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PROSPECTUS
"
MINERAL INvESTMENT OPPORTUNITIES IN ETIDOPIA
VOLUME Two: GEOLOGY ANDMINING
Presented by
Ministry of Mines & Energy of Ethiopia
-.
Executing Agency:
United Nations Department for Development Supportand Management Services
I- Funding Agency:
United Nations Development ProgrammeL.
Contractor:
Techno-Economic Consulting, Inc.
I, \
CONTENTS
PageAcronyms and Abbreviations
SECTION I. SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1
SECTION II. GEOLOGY OF ETHIOPIA 5
A. Geology. . 5
1. Precambrian Basement Rocks 5
a. Archean Rocks (Lower Complex) 5b. Early Proterozoic Rocks (Middle Complex) 5c. Late Proterozoc (Upper Complex) . . . . . . . . . . . . . . . . . . . . . .. 6
2. Phanerozoic Cover Rocks 7
a. Late Paleozoic to Early Mesozoic Sediments 7b. Mesozoic to Early Tertiary Sedimentary Rocks . . . . . . . . . . . . .. 7c. Tertiary Volcanicand Sedimentary Rocks 8d. Late Tertiary to Quaternary Volcanic and Sedimentary Rocks. .. 8
B. Economic Geology 8
C. Maps 10
1. Geological and GeophysicalMaps 10
2. Topographic Maps 11
SECTION III. ADOLA GREENSTONE REGION 14
A. Gold Mineralization 15
1. Primary Gold 15
a. Lega Dembi Ore Zone 15b. Digati Gold and Base Metal Prospect 15c. Dermi-Dama Gold Prospect 16d. Sakaro Gold Prospect 17e. Other Exploration Possibilities . . . . . . . . . . . . . . . . . . . . . . . .. 18
2. PlacerGold. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18
B. Kenticha Tantalum Deposit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18
C. Meleka and Chambe Rare Metal Prospects 18
D. Kenticha Feldspar-Quartz Deposit . . . . . . . . . . . . . . . . . " . . . . . . . . . . .. 19
E. Nickel and Chromium Mineralization " " 21
F. BombawohaKaolin Deposit 24
@Copyright, all rights reserved, 1994.
CONfENTS
...
... SECTION IV. AGERE MARYAM REGION AND AREROGREENSTONE REGION .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Agere MaryamRegion ......................................
B. Arero Greenstone Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Summary .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
..
1. Primary Gold Possibilites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2. Nickel,Platinum,Chromium,Cobalt,Copper, Vanadium. . . . . . . . .3. Molybdenum,Bismuth, Tin, Tungsten .......................4. RareEarth and Rare Metals. . . . . . . . . . . . . . . .. . . . . . . . . . . . . .
SECTION V. MOYALE GREENSTONE REGION .......................
A. Moyale TownArea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...
B. Hassamte-Haramsam Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SECTION VI. WESTERN GREENSTONE REGION . . . . . . . . . . . . . . . . . . . . . .
A. Gold and Base Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Azale-AkendayuGold andBaseMetalArea. . . . . . . . . . . . . . . . . . .2. AshashireGold and Base Metal Area .......................3. Boka-Daletti-BindakoroArea .............................4. Oda-GodereGold and BaseMetalProspect . . . . . . . . . . . . . . . . . . .5. MountDulGold and BaseMetalArea ......................6. OndonokGoldProspect .................................7. TuluKami ...........................................8. Metti...............................................9. :LegaBaguda. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
10. Chokorsa ............................................11. TuluKapiand Ankori . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12. Kata................................................13. BomuMenghi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14. Bascia...............................................15. GambelaMountain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16. Guba,Dura AbelliDrainage,BelesDrainage,Abumare,
Abteselo,Mekezen .....................................
B. Platinum .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
1. YubdoPlatinum Area. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2. Dalatti and Tulu Dimtu . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Bikilal Iron and Phosphate Area . . . . . . . . . . . . . . . . . . . . .
SECTION VII. AKOBOGREENSTONE REGION.. .. .....................
A. Geology of the Akobo Basin ..................................
B. Gold Placers in the Akobo Basin . . . . . . . . . . . . . . '. . . . . . . . . . . . . . . . .
1. Chamo Creek .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. ..
11
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J
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32
34
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36363737
44
44
46
50
50
505152525354545454555555555555
55
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57
65
65
67
67
CONTENTS
Page
2. Kari River. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 673. Kendibab Creek 674. Akobo River (Right Flank) 68
SECTION VIII. TIGRAY GREENSTONE REGION... . 73
A. Gold and BaseMetal Mineralization. . . . . . . . . . . . . . . . . . . . . . . . . . .. 74
B. Gold Occurances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 74
1. Aragab Mesha 742. Enticho. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 743. WesternTigray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 74
a. Asgede. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 74b. Terakimti (Adi Dairo) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 75c. AdizereSenai . . . . . . . . . . . . . . . . . . . .. 75d. Zager and Hargets 75
4. Mefalso and Adi Hageray 755. Adi Hoza 756. MekeleQuadrangle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 75
C. Nickel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . .. 75
1. Samre . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 75
D. Copper
1. TsehafiEmba CopperProspect . . . . . . . . . . . . . . . . . . . . . .. 762. TsalietRiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 773. East Limbof Negach Synclinorium 774. Samre. .. 77
. . . . . . . . . .. .. 76
E. I..ead and Zinc 77
1. Mariam Adista 77
SECTION IX. ETHIOPIAN RIFT ZONE
A. Soda Ash Resources 78
B. Potash ... . . . . . . . . ... 78
1. Deposits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 79
a. MuselyOre Body 79b. Crescent Ore Body 81
2. Reserves. . . . . . . . . . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . . . . .. 81III
a. MuselyOre Body 81b. Crescent Ore Body 82
C. ManganeseDeposits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 82
III
CONTENTS
Page
1. En Kafala . . . .. 832. Garada. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 83
D. Geothermal Energy Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 84
SECTION X. EXISTING MINING OPERATIONS 87
A Background 87
1. Ethiopian Institute of Geological Surveys (EIGS) . . . . . . . . . . . . . .. 872. Ethiopian Mineral Resources Development Corporation (EMRDC) . 88
B. Lega Dembi Gold Mine and Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 89
1. Geology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 892. Reserves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 893. Mining. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 904. Process. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 90
a. Primary, Secondary and Tertiary Crushing 90b. Grinding Circuit 90c. GravityCircuit- Free GoldRecovery. . . . . . . . . . . . . . . . . . .. 91d. Leach Circuit 91e. Amalgamation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 92f. Smelting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 92g. Tailings Detoxification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 93h. Electrical Control System. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 93
5. AncillaryFacilitiesand Utilities . . . . . . . . . . . . . . . . . . . . . . . . . . .. 93
6. Employment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 93
C. Kenticha Tantalum Mine and Pilot Plant . . . . . . . . . . . . . . . . . . . . . . . .. 96
1. Geology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 962. Reserves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 963. Mining. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 964. Pilot Plant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 97
D. Lake AbiyataSodaAshOperation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
1. Soda AshResource. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1002. Reserves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1003. Brine Collectionand Evaporation Operation 1004. Plant. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
E. Profiles of Other EMRDC Operations. . . . . . . . . . . . . . . . . . . . . . . . . . . 104
1. Adola Gold Development Enterprise . . . . . . . . . . . . . . . . . . . . . . . . 1042. Adola Mineral Evaluation and .
Development Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1043. Bole BulbulaConstruction Stone Production Enterprise .. . . . . . . . . 1044. Gem StoneDevelopmentProject. . . . . . . . . . . . . . . . . . . . . . . . . . . 1045. Ceramic Raw Materials Study and Development Project. . . . . . . . . . 104
References and Bibliography
IV
CONTENTS
ContentsAppendix
Ethiopian Transportation Companies, Service Firms, Contractors, Equipment Supplier
FiguresNumber Page
1 Target Areas 22 Chambe Pegmatite Rock Chip Samples . . . . . . . . . . . . . . . . . . . . . . . . . .. 193 Kenticha Vein 5 Reserves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 20
4 Adola Region Nickel Reserves Inferred . . . . . . . . . . . . . . . . . . . . . . . . . .. 235 Bombawoha Kaolinized Pegmatite and Gneiss Reserves . . . . . . . . . . . . . .. 256 Fire Assay Analyses of Rock Chip Samples from
Quartz Veins NNE of Moyale Town 457 BikilalDisseminatedApatite-IlmeniteOre. . . . . . . . . . . . . . . . . . . . . . . .. 598 Musely Potash Reserves 829 Geochemical AssayResults (Chemical) for Garada Area 84
10 Geochemical Assay Results (Emission Spectroscopy)for Garada Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 84
11 LegaDembi GoldReserves. . . . . . . . . . . . . . . . . . ~. . . . . . . . . . . . . . . .. 89
12 Lega Dembi Gold Mine and Plant Employment and Pay Ranges 9413 Process Flow Diagram of Lega Dembi Gold Plant . . . . . . . . . . . . .. 9514 Kenticha Tantalum Mine and Plant Employment. . . . . . . . . . . . . . . . . . .. 9815 Process Flow Diagram of Kenticha Tantalum Pilot Plant .. . . . . . . .. 9916 Lake Abiyata Soda Ash Complex Employment. . . . . . . . . . . . . . . . . . . . . . 10117 Plot Plan of Lake Abiyata Semi-Industrial Soda Ash Plant . . . . . . . . . . . . . 10218 Process Flow Diagram of Lake Abiyata Semi-Industrial
Soda Ash Complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
1-1II-III-21II-11II-2
III-31II-4III-5
III-6
IV-1
Maps
Metallogenic Map of Ethiopia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 4Major Tectono-Metamorphic Divisions of the Precambrian in Ethiopia ... 12Airborne Surveys of Ethiopia 13Diagrammatic Structural Map of Adola Greenstone Region . . . . . . . . . . .. 26Geologic Map and Cross-Sectionof Adola and KentichaGreenstone Belts 27
Mineral Deposits/Occurrences in Adola Greenstone Region . . . . . . . . . . .. 28Mapping and Exploration Targets in Adola Greenstone Region 29Geologic Map and Cross-Sectionof Kenticha Feldspar-Quartz Deposit,Adola Greenstone Region . . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . . . . .. 30
Geologic Map of BombawohaKaolin Deposit in AdolaGreenstone Region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 31
Location Map of Agere Maryam Region and Arero Greenstone Region . .. 38
v
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CONTENTS
Number
IV-2IV-3
IV-4
IV-5IV-6V-I
V-2
VI-I
VI-2VI-3VI-4
VI-5VII-lVII-2VII-3
VII-4
IX-l
IX-2
Page
Mineral Occurrences and AnomalousAreas in Agere Maryam Region . . .. 39Gold Occurrences and AnomalousAreas in Choricho-Kape-KelaltuArea, Agere Maryam Region 40Gold Occurrences and AnomalousAreas in Guduba Area,AgereMaryamRegion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41
Mineral Occurrences and AnomalousAreas in Arero Greenstone Region.. 42Gold Occurrences in Okote Area, Arero Greenstone Region 43Auriferous Quartz Veins NNE of Moyale Town, MoyaleGreenstone Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . .. 48Gold Occurrences in Hassamte-Haramsam Area, MoyaleGreenstone Region . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 49
Precambrian Tectonic Features and Ultramafic Complexesof Western and Akoho Greenstone Regions 60Location Map of Oda-Godere Area in Western Greenstone Region. . . . .. 61Geologic Map of Kata Area in Western Greenstone Region. . . . . . . . . . .. 62Geologic Map and Cross-Sectionof Yubdo UltramaficComplexin Western GreenstoneRegion. . . . . . . . . . . . . . . . . . . . . . . . .. 63Geologic Map of BikilalArea in Western Greenstone Region 64Geologic Map of Akobo Greenstone Region . . . . . . . . . . .. 69GeologicMap of Akobo Basin, Akobo Greenstone Region. . . . . . . . . . . .. 70Anomalies in Stream Sediments in Akobo Basin, AkoboGreenstoneRegion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 71Placer GoldExploration Area in Akobo Basin, AkohoGreenstoneRegion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 72
Location, Topographic and GeologicMap of Danakil Depressionin Ethiopian Rift Zone . . . . . . . . . . . .. 85Cross-SectionThrough Potash Interval of Musely Area inDanakil Depression, Ethiopian Rift Zone 86
Metallogenic Map of Ethiopia, 36"x36"(in jacket at back of this volume)
VI
ACRONYMS, ABBREVIATIONSAND CHEMICAL SYMBOLS
ACRONYMS Ni nickelAGDE Adola Gold Development Os osmium
Enterprise P phosphorusAMEDP Adola Mineral Evaluation Pb lead
and Development Project Pt platinumEIGS Ethiopian Institute of Rb rubidium
GeologicalSurveys Re rheniumEMRDC Ethiopian Mineral Resources Rh rhodium
Development Corporation S sulfurUNDP United Nations Development Sb antimony
Programme Sn tinSr strontium
ABBREVIATIONS Ta tantalumBM base metal Ti titaniumem centimeter Tl thalliumgm gram U uraniumgm/m3 grams per cubic meter V vanadiumglmt grams/metricton W tungstenkm kilometer Y yttriumm meter Zn ZIncmm millimetermt metric ton COMPOUNDSpH symboldenoting the degree Al203 alumina
of acidityor basicity of a BaO barium oxidesolution CaO lime
ppm parts per million Fe203 iron oxide, hematiteFeO iron oxide
CHEMICAL SYMBOLS KCI potassium chloride, sylviteAg silver K20 potassium oxide, potashAs arsemc Li20 lithium oxideAu gold MgCl magnesium chloride,Ba barium bisholiteBe beryllium MgO magnesium oxide, peric1aseBi bismuth Mn02 manganese dioxide,Br bromine pyrolusiteCo cobalt MoS2 molybdenum disulfideCr chromium NaCl sodium chloride, saltCu copper NCo3 sodium carbonate, soda ashFe Iron NO sodium oxideK potassium Nb20S niobium pentoxideLi lithium OSS2 osmium sulfide, erlichmaniteMg magnesIUm P20S phosphateMn manganese Si02 silica, quartzMo molybdenum TOs tantalum pentoxideNa sodium Ti02 titanium oxideNb niobium V20S vanadium pentoxide
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SECTION I
SUMMARY
SECTION I
SUMMARY
This is the secondvolume of the Prospectus whichhas been prepared for international investorswho wish to investigate mineral investment opportunities in Ethiopia. In this volume, thegeology and mining of Ethiopia are reviewed to give the reader an appreciation of its largelyuntouched mineral wealth. .
To determine which minerals will be of most interest to investors, the Ministry of Mines andEnergy studied the mineral resources of Ethiopia and world demand for them. It was decidedthat deposits of the following minerals have the most potential for development:
. Gold· Tantalum. Soda Ash. Potash. Nickel. Platinum
The most promising deposits/occurrences of these minerals and the regions where they occur arelisted in Figure 1 on the following page.
Section II describes the geology of Ethiopia. In Sections III through IX, information on eachregion is given. Existing mining operations are described in Section X.
Geologists from the World Bank and from Techno-Economic Consulting, Inc. who have visitedsouthern Ethiopia believe that the geology of that region offers one of the finest prospects forgold mineralization anywhere in the world. The first primary gold mine in the country, LegaDembi, began operations in the Adola region of southern Ethiopia in 1990.. The proven reservesof the three known ore bodies at Lega Dembi are 62.146 metric tons of gold.
Discovered at the same time as Lega Dembi, the tantalum-niobium deposit at Kenticha has alsobeen developed. Surface mining techniques are being used and a pilot plant is producing 20metric tons of tantalum pentoxide concentrate per year. Reserves are stated to be 2400 metrictons of T~Os averaging 0.015% T~Os and 2300 metric tons of Nb20S.
Evaporation ponds at Lake Abiyata yield trona and a semi-industrial plant has a 20,000 metricton per year design capacity. Studies indicate that Lakes Abiyata, Shala and Chitu Contain 460million metric tons of sodium carbonate at concentrations ranging from 1.1% to 1.9%.
The Dallol potash deposits in the Danakil Depression of northern Ethiopia constitute a majorsource of potash. Total proven, probable and possible reserves are estimated to be 160 millionmetric tons with an average 32.52% potassium chloride content.
Except for the Dallol potash depositsand the Ondonokgoldp"rospectin the Western GreenstoneRegion, all targets can be initiallymined by surface miningmethods.
A 36"x 36"Metallogenic Map of Ethiopia to 1:2,000,000scale is included in the jacket at the endof this Volume. A reduced, 8%"x 11"Metallogenic Map is included at the end of this Section.
1
SECfION I. SUMMARY
FIGURE 1
TARGET AREAS
Region Deposit/Occurrence Page
Adola Greenstone Region . Lega Dembi (existing mine and plant) 89
.Digati 15
Dermi-Dama 16
.Sakaro 17
, Megado, Bore, Upper Bore, Lega Geshe, 18Cheketa-Serdo.
Agere Maryam Region 33
Arero Greenstone Region
Moyale Greenstone Region
Choricho, Kape, Kelaltu, Guduba, Ogo Basin,Demi-Rufo, Bekaka
Okote, Kelensa-Ebicha, Wondimu-Ibrahim
'Moyale Town
Western Greenstone Region
,lIassamte-lIaramsam
Azale, Akendayu
35
44
46
50
Ashashire 51
Boka, Daletti, Bindakoro,'Oda-Godere 52
. Mount Dul 53
Ondonok, Tulu Kami, Metti, Lega Baguda 54
Chokorsa, Tulu Kapi, Ankori, Kata, Bomu 55Menghi, Bascia, Gambela Mountain, Guba,Dura Abelli Drainage, Beles Drainage,Abumare, Abteselo, Mekezen
.Chamo Creek, Kari River, Kendibab CreekAkobo Greenstone Region 67
Tigray Greenstone Region
.Akobo River
Aragab Mesha, Enticho, Asgede
Terakimti (Adi Dairo), Adizere Senai, Zager,lIargets, Mefalso and Adi lIageray, Adi lIoza,Mekele Quadrangle
68
74
75
2
SECTION I. SUMMARY
Region DeposiJ/Occurrence Page
Adola Greenstone Region ~'Meleka, Chambe 18I
. Kenticha (existingmine and plant) 96
Ethiopian Rift Zone Lakes Abiyata, Shala and Chitu; (existing 100evaporation ponds and plant at Lake Abiyata)
Ethiopian Rift Zone Musely 79
Crescent 81
Adola Greenstone Region Digati 15
Tula, Ula Ulo, Monissa, Dubicha, Kenticha, 22KiIta
Arero Greenstone Region
Western Greenstone Region
Tigray Greenstone Region
(name unknown)
Yubdo
Samre
35
56
75
Arero Greenstone Region
Western Greenstone Region
(name unknown)
Yubdo
36
56
57Tulu Dimtu, Dalatti
3.
1
METALLOGENIC MAP OF ETHIOPIA
1MINISTRY OF MINES AND ENERGY OF THE
TRANSITIONAL GOVERNMENT OF ETHIOPIAAND
UNITED NATIONS DEVELOPMENT PROGRAMME
SUDAN
Based on .he Geological Map of Ethiopia to 1:2,000,000 publishedby the Ethiopian Institute of Geological Surveys, 1992.Compiled by Techno. Economic Consulting, Inc.. in collaborationwith the Mineral Resource Explorationand DevelopmentControlDepartment and the Ethiopian Institute of Geological Surveys.Approved for publication by Hon. Shemsudin Ahmed, Vice Ministerof Mines; Ministry of Mjnes and Ener9Y. Transitional Government ofEthiopia.Prepared for the Ministry of Mines and Energy, TransitionalGovernment of Ethiopia, under United Nations CON 7/92 . ETH/90/016.Executing Agency: Sustainable Development and EnvironmentalManagement Branch, Division of Economic Policy and SocialDevelopment. Depanment for Development Support and Managem-ent Services.Funding Agency: United Nations Development Programme.Contractor: Techno - Economic Consulting, Inc.. New York. NY..USA; H.Reid Craig, Jr., compiler of map.Cartography and Printing: Ethiopian Mapping Authority, AddisAbaba, Ethiopia, 1994..Thedesignations employedand the presentation of material on thismap do not implythe expressionof any opinion whatsoever on thepart of the Secretariat of the United Nations concerning the legalstatus of any country. tenitory, city'or area or of its authorities, orconcerning the delimitation of its frontiers or boundaries.\!:) Copyright all rights reserved. 1994
j
Tertiary sediments.
. Tertiaryvolcanics
Mesozoicsedimenls
Greenstones, Late Proterozoic ~Gneissicterrane.Archean 1
UI tramafic bodies
....................
Existing Mining Operation
Railroad,AddisAbabato Djibouti
. Primaryroad
. Nationalcapitalcity
. City
i
,L
SECTION II
GEOLOGY OF ETIllOPIA
SECTION II
GEOLOGY OF ETHIOPIA
Ethiopian geology consists of a high-grade metamorphic terrane of Archean to Early Protero-zoic age, Late Proterozoic greenschist facies metavolcanics and metasediments, negligibleamounts of Paleozoic sediments, Mesozoic marine sediments, Tertiary sediments (easternEthiopia) and volcanics (western and central Ethiopia), and Quaternary sediments, volcanicsand evaporites in the structural rift system.
The structure of Ethiopia is dominated by the north-trending Ethiopian Rift Valley, a failedarm of the triple junction with the Red Sea and Gulf of Aden. In the southwest, a strong,northwest-striking shear zone with sinistral movement cuts the Precambrian metamorphicsand rotates their regional, generally north-south schistosity, to a direction parallel to theshear direction.
Known mineral deposits and occurrences, and their geological environments are shown on theMetallogenic Map of Ethiopia (in the jacket at the end of this Volume).
A. GEOLOGY
1. PRECAMBRIAN BASEMENT ROCKS (MAPS II-I)
a. Archean Rocks (LowerComplex)
Known in southern, western and eastern parts of Ethiopia, the Lower Complexconsists of high-grade gneisses and granitoids. Granulites and migmatites arenoted. The published descriptions suggest that the bulk of these are para-gneisses, although strongly metamorphosed basic igneousrocks are seen in thelowermost unit, the Konso gneiss.
On the latest geologic map of Ethiopia, the Lower Complex is divided into fivegroups of gneissic rock. From oldest to youngest, they are Konso, Alghe,Awata, Yavello and Baro. In the Adola and Agere Maryam areas of southernEthiopia, the Awata has been divided locally into the Bora and the Bulukaformations.
b. Early Proterozoic Rocks (Middle Complex)
The lowest unit of the Middle Complex is the Wadera Group, which consists ofmeta-sandstone, quartzite and biotite and muscovite schists. Contrary to earlierwork, the latest geologic map places the .Mormora Group in the MiddleComplex rather than Late Proterozoic. It consists of biotite schist, gneiss,marble and graphitic schists, and is found in a narrow belt east of Kibre Mengistin the Adola region.
5
SECI'IONn. GEOLOGYOF ETIDOPIA
c. Late Proterozoic (Upper Complex)
Discussion of the formations of the Late Proterozoic must be divided into two
geographical parts: the units in the Adola Group of southern Ethiopia andthose in the Western, Akobo (southwestern Ethiopia), and Tigray (northernEthiopia) Greenstone Belts. These two geographical parts have yet to becorrelated with any certainty. It is generally considered that the units in theAdola Group are older than the other groups. Folding is locally isoclinal andeven recumbent, with thrust faulting in certain zones.
The Adola Group, which has been broken down into the Chakata and Finki1chaformations and the Kajimiti beds, is developed in the area commonly called theAdola Goldfield. It consists of amphibolites of intrusive and volcanic origin, asuite of mafic and ultramafic rocks, quartzites, both iron-bearing and graphitic,and chlorite and graphitic phyllites. Metamorphism is generally greenschistfacies, although it may reach amphibolite facies locally. The Kajimiti beds,consisting of meta-conglomerate and meta-sandstone, overlie the Adola Group.They are restricted to a narrow belt between Shakiso and Digati in the AdolaGreenstone Belt.
The Late Proterozoic in the Moyale area, farther south, is considered to be anextension of the Adola belt based on lithologic similarities.
