) described a phosphate enrichment also in the last stages of carbonatite deposition - as phosphatic carbonatite with brookite and baryte (red-vein stage), as silicified carbonatites with fluorapatite, pyrochlore, baryte and finally as fluorapatite, probably during the postmagmatic stage. Carbonatites of the magnesium type "rauhaugites" located in the central part of the dome contain phosphates. Metasomatic mineralization of phosphate occurs in two stages: I stage of microcrystalline apatite with cellophane II stage with recrystallized apatite Phosphate is disseminated in carbonatite, but also layers 1 m thick occur in buff carbonatite with more that 60% of apatite. However, an average content of P2O5 is generally 1-2%. If apatite were to be economically recovered, other minerals with Nb-Ta, Sr and RE should be extracted as the main product. Carbonatite deposits with apatite and uranium minerals at Luicuisse are situated 240 km NE of the town of Lichinga in the Niassa Province. There are many fracture zones with carbonatites within the big ring structure. Along these zones carbonatites are mineralized with RE, uranium and apatite. Residual deposits of a thickness of 7-8 m are present and developed throughout the area and contain columbite, pyrochlore, apatite, monazite, magnetite, concentrated by weathering of underlying carbonatites, granites, syenites and metapyroxenites. In some sectors, the eluvial deposit is more than 30 m thick. Apatite was determined in 33.8% of samples. The content of P2O5 varies, being 2.34% on the average (in 84.4% out of all analysed samples), in 26 samples it was increased up to 6.77% P2O5.

In Mozambique, hydrothermal phosphate minerals, some very rare, were described by Neves and Nunes (1968) from pegmatites of the Alto Ligonha district. They are just of mineratogical importance. Amblygonite, formula (Li, Na) Al [(PO4) (F, OH)], quite frequent in occurrence, was obtained from Nahora pegmatite NNW of Gile. It is milky white with a brown film (lithium crust). Elsewhere it was found in Morrua pegmatite and at a site near Mutala. Composition of the Nahora sample: % P2O5 47.5, Al2O3 34.6, Li2O 9.48, Na2O 0.73, F 5.4 and H2O 4.6. X-ray determination disclosed also Rb, Sr, Sn and Fe. Montebrasite (Li, Na) Al [(PO4) (OH, F)] again from Nahora occured in an intimate association with hureaulite, eosphorite, variscite, quartz and zircon. Triplite was found in pegmatites E of Nuaparra. It is allotriomorphic, brownish in colour, formula (Mn, Fe2+), [F / PO4] composition: % P2O5 32.58, MnO 52.90, FeO 8.77, K2O 0.17, Na2O 0.06, H2O 0.40, F 8.51. Triplite occurs in association with quartz and is enveloped by supergene hydroxides of Fe and Mn. Apatite occurs commonly in many pegmatites, at Nahora and Morrua, it is of a blue grey colour, and associated with quartz, clevelandite and lepidolite. Ilodo pegmatite contains also apatite associated with beryl, mica and green tourmaline.



Chemical analyses of apatite (in %):

Nahora Morrua IlodoP2O5 40.80 41.84 41.52CaO 52.80 53.70 50.96Fe2O3 0.15 tr. tr.MnO 2.79 1.99 5.41F 2.00 3.37 3.40H2O 1.50 0.50 0.90Total 100.04 101.40 102.19

X-ray analyses disclosed in Nahora apatite Cd - 0.21% and traces of Th and Fe, in that of Morrua traces of Y - 0.05%, Sr, Th and Fe, in Ilodo apatite Y - 0.35%, and traces of Ce, Sr, Fe, Ho and Gd. Hureaulite, formula (Mn, Fe2+)5 H2(PO4)4 • 4H2O is a rare mineral which occurs normally as a product of hydrothermal alteration of lithiophylite. The Nahora hureaulite is light rose, enveloped in a black mass of cryptomelane, Mn-oxides and phosphosiderite and associated with earthy phosphosiderite. Chemical analysis (in %): P2O5 39.16, MnO 33.96, FeO 13.98, H2O 13.10. Phosphosiderite is composed of Fe3+ (PO4) • 2H2O, and is a alteration of primary phosphates. It was found in pegmatites of Nahora and Nuaparra. Nahora phosphosiderite contains 36.8% P2O5, 43.3% Fe2O3 and 19.8% H2O. It is of supergene origin. Variscite Al (PO4) • 2H2O from Nahora is of a rosy colour forming fine films over montebrasite of which it is a supergene alteration. It is found in association with saccharoid quartz. Bermanite Mn2+ Mn3+ [(PO4)(OH)] • 4H2O from Nuaparra pegmatite is a product of alteration of triplite. Eosphorite (Mn, Fe2+ Al [(OH)2, PO4] • H2O is very rare. It was described from Nahora associated with montebrasite and zircon. Chemical composition (in %): P2O5 31.18, FeO 7.70, MnO 23.99, Al2O3 22.67, H2O 14.46. Sedimentary deposits of phosphorites were found near Magude (2.7-3.1% P2O5 only), thickness 25-50 m and 50% of glauconite are presumed. Their presence in the N of the Rovuma basin has been anticipated on the basis of the fact that phosphate layers are developed in the Majunga basin on the W coast of Madagascar, i. e., in a geologically similar environment within the Mozambique geosyncline. The recent borehole Mocimboa 1, situated 14 km SW of the town of Mocimboa da Praia was completed in 1986. It was drilled to a depth of 11 240 feet going through the Oligocene, Paleocene, Lower Senonian, Turonian, Cenomanian up to the Albo-Aptian. No traces of gypsum, salt, glauconite and phosphates are presented on the drilling log. Geophysical exploration revealed anomalies of gama radiation in the S- Mozambican basin. Together with certain doubtfull traces of phosphates in outcrops these formations appear promising: Grudja Formation - Paleocene Cheringoma Formation - Eocene Jofane Formation - Miocene. The following areas within these formations should be investigated: Cheringoma plateau, River Buzi bay, River Save bay, bays of the rivers Rio Elefantes and Incomati and the S- part of the Mozambican basin. The most promising are those sections in the sedimentary sequence which contain transgressive sediments of the Cretaceous and Tertiary with a possible uranium mineralization (see Fig. 4.13.7).



Fig. 4.13.7. Probable phosphorite occurences in some deep oil-wells (ENH, 1986) (429 kB) Deposits of bat guano were investigated in all karst areas of Mozambique in which cavities were present - Jofane Formation near Vilanculos, Cheringoma Formation of the river Buzi area and the Cherimgoma plateau, and along the Urema through. In 1953, Bettencourt Dias described deposits of guano in seven caves about 60 km NW of Vilanculos. The caves are located near the village Chefe Buchane at the road to Nhacolo. They have usually a surface entrance of oval shape of sinkholes and an irregular underground plan (Fig. 4.13. 8). The floor of the cave is covered with a layer of bat guano about 1 m thick of ununiform quality. Reserves estimated for seven caves amount to 14,000 m3 of guano.

Fig. 4.13.8. Example of two caves near Vilanculos with guano of bates (Bettencourt Dias, 1953) (329 kB)

Simplified analyses:

Samples % humidity N P2O5 K2O

surface - 1 13.31 3.73 9.80 0.61

surface - 2 15.50 7.71 7.21 1.05

1 m depth - 1 8.43 1.19 8.34 0.86

1 m depth - 2 8.34 2.85 12.80 0.65

Guano for local use is hand extracted, which is dangerous because some caves may be filled by gas. Lächelt (1985) presents a survey both of guano reserves and its quality.

Composition % Vilaculos Area of Búzi Area of Cheringoma

NO3 5.22 3.26 2.74

P2O5 3.32 3.88 5.14

K2O 2.95 1.52 1.37

Reserves 30,000 t 132,700 t 600,000 t

In the caves guano covers an area ranging between 25 and 65 m2, in depths of 1 to 17 m, thickness of guano layer 1 to 10 m. Total guano reserves represent 762,700 t. In 1953 - 1960, about 6,000 t of guano were extracted at Vilanculos, 100 t at Buzi.

Conclusions: Reserves of apatite in the Monte Muande deposit are 4,150 000 t P2O5 with 5.00%, as an average content in ore; in the Evate deposit, 155,413 000 t ore with an average content of 9.32% P2O5, i.e., 14.5 million t of P2O5. Reserves of carbonatite deposits are not yet known, but the content of apatite is low and irregular. Phosphates from this type of deposits can be extracted as a part of agricultural lime. Guano deposits in caves may just cover local agricultural needs. The two commercially interesting deposits of apatite - Muande and Evate - are low-grade phosphate deposits. Muande apatite may be utilize economically together with an extraction of iron ore; apatite from Evate will need further technological testing.





Cilek: 4.14. Quartz

4.14. Quartz raw materials

Quartz raw materials include these varieties: quartz crystal quartz vein, pegmatite, segregation quartzites flint, chert quartz sand and pebble. All these materials are composed of quartz with a minimum content of SiO2 96%. Quartz is a mineral composed of SiO2, normally close to 100% SiO2, with trace amounts of Fe, Mg, Al, Ca, Li, Na, K, Ti ,(46.7% Si and 53.3% O), specific gravity 2.65 g/cm3. Quartz is a very common mineral of widespread occurrence and is found in nature as coarse crystallized variety (quartz with well-formed crystals or in irregular masses) and of a microcrystalline variety (chalcedony). Ordinary quartz (alpha type) transforms at about 573°C to beta quartz or high quartz, at 876°C to tridymite and at 1, 470°C to cristoballite, which is the main constituent of refractory silica material. At about 1, 730°C quartz melts to silica glass. During the development of polymorphs of quartz changes occur in volume weight and volume and structural water is released. Of commercial interest are pure quartz varieties without any impurities. Quartz crystal. Clear colourless quartz in monocrystals, twinning is not acceptable, without bubles, vacuoles, mineral particles and colour variations is the only grade which is accepted in a production of prisms, lenses in microscopes, electronics (main consumer), radio oscillator circuits, watches and as filter plates. Electronics utilize quartz as a dielectric material and for its piezoelectric properties. In comparison with other similar materials, quartz has the advantage of a chemical and physical stability, high elasticity and its relative abundance (Harben, Bates -1984). Owing to numerous defects of natural quartz crystals piezoelectric-grade crystals are produced nowadays by a laboratory synthesis which, on the other hand, needs a feedstock of crushed pure quartz known as lascas from which saturated solutions of quartz are obtained and left to crystallize on a natural quartz chips-seed plates. These seed plates are made of clear quartz in crystals of cavity fillings and should contain Fe2O3, TiO2 and others in amounts of 1 or 2 ppm, alkalies in a similar amount and about 30 ppm of Al2O3. In Mozambique, quartz crystal is only known from pegmatite deposits. In the past, small quantities were exported for piezoelectric purposes (200-600 kg a year) as an ocassional byproduct. Quartz crystals occur in several pegmatite mines, in the quartz core of pegmatites at Monea, Munhamola, Nuaparra, Namacotche, Nahia, Naipa and Muiane. Some crystals are really museum specimens, almost 1 m long, of a perfect crystal form. Barros-Vicente (1963) described crystallization of quartz at a temperature of about less than 600°C with grey, and then violet quartz, white milky, hyaline, and as the last stage, as an amethyst below 400°C. Quartz is almost the last mineral of the crystallization sequence. Quartz in vein, pegmatite and segregation. This includes massive milky and hyaline varieties of high purity. Vein quartz is usually found in fracture zones in the form of tabular bodies or lenses in several generations and varieties, from coarse to fine-grained crystalline. Some vein deposits are of regional importance owing to their extension of several km and thickness of more than 100 m. They are usually of a lower purity than quartz crystals containing about 96-97% SiO2. Quartz is found also in many hydrothermal veins, often mineralized, for which some parts only, mainly the central ones, contain pure quartz. Large quantities of massive quartz are present in central and marginal pegmatite zones. The pegmatite quartz nucleus is composed of pure massive quartz, often with an admixture of some minerals and therefore of a lower quality. Segregated quartz is generally metamorphosed quartz developing during the regional metamorphism, both with irregular bodies and grain, but the "reworked" variety with a small amount of gaseous and liquid inclusions - is suitable for production of quartz glass. This quartz is used in ceramics (minimum SiO2 95-99, 97%, maximum 0.03-0.7% Fe2O3, 1.5-3.0% Al2O3 and 0.2-0.4% TiO2), in the production of quartz glass which is in fact, pure melted quartz with more than 99.2% SiO2, 0.02% Fe2O3, 0.1% TiO2 and 0.2% Al2O3; futher utilization is in metal silicon (minimum SiO2 99.0%, maximum 0.35% Al2O3, 0.05% Fe2O3, 0.4% CaO + MgO), ferrosilicon (minimum 97% SiO2) and silicon carbide SiC (over 99% SiO2). Special attention must be paid to the quality of quartz for quartz glass and only the production of testing glass ingots can prove which quartz is suitable (the absence of bubbles from gaseous and water inclusions). In Mozambique, descriptions are available of many localities with vein -and segregation - quartz, but analyses were not made. The only quartz deposits tested are of pegmatite origin. The pegmatite core of the kaolin deposit Boa Esperanca, at Ribaue was also tested with these results (Geol. Institute, Beograd, 1984): %


Cilek: 4.14. Quartz

Sample No. 0036 N. 110036

SiO2 97.24 96.04

Al2O3 0.18 -

Fe2O3 0.71 2.61

FeO 0.09 0.14

MgO 0.02 -

CaO 1.26 0.36

Na2O 0.04 0.36

K2O 0.02 -

TiO2 - -

The guality of quartz is low and the material may be used in the metallurgy of basic ores. Another quartz pegmatite was tested during a feldspar exploration on the Nuaparra deposit (Duda, 1986). The pegmatite does not possess a distinctive quartz core, but consists of three zones: marginal zone of graphic texture, pegmatite with small crystals and quartz in grains from 1-10 cm and an inner zone with feldspar and quartz in block of > 1 m in diameter. Quartz is white, greyish, rose and smoky. Spectrometric analyses revealed an interesting composition of each quartz variety:

Mineral 10% 10-1% 1-0.1% 0.1-0.01% <0.01%

quartz white greyish Si Al, Ca Fe, Bi Ba, Mg, Na, Ti, Nb, Mn, W, Zr

Ag, Cr, Cu, Ni, Ga, Pb, Sr, Be

quartz smoky Si Al, Ca, Mn Fe, Bi, B, Nb, Th, W, Sn, Zr

Ba, Be, Na, Ti, Sc, Sr, Ni

Ag, Cr, Cu, Ni, Mo, Ga, Co, Pb, Yb?

quartz rose Si Al, Ca, Be, P, Bi Fe, Mn Ba, Mg, Na, Li, Nb,

Sb, Pb, Sn, ZrAg, Cr, Cu, Ni, Ga, Ti

According to the analyses, the different varieties have a different composition because they were formed during different mineralization phases and under different geochemical conditions of pegmatite development. Quartz rose, for example has an increased content of Be, Bi, Li and P; by contrast, typical of quartz smoky is the presence of Sc, Mo, Co and an increased amount of Nb, Ta, W, Sn and Sr. According to Duda (1986) the following paragenesis - crystallization is typical of quartz: quartz of granitic pegmatite ===> quartz of graphic zone ===> quartz smoky ===> quartz white greyish ===> quartz rose ===> quartz crystal. Three composite samples were prepared from drilling cores:

Composition % Borehole F-4 (0-3.5 m)F-4 (20.4-20.7 23.2-33.4 m)

F-7 (5.15-6.6 m)

SiO2 97.23 95.85 98.00

Al2O3 0.51 1.02 0.25

Fe2O3 0.33 0.30 0.51

FeO 0.27 0.16 0.38

TiO2 0.01 0.01 0.01

CaO 0.03 0.03 0.06

MgO 0.09 0.004 0.02

Na2O 0.09 0.13 0.06

K2O 0.27 0.10 0.09

Li2O 0.004 0.046 0.005

BeO 0.0007 0.0649 0.0007


Cilek: 4.14. Quartz

Bi2O3 0.003 0.003 0.003

All quartz samples do not comply to the requirements for the production of quartz glass, metal silicon or glass. It could be used in ceramics or lower-quality glass after beneficiation. Pegmatite quartz, if not concentrated in the core or even in quartz crystals, contains a certain quantity of mineral impurities. Therefore, a small part only complies to the requirements. Quartzites are rocks composed mainly of quartz with an admixture of micas, feldspar, clay minerals etc., of sedimentary origin and also metamorphic. They originate from a silicification of sandstones, a cementation of quartzitic sandstone by siliceous cement and also from an alteration of siltstones. There are several transitional stages between quartzites and sandstones; limnoquartzite is a special type of freshwater rock composed of opal or cryptocrystalline silicon. Industrial grades of quartzite: amorphous crystalline Amorphous quartzite is a sedimentary rock - ganister quartzite - composed of quartz grains (0.04-0.08 mm) cemented by a very fine material, probably recrystallized opal (grain size 0.0003-0.002 mm) which originates during a superficial kaolinization at which the colloidal silica is precipitated and deposited in sandstones. The composition of this quartzite is 96-99% SiO2, 1.5-0.3% Al2O3, 0.3-0.5% CaO and 0.01-0.02% P. It is a very important material in the production of acid refractories-silica bricks or dinas (used in temperature over 1, 550°C), in metallurgy for metal silicon and ferrosilicon. Crystalline quartzites are also of sedimentary origin formed by a silicification of sand stones with bigger quartz grains. It is used mainly in the production of ferrosilicon. In Mozambique, analogous sedimentary quartzites have neither been found nor tested. These materials may probably occur in a lower sequence of the Karroo Formation, in the Lupata Formation of Cretaceous age and in Tertiary beds. In order to discover quartzites of an appropriate quality sections ought to be examined in which sedimentation was interrupted and the sandstone was exposed and influenced by superficial weathering. In Precambrian formations, thick beds were found of metamorphosed quartzites although, generally, these rocks are impure and seldom only fit for industrial use. However, some areas of metamorphic quartzites may be found suitable: 1 Chidue Group with impure quartzites within the metasedimentary complex (banded quartzites) 2 Zambue Group with extensive pure quartzites around the Aruangua valley. Quartzites are grey, glassy, medium - to coarse - grained, with a minor proportion of feldspar, biotite, sillimanite and muscovite.Pure quartzites enclosed in gneiss occur in the region of Cassenga and Chingoa. Some quartzites contain feldspar, sulphides, garnets and pass into banded ironstones. 3 Fingoe Group-widespread are siliceous granular metasediments ranging from very fine-grained rocks-cherts-to medium-and coarse-grained quartzites. They build the prominent Fingoe ridge, are grey, pinkish or cream, composed of quartz, plagioclase, epidote, biotite. Industrially promising may be the very fine-grained siliceous metasediments which might be metamorphosed cherts or siliceous oozes, or well sorted fine-grained sandstones (Hunting, 1984). 4 Barue Group contains upstanding sinuous ridges of quartzites N of Nhacainga, W of Canxixe, NW of Guro and in the Serra Nhandrura. The quartzite areas correspond partly with the marble extension. 5 Gairezi and Fronteira Groups consist predominantly of white orthoquartzite and pelitic schist. Quartzites dominate in the Chimanimani Mts. and the Serra Sitatonga. They are sugary granular recrystallized rocks composed of quartz with a small amount of zircon, magnetite and sericite. 6 Umkondo Group of almost unfolded metasediments contains quartzites in a sequence of phyllites, siliceous dolomites and metasiltstones. 7 Mozambique belt s.l., in N- Mozambique, is divided into a number of units of which the geosynclinal and platform deposits contain metasediments-crystalline limestones, schists and quartzites scattered over the higher degree metamorphosed rocks. Quartzites occur in the Lurio belt, the Morrola structure and the Niassa Province. Flint, chert, forms concretions of opal-chalcedony composition and, when pure, could be used in silica bricks production. In Mozambique, chert may be found in Karroo volcanics and if redeposited, in younger sedimentary formations such as Lupata or Sena. Quartz sand and pebble are nowadays widely used to replace quartzites. Sands of the glass - and foundry - grade have been described already. Pebbles of pure quartz from alluvial river deposits in terraces or in deltas are, in some countries, the basic material for dinas and ferrosilicon production. In Mozambique, thick river deposits if properly sorted may also supply pure quartz pebbles. Some quartzites or quartzitic sandstones are used as grinding wheels, could be hardly replaceable by artificial abrasives. Spheric concretions of chert are used at ball mills in a preparation of the ceramic mass. Quartzites may be also used as a slag-forming admixture in metallurgy. Special high-purity quartz is used in optoelectronics in a production of silicon wires, which are replacing expensive metals.


Cilek: 4.14. Quartz



Cilek: 4.15. Salt

4.15. Salt Common salt or rock salt is composed of mineral halite, formula NaCI, hardness 2.5 and specific gravity 2.16. The chemical composition is sodium chloride with 39.3% Na and 60.7% Cl. It is often mixed with calcium and magnesium sulphate and chlorite, most common is anhydrite. Salt as a sedimentary rock occurs with shale, dolomite, anhydrite and other sediments together with other halides such as sylvite, polyhalite, carnallite, kainite and clay minerals. Salt has been used from time immemorial for direct human consumption and transported from the deposits along the well - known salt - paths for distances of hundreds of km. In Africa such famous salt localities are in the Taoudeni basin in the S of the Sahara or in the Danakil depression on the Red Sea. Nowadays the largest proportion of salt-about two thirds -is used in the chemical industry as a basic material in a production of chlorine and caustic soda, with limestone in the Solvay process to produce soda ash, with sulphuric acid to produce hydrochloric acid and sodium sulphate (see glass industry) and in many other products such as soap, herbicides, food seasoning, glazes in ceramics, in textiles and as a dye. In many countries it is used in a defrosting of roads in winter, which causes severe environmental damage. Salt is a very common mineral originating in large beds from an evaporation of seawater in restricted basins. As the sea water evaporates the concentration of salt increases up to the point of supersaturation - halite, gypsum, anhydrite, sylvite and other salts precipitate. It has been suggested that thick layers of pure salt may originated in partially separated bays with a limited intake of seawater, or in deep-water basins with layers of brine, and on supratidal mud flats of the type "sabhka". Because salt is a weak crystalline solid and is mobile within the crust, it can be pushed under compressional stress into the zones of lower pressure thus building salt domes-diapirs. Common salt occurs in several basins, gypsum-anhydrite beds in others and potassium salts in a few beds only. Salt is mined either by means of the room-and-pillar method, if deposited near the surface, or, with the help of boreholes, by pumping water down the hole to the salt horizon and precipitating the artificial brine under pressure. Salt deposits are salt beds of marine origin which developed in shallow basins along the passive continental margin or in grabens on continental platforms covering several thousand km2. Under a lateral pressure or simply by a higher specific gravity of the surrounding sediments these salt beds are transformed into diapirs, diapiric folds or salt domes of regular shape. The biggest salt reserves are contained in seawater (18 million km3) from which probably salt was first recovered by the primeval man by boiling the water. In warm and dry climatic zones, salt is produced in artificial ponds along the coast of the oceans using the tide to fill or empty these salinas and solar energy to evaporite the seawater. Other type of salt deposits are either salt lakes of the playa type in arid areas, or salt lakes as relics of marine basins after regression, and continental lakes supplied with salt solutions from surrounding salt deposits. A special case are salt deposits with dissolved Na, Mg, Ca and K chlorides, sulphates and carbonates in rift valley basins to which salts are delivered by hot springs on fracture zones. Such deposits occur at Lake Rukwa and Lake Natron in Tanzania, Lake Magadi in Kenya and several other localities within the African Rift System.


Cilek: 4.15. Salt

Finally, salt may be recovered from salt springs or boreholes containing brine either from buried "fossil" seawater or from water with dissolved salts collected en route from rocks and weathered rock layers. In Mozambique, the only source of salt are the salinas on the seashore of the Indian Ocean. Several are situated at Maputo, at Nova Mambone near the river Save, at Beira and between Quelimane to Quissanga N of Pemba. The best conditions are, of course, in the N, where the weather is warmer and the dry season is distinctive (see the map-Fig. 4.15.1).

Fig. 4.15.1 Occurences of salt (304 kB) The salinas cover generally several hectars in the mangrove belt, where the bottom is clayey and flat and the establishment of partial rectangular basins separated from each other by low bariers is easy. Oblong bigger basins are divided by channels suplied with seawater from the main channel closed with a sluice at the side facing the sea. The evaporation cycle depends on weather conditions. From a partially divided oblong basin, water with an increased concentration of salts is transferred to a second pond and finally to the production pond where CaSO4 and then NaCl precipitate and common salt is collected. Total production capacity of the Mozambican salinas is more than 120,000 t/year, although, owing to - the internal situation, about 22% only is produced and table salt is imported. Salt deposits of the country have never been seriously investigated. In my opinion, there are three other types of salt deposit: 1 bedded salt within the Temane Formation in the Mozambican basin. There are geological indications, that salt may be present along with anhydrite (gypsum), dolomite in this lagoonal (sebhka) deposit which covers an area of 30,000 km2; salt may be present in the centre of the basin. 2 salt in diapir in the Rovuma basin at Pemba, where Flores (see ENH report, 1986) suggests that the Pemba bay originates from a dissolution and collapse of the salt dome. The nearest salt diapir is in the Tanzanian part of the Rovuma basin at Mandawa, about 180 km N of Rovuma. The thickness of salt is over 2,000 m. 3 salt in Tertiary - Quaternary (?) beds on the floor or slopes of the Niassa Rift Valley, at northwards of the Lake Chilwa. Brines with salt occurring in the neighbouring Tanzania may be present in Mozambique along the fracture zones both in the rift valley, N-S direction, and in regional faults of the Mid-Zambezi-Lurio belt, W-E direction. According to A. Babij (personal communication) mineralized waters of natural springs, with higher content of salt, were found in several places. Near Mossuril in the Nampula Province, a spring of 46°C has the following chemical composition with mineralization

8.0Cl 90 . SO4 10 Ca 67 . Na 33

Si 97

Another spring is at Namacurra, water temperature 73 to 80°C, with mineralization


Cilek: 4.15. Salt

8.1Cl 96

Ca 46 . Na 53Si 87

Very interesting is the group of springs along the Zambezi rift valley, between Zumbo and Mt. Atchiza, with mineralized waters with NaCl, indicating a connection with deep-seated fractures. Artificial "springs"-artesian waters (?) occur in the area of the Temane Formation, with high content of salt from several oil exploration boreholes.

List of salinas in Mozambique (366 kB)



Cilek: 4.2. Bentonite-smectites

4.2. Bentonite-smectites The modern term smectites introduced to the literature in 1970 (Millot) includes several varieties of clays, similar to micas with pyrophyllite structure (gibbsite sheets between two sheets of silica layers). The general chemical formula is (Na)0.7 (Al3.3 Mg 0.7) Si8O20 (OH) • n H2O, which is usually different in nature owing to a substitution of Al for Si in a tetrahedral structure or Mg, Fe, Zn, Ni, Li for Al in an octahedral structure. The three-layered structure with water and ions of Ca, Na and K are loosely bound to each other to form an expanding-lattice structure. The group of smectite minerals includes montmorillonite, saponite, hectorite, palygorskite and beidellite. The name bentonite refers to a clayey rock characterized by a mixture of different clay minerals in which montmorillonite prevails which account for the typical properties of the rock such as a high absorption capacity, high cation exchange capability, swelling, plasticity and bonding power. The two most important smectites are sodium montmorillonite known as sodium bentonite, which is swelling, and calcium montmorillonite called calcium bentonite which is nonswelling. Magnesium montmorillonite is a saponite and an armargosite, potassium montmorillonite a metabentonite and lithium montmorillonite a hectorite. The principal admixtures of bentonite are kaolinite, illite, feldspar, quartz, biotite, pyroxene, remnants of parent rocks, calcite and aragonite in younger fissure fillings, opal, zeolites and cristobalite, and fragments of different rocks. Bentonite is used in many industrial branches - in refining, filtration and decolourization of vegetable oils, wine and drinking water, in cosmetics, pharmaceutical products, as fillers and extenders in paints, fodder and removal of radioactive waste-fixation of radioactive cations are by sintering at 1,000°C, in the paper industry. In the building industry, bentonite is used for its impermeability properties in grouting and lining canals, ponds, dams and everywhere, where the stability of the soil needs to be improved. The biggest part of bentonite is used in foundry sands (about 3-5% as binding agent) and in rotary drilling as a lubricant and coating material for an uncased wall of hole, and to increase viscosity of the drilling mud. The binding properties of bentonite are used in the production of iron ore pellets and molding sands. Requirements for foundries:

ion exchange capacity 45 at a minimum

green compressive strength 300-600 kpa

permeability 120 min.

shatter index 42-44 min.

Fe2O3 max. 14%

CaCO3 max. 2.5%

Rheological properties are used both in drilling muds, and ceramics in a production of china ware. Adsorption capacity of bentonite is used in refining sugar-cane juice, beer, oils and recently often in agriculture as a carrier of fertilizers, pesticides and hazardous chemicals. In animal food, bentonite acts as a binder and filler, it improves the efficiency of food and prevents disease. In several countries, it is used as a sorbent to improve the fertility of sandy soils, prevents wash-out fertilizers from the upper layer to the groundwater or into watercourses, to enhance water retention and add several trace elements as important nutrients directly to the soil. The amount of bentonite required for one hectar of sandy soil is 20 to 40 t and the crop yield increase, for several years, is 15 to 30% depending on the crop. Agricultural use of smectites: a) as a fertilizer mineral to supply directly N, P, K, Ca, Mg, S and micro- and trace elements such as B, Fe, Mn, Cu, Mo, Cl, Co b) as a sorbent in crop plant production in sandy soils c) as a sorbent in animal husbandry d) as a carrier of chemicals to protect plants against insects



Bentonite for agricultural purposes requires: ion exchange capacity, minimum 25 mg/100 g minimum 25% of montmorillonite the amount of remnants on the sieve depends on the type of machine used for dispersion; content of iron, fragments of rocks not important. Bentonite is used also in ceramics: the accepted maximum for coarse ceramics is 2.5% Fe2O3, for sanitary ceramics 1.8% and for fine ceramics 1.2% Fe2O3. The grain size of material below 1 micron minimally 30%. To improve the quality of natural Ca or Mg-bentonites for foundry, drilling and generally binding purposes, activated-natrified-bentonite is processed by adding sodium chemical, usually soda ash. On the other hand properties of nonswelling bentonite of the calcium type are used for its absorption ability, for which it can replace "Fuller's earth" (attapulgite, sepiolite) or bleaching clays. Synthetic bentonite is of the alumina type and is used for catalytic cracking, hydrogeneration and dehydrogeneration by a treatment of smectite clay with sulfuric and hydrochloric acid, followed by calcination to remove adsorbed alkalies, alkaline earths etc. in petroleum refining (Harben-Bates, 1984). Very important in an exploration of smectites is an exact knowledge of the genetic type of the deposit. Some bentonite layers in sedimentary and volcanic sequences are indistinct, and their contact with surrounding beds may be gradual. Sharp boundaries are typical of the genetic types: a) layers of volcanic ash altered in a marine or lacustrine environment immediatelly after eruption, during which under alkaline condition hot ash and warm water of a shallow basin was altered into bentonite b) during a prolonged groundwater effect, the layers of volcanic tuffs and tuffites can be altered in an alkaline environment of the sedimentary basin under conditions of good porosity of volcanic material and an unpermeable layer beneath it; often, a lower silica-rich horizon developed from a leached upper layer. The irregular shape of a bentonite body is typical of: c) hydrothermal bentonite deposits either on hydrothermal veins, or as bottom layers in alkaline lakes with hot springs (see bentonite and magnesite deposits on Lake Natron - Tanzania or the hectorite deposit in California). The most common origin of bentonite: d) surface weathering of tuffs, agglomerates, porous volcanic rocks and glass; towards the bottom, an increased amount of remnants of parent rock, silica and alkalies is evident. Some of these deposits are very thick (several 10 m) and large in extent. e) redeposition and mixing with other clayey material account for an origin of bentonitic clays. Some bentonite layers of type a) and e) may be enormously extended over hundreds km2 and could mark either a prominent volcanic explosive phase or stable sedimentary conditions. Often, these bentonite layers serve as "marker" beds in oil geology. In Mozambique, bentonite deposits are connected with volcanic rocks of Karroo Formation (see Fig. 4.1.1). These rocks accumulated in the upper part of Karroo of Triassic and Jurassic age in the Stormberg Series, which is composed of basalts and younger rhyolites and ignimbrites. Karroo volcanics form several prominent ridges and massifs. One of the most prominent structural units, even within the African continent is the Lebombo Mountains chain that runs along the border with South Africa for a distance of some 500 km, between 25°45' and 26°15' South. Average altitude is about 450 m and its width is 35km. Another Karroo volcanic chain extends along the S-African border, from Nuanetsi syncline to the Xiluvo carbonatite structure, for about 250 km in SW-NE direction; the Chibabawa rhyolites and other volcanic belts border the Cretaceous Zambezi basin in roughly N-S direction on the W side up to the brachysynclinat closure of the Cretaceous Lupata alkaline sequence. The last prominent massif of Karroo volcanics is the Massif Luia S of the Cabora Bassa Dam on the Zimbabwean border. The main and best known bentonite deposits have been located at about 40 km SW of Maputo in the Boane area on the slope of the Little Lebombo Mts. (see Fig. 4.2.1).

Fig. 4.2.1 Geological map of the bentonite deposit near Boane (different sources) (1012 kB)

This ridge forms an escarpment that can be traced over some 60 kilometres and has a general N-S trend. Several sites of occurence and deposits of bentonite were found in it. The bentonite areas are characteristic by a rather flat topography and



are often covered by swamps, with prominent rhyolitic rocks. The main river in the area is the Umbeluzi, fed mostly by perennial tributaries. During the rainy season, the freatic water table rises considerably and floods the low lying parts. Various deposits and old quarries of bentonite are situated in an area around Boane. Most of these deposits are easily accessible, within short reach of both the Maputo-Namaacha tarmac road and Maputo-Ressano Garcia road. A bentonite factory processing 12,000 t/y is situated near the Maputo-Namaacha road, about 6 km from the crossing near Boane (Luzinada factory and deposits in former reports). Regionally, rocks vary in age from Karroo to Quaternary. The Karroo is limited to the Stormberg Series and consists completely of volcanic rocks. They form an eastwards dipping monocline. To the W of Lebombo are Karroo sediments. Eastwards occur younger rocks, ranging from Cretaceous to Quaternary. The Stormberg Series can be subdivided into a basalt and rhyolite complex. -The basalts are interbedded between rhyolites and are also found in the plain on the E side of the rhyolite where they are covered by younger rocks. They are strongly eroded and occupy topographically low areas. -The rhyolites occupy higher ground and form ridges parallel to the Lebombo mountains. Cretaceous rocks consist of calcareous sandstones limited to a narrow belt E of the Lebombo hills. Tertiary rocks are siliceous limestones and calcareous sandstones and are found above the surface where the overlying Quaternary had been eroded by major rivers such as Maputo and Tembe. The Quaternary consits mainly of Pleistocene and Holocene dune fields. Terraces and alluvial deposits are found along the major rivers. In the Boane area, the Karroo consists almost entirely of volcanic rocks. Two volcanic phases can be distinguished in the field: a phase 1 consisting of rhyolites and porphyritic rocks and phase 2, including rhyolites, volcanic breccia and basalts. Younger rhyolitic intrusives of Cretaceous age occur locally, rare Quaternary alluvial deposits consist of clayey sediments (see Fig. 4.2.2).

