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Beyeme Zogo. 2009 Beneficiation Potential of Low Grade Iron Ore From a Discard Lumpy Stockpile and Fines Tailings Dam at Beeshoek Mine
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BENEFICIATION POTENTIAL OF LOW-GRADE IRON ORE FROM
A DISCARD LUMPY STOCKPILE AND FINES TAILINGS DAM AT
BEESHOEK MINE, NORTHERN CAPE PROVINCE,
SOUTH AFRICA
by
JEAN-CLEMENT BEYEME ZOGO
DISSERTATION
Submitted in fulfilment of the requirements for the degree
Magister Scientae
in
Geology
in the
FACULTY OF SCIENCE
at the
UNIVERSITY OF JOHANNESBURG
SUPERVISOR: Professor Jens GUTZMER
Co-SUPERVISOR: Professor Nicolas Johannes BEUKES
April, 2009
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TABLE OF CONTENTS
Acknowledgements……………...…………………………………………………………………….6
Abstract……………………………………………………………..…………………………………..7
PART I
MOTIVATION FOR STUDY AND INTRODUCTION TO GEOLOGICAL
SETTING, MINING AND BENEFICIATION AT BEESHOEK MINE AND
METHODOLOGY EMPLOYED IN THIS STUDY
CHAPTER I INTRODUCTION
1.1 Deposit Type and Material Studied……………………………………………………......11
1.2 Geographic Setting and History…………………………………………………………….11
1.3 Source of Waste Material……………………………………………………………………13
1.4 Motivation for Study………………………………………………………………………….14
1.5 Objectives and Method Employed…………………………………………………………19
CHAPTER II GEOLOGICAL SETTING
2.1 Regional Setting……………………………………………………………………………...21
2.2 Geology of the Maremane Dome………………………………………………………......22
2.3 Stratigraphy…………………………………………………………………………………...23
2.3.1 Wolhaarkop Breccia………………………………………………………………………….23
2.3.2 Manganore Iron Formation………………………………………………………………….25
2.3.3 Gamagara Formation………………………………………………………………………..26
2.4 Geology of the Beeshoek Iron Ore Deposit……………………………………………….30
CHAPTER III EXPLORATION, EXPLOITATION AND BENEFICIATION OF
IRON ORE AT BEESHOEK MINE
3.1 Introduction…………………………………………………………………………...………35
3.2 Ore Delineation……………………………………………………………………….………35
3.3 Mining and Beneficiation…………………………………………………………………….38
3.4 Iron Ore Types and Product Quality……………………………………………………….39
CHAPTER IV METHODOLOGY
4.1 Sampling………………………………………………………………………………………41
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4.2 Density Determination……………………………………………………………………….41
4.3 Preparation of Polished Sections…………………………………………………………..43
4.4 Microscopy……………………………………………………………………………………44
4.5 Communition………………………………………………………………………………….44
4.6 X-ray Powder Diffraction…………………………………………………………………….45
4.7 X-ray Fluorescence Spectrometry………………………………………………………….45
4.8 Titrimetric Fe Determination……………………………………………………………......46
4.9 Sieving………………………………………………………………………………………...48
4.10 Beneficiation Studies………………………………………………………………………...49
4.10.1 Spiral Gravity Concentration………………………………………………………………..49
4.10.2 Washing/Panning………………………………………………………………………….....49
PART II
INVESTIGATION OF THE LUMPY MATERIAL FORM THE DISCARDED
STOCKPILE AT BEESHOEK MINE
CHAPTER V LITHOSTRATIGRAPHIC AND PHYSICAL CLASSIFICATION OF
LUMPY MATERIAL 5.1 Introduction……………….............................................................................................53
5.2 Lithostratigraphic Classification………………………………………………………........53
5.2.1 General Stratigraphic Classification………………………………………………………..53
5.2.2 Fragments of the Campbellrand Subgroup………………………………………….........55
a. Ferruginous Manganese Ore……………………………………………………….55
b. Dolomite……………………………………………………………………………….55
5.2.3 Fragments of the Wolhaarkop Breccia………………….…………………………………56
a. Chert and BIF Breccia and Chert Breccia………………….……………………………..56
5.2.4 Fragments of the Manganore Iron Formation…………….………………………………56
a. Chert……………………………………………………………………….………………56
b. Banded Iron Formation (BIF)……………………………………………………………56
c. Laminated Iron Ore……………………………………………………...……………….56
d. Brecciated Iron Ore…………………………………………………………………..….57
e. Porous Iron Ore...…..……………………………………………………………………57
5.2.5 Fragments of the Doornfontein Member (Gamagara Formation)…...………………….57
a. Conglomeratic Iron Ore...……………………………………………………………………57
b. Aluminous Shale/Mudstone…………………………………………………………………59
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c. Highly Ferruginous Shale/Mudstone….……………………………………………………59
d. Shale Breccia.……………………………………………………………………….............59
5.2.6 Sishen Shale Member (Gamagara Formation)…………………………………………...59
5.2.7 Marthaspoort Quartzite (Gamagara Formation)….………………………………………59
5.2.8 Kalahari Formation..…………………………………………………………………………60
5.3 Modal Composition of the Discarded Lumpy Stockpile…...……………………………..60
5.4 Densities of Lumpy Stockpile Lithologies…...…………………………………………….64
CHAPTER VI PETROGRAPHY OF THE LUMPY MATERIAL
6.1 Campbellrand Dolomite………………………..……………………………………………67
6.1.1 Dolomite………………………………………………………………………………………67
6.1.2 Ferruginous Manganese Ore……………………………………………………...............67
6.2 Wolhaarkop Breccia……………………………………………………………..…………..67
6.2.1 Chert and BIF Breccia…………………………………………………………………….....67
6.2.2 Chert Breccia……………………………………………………………………………..…..68
6.3 Manganore Iron Formation………………………………………………………...………..69
6.3.1 Laminated Iron Ore………………………………………………………..…………………69
6.3.2 Brecciated Iron Ore………………………………………………..…………………………73
6.3.3 Chert and Banded Iron Formation (BIF) ………………...………………………………..73
a. Chert……………………………………………………………………………………….73
b. Banded Iron Formation (BIF)……………………………………………………………75
6.4 Gamagara Formation………………………………………………………………………..75
6.4.1 Doornfontein Member…………………………………………………………………….....75
a. Conglomeratic Ore……………………………………………………………………….75
b. Ferruginous and Aluminous Red Shale/Mudstone………………………...…………75
c. Aluminous and Green Shale/Mudstone……………………………………………….75
d. Shale Breccia……………………………………………………………………………..76
e. Shale/Mudstone Peloids………………………………………………………………...77
6.4.2 Sishen Shale Member…………………………………………………………………….....77
6.4.3 Marthaspoort Quartzite Member……………………………………………………………80
6.5 Recent Lateritic Ore………………………………………………………………………….81
6.5.1 Recent Detrital Iron Ore……………………………………………………………………..81
6.5.2 Porous Iron Ore………………………………………………………………………………82
CHAPTER VII GEOCHEMISTRY OF LUMPY LOW-GRADE MATERIAL
7.1 Major Element Geochemistry……………………………………………………………….85
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7.1.1 Group I………………………………………………………………………………………...86
7.1.2 Group II (Siliceous Lithologies)……………………………………………………………..89
7.1.3 Group III………….…………………………………………………………………………...92
7.1.4 Group IV………………………………………………………………………………………96
7.2 Trace Element Geochemistry……………………………………………………………….96
7.2.1 Shale…………………………………………………………………………………………..96
7.2.2 Siliceous Lithotypes………………………………………………………………………….98
7.3 Composition of the Iron Ore Fragments From the Discarded Lumpy Stockpile to the
Standard at Beeshoek Mine………………………………………………………………...99
PART III
INVESTIGATION OF THE FINES FROM THE TAILINGS DAM
CHAPTER VIII DESCRIPTION OF FINES MATERIAL IN THE TAILINGS DAM
8.1 Introduction……………………………………………………………………………….....105
8.2 Grain Size Analysis…………………………………………………………………………106
8.3 Geochemistry of the Fines Iron Ore………………………………………………….......109
8.3.1 Major Element Geochemistry…………………………………………………………......109
8.3.2 Correlation Between XRF and Titration Geochemical Results………………….........116
8.4 Petrography of Fines Material……………………………………………………………..119
8.4.1 Physical Characteristics of Particles……………………………………………………...119
8.4.2 Petrographic Composition…………………………………………………………………119
8.4.3 Mineralogical Variation in Fines Tailings Dam…………………………………………..121
8.4.4 Summary…………………………………………………………………………………….121
CHAPTER IX BENEFICIATION TESTS ON THE FINES MATERIAL
9.1 Spiral Separation……………………………………………………………………………125
9.2 X-ray Fluorescence Analysis of Spiral Fractions………………………………………..125
9.3 Pan Washing…………….………………………………………………………………….133
PART IV
DISCUSSION, CONCLUSION, APPENDIX, REFERENCES
CHAPTER X DISCUSSION AND CONCLUSION
10.1 Discussion…………………………………………………………………………………...139
10.1.1 Discarded Lumpy Stockpile………………………………………………………………..139
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10.1.2 Fines Tailings Dam……………………………………………………………………...….139
10.1.3 Discussion……………………………………………………………………….................140
10.2 Recommendation for Utilization of Lumpy and Fines Material………………………...140
10.2.1 Lumpy Material……………………………………………………………………………...140
10.2.2 Fines Material……………………………………………………………………………….141
10.3 Conclusion…………………………………………………………………………………..141
APPENDIX A
A.1 History of Pelletizing………………………………………………………………………..143
A.2 Preparation of Raw Material and Blending…………………………..…………………..143
A.3 Balling…………………………………………………….…………………………….……144
A.4 Hardening……………………………………………………………………………………144
A.5 Drying………………………………………………………………………………………..146
A.6 Pellet Properties……………………………………………………………………………147
A.7 Example of Pelletizing Model…………………………………………………………......148
REFERENCES………………………………………………………………………..…………….151
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Acknowledgements
To the people who really believed in me that I was able to undertake a Master project and
conduct it successfully till the end:
- Professor Jens GUTZMER, my supervisor from the day one, he has strengthened
the confidence in me by granting me the opportunity to do a Master degree. Special thanks to
him for his patience showed towards my person during the period of latency.
- Professor N. J. BEUKES, my Co-Supervisor, thank you for organizing the funding to
cover all the expense for my project and my stay in South-Africa for the period of 2006-2008,
also for your trust, truth and encouragement.
I am grateful to the staff members and students at the Geology Department and Spectrau,
University of Johannesburg. Special thanks goes to Alet Lamprecht and Wikus van Deventer,
my colleagues from second year geology to Master, thank you for the cohabitation and all the
translations English-Afrikaans-English during our stay at Beeshoek in Northern Cape
Province.
Also, I would like to thank Elsa MARITZ, the secretary, for all her help.
God had permitted me to bounce into a pastoral couple Pastors Janice and Raphael
LEKOSSI from Pentecostal Church of Gabon, who succoured me spiritually ten minutes
before the veritable breakdown.
The staff at the Metallurgical Laboratory at Doornfontein Campus, for their availability and
advice. Thank you to Mr. Jos Lurie, Mr. Mustard and Mr. Hermann for your interest in my
project and all the instruction in mineral processing methods.
My family: especially my mother Lydie OBONE NDOUTOUME; my beloved father Gabriel
ZOGO OBAME; Emmanuelle, Champion, Lenny and Orny; my two sisters Bernadette and
Blandine, and my brothers, have always been of great support in my life. They are the
locomotive that pulls all my efforts.
To all my good and bad days’ friends, they represent the barometer that speeded up my
efforts.
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ABSTRACT: by Jean-Clément BEYEME ZOGO (2009). Beneficiation potential of low-grade
iron ore from a discard lumpy stockpile and fines tailings dam at Beeshoek mine, Northern
Cape Province, South-Africa. Unpublished MSc thesis, University of Johannesburg, Geology
Department, pp 156.
An estimated 98% of the iron ore exploited in the world is used in the manufacture of pig iron
and steel, which are non-substitutable backbones of modern society. The rapid increase of
world steel production over the last few years, driven mainly by economic growth in China,
have required an equal increase in iron ore production, from 876.8 Mt in 2006 to 948.1 Mt in
2007. The increased rate of exploitation of iron ores has resulted in a rapid depletion of
known high-grade iron ore deposits. This, in turn, has led to a dramatic increase of prices,
especially for highly thought-after high-grade lumpy iron ores from BIF-hosted deposits. In
the absence of any major new discoveries of high-grade iron ore deposits, mining companies
have turned to lower-grade materials to assess their beneficiation potential to expand their
production base and beneficiation capacity, in order to satisfy future demand. Within this
existing framework, this research project was initiated to assess the beneficiation potential of
low-grade lumpy stockpiles and high-grade iron ore fines at Beeshoek Iron Ore Mine, owned
by Assmang Ltd. The mine is located 7 km West of Postmasburg, in the Northern Cape
Province of South-Africa, and processes currently 5.60 million tons of uncontaminated run-of-
mine ore per annum. Crushing, washing, classification and jigging are used to produce 2.12
million tons of (37.8% of ROM) of lumpy iron ore product. The balance (3.48 million tons) is
currently not used, but is stockpiled or discarded. This includes 0.90 million tons (16.2% of
ROM) of ore-grade fines, 0.86 million tons (15% of ROM) of tailings sludge and 1.74 million
tons (31% of ROM) of lumpy low grade material. Both ore-grade fines and low-grade lumpy
material are discarded separately; they are currently considered as waste. The low-grade
lumpy is stockpiled while the fines are used to fill-in mined-out open pits. The evaluation of
the beneficiation potential of these two material streams is the main goal of this study.
Representative samples were collected from ore-grade fines and the current stockpile for
low-grade lumpy material. Hand sorting and lithological categorization of the lumpy material
facilitated petrographic and mineralogical studies using light and scanning electron
microscopy, as well as X-ray powder diffraction studies. Major and trace element
geochemistry were determined using X-ray fluorescence spectrometry and titrimetry (to
accurately determine the concentration of iron). Whole rock densities were determined for all
lithotypes recognized in the low-grade lumpy material. The grain size distribution was
determined for the lumpy materials by actual measurement of the diameter of a
representative number of particles, and for fines by sieve analysis. Fines beneficiation tests
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were conducted using spiral separation and simple classification tests. Washing was used as
additional beneficiation method on the fines.
Description of physical aspects and hand sorting revealed the presence of different
lithologies within the discarded lumpy stockpile, amongst which there are different textural
types of iron ore, several types of shales, chert, banded iron formation (BIF), breccia,
quartzite, iron and manganese wad and dolomite. Interestingly, 35 to 50% of all particles in
individual samples were found to be iron ore with > 75wt% Fe2O3 (> 52wt% Fe), with low or
very low concentrations of deleterious elements. The determination of whole rock densities
reveal that porous iron ore particles have a volume-based (true) density very similar to that of
Fe-bearing aluminous shales, rendering the jig inefficient to concentrate porous lithotypes of
high-grade iron ore.
Geochemical analysis of the fines illustrate that these readily reach ore-grade, but would
need a slight improvement to become high-grade ore. Washing and spiral separation were
successfully used to upgrade this raw material. Iron contents within the fines vary rather
systematically with distance to the pipe that feeds the material into an old excavation.
Relatively high concentrations of iron occur proximal to the feeder pipe (up to 95.8 wt%
Fe2O3) and relatively low iron contents occur in samples collected distal to the feeder pipe
(81.7 wt. % Fe2O3). Mineralogical and grain size analyses indicate that light and/or fine
grained materials are deposited at the end of the dam whilst heavy and/or coarse grains are
found proximal to the pipe.
The results of this study clearly illustrate the beneficiation potential of both fines and low-
grade lumpy stockpile material streams currently discarded as waste. The utilization of these
lower-grade materials should be investigated further (pilot plant scale) and thoroughly
assessed before large-scale investments are made. In particular, the use of high-grade fines
appears promising, but would require the introduction of pelletization. Pelletization is not at all
a new process in the iron ore mining industry, but it has been in use since 1912. By
pelletization, iron ore fines can be transformed into balls of a certain diameter called pellets,
suitable for direct reduction and the blast furnace.
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PART I
MOTIVATION FOR STUDY AND INTRODUCTION TO
GEOLOGICAL SETTING, MINING AND BENEFICIATION
AT BEESHOEK MINE AND METHODOLOGY EMPLOYED
IN THIS STUDY
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CHAPTER I
INTRODUCTION
1.1 DEPOSIT TYPE AND MATERIAL STUDIED
The Beeshoek iron ore deposit is one of the several ancient supergene (~ 2.18 Ga) iron
deposits informally known as Sishen-type deposits, situated on the Maremane Dome
between Sishen and Postmasburg in the Northern Cape Province of South Africa. Beeshoek
Mine, owned by Assmang, a subsidiary of African Rainbow Minerals (ARM), is situated at the
southern end of the dome whereas the Sishen (owned by Kumba Iron Ore) and Khumani
(owned by Assmang) Mines are situated at the northern extremity of the dome. An
unexploited deposit, known as the Sishen South Deposit owned by Kumba Iron Ore, is
situated immediately south of Beeshoek (Fig. 1.1). The iron ore deposits occur within a
sequence of late Archaean to Paleoproterozoic (2.64 – 2.05 Ga) sedimentary rocks known as
the Transvaal Supergroup.
The iron ore in all of the deposits comprises hematitized iron formations of the Manganore
Iron Formation, the altered equivalent of the Asbestos Hills Subgroup of the Transvaal
Supergroup, overlying a distinct ferruginous and manganiferous chert breccia known as the
Wolhaarkop Breccia. These are preserved in paleosinkhole structures in the dolomite of the
Campbellrand Subgroup. This assemblage is truncated by an erosional surface upon which
conglomeratic iron ores of the basal Doornfontein Member and overlying shale and quartzite
units of the Gamagara Formation were deposited. All the formations are grouped with the
2.64 – 2.05 Ga Transvaal Supergroup.
At Beeshoek Mine about 0.93 Mt of contaminated lumpy low-grade material is discarded
annually. This discarded lumpy material comprises a mixture of high-grade hematite ore
fragments and various host rock lithologies. Fines are a by-product generated during the
processing of the raw lumpy material. Approximately 2.2 Mt of fines from both
uncontaminated and contaminated sources are annually pumped into the tailings dam
(Assmang Annual Report, 2007). Both, discarded lumpy low-grade ore material and fines
were investigated during this study.
1.2 GEOGRAPHIC SETTING AND HISTORY
The Beeshoek Iron Ore Mine is located 7 km west of Postmasburg and 70 km south of
Sishen Iron Ore Mine (Fig. 1.1). It is an open pit mining operation located on the farms
Beeshoek 448 and Olynfontein 475. The mine is divided by the Postmasburg-Beeshoek road
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into two geographically distinct sections that are referred to as North and South open pit
mines (Fig.1.2). Both mines produce high-grade iron ore, but the ore from the North Mine is
somewhat enriched in manganese, whilst the ore from the South Mine is enriched in silica
(ARM Annual Report, 2007). Processing and beneficiation of ore take place only near the
North Mine. South Mine currently provides virtually all of the ore material.
Exploitation of iron oxides in the area commenced long before the establishment of
Beeshoek Mine in 1935. Archeological studies of ancient excavations have documented that
the mining of coarse crystalline hematite, so-called specularite, took place as early as 40 000
years BC. The specularite was probably used as pigment by local tribes (ARM annual report,
2007).
Figure 1.1 Geographic map of South Africa showing the extension of the railway and the location of major iron ore mines, both operational and in development, including Beeshoek Mine near Postmasburg.
Beeshoek was originally a manganese mine that started operating in 1935. During the 1940’s
and 1950’s, the economic potential of the iron ore deposits in the areas was realised and in
the late 1950’s, Beeshoek began to produce iron ore (Mining Weekly, August 2005). A small
iron mine was established in 1964 utilising hand sorting as a beneficiation process. In 1975 a
full washing and screening plant was installed. For diverse reasons, Beeshoek closed down
between 1981 and 1984, and then reopened again in 1985. From 1993, Beeshoek gradually
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ramped up its production to the present 5 Mt per annum. Until 2001, all mining took place to
the north of the Postmasburg-Beeshoek road in the North mine. A new jig plant was
constructed and the extension of the mine to the south (Fig. 1.2) was commissioned at a cost
of R118 million in 2002. This jig plant enabled the mine to recover ore from contaminated
material, therefore improving the quality of the lumpy iron and thus extended the life of the
Mine (Mining Weekly, 3 August 2005). High-grade products are mainly exported through the
port of Saldanha Bay (Fig. 1.1) and a small quantity is used by domestic steel producers
(ARM Annual report, 2007).
Figure 1.2 Aerial view of Beeshoek Iron Ore Mine and Postmasburg, Northern Cape Province, South Africa (Google Earth).
1.3 SOURCE OF WASTE MATERIAL
In the South Mine, two types of ore are being mined, on-grade ore, which is only crushed and
screened before selling and off-grade ore that is crushed, washed and jigged (Fig. 1.3). The
discarded lumpy stockpile material comes from the discard of the jig plant.
Major infrastructure at the South Mine includes a primary gyratory crusher and a secondary
crushing plant and stockpiling facilities (Fig. 1.3). Iron ore is produced by blasting and then
loaded into trucks from different pits to the primary crusher tipping point. The run-off-mine ore
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is sent through the primary crusher, then washed and screened, then crushed further by
secondary crushers and stockpiled. The run-off-mine ore is stockpiled on blending beds in
two categories: ore from uncontaminated sources referred to as “on-grade” and ore
containing contaminant materials is known as “off-grade”. Contaminated “off-grade” ore is
discarded or sent through the jigging plant (Fig. 1.3). In the latter case the “off-grade” ore is
washed and screened, then crushed in tertiary crushers and, finally beneficiated through jigs
to remove contaminants. The “on-grade” material in contrast only passes through tertiary
crushers and bypasses the jigs (Fig. 1.3). Fines derived from the secondary and tertiary
crushers and from the jig plant (Fig. 1.3) are pumped to the fines tailings dam, which also
formed part of this investigation.