The Western, Akobo and Tigray Greenstone Belts are made up of a series ofmetavolcanics, from basalt to rhyolite, phyllites (chloritic, sericitic and graphitictypes), greenschists, limestone, quartzites, metasediments of different types,meta-cherts and amphibolites. Small bodies of serpentinite and pyroxenite alsooccur. These lithologies are broken down into three groups: Birbir, Tulu.Dimtu and Tsaliet. Between the Western and Akobo Greenstone Belts, thereare a number of granitoid intrusions, both post-tectonic and syntectonic.
Overlying the Tsaliet Group of metavo1canics and metasediments is theTambien Group of metasediments. This group is made up of chlorite, sericite,and graphitic phyllites, and limestone, slate and dolomite. It is well-developedin the Tigray Greenstone Belt. The contact with the underlying Tsaliet isgradational. The Tambien probably accumulated in relatively shallow water.
Conformably overlying the Tambien Group of metasediments is the Didikamaformation. It is well-developed in the Tigray Region and consists of dolomiteand grey, black or variegated slates. Unconformably overlying the older rocks,and also restricted to northern Ethiopia, is the Shiraro formation of sandstonesand conglomerates. This formation is less strongly folded than the underlyingformations.
The Matheos formation, the youngest of the Precambrian succession in Ethiopiais restricted to northern Ethiopia. It consists of limestone, dolomitic limestoneand dolomite, and overlies the older rocks unconformably.
6
SECTIONll. GEOLOGYOF ErmoPIA
The regional structural trend of the Late Proterozoic in the Akobo Basin isnorthwesterly, due to drag along a major shear zone. In the Western and TigrayBelts, the trend is generally northerly. Thrust faults in the southwest dip to theeast and suggest a west-directed movement. The thrusts in the Adola region dipto the west and an east-directed sense of movement is inferred.
2. PHANEROZOIC COVERROCKS
a. Late Paleozoic to Early Mesozoic Sediments
Late Paleozoic sediments are found in a number of restricted areas. Fluvio-
glacial sediments overlie the continental to shallow marine sands of the Permo-Carboniferous Enticho formation. Late Paleozoic to lowermost Mesozoic
continental clastics are found in the Abay (Blue Nile) Basin and in southeastEthiopia. These clastic sediments are generally localized in narrow grabens.Wells in the Ogaden Basin of eastern Ethiopia have cut thick pre-AdigratPaleozoic sediments, consisting of a basal arkosic sandstone, 1200 meters ofshale and siltstone, and 400 meters of sandstone with chert pebbles andanhydrite (Calub #1 well).
In the early Paleozoic, Ethiopia was landlocked in the interior of the ancestralGondwanaland. Erosion leveled the Precambrian terrain. In the Lower Perm-
ian, regional extension commenced, which resulted in the development ofnormal faults. These developed into a major rift system which ran down thepresent east coast of Africa. Although marine sedimentation has been identifiedin the Ogaden and Somalia, continental sedimentation predominated west of theOgaden.
b. Mesozoicto Early Tertiary Sedimentary Rocks
Three transgressive cycles have been identified in the Mesozoic: the Trias-sic-Jurassic, Albian-Aptian, and Cenomanian-Maestrichtian. The TriassicAdigrat in the Ogaden is the base of this first transgression. It consists ofsiltstone, shale, dolostone and marl. The Adigrat in northern Ethiopia isprobably lower Jurassic and consists of crossbedded sandstones. The formationgrades upward through a transition zone of dolostone and anhydrite into a thickJurassic carbonate unit, the Antalo Group in the Ethiopian plateau andHamanlei in the Ogaden.
The Middle to Upper Jurassic Antalo Group is divided into the older Abaybeds, the Antalo limestone and the Agula shale. In the Abay beds, there isalternating limestone, gypsum, dolomitic limestone, sandstone, and shales. TheAntalo is made up of limestone and marl with oolites and coquina. In theMekele outlier of northern Ethiopia, a sandy oolitic limestone is found in thewestern portion, sep~rated by a reefal facies from deeper-water marls and shalesin the Afar escarpment area. The Agula, overlying the Antalo, is a black pyritic
7
SEmON II. GEOLOGYOF ETHIoPIA
limestone with shale and marl interbeds. Overlying these older units is theUpper Jurassic to lower Cretaceous Amba Araden formation. It consists ofsandstone, shale and marl.
The Hamanlei is Callovian to Oxfordian in age, and is composed of a thicksequence of Liassic to Oxfordian carbonates and anhydrite. It is overlain byUpper Jurassic clastics, shales, and gypsum, with some carbonates.
c. Tertiary Volcanic and SedimentaryRocks
Tertiary marine sediments are found only in the Red Sea Basin and the Ogadeneast of the Marda fault zone. In the Red Sea Basin, evaporites and volcanicunits are interbedded with tuffaceoussandstones and conglomerates, shale andan uppermost limestone horizon. Thick sequencesofTertiary volcanics,rangingin composition from rhyolitic to basaltic, are found in central and westernEthiopia.
d. Late Tertiary to Quaternary Volcanicand Sedimentary Rocks
Late Tertiary to Quaternary sedimentary rocks are found in four general areasin Ethiopia. In the eastern Ogaden, both marine and continental sedimentationproceeded from early to Middle Tertiary. The coastal sediments of the Red Searegion consist of late Tertiary sandstone, evaporite and limestone. These werefollowed by Quaternary conglomerate, sand, silt, clay and reef limestone.Deposition in the Danakil Depression is found to be similar in character. In thelower Omo Valley, in southwestern Ethiopia, sands, sandstones and rarevolcanics have been reported.
The Danakil area is of particular interest owing to the occurrence of potash inthe evaporite sequence. Late Tertiary sediments outcrop on both sides of theDanakil Depression, fringing the thick evaporite sequence. They in turn areoverlapped by Quaternary volcanics. The Red Series, of Miocene to Plioceneage, consists of coarse, generally fresh-to-brackish-water clastic sediments.Above the Red Series is a thick evaporite formation of bedded halite, gypsum,anhydrite, potash and magnesium salts and shale. This sequence fills a basin inthe center of the Danakil Depression. Drilling has indicated a total thicknessof 1200 meters of halite and gypsum, some 40 meters of potash salts and 15meters of magnesium salts. The evaporitic formation is Pliocene to HoloceneIn age.
B. ECONOMIC GEOLOGY
The Late Proterozoic greenschist facies metavo1canics, metasediments and the associatedmeta-ultramafics offer opportunites for gold, platinum, niobium, tantalum, cesium andnickel in the Adola, Arero, Moyale, Western, Akobo and Tigray Greenstone Regions. Alsowith potential for these and others is the Agere Maryam area. The possibilities in these
8
..
SECl10N ll. GEOLOGYOF ETIDOPIA
areas have been studied to a variable degree, the greatest concentration of work havingbeen in the Adola region. Primary free gold, together with variable amounts of sulfides,occurs in quartz veins, in quartz lenses, as disseminations, and in swarms and stockworksof quartz veinlets in the host greenstones and associated intrusions.
It is possible that volcanogenic massive and disseminated base metal sulfide deposits maybe found in the Akobo, Western and Tigray metavolcanic-metasedimentary terranes.Evidence exists - remnant pillow lavas, ferruginous chert layers and water-laid tuffs - thatsubmarine volcanism was commonly the source of these lithologies. Auriferous sulfideswere reported in a number of areas in the Western Greenstone Belt, and base metalmineralization is common in this belt and the Tigray Greenstone Belt.
Although there has been little exploration directed specifically toward the base metalpotential of Ethiopia, occurrences and indications of copper, lead and zinc have beenreported in greenstone belts of metavo1canics and associated metasediments. The greatestnumber of these are in the Western, Akobo and Tigray Greenstone Belts. Some of thesemay indicate the presence' of volcanogenic massive to heavy-disseminated sulfide depositsat depth, possibilities of which are suggested in Oda-Godere, Azale-Akendayu, and areasnorth of Kurmuk, all in the Western Greenstone Belt. Copper and zinc mineralization hasbeen reported at a number of localities in the Tigray region, such as those near Aragab andSamre. The Tsehafi Emba copper occurrence in western Tigray has been studied, as hasthe Kata base metal and gold occurrence in the Western Greenstone Belt.
Belts of ophiolites, which are present in western and northern Ethiopia, as well as theAdola region, are known to have great mineral potential. Examples are found in Cyprus,western Colombia and northern Turkey.
The only known deposit containing a substantial tonnage of iron is at Bikilal in the WesternGreenstone Belt. The lenticular bodies of ilmenite-magnetite ore are associated with ananorthosite horizon within a belt of hornblendite.
A tantalite-bearing pegmatite is currentlybeing exploited at Kenticha in the Adola region.The pegmatite body lies along the gradational contact between a granite and a serpen-tinized ultramafic body. Other occurrences and indications of rare metals are found atMeleka and Chambe to the north of Kenticha, as well as in the Agere Maryam Region.
The Pliocene to Holocene deposits of saline evaporites in the northern Danakil Depressioncontain an appreciable proven tonnage of sylvite and other potassium and magnesium salts.The upper bed of potash ore has been only partially explored. The lower horizon has beenintersected by one drill hole; lateral extensions are unchecked. The possibilities forextensive potash reseIVes north and south of Musely are excellent.
Evaporitic deposits of potash, similar to those of the Danakil Depression, are found in theback-reef basins in Saskatchewan (Canada), New Mexico (United States) and variouslocalities in Europe. These have been producers for many years and the same may beexpected in Ethiopia.
9
SECTION II. GEOLOGY OF ETHIOPIA
Soda ash is being produced by evaporation of the waters pumped from Lake Abiyata in theRift Valley. The water in nearby Lake Shala also has a chemical composition suitable forthe extraction of soda ash by evaporation. The potential reselVes of soda ash from the areaare extensive.
The large areas of Tertiary felsic volcanics west of the Rift Valley have received little tono exploration for hot-spring type or large-tonnage, low-grade gold deposits. The felsic-to-intermediate volcanics, of which there are large thicknesses, should be considered asworthwhile exploration target areas for gold and associated metals.
In the western United States, similar volcanic terranes have hosted many such deposits, andrecent studies in Yemen have indicated the presence of exploration target areas in theextensive areas underlain by Tertiary volcanics. Large-tonnage, low-grade gold deposits inTertiary volcanic fields, amenable to open-pit exploitation, have recently been developedin Peru. Two of these are currently producing.
The regions underlain by Mesozoic shelf carbonates, such as the Mekele outlier, AbayBasin, and western and northern Ogaden, merit consideration for Mississippi-type lead-zincenvironments.
To date there has been no exploration of consequence for carbonate-hosted base metals,principally lead and zinc, in these areas. This type of deposit has been a great producerof ore in many areas of the world, such as the Mississippi Valley and Appalachian regionsof the United States, northern Mexico, the Pine Point area of Canada, France, Germanyand Brazil.
In summary, analogies between the several favorable geologic situations in Ethiopia andsimilar ones containing known mineral deposits in other parts of the world, strongly suggestthe likelihood of such mineralization occurring in Ethiopia as well.
c. MAPS
1. GEOLOGICAL ANDGEOPHYSICALMAPS
The Ethiopian Institute of Geological SUlVeys(EIGS) has mapped about 25% of thecountry at the 1:250,000scale. The geological and geophysical maps below areavailable from EIGS:
Geological Map of Ethiopia (1973), Scale 1:2,000,000
Geological Map of the Ogaden, (1985), Scale 1:1,000,000
Geological Map of the Adola Area (1988), Scale 1:100,000
Geological Map of Adola Area (1992), Scale 1:100,000
10
..
SEcrION n. GEOLOGYOFErHIOPIA
AdigratAdi RemetsDire DawaGoreMekeleNazretOmo Project Area
ND 37-7ND 37-9NC 37-12NC 36-16ND 37-11NC 37-15O.P.A
1977198219851987198719781979
The followingmaps are due to be published and are available as black and whitecopies:
Agere MaryamKurmuk, Asosa
NB 37-10 1993NC 36-7, 8 1987
A Bouguer gravitymap, a residual gravitymap and a regional gravitymap are beingprepared by EIGS at scalesof 1:2,000,000and 1:10,000,000. The geological map ofEthiopia is being digitized for future integrated interpretation of the gravity data.Airborne geophysicalsUlveysof various parts of the country have been undertakenover the years. Airborne coverage is shownon Map 11-2at the end of this Section.
The address of EIGS is as follows:
Ethiopian Institute of Geological SurveysP.O. Box 2302Addis Ababa, EthiopiaFax: 251-1-513877
2. TOPOGRAPHICMAPS
Topographic maps at various scales are available. The most important scales are:
Scale1:1,000,0001:250,0001:50,000
Coverage100%98%40%
Year of Publication198419721980-1994
The maps may be purchased from the Ethiopian Mapping Authority (EMA), theGovernment agency responsible for the establishment and maintenance of thenational geodetic network and for national mapping. The EMA's address is:
Ethiopian Mapping AuthorityMenelik AvenueP.O. Box 597Addis Ababa, EthiopiaTel. : 011-251-1-51 59 01Fax: 011-251-1-51 51 89
11
-- - ---
Map 11-1
Major Tectono-Metamorphic Divisionsof the Precambrian in Ethiopia
After Senbeto Chewaka and M. de Wit (1981)o 100 200 300 400
Kilometers
ERITREA
SUDAN
Calc-alkalinevolcanic-plutonic belt
Western ophioliticsuturebelt; ophiolites in Easternmetamorphic belt
Basement in calc-alkalinecalc-plutonic belt
Central high-grademetamorphic zone
Eastern metamorphic belt
Southwestern cataclasticbelt
Precambrian outcrop
SOMALIA
KENYA
12
SUDAN
4:ZOE
RED SEA
Map 11-2 +180NAirborne Surveys of Ethiopia
o 100 200
Kilometers
. 14'N~-f-
. 1338 I
-'1311 I
KENYA
12381L
SOMALIA
Survey No.1 031Magnetics - 1968No. line km: 24000Une spacing (km): 10
Survey No. 1238Magnetics - 1951No. line km: 8725Une spacing (km): 8
Survey No. 1337Magnetics -1983No. line km: 3436Une spacing (km): 3
Survey No. 1033Mag. & Radiometry - 1971No. line km: 35443Une spacing (km): 1
Survey No. 1311Mag. & Radiometry - 1970No. line km: 9726Une spacing (km): 1
Survey No. 1338Magnetics - 1970No. line km: 16978
Une spacing (km): 4.8
Survey No. 1035Magnetics - 1976No. line km: 14345Une spacing (km): 5
Survey No. 1312Mag. & Radiometry - 1970No. linekm: 15274Une spacing (km): 1
13
12"Nt (103) : ; : : (
GULF OF ADEN
100N1 }
12"N
ILI I I I .. \...
SOMALIAt1 OON
SECTION ill
ADOLA GREENSTONE REGION
SECTION III
ADOLA GREENSTONE REGION
The Adola Greenstone Region is located in southern Ethiopia, 500 kilometers south of AddisAbaba. (See Maps 111-1to 111-6.)
.The modem gold mining history of the Adola Greenstone Region can be divided into threeperiods. The first period began in the 1930s with the discovery of placer gold in BedakessaValley in the Adola area. A large number of placers with high gold content were put intoproduction in a short time. In 1944 alone, over 2500 prospectors recovered 1630 kilograms ofgold. Between 1945 and 1950 the first attempt was made to examine the gold potential of thearea systematically.
During the second period, from the early 1950s to 1978, gold production declined since the richand easy-to-work placers had been nearly exhausted. Exploration efforts identified approximately150 placer gold deposits. The discovery of gold lodes by prospectors at Dermi Dama and Sakaroin 1975 strongly suggested the existence of major primary gold deposits in the Adola area.
The third period began in 1978,when the Adola Gold Exploration Project was established withSoviet technical assistance to evaluate the mineralization in the Adola area. The Projectexplored for placer and primary gold deposits, as well as for rare metals and ceramics. This workresulted in the discovery of the primary gold deposit at North Lega Dembi and the tantalumdeposit at Kenticha.
The area covered by geological mapping is underlain by units of the Precambrian basementcomplexes. Only the Middle and Upper Complexes have been studied in any detail. These havebeen deformed in linear north-trending folds, which have been cut by deep-seated longitudinalfaults, and flexures trending northeast and northwest. The Upper Complex, the Adola volcano-sedimentary sequences, is confined to the 20-25 kilometer-wide Megado graben-syncline. Thesyncline is a down-faulted and folded block bordered by the higher metamorphic grade MiddleComplex units.
The Middle Complex is divided into two groups, the Awata and the Mormora, which representtwo major cycles of sedimentation. They are metamorphosed to the amphibolite facies. TheAwata is the older of the two and is made up of migmatitic biotite-hornblende gneiss (Boreformation) and a biotite gneiss (Buluka formation). The Mormora Group consists of a lowerpsammitic lithology (Zembaba formation), which grades upward into the pelitic Aflata formation,which in turn grades into the carbonate-pelitic lithology of the Kenticha formation. These havebeen intruded by the Gariboro ,granites, which have been dated at 680:t30 million years.
The Upper Complex Adola Group is weakly metamorphosed and consists of the volcano-sedimentary Chakata and terrigenous Finkilcha formations. Overlying these formations uncon-formably are the metaconglomerates and metasandstones of the Kajimiti beds. Accompanyingthe volcanic activity of the Upper Complex units was the pre- Kajimiti emplacement of ultramaficand gabbroic rocks along the deep, north-south trending faults. A number of cross-cuttingpost-Kajimiti granite bodies intruding the area have been dated at 515:tl0 million years.
14
SECTIONm. AnOLA GREENSTONEREGION
A helicopter-borne geophysical sUivey was done by a Canadian contractor. Magnetometer,electromagnetic and radiometric data were collected along the flight-lines. The results in hardcopy and CD-ROM will be available in December 1994.
A. GOLD MINERALIZATION
The majority of the known gold-bearing areas are in the Adola Greenstone Belt, whichis composed of Late Proterozoic metavolcanics and metasediments. The Adola belt is 20-25 kilometers wide by some 150 kilometers long. Both alluvial and primal)' gold occuralong this north-striking zone. The Kenticha Greenstone Belt, lying 12 to 15 kilometerseast of the eastern marginal thrust of the Adola belt, contains some gold, but is chieflyof interest for nickeliferous laterites and rare metals, associated with ultramafics andpegmatites respectively.
1. PRIMARY GOLD
a. Lega Dembi Ore Zone
The Lega Dembi ore bodies, mine, plant and reseIVesare described inSection X.
. b. DigatiGoldand BaseMetal Prospect
The Digati prospect is situated at N05000'00", E38°50'00", 72 kilometerssouth of the town of Shakiso. The lithologies obselVed are amphi-bole-chlorite schist, meta-gabbro, meta-ultramafics, and plagioclase-amphi-bole-tremolite rock. Associated with these principal lithologies, metavol-canic breccias, quartz veins of varying textures, and basic and aplitic dikeshave been mapped. These show both concordant and discordant relation-ships with the strike of the main lithologic units. Varying types of alter-ation are noted in the different lithologies and to a lesser extent in theamphibole-rich rock. The most common types are silicification, chloriti-zation, epidotization, biotitization and sericitization.
The rock formation strikes NlOoWto NlOoE and dips moderately to steeplyto the west as a rule, although an occasional dip to the east is found. Atthe contact between the amphibole-chlorite schist and the amphibole gneissthere is a 160-180 meter wide shear zone. This has a strike generallysimilar to the rock foliation.
Disseminated sulfides consist of chalcopyrite, galena, pyrite and pyrrhotite.In the quartz veins, galena, pyrite and chalcopyrite are seen in associationwith free gold. A total of 11 veins with free gold are known in the prospectarea. Two of these are near Digati, hosted by a biotite-amphibole gneiss.The remainder of the veins are southeast of Digati, hosted by amphibolegneiss. Fine- to vel)' fine-grained gold grains are found in sulfide-bearingquartz boulders in the creek and in the sulfide-bearing quartz veins in the
15
SECfIONm. ADOLAGREENSTONEREGION
southern part of the area. In the central part, primary gola was alsoobseIVed in quartz veins hosted by amphibolites.
Placer gold in terraces is found near the Dawa bridge and up the MaraloValley. Geochemical stream sediment samples showed high copper andnickel values as well. Soils gave values up to 2400 ppm Cu and 5400 ppmNi in the area underlain by meta-ultramafics.
Three zones of interest for gold and Cu-Ni mineralization by were foundby geophysical exploration. The central zone is the most promising.Quartz veins with gold and associated sulfides are found near the contactof amphibole-quartzo-feldspathic gneiss and amphibole gneiss (central part),and near the contact of amphibole gneiss and amphibole-chlorite schist(southern part). Quartz veins are considered to be the host rocks of theprimary gold mineralization.
The placer possibilities have been examined and the wash thicIaiess variesbetween 0.2 and 2.0 meters, carrying 0.13 to 2.59 grams Au per cubicmeter. The overburden varies from 3.0 to 5.2 meters thick in the lower partof the Dawa terraces in the 40-meter-wide valley. The overall grade variesfrom 0.12 to 0.76 grams per cubic meter. The part of the valley near theDawa bridge requires further prospecting.
c. Denni-Dama Gold Prospect
This prospect area is located at approximately N05°00'00",E39°00'00". Itis in the Kentichabelt, 2 kilometers east of Dermi-Dama Village, on theleft side of the Mormora River.
There are two principal lithologic units in the area, biotite schists andaltered ultramafics. Foliation dips variably to the east. Lenses of quartz,up to one meter thick, ultramafics and amphibolites are found within thebiotite schist. Quartz veining and pegmatite bodies are obseIVed in themain lithologies. The ultramafics have been altered to talc, chlo-rite-tremolite-talc schist and serpentinite. The biotite schists have under-gone various types of alteration, silicification, introduction of calcite,chloritization (of Ti-rich biotite), and tourmalinization. The biotite schistsand quartz veins contain generally less than 1% disseminated pyrite andpyrrhotite. The primary gold occurs in quartz veins and veinlets withoutappreciable amounts of sulfides. The host rocks are usually biotite schistsnear the contact with the ultramafics.
The Dermi-Dama gold prospect is of the stockwork type, associated withthe general Mormora gneissic terrane. The mineralized zone, as presentlyknown, is 200 meters long and 15 to 30 meters wide.
16
SECTIONm. ADOLAGREENSTONEREGION
Another type of gold mineralization has been explored in the area, appar-ently in biotite schists within gamet-amphibolite (green rock) intercalations.Three drill holes were put down. DDH #1, at a depth of 125.34 meters,cut 1 meter containing 11.3 ppm Au. A 4.6 ppm Au intersection was alsocut. These were fire-assay results. These intersections were in gar-net-biotite-amphibole and a staurolite-gamet-biotite schist. DDH #2 cuttwo gold-bearing zones. Three samples from DDH #3 were analyzed byatomic absorption spectrometer and gave 0.1 ppm Au.
Sixty-one rock samples were analyzed for gold. Seven of these containedmore than 10 grams of gold per metric ton, 28 had more than 1 gram perton. One of the samples, in the vicinity of an old pit, reported 68 grams ofgold per ton. During the exploration work, 130 pits were dug, of which 96gave positive gold indications.
High Pb values, 36 to 70 ppm, were obtained in the southeast part of thearea, where the underlying rock is serpentinite. At Lega Dembi high leadvalues are related to the areas of gold mineralization.
d. . Sakaro Gold Prospect
This prospect is located at N05°38'54", E38°51'58", about 9 kilometerssouthwest of Shakiso, in the Adola belt. The area is underlain by metasedi-ments (biotite-sericite schist interlayered with micaceous and graphiticschists), basic meta-igneous rocks (amphibolites), meta-ultramafics (talc-tremolite and chlorite-actinolite schists), and amphibole-plagioclase gneiss.The foliation strikes north-northeast and dips westerly.
The mineralized zone is in the Adola belt, along the eastern margin of theMegado graben-syncline. Four gold-bearing quartz veins are found Theveins strike N700E and dip NW50o-60°. Sulfide mineralization includespyrite, pyrrhotite and rare chalcopyrite, but the gold mineralization ingeneral is interpreted as low-sulfide, quartz type. The gold in the quartzveins is reported to be both crystalline and sheet-like.