Fig. 4.2.2. Cross section of bentonite deposit Luzinada-Cooperativa II. (Zuberec-Ivanicka, 1981) (410 kB)

Faulting occurred in Post-Karroo times and may be linked with a rift system. The faults have mostly N-S trend and are almost vertical. The first exploration for bentonite started in 1962 just close to the present Luzinada factory. Actual production at the factory begun in 1967. Its capacity is 12,000 t/year of proccesing of raw material with an output of natrified bentonite (2% of soda ash) of about 5-6,000 t/y. Raw bentonite is extracted from an open pit about 3 km from factory, from an area known as Cooperativa I. The bentonite originated from an alteration of rhyolitic rocks-rhyolites and tuffites with volcanic glass of the second eruptive phase, which is typical of the development of obsidian of a perlitic texture at the base. Practically the whole perlite seam, throughout its course has been altered into bentonite. Rhyolitic rocks overlay the perlite while Quaternary sediments are found on the top of the sequence. The bentonite layer has a N-S strike and is bounded by N-S trending faults. Due to faulting, the whole area is subdivided into smaller blocks with different thickness of bentonite. The layer of bentonite varies from 2.1 to 10 m, while overburden thickness ranges from 0.9 to 3.8m. Composition of treated bentonite from the factory (Noticia explicativa, Carta de Jazigos,1974):%

SiO2 73.18 Colour-white

Al2O3 13.79 pH 9.6

Fe2O3 1.03 viscosity-15 cp c/7% suspension

TiO2 0.13 Green resistance-8 to 8.5 pounds/inch2

CaO 1.73 Resistace after drying-40 to 50 pounds/inch2

MgO 2.50 Filtration loss -16 to 100 cm3

KaO 0.12 Durability-very good

Na2O 1.93 Fusion point 1,240°C

L.i. 5.38 The main impurity is cristobalite



In the surroundings of Cooperativa I, in a belt stretching northwards, several other small bentonite pits have been opened such as Mina Ceramica, Ultra, Verga, Movene, Maro and Portella, over a distance of about 40 km. From the mine Portella, bentonite was mined from a depth of 4 to 31 m of clean montmorillonite clay with reserves over 500,000 t and of this quality: %

SiO2 66.28

Al2O3 13.10

Fe2O3 2.38

TiO2 0.95

CaO 4.68

MgO 3.38

Na2O 0.45

This bentonite of the calcium type was activated by soda ash (2-3%) and about 3,000 t/year were exported to Europe. In other mines, the thickness of the bentonite layer, under a Quaternary cover of several m, was 6 m at Ceramica with white bentonite, 9 m at Verga and over 20 m at Movene. It was observed, that the thickness of the bentonite layer depended on the presence and density of faulting. The bentonite horizon, stretching for many km along the foot of Little Lebombos could therefore be interrupted by blocks of less altered rhyolitic material with inferior bentonite properties. Several bentonite bodies at all stages of alteration were discovered during prospecting. In some instances, the bentonite may grade over a very wide range of intermediate stages into fresh unaltered rock, in other instances, there may be a sharp contact with the parent rock. In some places, the clay may contain a very large number of calcareous concretions. The appearance of bentonite varies from a wax-like material, yellow-green in colour through a stage of green clay (a green or blue colour is caused by Fe3+ in a reducing environment) of an almost granular appearance to ultimately a pale yellow clay, which is streaked with red and alters in parent rocks of the lower red tuffs and agglomerates. Throughout the bentonitic layer, relicts of rhyolite with some fresh rock fragments can be found in all altitudes and positions. The estimated reserves of the whole belt calculated during this first prospecting stage amounted to 15 million t. Several chemical analyses of different rock types showed clearly the degree of alteration into a bentonite mass (Zimro (PTY) Ltd., 1977): %

Rhyolite (base)Weathered tuff rhyolite

PerliteWelded tuff

rhyoliteKarroo basalt

(Goba)

SiO2 76.64 74.33 67.82 70.34 46.10

Al2O3 17.14 17.95 16.20 17.69 22.25

Fe2O3 1.84 1.23 0.41 0.65 10.12

TiO2 0.10 0.01 0.01 0.11 2.51

CaO 0.35 0.49 0.78 0.20 5.60

MgO 0.19 0.28 0.50 0.48 2.90

K2O 0.23 0.37 5.91 7.98 1.53

Na2O 0.18 0.28 1.85 1.84 3.41

L.i. 3.88 4.53 6.10 1.05 H2O 2.30

Total 100.60 99.47 99.58 100.34 100.40

The analyses indicate, that all rhyolitic rocks have a very similar composition, but differ mainly in the content of alkalies. The best material for an alteration to bentonite is volcanic glass. The example of the other volcanic Karroo rock-basalt from



Goba shows clearly, that this rock is an unsuitable parent rock for bentonite origin and in that the degree of the alteration process is low - rhyolitic parent material, just sligthly altered, may be favourable for the genesis of these bentonites. In 1981, the geology of the deposit Cooperativa I. was re-evaluated by a new exploration programme and additional reserves were discovered (Cooperativa II)-Zuberec et al., 1981): Bentonite of the area contains generally 45-70% montmorillonite 26-52% cristobalite 3- 6% feldspar, oxides Fe,Ti, others Results of an analysis performed by XRD: 54% montmorillonite (96% < 0.063 mm, 4% above 0.063 mm) 35% cristobalite 5% kaolinite 3% calcite 2% quartz 1% dolomite Chemical composition of Cooperativa II (average of samples from boreholes):

maximum % minimum %most commonly

occurring average %GDR

SiO2 55.10 64.30 58-63 68.8

Al2O3 6.95 14.60 8-11 11.8

Fe2O3 1.38 5.92 3-5 2.6

CaO 0.98 9.39 1-6 3.8

MgO 0.71 3.88 1-3 2.2

TiO2 0.12 0.35 0.15-0.25 0.3

K2O 0.03 1.28 less than 0.3 0.1

Na2O 0.43 1.72 0.7-1.4 1.1

H2O (105°C) 1.90 15.32 7-11 -

L.i. (1,100°C) 5.70 17.99 7-12 -

MnO 0.01 0.06 less than 0.1 _

P2O5 0.007 0.015 0.07-0.08 -

SO3 - 0.14 0.01 0.1

This material can be beneficiated to a commercial bentonite grade. The Fe2O3 content of most samples is above 3%, which is the limit for use in ceramics, glass and the foodstuff industries. The ion-exchange capacity which should minimally be 40 mval/100 g (except for some uses, e. g. in agriculture) is 39.9-75.71 mval, with a prevailing value of 40-60 mval/100 g in Cooperativa I. The lower value of exchange capacity than expected in this type of bentonite, is due to a high content of cristobalite. Results of cation-exchange tests and grain-size analysis (Cooperativa II):

Core Sm 4

Cation-exchange analysis Mval/100 g Screen analysis (%)

sample interval (m)

0.15 N NH4Cl

from to Ca2+ Mg2+ Na+ K+ Tot.2.00 mm

1.00 mm

0.325 mm

0.208 mm

0.105 mm

0.053 mm

Tot.

4/1 5.90 6.40 22.20 13.06 1.96 0.52 35.74 8.30 12.82 13.15 3.63 5.45 4.35 47.7



4/2 6.40 9.00 22.57 24.93 0 0.64 48.14 1.47 2.38 4.46 1.72 2.55 1.78 14.3

4/3 9.00 12.20 21.39 28.50 0.44 9.46 59.79 0.60 1.25 4.48 3.83 6.47 3.32 20.3

4/4 12.20 15.95 17.82 24.34 6.96 0.71 49.83 0.25 0.78 1.38 1.04 3.00 2.25 8.7

4/5 15.95 16.15 9.50 24.93 13.92 18.26 66.61 3.30 3.70 5.70 2.20 4.80 6.32 26.0

4/6 16.15 17.70 17.23 27.90 8.35 0.96 54.44 0.27 0.12 0.40 0.23 0.41 0.36 1.7

4/7 17.70 19.30 26.14 29.68 6.84 0.81 63.47 1.00 1.25 3.00 2.66 4.21 1.61 13.7

4/8 19.30 21.95 24.95 23.75 5.00 1.02 54.72 8.74 7.53 7.93 3.43 830 3.20 37.1

The main bearers of ion-exchange properties are Ca2+ and Mg2+ followed by Na+ and K+. A maximum of 30% of grains on sieve 0.053 mm is fulfilled according to requirements because the value is between 1.79 and 28.70%. Firing tests at temperature 1,150°C disclosing a brownish, greenish and brown colour, point to a high Fe2O3 content which excludes this bentonite from use in ceramics. Bentonite suitability in foundry sands was tested in the GDR (the norm requires a minimum of 5.39 N/cm2 at 3% humidity): the results of samples of bentonite - 6.26 and 6.28 N/cm2 obtained in 1979 fullfilled the requirements for foundry sand. Generally, it was confirmed that bentonite from the new deposit Cooperativa II could be used in foundries, as drilling mud, in the building industry and agriculture.

Calculated reserves: north of Cooperativa I/old pit 64,600 t

north of Cooperativa I/old pit 356,565 t

north of Cooperativa II 163,395 t

Further prognostic reserves N of these deposits 4,100 000 t.

Before independence Mozambique produced annually some 4.000 t. Figures of production and export:

Year Production t Export t Internal use

1971 6,373 4,820

1972 3,722 2,153

1973 4,421 3,216

1974 4,699 4,218

1975 1,400 -

1976 1,610

1977 2,643

1978 1,976 1,542 200

1979 1,656 1,007 252

1980 848 606 205

1981 716 180 632

1982 1,455 20 595

1983 250 20 506

1984 414 58 830

1985 361 - 589

1986 1,112 40 515



Additional tests for bentonite from the factory Luzinada (deposit Cooperativa I) made in 1983 by Cullinan Minerals Ltd. indicated a declining quality of the product.

The foundry tests non-activated activated bentonite (2% of Na2CO3)

moisture % 13.5 11.4

initial viscosity sec 23 24.1

base exchange 50 68

grit on + 53 micron % 2 -

permeability 120.5 112

green compr. strength (kPa) 94.9 103.2

dry compr. strength (kPa) 267 132.8

Shatter index % 32.5 31.5

The tests showed a poor compactness and, therefore a high water demand as well as a low shatter and dry strenghts. Base exchange and viscosity was low. According to Cullinan, this bentonite should be mixed with a good-quality bentonite and used in iron foundries making castings. On the other hand, the quality requirements were much higher than European demands (here, for example, the foundry grade bentonite required 80 mval/100 g ion-exchange). Drilling tests by Cullinan showed that viscosity and filter loss were very low and therefore not fit as a drilling grade. Also other Karroo volcanic ranges may be potential areas for bentonite discovery: Chibabawa rhyolites Rhyolites and andesites on the western side of Zambezi basin Rhyolites of Luia massif The most important problem to be solved for a future exploration is the genesis of Mozambican bentonite deposits, whether deposits of the Little Lembombo Mts. originated: a) from a surface weathering of tuffs, tuffites and volcanic glass or b) from an alteration in the alkaline lacustrine environment or c) from hydrothermal action with the aid of hot springs Remnants of parent rocks in bentonite are in favour of a) point while irregular shape, no evidence of chemical changes towards the bottom, great thickness of the bentonite layer and sharp boundaries are in favour of b) and c) points. In my opinion, there is evidence of some action of hot waters in the alkaline environment. This possibility-almost syngenetic alterations of volcanic material in lakes and hot waters on the fractures as a postvolcanic agent, may bring forth a much wider extension of bentonite deposits than surface weathering.

Conclusions: The Mozambican bentonite deposits are connected with rhyolitic parent rocks of Triassic Karroo volcanics (Stormberg Formation) and originated either by surface weathering and/or hydrothermal action of low temperature waters in an alkaline environment. Bentonite deposits have been explored in the vicinity of Boane on the dipslope of Little Lebombo Mts. and bentonite has been mined since 1967. Bentonite is of the calcium type and is activated - natrified. The high content of cristobalite lowers the quality and the utilization is as a foundry sand, in the building industry and agriculture. Further research on beneficiation of this bentonite will be necessary and will be justified by big reserves, attaining possibly a minimum 15-25 million t.



Cilek: 4.3. Clays

4.3. Clays Clays are very fine-grained sediments consisting of a single or several clay minerals in addition to non-clay materials. Clay minerals as the main constituents of clay can generally be divided into three groups: kaolinite, montmorillonite and illite minerals. Clays are sediments with more than 50% of clay, the composition of which depends on the chemical properties of the parent rock, weathering conditions and the sedimentary environment. Classification of clays is based on 1) their origin - residual and transported (fluviatile, lacustrine, marine, lagoonar etc.) 2) their composition - monomineral (kaolinitic, montmoritlonitic, illitic) 3) their utilization - refractory, plastic, earthen - and stoneware clays Clay minerals originate under hypergenic conditions, rarely under hydrothermal conditions, and display specific physical and chemical properties. They are divided with regard to their mineralogical structure into those with molecules of (H2O) or ions (OH+). The clay particles are usually below 2 microns with colloidal properties (sorption capacity, coagulation from suspension, electrophoresis, tixotropic properties, rheology etc.). During firing clay minerals display characteristic endothermic and exothermic reactions, caused by an escape of water or structural changes (see, for example, DTA). The main clay mineral is kaolinite with a composition of HAl2Si2O9, or Al2O2 • 2 SiO2 • 2 H20. Besides kaolinite, two other modifications are known - nacrite and dickite. The main structural unit is a silica-tetrahedral sheet which is similar to micas of the total composition (Si2O5) combined with octahedral groups of a total composition [Al2(O, OH)6]. Both layers are bound by oxygens and the structure does not expand with added water, their cation-exchange capacity is low. Kaolinite particles are flaky, of hexagonal shape, often well arranged; sometimes the stacking of these layers may be disordered as this is common to refractory clays. Smectites have already been described in the chapter "Bentonite". Illite is a clay mineral of a structure very similar to that of mica, with few interlayer cations, resulting in weak binding forces between layers and disordered stacking. The illite group often called hydromicas, has a varying chemical composition with less alkalies and more SiO2 than micas. The general composition is that of mineral phengite: from 3 Al2O3 • 6 SiO2 • K2O • 2 H2O to 2.5 Al2O3 • 7 SiO2 • 0.5 K2O • 2 H2O • n H2O. Illite has a good sorption capacity and therefore, if substantially concentrated, may become a valuable ceramic material. Other clay minerals include halloysite, chemically similar to kaolinite, attapulgite (also known as palygorskite), composed of (Mg, Al)2Si4O10(OH) • 4 H2O and sepiolite, a magnesium silicate of a theoretical formula (Si12) Mg9O30 (OH)6 (OH)2 • 6 H2O. In terms of their utilization, the main kaolinitic clays are divided into four big groups: 1. Refractory clays 2. Ball clays (plastic clays, earthen - and white ceramic clays) 3. Stoneware clays 4. Common clays 1. Refractory clays or fire clays are composed mainly of kaolinite and are resistant to temperatures of more than 1,580°C (equivalent to No. 26 Seger pyrometric cone). These clays are used in the production of refractory bricks or monoliths for a lining of blast furnaces, metallurgical furnaces, cement and lime kilns, in alloys metallurgy etc. A big portion (30% or more) of fire clays is used in the production of chamotte - a refractory aggregate which is crushed after firing, then cemented with refractory bond clay, moulted into required shape and fired anew. The result are chamotte bricks or monoliths used as medium-quality refractory material. The fire clays, due to a competition with magnesite, bauxite, sillimanite and the like, have a declining market and therefore, are more


Cilek: 4.3. Clays

often used in non-refractory products formerly the domain of ball- and stoneware clays. Various requirements for refractory clays in the different countries, (Polak, 1972).

PropertyClasses

1 2 3 4

Refractoriness Seger cone Temperature °C

34

1750

33-34

1730-1750

32-33

1710-1730

31-32

1690-1710

Sintering Temperature °C range of sintering °C

easily sintered 1250 300

sintered 1250-1350

300

difficult sintered 1350-1410

200

very diff.sintered 1410 100

Plasticity (bonding) % of opening material

highly bonding 60

bonding 60-30

little bonding 30-10

non-bonding 10

Chemical characteristics content of Al2O3 after firing at 1000 °C

extra high aluminous

40

highly aluminous

40-37

medium aluminous 37-34

weakly aluminous 34-30

Fe2O3 % Maximum 1.5-2.0 1.5-3.0 1.5-6.0 6.0

Grain size > 0.09 mm max. %

0-2 1-5 1-10 1-20

2. Ball clays or plastic clays contain about 70% of kaolinite (disordered), some illite, quartz, smectite, chlorite and carbonaceous material. Organic matter in ball clays darkens the material, sometimes even to black colour, but disappears during the firing. Ball clays are highly plastic, of a high green strength, and are refractory. Plastic clays are highly regarded in the ceramic industry for their long vitrification range and are used in vitreous china, sanitary ware, stoneware and wall tiles. A specific utilization have earthenware clays in the production of porous-biscuit-unglazed porcelain, in sintered porcelain and heavy china. Special ceramics are made of earthenware clay such as majolica or faience. They sinter in a whitish colour at 1,250-1,300°C. General requirements for plastic clays (Polak, 1972):

PropertyClasses

1 2 3 4

Whiteness After firing at 1250 °C

snow white 80

white 80-75

less white 75-65

whitish 65-50

Grain size 0.09 - 2 mm max. % 0.06 mm max. %

very fine 2

10

fine 5 - 5 20-10

fine to medium 2-10 0-20

medium

Fe2O3 % TiO2 %

1.0-1.5 0.4-0.8

1.0 0.4-1.2

1.0 0.8-1.6

- -

Sintering Temperature °C range of sintering °C


sintered 1250-1350

300

difficult sintered 1350-1410

200

very diff.sintered 1410 100

Plasticity % of opening material

highly bonding 60

bonding 60-30


- -


Cilek: 4.3. Clays

Water absorption, weight % 19 12-19 8-12 2-8

Shrinkage at 1250 °C 6 6-12 12-15 15

3. Stoneware clays are partly plastic clays of a lower grade used in heavy products such as sintered ceramic products, pipes, bricks and floor tiles. The fusion point is below 1,280°C (Seger cone below 26) and the vitrification range - i. e. the difference between sintering and deformation temperatures should be at least 100°C. Also lower-grade fire clays can be included in stoneware clays. General requirements for stoneware clays (Polak, 1972):

PropertyClasses

1 2 3 4

Sintering Sintering Temperature °C vitrification range °C


sintered 1250-1350

10

- - -

- - -

Plasticity % of opening material

highly bonding 60

bonding 60-30


- -

Acid resistance resistivity %

highly resistant 97

sufficiently resist. 97-95

little resist. 95

- -

Refractoriness Seger cone Temperature °C

highly refractory 32

1710

medium refractory 29-32

1650-1710

low or non-refract. 29

1650

- - -

Grain size >2.00-7.00 mm max. % >0.09 mm max. %

very fine 0 2

fine 1 5

fine to medium 1 10

coarse 1

20

Shrinkage during sintering % 10 10-14 14 -

In the practice, stoneware clays should sinter at 1,250°C, refractoriness should be below 1,350°C and vitrification ought to range between 200 and 300°C. High-quality stoneware clays are highly plastic with a good refractoriness and could be used as low-grade refractory clays. In the manufacture, two types of ware can be distinguished: fine and coarse stoneware. The first group comprises fine floor tiles and sintered wall tiles, the second group agriculture ware, pipes, chemical and highly acid-resistant stoneware. Stoneware is either glazed or unglazed. A lot of it is used in the household and as ornamental stoneware. Both stoneware clays and ball clays with a high plasticity are used in heavy and fine ceramic uses, a high amount of ball clays together with kaolin, feldspar and quartz for the production of porcelain, pottery, tiles, earthenware, sanitary ware and different technical ceramic products. The clays used in ceramics must be processed to remove numerous impurities-admixtures such as quartz, mica, rock fragments, calcite, dolomite, siderite, gypsum, opal, sulphides, heavy minerals, organic matter etc. The industry utilizes these distinctive physical properties of clays: plasticity - enables the preparation of mass by adding water swelling - increase in volume by absorbing water shrinkage - loss of water by drying at about 110°C and firing at about 1,250°C sintering - partial melting at temperature betwen 450 and 1,400°C depending on clay composition colour - ceramic clays-whitish colour after firing, other tints by coloured clays


Cilek: 4.3. Clays

4. Common clays usually coloured are widespread clays which do not require a particular specifications and processing; they are for local consumption. They are structural clays used in the production of building bricks, roofing tiles, drain tiles, sewer pipes and different structural units of either red or other colour depending on the raw material. These clays are plastic enough for molding and vitrification below 1,100°C. They are composed mainly of illite, kaolinite, smectite, different mixed layered clays, chlorite, mica etc. Some contain more quartz and must be corrected by adding plastic materials, some are highly plastic and are corrected by adding quartz or other hard material such as shales, weathered crystalline rocks etc. About 50% of common clay is used in the production of building bricks and aggregates, roofing tiles etc., 20% is used in portland cement as a source of alumina and silica and the remaining part in different other branches of the building industry such as lightweight aggregates (expandite, keramzite), small household - and agricultural products, even in the wall tile production etc. In Europe, the brick factories are located at many strategic points so that the distance of transport does not extend more than 100 km. Clays for building bricks and similar products should fulfil these requirements (Polak, 1972):

Quality Class 1 2 3 4

Plasticity highly plastic plastic medium plastic lean

Strength modulus of rupture kp/cm2

after drying minimum after firing at 950 °C

50

90

25

150-40

15

40-20

6

below 25

Liquid limit minnimum % 40 25 20 below 20

Drying shrinkage % 12 7 4.5 below 4.5

Sintering shrinkage % 850 °C 950 °C 1050 °C

>13 >14 >15

7.2-13.5 7-14.5

8.5-15.5

4-7.5

4.5-8.0 4.7-9.0

below 4.6 below 4.8 below 4.9

Water absorption, weight % after firing at 850-1050 °C

8 12 15 15

Grain size > 7 mm maximum 0 2 5 20

Grain size > 2 mm maximum 1 15 35 70

Besides the composition clay should posses: total fineness 65-75% with clay content 30-40%, salts not more than 1%, iron content not more than 5%, CaO and MgO content up to 1.5%. Winkler diagram of requirements for different building - brick products based on grain size dustribution (Fig. 4.3.1): Fig. 4.3.1. Winkler diagramme for classification of brick materails with regard to grain size distribution (231 kB) The genesis of all clays in connected with alteration processes due to weathering of alumosilicate rocks and transport with subsequent deposition.


Cilek: 4.3. Clays

Types of clay deposits suggested by Kuzvart (1984): 1. eluvial clay deposits - weathering of carbonate rocks with an origin of smectites 2. proluvial clay deposits - poorly sorted, sandy 3. collucial clay deposits - on slopes 4. alluvial (river) deposits - unsorted clays 5. lacustrine deposits - first-rate refractory clays wilth organic matter 6. salty lakes deposits - hydromicas, smectites, chlorite, admixtures of salt, gypsum etc. 7. glacial, morainic or boulder clays - poorly sorted, hydromicas for solid bricks 8. glaciofluvial clays - rewashed clays of type 7, typical varves 9. eolian clayey-silty rocks - loesses, for bricks and as a corrective component of cement 10. clays of brackish lagoons - low refractory, mixture of clay minerals 11. clays of salty lagoons - alternate with salt and carbonates 12. shallow-water shelf marine clays - < 50 m, in bays 13. shelf deep-water (50-200 m) hydromica-beidellite clays - highly dispersive 14. volcanogenic marine clays - smectites by halmyrolysis of tuffs Also glauconite belongs to the group of clay minerals; it is a hydrous silicate of iron and potassium, but, usually, being a mixture, it varies in composition.Potash ranges from 2.2 to 7.9%. Glauconite is known as green sand, because of its dark green to blueish green colour. Usually glauconite occurs in an admixture with sands and marls of marine origin of the Mesozoic or Tertiary age. For its potassium and kalium content, it is used as a fertilizer in agriculture and as a water softening agent. When mixed with sand it is also used in foundry sands. Other material of this group are claystones of various genesis. Some claystones from older sedimentary formations of the Paleozoic or the Mesozoic are valuable ceramic materials, mainly refractory, known, for example, from productive Karroo beds of the Ecca Formation. In Mozambique there are many deposits of different clays and their distribution is apparently widespread. Most of Mozambican clays are of a low quality, the dominant type is common clay of a reddish colour, less often plastic clay with a whitish tint. In the past, clays, mainly reddish clays, were used in local pottery, and some areas were famous, for example, the coastal area of Xai-Xai and Inharrime, in the N an area in the vicinity of Pemba, inland the area Nacala and some places on the shore of Lake Niassa. While a Portuguese colony, many brick factories were built in different localities using clay from the neighbourhood. Usually, no laboratory tests were made because the experience and estimate of the material were sufficient. With a few exceptions, the only clays used were of Quaternary age-residual or alluvial in origin, mainly highly plastic which needed sandy corrections. All clays of reddish, brownish, yellowish, whitish and greyish colour are common clays. In Mozambique, common clays, even those for brick making, are called "ceramica vermelha" (reddish ceramic), and white plastic clays may, sometimes, be even of a refractory grade. The testing of these clays started a few years ago and is decribed below. Almost no data are avaiable on clays of sedimentary formations from the Karroo up to present. It has been anticipated, that lower Karroo formations may contain ceramic-grade clays and refractory clays. Cretaceous clays are used at Nacala in an alumina-silica correction of pure limestones in the cement production. Tertiary clays were tested at Sabie near Maputo, but were found to be calcitic. The main source of clays for local production are Quaternarydeposits. Calculation of reserves of several explored localities: Ar 1 Namaacha reserves of 9,985 t for white ceramics Ar 2 Umbeluzi reserves C1 + C2 of 972,400 t for white ceramics Umbeluzi reserves prognostic of 529,520 t for white ceramics Umbeluzi reserves C1 + C2 of 3,081 210 t for coloured ceramics


Cilek: 4.3. Clays

Umbeluzi reserves prognostic of 1,960 050 t for coloured ceramics Ar 9 Xai-Xai reserves B + C1 of 1,889 400 t for coloured ceramics Ar 11 Inharrime reserves C1 of 747 000 t for coloured ceramics Inharrime reserves C2 of 210,000 t for coloured ceramics Ar 18 Dondo-Inhamizua reserves C1 + C2 of 648,280 t for coloured ceramics Ar 20 Quelimane reserves C2 of 2,950 000 t for coloured ceramics Ar 23 Namacurra reserves prognostic above 15,000 t for coloured ceramics Ar 32 Nampula reserves C2 of 81,990 t for coloured ceramics Ar 35 Pemba reserves A of 1,360 000 t for coloured ceramics Ar 37 Lichinga reserves C2 of 479,400 t for coloured ceramics Ar 38 Area of N'guri-Diaca with reserves A of 709,400 t for coloured ceramics Area of N'guri-Diaca with reserves prognostic of 867,000 t of coloured ceramics Selected clay localities are shown in the attached map (Fig. 4.3.2).

Fig. 4.3.2. Occurences of clay and kaolin (413 kB)

Fig. 4.3.3. Cross section of clay deposits in Maputo valley (Geol.Institute, Beograd, 1982) Bela Vista, Salamanga (506 kB) In order to obtain a better understanding of the situation in the ceramic industry of Mozambique data are present on some more recently investigated clay localities (from S-N). In the vicinity of Maputo, the locality Salamanga (Bela Vista) was examined in 1979 and again in 1985. The clay deposit is of Quaternary age, and of sedimentary origin, the clays were deposited in a marine environment. Diallo (1979) estimated reserves of 2,093 023 t of clay suitable for the production of bricks and tiles. The belt of clayey sediments is about 300-500 m wide and stretches over 25 km in N-S direction. The thickness of the clay layer is 6 m and below it interlayers of sandy clay and sand with marine shells were intersected (see Fig. 4.3.3). Technological tests disclosed that the clay is very fine and highly plastic, with a high liquid limit and linear shrinkage. Its colour after firing is red and some samples have a unidimensional expansion similar to vermiculite (by 1,000°C). The plasticity limit is very low and the clay must be corrected by sand or ash to be used as brick material, with a maximum firing temperature below 1,000°C. Chemical analyses of some samples (in %):

% SiO2 Al2O3 Fe2O3 CaO MgO SO3 K2O Na2O Cl L.i.

1583-D 53.0 19.5 7.1 0.9 - 2.1 0.15 0.18 0.8 18.4

1586-D 56.9 16.8 6.4 0.6 1.7 4.1 0.14 0.13 1.6 18.4

1591-D 52.2 21.1 11.2 0.7 - - 0.12 0.8 - 10.9

1592-D 48.8 22.5 12.8 0.6 - - 0.12 0.12 - 10.4

Liquid limit in %

1583 - D 1586 - D 1591 - D 1592 - D

38.9 30.4 48.2 48.2

Linear shrinkage % 11 7 13 13.1

after 800 °C 11.3 - - -


Cilek: 4.3. Clays

after 900 °C 12.3 13.4 15.8 16.0

after 1000 °C 13.3 - - -

after 1100 °C - - - -

Water absorption % after 800 °C 16.8 19.0 - -

after 900 °C 17.9 19.1 18.0 17.0

after 1000 °C 14.0 21.7 - -

after 1100 °C - 17.6 - -

Plasticity limit (MPa) dried in air 1.97 3.94 1.37 0.96

after 900 °C 9.01 - 0.56 -

after 1000 °C - 1,87 - -

In 1985, the Geological Institute, Beograd checked the same area with the result that the extension of clay deposit is much smaller and the clay is hardly suitable for brick making. An area of 1.5 km in length and 350-950 m width was explored up to the underground water table. Average chemical analysis (in %):

SiO2 51.30 TiO2 0.99

Al2O3 16.80 P2O5 0.99

Fe2O3 7.64 MnO 0.02

FeO 0.64 Na2O 1.39

CaO 0.24 K2O 1.64

MgO 0.99

The clay shows a low alumina content, a high iron and an increased alkalies content. The only ceramic factory in Mozambique producing wall tiles is situated at Umbeluzi about 30 km W of Maputo. Until 1972, the factory had been supplied with a ceramic mixture imported from Portugal, but afterward production ceased due to a lack of material. Repeated efforts were made to replace imported material and of course first area to be explored for possible clay deposit was the vicinity of the ceramic factory. The areas at Goba Fronteira, Changalave, Resano Garcia, Muamba, Sabie and at Namaacha were explored for white clays. Assenov and Diallo (1982) described the exploration at Namaacha. The deposit near the Anglican church in the town of Namaacha on the border with Swaziland is of eluvial origin; it developed in two weathering zones, the upper one of reddish clay with remnants of rhyolites, the lower one of greyish clay - the zone of removal of sequioxides over the underlying rhyolite body. The thickness of clay is maximally 5 m. The grey clay displays a higher silica content, a lower alumina and iron content. But it is of low plasticity, and possesses average mechanical properties and is reddish in colour after firing. It could be used in the production of tiles and bricks, but not in the production of wall tiles. Results of an analysis of selected samples:

Sample % 2134-C 2262-C 247-D 203-D

SiO2 72.7 77.9 73.9 71.1


Cilek: 4.3. Clays

Al2O3 11.4 10.9 13.1 15.7

Fe2O3 8.5 3.8 4.8 2.5

CaO 0.3 0.4 0.6 0.2

MgO 0.3 - - -

L.i. 4.2 - - -

Liquid limit 28 31 34 33

Plasticity limit 18 19 19 15

Shrinkage limit 9.6 9.9 9.8 9.1

< 2 micron 11 - 22 18

3-20 micron 26 - 28 28

> 20 micron 63 - 50 54

> 74 micron 30 - 15 21

Firing temperature oC 1,100 1,100 1,100 1,200

Shrinkage linear % 6 4 3 7.5

Colour after firing reddish yellowish orange dark yellow

Water absorption % 20 17 18 14

Plasticity limit MPa - 6.4 6.4 8.9

Compression strength - 20.6 14.9 21.8

About 150 km N of Maputo, at the confluence of the rivers Sabie and Incomati, the area was investigated for limestones by Italian geologists. In Tertiary sediments, they discovered a bed, 5 m thick, of clay overlying calcarenites and several smaller beds of marls and calcitic clays (Zuberec et. al., 1981). Macroscopically, the clays are calcitic, of medium grain and of a yellow to brown colour. Analysis of two samples (in %):

% Sabie - 1 Sabie - 2

SiO2 61.66 63.46

Al2O3 5.09 4.88

Fe2O3 4.19 4.26

CaO 6.44 1.46

MgO 3.42 1.85

L. i. 16.33 -

Granulometric analysis of sample Sabie 2: 3.27 mm - 13.85%, 2 mm -13.62%, 1 mm - 10.0%, 0.707 mm -3.20%, 0.5 mm -2.16%, 0.305 mm - 2.02%, 0.208 mm - 3.20%, 0.105 mm - 13.95%, 0.074 mm - 8.50% and 0.053 mm - 2.70%. After firing at 1,250°C, the colour of the clay fraction below 0.074 mm is buff with brown spots. The clay can be classified as arenite calcitic-argillitic with a high iron content unsuitable for ceramics. Other clay localities nearby are situated along the river Incomati at the village Xinavane, E of the town of Magude. Two brick factories were in operation at Xinavane and at Maholela exploiting extensive clay deposits of alluvial origin of the river Incomati. The thickness of clay is minimally 5 m, it is plastic, fine-grained and greyish


Cilek: 4.3. Clays

in colour. It was used for a production of bricks and tiles, and it is still used in pottery at Maholela (Diallo, 1980). Other clay localities are N of Inharrime, where the brick factory at the Muramba river about 23 km SWS of Inhambane is in production. The clays are again of alluvial origin, stretching along the river for the distance of 20 km and a width about 2 km. On both sides, the area is covered by high older coastal dunes. The clay used in the factory is grey, locally reddish, sandy and calcitic, plastic to semiplastic, yellowish to dark reddish after firing. After mixing with sand it is suitable for a production of bricks and blocks. The reserves are 747,000 t of category C1 and 210,000 t C2. In order to build a brick factory in the area Xai-Xai, two localities were examined (Tzonev et Dimitrov,1982): clay-deposit 1. -12 km N of the town Xai-Xai, deposit 2.-1 km out of town, near the road to Inhambane. In addition, one sand locality was examined during the investigation. Both clay localities are alluvial deposits of the river Limpopo. In deposit 1, clay is typically dark grey, humic, very well sorted and plastic, of a type common to the alluvial plain of Limpopo, where big rice plantations are being established. The clay of deposit 2 is brown, very plastic clay at a higher elevation, locally sandy, developed in a swampy river bay. Clay of deposit 1 contains about 20% of volatiles and 70% of particles below 2 micron. It is highly plastic even if mixed with 15-20% of sand and ash, and can be used for a production of bricks of low mechanical strength suitable in inner walls. The clay of deposit 2 is more suitable for brick production, if mixed with 15% sand and 5% ash. In both samples, DTA determinations disclosed more illite than kaolinite. Some results of analyses are following:

% SiO2 Al2O3 Fe2O3 CaO MgO TiO2 K2O Na2O SO3 L. i.

Deposit 1 45.44 16.69 10.38 0.56 1.16 0.61 1.03 0.83 0.52 19.89

Deposit 2 43.40 16.34 8.80 2.10 1.93 0.96 1.03 0.90 0.40 21.10

Reserves of deposit 1 are 790,312 m3 of category B + C1 and estimated 230,000 m3, in deposit 2 - 321,100 m3. The technological tests indicate that the firing temperature must be below 900°C, the clay must be mixed with 15-20% of sand and ash for brick production, and with ash only for a production of tiles; the mixture must be slowly and carefully dried before firing. Several tests were performed with natural material (also with different mixtures):

Granulometry: % (average values) Deposit 1 Deposit 2

< 2 micron 52.17 55.28

2-20 micron 36.22 21.71

20-200 micron 9.56 19.00

> 200 micron 2.50 3.33

1 - 3 mm 0.00 0.11

> 3 mm 0.00 0.00

Liquid limit 79.92 64.00

Plasticity limit 36.92 30.00

Shinkage limit 4.67 6.97

Total shrinkage occurs of clay 2 at 850°C with values of 14.26%, liquid limit 13.36% and plasticity limit 6.84 MPa. The mineralogical determination of the composition by X-rays:


Cilek: 4.3. Clays

Sample 828 - B 835 - B 844 - B 848 - B

Montmorillonite + + + +

Kaolinite + + + +

Montmorillonite-illite + + + +

Quartz + + + +

Tridymite - - - -

Cristobalite - - - -

K-feldspar - - - -

Plagioclase + + + +

Carbonates - - + +

No muscovite and Fe-minerals are present. An example of the suitability of clays for different ceramic end-uses is presented in the Winkler and Avgustinik diagrams. According to Winkler's diagram, some clay samples may be suitable for a production of solid bricks, holed bricks and tiles; the Avgustinik diagram indicates a suitability for stoneware (one sample), tiles (one sample), clinker (one sample) and brick production (Fig. 4.3.4 a, b).