High-grade iron ore products of ASSMANG are categorised by particles size, including:
lumpy (32 ±6.3 mm); fines (6.3 ±0.212 mm) and DRI (direct reduction iron 18±6.3 mm).
Lower grade lumpy ore is stockpiled while fines are discarded into former open pit
excavations that function as tailing dams. Currently, an excavation located in the Northern
mine area is used for this purpose.
Figure 1.3 Simplified flowsheet of the processing of raw ore material (R.O.M.) and beneficiation of iron ore at Beeshoek Mine.
1.4 MOTIVATION FOR STUDY
During 2007 the mineral resources of Beeshoek Mine decreased from 147.8 to 134.5 Mt, due
to the annual production drawdown. Mineral reserves decreased drastically from 37.4 Mt to
28.6 Mt, due to the exclusion of the iron ore deposit under the current Beeshoek village. Only
33% of the 28.6 Mt of ore reserve is suitable for ordinary mining and screening. This reduces
the life of the mine to only a couple of years, if present production rate is to be maintained.
The evaluation of low-grade iron ore materials from the discarded lumpy stockpile and the
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use of the fines iron ore investigated during this study could extend the life of Beeshoek Iron
Mine. To assess this potential is the motivation that underlies this study.
Apart from this local mine-related motivation for this study, the general increase in demand
for iron ore and depletion of high-grade iron ore resources worldwide in recent years,
necessitate that available resources are optimally utilised. It is thus essential that material
currently considered as waste or low-grade potential ore material be investigated in more
detail.
Iron is not only the fourth most abundant cation in the Earth's crust, accounting for about 5
wt. %, but it is also the most widely used metal in modern society, with a current consumption
of about 1.1 billion tons (Fig. 1.4). Iron ore is exploited from a number of ore deposit types,
but high-grade BIF-hosted deposits, such as Beeshoek and others on the Maremane Dome,
are of predominant importance, contributing about two-thirds of all iron ore mined annually.
The principal ore minerals are hematite (Fe2O3), magnetite (Fe3O4), siderite (FeCO3), and
goethite (FeO(OH)). An estimated 98% of the ore produced in the world is consumed in the
manufacture of iron and steel. The remaining 2% is used in the manufacture of cement,
heavy-medium materials, pigments, ballast, agricultural products and speciality chemicals
(Williams, 2001).
Figure 1.4 Estimated world iron ore mine production for years 2006 and 2007 (Source: U.S. Geological Survey, Mineral Commodity Summaries, January 2008).
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In 2006, the world production of iron ore grew by 12% to reach 1.5 billion tons (United
Nations 2007). China, the world’s leading steel producer, steel consumer, steel exporter, iron
ore importer and previously first largest iron ore producer (but now second), now accounts for
more than 43% of global iron ore consumption. In response to the increasing demand, the
world iron exports have increased by 6.1% in 2007. Australia maintains the leading exporter
position, accounting for ~ 248 million tons of global exports (UNCTAD first semester report,
July 2007).
The uses of steel continued to grow strongly with developing countries leading the growth in
world steel demand. Steel use projections for next year (2009) suggested a global growth
rate of about 6.3% with Brazil, Russia, India and China in front (Source: IISI 2008). Iron ore is
the major ingredient of steel and 98% of the world iron ore is used in the steel industry (Fig.
1.5). The increasing demand of steel worldwide has led to the price hike of the iron ore
controlled by the largest iron ore producers companies which are Rio Tinto, Companhia Vale
do Rio Doce (CVRD) and BHP Billiton. The rising of Asian countries as India and Malaysia to
the circle of developed countries and the waking up of some African countries into the battle
of development may increase exponentially the consummation of steel and as a result the
production of the major steel making ingredient, iron ore (see table 10.1). Despite the efforts
of major companies for massive exploration and improvement of the grade of low grade iron
ore, the sustainable use of known sources of iron ore is the new challenge.
The world’s iron ore resources were estimated at 300 billion metric tons (USGS, 2008) but
ores greatly differing in quality are included in this figure, and, only a smaller part of the stock
available, corresponding to roughly 30 billion tons of metal, can claim properties satisfactory
for the present-day requirements to be directly processed in a blast furnace. The remainders
are medium grade and low grade ores. The shortage of rich iron ores, and the ever
increasing call for good-quality feed materials have provided a stimulus for extensive mining
of, and processing and dressing of , lower-grade iron ore deposits
Data reported in tables 10.1 and 10.2 show the world production and the apparent use of
crude steel and finished products. As iron ore is the most essential ingredient in steel making,
the lack of exploration success would spill a global crisis. Alternatively, industry may need to
consider the use of low to medium grade iron ore resources.
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Table 1.1 World steel use from 2000 to 2007 in million metric tons of finished steel products with a special focus on South Africa.
2000 2001 2002 2003 2004 2005 2006 2007 Africa 14.5 17.8 20.0 19.0 20.1 21.8 24.1 25.4 Australia and New Zealand 6.7 6.3 7.2 7.5 8.0 7.9 7.9 8.6 Central and South America 28.1 29.2 27.5 28.5 33.0 32.2 36.5 41.6 China 124.3 158.0 191.3 240.5 275.8 331.8 361.3 408.3 CIS 34.1 37.9 35.4 36.3 37.9 41.6 48.0 54.9 European Union 162.6 159.3 158.7 160.1 171.0 164.3 186.3 193.2 Japan 76.1 73.2 71.7 73.4 76.8 78.0 79.0 80.1 Middle East 19.7 23.1 25.4 29.8 31.2 33.7 35.4 47.6 NAFTA 146.6 134.3 137.5 131.3 149.0 139.8 155.6 141.5 Other Asian Countries 122.6 121.5 136.4 140.0 150.9 155.2 161.0 176.1 Other European Countries 21.1 16.4 17.5 29.9 23.0 25.1 29.4 31.3 Total 756.4 777.0 828.6 886.3 976.7 1031.4 1124.5 1208.6 South Africa 4.0 4.2 4.9 4.1 4.9 4.7 6.0 6.0
(Source: International Iron and Steel Institute)
CIS: Commonwealth Independent States
NAFTA: North American Free Trade Agreement
Table 1.2 Geographic distribution of steel production (A) and use (B) in 1997 (world production total: 799 million metric tons of crude steel) and 2007 (world production total: 1344 million tons of crude steel)
A- Production of Steel (%) B- Use of Steel (%)
Geographic Distribution of Steel 1997 2007 1997 2007
Africa 1.6 1.4 2.2 2.1 Australia and New Zealand 1.2 0.7 0.9 0.7 Central and South America 4.8 3.7 4.0 3.4 China 13.6 36.4 14.6 33.8 CIS 10.1 9.2 4.0 4.5 European Union 24.3 15.6 20.8 16.0 Japan 13.1 8.9 11.6 6.6 Middle East 1.2 1.2 2.3 3.9 NAFTA 16.1 9.8 19.8 11.7 Other Asian Countries 11.9 10.8 17.4 14.7 Other European Countries 2.1 2.3 2.4 2.6 Total 100 100 100 100
(Source: International Iron and Steel Institute)
CIS: Commonwealth Independent States
NAFTA: North American Free Trade Agreement
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Figure 1.5 Geographic distribution of steel production in 1997 (A) and in 2007 (B), and use
in 1997 (C) and in 2007 (D) and 2007. To keep up with demand for iron and steel, iron ore mining companies have in recent years
continued to upgrade and expand their production and beneficiation capacity. During the first
quarter of 2007, rapid growth continued leading to a mark-up of 9.5% for the price of iron ore
fines. That growth has continued in early 2008, as major iron ore producing companies like
BHP Billiton, CVRD and Rio Tinto agreed with consumers to increase prices by about 60-
70% (Rushton and Marsden, 2008). Related to these increases and the rapid depletion of
production capacity, iron ore producers expand existing mines, advance exploration projects
and make attempts to utilize low-grade (less than 60% Fe) resources. This includes the use
of low-grade stockpile and reprocessing of tailing materials.
In South-Africa, the following initiatives are currently carried out to react to improved market
conditions and demand for iron ore:
(1) The Khumani Mine, which is currently being brought into production by ASSMANG, is
located on the farms Bruce 544, King 561 and Mokaning 560. These farms are located to
immediately south of Sishen Iron Mine. This new mine will assure ASSMANG high-grade iron
ore production of ca 10 Mt per annum for at least 30 years. Blasting of 0.6Mt of ore at the
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Khumani Mine was completed in May 2007. First rail exports commenced during the first half
of 2008 (ARM Annual Report 2007).
(2) Kumba Iron Ore, a unit of Anglo American Plc, is planning to open up a mine at the
Sishen South deposit immediately to the south of Beeshoek Mine. The company is planning
to spend some 8.5 billion Rand to raise the output of the mine to 9 million tons per year, with
production expected to start in the first half of 2012 and to reach full capacity by 2013
(Source: Mining Weekly, December 2008).
(3) The construction of a pipeline between Sishen Mine and Saldanha Bay for the export
of iron ore fines by Kumba Iron Ore has been proposed. This would to grow the production
capacity to more than 70 Mt per year by 2015 (Kumba Annual Report, 2007).
(4) The Sishen expansion projects I and II of Kumba Iron Ore, aiming to extract saleable
iron ore products with 64 wt. % Fe from 21 Mt of feedstock per annum that were previously
regarded as waste. The study considers additional production capacity of between 13 Mtpa
and 20 Mtpa for both Sishen I and II, respectively. Production is intended to commence in
2011(Kumba Annual Report, 2007).
(5) The Phoenix Project of Kumba Iron Ore at Thabazimbi Mine. This project extended the
life of the mine from four to thirty years by exploiting medium grade in situ altered banded
iron formation (low grade ore with < 60 wt. % Fe) which, when mixed with high grade
hematite, represents an economically viable iron ore feed with 64 wt. % Fe (Kumba Annual
Report, 2007).
(6) The Palabora Mining Company considers to build a 300km pipeline, from its mine site
in Phalaborwa (South-Africa) to Maputo in Mozambique in 2009 for export of low grade
stockpiles of Ti-rich magnetite. But the preferred option was to increase the shipments to
Richards Bay and Maputo. The company will export more than 240 Mt of magnetite, a by-
product of copper exploitation, containing between 56 and 60 wt. % Fe to China (Mining
Weekly, April 2008).
1.5 OBJECTIVES AND METHODS EMPLOYED
The present study has two main objectives. The first objective is the characterization and the
possible utilization of the material that comprises the discarded low-grade lumpy stockpile at
Beeshoek Mine. The second objective is the evaluation and assessment of the beneficiation
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potential of iron ore fines deposited as tailings in a slimes dam at Beeshoek Mine. Materials
were characterised with respect to their lithology, mineralogy, density and chemical
composition. Large representative samples were then used to assess the beneficiation
potential of these materials currently considered as waste.
Different analytical techniques were used to conduct the investigation of the fines from the
tailings dam and the lumpy material from the low-grade stockpile. Mesoscopic categorization
by hand-sorting proved very valuable to obtain reliable lithological descriptions of the low-
grade lumpy material. The different lithologies were then studied using X-ray powder
diffractometry (XRD), paired with light and electron microscopy to obtain mineralogical
information. Numerous sample blocks were used to determine the average and range of
densities of the various lithologies. Finally, the major and minor elements composition of the
lithologies was determined by X-ray fluorescence spectroscopy (XRF).
Careful sorting (using a hand lens) of iron ore fines revealed the presence not only of
hematite but also of other lithologies in the fines. The beneficiation potential of the fines was
assessed using spiral separation and simple washing. Each fraction obtained during these
tests was analyzed for major element composition and the recovery and grade were
evaluated. Results from XRF analyses were verified by volumetric titration for the
determination of total iron in the fines.
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CHAPTER II
GEOLOGICAL SETTING
2.1 REGIONAL SETTING
In order to understand the origin of the material (low-grade ore currently considered as
waste) investigated during this study, it is necessary to have a background of the geological
setting of the iron ore bodies mined at Beeshoek. The Beeshoek iron ore deposit occurs in
the Neoarchaean to Palaeoproterozoic Transvaal Supergroup in the Griqualand West region
(Fig. 2.1) (Beukes, 1986; Grobbelaar et al, 1994; Dorland, 2004; Beukes and Gutzmer,
2008). The Transvaal Supergroup in the Griqualand West region is subdivided into the
Ghaap and Postmasburg Groups. These two groups are equivalent to the Chuniespoort and
Pretoria Groups, respectively, in the Transvaal region (Fig. 2.1).
High–grade iron ore deposits of the Transvaal Supergroup are intimately associated with
voluminous iron formations of the Asbestos Hills Subgroup in the Griqualand West region
and the laterally equivalent Penge Iron Formation of the Transvaal region (Fig. 2.1). Some of
the iron ore deposits are structurally-controlled and considered to be of hydrothermal origin
(Beukes et al., 2003), most notably the ore bodies of the Thabazimbi deposit (Fig. 2.1) in the
Transvaal region.
In contrast to Thabazimbi, the economically important high-grade iron ore deposits of the
Sishen-Postmasburg area on the Maremane Dome in Griqualand West region (Fig. 2.1) are
thought to be of ancient supergene origin. They are associated with an erosional
unconformity that separates the Manganore Iron Formation (oxidized and altered lateral
equivalent of the Asbestos Hills iron formations) from overlying red bed sedimentary rocks of
the Gamagara Formation. The red beds of the Mapedi/Gamagara Formation were long
considered part of the Olifantshoek Group (Beukes, 1986, Van Schalkwyk and Beukes, 1986)
but recent studies have assigned these formations to the Postmasburg Group (Van Niekerk,
2006) of the Transvaal Supergroup.
2.2 GEOLOGY OF THE MAREMANE DOME
The Maremane Dome is a double plunging anticlinal structure between Sishen and
Postmasburg (Fig. 2.2). It is defined by dolomites of the Campbellrand Subgroup and iron
formation of the Asbestos Hills Subgroup of the Transvaal Supergroup. Only the eastern half
of the dome is exposed because the western half is covered by the unconformably overlying
strata of the Gamagara Formation forming the Gamagara range of hills (Fig. 2.3). Further to
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the west, at the back of the Gamagara range, older strata of the Postmasburg Group of the
Transvaal Supergroup have been thrusted back over the Gamagara Formation along the
Black Ridge thrust (Fig. 2.2 and Fig. 2.3) (Beukes and Smit, 1987).
Figure 2.1 Distribution of the Transvaal Supergroup, Southern Africa (modified after
Button, 1986; Moore et al., 2001).
The iron ores of Sishen and Khumani along the northern limit and Beeshoek and Sishen
South (Welgevonden) along in the southern limit of the Maremane Dome (Fig. 2.3) are all
situated in either hematitised Manganore Iron Formation (altered lateral equivalent of the iron
formations of the Asbestos Hills Subgroup) or hematite pebble conglomerate of the
Doornfontein Conglomerate Member of the Gamagara Formation (Fig. 2.3) (Van Schalkwyk
and Beukes, 1985; Grobbelaar and Beukes, 1985; Gutzmer and Beukes, 1998). In the
central part of the Maremane Dome, karstic manganese deposits are associated with
manganiferous dolostone below the Gamagara unconformity at Lohathla, Glosam and Bishop
(Fig. 2.3) (Grobbelaar and Beukes, 1985; Gutzmer and Beukes, 1997 and Gutzmer and
Beukes, 1998).
The iron ores derived from hematitization of Manganore Iron Formation (laterally equivalent
to Asbestos Hills iron formations). Reworked equivalents of the iron ore form part of the
Doornfontein Conglomerate of the Gamagara Formation preserved as infills of large karstic
depressions in the underlying Campbellrand dolostone. Conglomerates composed essentially
of iron ore pebbles are mined as so called conglomeratic ore. The large mines at Sishen,
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Khumani and Beeshoek exploit both laminated ores of the Manganore Iron Formation and
conglomeratic ores of the Doornfontein Conglomerate at the base of the Gamagara
Formation. In the Western Belt, ferruginous manganese ores occur (Bishop, Lohatla and
Glosam) at the base in the central part of the Gamagara Ridge, where the Gamagara
Formation unconformably overlies the manganese-rich dolomite of Reivilo and Farfield
Formations (Schalkwyk, 2005). The unconformable contact between the Manganore Iron
Formation and the karstic dolostones of the Campbellrand Subgroup is marked by the
occurrence of the Wolhaarkop Breccia (Fig. 2.3) that is locally manganiferous, i.e. the breccia
contains lenticular pockets of high-grade siliceous manganese ores (Gutzmer and Beukes,
1997, 1998).
2.3 STRATIGRAPHY
2.3.1 Wolhaarkop Breccia
The Wolhaarkop Breccia (Fig. 2.3 and 2.4) is an enigmatic lithology that occurs intimately
associated with the manganese and iron ores on the Maremane Dome. Recently, Schalkwyk
(2006) provided the first detailed investigation into the characteristics and origin of the
Wolhaarkop Breccia. The breccia separates the Manganore Iron Formation and associated
iron ores from the underlying dolostones of the Campbellrand Subgroup. It varies greatly in
thickness, ranging from less than a meter thick to tens of meters in thickness. It consists of
matrix supported unsorted angular milky quartz fragments that were derived from the
underlying dolostones of the Campbellrand Subgroup (Beukes and Smit, 1987). Secondary
quartz or chalcedony abound, thus indicating that the breccia originally had an open
framework structure (Gutzmer and Beukes, 1998).
Gutzmer and Beukes (1998) suggested that the Wolhaarkop Breccia originated as a solution
collapse breccia composed of insoluble residue of the manganese and iron-rich dolostones of
the Campbellrand Subgroup. This mode of formation relates the Wolhaarkop Breccia closely
to the Gamagara Formation, even if it is physically separated from it by the Manganore Iron
Formation.
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2.3.2 Manganore Iron Formation
The Manganore Iron Formation (Fig. 2.3 and 2.4) occurs exclusively on the Maremane Dome
and is closely associated with the Wolhaarkop Breccia (Schalkwyk, 2005). Van Schalkwyk
and Beukes (1986) indicate that the Manganore Iron Formation is an oxidized and locally
ferruginized correlative of the iron formations of the Asbestos Hills Subgroup of the Ghaap
Group of the Transvaal Supergroup. The Manganore Iron Formation can be subdivided into
seven different lithological zones that are equivalent to the major units of the Asbestos Hills
Subgroup. Spotted and carbonaceous dark brown shales comprise the basal unit of the
Manganore Iron Formation (Fig. 2.4). These shales are characterised by the presence of
chert pillows and hematite nodules within very fine shale matrix and correlates with the
Tsineng Member of the Campbellrand Subgroup (Van Schalkwyk and Beukes, 1986). This
unit is referred to as a zone I of the Manganore Iron Formation. It is overlain by an alternating
succession of hematite and microbanded white chert interbedded with intraclastic chert and
black to brown shale of Zone II (Fig. 2.4) considered equivalent to the basal Kliphuis Member
of the Kuruman Iron Formation. Zone II is in turn overlain by a sequence of chert-banded iron
formation of Zone III. The lithologies in Zone III vary from layers of chert and laminated
hematite ferhythmites within which sedimentary cycles of (1) hematite bearing shale or
hematite lutite, (2) hematite microbanded chert, (3) hematite bandrhythmite, (4) hematite
ribbon-wave and pillow-rhythmite were recognized (Van Schalkwyk, and Beukes, 1986).
Zone III is in turn overlain by laminated ores derived from hematite rhythmites of Zone IV.
These laminated ores are overlain by a unit of hematite-greenalite-bandlutite known as Zone
V. Zone V grades upwards into a hematite disclutite unit consisting of concretionary chert
nodules (Zone VI). The last unit of the Manganore Iron Formation is composed of hematite
lutite with mesobands of hematite peloidlutite and massive hematite bearing chert, and is
known as Zone VII. Zone IV-V correlate with the upper units of the Kuruman Iron Formation,
Zone VI to the Ouplaas Member of the Kuruman Iron Formation and Zone VII to the
Griquatown Iron Formation.
Although the simple lithostratigraphy of the Manganore Iron Formation corresponds very well
with that of the Kuruman and the Griquatown Iron Formations of the Asbestos Hills Subgroup
(Van Schalkwyk and Beukes, 1986), the mineralogy and the petrography are very different.
The reason for that is that minerals like siderite and magnetite, present in abundance in the
Kuruman and Griquatown Iron Formations, have all been transformed to hematite in the
Manganore Iron Formation.
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Three texturally distinct types of high-grade hematite iron ore are present in the Manganore
Iron Formation namely:
(i) Laminated iron ore that is by far the most abundant and consists of alternating finely
laminated to massive and more porous layers of fine-grained hematite ranging in
thickness between 2 to 15mm comprising ferruginized microbanded BIF;
(ii) Massive iron ore formed by enrichment of lutitic iron formation in the uppermost part
of the Manganore Iron Formation. It consists of massive to very poorly bedded and
microplaty hematite with remnants of chert;
(iii) Brecciated iron ore known locally as Blinkklip Breccia consisting of poorly sorted
angular fragments of ferruginized BIF in fine-grained hematite cement (Van
Schalkwyk and Beukes, 1986).