Geochemical and geophysical anomalies were found generally overlappingalong the zone. Pitting and drilling were done, with values up to 5.79 ppmAu reported. The maximum value was at 159 meters depth from a bio-tite-sericite schist. Below 57 meters, pyrite decreases and pyrrhotitebecomes the dominant sulfide. Geophysical study outlined a 1.6 kilometerlong anomalous zone, and the gold- mineralized zone can be traced for 760meters along strike.
The placer deposits in the Sakaro and Wollena Valleys are considered tobe exhausted for all practical purposes.
17
SECTIONm. ADOLAGREENSTONEREGION
e. Other Primary Occurrences
There are a number of known primary gold occurrences in the AdolaGreenstone Region. Among these is the area from Megado south. Nearthe exhausted Upper Bore gold placer, there is a zone of gold-bearingquartz veins that merit further exploration. The occurrence near Megadois in quartzites. There are also primary quartz vein gold possibilities atBore I and II, and Lega Geshe.
Occurrences worthy of concentrated exploration efforts exist in the Cheketaarea and in an area about 7 kilometers north of Digati and above the DawaDigati drainage area.
2. PLACER GOLD
The locations of some of the known placer deposits are marked on Map 111-3,butonly those where some geological studies have been made. Quite apart from thepossibilities for small- to medium-scale alluvial mining, these placer accumulationsare an excellent guide to primary gold possibilities.
Artisanal mining operations are not uncommon in the Upper Mormora River andat Shorte, near the town of Megado. A semi-mechanized operation has beenundertaken at Kajimiti. The Bedakessa placer, a short distance north of Shakiso,remains 70% unexploited, and the Kelecha placer, in the Shakiso area, is only 20%worked. The Cheketa-Serdo placer in the Wanza and Serdo Valleys, at N05°38',E38°50', is worth further examination.
B. KENTICHA TANTALUM DEPOSIT
The geology and reserves of the Kenticha tantalum deposit, and the operations of theKenticha mine and pilot plant are described in Section X.
C. MELEKA AND CHAMBE RARE METAL PROSPECTS
The Meleka prospect is located at N05°52'48"-N06°04'07",E38°48'38"-E38°55'00".TheChambe prospect is30 kilometers northof KibreMengist,between N06°00'00"-N06°10'00"and E38°54'34"-E39°00'00".These prospects lie on the northern extension of the Adolabelt, and the general rock types and structural trends are similar to those in the southernpart of the Adola belt.
The area in general is underlain by Upper Complex rocksof the Chakata and Finkilchaformations and by Middle Complex rocks of the Aflata and Kenticha formations. TheChakata and Finkilcha are volcano-sedimentarywith ga:bbroicintrusions. The latter twoformations are biotite-amphibole,biotite-plagioclase-quartzand quartz-hornblendeschists,and biotite-quartz-feldspar and quartz-hornblende gneisses. Two.-mica and gneissosegranites are exposedalong the right side of the Genale River. The regional trend of theunits is north-south.
18I
~
SECflON m. ADOLAGREENSTONEREGION
Concordant and discordant quartz veins occur in zones of hydrothermal alteration.Malachite and copper sulfides occur inquartz veins cuttingthe basicrocks. Alluvialgoldwas also found in severalof the rivers- the Abeba, Oda-Buta, Udetu, Hortumie and Hill.Pegmatites with associatedberyl, amazonite (microcline), tungsten, molybdenum and, insome cases, columbiteminerals were seenaround the townof Chambe. A pegmatite withcolumbite was located five kilometers south of Chambe.
Mineralization in the area consists of twotypes,placer goldand tantalite-columbite. Chipsamples taken from the-Chambe pegmatites are reported to have returned the followinganalyses:
Figure 2Chambe Pegmatite Rock Chip Samples
Deposit
Chambe West
Chambe East
SOURCE: Ethiopian Institute of Geological Surveys internalreport, 1987.
Exploration samples from the alluvium in the Hobone Valley gave an average 0.396gramsAu per cubic meter. A gold halo was found along the Abeba River in panned concen-trates (this area included the town of Chambe).
D. KENTICHA FELDSPAR-QUARTZ DEPOSIT (MAP 111-5)
This deposit is situated between N05~9'09"-N05~9'29" and E39°01'30"-E39°01'58". Itlieson the northwest slope of Kenticha Mountain, approximately 49 kilometers southeast ofShakiso, in the Kenticha belt.
The eastern part of the area is underlain by the Aflata formation of aIternating biotitegneisses and schists, amphibole schistsand amphibolites. These strike north and dipgenerally westward. The western part of the general area is underlain by rocks of theyoungerKenticha formation. These arebiotite and muscoviteschists,graphite schists,andsome marble and amphibolite. They strike northerly with variable dips.
Between these two is a northerly-trending massif of ultramafic rock, 4 to 5 kilometerswide. The massif is made up of lenticular serpentinites and talcose rocks with zones oftalc-chlorite schists and tremolite-ta1c rocks. Large elongated masses of relictmetamorphics were noted within the massif. A few 100 to 200-meter-wide bodies ofmuscovitic, aplite-like pegmatoid bodies are encountered in various parts of the massifand in the stratified metamorphics.
19
Niobium TantalumPentoxide Pentoxide
% %
0.52 0.08
35.06 6.709
SECfIONm. AnOIA GREENSTONEREGION
The Kenticha feldspar-quartz deposit incorporates a group of pegmatite veins within theserpentinites. They are variably northerly-striking along with linear zones of tremolite-talcrocks. Eight pegmatite veins were identified. Veins 1 and 5 undeIWent the most detailedexploration. Vein 1 is found in the southwestern part of the area. It is 1.5 kilometers longand between 50 and 150 meters thick, and trends northeast, dipping 50 to 70 degreessoutheast. It contains isolated occurrences of quartz blocks, the largest of which is 52meters long by 30 meters wide. The smallest is 13 to 15 meters long by 4 meters wide.The blocks are highly jointed.
The quartz is pure milky-white and translucent to glassy. The texture is massive- tocoarse-grained, occasionally cryptocrystalline. Samples from these blocks showed 98.7%SiOzless than 0.1% alumina, lime, magnesia, soda, potash, titania, manganese oxide, andloss on ignition. Less than 0.4% Fez03 was reported as well. The material appearssuitable for the ceramic and glass industries. The total inferred reseIVe is 268,000 metrictons of quartz.
Vein 5 is located in the eastern and southeastern parts of the area. It pinches to thesouth and is cut off on the north by a northwest-striking fault. This vein is 650 meterslong and averages 27 meters thick. It trends northerly and dips variably between 38 and80 degrees east. A lens of serpentinite, 380 meters long and up to 10 meters thick, isfound in the central part of the vein. Five boreholes were drilled, for a total of 337.5meters, geologic mapping of 5000-scale was done, as well as pitting and trenching.
Vein 5 is made up of orthoclase, quartz and muscovite, with occasional spodumene, beryland tourmaline. Chlorite and talc are found near the contacts. The orthoclase is coarselycrystalline, microclinic, with intergrowths of albite (5% to 10%). The quartz is massive,translucent, and milky-white to light gray, and is chiefly confined to the central part of thebody. Quartz may constitute 3% to 10% of the pegmatite mass. Aside from intergrowthswith feldspar, the quartz may be in blocks up to 1 meter across. Panned concentratesshowed what are considered to be background amounts of rare metals: UzO 0.05%;TazOs 0.22%; and NbzOs 0.12%.
The Vein 5 reseIVes are given below. With selective mining and some beneficiation, thismaterial can meet industrial requirements for ceramics, glass, insulators, abrasives, glaze,and other products.
Source: Sabov, Y. V. et aI, "Bombawoha Kaolin and Kenticha Feldspar Quartz Deposits,"Ethiopian Institute of Geological Surveys internal report, 1985.
20
Figure 3Kenticha Vein 5 Reserves
Reserve
I Reserves
Feldspar Feldspar with Quartz Tails
Category mt % mt % mt % mt000 000 000 000
Probable ! 366.4 I 50.4 184.5 I 35.7 130.9113.9
51.0
Possible I 775.8 I 40.8 316.5 I 51.1 396.4[ 8.1 62.8
SEcnON m. AnOIAGREENSTONEREGION
It is calculated that 420,700 metric tons of overburden must be stripped to exploit Vein5's probable reserves of 366,400 metric tons, giving a stripping ratio of 1.15:1, waste topegmatite. The ratio of waste to ore in both reserve categories is 3.5:1.
Vein 4 is 70 meters long and 2 meters thick, and Vein 10 is 150 meters long and 4 metersthick. They are undifferentiated pegmatites made up of feldspar, quartz, muscovite andoccasional spodumene.
Vein 2, the largest and longest, has an inconsistent composition along and across strike.To the south, the eastern veIn material is feldspar and quartz, whereas the western veinmaterial is undiffere~tiated and ferruginous pegmatitic material. Locally, 90 x90-centimeter blocks of pure microc1ine are found. The northern part is composed ofundifferentiated, ferruginized pegmatitic material, with highly-weathered spodumenemaking up 10% of the total mass.
Vein 3 is 150 meters long by 2 to 25 meters wide. It strikes north-northeast and dips 30to 25 degrees east. It is made up of feldspar, quartz and spodumene, with local muscoviteplates. Veins 7 and 11 are small quartz-muscovite-feldspar bodies, which are poorlystudied.
E. NICKELANDCHROMIUMMINERALIZATION
Nickel and chromium mineralization are associated with ophiolitic rocks of the LateProterozoic Adola Group. These crop out in the north-south striking Adola and Kentichabelts. The nickeliferous bodies occur in two alignments of ultramafic bodies within aserpentinite belt that goes from Cabalanca in the north to the Burjiji River in the south.A second, parallel belt exists about 60 kilometers to the west. This also containsultramafic bodies, which have not been well examined.
The Adola belt is flanked on both sides by high-grade basement gneisses. The easterncontact is undoubtedly tectonic, a thrust zone. The Adola belt consists of altered ultra-mafic and mafic igneous rocks (Adola Group) and associated sediments (MormoraGroup). The ultramafics are altered to talc, talc serpentine and locally anthophylliteschists, and occur as lenses up to tens of kilometers in length. Massive serpentinites arealso included in this length. The altered mafics are amphibolites and diabases, bothmetamorphosed. The lower parts of the amphibolites display a gneissic structure, whereasthe upper parts locally have pillow structures as well as intercalations of graphiticphyllites. These upper parts thus appear to be products of submarine basaltic eruptions,and are interpreted as being part of an ophiolitic sequence.
Metasediments in the Adola Group are younger than the amphibolites, as may be seenin the outcrops at Kajimiti Village. These are psammitic, pelitic and graphitic schists, andgraphitic and ferruginous quartzites.
The Kenticha belt is 12 to 15 kilometers east of the eastern marginal thrust of the Adolabelt. It consists of two parallel zones of talc and talc-serpentine rocks, separated by a thin
21
SECfION m. ADOLAGREENSTONEREGION
strip of granitic gneisses. The Kenticha belt can be traced along strike for at least 60kilometers. The east contact is with metasediments of the Middle Complex WaderaGroup. The west contact shows strong evidence of shearing. Structurally the belt consistsof three or more tectonic slices overthrust to the east. The soles of the two largest slicesare represented by zones of talc-serpentine-chlorite schists up to 1.5 kilometers thick.
Mineralization is associated with serpentinites and serpentinized peridotite lenses sur-rounded by extensive belts of chlorite-tremolite-talc and talc-serpentine schists. Peridotiteis often altered to the "lizardite" form of serpentine. These are remnants of a once moreextensive and continuous ulframafic mass that was subjected to shearing and alteration.
There are at least 25 major bodies of serpentinite, in two groups, whose dimensions areknown roughly. One group consists of isometric lenses 0.5-1.5 kilometers long associatedwith gently-dipping thrust planes. Examples are the Dubicha, Monissa and VIa VIobodies. VIa DIo has dimensions of 1000 meters by 600 meters, and dips W75°. Kilta is950 meters by 300 meters. The second group consists of steeply-dipping elongated bodiesup to 6 kilometers long which follow steep dislocations. An example of this group is theKenticha body, which is 5.7 kilometers long.
On the surface the serpentinites are strongly weathered, leached and limonitized. Freshserpentinites contain less than 0.5% Ni and 0.05% Cr. There are three layers in theweathered zone: lateritic iron to ochre, now largely eroded; red clay with weatheredserpentine fragments; and weathered serpentinite not yet gone to clay (lowest layer). Thenickel is mostly in the second layer, and in the upper part of the altered serpentinite. TheVIa DIo, Kilta and Tula deposits are typical of the nickel deposits in the western align-ment of serpentinite bodies. At VIa VIo, grades range from 0.66% to 1.82% Ni, andfrom 0.28% to 0.79% Cr. According to reports, garnierite was identified. Thenickeliferous residual soils overlying the VIa VIo, Tula and Kilta serpentinite bodies are2.2, 5 and 6 meters thick, respectively.
No nickel sulfides have yet been discovered in the region. The secondary enrichment isattained during serpentinization and weathering by the breakdown of the crystallinelattices of olivineand pyroxene. Chromite is a commonaccessory. In the Budussamassif,chromite is in cumulate lenses up to 3 meters long by 0.2 meter thick. No economicconcentrations of chromite have been found.
Of interest is the discovery of the platinoid mineral siserskite (osmium 70%, iridium 30%)in heavy concentrates from the alluvium in the Demi Denissa River, a tributary of theBore River. The source has not been located, but the siserskite may be related to orderived from a talc-serpentine schist near the upper reaches of the Demi Denissa stream.
Of the known bodies, seven have been explored either by pits or boreholes, or both. Theresults of this work are tabulated below.
22
SECI'lONm. AnOIA GREENSTONEREGION
Figure 4Adola Region Nickel Reserves
Inferred
Grade%
1.33
1.60
1.52
1.20
1.28
1.20
1.38
TOTAL - 10,579,219
SOURCE:EthiopianInstituteof GeologicalSurveys.lCalculated.
The cutoff grades used in the above calculation were not consistent. Material grading0.5% to 0.8% Ni was either not considered or was improperly assessed.
The borehole gradeswere checked by digging 16 pits over 16 boreholes in the VIa VIodeposit and samplingthem. The borehole grades were consistently 7% lower than thecorresponding pits, e.g., a 1.38% Ni borehole was 1.47% Ni in the pit.
The reserve estimates from the earlier study may be low, for the following reasons:
· Borehole grades are consistentlylower than those obtained from pits;
· A large number of boreholes did not penetrate the total thickness of the deposits,stopping in the well-mineralizedzone;
· An insufficientnumber of holes were drilled in some cases, which did not allowfor contouring the zones on a grade basis for mining;
· A considerablepotential tonnagewas disregarded for insufficient information andlack of continuity;
· Study of the reserve calculations suggests that there may be more tonnage whenexploration is completed;
· There has been no drilling for the roots of the deposit below the lateritic mantle;
'\
23
Deposit Boreholes/Pits ReservesMetric Tons
Tula 27 boreholes 466,000
Via Vlo 138 boreholes 2,973,981
Lolotu 65 pits 817,000
BigDubicha 98 pits 1,573,452
Kenticha 386 boreholes 3,780,978
Small Dubicha 46 pits 783,999
Kilta ? pits/holes 260,000
SECI10N ID. ADOLA GREENSTONEREGION
· Only 7 of the 24 known serpentinite bodies have been partly examined; those 60kilometers to the west have not been studied.
The Monissa Guba body has also been explored by boreholes. High-grade ore, 3.1% to4.4% Ni, was found in well-weathered serpentinite but reserveswere not estimated.
Taking into account that very preliminary work on some of the bodies for which reserveshave not been calculated, has verified the presence of significant nickel grades, consider-able additional tonnage can be reasonably inferred to exist.
F. BOMBAWOHAKAOLINDEPOSIT (MAP 111-6)
This deposit is located between N06°04'40"-N06°05'00" and E38°45'50".E38°46'40". Themain road between Kibre Mengist and Awassa crosses the deposit. The deposit is nearthe contact zone of the Kenticha and Chakata formations, which are separated by anortherly-trending fault. The Kenticha formation (Middle Complex) is dominated bybiotite gneiss, containing amphibolite, garnet and staurolite schists, as well as marble.The upper part of the formation contains graphitic schists. The Chakata formation of theUpper Complex consists chiefly of amphibolite, chlorite and chlorite-actinolite schists andquartzites. The Chakata is confined to the north-trending Megado graben-syncline.
Post-tectonic granitic and quartz diorite intrusions, dominated by leucocratic granites andpegmatites, occur in the Adola Region. The general dip of the units is E300-35°. Raremetal-bearing pegmatites are considered to be associated with these intrusions andinjections. The upper parts of the pegmatites and the granitic gneiss have been kaolinized.
The Bombawoha deposit is located in a massif of highly-weathered granitic gneiss andcovers an area of 1.5 square kilometers. Exploration consisted of 78 pits, 34 trenches and2 boreholes, complemented by geological mapping. The grid that defined probable orewas 25-50 meters by 5-5 meters.
Two deposits have been defined, some 300 meters apart. Bombawoha I, the larger of thetwo, is composed ofkaolinized pegmatite and granitic gneiss, to a depth of 23-25 meters.The pegmatites are made up of strongly-kaolinized feldspar, quartz, mica and tourmaline.Bombawoha I trends east-northeast to northeast, and enters a highly-weathered mica-amphibole gneiss to the east. The width of the Bombawoha I pegmatite ranges from 20to 80 meters, and encloses a 20-meter-wide zone of red granite gneiss. It dips approxi-mately 580°. The Bombawoha II deposit trends north-northwest and is 4-6 meters wide.The wall rock is the same red granite gneiss. The pegmatite dips W80°.
The Bombawoha kaolin deposits are amenable to open-pit mining, and the mineralogicaland chemical characteristics are believed to meet the requirements of the ceramicsindustry. Details of the probable and inferred reserves of kaolin, and the averagechemical make-up of the ore and the kaolin are found in Figure 5.
24
SECTIONm. ADOLA GREENSTONEREGION
Figure 5Bombawoha Kaolinized Pegmatite
and Gneiss Reserves
ReserveCategory
ReservesMetric Tons
000
KaolinGrade
%
KaolinMetric Tons
000
BombawohaI
1. Probable 726.3
653.7
35.7
37.9
259.3
247.8-I
2. Inferred
BombawohaII,.....
Reserve
Category
3. Inferred
rBombawohaI
rI
1. Probable 67.6
67.0
20.0
20.6
0.94
0.89
2.22
2.442. Inferred
BombawohaII
rrr
3. Inferred 68.7 18.6 1.00 3.06....................................................................................................................................................................................................
r"
I-3. Inferred 48.7 34.2 0.86 2.09
SOURCE:Sabov,Y. V. et aI, "BombawohaKaolin and Kenticha Feldspar-Quartz Deposits";Ethiopian Institute of Geological Surveysinternal report,1985.
...,
-25
35.7 34.7 12.4
Si02 AI203 F03 CaO+ MgO+NO+ K20
% % % %
BombawohaI
1. Probable 47.2 35.0 0.93 1.69
2. Inferred 47.2 35.1 0.96 1.49
BombawohaII
N'"
6°13'NwCoMfoM
6°13'N
wCoMfoM
w\'""\'""°(I)M
L
.~.4{ t
f.f-
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5°09'N
123
CS:=J
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~ I:!!I1 I:~) (, ~I Axesofthe second orderfolds: 1. Anticli ne;2. Syncline2 >--<>-<
1 I'" , Axes of the third order folds: 1. Anticline; 2. Syncline2 ~....
I ~~~~~ I Paleogene lava flow
I:+:+~+I' Post-tectonic granite
I I
e
[IJ
Map 11I-1Diagrammatic Structural Map of
Adola Greenstone RegionScale 1:500,000
Upper Complex: Central Block (Megado graben-syncline)
Middle Complex: 1. Western Block; 2. Eastern Block - Mormorasub-block; 3. Eastern Block - Awata sub-block
NS-trending deep fault
Deep fault bordering the Megado graben-syncline
Diagonal fault
Axes of the first orde~folds: 1. Anticline; 2. Syncline
Gabbro and gabbro-amphibolite
Adola Magmatic SeriesUltrabasic rock
Subvolcanic intrusion
Dome of granite-gneiss
SOURCE:Shiferaw Demissie,Yu. Marchuk, V. Evdokimov. Summary ofthe Geology and Mineral Potential of the Adola Area. EMRDC,1987,p17-18. Based on Adola Gold Exploration Project data (1982).
zoooCO
zoC')oto
SOURCE:Senbeto Chewaka and M. J. de Wit
(editors). Plate Tectonics and Metallogenesis:Some Guidelines to Ethiopian Mineral Deposits,EIGS Bulletin No.2, July 1981, P 89.
27
\ / Cabafanca/,./
Map 11I-3Mineral Deposits/Occurrences
In Adola Greenstone Region
'~~Ie.:,
.:..----.'., PuJanto
L::-II
)
o 9 18
KIlometers(Scale Is approximate.)
6'30'N
~ River, stream
Road
6'OO'N
, Kabessa(NI)
Big Dubicha
I (Nj.Cr)
. Small Dubicha(Ni)
S'30'N
28S'OS'N
X Miningoperation
. Placergold
. Primary gold, Uttrama/ic bodies
. Town
, 1I IIIII
S04S'N
II
r JIIIIIIII
IIII
IWERSETIIIIIIIIIIIIIIII- '----
ULA-ULOS030'N
KAJIMm
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BURSAND/f!j
Map 11I-4Mapping and Exploration
Targets in AdolaGreenstone Region
r----t___J Geological Mapping 1: SO,000
EZ:) Geological Mapping 1: 2S, 000
G Follow-UpExplor~tion
S DetailedExplorationTargets
~ Lega Dembi Open Pit
o 2 4 6 8I I I I I I I I II I I I I Io 2 4
10km.J18mi
The boundaries and names shown on this map do not implyofficiel endcrsement or 8CC8ptatlCftby t1Ht United Nations.
r::L MARECHA
8 MoDI<:;ATI-DAWA
S01S'N
S"30'N
IIIIIIIIIIIIIIIIIS01S'N
38°4S'E
--------------------------------------39°00'E
SOURCE: Map No. 3656, United Nations,October 1991. 29
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Map 11I-5Geologic Map and Cross-Sectlon ofKentlcha Feldspar.Quartz Deposit,
Adola Greenstone Region
After Sabov ef a/. (1985)
C
o 50 100 150 200 250l I I 1_ t I
rc:cl~1J<11r+--:-+l~
~1m~[3]
.......... ....
~~
A
Meters
Serpentinite
Talc-tremolite -rocks
Granitoid
Pegmatite veins
Feldspar-quartz
Quartz-feldspar-muscovite
Kaolinlzed pegmatite
Fault
~ 7 'I',/'j,"<: <:filed'f"t,
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+ -r'" 4- 4- " ......r ... !-. -r ,.. 1""" 1-r
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A'
1800 m
1700m
1600 m
1500m
..
" /'
'-- ./
'-- /
,..
Mica amphibole gneiss,heavily weathered
,... x.....
/,.. /'
Granite-gneiss, yellowish-white, highly kaolinized
\(
"/
Kaolinized pegmatiteI - Deposit III - Deposit II
-
~ Granite-gneiss, red, highly~ weathered
m8b--c _._.
)I. ( ...
Contactsa - Observedb - Inferredc - At depth
Fault
Attitude
31
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....
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,......
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....
SECTION IV
AGERE MARYAM REGION ANDARERO GREENSTONE REGION
SECTION IV
AGERE MARYAM REGION ANDARERO GREENSTONE REGION
A. AGERE MARYAMREGION (MAPS IV-I TO IV-4)
The Agere Maryam area is some 260 kilometers southwest of the town of Kibre Mengist.A 1991 Ethiopian Institute of Geological Surveys report by Teferi Birru and E.P. Zhbanovsummarizes the work done in this area by a joint Ethio-Soviet program. Work includedregional and follow-up heavy concentrate geochemical surveys, regional and follow-uplithogeochemical surveys, and detailed geological prospecting and exploration in selectedparts of the area.