Fig. 4.3.4. a. Triaxial diagramme of grain distribution of Winkler: Deposit 2. Xai-Xai b. Avgustinik's diagramme of clay utilization and chemical composition: Deposit 2. Xai-Xai (506 kB) A brick factory and the clay deposit Inhamizua are located at about 30 km NW of Beira. The deposit is of alluvial origin, marine-fluviatile developed on the bank of the river Pungoe near its estuary. The tide of the sea conditioned the growth of mangroves and a swampy environment. The clay is grey or greenish grey, very plastic (see granulometry and skrinkage limit) with a high content of lignitic material, sometimes with intercalations of sand, remnants of roots and brackish water shells. The thickness is about 3 m up to the ground-water level, and widely extended. This mangrove clay, in fact, the mangrove soil deposited under reduction conditions, very common to coastal areas, is unsuitable for brick production. It is more convenient for the production of light-weight aggregates, because it is expandable - swelling, when properly fired. For brick production it must be corrected by adding about 30% of sand to minimize the high degree of shrinkage; a higher amount of sand lowers futher its mechanical properties. A better corrective material would be ash or milled slag, but these materials are not avaiable. Thonen (1981) calculated reserves of the clay to be 447,000 t of C1, and 220,000 t of category C2. Chemical composition and mechanical properties of several samples:

Samples % 1 (0,3 m) 6 (0,4-2,0 m) 8 (0,3-1,9 m) 18 (0,2-1,5 m)

SiO2 54.76 54.96 54.15 62.00

Al2O3 23.22 24.56 21.77 18.69

Fe2O3 6.39 5.56 6.77 4.44

CaO 0.98 0.85 2.15 2.15


Cilek: 4.3. Clays

MgO 2.26 2.36 2.49 1.76

SO3 0.59 0.75 0.46 0.32

L.i. 9.78 9.40 10.86 8.67

< 2 micron 53 43 60 28

2-20 micron 21 28 22 15

20-200 micron 16 15 16 32

> 20 micron 10 14 2 25

1-3 mm 1 1 0 6

> 3 mm 0 0 0 0

Liquid limit 80 78 71 54

Plasticity limit 34 33 37 20

Shrinkage limit 8.89 8.64 8.55 8.74

Total shrinkage after firing 15.0 15.9 18.4 10.7

Good-quality clay is known from Pemba, where the brick factory is situated between the harbour and the airport. The deposit developed as residual clay over Tertiary clays and limestones. Three samples only were collected around the factory. The clay is suitable for the production of bricks and tiles; some sections of the deposit may provide clay of a better quality usable in the production of glazed sewer pipes. This lateritic red clay is of medium plasticity, has a satisfactory value of shrinkage and is dark red after firing. A negative property is its high calcium content, responsible for a development of concretions inside and on the surface of the body. Chemical composition and results of mechanical tests (Laboratorio de Engenharia de Mozambique -1982, Estudo da Aptidao de Argila de Pemba):

Sample % 1 2 3

SiO2 58.8 59.8 58.2

Al2O3 16.1 17.4 20.4

Fe2O3 4.7 4.9 1.9

CaO 5.1 3.9 4.3

MgO 1.9 2.1 3.9

SO3 0.0 0.1 0.1

L.i. 10.2 7.6 7.7

< 2 micron 28 35 35

2-20 micron 28 17 18

20-200 micron 26 28 37

> 200 micron 18 20 10

1-3 mm 1 1 1

> 3 mm 0 0 0

Liquid limit 58 67 62


Cilek: 4.3. Clays

Plasticity limit 24 24 24

Shrinkage limit 8.66 9.20 9.14

Samples 1 and 2 tested after firing at

920°C 965°C 1,000°C

Water absorption 25.5 27.4 25.5 27.4 25.5 27.4

Total shrinkage 11.4 11.3 11.1 11.2 11.5 11.6

Plasticity limit MPa 6.8 5.1 5.4 4.9 6.7 6.3

Compression strength MPa 11.6 8.3 10.4 12.7 12.4 17.6

Shrinkage limit 10**(-10) MPa

2.36 2.64 - - - -

In the vicinity of Nampula, there are two brick factories, one in the town, one at Momola, 14 km outside the town. The clay deposit was investigated S of Nampula on the bank of river Muapelume. It is a residual deposit with about a 1.5 m thick layer of brownish sandy clay underlain by an about 2.0-2.5 m thick layer of compact grey clay. Calculated reserves were 82,000 t of C2 category, but results of the tests are not known. A bulk sample tested at the brick factory Liberdade in Nampula showed a good quality for brick making (Tzonev, 1981). Widespread in Mozambique are residual deposits of laterite, lateritic clays and lateritic-kaolinitic clays of a different development. One locality near Gurue W of Nampula and N of Quelimane was investigated by Italian geologists as a possible source of clay for brick making. In the area of tea plantations, about 15 km S of the town, an investigation of weathering profiles in morphological depressions disclosed a thickness of about 1.5 m, overlying Precambrian granites-monzonites and migmatites (Bascia-Mariani, 1982). Three samples from different localities: 1 - 0.3 to 0.8 m - white clay 2 - 1.1 to 1.6m - white clay 3 - 0.3 to 1.4 m - weathered clayey rock horizon Results of chemical analysis:

Sample% 1 2 3SiO2 48.2 48.46 58.70Al2O3 30.07 31.12 23.61Fe2O3 2.00 1.92 5.45CaO 0.85 0.57 0.01MgO 1.20 1.10 1.17SO3 0.00 0.01 0.10L.i. 12.44 11.96 9.35< 2 micron 37 50 482-20 micron 15 14 920-200 micron 15 23 8> 200 micron 33 13 351-3 mm 10 5 10


Cilek: 4.3. Clays

> 3 mm 0 0 0Liquid limit % 43 49 55Plasticity limit % 20 24 35Shrinkage limit % 9.27 9.02 10.9

The results show a high content of particles below 2 micron, small plasticity and low mechanical strength. The clay is probably kaolin in the upper part of the profile. It is not suitable for brick production.

Conclusions: Exploited clay deposits of Mozambique are mostly Quaternary alluvial or residual clays of reddish or greyish colour and high plasticity, which need to be corrected by sand or ash to be suitable for a production of bricks, tiles and pottery. Some deposits could probably be used in the production of stoneware and heavy technical and agricultural ceramic products. Ball clays or refractory clays have not been found, but may possibly exist within the sedimentary formations from Karroo to Quaternary. They may be discovered in systematic search for these formations. Fire clay should be developed in the Beaufort Formation of Karroo in the Tete Province.



Cilek: 4.4. Decorative stones

4.4. Decorative stones This group of stones includes a vast variety of commercially valuable stones of igneous, sedimentary and metamorphic origin which can be cut, polished and sculptured and give striking effects with regard to their texture and colour. The value of decorative stone is much higher than that of a common building stone and the products made include such articles as ashtrays, fireplaces, wainscoting material, baseboards, souvenirs, art objects, but mainly slabs, columns, steps, gravestones, monuments, memorials etc. Decorative stones can be used either for exterior or interior purposes. Most of the stones are used in the production of slabs in the exterior using hard resistant igneous rocks, and mainly marbles in the interior. At present, a large number of polished decorative stones are replaced by cheaper crushed ones used in artifical stone and terazzo flooring. Generally, the extraction of decorative stones applies to the minimum volume of 0.5 m3, with a yield of about 25% of total rock volume (normally 30-50%), but in the case of rare decorative stone, even the blocks of several cm3 are extracted. From a genetical point of view, these groups of decorative stone are known: 1. igneous rocks: dark colour such as gabbro, dolerites, serpentinites, diabase; light colour such as granite, anorthosite, syenite, labradorite 2. metamorphic rocks: marbles (crystalline limestones) and its varieties 3. sedimentary rocks: limestones, travertine Decorative stones encompass also a group of rare decorative stones such as dumortierite, amazonite, rhodonite, silicified wood, anyolite etc. In case of rare decorative stones even very small deposits with reserves of several m3 and a size of several cm3 can successfully be mined. Acceptive specifications for an extraction of decorative stones: compressive strength minimum 40 MPa, normally 80 to 110 MPa flexibility strength, dry or water saturated, 10 MPa resistance to scrub wear (abrasion) 0.55 % loss of rock/cm2 porosity up to 3% water absorption < 0.5% specific gravity for marble 2.4 the rock must be easy to polish, resistant to weathering, with small thermal dilatation and conductivity etc. In nature, decorative rock should have certain uniform properties-texture and colour to be able to secure the delivery for many years ahead. An important property for mining is a development of joints and fractures; a high density be deterrent to their utilization as dimension blocks, while a proper system of joints facilitates extraction. Generally, three systems of joints are present in igneous rocks: sheet joints, in subparallel or parallel direction to the surface structure (on small massifs like onion sheets) separating the rock into sheets or beds; "headers", almost vertical joints, which traverse the rock mass and divide it into blocks; rift or "run" joints, also grain joints are vertical and transverse. In igneous decorative stones, these joints marked L, Q and S, are often at right angles and are essential in an extraction of blocks.



In sedimentary rocks, the bedding planes are of greatest importance, whereas in metamorphic rocks the fotiation planes play the decisive role in that they divide the rock mass into small blocks and slabs, often not marketable. Also of importance is the mineralogical composition of decorative stone: in marbles, the presence of hard minerals or soft and porous particles can cause difficulties in polishing; prevailing minerals of good cleavage, minerals with sheet structure are ill polishable and may cause discontinuous polished surface. The durability of polish under climatic conditions depends on the rock - marbles are excellent in a dry climate, but desintegrate under wet conditions. Typical is damage of soluble decorative stones of calcitic composition - dull polish surface and disintegration into thin layers in the aggresive acid environment of modern cities. Therefore natural stones in the form of slabs for a cladding of buildings is less often used and interior applications prevail. Marble slabs of a very small thickness and hence, cheaper, substitute the former thick slabs. In Mozambique almost all decorative stones used on buildings, such as slabs, interior and exterior, steps, small decorative articles and monuments were imported mainly from Portugal in the past. A very small quantity was produced locally using marble from Montepuez in the Province of Cabo Degado. The country is extremelly rich in many types of decorative rocks ready for exploitation and processing. Small workshops were and still are active in Maputo, processing marbles from Montepuez and small scale production of rare decorative stones in art objects and jewellerly is part of the semiprecious and precious stone industry (see Fig. 4.4.1). Decorative stones of Mozambique can be divided into: a) igneous rocks dark coloured "black granites" (gabbros), serpentinites red granites, syenites and brown granites, light coloured "granites"-anorthosites, norites, diorites, granites, rhyolites b) metamorphic rocks marbles (crystalline limestones), lamboanite c) rare decorative stones dumortierite quartzite, amazonite, rhodonite Sedimentary decorative stones have not been investigated as yet in Mozambique.

Fig. 4.4.1. Occurences of marbles and ornamental stones (398 kB) a) Igneous decorative stones Dark coloured "black granites" are, in fact, gabbros and serpentinites developed in many small massifs and sheet-like bodies from Archean to post-Karroo times. So far, this rock has not been extracted in Mozambique. One small locality was explored near Chimoio in the Beira corridor (Geol. Inst. Beograd, 1982). It is a dioritic gabbro intrusion divided into three different outcrops of which the most extensive is on Monte Mecatacata. The hill, NW of the village of Gondola and just 29 km N of the main tarmac road, arises about 80 m above the surrounding plateau built by the Barue Formation-Precambrian gneisses and migmatitic gneisses. Quartz veins and lenses are frequent and run in NE-SW direction. Around the gabbro plutons are large slope debris deposits and many spheroidal blocks up to 15 m3 in size. These blocks represent a part of the reserves.



Gabbro is dark grey and contains hornblende, little quartz and biotite, and plagioclase. It can be classified as a gabbro-metadiorite. The weathered cover on Monte Mecatacata is about 10 m thick with typical rounded blocks of gabbro inside. The area of pluton is small-about 2 km2. Results of physico-mechanical tests of four samples: Compression strength maximum 2,591 - 2,428 kg/cm2 minimum 2,264 - 1,816 kg/cm2 Compression strength-water-saturared samples: maximum 2,489 - 2,295 kg/cm2 minimum 1,989 - 1,795 kg/cm2 Compression strength after freezing: maximum 2,438 - 2,244 kg/cm2 minimum 2,338 - 1,734 kg/cm2 Water absorption at N. P. conditions 0.10-0.07% Apparent porosity 0.02 % No colour or structural changes were noticed after a freeze-defreezing test and Na2SO4 treatment. The gabbro is of very good quality and has decorative properties. It can be used in exterior horizontal and vertical linings, monuments, curbs, naturally in the form of a crushed aggregate. It can easily be cut, dressed and polished. Reserves calculated for three gabbro outcrops: 800,000 m3 probable 1,153 000 m3 prognostic 1,953 000 m3 total Another locality of olivine gabbro was investigated at Monre Mesa NW of Memba, N of Nacala port and near the seashore. Monte Mesa is a prominent inselberg about 120 m high, 1.5 km wide and 2.1 km long. The rock is almost black, compact, disintegrating into blocks of 2-10 m3. It is of kelyphite texture and is composed of plagioclase, rhombic and monoclinic pyroxene, olivine, amphibole and blades of biotite. It lends itself well to cutting, polishing and possesses highly decorative properties. It is an ornamental stone which can be used both for small decorative objects and monuments, gravestones and slabs. Its properties are these (Research Institute of Materials and Structures, Beograd, 1984): Resistance to pressure: dry maximum 250 MPa minimum 230 MPa water-saturated maximum 235 MPa minimum 230 MPa after freezing maximum 226 MPa minimum 217 MPa Resistance to scrub wear 7.68 cm3/50 cm2 mass volume gp 2.97 Mg/m3 porosity 0.020 %



persisting resistance to Na2SO4 One of the biggest sites of gabbro occurrence in Mozambique is the post-Karroo ring complex of Gorongosa situated W of the Urema trough. It is about 30 km long (N-S) and 25 km wide. On the E side it is composed of syenites and granites, the W-part of the ring is of gabbroic composition. It rises 2,000 m above the surrounding plateau. The gabbros have intruded first, probably in the form of a flattened lopolithic body. This was later intruded by a granitic diapir and finally, a narrow subvertical sheet of gabbroic rocks intruded the central granitic core. The gabbro is a compact dark rock with good mechanical properties; it consists of tholeiitic gabbros with labradorite and clinopyroxene and some norites and olivine gabbros. An interesting rock with probable decorative properties is micropegmatite granite (graphic granite) with albite, orthoclase, quartz, clinopyroxene, hornblende, chlorite and biotite forming the central core of the complex (Hunting, 1984). Many other gabbroic massifs occur within the Mozambican belt. Just recently, a small massif of gabbro was investigated at Machipanda on the Zimbabwean border. The gabbro is almost black, very fine-grained, with alternating green and black minerals of about 1 mm. It disintegrated into blocks of different size. It is an excellent rock for a production of polished stabs. The extension of the massif is 2 x 1 km. Several types of dark rocks are present in the Tete gabbro-anorthosite Complex. Ultramafic rocks are poorly represented, but occur in some localities. Pyroxenites form green, granular medium-grained rocks with augite, hypersthene and plagioclase with olivine which, if predominant, produces peridotites. Numerous basic dykes of dark grey dolerite composed of plagioclase, augite and less pyroxene cut through the massif Some are 10 m thick (see Fig. 4.4.2).

Fig. 4.4.2. Schematic Map of Mid-Zambezi Province with Zambezi rift and "the Mylonite Zone" (Hunting, 1984) (607 kB) In the Manica Province, many thick and long dolerite dykes cut the Archean rocks. One of this dyke is in fact diabase composed mainly of serpentinite and amphibole. Serpentinite-metamorphic product of peridotite and related rocks was known to the old Greeks and Romans as verd antique. It is a beautifull rock of deep green colour often with streaks of light-colour calcite. This rock is often too much jointed and therefore unsuitable for use as dimension stone. In Mozambique, serpentinites are connected with deposits of asbestos and talc and are found at Manica (Serra Morrumbala and several other belts of the so-called green schists), in the area of Mavita, in small localities of the Cabo Delgado Province and in bigger accumulation in the Monte Atchiza Complex in the Tete Province. The complex consists of serpentinite, gabbro and norite with minor peridotite and pyroxenite (Real, 1962). All these rocks may represent a nice decorative material. The second group of igneous decorative rocks include red granites, syenites and brown granites. The only locality of red granite, resembling the Scandinavian rapakivi red granite was discovered on the bank of Lake Niassa at Monte Tchonde E of the village of Meponda in the Niassa Province. The massif covers about 12 km2 of ring-like structure which penetrated the surrounding Precambrian migmatites, which were uplifted and deformed. Over an area of 12 km2, 95% of the massif consists of granite. Several facial changes were observed in the size of phenocrysts, the colour of feldspars and the quartz content. Red granite covers an area of about 6 km2, blocks of extractable dimension attained up to 10 x 5 x 5 m and the reserves of 60 million m3 were calculated (Fig. 4.4.3).



Fig. 4.4.3. Monte Tchonde - red granite (615 kB) The rock of interest is of pink colour from K-feldspar, coarsely grained. It contains also white grey plagioclase and glassy quartz, biotite, traces of zircon, epidote, apatite and muscovite. The texture is allotriomorphically granular. Result of physico-mechanical tests: volume weight g/cm3 dry particles 2.51-2.64 saturated 2.60-2.65 water absorption % 0.4 - 0.6 aggregate impact value % 24.9 - 29.5 aggregate abrasion value % 20.0 - 39.5 Syenites of Mozambique form several young massifs connected with movements along the East-African rift valley. Nepheline syenites have been already described. Apart from these there are several other syenite facies. A typical example is Monte Morrumbala a big massif N of river Zambezi composed of syenite, granite and minor feldspathoid syenite. Alkali granite is pink, medium-to coarse-grained, with 10% of alkali amphibole, 60% of orthoclase-perthite and 20-30% of quartz. Alkali syenite with quartz contains 10% of mafic minerals, 3-10% of quartz and orthoclase-perthite. Alkali syenites from Morrumbala contain 10-20% of coloured constituents (augite, riebeckite) and are of a light pink colour. Other massifs such as Chiperone, Tumbine, Mauzo consist mainly of nepheline syenites, an excellent ornamental stone for slabs, sculptures, monuments etc. Other massifs such Salambidua with hornblende-syenite (Conguene, Chiperone etc.) and with part of the massif composed of syenites, cannot be used as ceramic raw material but, could serve as a source of decorative stones. Brown granite called "granito castanho" in Mozambique known from the provinces of Tete, Manica, Sofala and Zambezia is, petrographically, a charnockitic granite. It is a dense, brown, tough rock, medium to coarse grained, of equigranular or porphyritic texture. Fresh surface is mainly dark grey or black and quartz and feldspars have a characteristic dark grey colour with a greasy lustre (Hunting, 1984). They are composed of quartz, alkali feldspar, plagioclase, hypersthene, augite, biotite, hornblende, with abundant opaque minerals. In composition, they range from true granite and syenite to granodiorite and quartz monzonite. The textures of the rocks are either even-grained or porphyritic. They form masses or conformable sheets and are developed as mountains and ranges NW of Tete and near Furancungo. They are mainly conform to the country rocks but intrude in fact, the Chiperone complex and the Luia Group. The age of brown granites is 1,050 + 20 -10 m.y. (Hunting, 1984, pg. 128). These granites could certainly be used as decorative stones, but nobody checked their properties as yet. The last group of igneous origin are light-coloured rocks. These rocks are well known from the Tete gabbro-anorthosite Complex, which is composed predominantly of light-coloured gabbro and norite with subordinate anorthosite in layers or later intrusions. The textures are medium -to very coarse -grained, with a widespread replacement of original minerals, in places, zones of cataclasis and shearing



are common. Fresh gabbro and norite is light grey, homogeneous, unfoliated granular rock composed of plagiclase, pyroxene and iron-titanium oxides. The plagioclase is sodic labradorite. The pyroxene is either augite or hypersthene (Hunting, 1984). Anorthosite is light grey or white composed of andesine or sodic labradorite, with a minor proportion of pyroxene and opaque minerals. Alkali feldspar, biotite, sphene, sulphides and garnet occur as accessory minerals. The textures are granular and, similar to the gabbros, plagioclase is replaced in some places by scapolite and pyroxene by hornblende. Some localities of the Tete complex were investigated by the Geol. Inst. Beograd (1982), which described an anorthosite massif of the Monies Inhangoma and Sicarabo with labradorite of grey to purple colour, fine grained with huge reserves and of ornamental quality (near Moatize). Another site of occurrence of ornamental stone has been described from a norite massif at Necungas close to a railroad in the SE corner of the Tete complex, with good quality stone. Light-coloured decorative stones can also be found in big lava layers and intrusive bodies of rhyolites of the Stormberg Formation of the Upper Karroo in the Lebombo Mts., and in other volcanic rock areas of the Karroo. The rhyolites are greyish to whitish in colour, dense and compact and, generally, of high mechanical strength. Rhyolites and trachytes are part of light-grey, acid lavas group forming several lava flows interlayered with amygdaloid basalts, tuffs and pyroclastics stretching from the Lebombo Mts. to Chibabava, Lupata and the Mid-Zambezi rift.

b) Decorative rocks of metamorphic origin The only locality in Mozambique which produces marbles of decorative quality is Montepuez in the Cabo Delgado Province. There are several deposits within the belt of crystalline rocks stretching over 30 km at a width of 1.5 km. The main quarries are situated 3 km N of village. The deposit is connected with the port of Pemba by a tarmac road of 215 km. The deposit is part of the Supergroup Chiure of sedimentary origin and 780 m. y. Apart from marbles the productive belt includes amphibolites, gneisses, quartzites and some intrusive granitic massifs. The belt is highly folded and tectonically disturbed by the grade of metamorphism diminishing in SW direction. Several isoclinal structures are developed, with monoclinal folds of NE-SW direction and inclination in the quarry area of 55°. The marbles are macrocrystalline with quartz, feldspar, pyrite, chalcopyrite and rutile in some places with wollastonite. The genesis of marbles is a marine deposition of limestone with some intercalations of silt, sand and clay followed by regional metamorphosis of thermal type and concluded by contact metamorphosis and hydrothermal alteration with the origin of sulphides, recrystallization of calcite (big crystals) and an origin of druzes of quartz. The marble contains about 50% of calcite and 50% of dolomite with layers of amphibolites, gneisses and schists 5 to 50 cm long and 2-6 cm thick. The weathered surface zone is 4-5 m thick, with iron hydroxides and hematite. There are three systems of joints which enable an extraction of blocks averaging a volume of about 1 m3. Types of marbles produced (according to their classification at the Montepuez quarries and workshops in Maputo): marmore branco - MB - white marble marmore branco de neve - MBN - snow white



marmore branco cinzento claro - MBC - white to light grey marmore branco com amphibolite - MBA - white with amphibolite marmore cinzento - MC - grey marmore cinzento claro - MCC - light grey marmore cinzento escuro - MCE - dark grey marmore tipo magram MM. The most interesting is the magram type marble representing a mixture of all marbles described above with a higher content of silicates, feldspar, amphibole, schists and secondary calcite in big crystals. Generally, the Montepuez marbles are high-quality ornamental stones except for layers with hard minerals such as quartz and rocks with quartzites and pegmatites. The best-quality marble is expected to be snow-white saccharoidal. The marbles are used in small artistic objects, souvenirs, monuments, sculptures. Naturally, they can be used as building material (impure layers), in metallurgy, a refining of sugar, soda production, in foodstuff and agriculture. Their possible exploitation has been known to local inhabitants for many centuries, however small-scale mining was started as late as after World War 2 by the company Monteiro Lda. Systematic exploration started in 1981. The production of blocks (1.3 - 1.5 m3) is fairly small:

1979 304.5m3 1982 562.7m3 1985 2241m3

1980 295.5m3 1983 406.0m3 1986 11372m3

1981 126.8m3 1984 574.0m3

Reserves calculated by Bulgargeomin (1983):

White marble category C1 3,800 000 m3 category C2 2,360 000 m3

Light grey category 2,400 000 m3 category 870 000 m3

Grey category 7,650 000 m3 category 4,000 000 m3

Magram category 2,150 000 m3 category 2,600 000 m3

Total reserves 25,844 000 m3. Estimated block recovery is between 40 and 50%. Technology properties: porosity 0.58% water absorption 0.21% density 2.85 g/cm3 Compression strength dry 2.839 kg/cm2 Compression strength saturated 2.893 kg/cm2 Hardness coefficient Kb very high = 1 Many other marble deposits are known to occur within the Mozambican belt of which some may represent decorative stones of high quality such as in the Formation Barúe, Fingoe, locaties in Angónia,



near Lichinga, E of the Chiré trought and others. Another metamorphic decorative rock discovered in 1983 by the Jugoslav geological team is lamboanite, a variety of migmatite of extraordinary quality (see Fig. 4.4.4).

Fig. 4.4.4. Geological map of the lamboanite occurence - Namiola area (Geol. Institute, Beograd, 1984) (474 kB) It occurs in the quarry at Monte Xica 35 km W on Monapo and at about 100 km from Nampula. The quarry produces crushed stone. A lens of lamboanite 500 m long and 80 m wide directed from NNW to SSE occurs at the bottom of the hill (Fig. 4.4.5).

Fig. 4.4.5. Lamboanite quarry on Monte Xica-Namialo (Geol. Institute, Beograd, 1984) (268 kB)

Lamboanite is a rock of light grey colour with a greenish shade, medium-grained, containing microcline perthite, plagioclase, quartz, amphibole and biotite. The face of the quarry is 100 m long and 20 m high. The estimated volume of dimension blocks is about 30%. Ornamental qualities of the rock are obvious and its extraordinary pattern is due to a succesion of dark and light-coloured mineral concentrations. The rock is tough, difficult to cut and polish. Isometric grains prevail over platy minerals and this is reflected in its indistinct foliation. It can be used as a facing and building stone in civil engineering, and a production of slabs both for the interior and the exterior. Reserves amount to 1,530 000 m3 of which about 500,000 m3 can be extracted in dimension blocks. Compression strength in a dry state minimum 132 MPa maximum 143 MPa Compression in a water saturated state minimum 131 MPa maximum 140 MPa Bonding strength maximum 12.5 MPa minimum 10.8 MPa Resistance to abrasion at machine cutting As 8.28 cm3/50 cm2 Water absorption 0.26% volume mass 2.61 Mg/m3 porosity 0.019 Generally the compressive strength is moderately high, bonding strength good and abrasion very good. c) Rare decorative stones include these varieties: dumortierite amazonite rhodonite, rhodochrosite others Dumortierite is, in fact, quartzite with dumortierite known to occur in one locality only, i. e., at Chicoa in the Tete Province near the Cabora Bassa dam. The rock is extremely distinctive in colour, a cobalt-to



greyish blue and is collected from the surface of the eluvial deposit as pieces measuring several 10 cm3. It is used in the production of small ornamental articles. Amazonite is a green feldspar of very distinctive colour, with excellent cleavage found in many pegmatite deposits of the Alto Ligonha district, in the Monapo structure, Tulua pegmatite near Nacala, Nipepe in the Niassa Province and other places. It is mined in small blocks and used in the production of small articles of cheap jewellry such as bracelets, necklaces, pendants etc. Reserves are difficult to calculate, in some pegmatites they range in volume between 10-50 m3. Rhodonite is a brownish-reddish, and also pink manganese silicate with typical black veins of manganese of the formula Mn(Si03). It is used as an ornamental stone for small-size objects and souvenirs such as ash trays, stone eggs, book supports, pendants etc. In Mozambique, it occurs at the Tete Province in the form of nodules in manganese mineralization zones of the Formation Rushinga near the Zimbabwean border. According to Alves (1961,1964) it is found in four zones: Mazoe N Mazoe S Catambula Blaundi Bonga Manganese mineralization with Mn-oxides and Mn-silicates and carbonates (the latter at Mazoe N) occurs in gneisses in the form of lenses associated with Mn-garnets. The thickness of zones is a few meters (2-5m) at a length of a few km. In terms of its genesis it originated from metamorphosed sediments in contact zones, giving rise especially to the origin of rhodonite. Rhodonite occurs mainly at Catambula-Serra de Inhandendje inside nodular gneisses measuring between several cm and one m. Mn-minerals are pyrolusite and rhodonite accompanied by spessartite, rhodochrosite, hematite, magnetite and Mn-garnets. Composition of rhodonite (Real, 1966): 44.69% Mn, 24.30% SiO2 and 0.006% P. Rhodonite can serve exceptionally as manganese ore in small quantities in steel production. Other decorative stones used in jewelry and small decorative articles in Mozambique include banded ironstones found in many iron deposits, or iron-titanium oxides of the Tete anorthosite complex which may have very interesting colour after polishing.

Conclusions: Mozambican decorative stones include large-volume rocks such as marbles, gabbros, serpentinites, red granites, syenites, anorthosites and lamboanite and, rarely, decorative stones of a small volume such as dumortierite, amazonite, rhodonite and others. The desire of mankind for natural stones of distinctive decorative properties at present and in the future will certainly secure the development of the manufacture of slabs, dimension blocks for monuments, decorative objects and souvenirs. The recent discovery of exotic migmatite-lamboanite will be certainly followed by discovery of other interesting decorative stones.



Cilek: 4.5. Diatomite

4.5. Diatomite Diatomite or diatomaceous earth or kieselguhr is a lightweight, white to gray coloured friable sedimentary rock composed mainly of shells or frustules of diatoms. The algae Diatomaceae - are unicellular floating plants living in fresh, brakesh or marine environment of shallow water. The shells are made up of silica extracted from the water and, therefore, the biggest accumulations of diatoms are present in basins near the volcanic centres with a high supply of dissolved inorganic salts. The cell measures 5 to 1,000 micron, but mostly within a range of 50 - 100 micron. One cubic meter of water may contain one billion diatoms and their reproduction is so fast that a layer of several mm can develop during one year. Diatomite deposits range in thickness of several to several ten and hundred of meters. They contain clay, silt, volcanic ash and other impurities and grade into diatomaceous shales after diagenetic changes. Commercial diatomite contains over 80% of silica, the remaining compounds are Al2O3 and Fe2O3. Bulk density of diatomite is about 0.5 to 0.9 kg/cm3, bulk specific gravity 2.1 and more. The porosity is extremely high reaching 90% with up to 30 millions of shells in 1 cm3. They are used mainly (60-70%) as a filtering aid in clarifying liquids. The principal requirements are diatom skeletal constitution, density and soluble impurites. Their main application is in a purification of water, wine, beer, juices, mineral oils, filtration of dry-cleaning fluids and separation of oils and chemicals. Another major use is that of a filler, a flatting agent in paints, anti-blocking agent in polyethylene production, reinforcing agent in silicone rubber and paper filler. In addition they are used as pesticide carriers, storage and transportation of hazardous liquids, as a mild abrasive and in polishes. They used to be of importance in the production of dynamite. A large proportion of impure or low-quality diatomite is used in the building industry, e. g., for thermal and acoustic insulations. The main increase is expected in their application as filters where diatomite is by far superior to other materials. Although raw diatomite was used in the early days of the filtration industry, nowadays most material is calcined in order to burn all organic matter and render it less susceptible to chemical attack by acids and alkalies. Furthermore, calcination converts all impurities to fused slags which can be removed at a later stage. Flux calcination is applied to obtain grades with the biggest filtration speed, using mostly soda ash as fluxing agent. Chemical composition of diatomite:

% 1 dicalite USA 2 Idaho USA 3 Kenya Soysambu 4 USSR Kamyslov

SiO2 86.8 89.82 84.50 79.22

Al2O3 4.1 1.82 3.06 6.58

Fe2O3 1.6 0.44 1.86 3.56

TiO2 - 0.07 0.17 0.48

CaO 1.7 1.26 1.80 1.43

MgO 0.4 0.54 0.39 0.98



Na2O K2O

0.81.03 0.22

1.19 0.91

0.65 0.72

L. i. 4.6 4.02 6.08 4.91

In Mozambique, several promising deposits of diatomite are present in the coastal belt. All these deposits are of Pleistocene - Holocene age and probably originated in lagoons, river depressions and lakes on different elevation levels. In my opinion, the best conditions for an origin of these deposits must have been available in interglacial times of the Pleistocene, when a rise in the water table of the sea level chocked the openings of the rivers and extensive inner lakes (ria lakes) originated along the river beds. Nowadays, many sites of diatomite occurrence, which may probably have been eroded with prograding denudation during glacial times are covered by dune sands. Several still unknown deposits may be discovered in sedimentary sequences of the Tertiary or Cretaceous especially in the S- part of the country formed during the development of the Limpopo paleodelta, in the Zambezi paleodelta, Mid-Mozambique and in depressions of the rift valleys, i. e., Shire and Urema troughts, Niassa rift and in a sedimentary basin on the coast of N-Mozambique. Diatomite areas from S to N (see Fig. 4.5.1):

1. South of Maputo-Bela Vista, Boane 6. Panda

2. Marracuene-Manhica 7. Inhambane

3. Macia-Ch6kwe-Magude 8. Nova Mambone

4. Chicomo-Manjacaze 9. Pemba

5. Inharrime-Chidenguele

Fig. 4.5.1. Occurences of diatomite, glass and foundry sand, building sand-gravel (392 kB)

Diatomite deposits have been known since 1940, detailed exploration started in 1960. In 1970 the deposit Diana at Manhica was explored. The deposit Beta Vista contains diatomite of no economic importance. It developed in occasional swamps and marshes of the younger Quaternary at the elevation of 140 m above sea level. Nowadays the whole area is covered by dunes underlaid by silt, clay of dark colour and clayey sand with some diatomite. It is expected that diatomite layers may be found in deeper layers of Pleistocene deposits. Around Boane, 30 km W of Maputo, diatomite layers of 0.25 to 0.80 m are known overlying Pleistocene sands of the dune. Diatomite is directly on the surface and part of the deposit may be eroded already. Its bulk density is 0.6 g/cm3, average thickness 0.5 m, and it covers an area of about 1 km2. Estimated reserves are 300,000 t, but futher reserves in the vicinity may be up to 1 and 2 million tons. Chemical analyses of diatomite Boane deposit (Geol. Inst., Beograd -1984):

Sample 2010 2021 2014

SiO2 % 92.09 87.42 88.84

Fe2O3 0.60 1.59 0.79



Al2O3 2.49 4.86 1.01

CaO tr. 0.16 0.17

MgO 0.20 0.23 0.41

P2O5 0.03 0.0.02 0.11

TiO2 0.33 0.35 0.16

Na2O 0.30 0.21 0.18

K2O 0.12 0.09 0.20

L.i. 3.73 5.02 8.22

The investigation at Boane (1982-84) disclosed a greatly erratic incidence, diatomite had not been deposited in situ, but transported and later eroded. The area, about 280 km2, is not very promising. The best deposits of diatomite are located in the vicinity of Manhica, where in 1970 the beneficiation plant should be constructed. The probable area with ditomite layers covers about 1,100 km2 (see Fig. 4.5.2). Another area known as Alvor investigated already is situated at about 15 km NW of Manhica. There 2,600 m2 were stripped of overburden and a diatomite layer of 1 m thickness was uncovered. The deposit is of elongated shape in N-S direction, 550 m long and 200 m wide. Estimated reserves on 2 km2 are 960,000 t (average thickness 0.8 m).