2.3.3 Gamagara Formation
The Gamagara Formation is a succession of aluminous and ferruginous texturally variable
red beds that unconformably overlie the Campbellrand dolostones and the Manganore Iron
Formation on the Maremane Dome (Fig. 2.3 and 2.4). The origin of the Gamagara Formation
as part of the Transvaal Supergroup has been the subject of protracted debate (De Villiers,
1967; Beukes and Smit, 1987), but as already mentioned recent studies have attributed this
formation to the Postmasburg Group of the Transvaal Supergroup (Dorland, 1999; Van
Niekerk, 2006). This implies that the major unconformity-bounded hematite iron ore deposits
at Beeshoek and Sishen are also part of the Transvaal Supergroup (Fig. 2.3).
Gutzmer and Beukes (1998) described pisolitic laterites in the basal part of the Gamagara
Formation as paleosols formed in an ancient tropical environmental. Van Schalkwyk and
Beukes (1986) described the stratigraphy of the Gamagara Formation and subdivided it into
four members (Fig. 2.4). In the lower part, a sequence of hematite and banded hematite
conglomerates interbedded with shale is referred to as the Doornfontein Member (Fig 2.4).
Some of the conglomerates are composed of hematite ore pebbles and comprise part of the
iron ore resources on the Maremane Dome. Also part of this Doornfontein Conglomerate
succession is gritstone, peloidal mudstone, highly ferruginous shale and green to white highly
aluminous shale. The Sishen Shale Member (Fig. 2.4) overlies the Doornfontein
Conglomerate Member and consists of reddish brown banded to spotted shale that grades
upwards into cross bedded ferruginous quartzite. A conglomerate unit (Fig. 2.4) separates
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the quartzite from overlying creamy and purple shales. The Marthaspoort Quartzite Member
overlies the Sishen Shale Member and is composed of light purple quartz arenite (Van
Schalkwyk and Beukes, 1986). Quartzite grains in these well sorted quartzites are coated by
hematite and cemented by quartz. The coarse-grained quartzite fines upwards and is
overlain with a sharp contact by the Paling Shale Member that constitutes the uppermost unit
of the Gamagara Formation (Van Schalkwyk and Beukes, 1986).
The unconformity at the base of the Gamagara Formation is apparently developed across the
entire Transvaal basin. It is marked by the presence of ferruginous lateritic weathering
profiles in the rocks immediately underlying it. Weathering took place around 2.18 – 2.2 Ga,
following a period of folding and uplift of Transvaal strata (Beukes et al., 2002).
The Gamagara Formation has been correlated with the Mapedi Formation (Fig. 2.3), a red
bed succession that occurs in a similar lithostratigraphic position outside the Maremane
Dome (Beukes and Smit, 1987). That correlation is based on lithological similarities, the
stratigraphy and the sedimentary cycles of both the Gamagara and the Mapedi Formations,
and implies that the Gamagara and Mapedi Formations were deposited as a single unit along
a major unconformity overlapping successively from the Campbellrand dolostones of the
Maremane Dome, northwards over the Asbestos Hills Iron Formations, the Ongeluk
Formation and the Voëlwater Subgroup. The red beds in all areas commence with a basal
hematite-pebble conglomerate that fines upwards into alternating shale and quartzite arenite
beds. The major differences between the Mapedi and Gamagara Formations include (i) the
thickness of different lithologies and (ii) the restriction of high aluminous mudstones to the
Gamagara Formation (Beukes and Smit, 1987).
Two tectonothermal geological events are recognized in Griqualand West region, namely the
earlier Kheis event and the post-Kheis tectonothermal event or Namaqua orogeny
(Grobbelaar et al., 1995). The Black Ridge thrust (Fig. 2.2) is related to the Kheis orogeny.
The Namaqua orogeny is characterized by complex ductile deformation episodes in the
western part. And it was form as a result of north-directed of major transcurrent dextral
shears called by Stowe (1986) as the Namaqua compression. A metamorphic event
corresponding to the Namaqua orogeny (1.1 -1.03 Ga) was detected by Altermann et al.
(1992) on neogenic mica from the shales of the Campbellrand Subgroup.
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2.4 GEOLOGY OF THE BEESHOEK IRON ORE DEPOSIT
The iron ore bodies at Beeshoek Mine (Fig. 2.5) are restricted to the Gamagara unconformity
(Grobbelaar and Beukes, 1986). The ore bodies occur in paleosinkhole structures that are
thought to have formed in the dolostones of the Campbellrand Subgroup prior to and during
the deposition of the Gamagara Formation (Grobbelaar and Beukes, 1986). High grade iron
ores (> 60 Wt. % Fe) occurs in three different stratigraphic positions:
(i) Laminated, massive and brecciated iron ores. Laminated or massively-textured
ores occur immediately below the Gamagara unconformity and are restricted to the
Manganore Iron Formation. Locally, the laminated ore is underlain by brecciated
hematite ores known as Blinkklip Breccia.
(ii) Conglomeratic iron ore (Doornfontein Conglomerate) forms the base of the
Gamagara Formation and erosively overlies iron ores. The shale and conglomerate
units of the Doornfontein Conglomerate Member show upward-fining sedimentary
successions (Van Schalkwyk and Beukes, 1986).
(iii) Detrital iron ore (potato ore) occurs in minor amounts as part of the thin Cenozoic
cover surrounding the outcropping ore bodies. This iron ore type is economically
insignificant at present. It consists of angular fragments of hard iron ore either
unconsolidated or partly cemented by recent calcrete-cemented. Detrital ore is not
high-grade ore as much as other types and requires considerable beneficiation.
The iron ore deposits were affected by karstic slumping, as can be seen at Beeshoek Mine,
where thick iron ore successions occur in the karst structures, in contrast with the not
collapsed areas, where the iron ore is very thin or absent (Fig. 2.6). During the early stages
of Gamagara deposition the laminated iron ore (Manganore Iron Formation) was eroded and
redeposited as alluvial fans at the base of Gamagara Formation, and now constitutes the
Doornfontein Conglomerate Member (Fig. 2.6).
Iron ores of the Beeshoek deposit and other similar deposits associated with the Gamagara
unconformity (Sishen, Khumani, Manganore, Sishen South and Rooinekke) (Fig. 2.2) are
considered to be type examples of ancient supergene high grade BIF-hosted iron ore
deposits (Gutzmer et al, 2003). According to the supergene model, the ores of the
Manganore Iron Formation derived from oxidation of iron and leaching of chert from the
Asbestos Hills Subgroup iron formations during lateritic weathering associated with the
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development of the Gamagara unconformity. Large deposits of high-grade iron ore are
developed in karstic solution collapse structures, where iron formations of the Asbestos Hills
Subgroup slumped into karstic cavities developed in the dolostones of the Campbellrand
Subgroup (Fig. 2.6). In these karstic slump structures the iron ores are closely associated
with aluminous shales and pisolitic laterite profiles of the Gamagara Formation (Gutzmer and
Beukes, 1998).
Paleomagnetic data indicate that ore formation and deposition of overlying Gamagara red
beds took place in near equatorial setting (Evans et al., 2002), supporting a lateritic
supergene enrichment origin for the Sishen-Beeshoek deposits. A positive paleomagnetic
test of hematite pebbles in the basal Doornfontein conglomerate member of the Gamagara
Formation indicates that the ores formed prior to transport and deposition of the pebbles
(Evans et al., 2002).
The ores of the Manganore Iron Formation can be described as ancient saprolite, because
they have preserved original textures and banding of the iron-formation precursor (Van
Schalkwyk and Beukes, 1986). These ancient supergene ores have been locally affected by
hydrothermal alteration as manifested by the presence of coarse specularite which fills
secondary pores and veinlets in both laminated and conglomeratic ores. The specularite
must have developed late in the history of the succession because it also occurs in veinlets in
the overlying Gamagara shale and quartzite (Grobbelaar et al., 1994).
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Figure 2.5 Cross section and geological map of the Beeshoek Mining area
(After Grobbelaar et al., 1994)
- 35 -
Figure 2.6 Schematic cross-section of Beeshoek-type iron ore deposits (Modified after
Grobbelaar and Beukes, 1986)
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CHAPTER III
EXPLORATION, EXPLOITATION AND BENEFICIATION
OF IRON ORE AT BEESHOEK MINE
3.1 INTRODUCTION
Iron ore at Beeshoek Mine (Fig. 3.1) is mined from a number of open pits (Fig 3.2). The basic
infrastructure consists of a crusher, a primary crusher, a secondary crusher, a tertiary
crusher, a jig beneficiation plant and a stockpiling facility. Different types of iron ore products
are transported by conveyor belt and stored in stockpiles. A small proportion of the ore
produced at Beeshoek Mine is consumed by the local steel industry but most is exported
through Saldanha Bay and transported using the Sishen-Saldanha railway line.
3.2 ORE DELINEATION
The iron ore at Beeshoek is extracted from several open pits (Fig. 3.2) where it is selectively
mined and blended to provide ore to meet customer specifications. Because the shape of the
high-grade iron ore bodies is very irregular, careful delineation is required prior to
exploitation. This is achieved by surface mapping, followed by ground geophysics and
drilling. Drilling is mostly restricted to percussion drilling, with selected diamond drill cores to
amend geological knowledge. Drilling commences first on a 200m X 200m grid, which is then
reduced to 100m X 100 and finally to 25m X 25m. The choice of grid spacing depends on the
apparent complexity of a specific ore body. Over the last forty years, numerous exploration
programmes were completed at Beeshoek to improve the mining methods, and a total of
1517 holes were drilled thus far (ARM Annual Report, 2007).
All drill holes are sampled and analysed for density and for chemical composition. The
material stream through the beneficiation process as well as the final product stream are
sampled regularly and analysed for quality control purposes. After logging the ore body
intersections, the cores are split using a diamond saw. Half of the core is crushed for
chemical analyses, while the other half is stored. Before being submitted for chemical
analysis, the half-cores are crushed, split and pulverized. Only samples that yield
concentration more than 60 wt. % Fe are included in the definition of the ore bodies. Any
lower-grade materials inside the ore body are defined as internal waste and modeled
separately. Each zone is modeled per section, and then wire-framed to construct a three-
dimensional (3D) model.
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Figure 3.1 Location of Beeshoek Mine and regional map of the Maremane Dome showing
the location and the extent of the iron and manganese ore deposits along the Gamagara Ridge (Western Belt) and the Klipfontein Hills (Eastern Belt) with the occurrence of the Wolhaarkop chert breccia (modified after Gutzmer, 1996).
Ordinary kriging interpolation within the “Datamine” mine planning software is used to
estimate the grade of each 10 x 10 x 10 meter block generated within the geological model.
Density in the resource model is calculated using a fourth degree polynomial fit applied to the
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estimated Fe grade. Densities range from 4.38 t/m3 (60 wt. % Fe) to 5.01 t/m3 (68 wt. % Fe).
A default density less than 3.2 is used for waste (Minerals Engineering International, 2002).
Figure 3.2 Open pit locality plan of Beeshoek Iron Mine, showing both Northern (older) and Southern mines (ARM Annual Report, 2007).
At Beeshoek all blast holes are sampled per meter, but composited per hole. All samples are
analyzed for density and blast holes in ore are sampled and analyzed for Fe, K2O, Na2O,
SiO2, Al2O3, P, S, CaO, MgO, Mn and BaO (table 3.1). Every fifth blast hole is geologically
logged per meter. This information is used to update the geological model. The chemical
results of these holes are used to update the ore block model. Approximately 45,000 blast
holes are drilled per year and 9,000 blast holes are used every year to update the geological
model. The major analytical technique for elemental analyses is XRF spectroscopy.
Volumetric titration is used as verification method for the determination of total iron in the ore.
International standards (e.g. SARM11) and in-house iron standards are used for calibration of
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the XRF spectrometer. The Beeshoek laboratory participates in a round-robin group that
includes seven laboratories for verification of assay results (Assmang Annual Report, 2006).
3.3 MINING AND BENEFICIATION
The mining process at Beeshoek Mine is based on conventional drilling and blasting followed
by loading and transportation of ore and waste by shovel and truck. Two types of ore are
selectively mined. “On-grade” ore is of such good grade that it needs no further treatment
than crushing, washing and screening before being shipped. The second type of ore can be
described as “off-grade” or low-grade ore, and this material is upgraded in a jig plant. The
run-of-mine ore is processed through a crushing, washing and screening plant. Crushing
consists of three different stages, namely primary, secondary and tertiary crushing. Washing
and screening take place between each crushing step. Washing facilitates sorting and is
often performed after first crushing to remove slimes from the ore particles. Screening
consists of the selection of particular sore fractions suitable to enter the next crushing stage.
Table: 3.1 Average chemical composition of Lumpy, DRI and Fines. ELEMENT LUMPY DRI FINES
Fe 65.25 64.41 64.25
SiO2 3.60 4.21 4.82
Al 2O3 1.60 1.77 1.84
MgO 0.04 0.05 0.06
CaO 0.08 0.09 0.10
Na2O 0.03 0.03 0.03
K2O 0.23 0.27 0.25
P 0.04 0.04 0.04
Note: all data in wt. % (Data source: ASSMANG Annual Report, 2007) In 2000, at Beeshoek a new jig plant was installed in 2001and enables the mine to treat and
to recover ore from the material that was previously discarded and considered as waste, i.e.,
the so-called “off-grade” or low-grade ore. The Batac Jig System consists of two air pulsed
jigs, one of which is utilised to process lumpy ore while the other processes the fines. The
principle is based of the use of an underlying air pulse and material segregation according to
density. Financially, the new jig plant has permitted to reduce the processing costs, to
ameliorate the quality of the product and also to slightly extend the life of the mine (Mining
Weekly, 3 August 2005; ARM annual report, 2007).
In August 2002 the mine equipped the plant with 1800mm Kawasaki Cybas Cone crushers
for primary crushing and 7’ Symons Cone crushers for secondary and tertiary crushing to
- 41 -
meet the requirements of the new jig plant and the product quality (IMS Engineering,
November 2001).The current beneficiation plant consists of tertiary crushers, scrubbers,
coarse and fine jigs known also as Lacoderms, elutriators and upward flow classifiers for
lumpy, fines and medium size product stockpiles and a rapid load-out facility.
A computerised geological database is used for planning, scheduling and grade control. The
analytical results of all blast holes are continuously reconciled with the computer-generated
grade models to ensure that the correct grade is mined and supplied to the beneficiation
plant. A continuous sampling process at various points in the treatment and loading plants
ensures the production of a consistent grade of ore that meets the requirements of national
and international markets.
3.4 IRON ORE TYPES AND PRODUCT QUALITY
Three types of beneficiated iron ores are currently produced at Beeshoek Mine. These are
known as lumpy, direct reduction iron ore (DRI) and fines. Classification of these ore types is
done by particles size and chemical composition:
(1) Lumpy: -32 +6.3 mm with 5% >32mm and 7% <6.3mm;
(2) DRI: -18 +6.3mm with 5% >18mm and 10% <6.3mm;
(3) Fines: -6.3 +0.212 mm with 2.9% >8mm and 5% <0.212mm.
Ore types (1) and (2) are stockpiled and sold Fines are currently discarded into tailings dams.
The fines ore one of the material types investigated during this study.
Iron ore produced at Beeshoek Mine is primarily supplied to the international market, with
only a small fraction consumed by local steel industry. The iron ore for export is first railed to
Sishen, 60 kilometers north of Beeshoek Mine, where the trucks are then transferred onto the
Saldhana Bay Harbour railway line by Transnet. The logistic facilities including siding and
loading at Beeshoek Mine are capable of handling four hundred trucks of 85 tons each per
twenty four hour shift. The siding facilities have the capacity of handling six millions tons of
iron ore per annum. At the harbour, the ore is loaded into ships by two buffing, slewing and
travelling ship loaders, fed by a common belt conveyor and capable of operating alternatively
on a continuous basis (ASSMANG, 2007).
In the period 2002-2007 Beeshoek produced an average about 7.7 million tons of ore per
year with 2007 an exceptional year with a production of 13.3 million tons (Fig. 3.3).
- 42 -
7720000
71100007570000
7860000 7720000
13260000
5000000
7000000
9000000
11000000
13000000
15000000
2002 2003 2004 2005 2006 2007
Year
Pro
duct
ion
(Ton
s)
Figure 3.3 Annual production of iron ore from Beeshoek Iron Ore Mine for the period 2002-2007 (source: ARM Annual Report, 2007).
- 43 -
CHAPTER IV
METHODOLOGY
A number of analytical methods were used in this investigation of the beneficiation potential
of discarded lumpy material and the fines from Beeshoek Mine. The methods included the
mesoscopic description and identification of physical aspects, mineralogical and lithological
characteristics as well as the determination of the chemical composition of various rock and
ore types. Several mineral processing techniques were tested to evaluate the possibilities of
beneficiating the discarded material.
4.1 SAMPLING
Eleven samples, each weighting ~ 8 to 10kg were collected randomly at different places from
the bottom, middle and the top of the discarded lumpy stockpile and stored in plastic sample
bags. The samples were then hand-sorted with the aid of a hand-lens into their constituent
lithologies. The colour was the first criteria of selection followed by density and hardness of
samples. Samples were washed and a small diamond saw was used to cut the particles to
reveal internal textures to ascertain correct classification. Each category represents a certain
rock type with different textural subtypes.
The tailings dam was sampled using an auger drill in a grid that was set out over the tailings
dam from proximal to distal settings from the outlet of the feeder pipe. The auger only
allowed reaching a maximum penetration depth of three meters of sampling. Samples were
pre-examined with a hand-lens to differentiate fines ore particles from other particles and to
determine grain sizes.
4.2 DENSITY DETERMINATION
Density determination of lumpy samples was performed in the gemmological laboratory of the
University of Johannesburg located on the Doornfontein Campus under the supervision of Dr.
Jos Lourie. Five to ten specimens were selected per category from each sample for density
determination. Density determination of lumpy hand specimens was performed using the
method of Archimedes. In total, the densities of more than 400 particles were determined.
The process consisted of weighing each particle in air followed by weighing in water. Both
weights were recorded in grams.
Porous particles were first weighed in air and then coated with beeswax to prevent water
from filling pore spaces. The coated samples were again weighed in air and in water. Each
- 44 -
measurement was recorded. The mass contribution of the wax to the sample was determined
by renewed weighing of the particle in air after coating:
Mass of Wax (g) = Mass of coated sample in air (g) - Mass of original sample in air (g) 1)
The coated particles were then weighed in distilled water. As the water temperature was kept
between 23oC to 24oC (considering the laboratory room temperature), the density of distilled
water was considered to be 1g/cm3.
The density of non-porous particles was determined by applying Archimedes’ Principle of
floating or submerged bodies.
waterair
fluidair
MM
M
−=
ρρ
* (2)
where ρ = Density of the sample (g/cm3);
ρ Fluid = Density of the fluid (g/cm3);
airM = Mass of the sample in air (g);
waterM = Mass of the sample in water (g).
Since the density of distilled water was assumed to be constant 1g/cm3, the above equation
can be simplified as:
waterair
air
MM
M
−=ρ (3)
The density of porous particles that were coated with beeswax was calculated as follows:
The density of porous particle was determined by first determining the density of the coated
particle and then correcting this density. The true density of the coated particle can be
calculated as described by Gutzmer (1996):
waterwatercoatedaircoated
aircoatedcoated MM
M
ρρ
×−=
)( //
/ (4)
- 45 -
where coatedρ = Density of coated sample (g/cm3);
waterρ = Density of distilled water (1g/cm3);
aircoatedM / = Mass of the coated sample in air (g);
watercoatedM / = Mass of the coated sample in water (g).
This result was then corrected for the contribution of the beeswax coating to the calculated
density. The following formula was used to calculate the true density of the particles
(Gutzmer, 1996):
air
airaircoatedwax
air
aircoatedcoatedtrue M
MM
M
M )( // −−=
ρρρ (5)
where trueρ = True density of the sample (g/cm3);
waxρ = Density of the beeswax (0.97 g/cm3);
coatedρ = Density of coated sample (g/cm3);
waterρ = Density of distilled water (1g/cm3);
aircoatedM / = Mass of the coated sample in air (g);
airM = Mass of the sample in air without beeswax (g).
4.3 PREPARATION OF POLISHED SECTIONS
Preparation for microscopic work on lumpy hand specimens was undertaken in the sample
preparation laboratory of the Geology Department at the University of Johannesburg,
Auckland Park Campus as described by Camuty and McGuise (1999). The process
comprises of seven steps:
• Pre-selection of the lumpy fragments : Five lumpy fragments were selected per
lithology for each sample.
• Cutting : Each lumpy fragment was carefully cut in half using a small diamond saw.
• Selection : At least one of the five fragments per lithology of each sample was chosen
to be studied and further processed.
- 46 -
• Leveling : The selected rocks fragments were ground on a diamond-impregnated disc.
This was done to level the sample before polishing.
• Grinding: Grinding steps followed from coarse (600), through medium (400) to fine
(200) grain sizes. Different carbide powders were used on glass plates.
• Polishing, glueing and cutting : Once the ground block was smooth enough, the
selected side was glued on a conventional microscopy glass of 4.5 X 2.6 cm and left
to dry for at least one day. The dried sample was trimmed with a small diamond saw
and then further ground and polished till about 30µm thick.
• Lapping and polishing : The obtained thin section was submitted to lapping and
polishing using an automated polishing machine and different diamond pastes on
lapping cloth. Samples were polished for at least two hours.
4.4 MICROSCOPY
Light microscopic work was performed at the Geology Department, University of
Johannesburg, Auckland Park Campus, in both transmitted and reflected light. The polished
thin sections were examined using a Leica DMLP microscope equipped with a camera and a
computer facility to collect digital images. Scanning electron microscopic studies were
conducted using a JEOL 5600 SEM, equipped with a NORAN EDS detector at Spectrau, i.e.,
the Central Analytical Facility of the University of Johannesburg.