The heavy concentrate geochemical sUlveys found priorite, probably tantalaeschynite([Y,Ce,Ca][Ta,Ti,Nb]206)' carrying up to 5% Ta, in streams draining granosyenitic rocks,granites and aplites. The source of this mineralization was not located, but was hypothe-sized to be a large concealed subalkaline pluton underlying the roughly circular area of rareearth and rare metal anomalism. This anomalous area tends to run transverse to the
regional north-south to north-northeast structural grain. Anomalous samples were foundin Dega Burka, Lega Kiticha and Titu streams.
These surveys located gold anomalism along a north-south zone some 48 kilometers longby 4 kilometers wide. In the Ogo Basin the coarser gold grains are probably derived fromquartz veins, whereas the finer gold is from pyrite which is found as disseminations andstringers, predominantly in graphitic quartz-mica schists. Overall, the low-metamorphicgrade schists are the host for the gold in this basin.
During the regional lithogeochemical survey, tantalum dispersion trains were located overthe gneisses of the Buluka and Bore formations. The anomalism has associated Nb, Li, Sn,Pb and Mo. These, coupled with the high tantalum contrast between background andanomalous contents, suggest that they are related to rare earth mineralization, and hypo-thetically linked paragenetically to albitite apogranites formed by metasomatism (TeferiBirru and Zhbanov, 1991).
The regional survey defined four regional geochemical zones:
. The east-central part of the area is marked by anomalous amounts of the lithophileelements Ta, Nb, Be, Sn, W, and Bi. .These are located over a hypothesized, con-cealed granitic pluton, whose inferred location is in the crest of a northerly- strikinganticlinal fold which dips steeply to the west. Acidic metasomatism in this geochem-ical environment is indicated by faint greisenization and quartz-pegmatite veining inthe apical part.
. In the same general area as above, there is anomalismin As, Bi, and Pb. This is afavorable indication for gold-sulfidemineralization in the area.
32
SECTION IV. AGERE MARVAM REGION AND ARERO GREENSTONE REGION
. In the northwest, north and northeast portions of the area, there is anomalism inchalcophile (As, Bi and Pb), siderophile (Cu and Ni), and lithophile (Nb, Sn, W, andMn). These are attributed to both basaltic magmatism and the reactions of hydro-thermal solutions with crystalline basement rocks. It is inferred that this mineraliza-tion is epigenetic. The presence of arsenic and a high Au:Ag ratio suggest thepotential for gold-tellurium mineralization.
. In the western, southern and southeastern parts of the Agere Maryam area, anoma-lous amounts of both lithophile and chalcophile elements were found in the northernportions. In the southern portions the elements were predominantly chalcophilic. Ar-senic, bismuth and lead, found particularly in the northern sections, suggest thepotential for gold mineralization, probably related to deep-seated faults. Consideringthat Sn, Wand Bi anomalism is found in the southern portions, there is the possibilityof trace metals with superimposed Au-As- Bi mineralization.
Follow-up lithogeochemical sUlveys in the Ogo Basin showed anomalous concentrations ofAg, Bi, Pb, Sb, Li, Be, and Nb. These are related to quartz-sericite alteration on one hand,and to propylitization on the other. The Ag-Bi-Pb-Sb assemblage is related to the formeralteration type, and the Li-Be-Nb to the latter. The Ag-Bi-Pb-Sb group is considered apathfinder for gold in the area. Target areas indicated by these sUlveys are the following:Choricho-Kape-Kelaltu, Guduba, left side of the middle Ogo Basin, the Demi-Rufo areaand the Bekaka area.
Detailed work was done in the Choricho-Kape- Kelaltu area and the heavy concentratesdefined three centers of gold mineralization. (See Map IV-3.) The association of lead,copper and silver, as well as molybdenum and tin anomalism suggests that the gold isrelated to sulfides. The gold anomalism was in areas underlain by carbonate sedimentsenriched with sulfides, and in areas of silicified rocks with stringers of quartz. Hosts forthe gold are silicified quartzo-feldspathic, graphitic, quartz-mica and quartz-sericite schists.
Mineralization is believed to be confined within zones of silicification and stringers ofsulfide and quartz veinlets in these units. Resistivity data suggest that a mineralized bodyor zone is at least 100 to 150 meters below the surface.
In the Guduba area, a heavy concentrate geochemical surveyindicated three centers of goldmineralization. (See Map IV-4.) The conclusions drawn by the geologists involved are thesame as for the Choricho-Kape-Kelaltu area, except that the resistivity survey puts themineralized zone at not less than 150 to 200 meters below the surface.
Three areas containing placer gold were found in the Agere Maryam area and determinedto be suitable for small-scale mining operations:
. Most of the tributaries in the northern and central zones of the Ogo River Basin werefound to be gold-bearing. The northern zone of the basin is 8 kilometers long by 3.5kilometers wide. The central zone is 10 by 3.8 kilometers. The pay streaks in bothare thin and average about 0.1 grams of gold per cubic meter. Higher-grade portions
33
SECfION IV. AGERE MARYAM REGION AND ARERO GREENSTONE REGION
might be found by more detailed work. The Ogo River Basin is underlain bybasement rocks, probably biotite and amphibole-biotite gneisses.
· The Kape Valley is underlain by Tertiary basalts in its upper reaches and fresh-to-weathered basement in its middle and lower course. The basement rocks are quartzo-feldspathic gneiss, amphibole gneiss of the Buluka formation, and biotite-bearing,quartzo-feldspathic gneiss with subordinate amphibole schist, chlorite-mica schist andquartz-sericite schist. These are commonly cut by submeridionally striking quartzveins and veinlets, between 15 and 80 centimeters wide by a few meters long. Thebasement rocks have a northerly trend and dip moderately to steeply to the east.Occasionally the weathered rocks contain minor amounts of gold. Exploration in thisvalley was done on profiles of 200-600 meters. Pits were dug every 20-40 metersalong the profiles, and auger and Banka drillholes were put down on profiles passingthrough marshy parts of the area. Trenching was done to control the pit and drilldata. Geophysical methods were utilized to trace recent and old alluvial deposits.Placer gold was found restricted to the alluvial sediments of the flood plains and tocertain terrace levels. The valley-floor placer length is 2.9 kilometers, with an averagewidth of 67 meters. The wash (pay) grade was 0.742 grams of 950-fine gold per cubicmeter. A reseIVe of 174 kilograms of gold was calculated.
· The Kadida is a seasonal tributary of the Ogo River. It is underlain by basementbiotite gneiss and amphibole-biotite gneiss. The gneissosity trends northerly and dipsmoderately to the east. Pegmatites and quartz veinlets are commonly seen in thegneiss. Channel and flood-plain sediments are the only gold-bearing alluvials. Paystreaks in the gravels are found in the lower part of the river, and are 0.7 to 2.0meters thick and highly irregular. The placer is 2.2 kilometers long by 18 meterswide, with overburden between 0.0 and 3.5 meters thick. The pay-gravel to overbur-den ratio averages 0.6. ReseIVes were estimated to be 163 kilograms of gold frommaterial grading 100-5251 milligrams per cubic meter of material, averaging 4528milligrams per cubic meter.
B. ARERO GREENSTONEREGION (MAPSIV-I, IV-5 ANDIV-6)
The Arero Greenstone Region is some 100 kilometers south-southwest of the town ofKibre Mengist. It is the southern extension of the Adola Greenstone Belt. The work in
the Arero region was presented in the same report as the work in the Agere MaryamRegion (Teferi Birru and Zhbanov, 1991) and followed the same procedures, i.e., regionaland follow-up heavy concentrate surveys, regional and follow-up lithogeochemical sUIVeys,and detailed prospecting and exploration surveys in selected parts of the area.
The regional heavy concentrate work demonstrated that high gold contents were associatedwith high contents of pyrite. The auriferous pyrite occurs in metabasic and meta-ultramaficlithologies. Bismuth, tin and tungsten anomalies are confined to a northwest-trending zonewhich crosses the regional structure and lithologic trend. It was suggested that thisgranitophyllic-type mineralization is controlled by a northwest structure. It may be relatedto the localization of late subalkaline to acid intrusions.
34
SECI10N IV. AGERE MARYAM REGION AND ARERO GREENSTONE REGION
The conclusions drawn from this first phase of work were that there are three types ofmineralization. One type is gold related to pyrite-bearing metabasic and meta-ultrab asicrocks which are confined to two zones within a northwest-trending zone. The second typeis Cr-Co-Ni- V-(Pt?) related to meta-ultramafic rocks occurring along deep-seated faults orperhaps along a northeast-trending thrust zone. The third type contains Bi-Sn-W-(Nb?)related to intermediate-to-acid alkaline intrusions occurring as dikes and veins withinmetabasic to meta-ultramafic rock units. These are confined to a northwest-trendingmetallogenic zone discordant to the general regional geologic trend.
In the Okote area, the follow-up heavy concentrate surveys found that the anomalies wereconfined within the metabasics and the inner parts of the contact zones of the meta-ul-tramafic units. (See Map IV-6.) Here the units are enriched with syngenetic sulfides(pyrite). The inner parts of the contact zones of the meta-ultramafic bodies are typical ofcontact metasomatism, although silicification and chloritization are found as well. Quartzveins are the likely sources of the coarser gold found in the dispersion trains. The finergold is believed derived from either quartz veins or auriferous sulfides, or from the hydro-thermal and/or metasomatized alteration zones.
Nickel generally has the same dispersion train as cobalt and chromium. The stronger nickelanomalies follow the northeast-trending meta-ultramafic zone.
From the follow-up survey it was concluded that there are three types of mineralization inthe general Arero area. One type is hydrothermal (or metasomatic) gold in quartz veinsand alteration zones. Silicification zones in metabasics and contact zones in metaultramafics
are seen at Kelensa-Ebicha, Okote and Wondimu-Ibrahim. The second type is the mag-matic Cr, Co and Ni mineralization in the meta-ultramafic suite of rocks along thenortheast thrust or deep-seated fault zone. The third type is the W, Mo, Sn, and Bi ingranitic massifs.
The lithogeochemical surveys resulted in dividing the Arero area broadly into east and westgeochemical blocks, separated by a thrust or deep-seated fault zone. The east block ischaracterized by acidic intrusions, and the west block by metabasics and metaultramaficsintruded by basic and acidic dikes, pegmatites and quartz veins.
It was concluded that in the two regional geochemical zones of the eastern block, concen-trations of Mo, Sr, Bi, Li, Nb, and Zn are genetically related to two granitic massifs in thearea. The greisenized and albitized portions of the massifs that have not suffered greatlyfrom erosion are the most favorable geochemical sites for mineralization of trace and raremetals.
In the western block, two geochemical zones with concentrations of Mo, Sn, Be, Nb, andZn are genetically related to small intrusions of plagiogranites, granodiorites and pegmatitedikes, while Cu, Co and Ni are related to ultramafic units. Anomalous concentrations ofAg, Bi and Pb are related to auriferous quartz veins and wall-rock alteration zones of thehost basic and ultramafic rocks. Therefore, the western block was considered favorable for
35
SECTION IV. AGERE MARVAM REGION AND ARERO GREENSTONE REGION
hydrothermal auriferous sulfides and magmatic Co, Ni, and perhaps Pt mineralization.
Follow-up work in the Okote area found that anomalous Pb, Mo and Sn are found instream sediments derived from the basic and ultramafic rock units (Chekata formation),and are indicators for gold mineralization. Anomalous Be and Bi in stream sediments arederived from granites and the AfIata formation. These may indicate trace and rare elementmineralization.
The Okote area is underlain by the Chekata formation. Numerous quartz veins andveinlets were found during detailed exploration. Hydrothermal alteration, i.e., silicificationand calcitization, is characteristic in the area. The heavy concentrate survey indicated threecenters of mineralization. In the litho-geochemical survey, pyrite samples gave from 0.3 to20.0 ppm Au. The conclusion was reached that the gold is related to disseminated pyritein silicified host rocks and quartz veins. In the Ebicha zone, in the northern part of thearea, the Chekata formation is composed of schists and amphibolites. Silicification ispronounced, especially in the amphibolites.
Placer gold possibilities were investigated along one part of the valley of the BUljiji River,a tributary of the Dawa River. It was explored along a 5-kilometer stretch, by profiles at200-800 meter intervals, with 40 to 60 meters between pits. The width of the valley wasbetween 20 and 30 meters. The gold distribution was irregular and the auriferous gravelsdiscontinuous. For these reasons only an approximate estimation of reserves was possible,of some 163 kilograms of gold.
The Burjiji Valley is underlain by units of the Chekata and Aflata formations, includingamphibolites, chlorite-epidote schist, chlorite-actinolite schist, talc-tremolite schists, andbiotite-amphibole gneiss and biotite gneiss. Schistosity is northeast-striking, dippingmoderately to the northwest. The units are intruded by quartz veins and veinlets, as wellas by aplitic and granitic dikes. Silicification, chloritization and calcitization are commonlynoted.
c. SUMMARY
1. PRIMARYGOLD POSSIBILITIES
Gold mineralization is confined to north and northwest-trending belts in AgereMaryam and Arero, respectively. The auriferous belt of Agere Maryam is mainlyconfined to rocks of the Buluka formation that have undergone hydrothermal-metasomatic alteration, i.e., silicification, sericitization, chloritization, fuchsitization,carbonatization and pyritization. The auriferous belt of Arero is mainly confined torocks of the Chakata formation which have undergone hydrothermal alteration, suchas silicification, carbonatization and pyritization.
2. NICKEL, PLATINUM,CHROMIUM, COBALT,COPPER, VANADIUM
Anomalous amounts of these minerals are found chiefly in the Arero area. Theassociations of anomalies in these elements are confined to a meta-ultramafic massif
36
SECTION IV. AGERE MARYAM REGION AND ARERO GREENSTONE REGION
some 4 kilometers wide and 18 kilometers long. It was probably emplaced along adeep-seated fault or thrust zone. There appears to be a zonal pattern to the metaldistribution. Cobalt and nickel are confined to the serpentinized core; chromium isconcentrated in the inner part of the contact zone of the massif; vanadium is foundin both inner and outer parts of the contact zone.
3. MOLYBDENUM,BISMUTH,TIN,TUNGSTEN
The occurrence of mineralization of these metals is mainly related to pegmatitic,granitic and aplitic dikes, as well as to quartz veins. This granitophyllic suite/zonepartly overlaps the Arero auriferous belt. The relationship of the two is not known,but the granitophyllic suite is assumed to be related to late tectono-magmatic activity.
4. RAREEARTHAND RAREMETALS
Conspicuous dispersion trains of priorite, xenotime, and monazite are found in thesoutheast part of the Agere Maryam area. The priorite, by X-ray analysis, containedup to 5% Ta and 11% U. The zone containing priorite and xenotime in AgereMaI)'am is roughly circular and is associated with either a concealed granitic plutonor U-bearing granitic pegmatites and albitites.
37
Map IV-1Location Map of Agere Maryam Region
and Arero Greenstone Region
o 25 50 75 100 125
Kilometers
I' Add" Ababa. Awasa
Kibre Mengist
Dila \
Agere \ Maryam
Yabelo."-..- - . '"". ....--
Arero
1 - Agere Maryam Region
2 - Arero Greenstone Region
38
39
Map 1V-2Mineral and Anomalous Areas in
Age... Maryam RegionAfter Telerl Birru and E. Zhbanov (1991)
\\-
Aurifelous beft (Au occurring in quaru veinsend pyrit. hosted by smofied grephitebeering QUORZ ,.schisI, auanz.sericit.__~lic;schisQMetanogen;czone 01 metels (perhaps_lOled with_ _ plutonsend_tites)Auriferous %ones
I Nonhemn Controlm SouIhem
TOM!
AI_108II
_or_GeochemCei enometies
AI Prim8rygold -Ct>oridto (See Mop 1V-3)~ Prim8rygold. Kepehe. ..KJ Prim8ry;".J -K_ AreaM Prim8rygold . G_ _. (See MapIV..)A5 Prim8rygold -I.en bank 01Ogo heaA8 Prim8ry gold . [)em;.Rulo__A7 Prlmarygold'__M . Prim8rygoldA9 Y1trium.cerium.__A10 Primary goldAll_e._A12 MolybdenumA13_e._A1. Priorite.xenotineA1s Prim8rygoldA18 Prim8rygold
~ M_.' OccurTencesB1 Chrysotile. asbeslosB2 Graphite in graphite be8ring quartZ.
_schistB3 CIvysotiIeasbes10sB4 SameasB2_Bs Chfysotile asbeStosBe MoS, in pegrnelitesB7 Muscovit. in pegmalrtesBe Euxenite in _litesag PenUandileend pyrmotite ...
unr fierockSB10 _.in_lites811 ~ in QU8IZiIe
Map IV-3Gold Occurrences and Anomalous Areas in
Choricho-Kape-Kelaltu Area (A1-A3on Map IV-2)Agere Maryam Region
After Teferi Birru and E. Zhbanov (1991)
o 100 200 300 400 500
Meters
Choricho Area
Kape Area
!.I.INMGo-ocoM
......
......
...
Ag, Mo',Pb,Sn \
II
....,..-~-
Kelaltu Area
o
1I
~I 0Co-ocoM
,40
Geochemical anomalous zone ofsilver, lead, molybdenum and tin
. Gold-bearing heavy concentrate
o High content of gold in bedrock,fire assay analysis
Ag-Pb-Mo-Sn
5°37'17.N-uJ
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~ ',/ \
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kMO \~ I
( I, '\ ,/\ "\ /, /, " "--
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Map IV-4Gold Occurrences and Anomalous Areas in
Guduba Area (A4 on Map IV-2),
Agere Maryam RegionAfter Teferi Birru and E. Zhbanov (1991)
o 100 200 300 400 500I I I I I I
Meters
---I" ... Geochemical anomalous zone of silver," _ _ .; I lead, molybdenum, tin, copper and vanadium. Gold-bearing heavy concentrate
5°34'03"N /7 Cu-Pb./ ~- /
( ./, ./,-
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./ :,. y'. Oulline 01 geochemlcel anomelie.
Observed MineralOccurrencesBI Au In quartz vein. in
amphibolite.Au in quartz veins and pyriteIn amphibolita and laic-"emolita-actinoliteschisthostsMalachite showings inmetabasic lithologic unit.Bismulhinile In acidic dikesChromlte and nalive coppar Inacidic dikesChromilile in meta.ultramaf,clitholgic units
"
Geochemical AnomalieaAI Primary gold1>2 PrimarygoldA3 Prlmery gold . Kelense.Eblcha
Area .Primary gold -Ok ole Area(See Mep IV-S)Primary gold - Wondimu-IbrehimAreaCr,Co,NICr.VCr,VCr,Co, Ni,V,CuCo,NiCo.NI8I,WBi,Sn,W81,Sn, WBi,Sn,WBi,W8I.W81,Nb81,SnWSn,Nb81,Sn. NbSn,8I
B6
B2
A4B3
ASB4B5AS
A7ASA9A10AllA12A13A14A15AISA17AISA191>201>21A22A23
wMI/)10M
42
\'\
( ', )\ I
. \" ) t,.',.-"
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u.(
,< y/y
0,/
/" ";-/' .Y',,'. Oulline 01 geochemlcel anomelie.
Observed MinerelOccurrencesBI Au In quartz veins in
amphibolite.Au in quartz veins and py,ilaIn arnphibolila and laic-"emolita-actinoliteschisthostsMalachile showings inmelabasic lithologic unit.Bismulhinile in acidicdikesChromlte and nalivecoppa' Inacidic dikesChromilile in meta,ultramaf,clitholgic units
"
Geochemical AnomaliesAI Primary gold1>2 P,imarygoldA:J Prlmery gold . Kelense.Eblcha
Area 'Primary gold -Okole Area(See Map tV-S)Primary gold. Wondimu.Ibrahim AreaC"Co,NIC',VC',VC" Co, Ni, V, CuCo.N!Co.N!BI,WBi,Sn,WBI, Sn, WBi,Sn,WBi,WBI,WBI, NbBI, SnWSn,NbBI, Sn, NbSn, BI
B6
B2
A4B3
ASB4B5A6
A7A6ADAIOAllAI2A13A14A15AISAl7AISAle1>201>21A22A23
wi->..10..
42
. Gold-bearing heavy concentrate
o Gold-bearing quartz vein on panningand/or fire assay analysis
O Gold-bearing pyrite on panningand/or fire assay analyses '
43
Map IV-6Gold Occurrences In Okote Area (A4 on Map IV-5),
Arero Greenstone RegionAfterTeferiBirruand E.Zhbanov(1991)
o 100 200 300 400 500I I__~ I I I
SECTION V
MOYALE GREENSTONE REGION
SECTION V
MOYALE GREENSTONE REGION
The Moyale Greenstone Region is in southern Ethiopia, on the border with Kenya. Owing toits location almost due south of the Adola Greenstone Belt and to similar lithologies, it isconsidered to be a southern extension of the Adola Greenstone Belt.
Exploration is currently in progress in the Moyale region but the results of this work are notyet available. Two areas in this region are discussed below: an area near the border town ofMoyale, and the Hassamte-Haramsam area east of Moyale Town.
A. MOYALE TOWN AREA (MAP V-I)
This area is about 2 kilometers north-northeast of Moyale Town, and is bounded byN03°33'09"to N03°34'14" and E39°03'02" to E39°04'18". The geology of the area isrelatively simple. A metagranodiorite (orthogneiss) batholithic body underlies the area.It is in tectonic contact with basic to ultramafic rocks on the east and on the west
(Solomon et al. 1991). It is cut by two long, north-south trending metagranite sills,whichare between 4 and 8 meters thick. Other lithologies consist of quartz veins, aplites andpegmatites. For the most part, the latter two follow the northerly-striking foliation of theorthogneiss (Amanuel et al. 1991). The pegmatites tend to be massive and gar-net-bearing.
There are many quartz veins in the area. They have three general orientations: north-south (following the general foliation), N35°.700E, and N800W. The quartz veins parallel-ing the foliation are 300 to 350 meters long and dip to the west. They are up to 3 meterswide, and pinch and swell along strike (Amanuel et al. 1991).
The veins that strike northeasterly have a limited strike length of 70 to 80 meters and aN40°.700W dip, and range from 25 to 40 centimeters in width. These generally form anen echelon pattern and characteristically contain galena along with free gold (Amanuelet al. 1991). This vein system was discovered by trenching, as the structures are coveredby soil and erosional debris.
The N800W-striking quartz lode has a strike length of 80 to 85 meters, dips N75°-80° andvaries between 16 and 20 centimeters in width. Free gold is present in this lode, as wellas pyrite and chalcopyrite, but galena is scarce (Amanuel et al. 1991).
At least 10 of these discordant veins have been uncovered by trenching, and the assump-tion is that there are more. They are clustered in the southwest quadrant of the area.The mineralization is of two types: gold-sulfide in quartz, and gold-quartz without or withvery minor sulfide (Amanuel et al., 1991). The gold-sulfide quartz veins are characterizedby appreciable lead, copper, zinc and pyrite. This mineralization is in the discordant veinsthat are essentially en echelon gash veins within conjugate shear planes (Amanuel et al.1991). The gold is largely free, both visible to the naked eye and in panned concentrates
44
SECTION V. MOYALEGREENSTONE REGION
of the crushed vein material. The low-sulfide gold-quartz veins and veinlets are concor-dant with the foliation and have subvertical dips. Their gold content is low.
The quartz vein rock chipsamplesare numbered on Map V-I. The fire assay results ofthe quartz veins chip samplesare tabulated below.
Figure 6
Fire Assay Analyses of Rock Chip Samples fromQuartz Veins NNE of Moyale Town
(Locations shown on Map V-I)
45
Vein Fire Assay GoldSample Sample ppm
MC9 MC-9 0.5
MC35 MC-35 <0.1
MC 41-43 MC-41 5.0
MC-42 21.0
MC-43 54.5
MC45 MC-45 2.2
MC 53-56 MC-53 9.0
MC-54 0.3
MC-55 0.2
MC-56 <0.1
MC59 MC-59 29.0
MC 62-64A MC-62
MC-63 0.2
MC-64a 8.5
MC65 MC-65 22.8
MC76 MC-76 14.0
SOURCE:Amanuel,Kassahun, Tesfaye and Tewolde (1991).ppm: parts per million.