Fig. 4.5.2. Block diagramme of trench on Manica diatomite deposit (Geol.Inst., Beograd, 1984) (211 kB)

In the area of Manhica the deposits of Diana and Marina were investigated. The Diana deposit is located at about 20 km NW of the village of Manhica. There are both a tarmac road and a railroad between Manhica and Maputo. The deposit is roughtly oblong in shape, 3.6 km long and 450 m wide, oriented in a N-S direction (Fig. 4.5.3). It consists of three layers of diatomite: * The upper section is a compact material of about 0.5 m in thickness which should be regarded as overburden. * The central part is separated from the upper section by a 1.5 m thick sand bed. * The lowest section is represented by the oldest diatomite bed, separated from the central part by a 0.5 to 1.0 m thick layer, and continues to a depth of more than 9 m. The middle layer is fairly sand-contaminated. The lower layer consists of almost pure diatomite. A study of this lower layer disclosed the presence of about 27 genera and 100 different species. The diatomite is of Upper Pleistocene age and was deposited in brackish to freshwater environment (pH 6). The total thickness of the deposit is not known but an assumed depth of just 3 m and a bulk density of 0.32 kg/cm3 estimated resources are 1,500 000 t. Taking into consideration a loss of 50% due to processing, there should still be at least some 750,000 t of saleable diatomite which gives a mine life of 25 years at an annual production of 30,000 t. Fig. 4.5.3. Typical section of diatomite deposit Diana (202 kB)



A second area known as the Marina deposit is, in fact, an extension of the Diana deposit to the S. A concession for this deposit was requested in 1974. Total reserves for this deposit should also be in the order of 1.5 million t of dry diatomite. Three representative samples from the Diana deposit were subjected to extensive chemical and technologial testing. Sample A was taken from the middle layer, sample B from the uppermost layer of the boottom bed and sample C near the water table in the middle of bottom bed.

A B C

Diatomite content after elutriation test (%) 56 48.5 77

Sieve analysis + 30 mesh - 30 + 100 mesh - 100 + 200 mesh - 200 mesh

1.6 26.8 16.2 55.4

2.2 51.6 5.4 40.8

1.0 14.4 7.6 77.0

Percentage of sand in each fraction + 30 mesh - 30 + 100 mesh - 100 + 200 mesh - 200 mesh

1.6 25.6 15.4 13.2

2.2 47.2 5.4 5.6

1.0 14.2 7.0 8.0

According to these figures most of the raw material could be used without processing in a sand-separation plant.

Bulk density g/cm3 A B C

- 8 mesh raw - 200 mesh raw - 200 mesh calcined

0.72 0.26

-

0.88 0.34

-

0.44 0.163 0.160

Chemical composition of the Diana samples:

Constituent A B C

SiO2 % 79.38 78.23 85.97

Al2O3 7.24 8.27 3.77

Fe2O3 0.88 0.92 0.43

TiO2 0.38 0.32 0.18

CaO 0.17 0.24 0.13

MgO <0.05 <0.05 <0.05

Na2O 1.33 1.75 1.18



K2O 0.80 0.74 0.59

L.i. 9.04 9.08 6.56

Total 99.27 99.60 98.86

In 1983, the area was resampled; a total 22 samples were taken. Arithmetic mean and standard devitations of 22 samples:

Constituent Mean Standard deviation (22 samples)

SiO2 86.36 3.85

Al2O3 4.21 1.25

Fe2O3 1.18 0.35

TiO2 0.46 0.09

CaO 0.5 0.47

MgO 0.2 0.08

Na2O 0.11 0.03

K2O 0.81 0.17

L.i. 6.56 1.62

Total 100.39

N of Macia near the main coastal road the group of Santa Fe diatomite deposits were investigated. The area is also known as Mazivila. Deposits: a) Muduaine, about 700 m N of Mazivila with diatomite layers up to 1 m thick b) Lagoa Ramo, 5 km SW of Mazivila c) The zone N of the area Mabiele d) The zone of Chicomo about 35 km E of Chicomo covering an area of 11 km2 Important localities are Buana, Lagoa Mayuana, Maculuva and Lagoa Maticuana. The diatomite occurrence is known superficially only and the thickness of these Quaternary diatomite deposits ranges between 0.3 and 1 m. Several old claims were made in this area. For three of these claims, i. e. Nachene, Mazibila and Pequene, resources were evaluated. The claims are situated in an area situated basically within the coordinates 33°00'E and 33°10'E and 24°50'S and 25°00'S. Road connections are good with the main tarmac road from Maputo to the N running 5 km to the E of the area. The diatomite had probably been deposited during the Pleistocene by floodwaters from tributaries of the Nkomati river. Resource estimates for the three deposits:

Deposit Length (m) Width (m) Thickness (m) Tonnage (t)



Nachene 150 13,000 0.5 300,000

Mazibila 2,160 360 0.5 125,000

Pequene 900 720 2.0 415,000

Total 840,000

These results were obtained in 1965. In 1974, a concession was requested for the Pequene deposit. At that time, the applicants estimated total reserves in the order of 3.5 million t of dry diatomite. Chemical analysis of the Pequene deposit (1984):

SiO2 Al2O3 Fe2O3 CaO MgO L. i. Humidity

83.84 -

4.72 1.00 0.92 8.92 1.08

Total 100.48

During the mapping, several sites of diatomite occurrence were discovered; however, samples are not available for testing and analyses. Promising is the whole coastal belt from Macia to Inharrime and from there to Inhambane up to Nova Mambone on the river Save. The depression between the river Save and Beira, which is part of the East-African rift valley, may also contain diatomite, but it does not occur on the surface. The presence of diatomite was suggested by an observation near Pemba (SiO2 - 87.28%, Fe2O3 - 0.71%, CaO + MgO - 1.30%) and indicating some diatomite sites in the Rovuma basin on the Tanzanian border. Conclusions: Among the industrial minerals, diatomite represents a very valuable material of a wide range uses, the importance of which is permanently increasing. Apart from its role as a filter agent and filler, it increases in importance in the field of environmental protection. Mozambique, especially its southern low-lying coastal plain with sandy soil and little economic importance, is very rich in diatomite deposits. Although the reserves are not substantial, owing to the few localities investigated in the past, extensive areas may provide vast reserves of diatomite. The area near Manhica is, at present best prepared for exploitation and a beneficiation factory is in preparation with an annual production of 30,000 t of calcined diatomite (65-75% of the capacity) and 25-35% of flux-calcined diatomite. Minor quantities of dry product could be sold as additives. The present estimates of diatomite reserves surpass 3 million tons.





Cilek: 4.6. Glass sands and foundry sands

4.6. Glass sands and foundry sands Glass sand is a type of normal sand, which is either selectively mined or treated in such a way to comply with the requirements. A basic requirement for glass sand is its chemical composition-the main constituent is quartz with about 99% of SiO2 and 0.05% of Fe2O3 as the principal harmful ingredient, and the grain size of the sand required mainly within the range 0.1- 0.3 mm. The grain size affects directly the melting of the batch, the iron content is responsible for the colour of the glass. Economically acceptable are just psammitic rocks such as sandstones and sands, which can easily be washed, sorted, chemically treated and prepared in agreement with the requirements for each final product. Required chemical composition of glass sands (Polak, 1972):

Quality class A B C D E

SiO2 min. % 98.5 99.0 99.0 99.2 99.3

Fe2O3 max. % 0.040 0.025 0.021 0.020 0.016

TiO2 max. % 0.15 0.10 0.10 0.10 0.05

Al2O3 max. % 0.40 0.30 0.20 0.20 0.20

Requirement for grain size distribution (Polak, 1972):

Quality class A B C D E

< 0.100 mm max. 1.5 max. 1.5 max. 1.5

max. 5.0

min. 85.0 max. 10.0

max. 1.0

0.100 - 0.315 0.315 - 0.500 0.500 - 0.630

min. 90.0 min. 93.0 min.94.0 min. 84.0

0.630 - 0.800 0.800 - 1.00

max. 8.0 max. 5.0 max. 5.0 max. 15.0

1.00 - 1.25 max. 0.2 max. 0.2 - max. 0.2 -

Class A - sheet glass, container glass and certain technical sorts B - sheet, container, technical glass C - sheet, container, household and some special technical glass D - silica opaque glass E - crystal, semioptic and special technical glass Glass-sand raw materials normally contain clay and silt which fill the grains interstices. This material can be removed by washing. The next harmfull constituents are particles of feldspar, mica, dark silicate minerals etc. which usually are present in negligible quantities and are almost absent in well-sorted sand. The problem of a purity of quartz sand for glass can be interfered with by a presence of heavy minerals



such as ilmenite, magnetite, rutile, titano-magnetite and others. These constituents must be removed by magnetic and high-tension electro-magnetic separation, because they are not only the source of a high iron content in glass melt but responsible for the presence of the so-called "black stones" in the glass. After removing all these impurities either totally or partly, the quality of the glass sand will depend on the character of the quartz grains. Well-sorted quartz sand of the so-called polycyclic development is composed of isometric, well-worn rounded grains on which a surface layer of limonite and clay minerals is almost absent. But if present, a special treatment using abrasion or chemical removal methods must be applied. The presence of iron and titanium, besides chromium, vanadium and other elements, can be in connection with an intergrowth of these minerals with quartz (a typical example are spinelides) or in the form of a hematite - and limonite - coatings in deep minute cracks in quartz grains. These impurities cannot be removed by dressing. In the past, other glass raw materials were used - mainly vein quartz, quartzites and quartz pebbles. Pure vein quartz is still being used in the production of high-quality silica glass. Foundry sands are nowadays principally glass sands of a lower quality mixed with a binding agent such as bentonite or organic compounds to attain the required green and dry strength, permeability of the moulds and stability under certain temperature. Quartz sand must sometimes be replaced by chromium sand, when its resistance to high temperature is required. Natural foundry sands are often reddish, with a clay content of up to 30% for which they are called either lean or fat sands. Requirements for foundry sands (for steel castings) -an example (Polak, 1972):

Sand sort Clay binding agent %Harmfull components in quartz mass diam. > 0.01 mm

K2O + Na2O CaO + MgO Fe2O3

quartzitic max. 1 0.5 1.0 1.0

quartzitic 1-2 0.5 1.0 1.0

lean 2-8 0.5 1.0 1.2

semi-fattish 8-115-305 0.5 1.0 1.2

fattish 0.5 1.0 1.5

Very important is grain size distribution, which should be of a medium-size range and the content of fine sand (0.20-0.10 mm) should not be more than 5%, with maximally 1% of grains over 3 mm. Organic natural impurities are not acceptable. The average SiO2 content should be 90-95%, sulphur content below 0.025%. In Mozambique, glass sand deposits have been investigated in the vicinity of Maputo in order to supply a glass factory in Machava (industrial zone of Maputo). Glass sand resources are enormous in Mozambique (see Fig. 4.5.1). They include recent beach sands, dune sands of several zones from the so-called interior dunes to inland dunes, thick alluvial deposits around water courses, a filling of wide and extensive river valleys of interglacial phases development, vast proluvial sand deposits covering the whole coastal belt, cones and fans of sand around the escarpments, psammitic deposits within the grabens of rift valleys, older marine and fluviatile terraces etc. Of an older sedimentary sequence are sandstones of Karroo Formation, sands and conglomerates of



the Lupata group of Lower and Upper Cretaceous, the Sena Formation of the Upper Cretaceous and several sandy sequences of the Tertiary. Weathered profiles of crystalline rocks are generally too clayey, but are the parent material for the sand bodies when worked up in river streams and on the seashore. Within the coastal belt, the biggest reserves of sand are concentrated either in dunes or in thick deposits of river valleys, which were deepened during the glacial periods and filled up during interglacial periods. Some boreholes indicated a thickness of these deposits surpassing 50 m. Dune deposits are either white quartzitic sands, mainly in zone near the seashore, or older dunes of a reddish colour in inland zones. Glass-sand deposits can be found in white sands which are generally pure quartz sands with heavy minerals as the main source of impurities. Therefore, the main treatment of these sands should include washing to remove clay material and electro-magnetic separation to eliminate heavy minerals. The grain size of these sands is acceptable being mainly within the range of 0.1-0.3 mm; prevalent are fine-grained sands, medium-grained and coarse sands can be found around the mouths of rivers, derived from fluviatite sands. Natural foundry sands of an inexhaustible quantity can be found in red sands of older dunes, on which for example the City of Maputo was built. These extend from the S-African border through the provinces Maputo, Gaza and Inhambane to the provinces Zambezia, Nampula and Cabo Delgado. Red sands are naturally a semifattish or fattish variety of foundry sands. The reserves of sand are extremelly large, but mostly unfit for a direct use in the industry. However, various steps of sand treatment may provide all required sorts of sand for glass production and foundries. a) In the glass production, the sand from the deposit Marracuene is used. This deposit is situated at 5 km SW of Marracuene on the main coastal road, about 25 km N of Maputo. The sands are white, fine to medium grained and more than 4 m thick. They developed as marine sands of the Pleistocene age and are covered by 1 m thick red layer of argillaceous sand. The reserves are estimated to more than 1 million tons. Sands from this deposit are transported to the glass factory in Maputo. Analyses of sand (Zuberec et al., 1981):

% %

SiO2 97.78 97.84

Al2O3 0.16 0.18

Fe2O3 0.03 0.14

Cao 0.08 0.34

MgO 0.01 0.40

Na2O 0.16 -

K2O 0.20 -

SO3 0.34 -

TiO2 0.17 -

L.i. 0.34 -

Grain-size distribution (in % on sieves):



1 mm 0.707 0.50 0.315 0.208 0.105 0.074 0.053 total

0.01 0.88 10.10 28.22 36.12 20.04 0.42 0.18 95.97

0.02 0.60 4.25 16.98 39.87 30.46 1.81 0.48 94.47

Weight volume = 1.530 kg/m3 According to the mineralogical analysis the fraction 0.028 mm - 1.0 mm contains 95% of pure quartz, 3% of tourmaline and 2% of reddish-brown limonite; the fraction 0.053 - 0.208 mm has 95% of pure quartz, 3% of tourmaline, 1.5% of limonite and 0.5% of calcite. This sand used in the glass production without any treatment gives the glass a greenish tint. According to the requirements it could be used for container glass, but ought to be dressed before use in the batch in a production of household utility glass. This sand can also be used as ceramic grade in ceramic mixtures and as a foundry sand. b) Chemical composition of dune sand: %

SiO2 92.28 MgO 0.16

Al2O3 3.56 Na2O 0.40

Fe2O3 0.75 K2O 0.54

CaO 1.18

The dune sands are generally not pure in that they contain remnants of shells, feldspar and heavy minerals. Without dressing they represent a source of container glass grade only. c) Near Nacala, Zuberec et al. (1981) discovered kaolinitic sand, which could serve as kaolin, and the sands, after treatment, could-probably be used as glass or ceramic sands. One sample of treated sand: %

SiO2 98.18 MgO 0.01

Al2O3 0.05 Na2O 0.11

Fe2O3 0.78 K2O 0.10

CaO 0.01 TiO2 0.01

d) Mineralogical composition of samples from the town of Beira (in % weight). (Exploration of the Beira corridor for building materials), % of weight:

Sample 1 (from the river

Pungwe-channel)

Sample 2 (beach)

Sample 3 (beach and dune)

Shells 1.78 - -



Quartz 95.86 98.51 98.02

Feldspar 2.12 1.39 1.66

Garnet ind. - -

Mica ind. - -

Limonite ind. - -

Amphibole-pyroxene 0.08 - -

Ilmenite ind. - 0.08

Epidote ind. - -

Kyanite ind. - -

Silimanite 0.09 0.10 0.24

Andalusite 0.08 - -

Grain-size distribution of these sands is shown of Fig. 4.6.1. Also other minerals such as rutile, tourmaline, staurolite, leucoxene, magnetite, zircon and biotite are present (ind. = indicated, in grains below 10, i. e. 0.01%). Fig. 4.6.1 Example of grain-size distribution of sand from Beira (sample from channel dredging) Laboratorio de Engenharia, Maputo (223 kB) e) Highly promising in a production of glass and foundry sands is the mining of heavy minerals of beach and dune sands. Waste-washed and electromagnetically treated sand presents a high-quality quartz sand. If 100,000 tons of heavy minerals a year were to be recovered, and this is a modest enterprice, about 1 million t of quartz sand should be available to cover the needs of several Mozambican provinces for building sand and sands for the glass and ceramic industry. f) The foundry sands used in the only foundry in Maputo are white glass sands and reddish dune sands which are mixed and to which bentonite is added as a bonding agent. The quantity used is very small, hundreds of tons a year. Natural foundry sands are plentiful in Maputo: red dune sands, partly cemented into sandstones from Ponta Vermelha were used when building the old Maputo fortress and many old houses at the Baixa-suburb. Their properties have not been examined as yet. Conclusions: Reserves of glass sand of the investigated locality near Marracuene amount to 1-3 million tons. The sand is suitable for the production of container glass, but should be treated for the production of higher-quality glass. The foundry sand is either glass sand or clayey red sand of older reddish dunes, mixed with bentonite for use in foundry. The reserves of sand, expecially in the coastal belt, are inexhaustible, but the sand needs a particular treatment to be used in required industrial grades.



Cilek: 4.7. Gypsum and anhydrite

4.7. Gypsum and anhydrite Gypsum is a soft, transparent to translucent mineral, commonly in elongated tabular crystals of the formula CaSO4 • 2 H2O, hardness 2 and specific gravity 2.3. Common are "fish-tail" contact twins, the fibrous variety is known as "satin spar", the transparent variety as selenite and the massive fine-grained variety as alabaster. Theoretically, it contains 32.6% CaO, 46.5% SO3 and 20.9% K2O. Anhydrite is more widespread than gypsum and is supposed to be a primary mineral. It is the anhydrous form of gypsum, formula CaSO4, hardness 3.5 and specific gravity 2.98-3.00. Usually it occurs in cleavable masses of a vitreous or pearly lusture. Theoretically, it contains 41.2% CaO and 58.8% SO3. Gypsum and anhydrite are evaporites accompanied by limestone, dolomite and shale. A mixture of gypsum, sand and soil is known as gypsite. Artificial gypsum is a byproduct of the production of phosphoric acid from phosphate rock. About 4.5 t of calcium sulfate is contained in the production of 1 t of phosphoric acid. This byproduct known as "phosphogypsum" is produced each year in a larger quantity than whole gypsum-anhydrite, but is considered as waste because of its less suitable physical properties and impurities. Some countries developed a technology for the use of phosphogypsum in cement and building industries. Anhydrite has a limited industrial use; mixed with coke, shale and siliceous rock, sulphuric acid and cement clinker are produced. Futher uses are in artificial marbles and anhydrite cement. Gypsum is more useful, when heated it loses three-quarters of its water (at 107°C) and changes into the hemihydrate CaSO4 • 1/2 H2O known as plaster of paris. When mixed with water, it hardens into stucco. Plaster can be spread, cast, molded and used in the production of plasterboard - several plies of fiberboard, paper, etc. bonded to a hardened plaster core. For this purpose 40-60% of gypsum is used. Another 40% is used in the cement industry as a retarding agent (3-5% of clinker), in medicine, as a filler in paint and paper, the production of ceramic casting forms, as fertilizer in agriculture (expecially in peanut plantations), in toothpaste and drilling mud. Gypsum and anhydrite are evaporites which originate: 1) in shallow basins and salt flats under arid conditions with an inflow of water which evaporates forming a sequence of calcium carbonate, calcium sulfate and salts. From these shallow basins, a part or the whole gypsum/anhydrite sequence was leached, transported and deposited in deeper basin. This explains the development of several m to several 10m thick gypsum deposits. 2) in lagoons and sabkhas along the periphery of deeper basins with a sequence of lagoonal limestone, gypsum and dolomitic limestone and dolomite. 3) as a "caprock" of salt domes, overlying sharply the top of the dome and originating from a leaching of salt through water-saturated layers. Commercial deposits of gypsum are mainly flat-lying beds of a thickness of several m on the surface or near the surface. An alteration of anhydrite into gypsum is common, occurring from below the surface to a depth of 150 m by hydration whereby the volume increases by 30%. At a greater depth, gypsum loses water and changes into anhydrite. Most of the gypsum deposits originated just by a hydration of anhydrite, when the deposits were denuded. Gypsum is mined with conventional means using the room-and pillar method. After extraction, when still containing some impurities, it is dressed by washing or in heavy-media separation plants to obtain minimally a gypsum concentrate, of 80%, usable in a plaster production of wallboards or when of a higher grade, in medicine etc. In Mozambique literary data refer to five gypsum sites:

1 Porto Henrique Maputo Province

2 Divinhe Sofala Province

3 Vendas Gaza Province

4 Pemba Cabo Delgado Province

5 Bilibiza Cabo Delgado Province



In the area of Porto Henrique several boreholes were drilled and layers of gypsum about 0.5 m thick were discovered at a depth of 29 m. The gypsum was connected with limestone beds outcropping onto the bank of the river Tembe. The possible age of the deposit is Tertiary. In the province Gaza, several small outcrops of gypsum were found, but not evaluated. Even in the Province Sofala, a few remarks only inform on a gypsum occurrence. Lachelt (1985) described gypsum of a thickness of about 15m from evaporites of Temane called gypsum of Divinhe. He describes also sites in the province of Cabo Delgado stretching from the mouth of the river Lurio to the Tanzanian border. Particular gypsum sites were found in the vicinity of the ports Nacala and Pemba. The age of these gypsum deposits is supposed to be Tertiary to Quaternary. Many years of exploration, drilling for oil and gas in coastal Mozambique, revealed important data on the lithological development of post-Karroo formations, which were brought to light also by the discovery of extensive evaporite deposits (ENH, 1986). In Mozambique, two pericontinental sedimentary basins have developed, the S- Mozambique and the N- Rovuma basins. There are several interior rift basins, the Maniamba, Middle Zambezi and Lake Niassa. The most important are the two coastal basins. The Mozambique basin is composed of Cenozoic and Cretaceous marine, continental and deltaic sediments, with a maximum thickness of 12 km in the deepest part-the Zambezi depression. These sediments rest unconformably on Karroo sediments and volcanics. Cretaceous shales with sandstones and glauconitic sands contain commercial gas accumulations in three gas fields- Buzi, Temane and Pande. Gypsum and anhydrite were discovered by means of boreholes in the sedimentary cover of many localities. The oldest anhydrite deposit lies in the S- part of the Mozambique basin near Xai-Xai in an Upper Jurassic? (Lower Cretaceous/Cenomanian) sequence. Sedimentary layers called "Red Beds" are formation of continental origin, represented by red claystones with interbedding limestone, dolomite and red-brown anhydrite (?). These sediments extend apparently up to the outcrops of the Lebombo Mts. volcanics and fill up the S- grabens, discordantly resting on Stromberg basalts ( ENH, 1986). They are overlapped by marine sands of the Maputo Formation-Lower Cretaceous, cenomanian sediments. The extensive development of gypsum and anhydrite occurred in the Oligocene/Miocene sequence. The Oligocene marks the beginning of a general regression common to all of East-Africa with a marked unconformity between Eocene/Oligocene. The regression resulted in a local erosion or very reduced deposition mainly in the area S of Beira. A subsurface Buzi Formation consisting of marine sands and shales of Oligocene age is passing into the Lower Miocene in Buzi area. The Inharrime sandy limestone Formation is an equivalent facies and crops out in the coastal area. During the transition from Oligocene to Miocene a particular facies developed over a limited area mainly S of the river Save - the Temane Formation (Fig. 4.7.1). This formation consists of dark grey, red-brown shales, sandstones and layers of gypsum and anhydrite, stringers of gypsiferrous limestone and sand. The evaporite basin is confined to the central part of the Mozambique basin S of the river Save, to the E of the borehole Balane-1 and the S to the borehole Funhalouro 1. Southwards the evaporites are laterally displaced by red sediments of the Inharrime Formation. The thickness of the Temane Formation is 130-230 m. No detailed descriptions are available, the layers of gypsum and anhydrite are several m to 15 m thick, gypsum nodules and crystals are present in limestones and marls. Calcium sulphate may attain a total thickness over 50 m (Fig. 4.7.2).

Fig. 4.7.1. The map and list of wells in which the Temane evaporates are present (ENH, 1986) (342 kB)

Fig. 4.7.2. Sedimentary Column - Pande Gas Field (ENH, 1986) (363 kB) List of well profiles in Temane evaporites:

No. of ENH

NameTemane Formation

depth (m) thickness (m)

17 Mambone 1. 267-449 181

19 North Pande 1. 181-367 186

20 Pande 5. 192-364 172



22 Pande 1. 183-342 159

23 Lambo 1. 166-364 198

26 Chicuir 1. 155-387 232

27 Macovane 1. 163-392 229

31 Columbila 1. 207-460 253

32 Cherimira 1. 217-454 237

Of Inharrime Formation with evaporites33 Zualane 1.

201-398 398-523

197 125

36 Inhassoro 1. 228-457 229

37 Temane 1. 168-403 235

38 Chaimel 1. 175-384 209

43 Funhalouro 1. 536-679 143

Description of Temane evaporites as a subsurface unit (ENH, 1986, appendix): Type Locality: Temane well no. 1,640' - 1,240' (first observed) - ' denotes feet Paratype(s): Mambone well no. 1, 1,020' - 1,290' Unknown in outcrops Lithology: Gypsum, milky-white crystalline with inclusions and bands of dark green claystones. With stringers of gypsiferous limestone, and medium grained, poorly sorted gypsiferous sandstones. Paleontology: The calcarenites in Temane (gypsiferous) include Rotalidae and tracks of Molluscs Age: Upper Oligocene, based on evidence of fossils in over-and-underlying formations. Environment and Equivalents: Evaporitic, closed basin, more closed in Mambone then in Temane (the latter having limestone stringers and oolites). Equivalents: A Temane evaporite Equivalent (Otve) in Balane 1,200'- 2,100' in shaley, euxinic facies with small nummulites, ostracoda and fish 201 teeth, radiolaria and echinoidea. This section is marginal with regard of the evaporitic basin of Temane-Mambone. (This unit is in part corresponding to the one previously called Dark coloured shales in Final Report Balane 1)." The area covered by the Temane evaporites is shown on the map (Fig. 4.7.1) and extends over of about 35,000 km2. Part of the area is built by two elevated blocks - Pande-Temane high (No. IX of ENH) and southern high Nhachengue-Domo (No. 43 of ENH), the southernmost locality of Temane evaporites, lies inside the Mazenga graben bordering the gypsum area on the W; evaporites occur at great depth (top 536 m - Fig. 4.7.3).

Fig. 4.7.3 Lithological profile of Temane Formation in Pande-1 borehole (Legelt, 1987) (209 kB)

The most promising mining area, i.e., in shallow depth, should be in the Temane-Pande gas field or in ist close vicinity, on the top of the structural elevation (about 150 m deep - Fig. 4.7.4).

Fig. 4.7.4. Geological cross section of the Pande Gas Field (version 3, ENH, 1986) (297 kB) The reserves of Temane evaporites are prognostic only; neither detailed descriptions of beds or analyses are available. The average thickness of gypsum /anhydrite is roughly 10 m only and a reduction in the extension of gypsiferrous sediments is calculated on 20% only. Estimated reserves are still huge - 140 billion t. In 1978, Masson and Ulpiu evaluated evaporite deposits of two gas-fields at Pande and Temane. Quaternary deposits are about 10m thick overlying a Jofane Formation of Miocene age. This formation rests on the escarpment of river Save at the village Jofane, where the sandy calcarenites and limestones, oolithic limestones and sandy marls crop out at a thickness of 115 m. In wells, this formation is composed of hard microcrystalline limestones often dolomitic and locally oolithic. In the well Temane I, olive-grey clay with intercalations of limestone and an occasional layer of gypsum are present in the lower part of the Jofane Formation (thickness 30 m).



The underlying Temane Formation contains gypsum, pockets of anhydrite and gypsiferrous limestone. According to the authors, the gypsum of some wells, represents more than 50% of the Formation sediments. In most wells the thickness of particular evaporite layers attains about 15 m, in boreholes Pande 1 and Temane 1 more than 20 m. Unfortunatelly, just two cores were taken in the whole area. In well Mambone-1 a 3 m long core from a depth of 363 m; "70% of rock is made up of milky white hard gypsum, crystalline, almost pure, with several layers of dark-green compact clay (30%); in the well Temane 1, 2.4 m long core from a depth of 275 m: olive-grey sandy compact marl (0.3 m) and alternation of sandy gypsum with anhydrite and organogenic limestone." The reserves were calculated for an area of 25 km2 only, with an average thickness of 10 m of the gypsum layer, which may equal 500 million t of gypsum with a 50% of ore reduction = 250 million t of gypsum. Two areas recommended for exploration are: Pande and Temane-Columbila, in the stretch of 25 km only. The N- Rovuma basin, of a maximum width of 120 km, contains sediments, probably from Jurrasic? to the Recent age. The Lower Cretaceous consists of continental sandstones of Makonde beds of a thickness of about 450 m (probably Aptian). Overlying strata of marine origin of the Lower Cretaceous developed in a belt E of Makonde beds. They crop out, for example, at Pemba Bay, where they consist of different sandstones with Megatrigonia schwarzi indicating the Neocomian age. The thickness is about 100-150 m. In 1986, an exploratory well was drilled by the Exon Comp., International at Mocimboa 1, situated 14 km SW of Mocimboa; its depth was 3,522 m, penetrating the Tertiary to a depth of 2,303 m (Burdigalian, Oligocene, Paleocene), and the Lower Senonian, Turonian and Cenomanian up to the Albo-Aptian. No evaporite formation was intersected. However gypsum and anhydrite may still be found either near the basins margin, in a Tertiary-Quaternary formation, or as a caprock on a possible salt dome. This idea is supported by the presence of salt domes (Mandawa) in the N part of the Rovuma basin in S- Tanzania. The Upper Cretaceous is particularly well developed in a narrow belt running almost parallel to the coast at distances ranging from several km at Pemba to tens of km at Mocimboa da Praia in the N. Globotruncana marls are present at Pemba, at the base of the cliff and on the S- side of the bay. The marls are gypsiferrous, greyish-brown to brownish yellow, in places silty with typical limey concretions and gypsum flakes. They are of Maestrichtian age and 230 m thick. The same marls crop out at the N of the bay. Of great interest is a suggestion by Flores (in ENH report, 1986) that the physiography of the bay and the attitude of surrounding rocks indicate the presence of a salt diapir in the subsurface, originating probably in the bay and later influenced by a solution of salt and subsequent collapse. Mio-Pliocene beds (e. g. Mikindani beds) are of little thickness.

Conclusions: The rich gypsum deposits are still wholy untouched. They are of substantial importance in the building industry - cement production and plaster, and in other industrial branches. The deposits S of the river Save are traceable over an area of about 35,000 km2 in the Temane Formation with a gypsum (anhydrite) layer, 10-15 m thick. They originated from a chemical precipitation in lagoons during the regression stage of the Oligocene-Lower Miocene. The gypsum /anhydrite resources may be estimated to 140 billion tons, prognostic reserves in the area of the Pande-Temane gas fields to 250 million tons. The deposits are at a depth of 150-200 m, but may be nearer to the surface in some places. Underground mining using room and pilar method is envisaged. Other sites of gypsum occurence are known from wells in "red beds", Xai-Xai area, in Upper Jurassic-Lower Cretaceous (anhydrite), in the Upper Cretaceous of the Rovuma basin near Pemba and probably in younger Tertiary - Quaternary sediments in S- Mozambique.



Cilek: 4.8. Kaolin

4.8. Kaolin Kaolin is a clayey material, white or light in colour, plastic, composed mainly of clay-mineral kaolinite, formula Al2 (Si2O5)(OH)4 and a theoretical composition of 46.54% SiO2, 39.5% Al2O3 and 13.96% H2O. The structure of kaolinite is an indefinitely repeated silica tetrahedral sheet and a gibbsite sheet. The mineral does not expand, has a low cation-exchange capacity, forms flaky pseudohexagonal crystals, which may occur either in piles or be disordered. The crystal structure with flat platelets gives it an excellent covering power and together with whiteness, chemical inertness, nonabrasiveness, makes kaolin a very good filler and coating agent. Apart from kaolinite, kaolin contains other clay-minerals such as illite, montmorillonite, haloysite and others, futher quartz, feldspars, micas, heavy minerals, organic matter etc. Therefore raw kaolin is treated and beneficiated to remove all harmfull particles and to increase its clay content. Generally, kaolin after extraction is washed in troughs, in hydrocyclons and centrifuges, then treated with various chemical and physical methods such as flotation, flocculation, bleaching to remove coloured oxides, high-intensity magnetic separation and finally delamination to break down larger crystal units into individual flakes. Originally, kaolin was used in ceramics for the production of porcelain in China in the third century B. C., later, also in China, in the manufacture of paper. Its use in these fields of production continued up to the present. Other uses of kaolin are as filler in rubber, plastics, paints, cosmetics, catalysts, food additives and filter aids. In the ceramic industry, requirements for kaolin quality depend on its use for example, in fine ceramics, the content of Al2O3 should be a minimum of 34%, Fe2O3 + TiO2 maximum 1.6%, with good rheological properties, tension strength in bending minimum 6 kp/cm2, refractoriness minimum 32 SC. In the production of sanitary ware, white wall tiles and acid chamottes, kaolin of lower quality may be used: Al2O3 + TiO2 maximum 34%, Fe2O3 maximum 2.0%, fluxing agents (K, Na, Ca, Mg) maximum 3.0%, minimum refractoriness 33 SC and humidity maximum 13%. The paper industry requires the highest-quality coating kaolin of specific properties. The whiteness must be higher than 70%, usually over 80%, its viscosity very high and size particles very low (about 80% of particles < 1 micron). With regard to the type of paper produced, a different amount of kaolin is consumed, for example, in writing paper about 30% of the material. Kaolin used as a filler in the rubber industry should correspond to the grade of ceramic or paper kaolin, but the so-called "rubber poisons" should be:0.002% Mn at a maximum, 0.001% Cu and 0.05-0.15% Fe, SO3 < 0.20%. Kaolin for cosmetics can contain up to 1.5% FeO, it must be very fine and of a whiteness of more than 80%. With regard to the limited reserves of bauxite for alumina production, the use of kaolin or kaolinitic clays was tested. It was discovered that kaolin for alumina production should contain a minimum of 32% Al2O3 a maximum of 3% Fe2O3 maximum 47% SiO2, 0.6% CaO + MgO and 0.5% K2O + Na2O. The deposits of kaolin may contain 10 to 90% of kaolinite depending on the type of the deposit and the composition of the parent rock. Economic deposits of kaolin should have a minimum (10-15%) content of the useable fraction provided that, for example, kaolin sands can also be utilized. Normally, commercial kaolin deposits contain over 15% of clay. Raw kaolin has a limited use, in a production of building


Cilek: 4.8. Kaolin

ceramics, acid chamotte, stoneware etc. Waste removed by washing is mainly silt, sand and mica. All these materials can be used: sand in ceramic mixtures, silt, for example, in wall tiles mixtures and fine mica in the building industry in ornamental mortars. Washed kaolin cleared of sand and impure clay, is used in different industries. In ceramics, the ceramic mass requires about 50% of kaolin, 25% of quartz and 25% of feldspar. In cement production, about 20% is used in a mixture for the production of white cement, a large amount of kaolin is used in the production of refractory ware as chamotte or synthetic mullite (withstanding 1,550°C). Synthetic mullite replaces high alumina refractory minerals such as kyanite, andalusite and sillimanite. The mixture has to contain up to 73% Al2O3, which is accomplished by mixing kaolin with pure Al2O3 and using catalysts to help the crystallization of mullite. Kaolin deposits can be divided into three types: 1 weathering 2 hydrothermal 3 secondary The weathering type kaolin deposits are most common and originate by weathering-kaolinization of feldspar-rich rocks such as granites, gneisses, arkosic sandstones etc. The process of kaolinization does not depend on climatic zones, but on the environment: kaolinite originates mainly at the ratio Al2O3 : SiO2 = 1 : 2 and pH 4-5 (i. e. acid conditions). Kaolinization is supported also by the presence of humic acids, thermal waters containing CO2 and other agents. During the kaolinization process orthoclase (K Al Si4O8), which contains 64.63% SiO2, 18.49% Al2O3 and 16.88% K2O, loses all K2O and part of silica. In this case kaolinite contains more Al2O3 - 39.56%, less silica 46.50% and more water -13.94%. Weathered kaolinic profiles can attain the thickness of several tens of meters, exceptionally over 100 m. The white kaoline zone is usually underlain by a brown - red zone of partially altered parent rock, from which iron and alkalies had not been removed completely. Kaolin horizons also underlay the lateritic horizons crusts. The hydrothermal type of a kaolin deposit is common to hydrothermal vein deposits and occurs expecially in Cornwall, England and in solfatara areas of Mexico. Secondary kaolin deposits are widespread and, in fact, the largest world deposits are of this type. An example is the Pugu Hills deposit in Tanzania, where several hundred m thick sandstones with kaolin were deposited as Tertiary deltaic sediments on the Indian ocean seashore. The origin of kaolin can be explained in two ways: as a transport of kaolin and sand into the delta from primary kaolin profiles or by a weathering of feldspar containing sands within the delta and above the water table. In Mozambique, all three genetical types of kaolin deposits are present (see Fig. 4. 3. 2). The most important is the first type - weathering, known from several pegmatite deposits of the Alto Ligonha district; the second type - hydrothermal - has just a theoretical value and is known to occur in gold-bearing veins; the third type - secondary kaolin of sedimentary origin was discovered recently at Nacala and similar deposits may exist within the paleodeltas in Mozambique and the Rovuma basins. The only deposit in production is the Ribaue pegmatite mine. This mine known as Boa Esperanca produces also feldspar, besides a small amount of other economic minerals (see Chap.-feldspar). In the past, part of the kaolinized pegmatite was mined opencast, part underground by driving galleries. The greatest part of pegmatite is altered into kaolin, either white, which is utilized; or coloured, which is waste. The main pegmatite body around the quartz core is about 130 m long and 60 to 70 m wide. Altered


Cilek: 4.8. Kaolin

pegmatite is treated at a small plant directly at the mine, sieving (3 mm sieve) and about 20 - 40% of material is rejected. The rest is used as untreated raw kaolin and sold as such, 10 - 15% is sold after washing. The Geol. Institute, Beograd (1984) evaluated the whole deposit; a major part of it is mined out and the reserves of raw kaolin in category C 1 are 23,400 t only, of which the washed kaolin (15%) represents 3,500 t, i. e. a 7 year-life for the mine with 500 t/annual production. The main reserves of kaolinized pegmatite of 390,000 t were not tested, but could certainly be used in ceramics. The Yugoslav team tested in detail three samples of raw kaolin (Results in %):

SiO2 49.69 48.92 49.73

Al2O3 35.27 33.26 32.81

Fe2O3 0.28 2.38 1.09

FeO 0.03 0.22 0.19

MgO 0.09 - -

CaO 0.69 0.72 0.28

Na2O 1.44 1.58 0.19

K2O 0.65 0.58 3.67

L.i. 12.32 12.22 12.32

X-ray analyses have shown mineral composition of kaolinite (at a medium degree of crystallization), K-feldspar, Na-feldspar, quartz and mica. A differential - thermic and thermogravimetric - analysis is presented in Fig. 4.8.1. The DTA curve illustrates a distinct smaller endothermal effect at about 100 °C, which can be contributed to the presence of a clay-mineral of the illitic type. At 530°C, a large endothermal peak becames apparent and this is typical of kaolinite, similar to the very distinctive peak at 970°C. The TG curve illustrates clearly an original loss of water and a further loss at 470-550°C, of which the first can be attributed to the presence of illite; the latter to the presence of kaolinite. Total mass loss amounts to 9.5%. According to the Yugoslav evaluation, Ribaue kaolin can be used in ceramics, as filler and in the paper industry.