Polished thin sections were first carbon-coated to assure conductivity because specimens
examined in the scanning electron microscope needed to be coated with a thin film of
conducting material. This coating is necessary to eliminate or reduce the electric charge
which builds up rapidly on a non-conducting specimen when scanned by a beam of high-
energy electrons (Lawes, 1987). More than 150 specimens were examined in both secondary
electron (SE) images and backscattered electron (BSE) imaging modes. X-ray spectra were
collected by EDS to identify unknown minerals. Scanning electron microscopy was used
particularly to differentiate different alumo-silicates and to identify accessory minerals.
4.5 COMMUNITION
Sample powders of analytical finesses were required for further analyses by XRD (X-ray
powder diffraction) and XRF (X-ray fluorescence spectrometry). Representative amounts of
fines samples and rocks fragments remaining from the preparation of polished thin sections
- 47 -
of lumpy ore were used. A Siebtechnik vibratory disk mill with a chromium steel crushing
dish, available at the sample preparation laboratory of the Geology Department, University of
Johannesburg Auckland Park Kingsway Campus, was used. This device comprises of a
series of concentric rings plus an inner solid disc that is shaken back and forth vigorously and
it is very efficient to reduce powders to less than 50 µm in a matter of minutes. The vibratory
disc mill is the most common technique of grinding (Jenkins, 1988; 1996). Unfortunately it
could represent a source of contamination of the elements used in construction of the steel
rings and base.
4.6 X-RAY POWDER DIFFRACTION
To complement the microscopic studies, X-ray powder diffraction was used for mineral
identification. A Panalytical Philips PW3040/60 X’Pert Pro automated diffractometer available
at Spectrau, was used. The Philips X’Pert Pro diffractometer is equipped with an X’Celerator
detector and fitted with a diffracted beam monochronometer. Qualitative phase identification
was carried out using the X’Pert High Score Plus software and based on a semi-automatic
search-match procedure based on the Powder Diffraction File (PDF) database. The PDF
consists of a collection of single phase reference patterns (Jenkins, 1996).
4.7 X-RAY FLUORESCENCE SPECTROMETRY
Whole rock geochemical analysis was performed at Spectrau, University of Johannesburg,
Auckland Park Campus, by X-ray fluorescence spectrometry. X-ray fluorescence
spectrometry is based on the measurement of wavelengths and intensities of X-ray spectral
lines emitted by secondary excitation. It is a non-destructive method of qualitative and
quantitative chemical analysis for elemental composition of samples (Buhrke et al., 1998).
Pressed powder pellets and are used for trace element analyses. These were prepared using
approximately 9.6 g of sample powder mixed with of 2.4 g (12 tablets) of Herzog binder (90%
cellulose, 10% wax). The sample powder and the binder were mixed together in a milling
container placed in a magnetic shaker for 3 min. The mixture was poured in an aluminum
cup, then placed in a die set and pressed using a press at 20 tons for about 60 seconds.
Slowly, the pressure was released to avoid cracking of the pellet stuck in the die set. The
stuck pellet is collected by putting the die back into the press with slow increase of the
pressure. The binder holds the sample powder firmly together after pressing, minimizing the
degradation and dusting of the analytical surface and thereby prolonging the useful life of the
pellet.
- 48 -
Glass fusion beads for major element analyses were prepared using 3 g of a 50/50 flux
lithium tetraborate that is poured in a platinum crucible and followed by 1g of sample powder.
Another 3 g of 50/50 flux lithium tetraborate was added over the top of the sample powder in
the crucible. The crucible was covered with a platinum casting dish and placed in a mini-fuse
fusion machine. The mixture was fused at 650 oC for 15 minutes. The molten sample was
then poured into a platinum casting dish (Bedorf, 2006).
The analysis of both pressed powder pellets and glass beads were carried out on a 4kW
Magix Pro wavelength-dispersive X-ray fluorescence spectrometer (PANalytical) equipped
with a rhodium end window X-ray tube. A SuperQ software application was used for major
and trace elements analysis. Data were collected using a quantitative results application of
the software. Data are presented in weight percentage for major oxides and parts per million
(ppm) for trace elements. The data were corrected using the loss on ignition for major and
minor elements
The loss on ignition was determined using approximately 1.7g of sample powder which was
heated in a ceramic crucible in the muffle furnace for at least 1 hour at 1050oC. The
procedure included the following steps:
a. Weighing the empty ceramic crucible and note the mass (m1);
b. Addition of ca. 1.7 g of sample powder; accurate weighting of the filled crucible (m2 =
ceramic crucible + sample powder);
c. Placing the crucible into the oven for at least one hour at 1050oC;
d. Taking the crucible out and placing it onto the fibre ceramic plate. After 5 minutes
transferring the crucible in to desiccator.
e. Weighing of the cooled-off crucible at least 10 minutes after removing it from the oven
and note the total mass (m3).
The loss on ignition was then determined using the following formula:
)(
)(100%).(..
12
32
mm
mmweightIOL
−−
×=
The loss on ignition accounts for the abundance of volatile (H2O+, CO2, F, Cl, S…)
compounds in a sample.
4.8 TITRIMETRIC Fe DETERMINATION
Titration is a common and accurate method for determining the total content of iron in a
sample. Titration was done under the supervision of Mr. Herman Steyn of the Extraction
- 49 -
Metallurgical Department of the University of Johannesburg, Doornfontein Campus. This
method was used to complement the geochemical data from the X-ray fluorescence
spectrometry. Only samples from the fines tailings dam were analyzed using this method. For
the analysis, about 0.2 grams of sample powder were dissolved in 15 cm3 of concentrated
hydrochloric acid on a hot plate. As dissolution was difficult, about 0.5 cm3 of stannous
chloride was added at intervals with intermediate heating.
Dissolution of hematite takes place in hydrochloric acid according to the following equation:
Fe2O3 + 6H+ + 12Cl- -----------→ 2FeCl63- + 3H2O (1)
The analytical procedure is as follows:
1) The solution is diluted in ±25 cm3 distilled water, and boiled for two minutes to ensure
complete dissolution. The only solid residue which remains is white silica gel.
2) Into the hot solution, stannous chloride is dropped slowly until the FeCl63- yellow colour
disappears, plus two drops in excess.
3) At room temperature, 15cm3 of mercuric chloride solution is added to form a milky
solution.
4) Then the solution is diluted again to ± 100cm3 with cold distilled water.
5) To the cooled solution, 30 cm3 of 1:1 H2SO4 and 10 cm3 of phosphoric acid are added,
swirled to mix plus 10 drops of diphenylamine sulfonate indicator solution and titrated.
The resultant solution is titrated with a potassium dichromate solution according to the
reaction:
6Fe2+ + Cr2O72- + 14H+ ------------→ 6Fe3+ +2Cr3+ + 7H2O (2)
Example of determination of the total iron content:
The calculation of the iron concentration is as follows. A solution produced from 0.2g iron ore,
requires about 23.15 cm3 of 0.016 mol/dm3 of K2Cr2O7 for titration. The concentration of iron
in the hematite ore is:
1mol/dm3 K2Cr2O7 solution = 6Fe =6X 55.84 g Fe
23.10 cm3 of 0.016 mol/dm3 K2Cr2O7 solution
Thus 1000
15.23016.084.556 ×××
Concentration of Fe (wt %) in sample
- 50 -
1
100
2.01000
15.23016.084.556 ××
×××
= 64.52 wt. % FeTot.
The iron-rich solution is slowly titrated by adding drops of a calibrated solution of potassium
dichromate and a colour change from blue-green, through a grayish tinge to the first
permanent violet, is observed. The first appearance of the violet colour marks the end point
of the titration. The titration is conducted very slowly in the transition from grey to violet
because the oxidation of the indicator is somewhat slow at this point.
4.9 SIEVING
Grain size analysis was undertaken in the metallurgical laboratory of the University of
Johannesburg, Doornfontein Campus under the supervision of Mr. Mustard. The method
consists of passing a known weight of sample material successively through finer sieves and
weighing the amount collected on each sieve to determine the percentage on each size
fraction. Sieving was carried out with dry material from the tailings dam using one of the
vibrating sieve shakers available in the metallurgical laboratory.
Six sieves varying from 600µm to 75µm were arranged in a stack in this manner: coarsest
sieve on the top and a finest at the bottom. A tight-fitting pan or receiver was placed below
the bottom sieve to collect the undersize particles, and a lid was placed on top of the
coarsest sieve to prevent escape of the sample and the dust.
About 500 grams of each tailings sample was weighed and placed on the uppermost sieve or
coarsest sieve. The sieve shaker was set to vibrate for 15 minutes. During the processing,
undersize material falls through successive sieves until it is retained on a sieve with slightly
smaller aperture than the particle diameter.
After the required time, the stack was taken apart and the amount of material retained on
each sieve weighed. Samples were then separated in seven size fractions. Particles which
were blocked in the openings were removed by inverting the sieve and brushing gently. The
different weights were reported in grams and in weight percent (wt %) plus cumulative weight
of size factions were calculated to finally determine the loss during the process (typically
below 0.3%).
- 51 -
4.10 BENEFICIATION STUDIES
4.10.1 Spiral Gravity Concentration
As part of an exercise to establish whether the grade of the fines from the tailings dam could
be improved by technically simple physical beneficiation methods experiments were done
using the spirals in the Metallurgical Laboratory of the University of Johannesburg,
Doornfontein Campus. The spiral used during these tests is composed of a helical conduit of
modified semicircular cross section equipped with a motor pump (Fig. 4.1a & e). A fraction of
about six kilograms of each sample was taken to be separated. Hand sorting was done to
remove big particles that could damage the pump prior to processing.
The sample is mixed with 40 liters of water at the bottom of the spiral. The motor pump
aspires the fines and water from the bottom and feeds the spiral from the top of the spiral. As
they flow downwards, the particles stratify due to the combined effect of centrifugal force, the
different settling rates of the particles and the effect of interstitial trickling through the
following particle bed. The tailing is collected from the lowest end of the spiral conduit.
Separation mechanism is influenced by both the slurry density and particle size. The net
effect of spiral separation is reverse classification in which smaller and denser particles are
preferentially entering the concentrate. The sample ran in closed circuit through the spiral
from bottom to the top for approximately 10 minutes before samples were collected. Once the
perfect differential bed was formed, two ports were fixed at the ends of the two highest
conduits of the spiral. In total fourteen samples of iron ore fines from the tailings dam at
Beeshoek were processed in this manner.
Three separate factions were obtained namely concentrate , middling and tailing . The
separation of three different fractions is controlled by adjustable splitters (Fig. 4.2c). After
separation, each fraction was dried for a day in an oven at about 110oC and weighed to
determine the mass of each fraction.
4.10.2 Washing/panning
To further test the beneficiation potential of the fines, washing or panning of fines was carried
out in the Sample Preparation Laboratory of the Geology Department, Auckland Park
Campus. The process consisted of:
o About one kilogram of tailings material was loaded into a panning dish and the pan
then filled with water;
- 52 -
o The slurry was shaken in rotation movement from left to right; the aim is to retain
dense iron oxide particles and grains on the bottom of the panning dish, with low
density mineral grains and particles keeping in suspension.
o Mineral grains and particles of low density were swept out of the pan together with
the water. The process of shaking and sweeping was repeated until and the
heaviest material was left.
o About 50 grams of this concentrate was sampled dried and milled for X-ray
fluorescence spectrometry analysis.
Figure 4.1 MG1 spiral available in the metallurgical laboratory at Doornfontein Campus, University of Johannesburg.
- 53 -
- 54 -
PART II
INVESTIGATION OF THE LUMPY MATERIAL FROM
THE DISCARDED STOCKPILE AT BEESHOEK MINE
- 55 -
- 56 -
CHAPTER V
LITHOSTRATIGRAPHIC AND PHYSICAL CLASSIFICATION OF
LUMPY MATERIAL
5.1 INTRODUCTION
The discarded lumpy stockpile (Fig. 1.2) consists of fragments (3 – 8 cm in diameter) of
several lithologies derived from the stratigraphic succession in which high-grade iron ores
occur. This succession (Fig. 2.4) includes from the base upwards Campbellrand dolostones,
Wolhaarkop Breccia, Manganore Iron Formation, Gamagara Formation and the Kalahari
beds. It has been described in quite some detail by Van Schalkwyk and Beukes (1986);
Beukes and Smit (1987); Gutzmer (1996) and Schalkwyk (2005). Based on the stratigraphic
description, and after careful mesoscopic study of stockpile fragments, the stratigraphic units
from which individual fragments was derived could be identified. The fragments themselves
could be classified into nine categories of rock types based on lithological appearance and
physical properties such as colour, hardness and luster. The nine categories of rock are
porous iron ore; dense iron ore; shale; chert; banded iron formation (BIF); ferruginous Mn
ore; chert and BIF breccia; quartzite and dolomite (Table 5.1). One or more classes of rock
type could, in turn, be identified in each of the nine categories and then placed in to
stratigraphic context (Table 5.1).
5.2 LITHOSTRATIGRAPHIC CLASSIFICATION
5.2.1 General Stratigraphic Classification
Different categories and classes of rock fragments in the stockpile could be derived from
single stratigraphic entities in the succession (Table 5.1). Fragments of dolomite derived from
the Campbellrand Subgroup could be classified into sparry white and partly silicified grey
dolomite fragments (Table 5.1 and Fig. 5.1). Fragments derived from the Wolhaarkop Breccia
include ferruginous manganese ore, manganiferous chert breccia and chert-and-BIF breccia
(Table 5.1 and Fig. 5.1).
A large proportion of the fragments come from the Manganore Iron Formation which hosts
the high-grade laminated and brecciated ore bodies at Beeshoek. Fragments derived from
the iron formation include fibrous and nodular chert, BIF, laminated iron ore, brecciated iron
ore and porous iron ore (Table 5.1, Fig. 5.1).
- 57 -
Table 5.1 Summary description and classification of the lumpy material from the discarded stockpile.
STRATIGRAPHY CATEGORY CLASS DESCRIPTION
KALAHARI IRON ORE Detrital Partly cemented lateritic fragments of clasts supported
detritus of laminated fragments of iron ore.
Red purple shale Fine-grained red shale. PALING SHALE
MEMBER SHALE
Pale-yellow shale Fine-grained pale-red-yellowish creamy and massive
shale
MARTHASPOORT QUARTZITE Quartzite/arenite Very coarse quartzite with fine-grained iron rich
matrix.
Red shale Fine grained, highly ferruginous shale.
Fe-rich shale
Very fine-grained shale containing hematite clasts in
highly ferruginous matrix which is due to secondary
enrichment.
Green/Al-shale
Very fine-grained and massive, yellow pale to
greenish pale, sometimes with pigmentation of
hematite. It can be friable or hard.
SISHEN SHALE
Gritty mudstone Hematite granules welded by fine to medium grained
red mudstone matrix.
Shale-breccia Angular clasts of paly-yellow shale in ferruginous
shale matrix.
SHALE
Sandy ferruginous
Mudstone
Soft and fine-grained ferruginous reddish matrix with
clasts of hematite and rounded grains of quartz.
GA
MA
GA
RA
FO
RM
AT
ION
DOORNFONTEIN
CONGLOMERATE
IRON ORE Conglomeratic Round to sub-rounded pebbles of hematite ore in
hematite matrix.
POROUS
ORE Highly porous
Dull, porous with presence of platy hematite crystals
and quartz within a fine-grained matrix.
IRON ORE Laminated Finely-grained high-grade hematite ore with distinct
banding.
IRON ORE Brecciated Poorly sorted clasts of laminated and massive iron ore
in a fine-grained hematite matrix.
BIF Banded iron
formation
Banded iron formation with flat or wavy laminations of
hematite intercalating with chert.
Nodular chert Fine grained silica-rich rock with a dark brown matrix.
MANGONORE
IRON FORMATION
CHERT
Fibrous chert
Fine grained silica-rich with a brown to ferruginous
matrix containing probably remnant of organic
material.
Chert and BIF
breccia
Angular and poorly sorted clasts of chert and BIF
supported by fine-grained hematite matrix. WOLHAARKOP
BRECCIA BRECCIA
Mn-Fe chert
breccia
Shapeless and unsorted clasts of quartz-chalcedony
within a fine-grained manganese or iron rich matrix.
IRON ORE Ferruginous-Mn
ore
Dark-grey vuggy and porous manganese-rich
ferruginous ore.
Sparry white
dolomite
Coarse-grained white greyish massive carbonate rock
with lenses of calcite surrounding dolomite.
CAMPBELLRAND
SUBGROUP DOLOMITE
Silicified green
dolomite
Fine-to coarse-grained green silicified dolostones with
veins of chalcedony/quartz.
- 58 -
Conglomeratic iron ore fragments and pebbles were derived from the Doornfontein Member
of the Gamagara Formation (Table 5.1 and Fig. 5.2). Another very common category of
fragments in the lumpy stockpile is shale lithologies derived from the Gamagara Formation,
typical of the Doornfontein Conglomerate and Sishen Shale Members. The shale includes
aluminous and Fe-rich shale from the Doornfontein Member and cream- to red-coloured
banded shale typical of the Sishen Shale Member. The Sishen shale and Doornfontein
Conglomerate Member also hosts conglomeratic gritstone, peloidal mudstone and highly
aluminous shale, Fe-rich shale and green Al-shale (Table 5.1 and Fig. 5.1). A type of shale
breccia composed of angular clasts of pale yellow shale in a ferruginous matrix was identified
within certain samples.
Quartzite fragments (Table 5.1) are present in small number in the lumpy stockpile and must
have been derived from the Marthaspoort quartzite (Fig. 5.2). Detrital ore fragments
composed of lateritic weakly cemented fragments of iron ore are thought to have been
derived from laterite associated with the young cover of Kalahari beds (Table 5.1 and Fig.
5.2).
5.2.2 Fragments of the Campbellrand Subgroup
a. Ferruginous Manganese Ore
Fragments of manganese-rich iron ore samples were seldom and randomly found within the
lumpy sample material. The massively textured fragments are fine grained with no specific
features to really characterise their texture except that they are highly porous and readily
disintegrate. The wad samples consist of a very vuggy matrix with some remnants of
carbonate or chert. The voids are left by carbonate that is partly replaced by supergene
manganese oxides. The dissolution of the carbonate (calcite and dolomite) is related to
geologically recent weathering processes.
This type of iron ore occurs along the contact between Wolhaarkop and Campbellrand as
part of geological recent weathering by groundwater flow and modern karstification (Gutzmer,
1996). It formed as infill of karsts depressions and is conformably overlain by hematite pebble
conglomerate and aluminous shale of the Gamagara Formation (Gutzmer, 1996).
b. Dolomite
Coarse-grained silicified dolostone fragments as well as sparry grey dolomite were identified
in low amounts in the lumpy stockpile. Silicified grey fine-grained dolostones consists of
- 59 -
mixture of calcite lenses and dolomite with dark enrichments or remnants of organic matter
(Fig. 5.1).
Coarse-grained silicified dolostone appears yellowish green in colour with veins of
quartz/chalcedony. Both categories vary slightly in terms of their physical appearances, but
are attributed to the Campbellrand Subgroup (Fig. 5.1).
5.2.3 Fragments of the Wolhaarkop Breccia
a. Chert and BIF Breccia and Breccia Chert
Chert and BIF breccia consists of matrix-supported angular BIF and chert clasts set in a
siliceous, hematite-bearing fine-grained matrix.
The chert breccia fragments consist of random angular clasts of quartz or chert in either
hematite (iron-rich chert breccia) or manganese (manganese-rich chert breccia) matrix (Fig.
5.1).
5.2.4 Fragments of the Manganore Iron Formation
a. Chert
Two texturally distinct types of chert were distinguished namely: (i) nodular chert that is
composed of microcrystalline to cryptocrystalline quartz and (ii) micro-fibrous chert
pigmented by fine crystalline hematite. In general, chert fragments are rare and completely
absent from some samples from the lumpy stockpile. Both chert types vary in colour from
white brownish to dark green. Chert fragments are thought to be derived from the Kliphuis-
Tsineng Members of the Manganore Iron Formation (Fig. 5.1) and perhaps underlying
Campbellrand dolomite and the Wolhaarkop Breccia.
b. Banded Iron Formation (BIF)
Banded iron formation fragments were found in the stockpile in similar abundance as chert.
BIF fragments are typically finely laminated with thin laminae of hematite alternating with
bands of chert (Fig. 5.1). These fragments are typical representatives of chert-banded
rhythmite of the Groenwater (thickly banded) and the Riries (thinly banded) Members of the
Manganore Iron Formation (Fig. 5.1).
c. Laminated Ore
Laminated iron ore consists of thin dense layers of hematite alternating with vuggy laminae of
specularitic hematite. Lamination may be represented by: (1) thick wavy and undulating
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laminae of dense fine grained hematite, (2) thick laminae of hematite alternating with highly
porous laminae of hematite or (3) transition between the two types, showing attributes of
both. Hand specimens of laminated ore contain specular hematite that gives a shiny
appearance to certain laminae (Fig. 5.1). In some samples, remnants of banded iron
formation or shaly laminae are present. The laminated iron ore represents hematised finely to
wavy banded iron formation, which forms the upper part of the Manganore Iron Formation at
Beeshoek Mine (Fig. 5.1).
d. Brecciated Ore
The brecciated iron ore consists of poorly sorted angular clasts of laminated iron ore and rare
fragments of massive ore in a fine grained iron-rich matrix. In certain cases pores between
fragments are filled with secondary hematite and specularite or aluminous clay (Fig. 5.1).