SEcrION V. MOYALEGREENSTONEREGION
B. HASSAMTE-IlARAMSAMAREA(MAP V-2)
This area of 170 square kilometers is located east of the town of Moyale, within thefollowing geographical coordinates: N03<>J4'00"to N03<>J7'OO",E39003'00"to E39°15'00".
The rocks are metagranodiorite, amphibolite, amphibolitic gabbro, gametiferousgabbro, banded amphibolite, and chlorite amphibolite schist. Four stages of deforma-tion have been determined. The report on this area implies that high-grade metamor-phic effects have been retrograded to amphibolite and greenschist facies (Tolessa Shagiand Tefera Eshete, 1991). The same source states that the mineralization in the areais related to quartz-vein-filling of fractures related to shearing.
The amphibolitic lithologies are often interlayered with serpentinite and talcose rock.Gneissosity is developed in the south. There are narrow horizons of biotite-muscovite-quartzo-feldspathic schist. In the northern part of the area, very thin graphite schistis commonly interlayered and a small bed of crystalline limestone is also found in thesame general area. The banded amphibolite shows gneissosity on a 1-2 centimeterscale. There are many narrow horizons of talc-serpentine and amphiboliticmeta-ultramafics. Pegmatite veins are commonly seen in the Hassamte gabbro.
Quartz veins are sugary-textured, and are en echelon in the deformed granodiorite.They are 10 to 30 centimeters wide and contain galena along with some chalcopyriteand pyrite. The gold-bearing veins strike N45°-700E,whereas the barren quartz veinsstrike N200-500W in the granodiorite. Veins in the Haramsam amphibolite and in theschists are laminated and reddish-brown in color. Some are gold-bearing. These veinsare common and generally closely-spaced. They are associated with extensive shearzones.
The Hassamte veins are gray to white, massive, with voids after leached pyrite crystals.These massive quartz veins contain chalcopyrite, bornite and malachite. The 2-3centimeter-wide veinlets of this type are frequently observed within parts of themassive gabbro. The structures indicate a sinistral sense of movement. The shearzones in granodiorite trend N45°W. One of these is 60 meters wide and over 3kilometers long. Shears in the amphibolite and the Hassamte gabbro show a sinistralsense of movement, strike north-south and N800E, are 20-50 meters wide, and severalkilometers long.
Veins are of two general types. One is within the early S-foliations, and the other isat right angles to the S-foliation. In the granodiorite, concordant veins, parallel to thefoliation, strike north-northwest. The discordant veins are commonly discontinuous -N600W, n~rth to northeast and N300W - and are interpreted as extension gash veins,oblique shear veins and parallel shear veins .
Placer gold is extensive along the Satiche River and other tributaries of Haramsamstream (Ayele et al. 1991). Its occurrence appears restricted to areas underlain byhighly-shearedamphibolite. Placerthickness isvariable,the maximumbeing2.5meters
46
SECTION V. MOYALE GREENSTONE REGION
along the Satiche stream course. Here the angularity of the rock fragments and of thegold suggests a nearby source, probably amphibolite and quartz veins (Ayele et al.1991).
Primary gold is found in both amphibolite and granodiorite. There are differentgenerations of quartz veins with visible and invisible gold. The most prominent arequartz veins filling extensive gash fractures of the shear zone in the granodiorite. Mostof these are less than 50 centimeters wide. In the amphibolite, limonitized and stainedquartz veins contain visible and invisible gold. The intensely sheared part of theamphibolite contains fine, disseminated pyrite and chalcopyrite mineralization.
The zone is 20 to 30 meters wide and more than 400 meters long (Tolessa Shagi andTefera Eshete, 1991). It is greenschist facies through the retrogressive process ofdiaphthoresis. Rock samples of this zone returned 0.2 to 0.3 grams Au per metric ton.The intensity of mineralization is related to the intensity of alteration and shear-zonefracturing. The mineralization, therefore, could be epigenetic. Disseminated sulfidesare detected in the fresh Hassamte gabbro and surrounding amphibolite. Quartz floatwith sulfides and gold are found in the central part of the gabbro (Abnet et al, 1989).Crushing and panning the coarser pyite has revealed gold. Thus there are two typesof gold occurrence: one is within the pyrite crystals, and the other is gold depositionwithin zones of weakness related to shearing, i.e., the parallel and oblique fractures inthe gabbro.
47
Map V-1Auriferous Quartz Veins NNE of Moyale Town,
Moyale Greenstone RegionAfter Amanuel et al. (1991)
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Gold Occurrences In Hassamte.Haramsam Area,. Mayale Greenstone Region
After 10lessl Shag I and 1efera Esbale (1991)
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SECTION VI
WESTERN GREENSTONE REGION
SECTION VI
WESTERN GREENSTONE REGION
The Western Greenstone Belt lies between N8OJO'-12~O'and E34°10'-36OJO'.(See Maps VI-lto VI-5.) The predominant lithologies of the Western belt are chlorite, sericite and graphiticschists, phyllites, quartzites, and andesitic to rhyolitic volcanics. Iron-bearing quartzites andintraformational conglomerates are also present. The metamorphic grade is no higher thanupper greenschistto lower amphibolite facies, but commonlydoes not exceed lower greenschistfacies. Uralitized andesites and diabases, tuffaceous slates and graywackesdominate near theSudanese border.
The area is underlain by a plutonic basement of metadiorite-granodiorite, unconformably over-lain by the metavolcanic-metasedimentary sequence of the Late Proterozoic Tsaliet Group.Continuous volcanic and plutonic activity during rapid sedimentation is indicated by (1) thepresence of intermediate to silicic metavolcanics (andesitic, dacitic, rhyolitic), tuffs, lapilli tuffs,agglomerates and a vast amount of volcanoclastics, and (2) the presence of late-magmaticblue-quartz porphyries.
The metasediments overlie the metavolcanics and volcano-sediments; the conglomerates are mostcommonly found lying on the basement. There are infrequent calcareous rocks, ranging frompure marbles to thin-banded calcareous phyllites. A borehole at the Kata prospect showed themarble there to be heavily mineralized with chalcopyrite, pyrite and magnetite, though nomineralization. was noted at the surface. Both the greenschist metavolcanics and the meta-sediments may show disseminated mineralization.
A narrow belt of meta-ultramafics stretches from Yubdo to north of Gimbi in the southeastern
part of the Western Greenstone Belt.
Although various regional studies havebeen made in this region, as well as some more detailedwork in selected areas, it is relativelyunexplored along itstotal length. A number of mineralizedareas have been located, however, and these are described below.
A. GOLD AND BASE METALS
1. AZALE-AKENDAYU GOLD AND BASE METAL AREA
This area is 22 kilometers southeast of the town of Kurmuk. Proterozoic su-
pra-crustal rocks lie in a V-shaped inlier, infolded between Early Proterozoicgneisses to the west and an intrusive granite to the east. The major lithologic unitsinclude amphibolite, andesitic metavolcanics, metasedimentary schists, and smallintrusions. The metasediments include various compositions of quartzites(quartz-chlorite and chloritic quartzites), talc and amphibole schists. The unitsshow low-grade metamorphism and are aligned in a north east-southwest direction.North-northeast-trending faults, bounding the ridge on both sides, are the promi-nent structural features. Microfolds are commonly found in the area. Thevolcano-sedimentary pile tapers to the south and thickens toward the north.
50
SECTION VI. WESTERN GREENSTONEREGION
Mineralization is of two types: gold mineralization in the gossans and ferruginousquartzites of the Azale Ridge, and sulfide mineralization (pyrite, chalcopyrite, andthe oxidation products malachite and azurite) associated with the gossanous bodiesin the ferruginous quartzite zone. The geochemical work identified four anomaliesclosely associated with the gossaniferous metasediments (quartzites) and theircontacts with other rock types. AUthe anomalies trend about N15°E, parallel withthe generallithogic alignment. Copper appears to be dominant in the south; leadand zinc increase toward the north.
Soil geochemical results showed the following ranges of values: copper 5-3000ppm, lead 3-800 ppm, and zinc, for which 28% of the analyses were above thedetection limit of 6000 ppm and ranged up to 6100 ppm.
An induced polarization-resistivity survey showed high charge ability associated withthe metasediments, increasing with depth. The study strongly suggested that theAzale-Akendayu Ridge is mineralized. The gossaniferous material contains copperand gold, and the mineralization appears to be a base metal type containing gold.
2. ASHASHIREGOLD ANDBASEMETAL AREA
The Ashashire area is at NI0~9'32", E34~'34". The country-rocks of the areaare metavo1canics, metasediments, ultramafics, and granitoids of dioritic to graniticcomposition. The metavolcanics predominate, and include basic, andesitic andquartzcalcite-chlorite schists. The metasediments are conglomerate, slate, gray-wacke, quartz-sericite schist, chlorite-calcite-quartz schist, with cherts occurring inall parts of the area. The ultramafics are peridotite, dunite, pyroxenite, andhomblendite, with disseminated chromite and magnetite. The structural trend isnorth to north-northeast. Crossfaulting trends are west-northwest and east-north-east.
Mineralization is confined mainly to the metavolcanic and metasedimentary rocks.Gold is associated with disseminated sulfides, pyrite and chalcopyrite, and withbipyramidal magnetite. The bipyramidal magnetite is associated chiefly withferruginous quartz-sericite- (::!:chlorite) schist, and occasionally with granite anddiorite.
Alluvial gold is found southwest of the subject area, along Ashashire River andDul creek. Hematite and magnetite bodies are widely distributed in the form ofisolated lenses, beds and large irregular masses. Nickel and cobalt geochemicalanomalies are, in most cases, related to the meta-ultramafics. Geochemical studiesshowed the presence of copper, zinc, nickel, cobalt, lead and silver anomalies. Thecopper-lead-zinc anomalies are associated with metavolcanics and metasdiments.
The mineralization is apparently controlled by lithological and structural features.
51
SECTION VI. WESTERN GREENSTONEREGION
3. BOKA-DALEITI-BINDAKOROAREA
This area is between N9°55'OO''-10011'18''and E35oo7'33"-35°16'53". Geologicallyit is made up of greenschist facies metasediments and metavolcanics, locallyreaching to the amphibolite facies. The metasediments include marble, dolomarble,calcarenite schist, and quartz-hornblende schist, intercalated with carbonates andbiotite-garnet-staurolite-anthophyllite-cordierite-sillimanite schist. The metavol-canics are divided into intermediate to basic amphibolite and greenstones. Thelatter are greenschists, muscovite-quartz schist, meta-rhyolite, dacite and acidictuffaceous schists.
Mineralization in the area consists of sulfides, primary and placer gold, iron, andindustrial minerals such as marble and dolomarble. Primary gold is associated withveins and veinlets. The alluvial gold occurs as fine, irregular-shaped flakes,suggesting that the primary source is probably nearby. The primary gold appearsto be concentrated along specific zones in the quartz veins in metacalcareous hostrock. South-southwest of Daletti Village, sulfides occur within the biotite-gamet-staurolite-anthophyllite-cordierite-sillimanite schist.
Iron is concentrated in three localities. West of Daletti Village, hematite-magne-tite-ilmenomagnetite occurs; southeast of Indako Hill, iron occurs as a concentra-tion of hematite associated with calcareous metasedimentary rocks; and in the flatarea of the eastern border of the area, iron occurs as hematite-bearing chert incalcarenitic sediments. The iron showings seem to have a volcanogenic origin.Primary gold is associated with quartz veins and veinlets.
4. ODA-GODEREGOLD ANDBASEMETAL PROSPECT (MAP VI-2)
The Oda-Godere area is between NlOo14'50''-10016'52'' and E35OO6'05"-35OO8'01".It is located east of the Dabus River and some 75 kilometers north of the town of
Mendi. The area is underlain by metamorphosed volcano-sedimentary sequencesof Late Proterozoic age, later covered by Tertiary basalts and intruded by younggranitic bodies. The metavolcanics include metabasalts, chlorite schists and acidictuffaceous schists. The metasediments are marble, phyllite, quartzite, quartz--feldspar-chlorite schists, and brecciated and silicified rocks. They have a generalnortherly strike with steep dips. Two fault systems are seen in the area, trendingnorth-south and east-west.
Early studies indicated the presence of gold and some sulfides. Later studiesidentified pyrite, chalcopyrite, bornite, malachite and azurite. Chalcopyrite andpyrite occur in quartz veins and veinlets. Induced polarization sUlVeysoutlinedinteresting values of charge ability, interpreted as zones of probable mineralization.These zones correspond to brecciated and silicified zones at the contact betweenmarble and metabasalts.
Gold is concentrated within zones containing quartz veinlets with associated sulfidemineralization. Most of the geochemical anomalism appears to be associated with
52
SECTION VI. WESTERN GREENSTONEREGION
the marble, the metabasalts, and the alteration zones of brecciated and silicifiedrock. Lead and barium anomalies are confined to the eastern part of the area.A peak barium value of 3500 ppm is probably related to barite-bearing faults.One quartz vein, mineralized with chalcopyrite and pyrite has been traced for 400meters. It strikes N12°E and dips W60°. Its width varies between 0.30 and 3.0meters.
Mineralization is of the copper-gold-baritetype and the barium-polymetallictype.The latter suggestsa late-phase introduction of sulfidesand precious metals. Thepresence of massivevolcanogenic (Kuroko-type) sulfidesis a possibility.
5. MOUNT DULGOLD AND BASEMETALAREA
This area of 16 square kilometers is located between N10ozg'30".10OJ6'06" andE34OZ2'58"-34OZ4'35".Mount Dul is underlain by alternating volcano-sedimentarysequences dominated by metavolcanics, ultramafic bodies, metagranites andswarms of quartz veins and veinlets. The metavolcanics consist of meta-andesite,dacite and metabasalt. The metasediments are metaconglomerates, various typesof phyllites, chert and marble. The ultramafics include serpentinite, talc schist andhomblendite.
Geologists have defined the deformational events which resulted in the structuralfeatures noted in the area: foliation, folding, shearing and probable thrustingphenomena. The foliation trend generally north-south to north-northeast. TheS-folds have a steeply-plunging axis and are associated with shear zones having asinistral sense of movement.
The presence of primary gold and base metal mineralization was confirmed byfield obselVationand chemical analyses. Placer goldis also present on the slopesof and below Mount Dul. The free gold occurs in quartz veins and veinlets, inchert, metaquartzites and other metasediments. Disseminated gold is foundassociated with sulfidesin andesitic and metasedimentary rocks. Sulfide mineral-ization consistsof pyrite and chalcopyrite,and the oxidation products malachiteand azurite. The sulfidesare associatedwith metavolcanics,metasediments, quartzveins, and cherts.
Geochemical studies of soil and rock have been made. Anomalies of gold, arsenic,tungsten, silver and cobalt were delineated over the greenschists. Nickel waspresent as well. The cobalt was anomalous over the ultramafics. Rock-chipsamples showed that primary gold is associated with altered meta-andesite (mostsignificant), quartz veins and veinlets, ferruginous cherts, geenschist, metabasaltand phyllite (least significant). The gold mineralization is structurally controlled,but has a close association with volcano- sedimentary units, in a possible stockworkarrangement. Geologists and mining engineers with experience in the areaconsider the gold mineralization to be epigenetic and associated with a wide zoneof hydrothermal alteration.
53
SECTIONVI. WESTERN GREENSTONEREGION
6. ONDONOK GOLD PROSPECT
This prospect is located at NI0~0'00", E35OO0'00",some 55 kilometers northeastof the town of Asosa. Since thick overburden covers large portions of the area,the rock boundaries are largely speculative. The presumed oldest units are metav-olcanics and metasediments, chiefly greenstones, greenschists, and chloritic orsericitic phyllites. These are intruded by a deeply weathered metadiorite. Amedium-grained micaceous granite is believed to be post-tectonic. The quartzveining is believed related to this late granite. The veins strike generallywest-northwest or north, and dip to the west. They appear from the mapping tobe in the metadiorite and metavolcanics, crossing the north-northeaststrikingcontact.
Primary gold has been obseIVed in gently dipping quartz veins and lenses.Accessory minerals are tourmaline and siderite, with rare pyrite and chalcopyrite.There are three major veins, numbered 18, 19 and 20. Veins 18 and 19 weretested by an Italian mining group in the late 1930s. Vein 18 was studied byunderground drifts and winzes to 55 meters depth. It was traced on the surface for800 meters and examined intermittently over a length of 1200 meters. Some 450meters of tunneling, 170 meters of shafts and winzes, and some 150 meters ofpitting are reported to have been done. Work in depth stopped due to encounter-ing the water table and to the fact that the values were uneconomic at the 1930sgold price.
Ondonok was re-examined during 1975-1976by EIGS and UNDP personnel. Theaverage gold content was estimated to be 5 glmt, with the highest values being 8-9 glmt. Reported vein thicknesses averaged 0.50 meter, with gold values from 1-2glmt to 30-40 glmt.
7. TULU KAMI
Located 4.5 kilometers east of Nejo. Gold-bearing quartz veins occur inamphibolite schistson Tulu Kami and Lega Gimbi hills. Explorationwas accom-plished for 60 meters along strike and up to 80 glmt were indicated from theoxidized zone.
8. ME'ITI
Located in the Metti Valley, near the junction with the Birbir River. Auriferouspyrite associated with quartz veins in greenschist was reported.
9. LEGA BAGUDA
Located 4 to 8 kilometers southeast of Yubdo. Quartz inclusions rich in gold werereported in diorite or dioritic orthogneiss.
54
SECTION VI. WESTERN GREENSTONE REGION
10. CHOKORSA
Located 20 kilometers southeast of Nejo. Exploration operations were carried outin the past along quartz veins containing free gold.
11. TULU KAPI AND ANKORI
Located some 15 kilometers northeast of Yubdo. Quartz inclusions containingauriferous pyrite and chalcopyrite within schists, were reported from both areas.At Ankori the mineralization is in fine-grained diorite and the many quartz veinsoutcropping on the hillsides. At Tulu Kapi (UNDP Mineral SUlVeyProject, 1972),one of the three diamond drill holes, cut 24.7 grams Au per metric ton, 19.85grams Ag per metric ton, and 0.6% As between 69.3 and 71.5 feet. The core wassyenitic, cut by quartz veins containing pyrite and arsenopyrite, and micropegmat-itic veins, in which the higher gold values occurred.
12. KATA (MAP VI-3)
Located 7 kilometers east of Nejo. In one of three adits, talcose chloritic andcarbonate schists were reported. No gold analyses are available, however. Floatof blue-quartz porphyry is found on the hill above the granodiorite east of theKata 3 target. Up to 550 ppm Cu was reported from this area, which coincidedwith a well-defined, elliptical, deep-seated (150 meters) induced polarizationanomaly. The induced polarization high coincides with rocks of low conductivity,probably plutonics. The Kata 2 target contains mineralization along the deformedinterface between plutonic rocks and the metasediments. .
13. BOMU MENGHI
Primary gold has been reported near the old Bomu Village in the Bomu-Menghiarea between Asosa and Gizen.
14. BASCIA
Located 25 kilometers southeast of Asosa. A number of years ago, a Germangroup worked auriferousveins here and erected a stamp mill for gold recovery.No records of this operation are available.
15. GAMBELA MOUNTAIN
Located near the border with the Sudan, Gambela Mountain has long beenconsidered the source of the alluvial gold found in the rivers of the region.
16. GUBA, DURA ABELLI DRAINAGE, BELES DRAINAGE, ABUMARE,ABTESELO, MEKEZEN
There are indications of placer or primary gold in these locations.
55
SECTION VI. WESTERNGREENSTONE REGION
B. PLATINUM
1. YUBDOPLATINUMAREA(MAPVI-4)
The Yubdo platinum deposit was discovered in 1923-1924and miningwasstartedin 1926. Through 1976, approximately 2000 kilograms of platinum concentratewere produced.
The Yubdo area is underlain by an ultramafic complex of serpentinized dunite,pyroxenite and peridotite. It is bounded by a metamorphosed aureole of tremo-lite-actinolite-chlorite-talc serpentine, locally schistose. It is surrounded by meta-sediments of the Tsaliet Group. The complex is part of the predominantlytectonized Alpine-type, basic-ultramafic belt that trends northeast through theeastern part of the Western Greenstone Region. Several similar complexes occurnorth of Yubdo, such as the Dalatti and Tulu Dimtu complexes described below.
The platinum concentration occurs chiefly in laterites developed over the dunite,the lower parts of which are essentially in situ weathered serpentinized dunite.The laterites have a distinct layering as described below, from the top down.
· Wokassa layer. brown, fine-grained laterite; contains nil Pt and 0.26% Ni.
· Chirecha layer. deep red with semi-angular to rounded nodular grains oflaterite and some grains of chalcedony or quartz; it may be a fossilplacer;contains 0.3-4.5g/mt Pt and 0.29% Ni.
· UpperBondo: mottled yellowto brownishrotten bedrock; characterized byboulders of soapstone; contains 0.4-0.7glmt Pt and 0.25% Ni.
· Lower Bondo: same description as Upper Bondo; contains 0.4-1.3 g/mt Pt.
· Kua layer. in situ weathered bedrock, yellow-ochre in color; weathereddunite in placeswith thin silicified layers showingnetwork fabric;contains1.3-14g/mt Pt and 0.13%Ni.
In the Kope workings (southwest quarry), the Kua layer is a chaotic mixture ofserpentinized dunite blocks, from a few centimeters to meters in size, set essen-tially in a granitoid (granite-syenitic) matrix. The feldspars of this rock are alteredand replaced by talc-sericite. This chaotic zone is a contact reaction zone morethan 10 meters thick between the serpentinized dunite of the Yubdo Complex anda later intrusive alkali granite. A lithology known locally as "birbirite" is a para-quartzite interpreted by geologists working in the area as being derived from thelaterization of dunite. Others (de Wit and Berg) consider it to be an alterationproduct associated with serpentinization.
From nearby drainages, nuggets several millimeters across have been analyzed.They are a Pt-Fe alloy, with platinum far more abundant than iron. Minor copper
56
SECTION VI. WESTERN GREENSTONEREGION
is reported in them as well as smaller inclusions of osmiridium and erlichmanite(OSS2). Accessory pentlandite and chalcocite may be present.
The average composition of platinum concentrate from the Yubdo deposit isPt 79.48%, Pd 0.49%, Rh 0.75%, Os 1.41%, Au 0.49%. The remainder is iron.Reserve estimates vary widely due to insufficient data. Most experts are said toagree on a reserve figure of 2000 kilograms of platinum, from a proven volume of72 million cubic meters of material with an average grade of 0.031 gram per cubicmeter. Other estimates are much higher, from 12 to 30 metric tons, but the gradesutilized are considered unrealistic. Much of the platinum mineralization isextremely fine, and recovery of this material has not been possible to date.
2. DALATI1ANDTULU DIMTU
Platinum occurrences at Dalatti and Tulu Dimtu have been reported. At thelatter, platinum may occur as intergrowths or solid solution in heavy concentratesof magnetite and chromite along the western flank of Tulu Dimtu Hill. Gradesare low, 4 grams per cubic meter of heavy concentrate. However, zones may befound where favorable secondary enrichment has occurred, such as at Yubdo. Thegeologic history is similar at Yubdo, Dalatti and Tulu Dimtu, so additionalplatinum occurrences are possible along the northern extension of this mafic--ultramafic belt.
c. BIKILALIRON ANDPHOSPHATEAREA(MAPVI-5)
This area liesbetween N09°15'331-N09~0'36"and E35°51'421.E35°54'49".It is located 18to 20 kilometers northwest of the town of Gimbi. The area studied is underlain by threeprincipal rock groups:
· Amphibolite and amphibole schists occur as xenoliths within the amphiboleanorthosite. Amphibole schist, the oldest rock in the area, is intruded by theBikilalintrusiveand granite. The amphibole-richlithologiesare discontinuousandare scattered throughout the amphibole anorthosite, with sizes of tens of metersin length, and in the granite from 0.1xO.7to 0.02xO.1square kilometer. Titaniumonly rarely occurs in associationwith the amphibole schist.