Fig. 4.8.1. DTA and TG curves of sample No. 110058 - kaolin from Ribaue (113 kB) In 1977, the Institute of economy for raw materials in Dresden - GDR tested two samples from Ribaue - raw and washed kaolin. Composition of raw kaolin: 90% kaolinite 1% feldspar 5% muscovite 1% anatase 3% quartz The chemical analysis corresponds to this mineralogical composition and shows 43% Al2O3 and 1.3% K20 + Na2O. It is remarkable that raw kaolin does not contain Fe2O3. The volume of fraction > 63 micron is 10.1% and consists of 20% of kaolinite, 22% of feldspar and about 30% of quartz. The fraction < 2 micron is small in volume -15%. The quality of kaolin in ceramic mass is characterized by a high amount of water to cause fluidity of 33%, a 3% shrinkage after drying and a small degree of sintering at 1,300°C. The water absorption is


Cilek: 4.8. Kaolin

26% and the colour after firing is white. Washed kaolin displays almost the same properties as unwashed one, but the content of Fe2O3 is 0.8%. Rational analyses recalculated on the basis of chemical composition:

Raw kaolin washed kaolin Raw kaolin washed kaolin

clay% 91.3 91.5 feldspar % 7.7 4.9

quartz % 1.3 2.3 oxides % 0.5 1.1

The large quantity of kaolinite is causing a high uptake of water for fluidity and poor sintering is due to a small amount of alkalies, but otherwise kaolin can be used in the ceramic industry - fine - and coarseware production. Analytical results (Dresden, 1977):

Type of testingSample No2902 kaolin raw

(unwashed)Sample No2904 kaolin washed

1 2 3

1. weight volume (g/l) 1100 200

2. granulometry (%) fraction rest on sieve fraction rest on sieve

>63 micron 10.1 100 0.6 100

31.5-63 micron 1.3 89.9 1.9 99.4

20.0-31.5 micron 10.3 88.6 2.2 97.5

12.5-20.0 micron 11.1 73.3 8.7 95.3

6.3-12.5 micron 20.1 67.2 17.2 86.6

3.15-6.3 micron 21.1 47.1 23.6 89.4

2.0-3.15 micron 11.2 26.0 15.8 45.8

1.5-2.0 micron 2.9 14.8 5.6 30.0

>1,5 micron 11.9 11.9 24.4 24.4

3. mineralogical composition

X-ray analysismicroscopy of >0.063 mm

fraction

kaolinite (%) 90 20

muscovite (%) 5 5

quartz (%) 3 52

feldspar (%) 1 22

others (%) 1 1

4. chemical composition before firing after firing before firing after firing

L.i. (%) 12.0 - 13.0 -


Cilek: 4.8. Kaolin

SiO2 (%) 48.9 55.5 48.1 55.4

Al2O3 (%) 37.5 42.1 37.1 42.6

Fe2O3 (%) 0 0 0.7 0.8

TiO2 (%) 0 0.1 0.1 0.1

CaO (%) 0.4 0.5 0.4 0.5

MgO (%) 0.1 0.1 0.1 0.1

K2O (%) 0.7 0.8 0.5 0.6

Na2O (%) 0.4 0.5 0.2 0.2

5. ceramic properties

moisture plasticity (%) 33.4 33.1

shrinkage after drying (%)

3.0 5.2

firing temperature (°C) 1300 1300

shrinkage after firing (%) 8.7 11.6

shrinkage total (%) 11.4 16.2

water absorption (%) 25.8 18.0

colour after firing white whitish

The largest kaolin "producer" in the country is the Nb-Ta pegmatite deposit and the mine Muiane situated in the Alto Ligonha pegmatite district S of Alto Ligonha and 115 km from Nampula. The pegmatite body builds a distinctive hill above the surrounding plateau due to the resistance of the hard quartzitic core. The morphological position enabled kaolinization and at present the weathered zone is about 30 m thick. Pegmatite is of an oval shape with longer axis of 350 m in NNE-SSW direction and a shorter axis measuring 250 m. Pegmatite intruded Precambrian gneisses, schists and amphibolites and several zones developed around the quartz zone. Towards the centre, kaolinization diminishes. Kaolinized pegmatite is mined from around the quartz core and the material is slipped down to the dressing station, where quartz, kaolin and unaltered milled pegmatite, representing the waste, are pumped into a pond and deposited there. Mica, several precious stones, Nb-Ta minerals and beryl are the main products of mining. In my opinion, annual production of kaolin may reach about 10,000 t apart from a certain amount of feldspar and silty kaolin, which could be used also in the ceramic industry. In 1980, Thieke evaluated kaolin reserves in three zones - lithium zone, inner and outer zones in category C1 to 2,687 060 t and C2 628 282 t which makes a total of 3,315 342 t kaolin (50% kaolin content in kaolinized pegmatite). The content of mica is 1.1% of pegmatite. In the German Democratic Republic (1978) at the Institute of economy for raw materials in Dresden, three samples from Muiane were tested, one of raw kaolinized pegmatite from feldspathic zone (channel sample) and two samples of waste material - kaolin from the waste pond (0.0-0.4 m and 0.4-2.0 m), in which about 100,000 t of material are deposited. It may be possible to extract from it kaolin of commercial value. Mineralogical composition of kaolinized pegmatite: 60 % K-feldspar, 35% kaolinite, 5% quartz and mica


Cilek: 4.8. Kaolin

Chemical composition (%):

SiO2 58.5 TiO2 0.1 Na2O 0.5

Al2O3 24.1 CaO 0.6 K2O 10.4

Fe2O3 0.3 MgO 0.1 L. i. 4.7

The clay content < 0.063 mm is about 20%. It follows from these data that kaolinized pegmatite is poor on coloured oxides, it is coarse-grained and, in fact, has a high content of unaltered feldspar grains (microcline) and represents a mixture of kaolinite and feldspar of a very fine grain. The content of washed kaolin processed in two-phase hydrocyclones is 19-20% and in three-phase hydrocyclones 15%. The latter product has these properties (results from Amberger Kaolinwerke GmbH Hirshau, FRG):

fraction < 0.002 mm 68% kaolinite 46.5 %

K-feldspar (microcline) 52% Fe2O3 0.37%

Na-feldspar 1.5% whiteness (Eirepho) 87.3 %

These results show, that washed kaolin suitable for both the ceramic (fine ceramics) and the paper industry, can be produced from kaolinized pegmatite from Muiane. The content of kaolin-clay is somewhat low (15-20%), but the economy of kaolin recovery could be improved by utilizing the hydrocyclone product of fine feldspar. In 1981, several pegmatite and kaolin samples were tested in Czechoslovakia. The analyses showed a composition of kaolinized pegmatite which indicated a possibility of recovering kaolin-clay of high purity, whiteness and content. Sample of altered pegmatite - Muiane

Original sample (%)fraction below

0.053 mm above 0.053 mm 0.020-0.053 mm 0.0-0.20 mm

SiO2 45.09 43.93 46.90 43.85 42.88

Fe2O3 1.12 0.55 1.80 1.86 0.28

Al2O3 33.64 35.96 28.95 35.67 36.35

CaO 0.46 0.50 0.40 0.54 0.42

MgO 0.043 0.05 0.09 0.04 0.10

TiO2 0.09 0.09 0.09 0.05 0.18

P2O5 0.01 0.01 0.017 0.045 0.019

MnO 0.046 - - - -

Na2O 0.42 0.13 0.07 0.35 0.94

K2O 1.23 1.29 1.14 1.22 1.45

H2O 1.76 0.18 2.21 0.32 0.12


Cilek: 4.8. Kaolin

L. i. 16.22 17.05 16.86 16.48 16.72

Further tests showed clearly that a major portion of the sample consisted of kaolinized feldspar and quartz, in addition to muscovite and lepidolite, about 10% each. Granulometry above 0.053 mm was 50.09%, below 0.053 mm 27.72% , kaolin content 22.19%. The perfectly altered pegmatite of Muiane has contained less of particles above 0.053 mm - 43.96%, more particles below 0.053 mm - 39.47% and a kaolin content 16.57%. Chemical composition (in %):

Original sample (%)fraction below

0.053 mm above 0.053

mm 0.020-0.053 mm 0.0-0.20 mm

SiO2 46.66 44.58 47.66 45.18 42.70

Fe2O3 0.39 0.09 0.80 0.10 0.08

Al2O3 33.97 36.96 31.40 36.29 37.74

CaO 0.14 0.07 0.60 0.06 0.08

MgO 0.20 0.16 0.30 0.40 0.16

TiO2 0.19 0.22 0.16 0.27 0.10

P2O5 0.027 0.030 0.021 0.095 0.018

MnO 0.01 0.001 - - -

Na2O 0.16 0.16 0.21 0.20 0.11

K2O 0.38 0.14 0.43 0.06 0.24

H2O 0.62 0.24 2.33 0.98 0.79

L. i. 17.34 17.26 15.32 16.05 17.80

Interest in an investigation of Muiane kaolin was focused also on a utilization of waste in the waste pond composed of a mixture of kaolin clay and sandy material. The two samples collected from the upper layer (0.0-0.4 m) and the lower layer (0.4-2.0 m) were both of a similar composition (Dresden, GDR, 1978): 80% kaolinite, 10% muscovite and 5% quartz. The amount of quartz and feldspar was very low. This is understandable, because the "sandy" fraction had been removed together with heavy minerals for the treatment of Nb-Ta and precious stones, while the clay fraction, without grains of economic minerals, had been separated as waste. Rational analysis based on a chemical analysis showing composition of samples:

substance % sample 0.0-0.4 m sample 0.4-2.0 m

clay 87.5 85.2

quartz 1.3 2.1

feldspar 8.0 9.1

oxides 2.4 2.6


Cilek: 4.8. Kaolin

The average chemical composition was about 54% SiO2, 41% Al2O3, 1.8% Fe2O3 and 1.4% K2O. The high kaolinite content corresponded to the high loss of ignition -13%. The grain size was also typical: just 1-2% > 63 micron and 63-72% < 2 micron, and the fraction above 63 micron, consisted mainly of muscovite flakes, besides a very small amount of biotite, anatase, magnetite, quartz and rock remnants. Ceramic properties of this waste kaolin were characterized by a high volume of water needed for plasticity - 25% and a shrinkage of 5% after drying. These high values are typical of pure kaolinite and, together with K2O, Fe2O3 and CaO in minerals of biotite, feldspar and muscovite, cause a strong sintering just at 1,100°C, shrinkage 11-12% and water absorption 2-6%; the colour after firing is rose to grey. Very fine cracks in fired material are typical of plastic materials, can be corrected by adding 10-20% of quartz sand grain size 0.06-2.0 mm. Hence, it may be conduced that waste kaolin from Muiane, although hardly treatable for a removal of coloured oxides and alkalies to improve its quality, could be used directly, after adding corrective sand, in the production of special hard and light colour bricks fired at a maximum temperature of 1,300°C which could, in fact, serve as low-quality refractory material. Another important pegmatite mine - Marropino produces Nb-Ta minerals, whereby kaolin is again a waste. The ore-bearing pegmatite is deeply kaolinized, similar to other pegmatites of the Alto Ligonha district which crop out to the surface. In 1978, geologists of BRGM made technological tests of the kaolin. The investigation was intended both to determine the quality of kaolin and to check a possible content of Nb-Ta in the clayey fraction for recovery, which normally is lost in kaolin waste. Separation in hydrocyclone has shown a - 40 micron kaolin fraction in the order of 18.30% of which the part below 10 micron is 9.59% and above 10 micron 8.71%. X-ray and diffractometry analyses of Marropino pegmatite: 35% quartz 31 % feldspar (albite) 19% micas 12% kaolinite According to the results, the content of kaolin is fairly low; other economic minerals the main product of the mine - are these: SnO2 21 g/t Nb2O5 < 715 g/t = < 0.05 % Nb Ta2O5 < 610 g/t =< 0.05 % Ta BeO 505 g/t = 0.36 % beryl Gibbsite was not detected in the kaolin fraction. Very interesting is the presence of 0.13% Li2O, in the fraction - 40 micron, which improves the vitrification. This property may be common to all kaolins of albite type pegmatites with rare metals and lithium minerals in the Alto Ligonha district. Mineralogical composition of pegmatite and kaolin fractions (in %):

Pegmatite Fraction < 40 micron Fraction 10 micron

kaolinite 12 65 ~80

micas 19 4 -

albite 31 29 ~20


Cilek: 4.8. Kaolin

quartz 35 0 -

organic matter n.d. ~0.45 -

water hydroscopic 1.6 0.9 -

The chemical analyses include also Nb and Ta contents: the content of iron and titanium is low.

Pegmatite %

Fraction < 40 micron

%

Pegmatite %

Fraction < 40 micron

%

SiO2 69.90 51.90 K2O 1.05 0.47

Al2O3 18.30 32.25 Li2O 0.22 0.13

Fe2O3 0.26 0.12 P2O5 0.03 0.21

FeO 0.45 0.26 H2O- 0.30 0.25

MnO 0.20 0.15 H2O+ 3.85 10.55

TiO2 0.06 0.04 C organic n.d. 0.27

CaO 0.25 0.20 SO3 0.02 0.05

MgO 0.35 0.10 Nb <0.05 <0.05

Na2O 4.25 3.00 Ta <0.05 0.08

Sum 99.59 100.08

An analysis of trace elements in pegmatite (spectrography) disclosed a wide spectrum of elements from several minerals:

Elements Content g/t Elements Content g/t Elements Content g/t

Be 182 Cu 10 Ag <1

B <20 Zn 110 Cd <6

Sc <2 Ga 78 Sn 16

V <10 Ge <6 Ba 102

Cr 232 Sr <5 Yb <2

Co <5 Y 26 Pb 114

Ni 96 Mo 7 Bi 53

Also a determination of minerals was made on a dilatometric curve which shows generally kaolin with a low content of micas, the peak between 700-900°C is absent; pure kaolinite with feldspar is indicated on the distinctive peak between 975-1,100°C (fraction < 40 micron), see Fig. 4.8.2.

Fig. 4.8.2. Dilatation curve of kaolin Marropino (BRGM, 1978) (153 kB)


Cilek: 4.8. Kaolin

Technologial tests on - 40 micron kaolin indicated very good properties for a utilization in ceramics - fine ceramics, in the production of faiance and procelain: humidity pasticity after drying - 36.1%, shrinkage after drying 3.1%, shrinkage after firing 3.14% (1,100°C), 11.50% (1,300°C), 12.55% (1,400°C), and water absorption 37.04% (1,100°C), 7.49% (1,300°C) and 3.25% (1,400°C). The colour after firing at 1,100 - 1,400°C is white, the mass is homogeneous - porous - and has a porcelain-like aspect. Tests made for a utilization in the paper industry disclosed its low suitability - an increased content of abrasive minerals mainly feldspars, low rheological properties and an insufficient whiteness in the green stage, 82.5% (required are 87%). The example of Marropino pegmatite provides clear evidence for an inadequate treatment of the ore; the extraction of Nb-Ta minerals is a half-way process, part of these minerals get lost together with a number of trace elements, a big amount of high-quality kaolin, feldspar, quartz, mica, minerals of lithium and berylium. Undoubtedly, a better recovery of Nb-Ta minerals must go hand in hand with a utilization of the kaolin component of the pegmatite to improve the economy of mining. The only investigated deposit of sedimentary kaolin is situated near Nacala about 15 km to the S. The deposit consists of beds of kaolin sand with this profile: 1.4 - 1.6 m top soil with dark grey sand and little or no kaolin 1.6 - 12.0 m fine grey sand, with little or no kaolin; white kaolin sand and grey with a high content of kaolin; fine - to medium - grained sand with little kaolin; fine grey sand and yellow kaolin sand with a high content of kaolin. On an average, kaolin-bearing sands have a thickness of 12.5 m at a maximum overburden thickness of 2.2 m. The origin of these sands can be attributed to the transport of fluvio-alluvial sediments over a short distance. The kaolin comes from weathered crystalline rocks which are about 5 km W. In 1981, Zuberec et al. discovered the deposit and collected several samples, some of which were tested in Czechoslovakia. Results of chemical analyses showing this composition:

% Kaolin sandFraction below

0.053 mmAbove 0.053

mm0.020-0.052 mm 0.00-0.02 mm

SiO2 76.17 49.75 92.20 58.20 48.57

Fe2O3 1.22 1.29 1.20 0.20 1.20

Al2O3 12.93 30.79 1.76 27.88 33.67

CaO 0.61 0.10 0.98 0.18 0.06

MgO 0.66 0.23 0.90 0.30 0.20

TiO2 0.18 0.27 0.06 0.20 0.32

P2O5 0.01 0.01 0.005 0.005 0.045

MnO 0.001 0.01 - - -

Na2O 0.30 0.27 0.46 0.38 1.16

K2O 2.30 2.08 2.23 1.89 2.23

H2O(105oC) 0.70 0.02 0.18 0.26 0.57

L.i. 4.53 15.07 0.50 9.19 13.66


Cilek: 4.8. Kaolin

The clay content of kaolin sand is below 0.053 mm: 25-30% and 20-25% in fraction 0.00-0.020 mm. The main clay-mineral is kaolinite; quartz sand >0.053 mm can be used in the ceramic industry. Later, the deposit was explored in detail (Zuberec et al. 1984) and 51 boreholes were drilled. The results revealed that kaolin sands were not just of a lower quality than anticipated, but there was also a difference in both a lateral and vertical deposition. Average composition of sands composed of quartz grains, kaolin and K-feldspar (in %):

% Composition from - to Composition - prevailing Composition - Average

SiO2 51-84 60-71.5 64

Al2O3 9.6-31.5 15-23 21

Fe2O3 0.6-3.3 0.9-2.6 1.6

K2O 1.5-7.7 2.4-5.7 4

TiO2 0.02-0.6 0.1-0.3 0.17

CaO 0.08-1.8 0.1-0.2 0.15

MgO 0.05-0.5 0.1-0.2 0.17

Na2O 0.08-0.5 0.1-0.4 0.18

L.i. 0.08-0.5 4.5-7.5 7

MnO below 0.008 %

A granulometric evaluation revealed that the content of sand was 60-70%, while remaining 40-30% were silt and clay. The fraction below - 20 micron contains less than 10% of kaolin and is thus considered to be a poor kaolin deposit. From the economic point of view the production of washed kaolin is not to be recommended, both for a low clay content, and a low quality of kaolin. Its low quality was indicated by a separation of kaolin below 38 micron, a higher content of Al2O3, a lower amount of SiO2, but a high content Fe2O3 1.4-2.5%, exceptionally up to 4%. A higher amount of alkalies, mainly K2O, comes from unaltered remnants of feldspars. Also technological tests confirmed, that washed kaolin could not be used in better quality ceramic ware: the colour after firing at 900°C is yellow-pink, at 1,200°C clear pink and at 1,360°C light grey. The shrinkage of 6% is medium, bending strength 3 MPa. According to chemical, granulometric, mineratogical and technological tests, the raw material of Nacala deposit can be denominated as kaolinic feldspar sand. These basic properties are typical: 65-70% of sand 35-30% of clay with prevailing content of silt 10% and below of kaolin - 20 micron. After the treatment, i. e., a separation of coarse-grained particles and extraction of white kaolinic sand only, the composition is this:

SiO2 75.30 %

Al2O3 15.81 %


Cilek: 4.8. Kaolin

TiO2 0.15%

Fe2O3 0.66 %

CaO -

MgO 0.20 %

K2O 3.65 %

Na2O 0.10%

L. i. 3.97 %

It was suggested to use this kaolin sand in the production of tiles made of a ceramic mass containing 20-30% kaolin sand. The reserves were calculated with strong emphasis on specifications for kaolin sands suitable as part of the ceramic mass, of these basic requirements: Al2O3 over 15% Fe2O3 maximum 3 % Fraction below 0.06 mm (containing silt and clay) with a minimum content in raw material, i.e., 28%. The reserves of this "corrective ceramic material" are substantial: category C1 - 1,462 589 t C2 - 2,044 125 t total: 3,506 714 t Other sites of kaolin occurrence in Mozambique are not adequatelly known, many kaolinic weathered zones were encountered in many places during the geological mapping. Around Nampula, the lower kolin zones with coloured oxides and slightly altered granites were used in ceramics (see Chap.-feldspar) of an inferior quality. Many kaolin deposits may still be discovered in feldspar-rich massifs such as syenites, anorthosites or in sedimentary arkosic sandstones. The altered profile on syenite discovered near Manica on claimes of bauxite contains kaolin of this quality:

% SiO2 45.81 combined

SiO2 1.49 free

Al2O3 38.94

Fe2O3 0.06

H2O 13.70

Its analysis was published by P. Carvalho (1944) and the material was described as a kaolin "vein" in bauxite, with 98.5% of kaolin. In neighbouring Tanzania (Cilek, 1979), one of the biggest kaolin deposit in the world was described from the Pugu Hills near Dar-es-Salaam as Tertiary deltaic kaolin sands and sandstones. The Pugu Hills kaolin deposit is an uplifted delta, but such deltas do not occur in Mozambique. Nevertheless, kaolinic sands may be present in deeper layers within the paleodeltas of the rivers Limpopo, Zambezi or Rovuma. In the Rovuma basin, the Cretaceous Makonde beds or Neogene Mikindani beds contain sandstones with


Cilek: 4.8. Kaolin

cementing kaolinic material. Another kaolinic layer may be found within the Karroo sequence, mainly in coal measures, where refractory clays are known to occur in Zimbabwe. A small occurrence of kaolin of hydrothermal origin was found in gold veins of the Manica gold district and it will certainly be present on tin deposits around Inchope. Larger accumulations of kaolin may also be found in pegmatite subsurface bodies undergoing a slight hydrothermal alteration and albitization connected with pegmatite development.

Conclusions: Kaolin deposits of Mozambique are concentrated in the N part of the country in the form of an alteration product of pegmatite deposits. Outcropping feldspar-rich pegmatites, in a morphologically raised position underwent weathering with kaolin zones development. The only very small kaolin deposit in production is Boa Esperanca in Ribaue, W of Nampula. Other big deposits are on Nb-Ta-bearing pegmatites, kaolins are regarded a waste material and therefore not utilized. Reserves of these sites are large and a simple treatment of kaolin waste may result both in a kaolin recovery and a recovery of additional Nb-Ta minerals. Pegmatite deposits in production may yield several tens of thousand tons of kaolin a year of ceramic and partly paper grade quality, besides feldspar, quartz and other economic minerals. The only deposit of kaolinic sands of sedimentary origin near Nacala may yield the "corrective" sand with kaolin and feldspar in the ceramic mass. An investigation of kaolin deposits in the country is just in its first stage, but it is certain, that a permanent utilization of kaolin material on pegmatite mines should cover the entire need of the country and therefore there is no necessity to explore new localities.



Cilek: 4.9 Limestone and dolomitic limestone

4.9. Limestone and dolomitic limestone Limestone is a sedimentary rock containing mineral calcite as its main component. Calcite of a formula CaCO3, hardness 3 and specific gravity 2.71, is a soft, vitreous, transparent to translucent mineral of a perfect rhombohedral cleavage. It is composed of 56.0% CaO and 44.0% CO2 whereby part of the calcium may be substituted by Mn, Zn, Fe and Co. Calcite develops in several varieties known as Iceland spar (of a strong double refraction), satin spar (silky luster), Mexican onyx (banded calcite and aragonite), travertine, chalk and particularly in limestones, it is a dull compact rock, in marble a metamorphic equivalent of limestone. Besides calcite limestone may contain different admixtures, of which the most common is dolomite of the formula Ca Mg(CO3)2, the main constituent of dolomite rock ("dolostone"). On one end of the spectrum, is limestone with a high calcium content of 95%, on the other end dolomite with a high dolomite mineral content of 94% (43% MgCO3). Other admixtures are clay, sand, chert, organic matter, glauconite, pyrite etc. The colour of pure limestone is usually white, but it is commonly grey, reddish, greenish and black in nature. According to different admixtures in limestone, in quantities of about 10% and more, the rock is known as clayey, sandy, bituminous, glauconitic, etc. Similarly, differences in the classification of limestone are derived from its morphology, structure, texture, genesis and its use. According to the clay content, the spectrum accepted for commercial products is this (Polak, 1972):

high-quality limestone 98-100% CaCO3 clay content 0-2 %

pure limestone 98-95 % CaCO3 clay content 2-5 %

limestone 95-90% CaCO3 clay content 5-10 %

marly limestone 90-75% CaCO3 clay content 10-25 %

calciticmarl 75-40% CaCO3 clay cantent 25-60 %

marl 40-15% CaCO3 clay content 60-85 %

calciticclay 15-5% CaCO3 clay content 85-95 %

clay 5-0% CaCO3 clay content 95-100%

According to the dolomite content, this spectrum was accepted (Kuzvart, 1984):

limestone - up to 10% of CaMg(CO3)2

dolomitic limestone - 10 - 50 % of CaMg (CO3)2

calcitic dolomite - 50 - 90 % of CaMg (CO3)2

dolomite - up to 10 % of CaCO3

Limestones display also different degree of crystalinity, bed thickness, content of fossils, diagenesis, silicification etc. and, therefore, it is advisable to use proper adjectives. Most limestones originated as shallow marine water sediments composed of shells, skeleton remnants of corals, bryozoans, algae etc., which were fragmented to even a small size and cemented together by very fine grains of calcitic sand, limy mud calcite ooze. Many limestones are of coralline origin and these fossil reefs represent very pure limestones of high commercial value. Often, calcite precipitates directly onto the surface of small shell particles in the form of ooids and, in the zone of high energy and active water circulation ooids "grainstones" are made up of pure limestone, because the mud had been swept away by turbulent waters. In a lagoonal environment, micritic limestone of a high quality originates from deposited calcareous mud. The admixture of quartz grains usually does not surpass 5%. Part of the limestone, mainly coral-algal reefs, can be



replaced by dolomite by metasomatism or a direct growth of dolomite crystals in fossils. Chalk is a variety of organogenic limestone or micrite, it is white and soft and used as normal limestone or for writing on blackboards. Oolitic limestone or aragonite sand (aragonite is dimorphous with calcite but is less stable) is formed by a precipitation from seawater and consists of extremely small particles with a nucleus of shell fragments and laminae of calcite and aragonite. Its CaCO3 content is 96-97% (Harben-Bates, 1984), the lower layer is usually diagenetically consolidated in beds. Limestone is used in almost every branch of the industry. If the rock is compact, it can be used as crushed stone for the aggregate, and as a building stone for many other purposes depending on its physico-mechanical properties. Because limestone and dolomitic limestone (chemical composition is immaterial) deposits occur generally in many places, their use in the building industry is widespread. Some coloured limestones are also used as dimension stones, they can easily be cut and polished and were used in several monumental buildings, especially churches. Today, slabs of selected limestones are produced for inner linings. In some countries, over 50% of recovered limestone rocks are used as crushed stone. Owing to its chemical properties, limestone is an essential part of cement raw materials (75-80%). All types of limestones are used, from pure limestone and crystalline limestone to marls, chalk, calcitic sand, marine shells and limestone waste, and are supplemented by clay, shale, pyrite, slag and other silica-containing materials, alumina and iron. Exceptionally natural cement rock corresponds to the type "calcitic marl". Another important use is in the production of lime, at a calcination of calcium carbonate at 1,000-1,100°C (CaCO3 + heat ===> CaO + CO2). High-quality material is required, because each portion of silica and other impurities will double the loss of lime (44% of limestone weight is lost in the process). Part of the lime is converted to hydrated lime, but an essential amount is used in many industries; in a production of soda ash in Solvay process, as filler, as flux in metallurgy, in alkalies, in glass and ceramic industries, in water treatment; microfine-grained limestone is used as a specific filler in plastics, in treating pulp for paper production, in refining sugar, an extender in paint and finally in mortar and plaster. The last use was very important in the past, but nowadays, lime in mortar is replaced by cement. A demand for pulverized limestone or lime is increasing in agriculture to neutralize acid rain, correct soil acidity and support the growth of plants. During the past ten years, the calcium carbonate market underwent substantial changes. In the paper industry calcium carbonate (products 325 mesh and below) replaces kaolin, the use in plastics and paint is overwhelming. In all countries, in which limestone is available, it is used in these industries on the account of other more expensive materials. Because limestone is one of the most plentiful of the mineral of the earth - about 15% of its sedimentary crust-fine-ground products of calcium carbonate have the advantage both in terms of their geographical location and a good product performance. Remarkable is the utilization of calcium carbonate in plastics. An overall increase over the last 10 years averages 8% per year mainly in polyesters and polyvinyl chloride (PVC). Glass-reinforced polyester is composed of about 35-40% of resin, 20% of chopped glass and 40-45% of calcium carbonate, with a small amount of additives. The best example of the use of polyester is in automobile industry, nowadays every car contains calcium carbonate - in plastic door panels, front - end panel etc. Polyvinyl chloride is a thermoplastic material which is either flexible or rigid. Calcium carbonate of 3.0 micron grade participates in 15-20% in the plastic body. The main produce are pipes, mouldings, furniture, and the market is growing steadily. Calcium carbonate has been used for years in matte paper coatings and as a base coat pigment in card board, but just marginally as a filler. In Europe, the use of "whitings" is common and calcium carbonate is used at levels as high as 20% or more of the paper. Required grades for ultrafine material are 1.5-2.0 micron as a filler and 0.6-0.8 micron for coatings. To compile with the requirements for ultrafine-grade material, the very pure limestone deposits must be explored. For a classical utilization of limestone, some general requirements adopted in the past are these: Limestone for lime production: used in a production of burnt (pure) lime hydraulic lime



hydrated lime. Burnt lime (CaO) is produced by firing of limestone or dolomitic limestone at a temperature below the sintering point. The required CaO + MgO content is 80-85%, of which MgO should be below 7%, maximum loss of ignition 8% and CO2 5%. Hydraulic lime for mortar is produced by firing of limestones with hydraulic components (oxides of Si, Al, Fe) at a sintering temperature. It hardens in water. Hydraulic lime should contain a minimally 90% CaO + MgO (of which maximally 3% of MgO), maximum SiO2 5% and R2O3 4.5%. Both compression strength and dilatation strengh are also tested. Hydrated lime should have a CaO content of 64-70%, MgO maximum 5.5-2.0%, SiO2 and acid-insoluble remnants maximum 2.5%, humidity 3%. Accepted requirement for cement production:

CaCO3 minimum 80 %

MgCO3 maximum 7 %

MnO maximum 0.3 %

Sulphur maximum 1.0%

P2O5 maximum 0.1 %

K2O + Na2O maximum 0.5 %

quartz and chert maximum 3 %

Metallurgical limestone (used in blast furnaces, electrical furnaces for iron, production of steel, foundries) requires the highest possible content of CaCO3 and the possibly lowest content of SiO2, because every 1% SiO2 binds 2% CaCO3 (for example 100 kg CaCO3 = 103 kg limestone with 1% of SiO2 + Al2O3 or 106 kg limestone with 2% SiO2 + Al2O3 etc.). The minimum content of CaCO3 + MgCO3 should not fall below 95% (MgCO3 maximum 16%), Al2O3 maximum 1.5%, CaSO4 maximum 0.5%, SiO2 up to 3% and P maximum 0.07%. The limestone for alumina foundries requires an even better quality - over 96% CaCO3 and MgCO3 below 2%. Limestones for chemical industries must be pure with 96-98% CaCO3 + MgCO3 (MgCO3 up to 1%), SiO2 maximum 0.5%, Al2O3 + Fe2O3 maximum 0.3% etc.). Limestones for saturation in sugar plants should have 94% CaCO3, 3% MgCO3, 2% SiO2 + insolubles, Al2O3 + Fe2O3 up to 2%, alkalies 0.2% and SO3 maximum 0.25% (aggregate 80 to 200 mm). Glass factories use pure limestones with an Fe2O3 content up to 0.01%, a content above 0.5% gives the glass a greenish tint. The presence of TiO2, ZrO2 and other refractory oxides is also harmfull. Limestones for agriculture either for soil improvement or as feedstuff for animals, are of a different quality. For soil purposes even low-quality limestones (80% of carbonates), but finelly pulverized are used, for animals, the content of carbonates should be over 92%, a higher P2O5 content, trace elements except As, Zn, Pb and Cu, are welcomed. The group of limestones includes other rocks containing calcite, generally marbles and carbonatites known under the common name calcitic materials. In Mozambique, the types of calcitic rocks are these (see Fig. 4.9.1): 1. sedimentary -limestones, dolomitic limestones, marls, lacustrine limestones -the most important deposits 2. crystalline - marbles of different composition, used locally in the past for lime production 3. volcanic - carbonatites, mostly mineralized (apatite, rare earths etc.)