Quartz and chert clasts are rare.
e. Porous Ore
Massively textured, porous hematite ore is present in relatively high concentration in the
lumpy stockpile. The ore is massive in texture with dull luster and variable porosity. It is
composed of aggregates of platy hematite and some quartz within a fine-grained ferruginous
matrix. The colour becomes darker in samples with elevated manganese content. This type
of iron ore is present in the upper part of the Manganore Iron Formation (Fig. 5.1). It is related
to more recent weathering that preceded deposition of the Kalahari beds. It could therefore
also be classified as recent lateritic ore.
5.2.5 Fragments of the Doornfontein Member (Gamagara Formation)
a. Conglomeratic Iron Ore
Conglomeratic ore fragments are present in low concentration in the lumpy stockpile. The
conglomeratic iron ore is best described as poorly sorted, matrix or clasts supported
conglomerate and gritstone with hematite ore pebbles and granules respectively. Pebbles
vary in size (0.4 to 5.0 cm) and shape from sub-angular to rounded and include laminated
and massive hematite ore. Granules are 0.2 – 0.4mm in size. The matrix comprises of fine
grained hematite. Some impurities, such as chert and quartz fragments are present in the
matrix. As already mentioned, conglomeratic iron ore constitutes the bulk of the ore at
Beeshoek Mine and it is found in the Doornfontein Member at the base of Gamagara
Formation (Fig. 5.2).
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b. Aluminous Shale/Mudstone
Aluminous shale and mudstone are white to light green in colour; some have a spotted red
pigmentation (Fig. 5.2). They can be either hard or friable. Soft white and creamy aluminous
shale appear in similar abundances in the lumpy stockpile.
Red coloured shale or mudstones are found at the base in the Doornfontein Member. These
aluminous mudstones are confined to the Gamagara Formation (Fig. 5.2).
c. Highly Ferruginous Shale/Mudstone
Two highly ferruginous types of mudstone or shale are present in the lumpy material from the
discarded stockpile namely:
o Highly ferruginous mudstones with very abundant hematite. Some of mudstones
contain angular flat pebbles of hematite. These rocks could have formed as mud-flow
(gravity flow) deposits (Fig. 5.2).
o Peloidal shale – composed of massively textured lateritic mudstone as described by
Gutzmer and Beukes (1998). Quartz chalcedony and hematite fragments are present.
These mudstones are attributed to lateritic paleosols and reworked equivalents that
comprise the lowermost Gamagara Formation, in close association with conglomeratic
iron ore of the Doornfontein Member (Fig. 5.2).
d. Shale Breccia
A conspicuous type of shale-breccia was recognised in the stockpile samples. It consists of
angular clasts of white to light green shale in a red ferruginous shale matrix (Fig. 5.1).
5.2.6 Sishen and Paling Shale Member (Gamagara Formation)
Red brown mudstones or fine-grained and massively textured siltstones were identified.
Microscopically, no hematite clasts were identified (Fig 5.2). Banded red and cream-coloured
shale is most typical of the Sishen and Paling shale Members.
5.2.7 Marthaspoort Quartzite (Gamagara Formation)
Quartzite fragments are present in low quantity in the discarded lumpy stockpile. The
quartzite fragments are coarse-grained, with grain size ranging from 0.1 to 2.5 mm. the
grains appear to be of diverse origin including monocrystalline, well rounded quartz grains
and angular chert grains. Some lithoclasts derived from ferruginous quartzites were also
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found. The fragments are though to be derived from the Marthaspoort Quartzite Member of
the Gamagara Formation (Fig. 5.2).
5.2.8 Kalahari Formation
Detrital iron ore consists of aggregates of chaotic, angular and porous flat fragments of
laminated iron ore. This detrital ore contains virtually no matrix. Poorly sorted and clast-
supported, the pebbles are welded together by lateritic goethite cement. The angular and flat
shape of the fragments indicates that transport only took place over short distance.
Intergrowths of specularite develop in pore space between fragments. The fragments vary
from 0.2cm to 1 cm in length (Fig. 5.2). These detrital ore fragments are thought to belong to
the Kalahari Formation.
5.3 MODAL COMPOSITION OF THE DISCARDED LUMPY STOCKPILE
Bulk samples taken from the lumpy stockpile were hand-sorted into the various categories of
rock fragments according to the classification presented in the Table 5.1. The piles of lumpy
fragments of the various categories were then weighed and a modal weight percentage for
the different categories calculated for each of the hand-sorted samples. The sample modal
lithological composition of the eleven samples was then determined based on the total mass
contributed by each category of lumpy material. The results are compiled in Tables 5.2 and
5.3 (weight percentage), and the average composition is illustrated in figure 5.4. Because of
their low concentration in the lumpy discarded stockpile, the categories BIF, chert and
breccia (Wolhaarkop breccia) were weighted together (Tables 5.2 and 5.3; Fig. 5.4).
On average, the discarded lumpy stockpile is composed of 43.3 wt. % dense iron ore
(laminated, conglomeratic, brecciated and detrital); 15.4 wt. % highly porous iron ore; 32.5
wt. % shale (all classes); 4.2 wt. % ferruginous Mn ore (Fe and Mn); 2.4 wt. % quartzite; 1.8
wt. % dolomite and 1.4 wt. % siliceous rock composed of chert, breccia and BIF fragments
(Tables 5.2 and 5.3; Fig. 5.4). The content of high-grade dense iron ore fragments varies
from 28.9 wt. % to 53.3 wt. %. Iron ore fragments appear to be more common in the upper
part of the stockpile.
Shale is the second most abundant lithology present and is evenly distributed in the samples
of lumpy material (Fig. 5.4). Porous iron ore is the third most abundant lithology in the lumpy
material followed by ferruginous Mn ore. The abundance of high grade dense and porous
iron ore fragments exceeds 50 wt. % (Table 5.3) in the discarded lumpy stockpile (Fig. 5.4).
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Figure 5.2 Composite profile of the Gamagara Formation at Beeshoek Iron Mine illustrating nature of different rock types present in the discarded lumpy stockpile derived from the succession (Stratigraphy modified after Van Schalkwyk and Beukes, 1986 and Grobbelaar et al., 1994). For legend refer to figure 5.3.
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Figure 5.3 Legend to figure 5.1 and 5.2 (Grobbelaar et al., 1994).
This implies that the discarded lumpy stockpile that is currently considered as waste by the
mine can in fact be regarded as a potential source of iron ore.
LEGEND
Porous Iron Ore15.4%
Ferruginous Mn Ore4.2%
Shale32.5%
BIF/Chert/Breccia1.4%
Quartzite2.4%
Dolomite1.8%
Dense Iron Ore42.3%
Dense Iron Ore
Porous Iron Ore
Ferruginous Mn Ore
Shale
BIF/Chert/Breccia
Quartzite
Dolomite
Figure 5.4 Average composition of lumpy material from the discarded stockpile at
Beeshoek Iron Ore Mine (data are expressed in wt. %)
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5.4 DENSITIES OF LUMPY STOCKPILE LITHOLOGIES
Density determination of selected particles of lumpy material from the nine lithological
categories was performed using the method of Archimedes (see Methodology, Part I of
dissertation). Five to ten fragments (2-5cm in diameter each) were selected from each
category of rock material. The selection was made from five of the bulk samples that were
hand-sorted from the discarded stockpile. In total more than 400 particles were examined.
Results are summarized in the table 5.4 and illustrated in the figure 5.5.
Dense iron ores have greatest variable density of between 3.20g/cm3 and 5.08 g/cm3. The
latter density is close to the density of high-grade hematite iron ore of the Sishen-
Postmasburg area that varies between 4.38g/cm3 (60 wt.% Fe) and 5.01 g/cm3 (68 wt.% Fe)
as well as the density of pure hematite (5.20 g/cm3). The importance of porosity is indicated
by the fact that porous iron ore fragments have relatively low “effective densities” of only 3.74
– 4.09 g/cm3 compared to dense iron ore particles (Table 5.4). At Beeshoek mine, a default
of 3.20g/cm3 is used for waste (Source: ARM Annual Report, 2007).
Special attention was given to the shale category because of their diversity (Table 5.4). The
density varies amongst the different lithotypes with the ferruginous gritstone/mudstone the
densest on average (2.61 – 4.28 g/cm3), followed by peloidal mudstone (2.55 – 4.27 g/cm3)
and aluminous shale (2.07g/cm3 - 3.13g/cm3).The siliceous lithologies (chert, BIF and
quartzite) have densities between 2.6 g/cm3 and 3.7g/cm3 with BIF fragments denser than
other lithologies (Table 5.4).
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Figure 5.5 Summary of density variations of different lithological categories from five hand-sorted samples from the lumpy stockpile at Beeshoek Mine.
Figure 5.5 shows a graphic comparison of density variations recorded for each category in
each of the five hand-sorted samples used for density calculation. The similarity between
especially the average densities recorded for the different particles categories in the different
samples is remarkable.
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CHAPTER VI
PETROGRAPHY OF THE LUMPY MATERIAL
6.1 CAMPBELLRAND DOLOMITE
6.1.1 Dolomite
Two lithotypes of dolomite fragments were identified within the lumpy samples from the
discarded stockpile namely sparry white dolomite and silicified green dolomite (Table 5.1).
Both dolomite lithotypes show similar mineralogical characteristics but sparry dolomite
appears to be enriched in Mn-rich minerals while silicified dolomite shows abundance in
calcite and chert.
Hydrothermal sparry dolomite contains Mn-rich minerals veinlets (Fig. 6.1A). In silicified
dolomite, dolomite occurs as euhedral rhombs that are partly outlined by fine crystalline Mn
Oxides whereas hematite and apatite are rare (Fig. 6.1B). Hematite was identified in high
magnification with disseminated rutile (Fig. 6.1C). Fine crystalline quartz is present in the
matrix; sometimes in association with calcite.
6.1.2 Ferruginous Manganese Ore
Ferruginous manganese ore fragments derived from the Wolhaarkop Breccia are composed
of fine crystalline Mn and Fe oxides (Fig. 6.1 D-F). The fragments are quite porous and
therefore the overall texture appears to be botryoidal to collomorphous (cauliflower like) (Fig.
6.1D-F).
6.2 WOLHAARKOP BRECCIA
6.2.1 Chert and BIF Breccia
Chert-and-BIF breccia consists of angular flat clasts of chert and hematized banded iron
formation supported by a fine grained hematite matrix (Fig. 6.2A). The chert and BIF clasts in
the breccia have similar mineralogical characteristics to that of chert and BIF fragments in the
discarded lumpy stockpile. The chemical composition of the matrix varies from iron- to
manganese-rich. Psilomelane is present as botryoidally to collomorphous growths associated
with pyrophyllite and hematite in manganese-rich fragments (Fig. 6.2B). Some of the breccia
fragments also contain angular fragments of hematite ore (Fig. 6.2B). A feature of some of
the BIF-clasts is their kink-folded nature (Fig. 6.2A).
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6.2.2 Chert Breccia
The chert breccia consists of quartz or chert clasts supported by a fine hematite or
manganiferous matrix. Based on the composition of the matrix two types of chert breccia
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fragments were identified, namely (1) iron-rich chert breccia (Fig. 6.2C) and (2) manganese-
rich chert breccia (Fig 6.2D).
The iron-rich breccia consists of angular to subrounded clasts of quartz/chert supported by a
fine to granular hematite-rich matrix (Fig. 6.2C). The clasts are well-defined and easily
identified from the matrix and they consist of fissured megaquartz or chalcedony. Pyrophyllite
and minor manganese oxides are present in the hematite matrix. Braunite may be present in
tiny veinlets associated with hematite and authigenic quartz (Fig. 6.2D).
Unlike the Fe-rich chert breccia, the Mn-rich chert breccia is composed of pure chert and
quartz clasts within a fine crystalline braunite-rich matrix (Fig. 6.2D). Quartz clasts have a
sugary appearance. Apart from quartz and braunite there are also hematite and
cryptomelane present in the manganese-rich chert breccia. SEM studies revealed the
presence of trace amounts of apatite (Fig. 6.2D), muscovite and barite. Barite was
recognised within chert fragments (Fig. 6.2E).
6.3 MANGANORE IRON FORMATION
6.3.1 Laminated Iron Ore
Dense laminated iron ore consists of bright dense hematite-rich microbands and/or
mesobands alternating with dull porous hematite microbands and/or mesobands (Fig. 6.3A –
C). Mesobands are typically internally microbanded (Fig. 6.3 A & B). The porous mesobands
most probably represent original chert mesobands in iron formation precursor as chert is
sometimes preserved in them. In contrast, the dense mesobands most probably represent
original iron-rich mesobands of the parent iron formation. Both types of mesobands are
typically composed of aggregates of microcrystalline subhedral to anhedral hematite.
However, there is clear evidence of a secondary phase of bright hematite represented by
specularite. This specularite replaces earlier hematite along veinlets (Fig. 6.3B) or along
mesobands (Fig. 6.3 D & E). The specularite is clearly coarser grained than the
microcrystalline hematite. In some mesobands of the laminated ores, hematite in fact is
present as martite (Fig. 6.3A). This martite derived from magnetite in the BIF protolith.
Mixed granular-laminated iron ores are probably derived from the transition zone between the
Kuruman and Griquatown Iron Formations (Beukes and Klein, 1989). Some of the laminated
ore fragments from the stockpile are partly brecciated (Fig. 6.3D). This is often what is
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informally referred to in literature as “Blinkklip breccia” (Leisen and Klemm, 1995) because
the breccias are often enriched in secondary specularite.
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Laminated ores are commonly cut by veinlets (Fig. 6.4C). The veinlets are often
perpendicular to bedding and typically filled with fine specularite (Fig. 6.4C).These veinlets
often contain minor amounts of other minerals of which barite is most common (Fig. 6.4D). A
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very interesting variety of hematite may also be present in pores amongst specularite
crystals. This hematite occurs as very tiny spheres (Fig. 6.4F).
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6.3.2 Brecciated Iron Ore
Brecciated ore consists of angular to subrounded clasts of microbanded and mesobanded
laminated hematite ore within a dark grey ferruginous matrix (Fig. 6.5A). Breccias comprised
of microbanded fragments have been described as ferhythmite breccia ore whereas an
abundance of massive to thick mesobanded fragments have been referred to as lutite breccia
(Van Schalkwyk and Beukes, 1986). In polished hand samples, quartz and angular chert
fragments were found mixed with hematite clasts (Fig. 6.5 C-D). The chert represents the
remnants of the BIF and some clasts are partly ferruginized. Quartz and calcite may occur as
infilling of voids between clasts.
Microscopic and XRD studies suggested that apart from hematite, pyrophyllite and quartz are
present. Both microplaty hematite and specularitic hematite are present in the matrix. Other
accessories minerals such as diaspore, cryptomelane and pyrolusite are mentioned by
Schalkwyk (2005). SEM studies permitted identification of the presence of native copper and
apatite (Fig. 6.4E) surrounded by hematite and specularite, and phases of svanbergite
(SrAl3(PO4)(SO4)(OH)6) (Fig. 6.5F). A magnesium silicate or talc may be present in some
clasts (Fig. 6.5 E&F).
6.3.3 Chert and Banded Iron Formation (BIF)
a. Chert
Nodular chert fragments from the discarded lumpy stockpile consist of cryptocrystalline and
microcrystalline quartz (Fig. 6.6A-C). Despite the dominance of quartz, there are other
accessories present. At least two generations of hematite were identified. The first is
disseminated hematite laths in a very fine microcrystalline silica matrix as indication of iron
enrichment. The second generation is remobilized into veins or pseudo-microbands where
hematite is associated with greenalite (Fig. 6.6B). In one sample a euhedral crystal of barite
was found in chert (Fig. 6.6A).
Fibrous chert contains abundant veinlets composed of calcite, apatite and hematite (Fig.
6.6C). In addition, SEM studies revealed the presence of feldspar and phyllosilicate minerals
in some veinlets. XRD studies suggest that the phyllosilicates are represented by pyrophyllite
and muscovite.
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b. BIF (Banded Iron Formation)
BIF fragments from the discarded lumpy stockpile consist of alternating thin bands (~1-3 mm
thick) of hematite alternating with silica-rich bands (0.2 – 1cm thick) mostly made of chert or
jasper (Fig. 6.6D). Both types of bands are laterally continuous, and can be straight or
undulating. Internally hematite bands appear rather massive (Fig. 6.6 E). Euhedral to
subhedral fine grains of hematite are commonly present in microcrystalline silica in chert
bands (Fig. 6.6F). Traces of greenalite and stilpnomelane are also present in most SEM
images.
6.4 GAMAGARA FORMATION
6.4.1 DOORFONTEIN CONGLOMERATE MEMBER
a. Conglomeratic Ore
Conglomeratic ore fragments from the discarded lumpy stockpile consist of angular
subrounded and rounded clasts of massive hematite, supported by a fine to granular
hematite matrix. The dominant mineral is hematite but zircon, pyrophyllite and muscovite may
also be present.
b. Ferruginous and Aluminous Red Shale/Mudstone
Ferruginous aluminous mudstone/shale contains detrital particles of hematite ore in a highly
ferruginous matrix of diaspore, pyrophyllite, kaolinite, muscovite and anatase. Zircon, rutile,
illmenite and svanbergite were identified as trace minerals (Fig. 6.7A, B &E). Microplaty and
elongated specularite occurs as infill of pore spaces (Fig. 6.7C). Some of the shale fragments
contain rounded nodules of hematite (Fig. 6.7D). Samples of “brecciated shale” composed of
angular shale fragments situated in a fine hematite matrix are also present (Fig. 6.7.F).
c. Aluminous and Green Shale/Mudstone
The highly aluminous green shale fragments from the discarded lumpy stockpile are soft and
soapy when touched and consist of a very fine alumino-silicate matrix that in some cases
contains red mottles discoloured by fine disseminated hematite. Isolated grains of quartz (1-
2mm in size) occur in some samples. The greenish shale is massive and much harder than
the creamy white shale. The shale/mudstones are composed of diaspore, pyrophyllite,
muscovite and kaolinite, with trace amounts of hematite, illmenite, rutile, zircon and chlorite.
Rutile and zircon occur disseminated in a chlorite-bearing matrix within the green-shale
(6.8A), while diaspore is replacing muscovite in white creamy shale (Fig. 6.8B). The matrix is
composed of muscovite, chlorite and pyrophyllite (Fig. 6.8A-D).
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d. Shale Breccia
The shale breccia consists of mostly soft clasts of Al-rich shale supported by a ferruginous
matrix. The shale breccia has mineralogical characteristics similar to green and aluminous
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shales described in the previous paragraph. Hematite occurs between the clasts and
constitutes part of the matrix associated with manganese oxides, carbonate and a Fe-rich
phyllosilicate (Fig. 6.8E). The shale fragments are slightly porous. Granular grains of
hematite occur in the voids between shale clasts.
e. Shale/Mudstone Peloids
A yellowish red subtype of shale was identified within the fragments from the discarded
lumpy stockpile. Due to their round and soft physical appearances, they were named as
“Peloidal Shale/Mudstone” because of their resemblance to pellets. The peloidal
shale/mudstone have mineralogical characteristics similar to ferruginous shale (Fig. 6.9A-B).
This lithotype consists of rusted red-brick clasts of hematite in fine to granular ferruginous
matrix. The mineral assemblage is composed of hematite, authigenic quartz, pyrophyllite,
muscovite and other clay minerals.
6.4.2 SISHEN SHALE MEMBER
Red- to cream-coloured shale/mudstone fragments from the discarded lumpy stockpile
derived from the Sishen Shale Member have a cream mottled appearance due to secondary
leaching of hematite from the red shale. This results in the development of cream-coloured
bands or nodules in the shale. The coloration varies from dark red purple to cream purple.
These shales are composed of pyrophyllite, hematite, diaspore, anatase and svanbergite
with trace amounts of zircon (Fig. 6.9C - F).
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6.4.3 MARTHASPOORT QUARTZITE MEMBER
Ferruginous quartzite fragments in the discarded stockpile consist of rounded grains of quartz
(Fig. 6.10A-C). Accessory minerals include chlorite, feldspar and muscovite. Kaolinite, calcite
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and muscovite occur in the cement and seem to contain inclusions of iron and manganese
oxides (Fig. 6.10B & D). Some samples contain small concretions of quartz (Fig. 6.10A).
Clasts of chert and BIF may be present amongst coarse quartz grains (Fig. 6.10C).
6.5 RECENT LATERITIC ORE
6.5.1 Recent Detrital Iron Ore
Detrital iron ore consists of poorly sorted iron formation clasts weakly held together by
hematitic cement (Fig. 6.11A &F). The ore has very high porosity because of absence of
cement in pores between iron ore clasts. The bulk of the iron ore is composed of clasts of
variable size but do not exceed 1cm in diameter. The clasts are mostly remnants of
laminated iron ore and hematitized banded iron formation (Fig. 6.11A &B). Therefore, the
detrital iron ore, apart from porosity, shows similar physical and mineralogical characteristics
as laminated iron ore. The clasts are cemented together by fined dusty hematite (Fig. 6.11C).
Some of the detrital ore may in fact be ancient detrital ore belonging to the Doornfontein
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Conglomerate Member, but which has been affected by more recent weathering so that
leaching of matrix or gangue cement minerals took place. Detrital ore fragments from the
discarded lumpy stockpile belonging to this group (ancient detrital ore) is characterized by the
presence of elongated and microplaty specularite developed at the contact between clasts
with associated accessory minerals amongst which apatite and pyrophyllite are the most
common (Fig. 6.11D &E). Muscovite and zircon are also present either in pore spaces or
amongst specularite (Fig 6.11C &D). No quartz or chert is present. A close look at the clasts
at high magnification (X1000 SEI) reveals highly pitted and porous character of iron ore
clasts in the leached samples (Fig. 6.11F).