· The Bikilalintrusive is a basic rock,more or less ellipticalin shape, with major andminor axes of 19 and 17kilometers. From the core to the margin, the rock typesare porphyriticolivine gabbro, olivinegabbro, anorthosite, amphibole anorthositeand amphibolegabbro. Irregularlydistributedhornblendite and magnetite-bearinghornblendite occur in zoneswithinthe anorthosite and the amphibole anorthosite.
· Granite group rocks are widelydistributed along the boundary of the Bikilalbasicintrusive, and intrude it, givingrise to a migmatiticcontact zone. The granite hasgenerated dikes that cut the Bikilalintrusive and the periphery of the granite.
57
SECTIONVI. WESTERN GREENSTONEREGION
In the Bikilal deposit there are three ore types: ilmenite-magnetite, apatite-ilmenite, andilmenite. The ilmenite-magnetite bodies in the Bikilal area are genetically and spatiallyrelated to the basic intrusion, and are localized in the anorthosite in the hornblendite belt.
This belt is 1 to 1.5 kilometers wide and more than 15 kilometers long. Each iron-richlens is from 10 to 100s of meters long and up to 100 meters wide. The attitudes of theore lenses follow those of the hornblendite. In the northern part of the area they trendeast-west and dip 70 to 80 degrees south; in the southern part the lenses strike northeastto north-south, dipping 62 to 85 degrees northwest, and occasionally southeast.
At the surface, the sizes of the ore bodies vary in length from 60- 250 meters, and inwidth from 4-6 meters. BaITen ground between the ore lenses is 30-40 meters wide and
230-250 meters long. The total length of the ore body is 4900 meters. The averagelength of a given subzone is 700 meters, and 40-60 meters wide. The ore isilmenite-magnetite. The principal minerals are martitized magnetite and ilmenite. Chloriteand, rarely, phlogopite are found in the massive ore. The disseminated ore contains the
following minerals in varying quantities: acicular amphibole, plagioclase, epidote, orthite,melilite, biotite, olivine, pyroxene and garnet. Accessories in both massive and dissemi-nated ores are chrome spinel, pyrrhotite, pyrite, chalcopyrite and pentlandite.
The high-grade ore is generally massive with sharp contacts with the country rock. Thedisseminated ore is medium to low grade with gradational contacts with the country rock.Allotriomorphic texture is characteristic of the massive ore, sideroid texture being typicalof the disseminated ores. Magnetite and ilmenite are allotriomorphic with smoothboundaries. Their grain size is 0.2 to 0.5 millimeters. The ore is late orthomagmatic,genetically associated with gabbro-anorthosite magma.
Magnetic separation of the ilmenite-magnetite ore gives a high-grade concentrate because(1) the spaces between the mineral plates are large, from 0.05-0.1 millimeter, and (2)most of the magnetite grains are free from ilmenite. Regulating the grinding and themagnetic intensity of the separator results in a good iron concentrate.
In summary, the ore is 33-55%martitized magnetite, 30-40%ilmenite, and rarely, 5-10%hematite. The ore zone is 15 kilometers long. The length and width of the ore bodiesare 4.9 kilometers and 40-60 meters. Depth is 200 meters. A probable ore reserve isestimated to be 18 million metric tons of ore grading 44% Fe from 40 bodies. Bymagnetic separation, 30% of the iron and nearly 30% of the ilmenite goes into the tails.
The phosphate potential is in an apatite-bearing anorthosite gabbro formation. Spatiallyand genetically it is associated with an intrusion of gabbroic rocks. The intrusion,oval-shaped in plan, extends roughly north-south and is 9 kilometers long by 2.6 to 9kilometers wide. The intrusion cuts migmatite, metadiorite, and amphibole schist of theLower Complex. It is intruded in turn by a post-tectonic Late Proterozoic granite.
The apatite-magnetite-ilmenite deposit is represented by a zone of ore-bearing homblen-dite in the northern and northeastern part of the intrusive. Spatially, the zone is confinedto banded mesocratic hornblende gabbro. The total length is 15 kilometers; the width
58
SECTIONVI. WESTERN GREENSTONEREGION
varies between 0.7 and 1.2kilometers. The strikefluctuates from roughlynorth-south inthe eastern and southern parts to roughlyeast-westin the northern part. The bodies ofore-bearing homblendite dip W450_750and occasionallyup to W85°in the central portion.
The disseminated apatite-ilmenite ore is mainlyassociatedwith hornblendite in the upperpart of the pseudo-layered ore zone. This zone is 170-350meters above the hornblenditecontaining the major magnetite-ilmenitemineralization.Althoughthe apatite-ilmenite orebodies are not yet outlined in detail, observationsalong traverses indicate a 2-70meterthickness for the bodies, averaging between 10 and 50 meters. The number of bodiesseen and their thicknessesdepend on the amount of exposure. In good outcrop areas,a vertical succession of the ore zone reveals 2-5 ore bodies in a zone 66-87 meters thick.
The larger apatite-ilmenite bodies can enclose gabbro or anorthosite beds 1-10metersthick. Thinner bodies form frequent intercalations with gabbro and hornblendite.Erosion has uncovered the apatite-ilmenite ore to a depth of 240-250meters with noobvious changes in composition or grade.
Figure 7Hikita' Disseminated Apatite-Ilmenite Ore
Components Percent
Apatite 5-40, commonly10-15
Ilmenite or titano-magnetite 10-40
Pyroxene and olivine sporadic
::::i:i:i:!:i::!::i:i:iii:iiii::i:::i:i:::i:i::II'=II."i:il_ili:il:Jlli:I~JI:!lli::llllijl::::!!:i:i::!i:::i:::::::::!:!:::i:::::::::i:::::::::::~:i:::::::!iii!::::i:i:i:i:iiiii:ii:i:iiiiii:i::::!!i::
PzO, 456, commonlyhigher inupper part of ore zone
SOURCE:Serghienko,V.N. and AkliluAssefa. "Reconnaissanj:eSurveyto AssessApatite Ore Potential of an Anorthosite-Gabbroic Intrusive and Alkaline-UltrabasicRing Complexes in Ethiopia";EIGS internal report, 1988.
59
Pyrite 1-5
Hornblende 40-80
Biotite 1-5
Plagioclase 1-20-Chalcopyrite 1-3
Gamet 1-20
Actinolite 1-5
TiOz 7.32-FezO) 23.82
FeO 15.32
VzO, 0.03
Map VI-1Precambrian Tectonic Features and Ultramafic Complexes
of Western and Akobo Greenstone RegionsAfter Senbeto Chewaka and M.de Witet al. (1981)
o 100
Kilometers
II/ I
//I I
IAsosa \1\I'" \\\,
I)" ~ ~J~I \\ \ ./.'/9'II / ~ " \. v \ \ \ \ I" / /..
I / .- -- -~,-,~ \ (J "/. J&"'IBambesi ~~ \ \ \ I /t,/i Diddessa River
, ... \ I,../. ,'"Kata "'~II '?
i'..
(:.f~ Tulu Dimtu
"/"f . " .I /. t-.. Glmb./ / · -, \ ,~ Nekemte
~): .rDalattf',- - _.' .."~ "/; ~ Yubdo
-'. '/
SUDAN
Gore.,//.
/'. . / Ultramaficbelt./.
Ultramafic complexes
0-1//
//1Main structural trends
SUDAN
~ River
,/ Road....-....
60
10<>20N
fJ
/I
10"1ONwooo10C')
././
Map VI-2Location Map of Oda-Godere Area in
Western Greenstone RegionAfter Mewa et al. (1989)
o 10 155
Kilometers
1\\I,I Oda-Godere Area,
Oda
I
~ Bildigilu././
r,I/..-
W10oo10C')
wo.,..
'010C')
.w.10.,..o10C')
woNo10C')
I
I
l
61
" "" " ~
"
... ...(
, ,,I I,
I II I'. J
\ ,
--..----
MapVI.3Geologic Map of Kata Area InWesternGreenstoneRegionAfterSenbetoChewakaand
M. de Witet ai, (1981)
N
o 500I I
Melera
62
Marble
D Undmerentiatedphyllile
Phylliteo Intraformational
conglomerate" Intraformationalbreccia
f Greenschist (undlUerentiatedmetavolcanlcs,tuUs,volcani-clastics)
E2J Quartzite.......:: ......::
f [Z] Metadiorite/granodlorlteXXIC
Gneiss, myloniteULJ
[I[] Blue quartz porphyry, I" ,
K.1K-2 I Kataarea targetsK.3
Map VI-4Geologic Map and Cross-Section of Yubdo Ultramafic
Complex in Western Greenstone Region
Granite, granodiorite,quartz diorite, grano-syenite
Serpentinized dunite
Wehrlite (01and cpx)
Pyroxenite
Serpentinite
Birbirite
S Sulfides
Quarry
o 1500I I
Meters
~N
I
Laterites
,.. Birbirite stockwork
SECTION A - A'
SOURCE:Senbeto Chewaka and M. J. de Wit (editors). Plate Tectonics and Metallogenesis:Some Guidelines toEthiopianMineralDeposits. EIGSBulletinNo.2, July 1981,P 86.
63
64
Map VI-5Geologic Map of Blkllal Area In
Western Greenstone RegionAfter Sergfenko and Ak/ilu Assefa (1988)
o .5 1 1.5 2I I I I _I
Kilometers
Ogb Olivine gabbro
An Anorthosite, (eucocratic gabbro
Hbg Hornblende gabbro
... 00 0 Mineralized zone
)(
>< ')(.Magnetite-ilmenite zone.. . Apatite-Ilmenitezone
++ + Granite
J Migmatite
, 2 Amphibole schist...
r' Contacts+
,.--, \Facies boundary/ I
,----' Fault
SECTION VII
AKOBO GREENSTONE REGION
SECTION VII
AKOBO GREENSTONE REGION
The Akobo Greenstone Belt lies between N6°-9° and E34°30'-36°15'. (See Maps VII-I to VII-4.) The lithologic units here are generally similar to those in the Western Greenstone Belt
and are considered a southern extension of that terrane.
tittle exploration has been done in the region. In the 1970s the Omo River Project, by aCanadian-Ethiopian geological team, conducted reconnaissance, geological and geochemicalwork in the Akobo River Basin. The geological information on the Akobo Basin given insection A below is from The Omo River Project: Reconnaissance, Geology and Geochemistry ofParts of Illubabor, Kefa, Gamo Gofa and Sidamo, Ethiopia, Davidson, A., compiler, EIGSBulletin No.2, 1983.
EIGS recently explored some gold placers along valleys in the Akobo Basin (Map VII-4).The results are given in section B below.
A. GEOLOGY OF THE AKOBO BASIN (MAPS VII-2 AND VII-3)
The portion of principal interest lies in the Akobo Basin, at the extreme southern end of
the Akobo Greenstone Belt. The rocks here include relatively low-grade metasedimentaryand metavolcanic units which enclose ultramafic lenses. Also present are plutons rangingfrom gabbroic to granitic in composition. Unlike the general north-south trend of theEthiopian greenstone terranes, the structural trend in the Akobo Basin is northwesterly.
The five general lithologic types in the Akobo Basin, disregarding the plutons, are asfollows:
· Maficschist and gneiss(mapsymbolPbh): These are dark, amphibole-richschistsand gneisses. In the Akobo Basin they are mainly fine-grained amphibole schists,some highly mafic. Interlayered are granular amphibolites, smaller amounts ofgray feldspathic schists, chlorite schists, chlorite-sericite schists, calcareous and caIc-silicate-bearing schists, and rare cherty-textured quartzo-feldspathic rock with smallquartz eyes.
· Meta-ultramaficbodies(mapsymbolPuad): These are elongated massesconform-able with the trend of the layering or foliation of the enclosing rock units. Twelvebodies have been mapped, all of which are associated with the mafic schist (Pbh).The westernmost occurrences lie in a line, like lenses pulled apart from anoriginally larger mass. The commonest type consists of coarse, interlockingtremolite. Varieties of this type contain varying proportions of talc, chlorite,serpentine and carbonate, along with small amounts of opaque oxides. These areprobably slivers of tectonically emplaced plutonic rock. An ophiolitic origin maybe conjectured. .
· Metasedimentaryschists(mapsymbolsPs, Psmand Pqm): The dominant rock typein the Akobo Basin, it is highly fissile, and light buff gray to medium gray in color.
65
SEcrION VB. AKOBOGREENSTONEREGION
Sericite schist (Psm) often appears more phyllitic, and at other times has a highlyattenuated lenticular structure that suggests extension by shearing, resembling aphyllonite. Some outcrops have interlayered, very fine grained siliceous rock withsericitic partings and variable amounts of pyrite and hematite. This may be ametamorphosed chert or a cherty iron formation.
. Marble(map symbol Pc): This lithology occurs sporadically as thin interlayersinthe mafic schists.
. Undifferentiated schist and gneiss (map symbol Pe, s): These are occurrences ofmetasediments and mafic schists among rocks of more gneissic character. They aremainly gray, fine-grained hornblende and/or biotite gneisses, and light gray to pinkbiotite quartzo-feldspathic gneisses with or without muscovite. Some of thesegneissic rocks may be equivalents of Ps and Pbh lithologies.
These greenschist facies, supracrustal, Late Proterozoic rocks, are considered correlativewith the Tsaliet Group of the Western Greenstone Region. They are bounded to the eastby the Hamar terrane and to the west by the Surma terrane, both of which are highergrade, older gneisses.
The amphibolite facies Hamar rocks have been metamorphosed twice, and were intrudedby plutonic rocks both prior to and subsequent to the first metamorphic event. The oldermetamorphism was associated with development of a large upward-opening fan-fold deepin the crust whose west side forms most of the exposed Hamar terrane. Subsequent orcontinuing deformation, with partial retrogression of earlier-formed granites, was accom-panied by plutonism. Sedimentary and volcanic rocks were deposited on the west side ofthis complex, probably prior to the second metamorphic event. They were deformedbefore the west-directed overthrusting of the Hamar domain rocks. They were structur-ally modified and metamorphosed to a relatively low grade during this earlier event, thenrefolded following imbrication and introduction of thrust sheets from the east. Lastly,they were intruded by late to post-tectonic granites.
The latest event in the whole region involved the juxtaposition of the gneissic rocks of theSurma (west) domain against both the HaJ;Ilar domain gneisses and the youngersupracrustal rocks of the Akobo domain along a steep, northwest-oriented, sinistral shearbelt. The Surma rocks are essentially blastomylonitic gneisses. The pre-cataclastic meta-morphic grade was at least as high as micJdle amphibolite facies.
Placer gold is found south of the Akobo River in the Akobo River Basin. This area isunderlain by mafic schists commonly cut by quartz veins. Swarms of quartz veins arepresent in the lower-grade metamorphics of the Akobo Basin. The principal locations ofthe auriferous gravels are closely correlated with the distribution of low-grademetavolcanic and metasedimentary schists. They seem to be concentrated in areas wheremeta-ultramafic rocks are exposed in the area south of the Akobo River. North of theriver, ultramafic rocks are poorly, if at all, exposed. Primary gold has been reportedoccurring in quartz veins in the area. The placers are worked on a small, artisanal scale.
66
SECI'lON VII. AKOBO GREENSTONE REGION
The geologic and geochemical maps of the Akobo Basin (Maps VII-3 and VII-4) showthe anomalous areas, all associated with the meta-ultramafics. The Akobo Basin meritsprospecting for platinum as well as for gold and other metals such as copper and nickel.
B. GOLD PLACERS IN THE AKOBO BASIN (MAP VII -4)
The information in this section on goldplacers in the Akobo Basin is taken fromReporton Alluvial GoldProspectsof Chamo Creek,Karl,KandibabaandMiddle Akobo River,byTaye Habtewolde et aI., EIGS, 1993. Map VII-4 showsthe locations explored and thoseproposed for future work.
1. CHAMOCREEK
Chamo Creek is a dry seasonal rivervalley about 5 kilometers long and 70 meterswide on an average. It is a southern tributary of the Akobo River and drainsmeta-ultramafics,mainly serpentinites,talc chlorites, schistsand amphiboliteswithacidic dykesin its upper and middlereaches, and granodiorites and quartz dioriteswith simple pegmatites in its lower reaches. Minor quartz veins are obseIVedinall lithologies.
A total of 14 pits, 13 of whichsunk to bed rocks, were dug on three profile linesspaced 1.6km apart and with 20meters pit inteIVal. The average depth was 1.81meters and stripping ratio wasfound to be 0.515:1.295. A geological reseIVeof182.47kilogramsof gold was estimated, with gold content of 0.50 gm/m3in washand 0.381gm/m3overall.
2. KARl RIVER
Kari is a perennial stream and a major left tributary of the Akobo River. Thisstream drains basalts, silicifiedamphiboliteschists,phylites,chlorite schists,quartz-biotites, amphibolite schists, diorites, quartz-diorites, serpentinites, meta-sand-stones, and meta-conglomerates.
A total of 35 pits were dug, out of which24 pits were sunk to the bedrock and 11pits were incomplete because of boulders, ground water seepage and pit wallcollapse.
The average depth of the pits is 5.74 meters, with a stripping ratio of 3.23:2:03.A reseIVeof 853.7kilograms of gold is computed with goldvalues 0.123gm/m3inoverall and 0.342gm/m3in wash.
3. KENDIBABCREEK
Kendibab is a seasonal dry creek right tributary to Karl River. It drainsmetavolcanics and metasediments, such as amphibolites, quartz biotites,amphibolites and phyllites, chloriteschists. Numerous quartz floats and veins ofvarious sizes and generation are obseIVedin the locality.
67
SECTION VD. AKOBO GREENSTONE REGION
Twelve pits were sunk at 40-meter inteIValson two profile lines of 1.6kilometersapart. The pits were dug and all have reached bedrock. The average overalldepth of the pits is 2.5 meters, with overburden-to-wash ratio of 1.12:1.35. AreseIVeof 301 kilograms of goldwith gold content 0.18 gm/m3in overall and 0.35gm/m3in wash has been calculated at PI category.
4. AKOBO RIVER (RIGHT FLANK)
A rapid reconnaissance sUIVeywas undertaken to the right flank of the AkoboRiver east and west of the Akobo-Chamoconfluence. Thirteen pits at 40 metersapart were sunk to bedrock on two profiles 1.6 kilometers apart. Only threeconsecutive pits showed gold values of up to 0.56 gm/m3in a wash in the floodplain (old cemented gravel).
68
,,,,,.., ,
,\ P81S
\ , ,
\\
~ Pg,xI
\ ,,,,
\,\
, \" \
Map VII-1Geologic Map of Akobo Greenstone RegionAlter Orno Riller Project Report (EIGS, 1983)
o 10 20 30 40 50
",
'--~._------
p""
6"3O"N
Pv
Pv
69
Nms- Miocene basalt
Pa. Hamar terrane and Swma terrane
Pax Strongly lineated layered gneiss
P Gabbro, diorite and meta-equivalenls
Pbh Malic schist of predominantly votcanic origin;minor graywacke and metaconglomerate
Pc Marble
Pebh Undivided gneiss
PebI1It CataclasllC gneISSderived from Pebh
PernI> Predominantly muscovite-biolile grarlllaid gneissand rnagmallte
Pe,s Gneiss and schist of undivided sedimentary andvolcanic origin
Pg, Pre- and/or synlec:tonlc granite
Pgd, Pre- and/or synteaonic granodionleJtonalile
Pg,x Graniloid gneiss derived 'rom Pg, and Pgd,Pm Permian sandstOne and conglomerate
Pom Oligocene Mekkonen basalt ..Pqm Quanz-muscovite schist, minor quatUjle
Ps Sedimentary schist, melagraywacke, melapelile,meta-rhyotitic tull and metaconglomerate
Psm Sericite schist; minor pyritic and graphite phyUile;metachert
Puad Meta-ultramafic rocks, predominantly talc,amphibole schist, minor serpentlnae
Pv Eocene-Oligocene main votcarnc sequence, basa!\,rhyolite, trachyte, tull and ignimbrite
Ps IP_~'....
Pb,Pbh
Gabbro, diorite and metamorphosed equivalantsMahe schisl 01 predominant Iy volcanic origin;minor graywacke and metaconglomerateUnd~terentiated marbleCalche marble
Undivided gnaiss; predominantly biothe and horn.blende gnaiss, in part migmathic, whh minormetasedimentary gneiss, quartzo.leldspathicgneiss, a"1'hibolhe and granitoid orthogneissGneiss and schist 01 undivided sedimentaryand igneous origin
Muscovhe-biotite granhoid orthogneissStrongly lineated layered gneissPre-tectonic/syntectonic granite and pegmatheLate 10 posl-tectonic Precambrian granhePre.tectonic/synt ectonic granodiorh eltonalheTertiary hypabyssallelsitePermian sandstoneQuartz-museovhe schist; minor quartzheSedimentary schist: metagraywacke, metapelite,metarhyolite lull, metachertSeriche schist; minor pyritic and graphhe phyllhe;melachert
Mela.ullramalic rocks; predominanlly talc-amphibole schist; minor serpentiniteTertiary volcanics, undifferentieted
PcPeePebh
Pe,s
PembPexPg,Pg,Pgd,PhIPmPqmPs
Psm
Puad
v
34°4S'E
"/
I
,,\, .
\ \ ,,\\
" V )\ I" t
',-IPgd,
Pgd, V
v
S030'N
V
v
S01S'Nv
\\
\\\
\"II....-..." "
3so00'E V ...)I\"
Map VII.2Geologic Map 0' Akobo Bas'n,
Akobo Greenstone RegionAfter Omo River proJec' Report (EIGS, 1983)
II 12 18I I I I
KIlometers
V3so1S'E
70
"'-.,'----..
"\(
MapVII-3Anomalies In Stream Sediments In Akobo Basin,
Akobo Greenstone Region
After Omo River Project Report (EIGS, 1983)
o 8 12 18I I I .
Kilometers
6' 30'N:
6'15'N
/".
it\ [I "')
t\~- -X
~ ~,\ "
, \~"'\\.~ Y
I
Sireamsecii ~'-" . ·
menls In = 9221 '
. ..>,. ",.. "-.AJ
o Cu>45ppm \I!I N;"d C, r
~
y
34°45'E 3S000'E
71
\
[JtJ
r
I
3S01S'E
II
J
'\\
"-...
~
'1\
Map VII-4Placer Gold Exploration Area in Akobo Basin,
Akobo Greenstone RegionAfter Taye Habtewolde et a/. (1993)
o 5 10
Kilometers
L Explored
~ Proposed for future work
~ Stream
72
SECTIONvm
TIGRAY GREENSTONE REGION
SECTION VIII
TIGRAY GREENSTONE REGION
The Tigray Greenstone Region is located in northern Ethiopia. (See Metallogenic Map inSection I.) The Late Proterozoic Tsaliet Group is well developed in this region and consistsof propylitized andesites and diabases, tuffaceous slates and graywackes. This predominantlyvolcanic sequence merges into the overlying Tambien Group. The main rock types in thisgroup are slate and shale - commonly graphitic - with interbedded limestones. Small bodiesof pyroxenite and serpentinite are found in western Tigray. Metamorphism has reached thegreenschist facies as a rule, although locally it has reached the amphibolite facies.
The units have been folded and sometimes refolded in a generally regular fashion along anortheast axis. Locally the folding is isoclinal. Recumbent folding, occasionally accompaniedby thrust faulting, is evident in some areas.
Overlying the older units are Late Proterozoic dolomites and black to variegated shales, fol-lowed unconformably by sandstones and foliated conglomerates containing clasts of slate,phyllite and granite. The youngest sedimentary rocks in the Precambrian of northern Ethio-pia are limestones (with algal fragments and stromatolites), dolomitic limestone and dolomite.These are in the Shiraro area of Tigray.
Post-tectonic granitoids are abundant in Tigray. They are cross-cutting intrusive bodies thatcut the folded Late Proterozoic sequences.
In the volcano-sedimentary sequences, lithologic changes take place rapidly, and facieschanges are characteristic. Rapid thickening and thinning of local limestones is common.The relationships are mostly primary variations associated with rapid sedimentation and vol-canic activity. The metavolcanics comprise lavas and pyroclastics, from basalts to rhyolites.Poorly-developed pillow structures have been reported. The pyroclastics range from brecciasto fine-grained tuffs of aqueous deposition. The mudstones show gradations to cherts, closelyassociated with the volcanics, reminiscent of the environment for volcanogenic massive sulfidedeposition.