Fig. 4.9.1. Occurence of limestone (435 kB)

1. Sedimentary limestones and marls are present at different levels in the sedimentary sequence of coastal



Mozambique. The two sedimentary basins are: Mozambique basin in the S of the country from the border with South Africa up to the N margin of the Zambezi delta; the Rovuma basin on the border with Tanzania and finally, a narrow coastal sedimentary belt between both basins. Main limestone layers and some marls of the Cretaceous occur in Red Beds of the Neocomian overlying with disconformity Karroo volcanics, in the Sena Formation of Aptian-Albian. The Upper Cretaceous is mainly marly (Lower Grudja). The main accumulation of calcitic sediments occurs within the Tertiary. In the Upper Grudja Formation of Paleocene age are marls and calcitic shales. Limestones with a high carbonate content occur in the Eocene S of Maputo in the Salamanga Formation, and in the Cheringoma Formation in two areas - W of Beira along the river Buzi and in the type locality N of Beira on the Cheringoma plateau. The second important accumulation of limestones is in the Miocene, in the Jofane Formation (Fig. 4. 9. 2). A large area with outcrops of limestone extends from S of the river Save to the Inhambane.

Fig 4.9.2. Generalized Stratigraphy of the Mozambique Basin and Global Cycles of the Sea Level Changes (ENH, 1986) (612 kB) In the Rovuma basin, calcitic marls and marly limestones occur in the Cretaceous beds Conducia and Megatrigonia, in Globotruncana marls and again mainly in the Eocene of the Cheringoma Formation. Coral limestones were found over an area from Pebane in the S to Tanzania in the N. They are of Pliocene to Quaternary age (see general profile, Cilek, 1985). The coral reefs form platforms raised + 30 m, + 15 m and + 5 m above the sea level on the shore. Many coral islands on the shelf are + 5 m elevated and surrounded by coral platforms exposed during low tide, with living coral and algal colonies on the margin. Wide coral platforms fringe the whole seashore, from the llha Mozambique to the Rovuma river, except for small section influenced by fresh water. Scattered coral reefs could be traced from llha Inhaca in the Maputo bay to the Paradise Islands at Vilanculos. The coral reefs are a source of excellent pure limestone; around them wide layers of coral sand and mud are developing on the shelf. Lacustrine Quaternary limestone deposits are known to occur in several places of the Mozambique basin, between Maputo and the river Save as sediments of inland lakes originating during the interglacial periods within the older grabens.

2. Crystalline limestones - marbles are present in almost all crystalline complexes of Mozambique including Archean and Precambrian rocks. They are originally sedimentary rocks metamorphosed during several orogenetic phases and deposited either as a platform or geosynclinal sediments. The latter case is more common. There are still vast areas in which crystalline limestone deposits may be found. Primary attention should be given to mobile belts of the Precambrian with carbonatic sediments, to greenstones belts and generally to the upper structural level of the Mozambican belt with prevailing metasediments. The oldest crystalline limestones of Mozambique are those of the Archean Greenstone Belt - of the Zimbabwean craton. Of the three formations - Macequece, Mbeza and Vengo, the last consists of a band of sericite-chlorite schists and phyllites including black schists with minor bands of marble and conglomerate. The marble was used for lime production near the town of Manica. In other Archean rocks - in the Luia Group of the central Tete Province narrow bands of marble and banded ironstones are enclosed in granulites of acid composition. The marbles are coarsely granular, white or grey rocks, almost pure calcite, but also contain laminae of calc-silicate minerals. In part, they are dolomitic and always closely associated with the marbles. They occur mainly around the river Luatize NE of Fingoe and around Chiputo near the Zambian border. Precambrian formations are divided into several groups. The Chidue Group situated on the periphery of the Tete Complex over an area extending from Massamba to Estima represents metasediments outcropping as marbles, schists, quartzites and associated metasediments. Marbles of the Mufa-Boroma area are white or cream, medium-grained forming usually distinctive structural ridges such as Chacocoma marbles Near Tete, marbles were used in lime production.



In the NW part of the Tete Province, the Zambue Group was distinguished between the towns of Zumbo and Malowera, just in the corner frontering with Zambia. It consists of impure coarse-grained dolomitic marbles in a metasedimentary sequence with thin siliceous bands, known as Mvuvye marbles. In the Fingoe Group, a widely varied belt of predominantly metasedimentary rocks developed just E of the Zambue Group, in which marbles and metadolomites are abundant (see Chap. ornamental stones). The marbles are cream or white, medium-to fine-grained, often in dolomitic varieties. The main accumulations occur in the area Monte Mancupiti - Monte Manga. The extensive Barue Group stretching from the river Zambezi almost up to the river Save, E of the Zimbabwean craton, contains numerous bands of marble in the Sofala Province. The marbles are cream or grey, medium-grained, banded rocks with or without calc-silicate minerals, often with disseminated graphite. They occur at Meteme in the Tete Province and in many other localities of the Sofala Province N of Gorongosa, S of Canxixe and in an extensive belt of SW-NE direction between Meteme and N of Canxixe. The Umkondo Group lies at the border with Zimbabwe, near the towns of Rotanda and Espungabera. The group consists of slightly deformed phyllites, metasiltstones and quartzites with siliceous dolomite and limestones bands developed near the base of the sequence. The Rushinga Group is situated in the N part of the Luenha river along the road Tete Harare, just at the Zimbabwean border; it consists of banded gneisses and metasediments. The area had been prospected for manganese. According to Hunting (1984) the group is a Pan-African sequence of metasediments of a younger age than the Umkondo and Gairezi Groups. The calc-silicate gneisses form finely banded units up to 20 m thick in which occur thin discontinuous lenses of medium-grained calcite marble. The locality is known as Masanga and is situated WSW of Changara. Remnants of lime furnaces can still be seen in several places. Big, but less well-known sites of crystalline limestone occurrence have been mapped in the whole of N-Mozambique, in the provinces Nampula, Cabo Delgado and Niassa. The well-known marbles of Montepuez have already been described. Many other bodies within the Lurio belt were investigated, such as the locality Marese. Near the Tanzanian border, marble is known to occur at Negomano S of the river Rovuma and in other localities in the structure of Morrola (see graphite). During an investigation for graphite, several limestone deposits were discovered N of the mouth of the river Lurio. Other sites marble occurrence in connection with deposits of apatite, magnetite and graphite, are known from the Monapo structure. In the Niassa Province, where the deposit Malulo had been exploited in the past, an investigation of the Formation Geci disclosed marble in several sites. Reserves of crystalline limestones are substantial in the deposit Muande near Tete and in its neighbourhood, on Monte Fema, where iron ore and apatite were discovered. Small marble quarries for lime production were established at the genetically similar deposit Evate near Nampula situated within the Monapo structure.

3. Carbonatites in small volcanic massifs may yield an acceptable cement material. In Mozambique, carbonatite localities are these (from S to N): Monte Xiluvo NW of Beira, Monte Muambe, Buzimuna and Chandava E of Tete, Salambidua N of latter localities, but with central carbonatite on the Malawian side of border and finally Cone Negose on northern bank of Cabora Bassa dam. Several deposits were investigated in detail: The most southern limestone deposit is situated at Salamanga near the village of Boa Vista. In a narrow zone, 1.5-2.0 km, extending in N-S direction calcareous rocks are present which display typical karst phenomena such as sinkholes, small cavities, etc. The calcareous sequence is of Eocene age and is known as the Salamanga Formation. The limestone attains a thickness of about 10-15 m and is composed of heterogeneous layers with an admixture of sand, and underlain by distinctive greenish glauconitic sandstone. Overburden, 1 to 13 m thick, consists of sands, locally calcareous, of the Quaternary. A limestone quarry supplies limestone to a cement factory at Matola on the outskirts of Maputo, whereby lime furnaces are operating directly on the locality. The last exploration was performed by the Yugoslav team in 1985. They confirmed a great variability of limestone; the dip of strata was subhorizontal 3-5°/E. In the NE area, the thickness of carbonate rocks was 55.6 m, in the SW just 11.35 m. The average thickness was calculated on 31 m with the purest limestone composed on the top of an organogeneous layer with shells of Gastropoda and Lamellibranchiata (1.4-6.0 m). Most of the sequence is made up



of sandy limestone and carbonatic sandstone with glauconite up to 3%. Sandy limestone is organogenic-detrital with a carbonate component of 50-70% in the very sandy variety; a normal content is 70-87% of calcium carbonate. Average values for 19 boreholes:

% SiO2 10.60 MgO 2.55 Na2O 0.38 H2O 350°C 0.71

Al2O3 0.99 TiO2 0.095 K2O 0.40 H2O 105°C 0.83

Fe2O3 1.16 P2O5 0.26 SO3 0.12 CaCO3 78.55

CaO 44.44 MnO 0.44 L. i. 37.15 MgCO3 5.00

Average composition was asessed also from several trenches. Mean content of boreholes and trenches (in %):

SiO2 17.48 (10.60 and 26.95)

Al2O3 1.16 (0.99 and 1.40)

Fe2O3 1.17 (0.58 and 1.59)

CaO 41.45 (26.1 and 51.09)

Average of carbonates CaCO3 + MgCO3 is 78.13% (57.23 and 91.79%) MgO 2.03 (2.55 and 1.30) SO3 0.11 (0.04 and 0.33) The mining conditions are very favourable, the quarry is situated on an escarpment along the bank of the river Maputo. Results of control analyses of sample composition: %

% SiO2 Al2O3 Fe2O3 CaO MgO TiO2 P2O5 Na2O K2O CaCO3 MgCO3

Boreholes F-9 3.18 0.98 1.14 51.16 1.33 tr. 0.36 0.56 0.25 91.35 2.79

F-13 3.88 1.09 1.27 50.34 1.66 tr. 0.26 0.68 0.20 89.89 3.48

Trenches TR-23 36.22 1.88 1.36 32.07 0.90 tr. tr. 0.90 0.36 57.26 2.07

TR-39 21.34 1.21 0.67 40.87 1.33 tr. 0.40 0.70 0.19 72.96 2.94

The reserves of carbonate material suitable for a production of portland cement and hydraulic lime amount to 1,198,985 845 t (557,667 835 m3). In the Maputo and Gaza provinces, sandy limestones or marly limestones together with calcitic and glauconitic sandstones are present in outcrops on the E - slopes of the Lebombo Mts. They generally belong to the Lower Cretaceous-Aptian Maputo Formation, which begins at the base of the transgressive cycle with lagoonar sediments of black saline marls. The Upper Cretaceous consists mainly of continental facies, sandstones transgress over Karroo basalts in an area between Sabie and Rio dos Elefantes and from there to Singuedzi, followed by marine sandstones of Uanetze and Mahel outcroping about 25 km N of the river Incomati, E of older formations. Therefore, Cretaceous sediments are less important with regard to their carbonate content. Extensive limestone deposits are developed in the Tertiary. An equivalent of the Eocene Salamanga Formation in the S is the Eocene Cheringoma Formation in the N surfacing in two important areas: around the river Buzi W of Beira in the Sofala Province and in the type locality on the Cheringoma plateau and escarpment bordering the E- side of the rift valley- the Urema Trough. The Cheringoma Formation extend for about 100 km in NNE-SSW direction from Muanza in the S to the N of Inhaminga. The Cheringoma Formation along the river Buzi is not well known. One



analysis of limestone from the locality Inhaboa was made in London (1944). Outcrops of limestones occur over a distance of more than 50 km just E of the confluence of the rivers Buzi and Revue.

Limestone quality (in %):

CaO 54.80 CaCO3 content

MgO 0.49 97.76% is similar.

SiO2 0.92 to that of the

Fe2O3 0.23 Cheringoma

Al2O3 0.33 plateau

L. i. 43.34

Similar results of another analysis of Campos (1961) (in %):

Limestone quality (in %):

CaO 54.52 CaCO3 content

MgO 0.28 97.25

SiO2 1.43

Fe2O3 0.36

Al2O3 0.22

L. i. 43.19

Drilling for oil and gas in the Sofala Province revealed the basic stratigraphy of Tertiary formations. In term of carbonate, the Upper Grudja Formation of the Paleocene and partly Eocene may be promising just in some parts owing to decrease in some layers of limestone and dolomitic limestone. Sandstones with glauconite are dominant and according to a K/Ar determination of the Upper Grudja their age may be 60.0 ± m. y. (ENH, 1986). There is an angular unconformity on the top of the Upper Grudja and the Cheringoma Formation. Just the upper part of the Eocene system is present in outcrops both at Buzi and the Cheringoma plateau and this represents the carbonatic part. At the type locality, in quarries on the plateau near Muanza, the Formation is about 70 m thick and rests discordantly on the underlying Grudja Formation. The limestone is pure to sandy, whitish in colour with extremely abundant fossils - Nummulites atacicus, numerous Camerina sp., Operculina sp., gastropods and coral and echinoid remnants. The environment was warm clear water of neritic-bathyal depths. Changes of facies into marly limestones and marls proceed up to the present shoreline. The whole Cheringoma plateau is a typical karst area - deep sinkholes, extensive caves, steep canyons and subterraneous rivers are abundant. In 1944 (Carvalho), two analyses of limestones of the Cheringoma Formation were made in London on (in %):

Oxide Nhindini valley W slope of the scarp

CaO 51.0 49.90

MgO 0.84 0.92

SiO2 4.59 5.30

Al2O3 + Fe2O3 1.30 2.98

L. i. 41.48 39.65

CaCO3 90.98 89.02



First, the area was explored in 1952 by Bettencourt Dias by drilling boreholes over the area of the Urema trough escarpment to detect the best limestone deposits for the cement factory at Dondo near Beira. Unsuitable for cement production were limestone deposits S of the road Muanza-Urema but N of it good-quality limestone was discovered in the localities Codzo, Nhangatua, Condue, Massiquidze, Muanza and Mueredzi (from N to S). The last three deposits are the best, with a stable thickness and quality, while from other deposits, limestone of the best quality had partially been removed by erosion. The deposits Mueredzi, Muanza and Massiquidze fringe the escarpment, which originated in the last stage of rift valley development in the Pleistocene. All these deposits are about 25 km W of the Trans-Zambezian railway line and at 110.98 and 80 km respectively from the cement factory at Dondo. The Codzo deposit is made up of nummulithic limestone, 40 m thick, around the rapids of the river Codzo, which is partly subterraneous, partly flowing through a canyon and caves. On the surface, the limestone contains 90-95% CaCO3, in the borehole the carbonate content diminishes from 80 to 40% at a depth of 20 m (see Fig. 4.9.3).

Fig 4.9.3. Cross section of Rio Codzo limestone deposit (Bettencourt Dias, 1952) Fig 4.9.4. Geological profile of Rio Muanza limestone deposit (Bettencourt Dias, 1952) (521 kB) The deposit of the river Condue is similar to that of the Codzo, the CaCO3 content is higher on the surface and diminishing towards the depth (90% on the surface, 85% CaCO3 in 40% of samples, below 76% CaCO3 in 60% of samples). The Cheringoma Formation is intruded by a younger basalt vent forming the hill Nhaguere. In several samples, the content of CaCO3 was as high as 97.50%. The deposit Nhangatua located between Codzo and Condue displays variation in the content of CaCO3. The northernmost of the three deposits is Massinquize, with limestone outcropping over 7 km at a height of about 10m. The white fossiliferous limestone has a high CaCO3 content. Bettencourt Dias explored the deposit in 17 traverse sections. Examples of the limestone quality in some sections (CaCO3 in %): Section 1 - 98.88 % Section 2 - 97.88% Section 5 - 98.10% Section 7 - 89.30% Section 17- 95.45% The deposit Muanza is located on the river of the same name. The scarp is about 12 m high, part of the area is covered by reddish sand. About half of the area represents good-quality limestone, as evident in the sections (section 11 is the first with limestone, section 22 the last (in % CaCO3)): Section 11 - 88.00 % Section 12 - 95.94% Section 14 - 100 % CaCO3 in one sample, 98.00 % in the others Section 18 - 94.75% Section 22 - 93.11% The development of the Cheringoma Formation within the whole area is best demonstrated on the stratigraphical section (Bettencourt Dias, 1953 Fig. 4.9.4). The southernmost deposit on the river Mueredzi is the best investigated deposit of the lot. The regular development of the limestone bed is extraordinary, the section of calcareous rock of the Cheringoma Formation is uncovered and extensive outcrops are present in karst area. The river Mueredzi builds a canyon 16 m deep and over 600 m long, with a CaCO3 content in limestones of over 85%. About 60% of limestone samples contain 90-100% of CaCO3, 35% 85-90% of CaCO3. The reserves of limestone on both banks of the river amount to 10,230 000 t. In the whole area, there may be possible reserves of several hundred million tons.



In the Inhambane Province, near the seashore, extensive outcrops of Miocene limestone exist within the Jofane Formation. However, the size of the actual deposit is much bigger, but most of it is obscured by a Quaternary cover. The thickness of limestones is more than 100 m and the best outcrops developed near Urrongos and Jofane around the river Save. The whole area displays karst phenomena such as caves, sinkholes, chimneys and differently steep depressions which may be covered partially by Quaternary sand and clay. The caves originate usually from sinkholes of which some are filled by bat guano. The depth of the karst phenomena is not known, their surface elevations is 100-150 m above the sea and, taking into the account the water table of the sea of about - 70 m during glacial times, the whole carbonatic sequence of Jofane limestones could have been influenced by calcite dissolution. In the past there must have been some local lime production judging from the name of a village "Fornos" (furnaces) in the centre of the limestone area. The area has not been investigated in terms of its potential for cement and lime production. Few analyses were made of surface samples from these localities (Campos, 1961): %

% Massinga Mabote Macovane Vilanculos

SiO2 0.82 0.81 1.09 0.47

Fe2O3 0.27 0.07 0.04 0.30

Al2O3 0.11 0.17 0.22 0.22

CaO 52.12 55.46 54.94 54.24

MgO 0.36 0.06 0.17 1.10

L.i. 43.32 43.43 43.54 43.67

The sample of Mabote (on the parallel 20°S) is probably lacustrine limestone. Lächelt (1985) analyzed 9 samples of white, yellowish and rose limestones from Vilanculos:

Samples 33DP 43DP 143DP 143C 23G 238B 18G 132C 15DP 20G

CaO % 53.65 53.65 55.27 51.24 54.43 54.32 53.26 53.42 18.42 52.25

MgO tr. tr. tr. tr. tr. - tr. - 12.51 tr.

SiO2 1.76 2.26 0.63 5.21 1.00 0.76 1.92 1.44 36.80 4.05

Fe2O3+Al2O3 1.15 0.91 0.31 2.35 1.18 1.15 1.48 1.51 0.90 1.47

P2O5 - tr. tr. tr. tr. 0.02 0.02 tr. tr. tr.

SO3 - tr. tr. tr. tr. 0.02 0.02 tr. tr. tr.

Reserves were not calculated, but from the surface area of limestone (8,000 km2), the resources for cement and lime production and agriculture can be estimated to be 1,120 million tons. In the vicinity of the Nacala port, Pliocene - Pleistocene coral limestones from a raised coral platform, 5-10 m above sea level, are used and mixed with clays of Cretaceous age near the boundary of crystalline rocks. A cement factory at Nacala is quarrying coral limestone, thickness about 15 m, from the E- part of the Nacala peninsula, and clay of the Nacala bay (Fig. 4.9.5). A coral limestone deposit is at Relanzapo, clays are available from two localities: Quissimanlujo from Tertiary clays and Natimanga (Cretaceous). Average analyses, K. Legelt:

1 surface layer



2 coral limestone loose (Relanzapo )

3 coral limestone compact (Relanzapo )

4 control analyses of Relanzapo limestones

5 clays from Quissimajulo (Tertiary)

6 clays from Natimanga (Cretaceous)

1 (n=2) 2 (n=16) 3 (n=3) 4 (n=7) 5 (n=15) 6 (n=55)

SiO2 2.53 0.79 0.94 0.61 59.17 63.92

Al2O3 1.46 1.65 1.15 1.55 12.73 12.58

Fe2O3 1.40 1.15 1.33 0.57 4.84 3.10

FeO 0.94 0.52 0.53 0.12 0.72 0.69

CaO 53.25 50.07 50.53 49.34 6.93 2.66

Na2O 0.26 0.32 0.17 0.47 1.20 2.01

K2O 0.05 0.06 0.05 0.03 2.35 3.78

SO3 - 1.11 - 0.22 0.001 1.65

P2O5 - 0.06 - 0.09 0.06 0.16

L.i. - 43.58 - 43.48 11.66 8.70

SUM - 99.31 - 96.48 99.66 99.25

CaCO3 95.32 90.31 90.44 88.07

Fig. 4.9.5. Cross section of area Nacala port (Cilek, 1987)

Fig. 4.9.6. Schematic cross section illustrating the facies changes in the Fingoe Group (Hunting, 1984)(375 kB)

Miocene calcarenites (loose limestone composed of small fragments) were investigated for possible lime production W of Pemba. The thickness is about 2-3 m, with underlying Cretaceous beds of Megatrigonia Schwartzi. Two localities checked were - locality B with calcitic rocks of 78-80% CaCO3 and 14-16% SiO2 without substantial reserves, and the locality Plantacao Pinto where, in the past, lime was produced in a local furnace. However reserves are too small to be of economic value for industrial production. The analyses presented below show the composition of these sandy limestones and indicate the risk of an inadequate preparation for an investigation of these common materials:

% Locality B Locality Plantacao Pinto

SiO2 14.14-23.31 10.37-21.72

Al2O3 2.20-4.23 2.83-4.16

Fe2O3 0.01-0.21 0.13-0.30

CaO 38.46-45.34 41.18-48.47

MgO 0.64-1.30 0.44-1.36

SO3 0.01-0.06 0.00-0.06



Na2O 0.48-0.98 0.40-1.00

K2O 0.48-0.80 0.32-1.14

R2O3 2.28-4.44 CO2 21.40-24.80

R.l. 3.28-6.10 2.20-4.98

L.i. 30.02-34.83 30.03-37.26

CaCO3 68.45-80.70 73.50-86.60

The quality of calcarenites is low, but suitable for a production of hydraulic lime. Crystalline limestones of the Chidue Group build whole ridges of saccharoid marble around Chidue and Massamba, with a grain size of 0.8-4.0 mm, with calcite dominated by dolomite. Fine-grained quartz and green fibrous aggregates of malachite are present in some carbonates thus forming a nice ornamental rock. In the neighbouring Fingoe Formation, numerous small lenses or larger masses of crystalline limestones originated at different structural levels (see Fig. 4.9.6). Included in the Chidue Group is also the area of Monte Muande situated NW of Tete on the N bank of the river Zambezi. The same geological structure continues in the Monte Fema area S of the river. The whole region is known for its uranium mineralization, with centres at Mavudzi and Chacocoma. Mineralized zones are concentrated just in the Chidue contact zone of carbonate rocks with Tete gabbro and the norite complex. Davidite or mavudzite mined in the Mavudzi mine occurs in calc-quartz veins in shear zones. The crystalline limestones of Chidue are also bearers of tungsten, rare earths, copper and gold mineralizations. On Monte Muande, thorium anomalies were discovered by Hunting (1984). However, the locality is known as a deposit of iron and apatite (see Chapt. phosphates), and therefore, carbonate rocks only are described below. Marbles of Muande vary in thickness in a range of several hundred m (500 m and more) and can be divided in biotite marbles and magnetite-bearing marbles. Biotite marble with apatite contains 36.60% calcite, 18.30% dolomite, 26.70 biotite, 14.70% apatite and 3.70% metallic minerals. Another variety of dolomitic-calcitic marble is composed of 69.50% calcite, 16.90% dolomite, 0.40% magnetite, 11.60% apatite, 0.50% quartz and 1.10% orthite (Geol. Inst., Beograd, 1984). The crystalline limestones of the Barue Formation in Sofala and the Manica Provinces around Canxixe and Maringue were investigated by the Geol. Inst., Beograd (1984). In samples from the NW part of the area large lenses of coarse granular marble contained calcite grains up to 5 mm, forsterite, muscovite, quartz and metallic minerals. Two types were analysed - 1) pure calcitic marble - 2) impure marble with about 30% of quartz, muscovite and feldspar (between Canxixe-Mtene).

Sample 1 2

SiO2 % 0.02 26.68

TiO2 0.02 0.05

Al2O3 0.03 6.19

Fe2O3 0.27 1.12

FeO - -

MnO 0.05 0.03

MgO 0.31 1.00

CaO 56.20 34.77

P2O5 0.05 0.13

L.i. 43.15 28.78



Very pure limestones were detected in the northern part near Buzua (Geol. Inst. Beograd):

Samples 154 053 057 209 211/1

SiO2 0.89 0.37 0.02 2.53 1.13

Al2O3 0.24 0.23 0.03 0.45 0.56

Fe2O3 0.65 0.19 0.27 0.26 0.51

CaO 53.84 55.24 56.20 54.12 49.63

MgO 1.24 0.41 0.31 0.35 2.52

TiO2 0.02 0.04 0.02 0.02 0.04

P2O5 0.06 0.10 0.05 0.01 0.06

MnO 0.01 0.01 0.05 0.05 0.01

CO2+H2O+ 43.35 43.14 43.14 41.87 41.32

Total 100.03 99.73 100.09 99.66 95.78

% X-ray fluorescence of Sample 209: 10 ppm Nb2O5, 20 ppm Rb2O, 15 ppm Ta2O5 30 ppm Cs2O.

The limestones are very pure with MgO + Fe2O3 content 0.4-0.5% and may be used in the glass industry (some bands), cement and lime production and as a metallurgical grade. Small sites of an occurrence of crystalline limestone were found at Angonia, in the Ulongoe metallogenic zone in which marbles coincide with the W graphite zones (see Chap. graphite). The locality is named Fornos and remnants of old lime furnaces confirm the use of marble by the local population. The marbles at Chire in the Zambezian Province E of the Malawian border were and still are used in a production of lime for saturation in sugar refineries. The lime furnace is situated between the towns of Chire and Marire and utilizes several small marble lenses, 35 to 50m thick. In the surroundings are about 22 major bodies of marbles of which several had been investigated by a Russian team in connection with a possible utilization of nepheline syenite in the alumina production (Barmine, Tveriankine, 1982). The marbles are from 0.5 to 300 m thick, greatly variable in their composition, in conformity to both biotitic and granitic gneisses and quartzites in their vicinity. Marbles are commonly dolomitized with a MgO content ranging between 0.25 and 20.56% (dolomites) always with quartz, muscovite, biotite, hornblende, feldspar and graphite. Some sections are iron -impregnated up to 25% of their content. Two bigger deposits - Monte Chifuso and Bonesse, both in the area of Amosse were selected for a detailed investigation. The deposit Chifuso is a ridge of NNE direction, dipping E, 3 km long and maximally 300 m thick. It contains light, reddish and greyish calcite, fine graphite, biotite, quartz, feldspar, with lenses of biotite gneiss, 0.4 to 0.5 m thick with gradual changes in the phases. Locally, it is cut by dolerite dykes of 1 m thickness. The Bonesse marble is similar, it contains lenses of gneisses and quartzites.

Composition % SiO2 CaO MgO Fe2O3 FeO CaCO3 MgCO3Fe2O3

total

Chifuso (34 samples)

min 0.16 15.6 3.43

42.63 54.42 50.26

0.55 4.84 1.62

0.07 2.77 0.35

0.1 1.65 0.42

76.07 97.13 89.76

1.36 12.1 4.03

0.18 4.21 0.82

max

avg

Bonesse (6 samples)

min 2.58 5.44

26.78 44.95

5.64 20.32

0.18 0.78

0.14 1.22

47.96 80.22

14.0 50.42

0.67 1.79 max



4.21 36.58 12.84 0.46 0.54 65.31 31.85 1.06avg

Although these marbles do not answer the requirements for alumina production which are CaO minimum 53%, SiO2 maximum 2%, MgO maximum 1% and Fe2O3 maximum 0.6%; they may of course, be used in the production of lime or cement. In the Monapo structure, the Evate deposits of iron and apatite were investigated. Both economic minerals are present in crystalline limestone layers, which constitute about 70% of the deposit. The thickness of mineralized marbles is 5 to 100 m. In the area is a small quarry, which extracts pure marbles for the production of lime in a furnace. The content of CaO in marbles varies from 20 to 55% (average 35-45%) while the MgO content is regular in all types of rocks, in marbles 2.5-4.5%, in impure marbles even up to 22.7%. The reserves of marble are big, and certainly several times higher than the calculated reserves of 125 million t of apatite ore. Large areas with marble were discovered around and N of the river Lurio. The Namapa and Monote Formations around the mouth of the river Lurio contain many lenses of white and grey marbles with phlogopite and graphite; whitish marbles are mapped in the Metoro Formation around Jocolo belts: length 5 to 15 km, width 400-500 m. In the vicinity of Chiure, about 25 km N of the river Lurio, there are several older marble quarries. The marbles of Montepuez are extracted as ornamental stone. The waste of this production, together with an utilization of many other sites of marble occurrence in the whole region may serve as a base for lime and cement production. However, it ought to be considered that coral limestones of Pemba on the coast are a better and economically more feasible material than hard and often impure crystalline limestones. For the landlocked Niassa Province there is no other way than to use the local crystalline limestones in lime production. Jourdan and Paulis (1979) investigated the marble deposit of Malula 50 km N of Lichinga. The first utilization of this marble was in lime furnaces before World War 1 and it is believed that it was used by the local population many centuries ago. Five furnaces were still in production in the fifties and lime was used in mortars and tints. The Malula marbles are very variable in composition, with lenses and layers of phyllites, gneisses and graphite. Some are of a breccia structure with grains of dolomite and calcite as a result of a "solution and collapse" genesis (Fig. 4.9.7). The reserves are these:

E - deposit with CaO content over 50% 32,880 000 t

W- deposit with CaO content 46-55% about 10,000000 t

Fig. 4.9.7. Geological map of limestone deposit Malula-Niassa Province (Jourdan-Paulis, 1979) (374 kB)

Reserves were not calculated for the NE part, containing low-quality limestone with 20-27% CaO content. The authors divided carbonate rocks into grades:

limestone 0.0 - 1.1 %MgO

magnesium limestone 1.1 - 2.1 %MgO

dolomitic limestone 2.1 - 10.8 %MgO

calcitic dolomite 10.8 - 19.5 %MgO

dolomite 19.5 - 21.6 % MgO (one sample)

Chemical analysis of selected samples (in %) (total of 73 samples):



Type of rock

Sample SiO2 Al2O3 Fe2O3 CaO MgO L.i. R.I. CO2

limestone

37 1.1 1.1 0.1 55.3 0.8 41.6 1.2 32.2

38 1.1 1.5 0.5 54.5 0.7 42.1 0.5 32.3

39 1.4 1.6 0.1 54.5 0.8 41.2 0.2 33.0

40 0.9 0.6 0.1 55.1 0.5 40.4 0.1 32.7

magnesium limestone

32 0.8 0.7 0.2 54.6 1.2 42.7 0.4 31.8

33 1.5 1.8 0.2 54.1 1.2 41.2 0.3 33.1

dolomitic

limestone

19 5.0 1.8 0.4 44.2 8.3 41.6 0.6 32.1

20 1.8 1.7 0.3 53.1 4.2 42.5 0.5 32.6

21 2.4 1.4 0.3 48.6 6.5 37.1 0.9 29.9

calcitic

dolomite

1 1.3 1.3 0.5 34.0 18.9 44.9 0.3 32.4

2 2.5 3.8 0.4 35.0 17.8 43.4 7.8 31.9

3 1.6 2.8 0.4 39.0 13.3 43.1 7.6 32.3

dolomite 58 0.6 1.2 0.1 32.7 20.9 46.1 0.7 32.7

Some portion of the Malula carbonate rock may be used as dolomites in refractory products. Its major use is in the production of hydraulic lime and cement. The last group of calcium carbonate rocks are carbonatites. On Monte Xiluvo, a carbonatite massif, a big quarry has been in operation for many years; it produces crushed stone for aggregates and other building purposes. Results of tests and analyses of carbonatite (Cilek, 1987) in %:

Sample SiO2 Al2O3 Fe2O3 FeO CaO Na2O K2O P2O5 SO3 L.i. CaCO3

1. 17.86 2.29 5.00 2.76 35.23 1.23 1.25 3.60 0.95 25.15 62.89

2. 4.15 2.42 4.00 2.32 36.86 0.05 0.04 <0.01 0.93 39.05 65.79

3. 0.17 1.66 1.00 2.02 53.98 0.01 <0.01 0.01 0.73 41.26 96.35

14. 0.56 1.91 3.60 2.90 37.75 0.11 <0.01 2.08 0.51 41.85 67.38

In some sections of the quarry, the content of CaCO3 may be in agreement with the requirements of the cement industry, although a high content of phosphorus in many samples renders this material unsuitable for use in cement production. On the other hand, the higher the content of P2O5, the better the production of pulverised limestone for agriculture purposes. Certainly the Xiluvo carbonatite can serve as a part of raw material mixture in Dondo cement factory. The Monre Muambe carbonatite is an important source of fluorite. At its extraction a large volume of carbonate rock, a waste product, could be utilized in cement production. Pure carbonate contains more than 80% CaCO3 and about 0.2 to 6.15% of MgCO3. The low-grade rock contains about 40% CaCO3 with a high amount of silicates. The carbonatite covers about 40% of inner caldera and the estimated reserves may be more than 100 million t. The carbonatite massif of Cone Negosse contains several types of carbonatite rocks:

buff, fine-grained carbonatite with about 25% CaO, with bastnaesite

buff carbonatite with baryte, about 20% CaO

apatite-bearing and silicified grey porphyric carbonatite, about 30% CaO.



The carbonatites contain phosphorus and rare earths in small quantities. If these minerals were to be mined economically, calcitic waste could be used in cement production, e. g., as a high calcium carbonate correction of marbles of the Fingoe Formation for example.

Conclusions: Limestones and marls of sedimentary origin should cover the entire demands for calcium carbonate both in a production of cement and lime, and in other industrial branches such as ceramics and glass. Very pure limestones occur in the Cheringoma and Joffane Formations and should be used as filler in paper, plastics, rubber, foodstuff, paint, in ultrafine ground products. Estimated reserves are thousands million tons. Additional large reserves exist in coral limestones along the shore. Crystalline limestones can be used in a local production of lime as this was done in the past, and utilized locally in the cement production; some of it may be used even in the ceramic and glass industry and small portion as a source of magnesium.