6.5.2 Porous Iron Ore
A particular type of massive earthy iron ore is present within the lumpy stockpile and was
distinguished by its character to absorb water. The porous iron ore is massive and dull grey
and appears very fine-grained to the naked eye. In polished hand specimen the iron ore
consists of euhedral aggregate of platy bright hematite mixed with crystals of quartz, and
small fragments of hematite with abundant pore space partly filled with specularite (Fig. 12A-
C). The grains do not show any preferred orientation and the ore is thus poorly bedded.
Under the SEM kaolinite, pyrophyllite, muscovite and silica were recognized (Fig.6.12D). The
dominant texture consists of a vuggy network of microplaty hematite within a fine matrix
where laths of specularite are preserved (Fig. 6.12A-C). Collomorphous hematite fills or
partially fills some of the irregular pore spaces (Fig. 6.12E-F). Despite the porous character of
this lithotype, microfaults are developed in some of the collomorphous-textured hematite (Fig.
6.12E). Secondary mineralization of specularitic hematite is present along the microfaults
(Fig 6.12E).
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CHAPTER VII
GEOCHEMISTRY OF LOW-GRADE LUMPY MATERIAL
A geochemical investigation of the low-grade lumpy material was conducted at the Central
Analytical Facility (SPECTRAU) of the University of Johannesburg, Auckland Park Kingsway
Campus. The main purpose of this part of the investigation was to assess the iron content of
each lithotype and to determine the distribution and abundance of deleterious elements.
7.1 MAJOR ELEMENT GEOCHEMISTRY Lithostratigraphy and petrography were used to distinguish nine mesoscopically distinct
lithotypes, i.e., dense iron ore, porous iron ore, ferruginous Mn ore, shale, breccia, BIF, chert,
quartzite and dolomite. Major element data can be used to group the nine lithotypes into four
compositional distinct groups, namely:
(1) Group I: Iron Ore-grade material with more than 75 wt. % Fe2O3 and less than 15
wt. % SiO2. This includes iron ore lithotypes described during the classification of
fragments from the discarded lumpy stockpile (Table 7.1, Fig. 7.1).
(2) Group II: Silica-rich lithologies, i.e. samples that contain more than 75 wt. % SiO2
and less than 20 wt. % Fe2O3. Two subgroups are recognized, namely (a) BIF
samples that are more enriched in iron and (b) a highly siliceous group that
includes samples of chert, breccia and quartzite.
(3) Group III: Alumina-rich lithologies.
The third group is marked by alumina concentrations in excess of 30 wt. % Al2O3
with less than 45 wt. % Fe2O3 and 40 to 60 wt. % SiO2. This group comprises
aluminous shale and green shale.
(4) Group IV: Intermediate lithologies.
The fourth group is of intermediate composition that links the three previous
groups. This includes red and Fe-rich shale lithotypes. These are composed of less
than 60 wt. % Fe2O3, approximately 45 wt. % SiO2 and 15 to 20 wt. % Al2O3 (figure
7.1).
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The four geochemical categories are used as the basis for the presentation and discussion of
whole rock geochemical data. Mesoscopic lithotypes will be mentioned where necessary.
Figure 7.1 Binary plots (wt. %) illustrating the major element whole rock geochemistry of
the different lithologies represented on the low-grade lumpy stockpile at
Beeshoek Iron Mine (I-Group, iron ore; II-Group, silica-rich with IIa: iron-rich
subgroup and IIb: iron-poor subgroup; III-Group, alumina-rich and IV-Group,
intermediate).
7.1.1 Group I
This compositional group includes all samples containing more than 75 wt. % Fe2O3; it
includes the following lithotypes: laminated, brecciated, conglomeratic, detrital, porous and
manganiferous iron ores. The major element geochemistry of these iron ore lithotypes is
presented in table 7.1 and illustrated in figure 7.2. In general, the iron content varies between
75-100 wt. % Fe2O3 with low SiO2 concentrations (0-15 wt. %).
Samples of laminated and conglomeratic lithotypes yield highest iron concentrations with 95-
101 wt. % Fe2O3 and less than 3 wt. % SiO2. Samples of detrital and brecciated lithotypes
consist of 90-95 wt. % Fe2O3 and silica contents varying between 2 and 8 wt. % SiO2; porous
and manganiferous iron ore samples have iron contents between 75-90 wt. % Fe2O3 and
silica contents between 5-15 wt. % SiO2 (Fig. 7.2A).
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- 91 -
The aluminum content varies between 0.37-2.11 wt. % Al2O3 in laminated ores; 1.34-2.62 wt.
% in detrital ore; 0.58-2.56 wt. % in brecciated ore; 0.22-1.86 wt. % in conglomeratic ore;
- 92 -
2.54-6.04 wt. % in porous ore and 0.92-5.83 wt. % in manganiferous ore. Thus, porous and
manganiferrous ores contain the highest concentrations of alumina amongst the iron ores
(Fig. 7.2B).
TiO2 concentrations are always below 0.32 wt. % in the iron ores with the lowest
concentrations (0-0.18 wt. %) in laminated and conglomeratic ores and highest (0.04-0.32 wt.
%) in porous and manganiferous ores (figure 7.2C). Manganese contents, usually high, but
do not vary much except in the manganiferous ore where very high concentrations of MnO
are recorded for some samples. Lowest concentrations of manganese are recorded in
laminated (0.02-1.11 wt. % MnO), detrital (0.02-0.07 wt. %), conglomeratic (0.02-0.04 wt. %)
and brecciated (0.07-0.60 wt. %) ores (Fig. 7.2D). Porous iron ores displays moderate
concentrations of manganese (0.47-4.41 wt. % MnO). Concentrations of CaO and MgO do
not vary considerably ranging from 0 to 1.2 wt. %. Lowest and highest concentrations are
encountered in the conglomeratic and manganiferous ores, respectively (Fig. 7.2E). Alkali
elements (Na2O and K2O), in contrast, are especially abundant in manganiferous and porous
iron ore lithotypes, but are found at very low in concentrations in conglomeratic, detrital,
brecciated and laminated iron ore lithotypes (Fig. 7.2F). P2O5 contents vary randomly within
the iron ores, with a concentration of 0.56 wt. % encountered in a single sample of laminated
iron ore (Fig. 7.2F).
7.1.2 Group II (Siliceous Lithologies)
Major element data of silica-rich lithologies are shown in table 7.2 and illustrated in figures
7.1 and 7.3. The total iron content expressed as Fe2O3 is inversely correlated with the
concentration of SiO2 and these two constituents account for more than 90 wt. % of the
composition of the rock. A binary plot of Fe2O3 vs. SiO2 also defines two compositional
subgroups, namely (a) an iron-rich subgroup that includes all BIF and breccias samples and
(b) an iron-poor subgroup that includes all chert samples (Fig. 7.3A). Fe–rich breccia
samples contain up to 61.0 wt. % Fe2O3 and silica-rich breccia samples contain as little as
2.4 wt. % Fe2O3 (Fig. 7.3A). Chert samples are depleted in iron with concentrations ranging
between 1.37 and 8.67 wt. % Fe2O3 whereas BIFs contain much higher concentrations
ranging from 34.9 to 41.5 wt. % Fe2O3 and quartzites between 6.5 to 31.6 wt. % Fe2O3. Chert
and BIF contain very little alumina (2.0 wt. % Al2O3); breccia samples display a negative
correlation between SiO2 and Al2O3 contents. Some quartzite samples contain more than 16
wt. % Al2O3. TiO2 contents vary from below the limit of detection in the chert and BIF to 0.91
wt. % in the quartzite. Manganese is generally present in low concentrations in silica-rich
lithotypes, but some chert and breccia samples have concentrations ranging from 1.31 to
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5.84 wt % MnO (Table 7.2, Fig. 7.3). MgO and CaO contents are low and variable. The same
applies to Na2O and K2O as well as P2O5 (Fig. 7.3).
Figure 7.2 Binary plots (wt. %) illustrating the major element whole rock geochemistry of
ore-grade lithotypes from the discarded lumpy stockpile at Beeshoek Iron Mine.
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Table 7.2 Major element geochemistry of silica-rich rocks (Group II) from the discarded lumpy stockpile from Beeshoek Mine (all data in wt. %).
BIF(Banded Iron Formation) Chert Major Elements B10-
BIF B11- BIF
B8- BIF-A
B8- BIF-B
B7- BIF
B2- BIF
B7- Chert
B8- Chert
B6- Chert-A
B6- Chert-B
B11- Chert
B1- Chert
B3- Chert
SiO2 56.5 62.8 64.7 64.5 59.7 60.3 96.8 99.8 94.4 94.8 94.5 90.1 96.5
TiO2 0.00 0.02 0.00 0.02 0.00 0.06 0.00 0.01 0.01 0.01 0.15 0.04 0.00
Al 2O3 0.04 0.11 0.07 0.16 0.25 0.98 0.00 0.13 0.02 0.26 2.14 1.02 0.00
Fe2O3 41.5 39.4 38.1 34.9 40.5 40.8 1.73 1.43 6.06 4.84 2.39 8.67 1.37
MnO 0.01 0.02 0.01 0.01 0.01 0.72 1.31 0.03 0.01 0.01 0.01 0.05 0.14
MgO 0.19 0.18 0.19 0.20 0.19 0.22 0.18 0.17 0.17 0.16 0.15 0.32 0.19
CaO 0.19 0.18 0.19 0.20 0.20 0.20 0.23 0.32 0.20 0.18 0.24 0.26 0.23
Na2O 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.05
K2O 0.01 0.01 0.01 0.01 0.02 0.19 0.00 0.03 0.00 0.04 0.22 0.28 0.00
P2O5 0.02 0.02 0.02 0.08 0.05 0.05 0.02 0.01 0.02 0.03 0.03 0.03 0.09
S 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
LOI 1.70 0.20 0.20 0.90 1.02 0.90 0.20 0.20 0.90 0.80 1.50 0.20 1.50
Total 100.1 103.0 103.5 101.0 102.0 104.4 100.6 102.1 101.8 101.1 101.3 101.0 100.1
(Table 7.2 continued) Quartzites Breccia Major
Elements B2- Fe-Qtz
B10- Fe-Qtz
B8- Fe-Qtz
B11- Qtz
B7- Qtz
B6- Qtz
B7- Fe-Brec
B10- Fe-Brec
B8- Mn-Brec
B6- Fe-Brec
B10- Bre
B11- Brec
B1- Mn-Brec
SiO2 77.3 74.5 65.5 91.8 68.3 68.4 50.9 90.0 54.0 31.9 97.5 94.1 69.7
TiO2 0.11 0.11 0.03 0.19 0.91 0.88 0.06 0.02 0.07 0.16 0.01 0.19 0.09
Al 2O3 2.01 3.16 1.22 0.17 16.2 17.5 2.79 1.00 0.94 4.11 0.24 2.41 1.92
Fe2O3 20.7 26.0 31.6 6.45 9.53 8.34 44.2 8.77 35.6 61.0 4.64 2.39 26.1
MnO 0.16 0.24 0.24 0.01 0.00 0.00 0.70 0.05 5.84 0.65 0.01 0.01 1.21
MgO 0.19 0.20 0.21 0.17 0.01 0.39 0.33 0.23 0.28 0.33 0.16 0.18 0.25
CaO 0.20 0.20 0.20 0.20 0.02 0.06 0.21 0.27 0.42 0.25 0.19 0.20 0.26
Na2O 0.00 0.00 0.00 0.00 0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
K2O 0.33 0.59 0.34 0.05 0.02 3.30 0.85 0.28 0.19 1.09 0.03 0.23 0.45
P2O5 0.04 0.07 0.02 0.02 0.01 0.05 0.03 0.02 0.18 0.26 0.01 0.03 0.09
S 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.08 0.00 0.00 0.08
LOI 0.40 0.50 0.50 1.20 2.60 2.60 1.80 0.90 1.20 1.30 0.90 1.30 1.20
Total 101.4 105.5 99.9 100.3 97.6 101.5 101.9 101.6 98.6 101.1 103.6 101.1 101.4
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Figure 7.3 Binary plots (wt. %) illustrating the major element geochemistry of siliceous lithotypes (chert, BIF, breccia and quartzite) from the discarded lumpy stockpile at Beeshoek Iron Mine
7.1.3 Group III
The major element data for alumina-rich lithologies are presented in table 7.3 and illustrated
in figure 7.4. The inverse relationship between iron on the one hand and alumina and silica
on the other hand in this group is obvious (Fig. 7.4). This trend relates to the successive
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enrichment of iron from cream-coloured and green shales to ferruginous shales. The total
iron content varies from 42.8 to 64.7 wt. % Fe2O3 in the Fe-shale lithotypes whereas cream-
coloured and green shales contain only 0.23 to 1.57 wt. % Fe2O3 and 0.28 – 2.18 wt. %
Fe2O3, respectively (Fig. 7.4A). Peloidal, red-purple and red shales have intermediate and
variable contents of Fe2O3 respectively (Table 7.3). Green and aluminous shales contain the
highest concentrations of alumina with 15.9 to 40.6 wt. % Al2O3 and 33.0 to 38.2 wt. % Al2O3,
respectively (Table 7.3, Fig. 7.4B). Ferruginous shales contain 11.5 wt. % to 22.1 wt. %
Al2O3, while peloidal shale (21.7 – 22.8 wt. %), red-purple shale (0.37 – 35.8 wt. %), shale
breccia (15.9 – 37.2) and red shale (26.2 – 33.3 wt. %) contain moderate concentrations of
Al2O3. TiO2 contents are marked by similar trends with silica-rich shales (1.86 – 2.63 wt. %
TiO2) and aluminous and green shales (0.91 to 2.76 wt. % TiO2) with highest concentrations
(Fig. 7.4C). MnO contents (Fig. 7.4D) are very low and vary between 0.01 and 0.13 wt. % in
all of the shale lithotypes. Only a few Fe-rich types of shale contain some manganese up to
concentrations 0.64 wt. % MnO (Fig. 7.4D). MgO and CaO are very low in concentration and
their distribution is uniform with MgO contents that vary between 0 – 0.62 wt. % and CaO
contents between 0.20 – 0.31 wt. %. Na and K contents vary considerably but do not show
any distinct affinity to a particular shale lithotype, despite a slight enrichment from Fe-rich
shale to green shale (Fig. 7.4F).
Phosphorous concentrations vary randomly amongst the shale lithotypes, ranging between
0.05 to 0.89 wt. % P2O5. It appears strongly depleted in the green and Al-rich shales (0.04 –
0.09 wt. % P2O5). Red-shale, red-purple shale and shale breccia have highest P2O5
concentrations ranging between 0.09 – 0.89 wt. %, 0.07 – 0.32 wt. % and 0.06 – 0.38 wt. %
respectively (Fig. 7.4G).
Shale lithologies, show enrichment in some major elements compared to the average Post-
Archaean Australian shale (PAAS, Fig. 7.4) but they can also be relatively depleted in other
major elements. For example some lithotypes are enriched in Fe2O3, Al2O3, TiO2 and variably
in alkali elements (Na + K) with reference to the average post-Archaean shale. Whereas,
most shale samples are depleted in silica, manganese, alkali elements (Na and K) and
phosphorous relative to PAAS.
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Table 7.3 Major element geochemistry of shale lithitypes (Group III) from the discarded lumpy stockpile from Beeshoek Mine (all data in wt. %).
Shale Breccia Red-Purple Shale Peloidal Mudstones Major
Elements B8- Brec-Sh
B10- Brec-Sh
B11- Brec-Sh
B9- Brec-Sh
B6-Red- Purpl-Sh
B1-Red- Purpl-Sh
B7-Red- Purpl-Sh
B9-Red- Purpl-Sh
B6- Pel-Mud
B7- Pel-Mud
B8- Pel-Mud
B9- Pel-Mud
SiO2 74.3 41.8 45.2 52.7 43.6 45.2 58.6 43.7 26.9 28.0 28.4 26.8
TiO2 0.91 1.50 1.58 1.82 1.84 1.66 0.02 1.84 1.40 1.38 0.98 0.59
Al 2O3 15.9 32.5 35.3 37.2 33.3 35.7 0.37 33.3 21.7 22.8 22.05 18.8
Fe2O3 1.93 7.70 7.96 2.20 6.85 7.48 41.0 6.85 42.57 41.0 42.8 50.9
MnO 0.01 0.05 0.05 0.00 0.01 0.08 0.01 0.01 0.11 0.12 0.09 0.10
MgO 0.62 0.01 0.00 0.00 0.04 0.00 0.20 0.05 0.17 0.14 0.13 0.19
CaO 0.25 0.24 0.24 0.23 0.21 0.28 0.21 0.21 0.26 0.26 0.22 0.29
Na2O 0.00 0.00 0.00 0.00 0.04 0.00 0.00 0.04 0.02 0.00 0.10 0.07
K2O 3.33 0.23 0.24 0.28 9.55 6.29 0.05 9.58 1.81 0.20 0.44 0.51
P2O5 0.06 0.32 0.34 0.38 0.13 0.32 0.07 0.13 0.11 0.12 0.10 0.11
S 0.00 0.08 0.09 0.06 0.00 0.79 0.00 0.00 0.00 0.00 0.04 0.07
LOI 7.50 11.60 8.50 8.50 7.50 2.50 5.20 7.60 7.50 8.50 7.50 6.50
Total 104.8 96.1 99.5 103.4 102.9 100.4 105.8 103.4 102.6 102.5 102.8 104.9
(Table 7.3 continued)
Red-Shales Ferruginous/Gritstones Shales Major Elements B6-
Red-Sh B9-
Red-Sh B1-
Red-Sh B4-
Red-Sh B10-
Red-Sh B3-
Red-Sh B10-
Fe-Sh B8-
Fe-Sh B9- Grit
B6- Grit
B2- Fe-Sh
B4- Fe-Sh
SiO2 43.7 35.4 36.6 42.9 36.6 32.9 28.4 17.8 20.1 20.4 31.2 26.5
TiO2 1.84 2.34 1.06 1.20 1.45 1.25 0.98 0.52 0.92 1.16 0.51 0.57
Al 2O3 33.3 30.1 29.4 31.6 32.1 26.2 22.1 13.7 16.9 15.5 11.5 13.8
Fe2O3 6.85 26.5 24.8 15.4 18.7 27.2 42.8 64.7 57.1 56.6 53.8 55.9
MnO 0.01 0.01 0.13 0.13 0.01 0.02 0.09 0.05 0.09 0.03 0.64 0.12
MgO 0.05 0.03 0.17 0.21 0.02 0.07 0.13 0.14 0.17 0.16 0.24 0.19
CaO 0.21 0.22 0.24 0.25 0.31 0.22 0.22 0.21 0.25 0.21 0.23 0.22
Na2O 0.04 0.00 0.26 0.23 0.00 0.12 0.10 0.00 0.00 0.03 0.12 0.07
K2O 9.58 0.09 6.40 7.12 0.20 6.85 5.44 0.00 0.86 4.37 2.65 3.51
P2O5 0.13 0.11 0.09 0.24 0.89 0.14 0.10 0.11 0.11 0.07 0.09 0.14
S 0.00 0.00 0.04 0.00 0.34 0.00 0.00 0.00 0.00 0.00 0.00 0.06
LOI 6.50 6.40 2.50 2.50 8.40 4.50 2.50 6.50 6.50 6.50 3.80 3.80
Total 102.3 101.3 101.7 101.8 99.0 99.5 102.8 103.7 102.9 104.9 104.8 104.9
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Figure 7.4 Binary plots (wt. %) for the major element geochemistry of aluminous lithotypes
from the discarded lumpy stockpile at Beeshoek Iron Mine. The composition of
PAAS standard is plotted for reference. Also shown, is the composition of
intermediate lithologies of Group IV, namely, red and peloidal shale specifically.
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7.1.4 Group IV
This group is composed of rocks of intermediate composition that links the three previous
groups. This includes red shale, Fe-rich shale and some samples of the BIF lithotypes as the
samples of this group show geochemical characteristics intermediate between those of
groups I-III. They are not discussed in any detail here.
7.2 TRACE ELEMENT GEOCHEMISTRY
Trace element (Ba, Co, Cu, Ga, Nb, Ni, Pb, Rb, Sr, Th, Y, Zn, Zr, As, Sc, and U) analysis
was carried out for all major lithological groups with notable exception of Group I (iron ores).
The high concentration of iron prohibited trace element analysis of the latter group of
lithotypes. The results are normalized against PAAS (Taylor and McLennan, 1985) and
plotted on spider diagrams. The presentation of trace element data (in ppm) is based on the
lithological classification, with clear distinction between shales and silica-rich lithotypes.
7.2.1 Shale
The trace element data of shale lithotypes are presented in Table 7.4 and plotted in figure
7.5. All shale lithotypes from the discarded lumpy stockpile have a similar trace element
geochemistry and are marked by similar trends of enrichment and depletion. Relative to
PAAS, Ga, Nb, Th, Y, Zr and Sc are somewhat enriched in the studied shale lithotypes.
Interestingly, the element Ba, present in the form of minute but widespread barite crystals
(see chapter on petrography) is present in concentrations well below that of PAAS. Also
relative to PAAS, Co, Cu, Ni, Rb and Zn are consistently depleted within the shale lithotypes,
whereas Rb, Pb and U show variable concentrations. Green and aluminous shales have low
Pb but high U concentrations similar to PAAS. Brecciated, red and ferruginous, peloidal and
red-purple shales, in contrast, are depleted in uranium, but enriched in Pb. Rb is strongly
depleted in Al-shale, and variably depleted in all other shale lithotypes (Fig. 7.5).