The calc-alkaline volcanic activity, the rapid lateral variations and the evidence of slumpingand turbidity current activity suggest rapid deposition along the flank of a volcanic island arc.
Preserved by down-faulting, the Mekele outlier contains a sequence of Jurassic to Cretaceoussedimentary formations, from the basal Jurassic Adigrat sandstone, to the Antalo limestone,followed by the Agula shale. Overlying these Jurassic formations unconformably are thelower Cretaceous Amba Aradem sandstones and conglomerates.
Government geologists currently working in the Tigray Region will provide a solid databasefor future, more detailed exploration.
73
SECI10N VIII. TIGRAYGREENSTONEREGION
A. GOLD ANDBASE METAL MINERALIZATION
Recent exploration in the Tigray Greenstone Belt has increased our knowledge of themineral possibilities in the region. Inasmuch as the existence of massive and heavily-disseminated sulfide deposits is well-documented in neighboring Eritrea, the same typesof mineralization may well be expected in Tigray. The geological environment is thesame in both, and indeed the Tigray Greenstone Belt continues into Eritrea.
Mineralization in the known deposits is predominantly pyritic, with associated copper, zincand lead sulfides. Barite and/or quartz are typical gangue minerals. Base-metal occur-rences and geochemical indications are found in a number of areas in the Tigray region.Copper occurrences and geochemical anomalism are found associated with the Tsalietmetavo1canics in the lower Werri and Tsaliet River drainages as well as in west-centralTigray.
Lead and zinc anomalies in soils are present at Mariam Adi Destra, southeast of Hauzien,trending across the Giva River. These base-metal exploration targets are considered tobe hydrothermal in origin and associated with a late phase of the uppermost ProterozoicMareb granitic stocks. Gold in quartz veins is also known to be associated with thesestocks.
B. GOLD OCCURRENCES
1. ARAGAB MESHA
A gossan of about 50 meters by 2 meters is known to occur at this place. Adetailed soil surveycarried out has indicated Cu and Zn anomaliesassociatedwithgraphite-bearing sediments (schists). Cu up to 2% and Pb up to 2300 ppm werereported.
2. ENTICHO
Detailed geologicalinvestigationup to drilling(3 bore holes) has been carried outby Ethio-Nippon. Gossanswere reported to occur on the surface. Pyrite-bearingsediments were intersected by drilling.
3. WESTERN TIGRAY
Regional reconnaissance,follow-up and detailed investigations have been carriedout and gold mineralization is knownto occur. Local residents engage in panningfor gold along drainages.
a. Asgede
Quartz vein-hosted gold mineralization is indicated in two places. Manyanomalous localities are outlined fromdrainage heavy mineral concentratesurveying. Detailed investigations are underway.
74
SECfION VID. TIGRAYGREENSTONEREGION
b. Terakimti (AdiDairo)
Quartz vein-hostgoldmineralization is indicated. Further detailed explora-tion is being carried out.
c. AdizereSenai
Shear related gold-mineralization is indicated associated with ultrabasicrock (schists), andwideanomalous areas are outlined. A detailed investiga-tion is being carried out.
d. Zager and Hargets
Gold anomalies, from heavy mineral concentrate sUIVeying,are found inthese localities. They are the subject of a future exploration program.
4. MEFALSO AND ADI HAGERAY
Base-metal anomalies with some gold inciations are reported to occur in theselocalities.
s. ADIHOZA
Primary gold is found northeast of the town of Hauzien, near Adi Hoza. Thereare numerous gold-bearing quartz veins present. They are iron-stained withoxidizedpyrite containing traces of gold.
6. MEKELEQUADRANGLE
In the Mekele quadrangle of eastern Tigray,alluvialgold is known alongthe Werriand Bereh Rivers. A placer is found at N13°53',E39°12'. Potential gold-bearingalluvium along the Werri River is some 30 kilometers long and 20-300meterswide, and consists of both high and low terraces. Four pits gave reported valuesup to 117grams of gold per cubic meter. Primarygold in pyrite-bearing quartzveins was discovered during reconnaissance in the Werri area.
c. NICKEL
1. SAMRE
Stream sediments anomalousin nickel are found seven kilometers southwest ofSamre, at N13°02', £39°15', along a zone 3 kilometers long and less than 1 kilo-meter wide. The area appears to be underlain by metasediments and meta-volcanicsof the Tambien Group.
75
SEmON VIll. TIGRAYGREENSTONEREGION
D. COPPER
1. TSEHAFIEMBA COPPER PROSPECT
The Tsehafi Emba copper prospect is in western Tigray. The mineralizationoccurs within a meta-gabbro associated with other metamorphosed intrusions, allforming a syntectonic complex. This complex, known as the Firfira, lies within thelow-grade, regionally metamorphosed volcanics and sediments of the Late Protero-zoic Tsaliet Group. These are in turn cut by the post-tectonic Mareb granites.The regional strike of the greenschist facies metamorphics is northeast toeast-northeast, dipping vertically to steeply northwest. Two deformational episodeshave affected these rocks.
There are three groups of metamorphic rocks at this prospect: metavolcanics,metasediments, and the intrusive Firfira complex in the southeast portion of thearea studied. The metavolcanics and the metasediments are often found inter-
bedded, and gradations exist between graywackes and volcanic tuffs.
The metavolcanics range from basaltic to rhyolitic composition. Some relictstructures may be preserved, but the rocks have been completely altered to massiveor schistose greenstones.
The metasediments are graywackes, siltstones, mudstones, slates and thin marbles.The graywackes locally include conglomerates and breccias. Gradations existbetween gray-wackes and tuffs, and between graywackes, siltstones, mudstones andslates.
The Firfira complex ranges from granite to ultramafic in composition. These areconsidered syntectonic. Granites and granodiorites make up 70% of the complex,diorites and gabbros 15%, and fine-grained, mainly mafic rocks 15%. Deformationis variable in intensity. The gabbros locally show primary gravity layering. Somecontact metamorphic effects are present, but these are generally blurred by thesubsequent regional metamorphism.
There are few visible surface indications of copper mineralization at Tsehafi Emba.Some malachite staining is present, but no gossans. Finely disseminated sulfidesare visible in some of the less-weathered gabbros. The main evidence reported forthe presence of potential economic mineralization lies in the geochemical analysesof stream sediment, soil and rock samples. Copper values up to several thousandparts per million have been reported from the soils, and up to a few percent fromrock samples. Most values in the soils are greater than 1000 ppm, and malachitestains lie within the outcrop of gabbros. The more basic layered gabbros tend togive a high proportion of the higher copper values.
Mineralization at Tsehafi Emba probably predates the Mareb granites, as chalcopy-rite is found in the earlydeformed hydrothermal veins. Later veins have no copperminerals. The bulk of the copper is disseminated within the gabbros.
76
SECTION VID. TIGRAY GREENSTONE REGION
2. TSALIETRIVER
There are geochemical stream sediment copper anomaliesin the lower Werri andTsaliet rivers,and a copper anomalysouthof the Tsaliet Riverat N13°48',E39°03'.The anomalies are in Tsaliet metavolcanicterrane. The Cu threshhold is84ppm,with anomalous basins going up to 140ppm. Small gossaniferous outcrops arefound. The mineralization is perhaps related to the Mareb granite intrusion.
3. EAST LIMB OF NEGACH SYNCLINORIUM
About 20 kilometeres east of Mariam Adisto, at NI3°58', E39°42', streams withanomalous amounts of copper and zinc are found on the eastern limb of theNagach synclinorium,localizedalong a north-south fault. Copper values upto 178ppm, and zinc up to 113 ppm are reported. Malachite has been obselVedin thearea.
4. SAMRE
Information concerning an area about 7 kilometers south-southwest of Samre, atN13°02',E39°16',is available fromthe map ofthe Mekele quadrangle (ND37-11).
E. LEAD ANDZINC
1. MARIAMADISTA
Mariam Adista is southeast of the town of Hauzien. At N13°57',E39°32', zinc andlead soil anomalies cut across the Giva River. The highest Zn value was 3300ppm, with 1000ppm values common. The Zn threshold was 140 ppm; 11 of 16drainages were returned anomalous values. Anomalous Pb samples of 80 ppmwere coincidentalwith the zincs. The area appears to be underlain by the Assemlimestone of the Tambien Group.
77
SECTION IX
ETHIOPIAN ImT ZONE
SECTION IX
ETHIOPIAN RIFT ZONE
The Ethiopian Rift Zone forms a valley that cuts through Ethiopia in a general north-north-east direction. It is a graben, the failed arm of the Red Sea-Gulf of Aden triple junction,which was formed during the opening of what are today the Red Sea and the Gulf of Aden.
There are several saline lakes in the Rift Valley in southern Ethiopia. At one of them, LakeAbiyata, soda ash is being produced by solar evaporation. As the Rift Valley approachesDjibouti, the western boundary faults turn to a more northerly direction, forming the Afarand Danakil Basins. These lie east of the Ethiopian Plateau and are bounded on the east bythe Danakil Alps, which run parallel to the Red Sea coast in this area. The eastern boundaryof the Rift Valley, at roughly the same latitude, turns to the east toward the Gulf of Adenarm of the triple junction.
The Danakil Depression is some 120 meters (394 feet) below sea level and is east of thenormal fault zone that borders the Precambrian schists of the Tigray Greenstone Region.(See Map IX-I.) There are surface deposits of salt and sulfur, shallow manganese deposits,and subsurface evaporite deposits of potash salts. The latter have been explored by drillingand underground drifting. Between 1917 and 1929 approximately 70,000 metric tons of pot-ash was recovered.
Oimatic conditions in the Danakil Depression must be taken into consideration. Monthlyaverage temperatures are: minimum 27.8°C (82°F) and maximum 40.6°C (105°F). The tem-perature range at noon is 50.5°-68.1°C (132-152.9°F). The annual rainfall between Januaryand March is 2-5 mm (J. Matthews, 1968).
Access to the deposits in the Danakil Depression is from the Red Sea. The closest port isMersa Fatma, but Massawa, which may be reached from Mersa Fatma by truck or sea trans-port, is recommended. Land transport is rough. Dallol is accessible by road from Mersa Fatmaand there is a dry-weather road from Mekele to Dallol, which requires 4WD vehicles. A projectto build a 190-kilometer highway from Serdo to Afdera is being bid. The only other access toDallol is by air. Dallol is about 208 kilometers by air southeast of Asmara. The airstrip atDallol can accommode a DC-3 or equivalent aircraft.
A. SODA AsH RESOURCES
The soda ash resource is located approximately 200 kilometers south of Addis Ababa.The waters of Lakes Abiyata, Shala and Chitu have medium to high salinity and containsodium-chloride-carbonate. Soda ash is being produced from Lake Abiyata on a semi-commercial scale. The soda ash resource and reserves, and the Abiyata collection andevaporation operation and plant, are described in Section X.
B. POTASH
Major potash deposits exist between E39°45'-E45°00' and NI3°30'-NI5°15", near MountDallol within the Danakil Depression, The sylvite-bearing evaporite sequence is young
78
SECTION IX. ETHIoPIAN RIFT ZONE
(Quaternary) and relatively undisturbed. Subsidence along a rift zone has resulted in abasin containing at least 1000 meters of evaporites. Within the evaporite sequence,gypsum is the most widespread mineral on the surface. Isolated outcrop areas of haliteand potash salts are also present. Around Mount Dallol a sequence of evenly-beddedhalite is found interbedded with thin layers of clay and gypsum. Sylvite, carnallite andsulfur outcrop around the central crater of Mount Dallol.
1. DEPOSITS
a. Musely Ore Body(Map IX-2)
The Musely ore body, located 4.5 kilometers west of Mount Dallol, wasextensively explored during the 1960s. Three major fault systems affect thearea and the Musely ore body. The strongest trends N30°-400W withnormal displacement. The second trends N600-75°W and exhibits varioustypes of displacement. The third trends N30°-400E and shows lateraldisplacement.
Structurally, the northwest fault system has had the most effect on ore bodycontinuity, according to one interpretation of the data available. Anotherstudy, however, suggested that the amount of vertical displacement of agiven sylvite horizon was caused by £Iexuring rather than faulting. Thenortheast fault system is the most significant in that fresh water is carriedin it. Lateral facies changes are common in individual sylvinite horizonsand may be either subtle or abrupt according to a later office study.Thinning and thickening of individual beds are common features, butcomplete pinch-outs are rare.
The stratigraphy in the area of the Musely ore body was determined bydrilling and underground work. Overlyingthe evaporites are 6-45 metersof alluvial gravels and fine clastics with numerous gypsum layers. Theevaporite sequence consists of three parts: upper halite zone, Houstonformation, and lowerhalite formation.
. UpperHaliteZone
The upper halite zone is 6-180 meters thick, consistingof almostpure halite. It is light-colored, coarse-grained and porous, withvuggy interstitial openings. Toward the base this unit becomesdarker, denserand well-bedded,withincreased amount of anhydrite.
. Houston Formation
The Houston formation consists of four members. The uppermostmember is a marker-bed 4.5-15 meters thick consisting of laminatedanhydrite. This is a persistent and useful marker.
79
--
SECTIONIX. ETHIoPIANRIFf ZONE
The second part is the sylvinite member. It is variable in thickness,from 0-11 meters, and is not very distinctive from the overlyingmarker bed. It contains even, wavy gypsum layers. Distinct thinsylvinite beds alternate with thin, valVe-like anhydrite layers.Bedding is distinct, but often contorted, with slump features.Toward the base of this member, the content of sylvite decreasesand it becomes more impure with the increased content of othersalts.
The third, or intermediate member, which often contains appreciablesylvite, especially in the upper parts, is characterized by a complexand mixed mineralogy of several salts besides sylvite, such as kainite,kieserite, polyhalite, carnallite, anhydrite, and locally bischofite andrinneite. The thickness of this member is variable, up to 24 meters,and it may be quite rich in potash salts.
The fourth, or kainite member, 4-13 meters thick, is fine-grained,dense, massive, and amber colored. It contains about 25% ofadmixed halite. Toward the base, it becomes more impure, and thelast kainite bed marks the base of this member and of the potashformation.
· Lower Halite Zone
The lower halite formation is more than 150meters thick. It con-sists of dense, gray,medium-grained halite, and contains dissemina-tions and a few thin seams of anhydrite. One core hole penetratedthis third formation and discovered a second potash horizon appar-ently similar to the upper one described above. This lower potashhorizon has not been explored.
Three groups worked on the deposit between 1959 and 1970. Betweenthem, over 42,000 meters of drilling were done, and a 100-meter deep,3.3-meter diameter shaft, and nearly 900 meters of underground openingswere completed. A number of geophysical methods were employed aswell,including ground and helicopter-borne gravity, ground magnetics, andseismic refraction. Gamma and temperature logging were done to identifythe sylvinite members in the boreholes. A distinct quantitative correlationwas found between the intensity of gamma radiation and the KQ content.A pilot plant was built.
During the 1960sa foreignjoint venture companyconsistingof subsidiariesof Ralph M. Parsons Company and a shippingcompany owned by DanielK. Ludwig, an American entrepreneur, began drilling, shaft-sinkingandunderground workings. Transport was to be by water from a port on theRed Sea (the deposit is approximately 45 miles south of Mersa Fatma on
80
SECTIONIX. ETInOPIAN RIFf ZONE
the Red Sea). Operations were discontinued in 1968 after the mineworkings were flooded by fresh water. A combination of factors, includingthe depressed price for potash, forced ~bandonment..of the project.'"
As defined by the drilling, the Musely ore body is some 4 kilometers longin a N25°W direction, and about 1.5 kilometers wide. Reconnaissance
drilling and seismic work suggest that the ore horizon may extend longitudi-nally as much as 16 kilometers. As presently known, the ore body averages4.76 meters (15.6 feet) thick. In some areas, higher-grade ore exists nearthe top of the horizon; in others, the higher grades are found near the base.
During the underground mining, there was no caving or roof trouble ofconsequence associated with the leached zone, either in the ore or in theHouston formation. Formation tests were done to study the brine occur-rences in the different members of the upper salt formation. The resultswere controversial due to problems related to cementation.
Drilling also indicated the presence of a deeper potash-bearing horizon at500 meters depth, similar in character to that explored by the undergroundwork and shallower drilling. The potash beds are shallowest in the westernpart of the basin, and dip to the east. Drill-hole information suggests thatthe explored potash-rich horizon underlies an area of at least 19 kilometersin length in a north-south direction by nearly 11 kilometers in width.However, the full extent of this horizon is not yet determined.
b. Crescent Ore Body
The Crescent ore body, 1 kilometer southwest of Mount Dallol, wasdiscovered later than the Musely ore body in the course of exploration. Itis up to 1000 meters long by 100 meters wide. It is irregular in shape andrelatively flat-lying, and surrounds bubbling springs of MgQ. Potash occurson the surface and at a depth of 90 meters in the form of carnallite andsubordinate sylvite. The zone has a maximum thickness of 60 meters. Themineral body is composed of a mixture of carnallite, sylvite, halite, red ironoxides and clay, and is saturated with corrosive hot brines.
2. RESERVES
a. Musely Ore Body
The Musely potash reserves were estimated in the late 1960s by theParsons- Ludwig joint venture using a drill spacing of 300 meters. It wasdetermined that the Musely ore body contains 33.1% sylvite, 48.6% halite,13.3% anhydrite, 3.1% carnallite, 1.7% kainite and 0.1% kiserite. Orereserves were estimated at 98 million metric tons (proven and probable),averaging 33% KCI, using a cut-off grade of 25% KCI and a minimummining thickness of 2.1 meters.
81
SECTIONIX. ETInOPIAN RIFf ZONE
Figure 8Musely Potash Reserves
ReserveClassification
Metric Tons000-
66,228
32,331
61,897
160,456
KCI%
Proven 33.04
33.96
31.22-32.5
Probable
Possible
TOTAL
Source: Joint venture report; modified by Ethiopian Instituteof Geological Surveys,1965.
In December 1968, Mackayand Schnellman reviewedthe reseIVeestimatesand concludedthat the reseIVescalculated cannot be classified as provenor probable ore until they are justified by additional underground miningwork. Mackayand Schnellmanalso concluded that the assumptionsof 0.3meter roof cover above and floor cover below the ore horizon are unwork-able and unrealistic, and suggestedinstead a 0.6 meter cover.
It should be noted that the Musely ore body has been only partially ex-plored. There is lateral continuationto be considered, aswell as the deeperpotash horizon that was cut in the drill hole.
The work done at Musely suggeststhat underground miningmethods willhave to be used to extract the potash. Solution mining has been consid-ered, but it is unlikely that would be a successful technique.
b. Crescent Ore Body
The Crescent ore body reseIVeshave been estimated to be 10-12millionmetric tons of ore containing 3 million metric tons of KO, correspondingto 1.9million metric tons of K20.
c. MANGANESEDEPOSITS
Manganese ore has been reported in the Danakil Depression. The Parsons-Ludwigjointventure that explored the Mount Dallol area for potash reported the occurrence of anumber of small low-gradeshowings of manganese in the quaternary rocks on the eastand west of the Danakil Depression. These were all said to be of "secondaryorigin."(Geological Report prepared for R. M. Parsons Potash Exploration Company, 1965.)
Two occurrences of manganese ore have been reported in the Mount Dallol area:
82
SECTION IX. ErmoPIAN RIFT ZoNE
1. EN KAFALA
This ore body is in the En Kafala Valley 5 kilometers westof Mount Dallol. Themanganese appears in a bed 1-2meters thick above the basal conglomerate of thewhite series, composedof reef limestone, marble and gypsum,and below the reeflimestone. The upper part of the manganese ore body was quarried mainly byremoving 3-5 meters of the overburden of limestone. The area of quarrying is lessthan 1 km:!.(M. Beyth, 1965).
To the east, above the conglomerate, beds of manganese and iron oxide areinterbedded with brown clayof 90 em thickness. The results of chemical analysisof the lower part showedit to be of poor grade: Mn 22.27%,Fe 6.5%, Ba 0.1%,Sr 0.4%, and traces of Ti, Ni, Cu, Zn, As, Br, Rb, Y, and Sr. (M. Beyth, 1969).
The low-grade material is overlain bya bluish porous massivebed of almost puremanganese oxide, 110 cm thick. This middle part gave the following result onchemical analysis: Mn 60.78%, Fe 0.7%, Ba 0.8%, Sr 1.2%, and traces ofTi, Cu,Zn, As, and TI. The assay represents about 95% Mn02, a remarkably puredeposit. (M. Beyth, 1969.)
At the top of the manganese bed, there is a thin layer (25 em) of dark brownmanganese which looks like lignite. The chemical analysis shows the followingresults: Mn 52.52%,Fe 2.4%, Ba 0.3%,Sr 1.2%,and traces of Ti, Ni, Cu, Zn, As,Rb and Cr. (M. Beyth, 1969.)
Estimated production of manganese ore at En Kafala between 1965and 1967is4000metric tons (Getenehe Assefa, 1985).
2. GARADA
The Garada manganeseoccurrence is 36 km east-southeast of Colluli,38 kIDeastof Mount Dallol, and 50 km east-northeast of En Kafala. The manganese issedimentary (like that of En Kafala), dark to brown in color, and massive. Theexposed manganese is about 170 meters long, up to 12 meters wide, and 3 metersin average thickness. Results of preliminarychemical analysis indicate that theMnO content of the ore ranges from 11.1% to 31.3%.
Geochemical assayresults- chemical and emission spectroscopy- are showninFigures 9 and 10.
83
SECTION IX. ETlUOPIANRIFT ZoNE
Figure 9Geochemical Assay Results (Chemical) for Garada Area
Percent
SOURCE: Ahmet Mohamed and Admasu Mekete, 1973.
Figure 10Geochemical Assay Results (Emission Spectroscopy) for Garada Area
ppm
SOURCE:Ahmet Mohamed and AdmasuMekete, 1973.
D. GEOTHERMAL ENERGY RESOURCES
Geothermal energy resources in the Danakil Depression are described in Chapter VI ofVolume One.
84
Description SiO. AI.O. Fe-O. CaO MgO Na.O K.O 0.0 0.1 MnO BaO Srat over
HOC 40°C
Manganese ore 29.8 25 41.0 0.9 0.1 0.1 1.2 0.3 4.7 11.1 0.1from quarry T3.9
Calcite with 2.3 1.0 16.4 13.9 0.2 0.1 0.1 0.3 16.0 31.3 7.4 0.3manganese ore 27.0 15 0.3 15.3 0.1 0.1 0.4 0.3 14.9 25.4 6.1 0.2
Cherty calcite 90.0 45 0.3 1.1 0.1 0.1 2.2 0.1 1.1 0.5 0.3 0.'1band withoutore
Cherty quartz in 9.8 1.0 0.1 48.1 0.1 0.1 0.5 0.1 38.4 0.1 0.1 0.1calcite bandwithout ore
Description Pb Cu Ba Mo Be Ti V Co Ni Mn
Manganese ore from 5 5 0.30 20 3 30 50 - - 1.00quarry
Calcite with - 10 1.00 10 10 200 30 - - 1.00manganese ore
Calcitewith - 20 1.00 20 - 200 20 - - 1.00manganese ore
Cherty calcite band 5 100 0.02 50 - 200 30 8 30 0.20without ore
Cherty quartz in - - 0.02 - - 20 - 3 5 0.03calcite band withoutore
Map IX-1Location, Topographic and Geologic Map of
Danakil Depression in Ethiopian Rift Zone
LEGEND
COAASE ALLINIUM
CLAY OUTWASH
MUSlEY AREA
BRINE POOt..o HOT SPRING.COMPOSITION
INOICATED
o.
~ 4 eJ . .
MlES
8I
REDSEA
NREEF
LIMESTONE
REO-BEDS
REO-BEOS.G\'PSUt04.BASALT
BASAlT.GYPSUM.AHHYORITE
wurCRNCSCARPNCNT
O \I'OLC:.IINICCONC
SOURCE: J. G. Holwerda and R. W. Hutchison, .Potash-Bearing Evaporites in the Danakil Area,Ethiopia,. Economic Geology, Vol. 63, (1968), P 125 (reprinted with permission of Economic Geology).