Cilek: 5. DEPOSITS and INDUSTRIAL USE of building raw materials

5. DEPOSITS and INDUSTRIAL USE of building raw materials Undoubtedly building materials are essential for every country. They are bulk materials, cheep and locally used. The degree of production and industrial utilization of these materials points directly to the state of development of the national economy. Developing countries with an undeveloped utilization of building materials, despite the high amount of extracting industry in ores, demonstrate clearly the industrial backwardness, low cultural development and colonial dependence. In Mozambique, the building industry was quite well developed even before the independence in 1975. The country was able both to construct big, modern cities and villages and an adequate system of roads and railway lines. In spite of this a typical colonial policy surfaced several times. A good example is the ceramic factory at Umbeluzi, supplied with ceramic mass from Portugal, or the import of marble slabs and blocks from different European countries despite an availability of these materials in Mozambique. On the other hand, several plants were established for an extraction of building materials, a number of big and small quarries flourished in the vicinity of towns, along the roads and railways, small sand pits were everywhere, and sand and crushed stone were the main materials in concrete. The utilization of gravel was scarce and so was the use of lime in mortar and, generally, in the construction industry. Three cement factories served the needs of some provinces, a number of small and big brick factories near the towns served the population, and small indigenous furnaces near limestone deposits produced lime since time immemorial. As an example I should like to present a short extract from a book by J. Romero (1860) in which he describes the coastal zone of Cabo Delgado Province: "On the seashore there are numerous quarries, also on the islands, and the building stone is used in the construction of houses and lime production. Vila do Ibo is extracting large quantity of rock for lime both for the population and the government. Near Pemba, grey massive rock is extracted. In different places exist more than 140 workshops for pottery, and 27 furnaces for lime production. The manufacture of very good quality bricks and tiles is common. For the Governor at Ibo, the house was built and 1,200 barrels of lime were supplied ...." The construction of modern cities, small towns and villages, private houses and villas, naturally for the Portuguese "colons" mainly, all this was possible because of an adequate extracting industry of building raw materials. The raw materials used were these: 1. materials for cement and lime production 2. materials for brick production 3. resources and production of building stone 4. resources of sand and gravel


file:///X|/TK/TK40/TK406/TK4064/Veikko/Ind%20Min%20Moz/Ebook-version/Para5.htm31.7.2008 9:48:13

Cilek: 5.1.Raw materials for cement and lime production

5.1. Raw materials for cement and lime production The term of cement raw materials includes various natural and artificial materials, suitable for cement production. Cements are a powdery material, which when mixed with water hardens in the air or below the water. Several types of cements can be distinquished on the basis of their mineralogical composition: silicate, aluminous, portland (slag and blast-furnace subtypes), pozzolan, white and lime cements. Cement is produced from a mixture of raw materials ground to powder (10-15% remain on the sieve 4,900 openings/cm2), either in the form of dense mud (an older, so-called wet process of cement production) or dry (dry process, most modern because it saves energy). The grinded material is burned in a furnace at a sintering temperature of 1,400-1,450°C to a product known as clinker, which is ground, mixed with additional materials (mainly gypsum) and bagged. In the furnace, chemical reactions occur between the main components (usually 80% of lime, 20% of clay) of SiO2, Al2O3, Fe2O3, CaO and new minerals originate: tricalcium silicate about 50%, dicalcium silicate about 25%, tricalcium aluminate about 10%, tetracalcium aluminoferrite about 15%, and other minerals in small amount. The raw material for cement production must contain all components needed in the composition of clinkers mentioned above and besides these other compounds are present - FeO, TiO2, MgO, SrO, Na2O, K2O, P2O5, CO2, SO3. Some of these components are harmfull and must be limited (MgO maximum 5%, P2O5 up to 2%, K2O + Na2O up to 0.5%, heavy metals etc.). The main components of cement CaO, Fe2O3, Al2O3, SiO2 must be present in a certain amount and at a reciprocal ratio expressed by cement moduli:

1 Hydraulic modulus = CaO /(SiO2 + Al2O3 + Fe2O3) good quality cement has 1.7-2.3

2 Silicate modulus = SiO2 /(Al2O3 + Fe2O3) good quality cement has 1.8-3.3

3 Alumina modulus = Al2O3 / Fe2O3 this ratio lies between 1.5-2.5, but may reach even 12 in quick hardened cements.

By burning the cement mixture, all CaO must be converted into silicate and alumina compounds, because free CaO in cement causes a volume instability. The content of CaO is controlled by the lime saturation factor "LSF" which can be expressed by the formula 100 CaO / (2.8 SiO2 + 1.18 Al2O3 + 0.65 Fe2O3) and should be 85-100 after Lea-Parker. LSF is also calculated using the formula suggested by Kind-Jung [CaO - (1.65 Al2O3 + 0.35 Fe2O3 + 0.7 SiO2)] / (2.8 SiO2) which should be 0.92-0.95. Natural raw materials rarely correspond to these moduli (some clayey or marly limestones) and, therefore, the mixtures must be prepared from several components. One component is known as the "basic" one, usually limestone, the remaining are called "corrective" as for example, clay, shale, soil, quartz sand, bauxite, pyrite, slag etc. A corrective material could be also pure limestone, if marl or impure limestone were used as the basic material. General requirements for cement raw materials may vary from place to place and depend directly on the components locally available. Special grades of cement require also special corrective materials: for Portland cement, the content of MgO must be below 6%, the gypsum which is added to the clinker generally in 3-5% weight volume and serves as a retardant during the hardening of concrete, must be minimal, the physical properties of Portland cement concrete must be high and concrete must be resistant to aggressive solutions. Slag cements, using besides Portland clinker the slag of blast furnaces, must comply in the slag to the ratio (CaO + MgO) : (SiO2 + Al2O3) = 0.95; SO3 content maximum 3% etc. White cement mixed with raw kaolin to obtain the white colour, should contain maximally 2.0% MgCO3, 0.25% Fe2O3, 0.03% MnO and 1.5%SO3. In Mozambique, three cement factories, built before the indenpendence, were established in Matola near Maputo, at Dondo 30 km from Beira and at the port of Nacala (see Fig. 5.1). All factories are situated near the sea ports and have railway links at the site, except Nacala. The Matola cement factory operated originally three furnaces on the wet process, which were replaced in 1973 by one furnace on the dry process, with a daily production of 2,000 t clinker i.e. 600,000 t of clinker a year. The Dondo cement factory is situated on the railway line from Beira to Harare and is equipped with one furnace of wet process, with a daily production of 1,000 t clinker i.e. 300,000 t of clinker a year. The Nacala cement factory is situated directly at the port, it is the smallest one using a semidry process with a daily production of 300 t of clinker, i.e. 90,000 t annually.



The total capacity of clinker is 990,000 t, i.e. roughly 1 million t of the cement production capacity. The raw materials for the Matola factory are obtained mainly from the Salamanga limestone deposit, for the Dondo factory from the Muanza deposit and for the Nacala factory from the Nacala peninsula.

Fig. 5.1. Cement and lime production localities (367 kB) The example is given of the composition of cement raw materials for Matola factory. Its components are these: limestone of Eocene age from the Salamanga deposit (85-87%) clay from the Boane deposit (5-6%) sand from the Umbeluzi river fly ash and slag from the Sonefe Power Plant (3-4%). The following data are presented by the Geol. Institute, Beograd (1985). Quality criteria for raw material composition are: CaO 38-40 % MgO > 3.2 % Na2O < 1.0% Cl < 0.04 % In 1981, in the last year of full information, the Salamanga limestone was analyzed with these results:

Variation interval % x min. - x max.

Mean composition %

CaO 45.8-52.36 49.69

SiO2 4.01-12.50 7.24

Al2O3 0.51-1.91 1.00

Fe2O3 0.92-1.84 1.19

MgO 0.62-0.86 0.72

The table shows a higher CaO content than required by standards and, therefore, limestone is mixed with other materials: Salamanga limestone has LSF 2.35 or 2.23, silicate modulus 3.31 and alumina modulus 0.84. In 1982, the limestone used in the Matola factory had this composition:

average minimum maximumL.i. 37.34 36.31 37.87SiO2 9.97 5.28 12.09Al2O3 1.71 1.28 2.29Fe2O3 1.61 1.28 2.44CaO 47.07 45.64 50.96MgO 0.66 0.60 1.01

Clay (C) composition and ash (A) composition (in %):

average C average A minimum C minimum A maximum C maximum A

L.i. 14.28 21.51 13.13 20.44 16.18 22.95

SiO2 44.96 43.36 41.63 40.89 49.81 47.01

Al2O3 18.23 19.27 16.70 17.46 21.16 20.39

Fe2O3 13.95 4.11 12.06 3.87 16.04 4.27

CaO 5.76 9.24 1,68 7.00 8.40 12.60



MgO 0.96 1.36 0.60 1.01 1.41 2.02

SO3 - 0.69 - 0.32 - 1.19

Sand composition from 1985 (in %):

SiO2 78.64

Al2O3 9.69

Fe2O3 2.48

CaO 0.56

MgO 0.40

L. i. 4.88

The annual consumption of gypsum for all cement factories is about 40,000 t with a required SO3 content 41-43%. All gypsum is imported despite the fact, that huge reserves exist in the Temane Formation near Vilanculos. The last bulk of gypsum comes from the Palabora deposit in S-Africa, where it is a waste from phosphoric acid production. Gypsum composition (1986 import) (in %):

SiO2 3.00 CaO 36.40 insolubles 2.39

Al2O3 0.51 MgO 0.40 L. i. 12.25

Fe2O3 0.16 SO3 46.37

The cement factory at Nacala produces good-quality portland cement from a mixture of about 77.5% of limestone, 21% of clay and 1.5% of roasted imported pyrite (+ 5% of gypsum). The limestone is quarried at about 20 km E of the factory from Pleistocene coral limestone at Relanzapo, the clay, of the Cretaceous, from Natimanga, at about 10 km S of the factory or from Quissimanjulo S of Relanzapo. The silicate modulus is 2.33, that of alumina 1.54, lime saturation factor is 105. Average analyses show this composition (in %):

Mixture Limestone Clay Pyrite GypsumSiO2 12.51 2.59 50.24 3.40 0.7Al2O3 3.31 0.38 14.50 2.93 0.3Fe2O3 2.08 0.24 5.99 71.99 0.2CaO 42.28 52.08 10.64 1.96 33.0MgO 0.60 0.80 1.61 - 0.6H2O - - 7.00 13.19 43.97 SO3L.i. 35.60 42.87 13.22 - 14.7Total 96.38 98.96 102.72 93.47 93.47

The lime produced in Mozambique is used just marginally in the building industry, in agriculture and mainly for saturation purposes in sugar cane factories. Two lime production units operate on an industrial basis -the biggest unit is established in the Dondo cement factory, where one rotary kiln for cement was reconstructed for lime production. The kiln is heated by oil and has an annual production capacity of 35-40,000 t of lime. The raw material is pure Cheringoma limestone. The whole production goes to the sugar factories and it is envisaged its export to Malavi and Zimbabwe. The second unit is at Salamanga, S of Maputo, with two vertical kilns electrically heated, with an annual production capacity of 9,000 t. The raw material is Satamanga limestone mined at the spot, and the production goes also to sugar factories in S Mozambique. The hydraulic modulus was calculated and its mean value is 3.49 which shows that the lime is highly hydraulic. A proposed production of hydraulic lime and its utilization for construction purposes could therefore be established just at



Salamanga. Review of lime production units in Mozambique (see also Fig 5.1):

No Locality Province CompanyInstalled capacity

t/year

1 Salamanga Maputo C. Mozambique 9,000

2 Dondo Sofala C. Mozambique 40,000

3 Buzi-Estaquinha Sofala Acucar Buzi 800

4 Boroma Tete C. I. Tete 3,000

5 Chire Zambezia C. I. Zambezia 2,000

6 Corrane Nampula C. I. Nampula 800

7 Pemba (7 km) Cabo Delgado Cooperativa 200

8 Malulu Niassa C. I. Niassa 800

Total annual lime production capacity 56,600 t

Besides these lime furnaces operated on an official basis, small local furnaces are used and operated in many areas with an occurrence of limestone. The localities are these:

9 Morrumbene Imhambane, using Jofane Formation limestone10 Fornos Inhambane, in the centre of the Jofane Formation area11 Zamulanlomba Manica, crystalline limestone of Barué Formation12 Malona Manica, crystalline limestone of Barué Formation13 Muchanga Cado Delgado, Tertiary limestone14 Namuno Cabo Delgado, crystalline limestone



Cilek: 5.2. Raw materials for brick production

5.2. Raw materials for brick production These include all products of a natural decomposition of rocks which can be used in the brick production either in their natural state or after a necessary beneficiation. Brick materials are generally plastic and have the ability to be shaped into desired forms; they possess low sintering properties, burning below 1,100°C. Two main components in brickmaking materials can be distinguished-the plastic one and the nonplastic one. These two components may be present in desired proportions in natural clays, but usually the necessary blend must be prepared by adding either a plastic component (clay) or a nonplastic, opening component (sand, silt, ash, slag, fly ash etc.). The main brickmaking materials are clays and claystones, loam, marls, weathered schists etc. Harmful to the final products are calcitic concretions, fragments of rock, gypsum, siderite, organic matter etc.; can cause irregularites in the mass during the burning. Bricks are burnt at different temperature ranges - high temperature is used for a mass with a low alkali content, low iron content and high alumina and silica content, and hard-burnt products are obtained which can substitute even stone in buildings or roads pavements. The high content of alkalies, iron and organic substances may cause a premature melting of the brick and its deformation, and the burning temperature must be lowered. Unburnt bricks-adobe-are produced of brickloam, dried in the sun. Bricks have been used since time immemorial everywhere where stone was not available. Brick products fall into several groups: 1 wall materials - bricks common, massive, holed, light-weight, thin-waited, vitrified, enameled etc. 2 bricks and structural elements for chimneys 3 roofing material-tiles 4 ceiling structural units 5 sewer pipes and drain tiles 6 others - wall and floor tiles, paving bricks, crushed bricks etc. In Mozambique, as in many other countries, bricks are produced of different clays, loams and weathered natural materials such as lateritic clays, kaolinitic and illitic clays, alluvial clays and even clays of swamps and mangrove soil. In S- Mozambique, many clayey raw materials contain a high proportion of smectite from weathered Karroo volcanics and must be corrected by adding sand or ash, in the coastal zone often swamp deposits are used-which yield dark-grey organic clays of a very high plasticity. In higher elevated zones and within the crystalline rock zones, reddish lateritic clays are used of which good-quality bricks, tiles and pottery can be produced (see Fig. 5.2). In the past, many brick workshops and factories were built without any preliminary testing, by visual experience only, resulting in the production of low-quality bricks and tiles. When the production of light-weight bricks, holed bricks and tiles was started, the low quality of the raw material was reflected in a big amount of waste. In some brick factories waste is very high not just for the low quality of the raw material, but also for a lack of beneficiation of the material-diminishing the plasticity by using an opening material or by washing the clay to remove rock particles and sand to increase the plasticity. To supplement industrial brick products, small-scale brick units were established experimentally to be used by the population for building houses. Such experimental units using a mixer, shapper and a small kiln for 200 bricks have now been in production at Chimoio for several years.


Cilek: 5.2. Raw materials for brick production

Fig. 5.2 Brick factories - locality map (303 kB)

TABLE: Brick factories in Mozambique (340 kB) The total production capacity (planned or installed) of Mozambique in units (bricks, tiles, pipes) is about 32 million, the recent or possible output is 10 million units less. The main products are bricks, usually holed, exceptionally massive, full. One brick factory produces also coloured pottery (Maholela), sewer pipes are produced in Maputo and Nampula. Other small brick factories are situated at Chokwe and Massingir in the Gaza Province, at Caia in the Sofala Province, at Moatize and Ulongue in the Tete Province and at Montepuez and Mueda in the Cabo Delgado Province, at Mocuba and Molocue in the Zambezia Province. How many other brick factories had been in production in the past is not known. Small pottery workshops using brick clay are scattered throughout the country, one is near Chimoio. The biggest accumulation of brick - and tile factories is naturally near Maputo, other factories are almost regularly distributed throughout other provinces in places of population concentration.



Cilek: 5.3. Resources and production of building stone

5.3. Resources and production of building stone Building stone is the most common building material used in two main fields, as a dimension stone and a crushed aggregate. According to the utilization and the degree of dressing, the grades of dimension stone are these: rough stone or quarry stone, not dressed stone for rough products - paving blocks, vergas, ashlar, kerbs and coarsely worked elements for construction cut stone products shaped into building plates, paving stones, covering plates etc. dimension stone for statues and monuments curtain-wall panels and slabs for special purposes The rock for dimension stone should be "sound", unweathered, resistant to mechanical effects and chemical corrosion, with a compression strength of 40-180 MPa, an absorption capacity below 5%, with a surface of uniform composition. The requirements for each type of product have been established by standards. Crushed aggregate production is prevailing and in immense quantity when compared with dimension stone production. Crushed stone is handled in bulk and its value is low. The main cost of crushed stone is in the consumption of energy and transport charges. Therefore, the stone, besides toughness-resistance to impact, hardness-resistance to abrasion and soundness-resistance to climate and environmental impacts, should also easily be extracted with a dense network of cracks and joints and of appropriate hardness. Gabbro or amphibolite, for example, are expensive to crush when used for ordinary purposes, limestone or dolomite are softer and the energy consumption for crushing is low. Transport costs of a crushed aggregate are generally high and the transport distance should not exceed 50 km. Also the quarry capacity should not exceed the market needs within an economic transport distance, i. e. usually more than 1 million t per year. An exception are large railway quarries established at the railway lines, and using railway lines and railway trucks for a long-distance transportation of crushed aggregate. Therefore modern crushing units are mobile or semimobile, with a capacity of several hundred t/hr and moving from place to place in accord with the demands of the market. Building stone includes all possible types of rock of appropriate properties: granites diorites, gabbrodiorites and gabbros, amphibolites, trachytes, basalts, phonolites, andesites, rhyolites, quartzites, limestones, dolomites, gneisses, sandstones etc. The best-quality dimension stones are fine - to medium - grained granites and their varieties of the igneous rock group, limestones of sedimentary rocks and marbles of the metamorphic group. Excellent mechanical properties when crushed display basalts, dolerites, trachytes and fine grained granites. A crushed aggregate should be replaced everywhere by a natural aggregate - sand and gravel, because the latter is almost 50% cheaper and often of a higher quality in concrete. The establishment of quarries for building stone is determined both by local consumption and geological and geomorphological conditions. In Africa, the best places for a quarry are usually inselbergs, which represent remnants of an older peneplain and are generally rocks of a higher resistance to weathering. Inselbergs are composed of granitic intrusion or their composition is identical to that of surrounding rocks. An overburden is nonexistent on steep slopes, the top is slightly weathered. Convenient places for quarries are also steep slopes of lava flows and intrusive massifs of volcanic rocks. Dolerite dykes can form distinctive morphological ridges as well as quartzite beds. Young tectonic escarpments and surroundings of rift valleys offer excellent examples of different rock outcrops and extraction of stone. In Mozambique, deposits of building stone are immense and every place of consumption could be supplied from quarries located nearby. An exception is coastal S-Mozambique made up of young sedimentary formations, where the only building stone is represented by soft Tertiary limestone. A similar situation exist within the Zambezi delta, futher N the coastal belt is narrow with outcropping crystalline rocks close to it. Coral limestone-the



principal building stone of old swahili towns-is present both on the seashore and the islands (see Fig. 5.3).

Fig. 5.3. Building stone-quarries (according to the Ministry of Construction and Water) (395 kB) Many small and big quarries have been opened for a shorter or longer periods when even the need arouse. Few quarries are still in operation and several localities have been investigated to secure industrial reserves of building stones. Many are of ornamental stone quality, like the newly discovered labradorites at Moatize near Tete, black granites near Gondola and Lurio area, brown and red granites of the Tete Province and many others. It is impossible to present a complete lists of localities in Mozambique in which building stone occurs. The general review shows the distribution of the main rock types in the provinces:

Province Type of rock Area Remarks

Maputorhyolites and basalts limestones red sandstones

Lebombo Mts. Salamanga and S Maputo-Ponta Vermelha

also perlites, tuffs, tuffites, obsidian inferior quality, Pleistocene cemented sands

Gazarhyolites and andesites, basalts limestones

Lebombo Mts. Mapulanguene and Massingir

Cretaceous

Inhambanelimestones beach rocks

Rio Save-Vilanculos, Inhambane coastal zone

Miocene Jofane Formation Quaternary sandstones concretional limestones

Manica

dirrerent magmatic and metamorphic rocks - granites, gabbros, diorites, gneisses, marbles, quartzites, schists sandstones of Karroo basalt, andesitic basalts dolerites and rhyolites dolerites, serpentinites, gabbro

the whole province northern part SE part of Chibabawa near Manica

Arhaic and Precambrian Karroo Karroo post-Karroo

Sofala

metamorphic and magmatic rocks of Archean (Vila Machado Formation) and Precambrian gneisses, anatexites, granites, quartzites and marbles, basalts and rhyolites, gabbro and syenites trachytes, limburgites and augitites carbonatite sandstones limestones

western and northwestern part along the rift valley Gorogosa massif margins of rift valley nearZambezi MonteXiluvo Sena Formation Cheringoma Formation near Buzi-Cheringoma plateau

Karroo Post-Karroo Post-Cretaceous Cretaceous Tertiary



Tete

big variety of rocks gabbro-anorthosites granitic gneisses, charnockites brown granites, labradorites serpentinites marbles and quartzites marbles alkaline lavas rhyolites and andesites carbonatites

Tete Complex Angonia Monte Atchiza Fingoe Formation Chidue Bandur Tambara, Changara near E of Tete Cone Negose

Angonia, Fingoe arround Tete Complex Lubata on Zambezi river Lupata, L. Cretaceous Mid-Zambezi rift

Zambézia

granites, gneisses, syenites nepheline syenites marbles quartzites, schists

along the E margin of East-African Rift Valley

marbles also for lime production

Nampula

gneisses and granite-gneisses granites, charnockites, migmatites marbles, quartzites, schists amphibolites, serpentinites basalts and thoileites coral limestones

coastal belt near Angoche on the coast

igneous massifs Precambrian, amphibolite and granulite facies, Jurassic-Cretaceous Pliocene-Holocene, old towns of Mossuril and Mozambique

Cabo Delgado

granites, granite-gneisses migmatites gneisses marbles ultrabasic rocks and gabbroic massifs volcanic vents sandstones coral limestones

Montepuéz and river Lúrio belt within S of Rovuma river Rovuma basin coastal belt

tectonic graben grits and conglomerates of Cretaceous elevated coral platforms Holocene coastal and island reefs

Niassa

granites, granite-gneisses red granites and syenites carbonatites charnockites marbles sandstones

degree of knowledge is low NE of Metangula

red granite near lake Niassa Karroo

Quarries of building stone are scattered throught Mozambique. A few of these which are still in operation are marked in the attached map. Many other quarries around settlements, roads and railways have been abandoned, but could easily be reopened if the machinery were again newly installed. Typical is the situation in the Beira corridor where only two quarries, Xiluvo and Matsinho near Chimoio, operate. However, an other big railway quarry E of Matsinho called Garuzo could immediately be put into operation. In the following table, 26 localities are listed with an installed capacity of 1,625 m3/h representing an annual



capacity of about 6 million m3. With the start of new construction projects, the geological situation of the country can easily secure an additional production of building stone close to the construction sites as this had been arranged in the past, for example, at the Cabora Bassa dam, a recently errected dam in the Little Lebombos Mts. near Maputo and others.

Province Name Organization Capacity installed m3/h

MaputoEstevel I. Estevel II. Movene I.

M.C.A.Prosul120 150 45

Gaza Mabalane M.C.A.-C.I.G. 30

Inhambane Unguana M.C.A.-C.I.I. 20

Sofala Xiluvo I.,II.,III. M.C.A.-Promoc 45 (100, 10 no production)

Manica Chimoio M.C.A.-C.I.M. 45

Zambezia

Naciaia Móvel M.C.A.-CETA 30

Naciaia I. M.C.A.-CIZAM 20

Naciaia II. M.C.A.-CIZAM 20

Longoze M.C.A.-CETA 20 destroyed

Longoze Movel M.C.A.-CETA 20 destroyed

Mocuba M.C.A.-CETA 15

Mocuba M.C.A.-C.I.S.-C.T. 50

Gurué M.C.A.-C.I.S.-C.T. 50

Mugulamo M.C.A.-C.I.S.-C.T. 70

Alto Ligonha M.C.A.-C.I.S.-C.T. 70

Tete

Revuboe M.C.A.-C.I.T. 50

Aqua-Boa M.C.A.-CETA 10

Aqua-Boa M.C.A.-CETA 30

Ulonque M.C.A.-CETA 50

Songo M.C.B. 350 for the Cabora Bassa dam

Nampula

Namialo CFM M.I.S.-C.F.M. 70

Naguema M.C.A.-C.I.N. 30

Barragem M.C.A.-C.I.N. 20

Murrupula M.C.A.-CETA 30

Cabo Km 50 (Pemba) M.C.A.-C.I.C.D. 50

Montepuez M.C.A.-C.I.C.D. 10



Delgado Mueda M.C.A.-TAMEGA 25

NiassaBagarila M.C.A.-C.I.N. 50

Cuamba M.C.A.-C.I.N. 30

26 localities Total 1,625 m3/h



Cilek: 5.4. Resources of sand and gravel

5.4. Resources of sand and gravel Among the world resources, both metallic and nonmetallic, the tonnage and value of sand and gravel highly outrank all other substances. Neither gold nor copper, neither diamonds nor iron ore, but common building sand and gravel of a value of 2.5-3.0 US $ per ton represent the biggest mineral value. Millions of tons are produced annually in every country with a developed industry and billions of dolars are spent on these materials. Gravel and sand are used in the building industry as a natural aggregate in the production of concrete (in a mixture with 10-15% of cement), drainage and road base layers, stabilization layers etc. Sand is a elastic sediment, grain size 0.063 to 2 mm, below is silt and clay, above it gravel. Sand is usually divided into three classes fine-grained 0.063-0.25 mm medium-grained 0.25-1.0 mm coarse-grained 1.0-2.0 mm. Sand is dominantly quartz with more or less feldspar, mica, silt and clay and rock fragments, well-sorted with different range of grain size. The grains of a sand body that had undergone a polycyclic development are always uniform, e. g., beach-sand deposits. River deposits, alluvial and terrace accumulation are less sorted, in the upper reaches of streams ill-sorted, in the lower reaches and matured rivers well-sorted. The genesis of sand is reflected in some typical features such as degree of rounding, sphericity, surface-grain coatings, etc. By contrast, gravel, when compared with sand, is of a very variable composition, with grains and pebbles of different rocks reflecting the original geological environment - the source area. The granules of gravel have to be composed of sound resistant rocks, should be free of mica, clay, silt and flat grains and soft rocks. Gravel varies in grain size from 2 to 128 mm and again can be divided in three classes: fine-grained gravel 2.0- 8.0 mm medium-grained 8.0- 32.0 mm coarse-grained 32.0-128.0 mm Gravel and sand are usually mixed together and according to the ratio gravel/sand these classes are distinguished (Kuzvart, 1984):

grain >2 mm 100% 50% 25% 0%

gravel sandy gravel sand with gravel sand

grain <2 mm 0% 50% 75% 100%

For building purposes, the best-quality gravel-sand should have a wide range of grain size to be used in concrete and rounded grains to decrease the consumption of cement. In nature, sands and gravels are rarely pure; therefore, impurities of clay, silt, mica, weak rock types must be removed by washing, screening and, in some cases, by heavy-media separation. The modern building industry has strict requirements for sand-gravel quality and dressing is a standard necessity. Sand and gravel used in reinforced concrete should have grains below 30 mm and a main grain-size fraction within a range of 4-7 mm. Often, sand has to be removed if present in too big quantities. Harmfull ingredients are sulphides, alkalies, clay and organic matter. Specifications relate, apart from grain size, to compression strength (gravel must reach about 150% of strength to compare with the required value for concrete), resistance to freezing and thawing, sorption capacity, the property to bind the grains with the cement or bitumen, resistance to abrasion and other requirements similar to concrete specifications. Deposits of sand and gravel - a material which originates from a disintegration of rocks and a subsequent transport by stream followed by gradual sorting - are mainly alluvial deposits of streams, older alluvial deposits of terraces and fans, deposits made by meltwater from the glaciers, uplifted deltas and beaches with eolian deposits. Some sand deposits originate from a disintegration of sandstones and conglomerates of older geological formations. The enormous use of a natural aggregate has exhausted the inland deposits in many countries, also the protection or arable land and the environment has initiated a search for alternative sources. These have been found on the shallow sea floor, near the seashore, where dredgers can operate.



In Mozambique, huge accumulations of building sand and gravel developed in the coastal zone: on beaches, in the dune belt and on the shelf. The development of sand-gravel deposits is connected with the geomorphological development of the African continent. Late Cretaceous - Mid Tertiary African land surface with a widespread and deep weathering crust supplied detritus to the basins until the Pliocene during the Post-African land surface phases. The Late-Tertiary, mainly post-Miocene movements connected with the Niassa-Shire rift and finally the Pleistocene upheaval (Cilek, 1985) caused the transport of huge detrital masses from the African interior by streams to the shore. It is estimated that from then to the present, the continent at the Limpopo paleodelta (Cilek, 1985) spread for about 80 km over the shelf. The main sand and gravel accumulations exceeding 1,000 m are present in the Limpopo paleodelta, the Zambezi river paleodelta - first from the area of the present mouth of the river Buzi, later from the Quelimane area and recently from the Zambezi mouth -and from several other rivers. During the Quaternary, from the Main Glacial period before about 100,000 years till the Last Glacial Period (18,000-10,000 years), the streams straightened their courses while the seawater table was lowering, cut deep into the floor depositing sand and gravel on the shelf far from the present seashore line. Several distinctive canyons on the shelf are in support of this development. During interglacial periods with a higher sea level, the rivers lost theirs transporting power, their mouths become chocked with sediments and rivers started to meander. The present river valleys are extremaly wide, the river Buzi has about 8 km width at Beira, the river Lurio 6 km and the river Zambezi has shallows in its lower reaches of several km and sand bars. The thickness of sand and gravel deposits in these old river valleys attains sometimes 50-70 m, the thickness on river terraces is not known. Subrecent and recent tectonic movements along the rift valley formed different sand and gravel accumulations in different zones of the stream. For example, the river Zambezi, when leaving the narrow pass at Lupata volcanics near Tambara, discharges coarse grained sediments and widens its bed. When reaching the delta proper, the stream is slow, the river bed narrow with several channels and only fine silt with a high amount of mica is deposited on the shelf. The mouth of some rivers is chocked and are flowing over long distances parallel to the shoreline before entering the sea. This phenomenon is due to a rising sea level and a diminishing stream gradient in the lower reaches. The Limpopo river forms wide alluvial flats of dark clay soil near its mouth; other rivers e. g. the Save, Buzi etc. are surrounded by mangrove swamps with clay deposits. Besides alluvial sand and gravel, huge reserves of sand are on the beach and in the dunes. These sands are generally well-sorted, grain size mostly 0.1-0.2 mm. Sand and gravel with a grain size of more than 2 mm are present at the mouth of rivers in which a sorting by sea energy had not yet taken place. Eolian sands occur either in recent or subrecent dunes in a belt near beach - these sands are white or grey contrary to interior dunes which are generally of a red colour and underwent weathering. Red-dune sands are slightly clayey and useable as a 'building sand in stabilization layers and for other purposes (some of these may be natural foundry sands), but cannot be used as a part of aggregate. Other sand and gravel accumulations occur in river terraces and in local geomorphological depressions - in East Africa known as mbuga basins - where layers of detrial sediments alternate with argillaceous beds. Generally, coastal Mozambique may provide inexhaustible reserves of sand and gravel, the interior of the country has substantial deposits of sand and gravel in alluvial deposits (many are auriferrous). Localities of gravel and sand in the provinces of Mozambique:

Province Maputo: Rio Muira, Rio Umbeluzi, Rio Incomati, Goba, Marracuene and river terraces and coastal dunes

Province Gaza: Chokwe, Massingir, Macia, interior dunes and river terraces along the river Save, Jofane, Madindze, Divinhe, Vilanculos, Nova Mambone, beach and dune sands

Province Inhambane: along rivers Revue and others near Manica (with gold), Rio Muda, Pungoe, and tributaries of Rio Zambeze, Tambara, Dombe etc.

Province Manica: Rio Zambeze and tributaries, Rio Pungoe and Save, Chemba, Caia, Marromeu

Province Sofala: Rio Revuboe (with gold), depression at Rio Condedezi, weathered sandstones of Karroo and Post-Karroo

Province Tete: Rio Zambeze, Licuare, Raraga, Ligonha, belt of coastal beach ridges and eotian sands at Quelimane - Pebane - Moebase

Province Zambezia: Rio Lurio and tributaries, small sand bodies on the seashore, proluvial sands

Province Nampula: Rio Lugenda and Rio Rovuma, small streams and beach deposits beach deposits



Province Cabo Delgado: Province Niassa:

on Lake Niassa, Rio Lugenda and Lurio, Karroo sediments near Metangula



Cilek: 6.1. Ceramic industry

6. CERAMIC and GLASS INDUSTRY; REFRACTORIES 6.1. Ceramic industry The group of ceramic raw materials for the production of white-ware ceramic products includes three components: quartz, feldspar, kaolin or clay. Other materials that can be added to the ceramic mass are limestone, dolomite, bentonite, etc. depending on the technology of production and on the required properties of the final product. The old practice using "classical" materials for the ceramic batch, i. e., a silica-alumina composition, has changed and more flux materials are used nowadays -illitic clays with dispersed iron, alkalic rocks of which nepheline syenite is a typical representative, tuffs, lithium compounds and more feldspar and limestone. This results in a shift from silicate ceramic mass to calc-silicate composition. An increased portion of Na2O, K2O, CaO and MgO in the batch reduces the content of Al2O3, and SiO2 - minerals which need high sintering temperature - which means a saving of energy. The production of different ceramic products requires a large variety of ceramic mass composition: 1. hard porcelain - sintering temperature 1,400-1,450°C composition: kaolin clay, ball clay, quartz, feldspar 2. soft porcelain - sintering temperature 1,250°C 3. sanitary ware - sintering temperature 1,230°C 4. earthenware - sintering temperature 800-950°C 5. wall tiles - sintering temperature 1,050°C 6. white floor tiles-sintering temperature 1,300°C The content of kaolin clay in group 1 is about 40-65%, in group 3 20-30% only. Ball clay or other ceramic clay amounts to 5-10% in hard porcelain and is increasing towards lower temperature sintering products. Quartz constitutes about 10-20% of the body, feldspar about 20-40% in groups 1, 2, 3 but has a reduced content in groups 4, 5, 6. In the production of earthenware and tiles, dolomite and limestone are added in amounts ranging from several % to 15%. In fact, each ceramic factory uses different raw materials for different products and the mixture often depends on the availability of these materials in each particular country. However, basic requirements have to be observed such as SiO2 content, Al2O3 content and others - mainly coloured oxides, which may cause a colouring of the ceramic body after firing. The diagram shows relationships of different components (basic ones only) in different ceramic products (Fig. 6.1).

Fig. 6.1 The composition of different ceramic products (88 kB) Several auxiliary materials in the ceramic industry include opacifiers in sanitary ware such as tin oxide, zircon, rutile, apatite and glazes in porcelain such as feldspar, dolomite, limestone, talc, wollastonite and several other synthetic ones. Another important auxiliary material is gypsum used in a preparation of moulds. In Mozambique, the only "pure" white ceramics, i. e., wall tiles and minor production of ceramic table-ware were produced by the Umbeluzi ceramic factory situated about 30 km W of Maputo. The factory "rarity" is in that it lacks a section for the preparation of the ceramic mixture, because it used a ready-made ceramic batch imported from Portugal. A recent investigation revealed different sites of an occurrence of ceramic materials in Mozambique which can be used in the ceramic body for wall tiles production (see Fig 6.2).