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- 106 -
Figure 7.5 Multielement Spider diagrams for different shale lithotypes from the discarded
lumpy stockpile at Beeshoek Iron Mine, normalized against the Post-Archaean
Australian Shale (PAAS).
7.2.2 Siliceous Lithotypes
Trace element data of siliceous lithotypes (Table 7.5) were also normalized using the
average post-Archaean shale (PAAS) values from Taylor and McLennan (1985) and are
plotted in multi-element spider diagrams (Fig. 7.6). Silica-rich lithotypes from the discarded
lumpy stockpile show similar trends with moderate to strong depletion in all elements
compared to those of the average post-Archaean shale (PAAS). This is attributed to the
overwhelming abundance of quartz (SiO2) in these lithotypes. Within the framework of overall
depletion, Co, Ga, Ni, Pb, Zn, and Sc show positive anomalies, with Cu, Nb, Rb and Zr
marked by strong depletion . Other elements (Ba, Sr, Y and U) show variable trends.
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Figure 7.6 Multi-element Spider diagrams for different siliceous lithotypes from the
discarded lumpy stockpile at Beeshoek Iron Mine, normalized against the Post-
Archaean Australian Shale (PAAS).
7.3 COMPARISON OF COMPOSITION OF IRON ORE FRAGMENTS FROM THE
DISCARDED LUMY STOCKPILE TO STANDARD IRON ORE FROM BEESHOEK
MINE
Through all the years of mining at Beeshoek Mine, a standard composition for iron ore has
been developed (Table 7.6). The standards represent concentrations of some major oxides
(in wt. %) as measured at Beeshoek Mine by XRF and confirmed by total iron titration
(Assmang Annual Report, 2007). In order to evaluate the ore potential of the fragments of
iron ore extracted from the discarded lumpy stockpile, their compositions are compared to
that of the Beeshoek iron ore standard (Table 7.6). This comparison clearly illustrate that
conglomeratic, breccia, detrital and laminated iron ore fragments from the discarded lumpy
stockpile all have composition similar to or better than that of the average ore standard from
Beeshoek Mine (Table 7.6).
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- 109 -
Products of geologically ancient and recent weathering, namely manganiferous and porous
ores have the highest contents of Al and alkali elements as well (Table 7.6 and Fig. 7.7). The
porous ores represent materials located immediately below the Kalahari unconformity and
should be avoided during mining even if they contain significant amounts of iron (Fe).
Laminated and conglomeratic ores constitute a readily saleable product which does not need
any beneficiation with low silica, alumina and alkali contents compare to the Beeshoek ore
standard (Fig. 7.7). P2O5 occurs in different lithologies even in high grade laminated,
brecciated and conglomeratic ores; it is therefore distributed randomly with no recognized
systematic trend. Magnesium and calcium are also present at higher concentration within the
iron ores fragments from the stockpile than in the Beeshoek iron ore standard (Table 7.6 and
Fig. 7.7).
Table 7.6 Average chemical composition of iron-rich lithotypes from the discarded lumpy
stockpile compared to the composition of standard high-grade iron ore from
Beeshoek Mine (All data in wt. %).
Major Oxides
Porous Ore
(N=7)
Fe-Mn Ore
(N=8)
Conglomeratic Ore
(N=6)
Breccia Ore
(N=6)
Detrital Ore
(N=5)
Laminated Ore
(N=8)
Standard* Beeshoek
Ore
SiO2 10.6 8.87 1.89 5.34 3.62 2.63 3.6
Al 2O3 3.91 4.62 0.8 1.89 2.21 0.87 1.64
Fe2O3 82.6 73.8 99.2 99.2 94.1 95.1 93.3
MgO 0.26 0.29 0.17 0.26 0.25 0.26 0.04
CaO 0.24 0.43 0.2 0.24 0.25 0.21 0.08
Na2O 0.02 B.D.L B.D.L B.D.L B.D.L 0.01 0.03
K2O 0.87 1.06 0.19 0.36 0.27 0.14 0.23
P2O5 0.09 0.13 0.17 0.14 0.17 0.12 0.09
*(Data Source: ASSMANG Annual Report 2007)
B.D.L. : Below Detection Limit.
N. : Number of samples.
- 110 -
Figure 7.7 Multi-element Spider diagrams normalized against the average chemical
composition of lumpy standard values at Beeshoek Iron Mine.
- 111 -
PART III
INVESTIGATION OF THE FINES FROM THE TAILINGS
DAM
- 112 -
- 113 -
CHAPTER VIII
DESCRIPTION OF FINES MATERIAL IN THE TAILINGS DAM
8.1 INTRODUCTION
As mentioned earlier, fines are a by-product generated during the processing especially
crushing of the ore at Beeshoek Mine. That fine iron ore is pumped in one of the old pits of
the North mine (Fig. 1.2 & Fig. 8.1). Only a third of the tailings dam is filled up completely with
fine iron ore, the rest is filled with iron-rich mud. The fines iron ore comes from two different
sources, the first fraction (about 1.68 Mt/a) is generated during the processing of
uncontaminated raw ore material and the second fraction (0.48 Mt/a) is generated during the
jig beneficiation (Fig. 8.2). Each year approximately, 2.16 Mt is deposited into the tailing dam.
Figure 8.1 Aerial overview of the tailings dam at the North mine (Beeshoek) in the rainy
season (Source: Google Earth). Samples could only be taken on the exposed “delta plain” in front of the feeder pipe (Fig. 8.1
and 8.3A). A large part of the dam was under water when first sampling took place (Fig. 8.1).
Fine materials were sampled using a sediment auger (Fig. 8.3F). Three sets of samples were
collected (Fig. 8.4): One set of eight samples (H1 to H8) was collected longitudinal along the
tailings dam away from the feeder pipe (Fig. 8.4). The second set of samples (H9 to H14)
was taken across the tailings dam about halfway along the longitudinal set of samples (Fig.
Feeding Pipe
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8.4). Later on a third set of samples (H15 – H22) was collected to form a grit of samples
together with the first two set of samples in the dam (Fig. 8.4).
During the rainy season, unconsolidated fine sediment is sometimes eroded by rain runoff
into the tailings dam, leaving small erosion channels that expose the internal structure of the
fines sediment. It is primarily characterized by flat bedding (Fig. 8.3B). During the dry
summer season the sediment in the tailings dam develops spectacular mud cracks (Fig. 8.3
C). After early rain falls, plants start to grow in the mudcracks for a short period of time (Fig.
8.3 D). Strong winds roll grains of fines iron ore plus other sediments and deposit them in the
mudcracks.
Figure 8.2 Classification of the products after processing at Beeshoek Iron Ore Mine.
8.2 GRAIN SIZE ANALYSIS
At Beeshoek Mine all the particles that fall under 6.3 mm in size are classified as fines iron
ore. Preliminary hand sorting was performed on each sample taken from the tailings dam and
reveled that the grain size varies laterally along the dam. The fines materials vary from very
fine to very coarse according to the Udden-Wentworth grain size scale. In order to quantify
this variation, fourteen samples were sieved to obtain grain-size distributions. The results are
reported in table 8.1. Seven grain size ranges were obtained from each sample varying from
less than 75µm to more than 600µm in size. The results show that fine grains (105 - 75µm)
preferentially accumulated most distal to the feeder pipe. This is very well illustrated in
samples H7 and H8 collected most distal to the feeder pipe. Especially in sample H8, grains
<75 µm represent the highest percentage namely 34.6 wt. % of material (Fig. 8.5A).
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Particles of medium size (355 – 150 µm) seem to collect in most abundance proximal to the
feeder pipe down to about halfway along the sampled traverse away from the feeder pipe
(Fig. 8.5A) in the tailings dam. This grain-size fraction varies in abundance from 30 wt. %
proximal to the feeder pipe to 22.8 wt. % halfway down the longitudinal sample traverse (see
Table 8.1 and Fig. 8.5A & B). The tendency for medium-sized particles to concentrate
- 116 -
halfway down the longitudinal sample traverse in front of the feeder pipe is especially well
illustrated in the second set of samples collected transverse across the tailings dam (H9 –
H14). In this transverse section, the particles of medium size represent the highest
percentage in the samples (Fig. 8.5B).
Figure 8.4 Outline map of the old pit serving as a tailings dam for fines at Beeshoek North Mine with the sampled area and sample numbers.
Coarse particles show a very interesting “bimodal” distribution. They are relatively abundant
proximal to the feeder pipe, decease in abundance to the middle of the sampled transverse
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and then again increase in abundance to the most distal samples (Fig. 8.5A). The transverse
sample set thus contains intermediate concentrations of coarse particles (Fig. 8.5).
Samples collected in the center of the tailings dam show similar variations in grain size. The
different ranges of grain size have proportionally the same percentage amongst samples (H9
– H14) with medium sizes representing the highest percentage and fine sizes representing
the lowest percentage (Fig. 8.5B).
The distribution of particles sizes in the tailings dam, especially that of the coarse particles
indicates that the distribution of fine material within the tailings dam is related to two
parameters, namely size and density. Medium sized particles can roll down a certain distance
before settling halfway from the feeder pipe while small particles will be transported further
away. Large to medium-size high density particles tend to settle proximal to the feed area. In
contrast large low density particles are transported to settle distal to the feeder pipe together
with fine high density particles.
8.3 GEOCHEMISTRY OF THE FINES IRON ORE
8.3.1 Major Element Geochemistry
A fraction of each sample of fines from the tailings dam was milled to obtain fine powder for
major elements geochemical analyses. Each sample was analysed in duplicate (two fusion
beads) using the Phillips X-ray fluorescence spectrometer available in Spectrau at the
University of Johannesburg, Auckland Park, Kingsway Campus. The results are illustrated in
figure 8.6 and represented in tables 8.2, 8.3 and 8.4. Iron, expressed as Fe2O3, varies from
81.7 to 95.8 wt. % within the tailings dam. Amongst the samples collected longitudinal along
the tailings dam, there are considerable variation. Highest values are recorded within
samples (H4 and H5) collected in the center of the tailings dam while lowest iron
concentrations are recorded in the samples (H7 and H8) collected most distal to the feeder
pipe (Fig. 8.6 and 8.7). Sample collected proximal to the feeder pipe contain moderate iron
concentrations ranging between 90.94 to 92.28 wt. % (Fig. 8.6A). Samples collected
transverse in the tailings dam do not show considerable variations in their iron content, but
slight depletion in iron is noticed at the north end of the tailings dam (sample H11) (Fig.
8.7B).
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The silica content is variable between 3.60 to 12.23 wt. % SiO2 within the tailings dam. Silica
shows reverse affinity to iron. Highest silica contents are recorded distal to the feeder pipe
(samples H7 and H8) varying between 7.67 to 12.23 wt. %. These concentrations are three
to four times higher than the samples collected in the center of the tailings dam (3.60 to 4.38
wt. %) (Fig. 8.6A).
Aluminium (Al2O3), alkali elements (Na2O + K2O) and titanium (TiO2) show positive affinity to
silica (Fig. 8.6B, C & F). Alumina varies between 2.08 and 4.68 wt. % and highest values are
recorded proximal to the feeder pipe and lowest values in the center of the tailings dam (Fig.
8.6C). Highest concentrations of TiO2 are also present in samples H7 and H8 (distal to the
feeder pipe) (Fig. 8.6B). Sodium (Na2O) is completely depleted proximal and in the center of
the tailings dam and concentrated distal to the feeder pipe where it varies from 0.03 to 0.10
wt. % (Table 8.2). In contrast potassium (0.42 – 1.03 wt. % K2O) appears to be concentrated
proximal to the feeder pipe (Table 8.2, Fig 8.6F).
Other major oxides like P2O5, MgO and CaO do not show any specific trend (Fig 8.6 E &G).
MnO is rather evenly distributed in the tailings dam but nevertheless highest concentrations
are recorded proximal to the feeder pipe where it reaches values of 0.33 to 1.15 wt. % (Table
8.2, Fig. 8.6D). Contrary to other oxides, MnO is found in lower concentrations in the center
of the tailings dam (0.12 – 0.87 wt. %) (Fig. 8.6D).
Sulphur is also found at higher concentration proximal and distal to the feeder pipe and lower
concentrations are recorded in the center of the tailings dam.
It is important to note that the concentration of iron in the tailings dam is closely related to the
particle grain size distribution. Medium sized particles represent the densest fraction amongst
the fines particles and then settle mostly from the feeder pipe to the center of the tailings
dam. Therefore, iron is recorded at higher concentrations proximal to halfway from the feeder
pipe. Light and small particles represent gangue material and are composed of aluminium,
titanium and alkali elements. These particles have low iron concentrations and accumulated
distal to the feeder pipe.
Most important is to note that the fine tailings in the dam can be classified as fines ore
according to the fines iron ore standard at Beeshoek Mine (Table 8.5). The average
composition of the samples collected in the tailings dam compare closely with the average
composition of the fines standard (Table 8.5)
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Looking at the plots it is clear that the center of the tailings dam contains the best fines with
lowest contaminants.
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Table 8.5 Average geochemical composition of the fine material from the tailings dam compared to the standard composition for fines at Beeshoek Mine.
Major Element Sample Average
(From the tailings dam N=22)
Beeshoek Fines
(Standard *)
Fe (II) 64.1 64.2
Fe2O3 91.6 91.8
SiO2 5.74 4.82
Al 2O3 2.66 1.84
MgO 0.27 0.06
CaO 0.30 0.10
Na2O 0.01 0.03
K2O 0.49 0.25
P 0.05 0.04
P2O5 0.12 0.09
8.3.2 Correlation between XRF and Titration Geochemical Results
Volumetric titration using dichromate potassium was carried out at the chemical laboratory of
the University of Johannesburg, Doornfontein Campus, under the supervision of Mr.
Hermann Steyn. Fines sample powders that were used for XRF analyses were used in
duplicate to determine the iron content in Fe (II) by titration as described in Chapter IV. The
results are presented in table 8.6 and illustrated in figure 8.7.
In general the iron concentration obtained from the volumetric titration appear slightly lower
compared to that obtained from XRF analyses. However, the graphs show similar variation
amongst the samples collected proximal to distal within the tailings dam. The data clearly
illustrate enrichment in iron towards the centre of the tailings dam with moderate iron content
proximal to the feeder pipe and depletion distal to the feeder pipe. The third samples set
collected in the centre of the tailings dam shows a better correlation between the data
obtained from XRF and titration analyses (Fig. 8.7).
During the geochemical investigation of the fines material, it appears that the titration results
present better analytical totals compared to the XRF results for iron which are slightly too
high to normal.
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Figure 8.7 Comparison of the variation of iron Fe (II) within the tailings Dam as determined
by volumetric titration and X-ray fluorescence Table 8.6 Chemical composition in terms of Fe (II) of the fines ore material samples from
the tailings dam as determined from volumetric titration and XRF.
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Sample ID Mass M1 Mass M2 Mass M3 (M1-M2) Volume %Fe (Titration) % Fe (XRF)
H1A 10.15 9.95 0.20 22.85 62.95 64.27 H1B 9.74 9.54 0.20 24.25 64.90 63.88 H2A 10.05 9.84 0.21 23.85 63.27 63.60 H2B 9.66 9.45 0.21 25.55 65.00 63.69 H3A 9.67 9.47 0.20 22.55 62.09 64.65 H3B 9.75 9.55 0.20 23.05 60.36 64.54 H4A 10.32 10.11 0.21 24.65 64.46 66.86 H4B 9.91 9.70 0.21 24.25 63.26 67.03 H5A 10.10 9.89 0.21 23.95 62.63 65.83 H5B 9.77 9.55 0.22 25.45 62.96 66.79 H6A 9.77 9.55 0.22 24.75 63.22 63.72 H6B 10.09 9.89 0.20 22.65 60.50 64.13 H7A 9.68 9.47 0.20 20.25 54.77 57.16 H7B 9.76 9.55 0.20 20.75 54.44 57.27 H8A 9.91 9.70 0.21 19.95 53.46 57.50 H8B 10.32 10.11 0.21 21.45 55.55 58.33 H9A 10.08 9.89 0.20 22.35 62.73 65.23 H9B 10.06 9.84 0.22 24.05 59.66 66.30 H10A 9.66 9.45 0.20 23.35 62.76 65.48 H10B 9.76 9.55 0.20 23.15 60.62 65.69 H11A 9.75 9.54 0.21 19.65 52.08 62.79 H11B 10.18 9.96 0.23 24.95 59.36 62.38 H12A 10.05 9.84 0.21 25.35 66.96 66.30 H12B 10.04 9.84 0.20 25.65 69.86 66.23 H13A 9.68 9.47 0.21 24.05 64.01 64.11 H13B 10.09 9.89 0.21 24.65 63.65 64.17 H14A 9.75 9.55 0.20 23.75 65.96 64.48 H14B 9.92 9.71 0.21 23.95 61.02 64.25 HB1A 10.15 9.96 0.20 23.15 64.52 65.67 HB1B 9.67 9.45 0.22 26.30 62.93 66.23 HB2A 9.78 9.55 0.23 25.95 61.28 63.59 HB2B 9.75 9.54 0.21 26.25 66.59 63.89 HB3A 9.75 9.54 0.21 24.85 65.38 65.64 HB3B 9.66 9.45 0.21 24.95 64.89 65.33 HB4A 10.32 10.11 0.21 24.15 63.97 64.65 HB4B 9.75 9.55 0.20 23.95 63.40 64.39 HB5A 10.03 9.84 0.19 22.75 65.25 64.50 HB5B 9.73 9.54 0.19 22.85 63.69 64.24 HB6A 9.90 9.70 0.20 24.25 67.48 63.53 HB6B 10.09 9.89 0.20 24.15 63.55 63.33 HB7A 9.76 9.55 0.20 24.25 65.72 64.77 HB7B 9.67 9.47 0.20 23.80 64.11 65.00 HB8A 9.65 9.45 0.20 23.65 64.70 64.18 HB8B 9.65 9.45 0.20 23.65 62.88 63.86
Footnote : (1) Mass M1 : mass of the empty polytop; (2) Mass M2 : mass of the polytop with sample powder; (3) Mass M3 : difference between M1 and M2; (4) Volume : volume of the dichromate solution at turning point.
8.4 PETROGRAPHY OF FINES MATERIAL
8.4.1 Physical Characteristics of Particles
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The fines are composed of particles of different size and composition. Particles vary from
angular to sub-rounded; they are elongated to sub-spherical shape. Hematite ore particles
are dominant in the fines material and represent approximately 70-80% of the total particles.
Very fine grained-material includes shale and silica-rich particles, representing more than 20
% of the total particles, mostly present in samples collected distal to the feeder pipe.
Three textural types of hematite ore particles were identified namely, porous, laminated and
massive iron ore. The porous iron ore particles appear dull and blue in polished blocks of
grain mounts in reflected light, whilst particles of laminated and massive iron ore are dense
with sub-metallic luster. Shale particles vary from pale yellow (aluminous) to red
(ferruginous) in colour. Angular particles of BIF, chert and quartzites are rare.
8.4.2 Petrographic Composition
The petrographic composition of fines particles was studied in polished grain monts (Fig.
8.8A). Due to their small size, it would appear as if most particles represent only partial
components of original rock components as described from the fragments collected from the
discarded lumpy stockpile. Fines particles are thus often monomineralic.
Iron ore particles were derived from three rock types. Some particles appear massive with
rounded shape (figure 8.8A & E) and probably originated from conglomeratic ore. Other
particles with porous texture (Fig 8.10B) probably originated from detrital and porous ores
(Fig. 8.10). Laminated particles (Fig. 8.8D) must have been derived either from hematite
mesobands in BIF or from laminated iron ore. They have preserved their alternating texture
of shining-massive and dull-porous mesobands. Iron ore particles are predominantly
composed of hematite but some contains traces of quartz, pyrophyllite, barite and
specularite. In some particles there is evidence of supergene enrichment (Fig. 8.9E).
Barite was found as minute mineral grains as well as veinlets associated with specularite (Fig
8.10D, E& F).
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SEM studies permitted differentiation of Al-rich from Fe-rich particles (Fig. 8.9 A, C & E). Al-
rich minerals usually occurs as distinct particles mostly shale and do not occur together with
hematite in samples rich in hematite grains (Fig. 8.9A & C), except in the veinlets where they
are associated with barite (Fig. 8.9F). Ferruginous and aluminous shale particles are fine-
grained and massive. Some shale particles appear veined and may contain barite (Fig. 8.9A).
Other shale particles also contain hematite (Fig. 8.9C and Fig. 8.10F).
Fe-rich shale particles show gradual mineralogical and textural transition which is evidence of
iron-enrichment. These particles have similar texture as porous ore particles but vary from
aggregate to granular texture and from quartz to hematite-rich matrix (Fig. 8.9A and Fig.
8.10A & D). BIF particles vary from hematite-rich to microcrystalline silica-rich. In some
particles the original hematite and silica-rich bands are still preserved (Fig. 8.8B & D).
8.4.3 Mineralogical Variation in Fines Tailings Dam
X-ray powder diffraction (XRD) studies suggested not only the presence of hematite and
quartz, but also the presence of other minerals as such biotite, phlogopite, birnessite, dickite
and berlinite in particles from the fines tailings dam. Minerals such as biotite, dickite,
muscovite and diaspore were often encountered by XRD analyses distal to the feeder pipe.
Phosphorous (berlinite) and manganese mineral phases were found in higher abundance
halfway between the feeder pipe and the center of the tailings dam.