Fig. 6.2. Map of raw materials for white ceramics (389 kB) Zuberec-Lacko-Novysedlak (1984) present the results of some tests made for the Umbeluzi factory. In 1981, the first


Cilek: 6.1. Ceramic industry

bench test was made in Czechoslovakia with this mixture for wall tiles production: 1. clay from Umbeluzi deposit near the factory - 30% 2. limestone of Eocene age from Salamanga near Maputo - 20% 3. kaolin from the pegmatite mine Muiane, Nampula Province - 13% 4. kaolin - feldsphatic sand from Nacala, Nampula Province - 20% 5. sand from Marracuene N of Maputo - 17%. The composition of the mixture was calculated on the basis of the content of 68% SiO2 and 10% Al2O3. Results of chemical tests of above materials:

% SiO2 Fe2O3 Al2O3 CaO MgO TiO2 Na2O K2O1 76.17 1.22 12.93 0.61 0.66 0.18 0.30 2.302 7.42 3.15 1.97 43.88 0.71 0.11 0.67 0.193 61.17 5.94 16.22 0.70 1.36 1.36 1.26 2.144 46.66 0.39 33.97 0.14 0.20 0.19 0.16 0.385 97.78 0.03 0.16 0.08 0.01 0.17 0.16 0.20

The bending strength after drying is 1.57 MPa, after 45 hours of burning at 1,200°C 16.7 MPa, shrinkage 0.80%, water absorption 24.7% and volume weight 1,611 kg/m3. The tiles are of a white, slightly greenish colour, with water absorption of 21.3%, volume weight 1,609 kg/m3 and bending strength 19.1 MPa. They represent a product of good quality. The second bench test used a reduced number of raw materials in the ceramic body: 1. clay from Umbeluzi - 39% 2. kaolin - feldspathic sand from Nacala - 28% 3. limestone of Salamanga - 18% 4. sand from Marracuene - 15%. The same calculation and chemical analyses were made in Czechoslovakia:

% L.i. SiO2 Al2O3 TiO2 Fe2O3 CaO MgO K2O Na2O1 7.56 61.80 16.57 1.16 7.20 1.68 1.31 1.68 0.892 3.97 75.30 15.81 0.14 0.66 - 0.20 3.65 0.103 41.0 7.25 1.27 0.10 1.50 47.95 0.25 0.34 0.234 0.33 96.90 1.78 0.25 0.20 - 0.15 0.30 0.01

The analysis of sintered ceramic mass has revealed 68.9% SiO2, 10.6% CaO and 12.8% Al2O3. The colour of tiles is red, due to a high content of iron from Umbeluzi clay. The sintering temperature must not surpass 1,050°C. The ceramic mass may be improved by adding 0.2% of soda ash and 0.1% of sodium silicate. The second test proved that tiles can be produced without kaolin from Muiane. However, a variation in the quality of Umbeluzi clay may cause some problems in final products and the red colour body (at the level of brick or pottery quality) in wall tiles has to be covered up by a strong opacifier.



Cilek: 6.2. Glass industry

6.2. Glass industry Glass is made substantially by melting silica sand and fluxes in a glass-melting furnace. Batch materials for glass production are of a soda-lime-silica composition: pure silica sand as glass forming oxide, soda - Na2O as fluxing agent, lime - CaO or CaO + MgO as stabilizing material to provide chemical durability, Al2O3 and B2O3 as auxiliary materials for high strength and prevention of devitrification, and others - sulphur or sulphur oxides to improve melting and the refining process. Silica sand should be very pure (see chap. glass sand) with about 99% SiO2 and low in iron, alumina, chromium, titanium etc. Soda ash with Na2CO3 over 99%, with maximum 0.5% NaCl and 0.1% Fe2O3. Limestone content should have more than 54% CaO + MgO and maximally 0.1 % Fe2O3. Feldspar more than 19% Al2O3, alkalies more than 11%, and maximally 0.1 % Fe2O3. Soda ash produced in the Solvay process or from natural trona ore accounts for more than 50% of the cost of the raw material per ton of glass. Therefore, it is often substitued by cheaper materials such as nepheline syenite (potash feldspar and nepheline). The dissolution rate of silicate minerals in the glass melt depends on the ratio alkalies: silica and is in favour of nepheline with Na2O - SiO2 ratio 1: 2 which enables melting within 11 minutes at 1,350°C. When using albite, with Na2O - SiO2 ratio 1 : 6, melting requires 103 minutes at the same temperature. Other materials include aplite (Al2O3 more than 22%, Fe2O3 0.1-0.4%), sodium sulphate - salt cake (Na2SO4 more than 99%, NaCl 0.002%, Fe2O3 0.2%), gypsum and anhydrite, some decolouring and colouring agents etc. Part of the glass batch is broken glass - cullet (up to 35%) which melts at 800°C and, therefore, can accelerate the melting of the batch. All products of the glass batch must be 100% below 0.4 mm passing the 30 mesh screen. Fluxes are very important agents both in the glass and ceramic production because they a) facilitate reactions in the solid phase during sintering and hardening b) are a substantial part of the batch in glass production c) lower the energy consumption, the melting temperature, quicken the process of sintering and melting and enable to use shorter melting times. Modern fluxes include a number of raw materials: rocks with nepheline (perthite, nepheline) rocks with albite (higher SiO2) alkali-feldspar syenites (low-coloured oxides) rhyolites/phonolites: K2O/Na2O ratio = 7.5 - 51/0.6 - 0.7 only in coloured glass products wollastonite lithium minerals. An increased production of container glass, better, thinner and cheaper, fiber glass and foam glass (for insulating purposes) requires an increased use of cheap fluxes, represented by the above mentioned materials, of which the most used are nepheline syenite, phonolite, rhyolite, trachyte and Li-minerals. The production of the glass industry can be divided in these groups: 1 Containers glass (bottles and jars)


Cilek: 6.2. Glass industry

2 Pressed and blown glass (table, kitchen, art, novelty glass, lighting ware, glass fiber) 3 Flat glass (sheet or window glass, plate, laminated, safety glass) In Mozambique, container glass only was produced, when its production started in the Machava glass factory in Maputo in 1957, with a daily production of 4 t. Later, the production increased to 59 t per day (1972) including an automatic production of transparent and coloured bottles (brown and green). Nowadays, a reconstruction is under way for a production of 125 t per day of glass containers. Apart from this, furnaces produce daily 20 t of container glass, pressed and blown glass (cups, plates, lighting ware etc.) of natural colour (the glass has a greenish tint) and coloured glass using colouring agents such as amber, sulphur, coal minerals or charcoal, sodium bisulphate, chromite etc. Composition of the batch: 55-58% sand 18-20% soda 15-18% limestone 5- 6% feldspar cutlet, auxiliary materials. Sand is extracted at Marracuene, but is not dressed, limestone comes from Salamanga. Both materials are at about 40 km from the factory. Feldspar is normally obtained from N-Mozambique, from Ribaue or Tulua: other materials are imported - soda, sodium sulphate, sodium nitrate, arsenic and cobalt oxide. The main problem in the production of glass is the use of natural sand from Marracuene and limestone from Salamanga, of this composition: %

Sand LimestoneSiO2 89.6 89.9 10.4Al2O3 5.3 6.2 3.6Fe2O3 0.7 0.7 1.1CaO 0.1 0.1 46.6MgO 0.1 0.1 0.5Na2O 0.2 0.2 -K2O 1.8 1.7 -

Both sand and limestone have a high content of iron, limestone a low content of CaO and MgO. The quality of the glass batch could correspond to requirements of container glass, but barely to that of pressed and blown glass. The dressing of sand and limestone would be necessary.



Cilek: 6.3. Refractories

6.3. Refractories Classification of refractory materials is based on their general composition and, to lesser degree, on the physical properties, which must be heat-resistant (minimum 1,500°C), thermal shock resistant-capable to withstand different ranges of temperatures, resistant to mechanical stress and chemical attack. Refractory materials can be divided into three groups:

1 Acid refractory clays or fire clays melting point °C

kaolin - Al2O3, SiO2 1,785

silica-SiO2, as quartz sand, crushed quartz, quartzite, diatomite 1,700-1,615

2 Basic magnesia, MgO as magnesite 2,800

lime-magnesia (CaO • MgO) from dolomite 2,370

limestone CaO, CO2 2,485

zirconium oxide ZrO2 2,700

from zircon ZrO2, SiO2 2,303

barium oxide BaO from baryte BaSO4 1,920

3 Inert aluminium oxide Al2O3 2,050

between acid silica - bauxite or sillimanite, andalusite

basic magnesia kyanite, dumortierite

chromium oxide Cr2O3 2,430

chromite Cr2O3 • FeO 2,050

graphite (no oxigen or air) 3,700

In the past, fine clay and kaolin made up the bulk of refractories - aluminosilicate bricks, usually as a combination of flint refractory clay, some plastic clay and high-alumina clay or bauxite. These bricks were used in furnaces, boilers and for many other purposes. Modern high-alumina bricks of group 3 or alumina-silica refractories containing more than 50% of alumina consist predominantly of mullite (3 Al2O3 • 2 SiO2) crystals. The raw materials used are bauxite (Al(OH)3), diaspore (Al2O3 • H2O), kyanite, sillimanite, andalusite (Al2O3 • SiO2) and fused and sintered alumina (Al2O3). There is a steady trend towards the use of high-alumina brick and tile to replace fire clay. These modern mullite products are used in rotary kilns in the production of cement and lime, roof bricks for electric steel-melting furnaces, blast furnace lining and blast furnace stove bricks, ladle bricks and bricks for Al-melting furnaces. Basic bricks, mainly magnesia and chrome, are used for basic slags in metallurgical furnaces such as steel, nickel and copper, zirconia bricks as special refractories in electrical furnaces for refining precious metals. Silica bricks are acid bricks made mainly from ganister, a true quartzite, also from silica sand and diatomite. The bricks have the advantage of a common availability of the material and low price, they are resistant to the attack of iron oxides and have an excellent hot-load resistance at temperatures close to their melting point. They are still used in coke ovens, ceramic kilns and glass tank crowns, but minimally at present in electric furnaces for melting steel and roof brick for open hearth, because of raised operating temperatures and a reduced open-hearths use. Silica bricks tend to crack when heated rapidly at low temperatures. Special refractories are produced by a combination of graphite, silica carbide, zircon, borides, nitrides etc. Insulating bricks capable to withstand high temperatures, and but retaining their insulating properties are produced by adding, for example, diatomite as a light-weight aggregate. Several other raw materials are used in the production of refractories. Talc of white colour, with a low content of coloured oxides, is used in a production of insulators of high voltage, sparking plugs and in ceramic masses. Dunite is a basic material in the production of forsterite, refractory material such as serpentinite. In Mozambique, refractory materials are used in cement and lime factories, in brick and ceramic factories, in metallurgy and


Cilek: 6.3. Refractories

for steam boilers in power stations etc. Besides low-quality refractory materials are used in the production of small household appliances, linings of ovens and elsewhere in the building trade. Of the two production units in the country one is at Quelimane, one in Maputo. Both produce low-quality chamotte bricks and other products such as cooking plates and small electrotechnical elements. The cement and lime industry uses imported magnesite and chrome - magnesite bricks for temperatures of more than 1,500°C and high alumina shapes for temperature of more than 1,000°C. The small foundry industry imports magnesite bricks and rammed dolomite for refractory lining and heavy duty magnesite bricks, chrome-magnesite bricks and silica (dinas) bricks. Raw materials for refractories available in Mozambique or those that may be discovered are these:

1 fireclaymost probably in the Karroo Formation in Beaufort member of productive sequence; in the coal fields of the Tete Province (Moatize, Mecuco-Chicoa) and the Niassa Province

2 kaolin huge reserves in altered pegmatites of the Alto Ligonha district (Muiane, Ribaue etc.)

3 silicain hydrothermal quartz of pegmatite cores of the Alto Ligonha district; in vein quartz; in quartzites of Precambrian formations; in quartz sand and diatomite

4 magnesite at the Monte Atchiza ultrabasic Complex, at Serra Mangota near Manica together with serpentinites

5 dolomite in the crystalline limestone deposit Malulu in the Niassa Province; underground deposits of precipitated dolomite of the Temane Formation in the Inhambane Province

6 limestone many sites of occurrence both crystalline and sedimentary

7 zircon in beach sands of coastal Mozambique together with kyanite and andalusite

8 bauxite from claims Alumen near Manica, refractory, where bauxite is mined, kaolin is dispersed

9 sillimanite, kyanite, andalusite

large deposits in the Manica Province; the Tete Province and other localities, need to be investigated

10 graphite recently discovered, substantial reserves of flake graphite in the Cabo Delgado Province, other deposits were mined near Nampula, Nacala and in Angonia in the Tete Province

The production of refractories could be started in the existing factories at Quelimane and Maputo using bauxite of Manica and kaolin from Ribaue or Muiane. Binding clay in chamotte should be imported, otherwise local low-quality plastic clays must be used. Other raw materials for refractories will be made available as soon as the mining of heavy minerals is started -especially zircon may provide extra-quality special refractory products. Special high-temperature refractories could be produced from graphite, others from magnesite, sillimanite group minerals, serpentinite and talc.



Cilek: 7. PROSPECTIVE and POTENTIAL industrial minerals and their uses

7. PROSPECTIVE and POTENTIAL industrial minerals and their uses

In Mozambique, it would be not appropriate to talk about exhausted resources of industrial minerals which should be replaced by unconventional industrial raw materials because a major part of these resources has not even been touched as yet and it is to be expected that these materials-prospective and potential from the present point of view, will be utilized as soon as the particular industrial branches are going to be developed. Owing to a large variety of different industrial materials, both classical and prospective it will be advisable to select the most promising of these materials to the benefit of industrial growth. Three groups have been chosen to be discussed in this chapter: 1 potential industrial materials of big reserves with substantial present and future demands 2 prospective raw materials with a possible use in future industrial development 3 minor industrially interesting minerals. 1 The present review of industrial minerals and rocks indicates both strong and weak points in the development of these resources for industrial development. The weakness is in an absence of high-quality ceramic clays, in the low quality and small resources of asbestos and unknown reserves of magnesite, the absence of sulphur and pyrite, the lack of metallurgical bauxite and dolomite, the lack of phosphorites and a low content of apatite and finally the absence of common and industrial salts. The strength and advantage of industrial materials surpasses many times the lack of some of these resouces. Substantial industrial resources are these: Ceramic raw materials - big reserves of kaolin and feldspar as a waste material in the mining of columbo-tantalite of pegmatites of the Alto Ligonha district; Glass Materials - huge reserves of quartz sands in the coastal zone, feldspar and limestones of different quality, fluxes are available to secure the production of container-and pressed glass; flat glass and fibre-foam glass can also be produced; Cement-lime production - rich deposits of pure limestones for portland cement and lime production, limestones and marls of sedimentary origin for hydraulic lime and saturation lime, high quality limestones for ceramics and glass; Gypsum and anhydrite -huge reserves in the Temane Formation can cover, first, the needs of the cement industry, later the needs of the building industry (plaster and plasterboards) and, because of a lack of sulphur and pyrite, anhydrite can be used as a basic material for sulphuric acid production, and also in the glass production to replace sulphur and limestone; Graphite - of flake quality and amorphous grade for export and production of special refractories; Sillimanite, andalusite, kyanite - potential raw materials for refractories of mullite composition, big reserves are envisaged in the Fronteira Formation, lucrative export material; Fertilizers - apatites of Monte Muande and Evate, futher industrial rocks to improve the soil; utilization of fertilizer such as smectites (bentonite of Karroo volcanics), probably zeolites, tuffs and tuffites, lime and glauconite; can be used also as an aid in animal nutrition; Nepheline syenite-inexhaustible reserves for nepheline-feldspar production, RE as byproduct, for ceramic and glass production, alumina and cement production (with limestone); Diatomite - big reserves and good-quality material for filtration, as filler, light-weight building elements


Cilek: 7. PROSPECTIVE and POTENTIAL industrial minerals and their uses

etc.; Materials for metallurgy - big reserves of fluorite, limestone, ganister for refractory bricks, foundry sands and bentonite; Bauxite and kaolin -for the production of chamotte and other refractories; Protection of the natural environment materials - absorbtion materials such as smectites, zeolites, lime and ground limestone, diatomite, filtration sand etc. 2 Prospective raw materials, some of these unconventional, can be used when industrial development has mastered the technology of common raw materials utilization. Several proposals for the use of these materials: Rare-earths from monazite of beach and dune deposits, of alkaline rocks and pegmatites can be utilized as mixed compounds or, in a later stage, as pure elementar RE. A simple technology in producing mixed RE as mischmetal may result in a production of high-strength, low-alloy steels and ductile iron and increase several times the value of future steel production in Mozambique. RE could also be used in ceramics and glass industry and as petroleumcracking catalysts. As byproduct of monazite processing, thorium is obtained which can be used in the production of alloys with magnesia and in the future, as fuel in atomic reactors. Zircon from beach sands for special high-temperature refractories, but also, for a quite common utilization, as foundry sand. Lithium minerals are typical raw materials of the near future, at present they are used as lubricants, as air regeneration agent in submarines and satellites, in the glass industry as enamels and glazes, as an admixture in white ceramic mass and refractories; future uses are as fuel in thermonuclear reactors and as cooling agent and for storage of electric energy. Are available in pegmatites. Alkaline rocks, mainly nepheline syenites, as a source of alumina, cement and RE and trace elements. Talc as a filler, in ceramics and refractories. Glauconite as a fertilizer, in foundry sands and in water treatment; it occurs at Mague-Sabie in the Maputo Province in Cretaceous sandstones, 20 to 50 m thick, with 2.7-3.1% P2O5 and 4.1% K2O with a glauconite content up to 50%. 3 Minor raw materials include, for example, corundum which was mined near Tete as an abrasive material and exported; olivine in ultrabasic rocks as slag conditioner and a fluxing agent in blast furnaces, in refractories and heat-storage units, as abrasive; mica sheet and ground mica in electrical industry and as filler; quartz crystals in electronics; vermiculite as thermal and acustic insulator, in light-weight aggregate and in agriculture; garnet as abrasive material etc.



Cilek: 8. Minerogenetic provinces and epochs

8. Minerogenetic provinces and epochs The described minerogenetic provinces and epochs of industrial minerals and rocks in Mozambique indicate that our knownledge decreases with an increasing age of geological formations. In the Precambrian, there are still large regions, mainly in N- Mozambique, which will have to be futher investigated and where a discovery of new mineral deposits will be probable as suggested by recent findings of kimberlites, alkaline rocks with phosphate, RE and in many new localities, of pegmatites, marbles, zones of ultrabasic rocks with asbestos, talc, rich deposits of graphite, ilmenite rich zones and others. Minerogenetic epochs are limited periods of industrial minerals and rocks connected with one cycle of orogenesis or sedimentation either during plate tectonic development or geosynclinal or epicontinental phases. These epochs can be determined quite accurately in sedimentary deposits or young volcanic epochs, but just roughly deliminated within the Precambrian and the minerals and rocks represent quite common materials, because the exact minerals are hardly known. Minerogenetic units are represented by groups of minerals of related genesis and of similar history; some are well-determined, some are wide-range common materials. Building materials are generally not mentioned, because they could include most of crystalline rock materials and thus render the review very confused. The development of industrial minerals and rocks in geological epochs and units is shown in table below.

Minerogenetic Epoch

Characteristics Minerogenetic unit

Recent-Subrecent -100,000 years

oscillation of sea level placers with heavy minerals: ilmenite, rutile, zircon, monazite, kyanite, gravel-sand, diatomite

Miocene

Eocene

formation of bays, lagoons and epicontinental basins

limestones of Jofane Formation, evaporites: gypsum, anhydrite, salt, dolomite of Temane F., limestones of Cheringoma F., Salamanga

Mid Tertiary -

Late Cretaceous

Post-African Land Surface (mid-Late Miocene) African Land Surface period of peneplainisation and sedimentation

heavy minerals in transitional source, kaolin, clay, taterite, bentonite, kaolin, clay, bauxite, laterites

Pleistocene-Jurassic

- 150 m.y.

post-Karroo volcanic vents, volcanoes, ascending massifs in connection with zones of fractures along the East-African rift valley

basic and alkaline rocks, nepheline syenite with Al, P, Fe, RE; carbonatites with P, F; fluorite in veins and stockwork

Karroo Formation

150-300 m. y.

era of tectonic activity along the reactived fractures; era of deposition in tectonic depressions on continental platform

rhyolites, basalts, tuffs, bentonite, fireclay?, perlite, zeolites, agates

Upper Precambrian

450-700 m. y.

Pan-African (500±100 m. y.) - Katangan orogenies (700-500 m. y.) last metamorphic phase, reactivation of older tectonic zones; katangan deposits of small extent pan-African granitoids and pegmatites

apatite, magnetite in crystalline limestone, sillimanite, andalusite, kyanite, graphite, pegmatites: RE, mica, feldspar, quartz, beryl, lithium, precious stones RE in intrusive alkaline rocks

Middle Precambrian

900-1,100m.y.

denudation 900-700 m. y., main orogeny mozambican, multiphase metamorphism accompanied by granitic intrusions, granulites over granite and migmatites

apatite, Nb, U, RE; pegmatites: RE, gems, mica, fedspar; graphite in contact and high grade; metamorphic deposits, marbles


Cilek: 8. Minerogenetic provinces and epochs

Middle-Lower Precambrian

1,350-1,800 m.y.

Irumide orogeny and intercratonic; basin fill on active margin, metamorphism; Groups Gairezi, Zambue, Fronteira

quartzites; (ganister)?; sillimanite, andalusite, kyanite; asbestos and talc

Lower Precambrian 1,800-2,500 m. y.

geosynclinal deposition on Archean basement

quartzites, marbles graphite, asbestos and talc

Archean 2,500-3,800 m. y.

cratons of Zimbabwe and Transvaal; shallow water deposits, origin of nuclei of shield with greenstone belts

serpentinite, talc, asbestos, magnesite



Cilek: 9. SELECTED REFERENCES

9. SELECTED REFERENCES AfonsoR.S.(1978): A geologia de Mozambique. Noticia Explicativa da Carta Geol. Moc., 1 : 2,000 000, Imprensa Nac. Moc., pg. 1-191, Maputo. Afonso R. S. -Pinto M. (1967): Macicos alcalinos de Milange e Morrumbala. Pesquisa de bauxites. Inter. Rep., Institute Nacional de Geologia (ING), pg. 1-53, Maputo. Andrade C.F.(1929): Esboco geologico de Mozambique. Imprensa Nac. de Lisboa, pg. 1-232, Lisboa. Assenov B. - Diallo 0. F. (1982): Relatorio sobre as argilas da regiao de Namaacha. Inter. Rep., ING, pg. 1-22, Maputo. Bandet G.-Beauville J. L. (1978): Etude du kaolin de Marropino (Mozambique). BRGM, Inter. Rep., ING, pg. 1-21, Maputo. Barmine V. -Tveriankine J. (1982): Relatorio sobre os trabalhos de prospeccao e evaliacao dos sienitos nefelinicos do mocico Conguene e rochas calcarias de area Chire. Inter. Rep., ING, pg. 1-15, Maputo. Barros R. M. F.-Vicente C. A. M. (1963): Estudo dos campos pegmatiticos da Zambezia. Campanha de 1963. Inter. Rep., ING, pg. 1-133 I., 134-290 II., 291-439 III., Maputo. Bascia G.-Mariani F. (1982): Relatorio sobre a investigacao de depositos argilosos na zona de Gurue em Zambezia. Inter. Rep., ING, pg. 1-4, Maputo. Bateman A.(1951): Economic Mineral Deposits. Sec. Ed., John Willey & Sons, Inc., New York, pg. 1-916. Beltchev M.(1983): Relatorio sobre apatite de Evate, provincia Nampula. Bulgargeomin, Inter. Rep., ING, pg. 1-71, Maputo. Bettencourt Dias M. (1952): Depositos de calcareo nacircunsricao de Cheringoma, Inter. Rep., ING, pg. 1-41, Maputo. Bettencourt Dias M. (1953): Acumulacoes de "guano morcego" em cavernas nos calcareos da circunscricao de Vilanculos. Inter. Rep., ING, pg. 1-20, Maputo.



Bloomfield K.(1961): The Age of Chilwa Alkaline Province. Rec. Geol. Sur. Nyasaland, 1., 1959, pg. 20-45, Zomba. Borges A.(1950): O jazigo de bauxite da Serra de Mariangane. Inter. Rep., ING, pg. 1-21, Maputo. Bornhardt W.(1900): Zur Oberflachengestaltung und Geologie Deutsch-Ostafrika. Bd. VII., pg. 1-490, Berlin. BRGM(1986): Notice explicative de la carte geologique a 1:1,000 000 de la Republique populaire du Mozambique (1986), ING-BRGM, pg. 1-261, Maputo. Bulgargeomin(1983): Trabalhos desenvolvidos durante o ano de 1982 sobre pesquisa geologica de jazigo de marmore em Montepuez e o calculo de reservas. Inter. Rep., ING, pg. 1-25, Maputo. Bulgargeomin(1983): Geologia da Foz do Rio Lurio. Inter. Rep., ING, pg. 1-171, Maputo. Campos J.(1948): Ensaios de semimicroanalize qualitativa dalguns minerais raros de Mozambique. Inter. Rep., ING, pg. 1-14, Maputo. Campos J.(1961): Notas sobre alguns calcareos de Mocambique. Boll. Invest. Cient. Moc., Vol. 2., No. 1., pg. 31-37, Maputo. Carvalho P.(1944): Estudo dos jazigos mineiros da Colonia de Mocambique. Inter. Rep., ING, pg. 1-49, Maputo. Carvalho L.H.B.(1971): Formacoes vulcanicas de Carinde (Tete-Mocambique). Unpubl. PHD. Thesis, Univ. Aveiro, pg. 1-120, Portugal. Cilek V. (1985): Heavy Mineral Accumulations in Coastal Mozambique. Rozpr. CSAV, roc. 95, s. 1., pg. 1-91, Academia, Prague. Cilek V.(1987): Corredor da Beira. A Review of the building raw materials. Inter. Rep., ING, pg. 1-36, Maputo. Civitelli G.-Mariani F. (1984): Estudo geologico do sedimentar da provincia de Cabo Delgado finalizado a pesquisa de gesso. Inter. Rep., ING, pg. 1-44, Maputo.



Diallo O.R.(1979): Relatorio sobre a prospeccao pormenorizada das argitas de Bela Vista. Inter. Rep., ING, pg. 1-7, Maputo. Diallo O.R.(1980): Relatorio sobre a prospeccao pormenorizada das argilas para a ceramica vermelha na regiao de Inharrime (provincia de Inhambane) area de Ravene-Muhamba. Inter. Rep., ING, pg. 1-14, Maputo. Diallo O.R.(1980): Relatorio sobre visita de estudo das argilas de Xinavane. Inter. Rep., ING, pg. 1-3, Maputo. Duda J.et. al.(1986): Pegmatitos de Nuaparra (feldspato e mica). Inter. Rep., pg. 1-133, Maputo. ENH (1986): The Petroleum Geology and Hydrocarbon Prospectivity of Mozambique. Vol. I. pg. 1-132, Vol. II. pg. 1-321, Inter. Rep. of Empressa National de Hidrocarbonetos de Mocambique, Maputo. Ferrari J.H.(1981): Iron ore in the Peoples Republic of Mozambique. Inter. Rep., ING, pg. 1-83, Maputo. Ferrari J.H.(1981): Asbestos in the P. R. of Mozambique-evaluation and perspectives. Inter. Rep., ING, pg. 28-59, Maputo. Franken R.B.(1982): Asbestos prospect near Tzangano, Moatize-Angonia. Inter. Rep., ING, pg. 1-7, Maputo. Freitas F.(1950): Asbestos de Manica. Inter. Rep., ING, pg. 34-52, Maputo. Geological Institute Beograd (1982): Annual Report-Geol. Prospecting and Investigation in Manica, Sofala, Zambezia and Tete Provinces. Inter. Rep., ING, pg. 1-64, Maputo. Geological Institute Beograd (1982): Annual Report on works performed by Jugoslav expert team in 1981 (Report on investigations of "black granites" section. Inter. Rep., ING, pg. 58-64, Maputo. Geological Institute Beograd (1982): Prefeasibility Study on graphite exploitation Angonia deposit-Mozambique. Inter. Rep., ING, pg. 1-55, Maputo. Geological Institute Beograd (1982): Final Report on geol. investigation of asbestos, iron minerals, apatite and amazonite in Nampula Province. Inter. Rep., ING, pg. 1-62, Maputo.



Geological Institute Beograd (1984): Final Report on geol. investigation of ornamental stone in provinces Tete, Niassa, Nampula and Maputo-locality Namialo. Inter. Rep., ING, pg. 1-14, Maputo. Geological Institute Beograd (1984); Final Report on geol. prospection and exploration works in alkaline rocks complex of Chemba. Inter. Rep., ING, pg. 1-56, Maputo. Geological Institute Beograd (1984): Final Report on geol. investigation of magnetite and apatite mineralisation at Monte Muande, Tete Province. Inter. Rep., ING, pg. 1-214, Maputo. Geological Institute Beograd (1984): Final Report-Geol. Investigations of diatomite occurences and deposits in Bela Vista-Marracuene-Manhica, Magude-Chicano and Macia Xai-Xai areas, Maputo Provinces. Inter. Rep., ING, pg. 1-62, Maputo. Geological Institute Beograd (1984): Final Report on the geol. research of pegmatite in the region of the Ribaue mine. Inter. Rep., ING, pg. 1-48, Maputo. Geological Institute Beograd (1984): Final Report-geol. investigation of graphite deposits in the area Monapo-Itotone-Nampula. Inter. Rep., ING, pg. 1-15, Maputo. Geological Institute Beograd (1985): Final Report on geol. investigation of limestone in the Maputo Valley, Maputo Province. Inter. Rep., ING, pg. 1-81, Maputo. Geological Institute Beograd (1985): Final Report on the geol. research of ornamental stones in the Province of Niassa (Red Granite). Inter. Rep., ING, pg. 1-16, Maputo. Geological Institute Beograd (1985): Final Report on geol. investigation of limestone and clay in the Maputo valley. Inter. Rep., ING, pg. 1-35, Maputo. Godinho J. (1970): Relatorio sobre as possibilidades de exploracao de titanio no distrito de Tete. Inter. Rep., ING, pg. 1-19, Maputo. Gouveia J.C. (1967): Relatorio da visita a alguns locais do distrito de Cabo Delgado. Inter. Rep., ING, pg. 1-6, Maputo.



Gouveia J.C. (1974): Carta de jazigos e ocorrencias minerais (escala 1 : 2,000 000) com noticia explicativa. Direccao dos Servicos de Geologia e Minas, Maputo. Gula J. (1981): Report about non-metallic minerals in Mozambique. Inter. Rep., ING, pg. 1-45, Maputo. Harben P.-Bates R. (1984): Geology of Nonmetallics. R. Hartnoll Ltd., U. K., pg. 1-392, Cornwale. Haslar O. et.al. (1985): Relatorio final Evate-da jaziga de apatite. Intergeo-Geoindustria, pg. 1-133, ING-Maputo. Hunting Geology & Geophysics Ltd. (1984): Mineral Inventory Project. Final Report. Inter. Rep., ING, pg. 1-329, Maputo. Institute for economy of raw materials, Dresden (1978): Relatorio sobre resultados de investigacoes tecnologicas de mat. prim. em amostras de caulino, procedentes do jazigo de Muiane na zona pegmatitica de Alto Ligonha na Rep. P. do Mozambique. Inter. Rep., ING, pg. 1-13, Maputo. Intergeo, Prague (1985): Relatorio Final - Monapo, Prospeccao Regional Geoquimica, Mozambique. Inter. Rep., ING, pg. 1-105, Maputo. Ivanicka J. -Sykora J. (1982): Relatorio final e calculo de reservas no jazigo de Ressano Garcia (Vidro vulcanico). Inter. Rep., ING, pg. 1-34, Maputo. Jourdan P.(1986): The Mineral Industry of Mozambique. Raw Materials Report, Vol. 4., No 4., pg. 31-45, Lusaka. Jourdan P.-Paulis R. (1979): Avaliacao preliminar do jazigo de calcario de Malulu-Niassa. Inter. Rep., ING, pg. 1-14, Maputo. Jourde G.-WoIff J. P. (1970): Contribuicao para o conhecimento da geologia da area de Montepuez. BRGM au Mozambique. Inter. Rep., ING, pg. 1-45, Maputo. Kaspar J.-Pristoupil V. (1970): Industrial raw materials (Surovinove zdroje prumyslu), SNTL, pg. 1-382, Prague. Kimambo R.H. (1986): Development of the non-metallic minerals and the silicate industry in Tanzania. Vol. I, pg. 1-100, East Africa Publ. Ltd., Dar es Salaam.



King L.C. (1983): Wandering continents and spreading sea floors on an expanding earth. John Willeys and Sons, pg. 1-205,1983. Koscal M.-Kachamila J.-Stefanovic M.-Janjic M. (1985): Fluorite mineralisation of Monte Muambe carbonatite complex, Mozambique. Summary, World Congr. Non-Met. Min., pg. 103-114, Beograd. Kouzmine G. -Akimidze A. (1981): Obsidiana dos Pequenos Libombos. Inter. Rep., ING, pg. 1-18, Maputo. Kraft E. (1980): Relatorio sintesse sobre as ocorrencias de grafite na regiao de Angonia (provincia de Tete). Inter. Rep., ING, pg. 1-5, Maputo. Kuzvart M. (1984): Industrial Minerals and Rocks. Elsevier, pg. 1-454, Academia, Prague. Lamey C.A. (1966): Metallic and Industrial Mineral Deposits. Mc Graw-Hill, pg. 1-567, New York. Lachelt S. (1985): Contribuicao para o estudo geologico, tectonico e metalogenico de Mozambique. Inter. Rep., ING, pg. 1-362, Maputo. Ledder H. (1987): Noticia explicativa da carta de jazigos e ocorrencias de minerios nao metalicos. Inter. Rep., ING, pg. 1-55, Maputo. Lefond S. J. (1975): Industrial minerals and rocks (non-metallics other than fuels). 4th. ed., Am. Inst. of Mining, Metall. and Petroleum Eng., pg. 1-1360, New York. Mariani F. - Ballara G. - Uamusse M. (1984): Relatorio sobre a pesquisa de calcareos para cal em Pemba. Inter. Rep., ING, pg. 1-33, Maputo. Martins R. (1940): Reconhecimento geologico do Monte Chiperone. Rel. inedito, 45., Serv. Geol. Min. Moc., pg. 1-8, Maputo. Masson G.-Ulpiu S. (1978): Geological Report concerning perspectives and researches for gypsum in the Sul Save region (Pande-Temane). Inter. Rep., ENH, pg. 1-11, Maputo.



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Nota sobre a existencia de dumortierite em Cabora-Bassa (Mozambique). Garcia de Orta (Lisboa), Vol. 16., No. 2, pg. 243-248, Lisboa. Smirnov V.I. (1975): Geology of Mineral deposits. Mir., pg. 1-687, Moscow. Thieke H.U. (1980): Relatorio sobre a situacao das reservas de caulino e mica (moscovita) de jazigo pegmati'tico de Muiane. Inter. Rep., ING, pg. 1-12, Maputo. Tzonev O. (1981): Prospeccao preliminar de argilas Inhamizua-Beira. Inter. Rep., ING, pg. 1-25, Maputo. Tzonev O. (1981): Pesquisa preliminar de argila Nampula-Rio Muapelume. Inter. Rep., ING, pg. 1-9, Maputo. Tzonev O. - Dimitrov D. (1982): Relatorio da pesquisa de argila e areia da regiao de Xai-Xai. Inter. Rep., ING, pg. 1-46, Maputo. UN-TCD (1983): Geophysical Exploration in the Tete area. Inter. Rep., ING, proj. MOZ 80/013, pg. 1-9, Maputo. VAMI-Leningrad (1981): Mineralogical and technological study of Mozambique nepheline ores. Inter. Rep., ING, pg. 1-92, Maputo. Varley E. R. (1965): Sillimanite-andalusite, kyanite, sillimanite. Overseas Geol. Sur., Min. Res. Div., Her Maj. Stat. Off., pg. 1-165, London. VEB Kombinat Geol. Forsch. Halle (1983): Relatorio final-projecto pegmatito Marropino. Inter. Rep., ING, pg. 1-102, Maputo. Zuberec J.-Ivanicka J.-Sykora J. (1981): O estudo geologico e tecnologico das materias primas de ceramica nas localidades escolhidas na R. P. Mozambique. Inter. Rep., ING, pg. 1-30, Maputo. Zuberec J. -Ivanifcka J.-Sykora J. (1981): A Situacao geologico-tecnologica e o calculo das reservas da zona de bentonite Luzinada. Inter. Rep., ING, pg. 1-42, Maputo. Zuberec J.-Ivanicka J.-Sykora J. (1981): Prospeccao e pesquisa geol. das areias caulinicas na regiao de Nacala. Inter. Rep., ING, pg. 1-11, Maputo.



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Industrial Minerals of Mozambique