8.4.4 Summary
The fines contain a complex assemblage of ore and gangue minerals. Unsurprisingly,
hematite is the predominant mineral. Barite and quartz are the most conspicuous gangue
minerals. They both occur as small monomineralic particles, but also intimately intergrowth
with hematite in larger particles (Fig. 8.10A & D). Other important gangue minerals include
rutile, diaspore, pyrophyllite and muscovite. Most important is to note that the absence of
phosphorous and alkali-bearing minerals within fines of the tailings dam. This would be an
advantage for the processing of material from the tailings dam into a possible saleable
product.
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CHAPTER IX
BENEFICIATION TESTS ON THE FINES MATERIAL
9.1 SPIRAL SEPARATION
Samples of about six kilograms weight were taken to be separated and treated by spiral
separation. The net effect of spiral separation is reverse classification in which smaller and
denser particles are preferentially entering the concentrate. In the present study, this
concentrate fraction was found to be 32-56 weight percent of the original sample feed (Fig.
9.1) but with visible improved-grade and rather uniform grain size. The middlings fraction
represents between 27 and 56 weight percent of the original sample. This fraction invariably
contains noticeable larger proportions of gangue particles but was still rather uniform in grain
size. The tailings fraction contains numerous gangue particles as well as larger ore particles.
It accounts for 8 – 25 weight percent of the original sample mass (Fig. 9.1).
Very fine grained slimes and oversized particles (that were removed by hand prior to gravity
separation), represent 1-7 weight percent of the original sample mass and were lost during
processing. Thus more than 93 weight percent of fine material of the original sample was
recovered at the end of the separation.
Loss of suspended fine particles was higher in samples collected most distal from the feeder
pipe (H7 and H8) (Fig. 9.1A). This was to be expected as the samples also contained the
highest concentration of silicate gangue. Interesting enough, the concentrate fraction tends to
be lower in samples that have highest iron concentration and that are collected in the middle
of the tailings dam, i.e. samples H4 and H5 (Fig. 9.1A).
9.2 X-RAY FLUORESCENCE ANALYSES OF SPIRAL FRACTIONS
Concentrate fractions obtained from spiral separation were analysed for major element
composition by X-RF. About 100g of each fraction was milled and then used to make a single
fusion bead per fraction per sample. The geochemistry of major oxides is represented in the
tables 9.2, 9.3 and 9.4 respectively for the tailing, the middling and the concentrate.
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Improvement of the grade of iron ore is obvious within the first samples set collected distal to
proximal to the feeder pipe, especially within the samples H7 and H8 (distal to the feeder
pipe) (Fig. 9.2A). Most interesting is the fact that concentrate and middling fractions obtained
from these distal samples show most improvement in iron content compared to original fines
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material. The same improvement can be observed within the samples (H10, H11, H12, H13
and H14) collected along on transverse across the tailings dam. The iron seems to
concentrate in the concentrate and middling fractions of the spiral separation.
Unfortunately, the samples collected from the centre of the tailings dam, which previously
showed enrichment in iron, did not improve much and contrary to the original samples, spiral
phases show depletion in iron for both samples sets (Fig. 9.2 A and 9.3A).
The concentration of silica (SiO2) improved significantly within the concentrate fraction for
both sample sets except in the samples H4 and H8 collected longitudinally across the tailing
dam. The silica seems to be concentrated in the tailing and middling fractions except within
the phases from the samples H1, H5, H10, H11, H13 and H14 (Fig. 9.2B and Fig. 9.3B). The
alumina (Al2O3) in general has improved within concentrate phases from all the samples
except only in the sample H8 (distal to the feeder pipe). Improvement of grade was also
observed in the tailing and middling fractions derived from the samples H1, H5, H10, H11
and H13. In general, the silica does no show specific spiral phase preference. It varies
randomly within the spiral phases obtained from the fines material samples (Fig. 10.2C and
Fig. 10.3C).
The phosphate (P2O5) is not abundant within the fines iron material and thus does not show
preferential concentration in any specific spiral fractions. Nevertheless there was an
improvement (decrease in concentrations) in certain samples (H1, H4, H5, H7, H11, H12 and
H14) for all spiral fractions (Fig. 9.2D and Fig. 9.3D).
In summary, it can be said that results from the XRF analyses of the spiral phases indicate
that the concentrate fractions had improved iron concentrations of fine material and lowered
concentrations of silica and aluminum relative to the feed (original samples). Silica appears to
have become concentrated in the middling and the tailing fractions (see tables 9.2, 9.3 and
9.4). However, it is also clear that improvement in iron grade was not such that it would
necessarily warrant spiral separation. Similar improvement of grade could probably be
obtained by just removing fines that would go into suspension i.e. a second washing stage of
the tailing dam material. This suggestion is tested in the following section.
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9.3 PAN WASHING
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Washing by panning was the second method tested to try to improve the grade of the fines
ore material from the tailings dam. Commonly used by gold explorers, the technique consists
of plaing half a kilogram of fines material in a panning dish filled with water for few minutes
then start with simple swinging movements back and forth. Fine mud (light material) is
washed away in the overflow while the dense materials sink to the bottom of the panning
dish. Each washed sample was then dried in air for a few days. Fractions of the dried
samples were collected, milled and then tested for major elements geochemistry using X-ray
fluorescence spectrometry.
The XRF analysis of washed samples was undertaken at Spectrau, University of
Johannesburg, Auckland Park Campus. The results are presented within table 9.5 and
comparative illustration with the original samples in Fig. 9.4. An improvement (decrease or
increase) in certain elements was observed in some samples. As mentioned earlier,
improvement is measured in different ways, an increase of the iron concentration is
considered as an improvement while a decrease in other elements like SiO2, P2O5 is also
seen as an improvement. The iron grade improved significantly within the samples H7, H8
and H11 (Fig. 9.4A). The overall improvement varies from 0 to 10 wt % in iron and 0 to 6 wt.
% in silica. The aluminium and phosphate did not improve even by 0.1 wt. %. Concentrations
are too low (Fig. 9.4B - D).
Both methods, spiral separation and washing, permitted to improve slightly the quality of the
ore by increasing the grade of iron and reducing the concentrations of silica, aluminium,
phosphate and other deleterious elements. Most interesting is to note that simple washing as
described above, could improve the grade of the fines material considerably if the process is
repeated more than once. The washing was only performed once of the fines until the water
was clean enough without suspension.
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PART IV
DISCUSSION, CONCLUSION, APPENDIX AND
REFERENCES
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CHAPTER X
DISCUSSION RECOMMENDATIONS AND CONCLUSION
10.1 DISCUSSION
10.1.1 Discarded Lumpy Stockpile
The discarded lumpy stockpile is composed of lithologies derived from the Manganore and
the Gamagara Formations and the top of the Campbellrand Subgroup, during mining
operations and jigging. It is composed of a mixture of ore and non-ore fragments including
hematite ore, porous and manganiferous ore, aluminous and ferruginous red shale, chert,
banded iron formation (BIF), quartzite and dolomite.
At Beeshoek Mine, beneficiation is based on density separation as parameter, namely dense
medium separation (DMS, using ferrosilicon and water) and an air jig. Density
characterization of lumpy material, however, revealed that some lithologies, which were
classified as ore and waste, respectively (i.e. ferruginous shale) have similar apparent
density. Therefore, density is ineffective and not suitable to further beneficiate iron of the
lumpy material from the discarded dump. At the mine, the jig plant can only beneficiate
material with overall iron content of 35 to 55% and upgrade it to a concentrate with > 60 %
Fe. The material on the discarded lumpy stockpile is thus apparently unsuitable for the jig
beneficiation technique. Magnetic separation would likely be ineffective as well as hematite is
non-magnetic and magnetite is all but absent from both ore and waste rocks.
10.1.2 Fines Tailings Dam
In contrast, fines material from the tailings dam is a by-product generated during the
processing of the raw ore material. It is composed of different lithological particles amongst
which hematite ore is the most abundant and other like shale, quartz, chert and banded iron
formation (BIF) particles.
During gravity separation, using a spiral, dense material seemed to prefer the concentrate
fraction. The major element geochemistry of the concentrate fractions documents the
successful concentration of hematite fines particles. Despite the fact that a significant
improvement was observed in iron content, silica is still present in significant concentration in
concentrates from low iron samples. Other spiral fractions, namely middling and tailing
fractions, also showed significant iron content but with silica contents larger than 3 wt. %.
These fractions represent more than 50 % of the material fed to the spiral.
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10.1.3 Discussion
This study has shown that both the discarded lumpy stockpile and fines in the tailings dam at
Beeshoek Mine contain ore grade material. These materials, which were once considered as
waste, can be a potential source of saleable high-grade iron ore. The geochemical analyses
of both lumpy iron ore and fines material showed no major element that would preclude the
material from being developed into saleable high-grade product. Basically, it would only
involve further sorting or classification of the lumpy material into high-grade ore and waste
material, and also simple washing of the fines ore from the tailings dam to recover the high-
grade ore particles.
The most abundant contaminant in both lumpy and fines is SiO2 in the form of silica and clay
minerals. This can easily be washed away, though. Silica is from four different sources (chert,
BIF, quartzites and shale). Silica from chert, quartzites and BIF, is pure and low density,
easily removable by simple washing, but silica from the shale is often intermixed with iron
oxides and thus more difficult to remove. Washing by normal panning was not completely
effective, since the silica content was only reduced by 50%. Also, although very fine waste
particles were easily removed by washing but coarse waste particles remained behind with
iron ore particles during panning. The washing process may, however, be improved by size
classification and remilling of oversized particles. This, of course, will add additional cost.
10.2 RECOMMENDATIONS FOR UTILIZATION OF LUMPY AND FINES MATERIAL
10.2.1 Lumpy Material
Beeshoek began the production of iron ore in 1964 and the basic infrastructure was based on
hand-sorting as a beneficiation process. This is interesting because one of the simplest
methods to utilize the ore in the lumpy discarded material would be to hand-pick one-grade
material from it. This could possibly be done by placing the ore on a slow-moving conveyor
belt from which ore fragments can be removed by a team of workers. This could be an ideal
project for a small mining enterprise, which would then sell the ore to a major company to
facilitate transport and marketing.
The only other possibility for utilizing the ore fragments remaining in the discard dump would
be to crush the material to fines and then apply heavy medium separation methods. The fines
would then have to be pelletized (Appendix A). The effectiveness of such a process would
depend on the cost in aimed for crushing the low-grade lumpy material from the discard
dump to fines.
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10.2.2 Fines Material
The quality of the fines can be improved by multiple washing or a prolonged washing process
to eliminate the silica that constitutes deleterious element in the fines ore from the tailings
dam. This would lead to high-grade fines ore ideally suited for pelletizing (Appendix A).
Many mineral processing and beneficiation techniques were considered during the evolution
of this project. One of the most suitable methods is the pelletizing process that may be
applied to the fines to get coarser particles that are easily transportable and ready for
metallurgical processing.
The pelletizing process (Appendix A) consists of transformation of fine-grained iron ore
particles into balls of a certain diameter known as pellets, which are suitable for blast furnace
and direct reduction. Pelletization offers a solution for the processing of low grade iron ores,
with two leading pelletizing technologies, the travelling grate process and the steel belt
process, that today guarantee high product quality and low operating costs (Outotec, 2007).
10.3 CONCLUSION
This study has indicated that both the lumpy discard stockpile and fines tailings dam contain
significant quantities of iron ore particles of possible commercial interest.
With regards to the lumpy material from the discard stockpile, the simplest way to utilize that
ore resource would be by simple hand sorting; perhaps an ideal project for a small mining
enterprise.
Fines could also be beneficiated from the discarded lumpy stockpile if the material was
crushed and then separated by heavy medium methods. The fines in the tailings dam could
be upgraded to high-grade fine ore material by simple washing. These high-grade fines ore
could then be pelletized, if a small pelletizing plant would be constructed.
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APPENDIX
A.1 History of Pelletization
The method of balling (or pelletizing) was first introduced in Sweden, when A.G. Anderson in
1912 applied for a patent. Unfortunately the apparatus was not successful and did not
receive commercial acceptance. Later, in 1913, a similar process of balling, with additional
use of binders and strengthening at high temperatures proposed by C.A. Brackelsberg, was
granted a patent in Germany. In the 1920’s, with the introducing of the taconite mining in the
USA and the works of E. A. Davies from the University of Minnesota, the pelletizing process
evolved. Further after major improvements in crushing, grinding and dressing of taconites
and size enlargement of the concentrates produced, works culminated in 1943 when
experimental pellets were first fired in a shaft furnace. In 1950 it became evident that
pelletization was an economically viable beneficiation process of agglomerating fine-grained
iron oxide concentrates. The first pelletizing plant was commissioned in Sweden. Here the
pellets were fired in shaft furnaces with capacities of 10-60 tonnes. The first big plant with a
capacity in excess of 6 million tonnes of pellets annually started operation in the United
States of America in 1955. In the Soviet Union (USSR), pelletization was followed by large
scale self-fluxed sintering and self-fluxing pelletizing, between 1964 and 1967 (SRB and
Ruzickova, 1988). Today pelletization is a common process in producing high-grade iron ore
material widely used in the USA and Brazil.
A.2 Preparation of Raw Materials and Blending
The selection of equipment for raw material preparation is governed by the number of
available types of feedstock, and their physico-chemical condition. To form so-called green
pellets, water is added to the fine iron ore, to adjust the moisture content to approximately
9%, and the ore is mixed with small amounts of binding agents, such as bentonite
(approximately 0.5%) and fluxes such as limestone, olivine and dolomite (1-5%). These
agents give the pellets the prerequisite physical and metallurgical properties required for
further processing. The degree to which the materials are blended depends on the number of
constituents in the charge, their granulometric ratio, and moisture content. If the concentrate
has a moisture content slightly in excess of the required balling moisture, it can be adjusted
to the required level by adding a dry binder. The constituents are blended using one of the
following procedures:
(i) Binder is added to the concentrate before discharging it into bins;
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(ii) Binder is added to the concentrate after the bins, using a special mixing device
such as a paddle wheel or screw mixer;
(iii) Additions are made on the belt carrying the material towards the balling unit;
Mixing takes place in continuously operating drum or pan-type mixers with a capacity up to
1200 tonnes per hour.
A.3 Balling
On an industrial scale, green pellets are formed either in pelletizing discs or drums. The
balling drum is one of the units most commonly used to make pellets; it has proved most
useful for large scale capacity plants where iron ore pellets are produced. Drums are usually
being connected to roller screens used for separating undersized pellets which are returned
to the drum. This high level of circulation makes pelletizing drums less sensitive to variations
in feed material properties.
The disc pelletizer is a machine widely used at present in several industries. In contrast to the
balling drum, the feature of the disc pelletizer is that it can combine balling and screening in
one operation. Pelletizing discs need only a single process step to form pellets, their
classifying effect discharging the pellets from the disc rim within a very narrow size range.
Green pellet size can be precisely adjusted by varying the disc inclination, circumferential
speed, feed or water addition rates.
A.4 Hardening
Since green pellets have low mechanical strength of the balling process, they need to be
hardened. The green strength of pellets is hardly adequate and may be increased by
subjecting them to various treatments, which depend on the starting material for the pellets,
and further processing options. Drying may sometimes prove sufficient, possibly in
combination with the use of binders. Chemical hardening or heat hardening can also be
applied. Heat hardening is the most common method employed. The pellets are hardened
owing to recrystallization of iron oxides, formation of slag phases and secondary
components.
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Figure A.1 Charge preparation adapted from Whyalla Plant (Modified after SRB, and Ruzickova, 1988) 1- Ore storage bin; 2- Lime; 3- Returns feeder; 4- Scale; 5- Crusher; 6- Rotary dryer; 7- Burner; 8- Partitioned chute; 9- Lime or ore; 10- Mill; 11- Worm feeder; 12- Lime/ore storage bin; 13- Pneumatic pump; 14- Pan mill; 15- Mixer; 16- Returns storage bin; 17- Concentrate storage bin.
In ferrous metallurgy, the heat hardening of pellets plays a significant role (Outotec, 2007).
When iron ore pellets are hardened by oxidizing firing, the ore particles are strengthened by
recrystallization, or the gangue constituents fuse while a slag phase develops. The
mechanism of hardening depends on the initial chemical composition of the input material.
Hematite and magnetite concentrates, low in gangue, are strengthened by recrystallization of
hematite particles. Magnetite is oxidized to hematite before recrystallization, and the
completeness of this reaction is ensured by sufficient supply of oxygen reaching the
magnetite particles. The recrystallization of hematite is expressed, according to G. Tamman
(SRB and Ruzickova, 1988):
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t
V
T
T=α (1)
Where Tv is the firing temperature and Tt is the fusing temperature both expressed in oC.
Recrystallization take takes place at the minimum value of α = 0.66 and fusion will begin at α
value exceeding 0.8 to 1.0 in range.
The pellet hardening/firing temperature is shown in figure 11.2A, by the curve deflexion. The
increase of strength is due to the increasingly stronger bonding of ore particles, reaching a
peak at temperatures between 1200 – 1300oC. The strength begins to decrease above this
level as shown in figure 11.2B. It can be seen that above a certain temperature (1200 oC), the
hematite grains begin to grow appreciably and the pellet strength decreases.
Figure 11.2 Hardening of iron ore pellet properties. A- General curve for strengthening of
iron ore balls, showing temperature dependence and B- Hematite
recrystallization (Modified after SRB, and Ruzickova, 1988).
A.5 Drying
After hardening, the green pellets need to be dried. The basic process of drying green pellets
includes the following stages (SRB and Ruzickova, 1988):
(i) Transformation of the moisture in the green pellets into a gas and;
(ii) Withdrawal of the vapour, which is formed, from the material surface and discharge
of this vapour into the environment gas.
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Drying is usually a part of the heat hardening treatment. Occasionally, drying is the final
stage in case where the pellets are not expected to withstand considerable mechanical
stress. Drying depends not only on the heat conductivity of the material, conditions existing in
the heat exchange pattern, and pellet porosity, but also on the quantity and types of binders,
which can absorb the moisture; bentonite or lime are the most common binders used for this
purpose.
A.6 Pellet Properties
The determination of pellets properties has been the subject of arduous research from the
moment the first pellet was produced. The methodology of evaluation of pellets stems from
general principles applied to blast furnace burden evaluation. The pellet properties depend
greatly on the production technologies in addition to the initial chemical and mineralogical
composition and physical state, of the materials used. According to the present day thinking,
the vital metallurgical properties of the iron-bearing constituents of a blast furnace are those
given below (Outotec, 2007; SRB and Ruzickova, 1988):
(i) Chemical analysis of the material and its mineralogical composition .
Chemical and mineralogical compositions of pellets are determined stating the
content of iron, silica, basicity and deleterious admixtures.
(ii) Physical properties analyses comprise granulometry, porosity, bulk weight and
mechanical strength. The granulometric composition of balls depends on the ball
size, because hardly any change in size takes place during heat hardening, except
for siderite balls. Thus the pellet size depends on local requirements and can be
adjusted as required. The mechanical strength of pellets is described in terms of
compression strength, resistance to abrasion and to shatter. Porosity is a specific
property of pellets, and it plays an important role at all stages of pelletization. In
green balls, an appropriate porosity is a guarantee that the pellets produced will
have the required properties.
(iii) Metallurgical properties involve the reducibility, volume and strength changes,
degree of disintegration by reduction, thermoplastic properties. Specific reducibility
is the degree of reduction within a specified time unit and closely controlled
reducing conditions. Volume changes during reduction, or swelling, imply an
increase in volume. Strength of pellets under reduction is a property which
- 156 -
characterises changes of the initial strength of pellets depending on the degree of
reduction
A.7 Example of Pelletizing Model: The Lurgi Traveling Grate
A model developed by Outotec used the Lurgi Traveling grate, best thought of as an endless
chain of pellets (Outotec, 2007). The Lurgi Traveling grate accounts for two third of the
installed pelletizing process capacity worldwide, with a major advantage that pellets remain
undisturbed throughout the process. During hardening, a moving conveyor belt, for example
a double-deck roller screen with each deck separating out oversized and undersized pellets,
ensures that only pellets of the right size (generally 9.16mm) are evenly distributed across
the width of the traveling grate. The grate carries the green pellets on a bed 30-55 cm thick
through a furnace with updraft drying, downdraft drying, preheating, and firing, after firing and
cooling zones.
The traveling grates vary in size between 110-768 m2 as reaction area and 2.5-4.0m machine
width. The capacity starts at 0.35 Mt per annum to 7.25 Mt per annum in a single unit working
of 330-to 350 days per year. It has a specific production rates between 15 tons per days m2
for weathered ores and more than 35 tons per day m2 for high quality magnetites. For that
capacity, the consumption varies between 350 and 1500 MJ thermal energy per ton of
pellets, respectively, for natural magnetites and limonites. The total energy consumption for
the all process is around 25-35 kWh/t electric energy for mixing, balling and induration,
depending on raw material and plant capacity. An additional 0.05m3 fresh water per ton of
pellets is required for the cooling water circuits (Outotec, 2007).
The pellets produced are the required properties for use in the blast furnaces and direct
reduction processes with high porosity, reducibility and degree of metallization.
- 157 -
Figure A.2 Typical flowsheet of pelletizing process for iron ore (Source: Outotec).
The process utilizes a single process plant for pellet drying, preheating, firing and cooling
with several burners in preheating and firing zones. To ensure low maintenance costs, low
specific heat consumption and high availability, the Lurgi Traveling Grate uses several
recuperation techniques. The heat transfer is made by convection instead of radiation with
uniform heat treatment, leading to uniform product quality.
- 158 -
- 159 -
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