85
Map IX-2Cross-Section Through Potash Interval of Musely Area
in Danakll Depression, Ethiopian Rift Zone
"21Z "15t1 'ZII"'55
8.CM.CJ Holil.
;~!'!!'-"!'1. ':!!!~~~8.CJa.CJHalil.
~(~rtlca' and"""1' toIl
o .eoo 800.FEET
WEST
:: :: :.: : : : .:.:... ......~ :.:..::::::::=::::
. .:.::' :.: :.:.:-; .>: ::'~'. ::.:;.::: .~: : :: .:.::~v_~~JJ~~~_~~~_~~~~::.-=: = ...-
...-.. ... ;.. .;'''. . .-..
."..8... 8. . : . : . : . : .8. .._...::::.=.-===.::".: : I~ ---..-..-.---------.-...- --.-------------..-..-.- ..- -..
~f.':S~~~~:--s::--==-:;..:~~~.~:~ ::,,': :: :~ :'~~-=_~o:'.'~~?m-~~~I~':~;-; --:--=:.:=. -- -:-"'-.':~l'~'::~~.r}ot-~-:..:..~:. :'.':':~ ,.~.,.::..n"t4"..~_ ~-"'~!{'':~'''''''''''''''.V'':"!'';:-'''
--! ;:~~::~:~''.:''';:;;,;:;,G;;,:2Li:i::X:\'2/;iL
Nal. : ~, 170.1119or. broll.n OneJ,.clian oJ ""'ile omilltCJ in !hiSCJrawino10..,oin prooe. Slape OIllOp Of0010'" inl.r..o'
~1hOrilonla II
o ~OO eoo..FEET
Iv.rlicallo 100 200..
FEET
: 80S. oJ ko,nil. not Clrill.CJin ""'.,712.1~~.211
'''D "tJ.1000' ,all?
oluvium .CIOY.9YlIsum.an"~U.
TD IZS"
EAST. . . - - -
:.:: ~:~.;~:i ~.;.; ...-:. ...: .. .0~".' : ~.~.:..;._~...,~~=_..~_.':';'~:'"-',.~f.-~f~~~.-- =--::-~-==-.:~:...----..-..-..-..-..-..--.-.
ffi3c::amc:J~
~~-"':::- ~~ :~?:~: :_~~_.. :: :: ,:' .:.~i;':'i5r"~~~~~"~~~-"~.r;:~ .-- _~::.z.....__...."'1.'~'~~/f(;:'~~:.r~it~"::'~.:t\;r.ifl'}JL.~l~~l~~t~i~~~~J~
~~::~~:~.~:i~~~.Lj{U~.t)~.~~~.:~\~\.\:.::..\-.::..::.::.:.::::::::::::::~.:J('" 04_".:.:. ............
" ..." :., : "',.. .. '0."'''l. :., . ....
---'..\._~:~t"'Youno.r Holile
Mark..
5y1YU.m.mber
Int m.mber
Koinlle ~r
SOURCE: J. G. Holwerda and R. W. Hutchison, .Potash-Bearing Evaporites in the DanakilArea, Ethiopia,. Economic Geology, Vol.63, (1968),P 138 (reprinted with permission of Economic Geology).
86
SECTION X
EXISTING MINING OPERATIONS
SECTION X
EXISTING MINING OPERATIONS
A. BACKGROUND
The history of modem mining in Ethiopia is recent. Documents show that mineralprospecting and exploration began at the end of the 18th century. Gold and platinumhave been produced in western and southern Ethiopia since 1935.
Modem mineral exploration started in 1968-1969with the establishment of the EthiopianGeological Survey as a department within the Ministry of Mines and Energy to undertakesUlveys of the geology and potential mineral reserves of the country. Exploration formetallic and industrial minerals was also undertaken by foreign companies at that time.
A number of institutions and autonomous organizations directly accountable to theMinistry have evolved. In particular, the Ethiopian Mineral Resources DevelopmentCorporation (EMRDC) was established in 1982 and the Geological Survey became anautonomous body the same year, with the official name of the Ethiopian Institute ofGeological Surveys.
Since the establishment of the Geological Survey in 1968, various mineral explorationprojects have been undertaken by the Ethiopian government, both on its own and withthe assistance of outside organizations. Private foreign companies have also carried outmineral exploration. Surveys were carried out mostly in the Precambrian low grademetamorphic terrains. Exploration activities so far have outlined priority target areas, andsome reserves of precious metals (primary and placer gold), platinum, rare metals, basemetals and iron.
1. ETHIOPIANINSTITUTEOF GEOLOGICALSURVEYS(EIGS)
EIGS conducts geologic reconnaissance surveys, and mapping and explorationprograms, supported by laboratory services and drilling and geophysics units. Inmineral exploration, EIGS uses ground-based electrical, magnetic and electromag-netic techniques, permitting the execution of routine, relatively low-cost surveys ofsmall areas for solid minerals and groundwater. Once EIGS identifies a mineraldeposit, EMRDC undertakes detailed mineral exploration and development.
Mapping at a scale of 1:250,000 of 1030' by 10sheets was initiated in 1968, whenthe Geological Survey was founded. Since then, maps covering an area of about275,000 square kilometers, 25% ofthe country, have been produced. It is plannedto continue regional geological mapping until the whole country is covered. Themapping program focused on those parts of the country underlain predominantlyby low grade metamorphic Precambrian terrains in view of their more commonmineralization. The mapping work is followed by mineral exploration activities at1:50,000 and larger scales.
87
SECI'lON X. ExISTING MINING OPERATIONS
The chemical analysis division uses atomic absorption, X-ray fluorescence, emissionspectrometry and fire assay techniques. Mineralogical and physical analysis unitshandle ore microscopy, petrography and industrial mineral analysis requirements.
With its diamond core drilling capacity, EIGS is the only agency which can carryout deep rotary drilling. It currently has the equipment and manpower to drillannually up to 30,000 meters of diamond drill holes or hydrogeological boreholesto depths of about 500 meters. Similarly, up to 15,000 meters of oil and geother-mal wells to depths of 2000-2500 meters can be drilled annually.
2. ETHIOPIAN MINERAL RESOURCES DEVELOPMENT CORPORATION(EMRDC)
The principal objectivesof EMRDC are to:
. Undertake detailed mineral exploration of known mineral deposits; ex-cluded therefrom are petroleum, natural gas and geothermal energy;
. Develop economic mineral deposits;
. Produce and process mineral products;
. Participate in joint ventures in the development, production and sales ofminerals.
Since its establishment, EMRDC has explored many deposits. It has developedand currently operates three mining ventures, which are discussed in some detailin this section:
. Lega Dembi Gold Mine and Plant. This state-of-the art gold mine and milluses gravity extraction of coarse gold and carbon-in-pulp technology for therecovery of fine gold. The plant's design capacity is 3 metric tons (96,450troy ounces) of gold bullion per year. It has been in operation since thefirst quarter of 1990.
. Kenticha TantalumMine and Pilot ScalePlant. This plant uses weatheredcrust ore as feed material and has a 28-30metric ton per hour throughputcapacity. It produces approximately 20 metric tons per year of tantalum-niobium concentrate averaging 43 percent Ta20s.
. Lake Abiyata Soda Evaporation Ponds and Soda Ash Plant. The brines fromLake Abiyata are pumped to a series of evaporation ponds from which theprecipitated trona is collected. The semi-commercial plant has a 20,000metric ton per year output capacity. Current plant output is 14,700 metrictons per year.
The Ethiopian Government will consider privatizing the Kenticha Tantalum Mineand Plant and the Lake Abiyata Soda Ash Complex or operating them on a jointventure basis with investors.
88
SECfION X. EXISTINGMINING OPERATIONS
B. LEGA DEMBI GoLD MINE AND PLANT
1. GEOLOGY
The Lega Dembi ore zone is located in the Adola Greenstone Belt. The rock unitsin the area include quartzo-feldspathic gneiss, biotite gneiss, talctremolite schist,hornblende schist, actinolite schist, plagioclase-quartz-micaceous schist, chloriteschist and amphibolite. The metasediments are highly dissected by quartz veinsand stringers parallel to the foliation, especially near the contact zones with themore basic rocks.
Lega Dembi consists of three known gold ore bodies: North, Central and South.The North ore body is 7 kilometers southwest of Shakiso. It is approximately600meters long and 50 meters wide and has been proven to a depth of 200 meters.It strikes generally north-south and dips 70 degrees west. The gold is foundpredominantly in quartz veins and veinlet swarms, and as lower-grade dissemi-nations in the adjoiningschist. The hangingwall rockis a graphitic schist, and thefootwall a quartz-biotite gneiss.
The North ore body was explored both on the surface and underground. Approxi-mately 2000 meters of underground openings were made, including cross-cuttingand drifting. An 80-meter crosscut was driven 100 meters below the ore-zoneoutcrop until the gold-bearing zone was cut. The zone was drifted on to the northand south. Every 50 meters, crosscuts were driven across the zone and sampledat 3-meter intervals.
A drilling program at North Lega Dembi to explore ore unavailable to the open-pit operation will provide information for the development of an undergroundmine. Drilling from the surface began in 1993.
2. RESERVES
Ore Body
II Source: Verbal report by General Manager, Lega Dembi Gold Mine and Plant, May 1993.lCalculated average. 2EMRDCreports the provengold content of tbe tbree ore bodies as ofmid-1994is 62.146metric tons.
,89
Central,.
North
South-TOTAL
Figure 11Lega Dembi Gold Reserves-
Ore Grade GoldGrams per Content
Metric Tons Metric Tons Metric Tons
4,000,000 2.0 8.0
6,000,000 5.0 30.0
1,875,000 8.0 15.0
11,875,000 4.461 53.Q2
SECTION X. EXISTING MINING OPERATIONS
3. MINING
Run-of-mine ore is currently being obtained from the North ore body by aconventionalopen pit mine whichis designed to supply3000metric tons of oreper day to the process plant. The overall strippingratio is 5:1. Grade controlis accomplished by sampling the blast-hole cuttings. Drilling is done withtracked drills manufactured in the United Kingdom. Ammonium nitratecapped with dynamite is used for shooting.
The fragmented ore is worked with D6, D7 and D9 bulldozers, if required, andis loaded to 35 metric ton capacity, off-highway 769CCaterpillar trucks by 245BCaterpillar excavators. The total fleet consists of five 245B excavators andtwenty-two 769C trucks.
The mine operates 3 shifts per day, 8 hours per shift, 300 days per year. Whenoperations first started, the process facilities were located at a ridge approxi-mately 2000 meters from the open pit.
4. PROCESS
The process consists of crushing, grinding and milling of run-of-mine ore,gravityseparation, leaching,carbon-in-pulp absorptionand gold recovery. Theprocess flowdiagram is shownin Figure 13.
a. Primary, Secondaryand Tertiary Crushing
Run-of-mine ore is dumped onto a heavy-duty feeder which conveys theore to the primary crusher. Oversize material is removed by means ofa hydraulic grab installed on top of the primary crushing unit. Suitable-size ore is fed to the jaw crusher, where it is reduced to -100 mm size.
The coarse crushed rock, -100 mm, is transported by means of a beltconveyor to an open coarse-ore stockpile with a capacity of approxi-mately 10,000 metric tons. The ore from the stockpile is conveyedtothe secondary and tertiary crushing section.
The secondary cone crusher reduces the ore to 40 mm and the tertiarycone crusher, to 13 mm. This product is screened out and conveyed toa fine-ore open stockpile with a capacity of approximately 10,000 metrictons. Ore is withdrawn from the fine ore stockpile and fed to the millfeed conveyor by means of vibratory feeders onto the grinding section.
b. Grinding Circuit
The grinding circuit consists of a 3.4 meter diameter x 5.6 meter longrod mill, powered by a 800 kilowatt motor and a 3.8 meter diameter x6.2 meter long ball mill driven by a 1400kilowattmotor.
90
SEcrION X. EXISTING MINING OPERATIONS
The mill discharge is combined and screened for sizing at 2 mm.Oversize material is returned to the ball mill. The undersize is pumpedto a bank of cyclones for classification to give an overflow particle sizeof which 80% is less than 0.160 mm. This stream reports to the thick-ener for further processing in the leach circuit. The cyclone overflow,which contains the coarser fraction, forms the feed to the gravity circuit.
c. GravityCircuit - FreeGoldRecovery
The overall circuit is designed to maximize coarse gold recoveryby useof gravityseparation, the recoveryof fine or locked gold being achievedin the leach circuit. The gravitycircuit is designed to recover free goldcontainedin the ore. The circuitconsists of rougher and cleaner spirals,primary and reconcentration shaking tables, Knudsen bowls and mag-netic separator. The product from this section is a gold enriched con-centrate, whichis collectedandtransported to the amalgamation section.
d. Leach Circuit
The leach circuit is necessary to recover the fine or locked gold con-tained in the ore. This process requires that the major fraction of goldremaining in the ore be dissolved by adding sodium cyanide to the oreslurry. To achieve this, several processing steps are required, as de-scribed below.
Thickening. In the thickening step, the solid concentration of the leachfeed is increased from 24-45% solids. This is achieved in a 13.7 meterdiameter thickener. Flocculent is added to the thickener to increase the
settling rates of the solids. The overflow from the thickener, which isclear water, is recirculated to the gravity and grinding circuits and usedagain as process water. The underflow of the thickener, which is thethickened slurry, is pumped to the leach tanks.
Tank Leaching. There are six leach tanks in series. The pulp gravitatesfrom the first tank to the last one. Each tank can be by-passed ifrequired. The tanks are mechanically agitated. Milk of lime slurry isadded to the pulp to raise the pH to 10.5. This is required to makepossible the addition of a 10% sodium cyanide solution. At a lower pH,cyanide gas (which is extremely poisonous) would develop. The totaltank residence time of 40 hours is sufficient to dissolve approximately90% of the remaining gold in the ore. The gold dissolved in the cyanidepulp is passed on to the carbon in pulp absorption section for furtherprocessmg.
Carbon in Pulp Absorption. This circuit is designed to absorb the golddissolved by cyanide onto activated carbon. The Lega Dembi Plant
91
SECTIONX. EXISTINGMINING OPERATIONS
employs the Davy contactor, a new development in absorption. TheDavy contactor consists of six absorption contactors in series. Eachcontactor is mechanically agitated and fitted with four side screenassemblies and pulp discharge launders. The main advantage of thiscontactor is that it can be operated at high carbon concentrations, up to25% by volume, which results in a 20 percent smaller tank.
After the pulp has completely moved through the contactor, about 98%of the gold has been deposited onto the carbon, which then goes to theelution section. The remaining 2% is discharged with the slurry to thetailings pond.
Elution. In the elution section the circuit is designed to elute (desorb)gold from the loaded carbon by using a caustic cyanide solution, whichis heated to 120°C for better efficiency. The gold previously absorbedonto the activated carbon is again dissolved into the hot solution. Thenew gold-bearing solution (electrolyte) is pumped to a holding tank.The carbon is returned to a rotary kiln for reactivation and is then againused in the process.
Electrowinning. In this section, gold is deposited from the electrolyteonto packed steel wool cathodes. The steel wool is loaded to a maxi-mum of 4 kilograms Au + Ag. During normal operation about 2-4cathodes per day are removed from each electrowinning cell.
e. Amalgamation
The concentrates from the gravity section are moved to the smeltingarea for gold extraction by the amalgamation process. The gold-enrichedconcentrate is loaded into an amalgam barrel, where water, mercury andother chemicals are added. The barrel is then rotated for 2-8 hours to
enable the free gold to combine with the mercury to form an amalgam.
After several cleaning steps, the amalgam is placed in a retort andbecomesgold sponge after removalof mercury from the amalgam. Thegold sponge is transferred to a crucible furnace for smelting to goldbullion.
f. Smelting
The gold-loaded steel wool cathodes from the electrowinning section aredried and the steel wool is oxidized in an electric calcining furnace. Thecalcined residues, together with gold sponge from the retort furnace andflux, are smelted in an electric resistance crucible furnace. The moltengold is poured into bullion molds. The cast bullion is cleaned, weighed,assayed, and stored in the strong room prior to despatch.
92
SECTION X. EXISTINGMINING OPERATIONS
g. Tailings Detoxification
Tailings from the processing plant, containing barren gold ore andcyanide solution with a pH of approximately 10.5, are discharged fromthe plant by gravity to a storage pond. The storage pond was designedfor an initial storage capacity of two years' production. Under sunlight,most of the free cyanide in the sluny is destroyed by natural degrada-tion.
The tailings dam overflow, nevertheless, may contain residual cyanide,depending on weather conditions. Since the clear overflow could still bevery poisonous and harmful to the environment, it is detoxified by useof chlorinated lime. The tailings overflow is continuously monitored andchecked. If the cyanide level exceeds the predetermined level, thesolution is detoxified. To achieve this, the tailings dam overflow flowsinto two detoxification tanks.
Hypochloride solution is added to the first tank. The dosage is auto-matically controlled by a redox probe. Milk of lime must be added tooperate the system efficiently. The lime addition is controlled by a pHprobe. The detoxified solution is then discharged to the environment.
h. Electrical Control System
The gold plant is controlled from three control centers, located in thecrushing-screening section, mill building and gold recovery building.
5. ANCILLARYFACILITIESAND UTILITIES
The ancillary facilities and utilities consist of the following:
. Administration building
. Change house
. Workshops
. Warehouses
. Laboratory· Electrical switchyard and primary and secondary distribution facilities. Pipeline for process water supply· Other utilities for potable water supply, etc.
6. EMPLOYMENT
Employment and pay ranges at Lega Dembi are shown below.
93
SECTIONX. EXISTINGMINING OPERATIONS
SOURCE: Kebede Regassa Feyessa, Mining Engineer, Mineral OperationsDepartment.
94
Figure 12Lega Dembi Gold Mine and Plant
Employment and Pay Ranges
Classification Employees Pay RangeBirr/month
Managers 40 1000-1300
Engineers 160 500-1040
Operators, 400 200-500Journeymen
Laborers 200 200
TOTAL 800
..."...rc fine
CYCLO~ ~oar.e
HEAT
Figure 13Process Flow Diagram of Lega Dembi Gold Plant
-.. ~ -.. ~ .....
0_ / ~~ flocculentCRUSHINGI / ~ THICKENING (DEWATER)
water / / t I I
.~ ". ~ I,f?') cold cyanide
.~~~~~ lime.~ ~ solutionGRINDING I
/ / re-uae'f~ I LEACHING~"tJ4 e t-4--..
o / -0- I .- - W . carbon
SIZING '...' LEACHTAS!;O-.I. I ::RBONINPULP :..__i. fine -4-- -4-- -4--' I Ihot cyanide' I
0'"coar.. I c: · t,p.. aolutlont ,, ~ causticI GRAVITY I - '''J'''~ STRIPPING WASTEDAM I
LCONTACTORS , I
',. t tP., &~ V steel wool ,I -:Jr':'" mercury STRIPVESSEL ... .
AMALGAMATION. ~ ELECTROWINNINGl:::III EFFLUENTDETOX I
~ ~ "1 IJ. amalga~. t t ~~ ..-!J~ W ~
RETORTFURNACEf=t mercury ~I I U distillate CELL
t t~ -.. ~ -.. .....\.;I sponge gold
ore
~bullion
SOURCE: Ethiopian Minerai Resources Development Corporation
95
SECI10N X. EXISTING MINING OPERATIONS
-c. KENTICHATANTALUMMINE ANDPILOT PLANT
1. GEOLOGY
rI.
The Kenticha tantalum-niobium deposit is located approximately 50 kilometerssoutheast of the mining town of Shakiso, in the Kenticha Greenstone Belt ofthe Adola Region. The deposit was identified by the Adola Mineral Evaluationand Development Project. Exploration work was done between 1983 and 1987and in 1988 the ore body was delineated.
The pegmatite body is 2.5 kilometers long by 150 meters wide, with a truethickness of 50 meters. It strikes north-south and dips 20 degrees east. Thehanging wall is serpentine and the footwall is granite. The contact with thegranite is gradational. The TCizOsgrade increases toward the hanging wall ofthe body, whereas the Nb20S content increases toward the footwall. Thetantalum-rich zone is approximately 2 kilometers long. The richest niobium oreis found in the south end of the pegmatite body.
rJ
-
-. At the hanging wall contact there is a 50-centimeter zone of green micaceousselvage and other uncommon minerals. In the pegmatite body, a white beryloccurs as the hanging wall is approached. Spodumene and c1eavelandite (albitein lamellar masses) appear to be guides to good ore. The pegmatite has fingersgoing into the hanging wall serpentinite. The composition is mainly microclinefeldspar and glassy quartz, suitable as raw material for the ceramics industry.
rI 2. RESERVES
r Two types of ore have been recognized: weathered crust ore and primary ore.Intensive exploration of the weathered crust ore body has indicated the exis-tence of economic ore reserves. The ore reserves were determined by pittingand boreholes. Pits were put down on a 20 by 40 meter grid, and the boreholeswere on a 40 by 80 meter grid. Reserves are stated to be 2400 metric tons ofTCizOsaveraging 0.015% TCizOsand 2300 metric tons of Nb20S' A cut-off gradeof 0.005% was used for ore reserve calculation purposes. The primary ore zoneis open-ended and additional reserves will probably be identified.
,....
II
,...,.
Though detailed exploration of the primary ore zone has not been conducted,the limited geological information and chemical analyses available indicatereserves of TCizOsof 17,000 metric tons with 0.017% average grade.
...... 3. MINING
The open-pit mining operation uses the following equipment:
. Stripand stockpile: three D7D Caterpillars, 14 hours per day;Workstockpile: two D6D Caterpillars, 14 hours per day;Load: one 3 cubic meter Volvo loader, 16 hours per day.
.
.
96
~
SECTION X. EXISTING MINING OPERATIONS
4. PILOT PLANT
After the ore body was delineated in 1988, a concentrator pilot plant with 200-metric ton capacity per 8-hour shift was built. The plant, which has been inoperation since 1990, produces approximately 20 metric tons per year oftantalum pentoxide. A description of the process follows and a process flowdiagram is shown in Figure 15.
The ore is delivered to the feed bin's grizzly, which has 125mm openings.Oversize, + 125mm rocks which do not pass through the grizzlyare removedand stored separately. The undersize, 125mm product of the bin is transportedby water to the scrubber trommel where it is disintegrated and washed so thatuseful mineral constituents are separated from clays and rock. The undersizeproduct is classifiedinto two classesaccording to the grain size.
The -16 to 0 mm product passes throughthe openings of the scrubber trommeland then, by gravity feed, passes through 300 millmeter slurry pipes to twoimmobile, inclined 4 mm screens. The oversize product, -125to + 16 mm, isdelivered to a conveyorwhere the large-sizetantalite aggregatesare picked out.The remaining product is delivered to the dump.
The undersize, -4 mm, product of the screens is delivered to a dewatering coneto obtain two products, the overflow and the sandy condensed product. Theoverflow of the cone is directed to hydrocyclones of 150 mm diameter, wherethe product is classified and dewatered. The slurry is delivered to the concen-tration table; the underflow of the hydrocyclones is sent to the tailing-dump.The condensed product of each screen is transported for further processing tothe first spiral separates.
The oversize, -16 to 4 mm, product of each screen is transported for furtherprocessing to MOD-2m jigging machines. The jigging machines produce threeproducts: oversize concentrate, undersize middling and tailings. The tailings aredelivered by gravity to the dump. The oversize, -16 to + 2 mm, concentrate isremoved periodically, as it accumulates, from the screen of the jigging machineand hand-sorted to obtain monomineral, coarse-grained tantalite concentrate.
The middling, -2 mm, product of the jiggers, preliminarily dewatered in thecone, is delivered to the second spiral separator together with the product ofthe first separator.
The spiral separator produces three products: rough concentrate, middlingproduct and tailings. The tailings are sent to the dump, the rough concentrateis delivered for additional cleaning to the concentration table, and the middlingproduct is transported for a cycle of spiral separation.
;A
The tailings of the second spiral separator are also sent to the dump. Therough concentrate, together with the concentrate of the first spiral separator,
97
SEcrION X. EXISTINGMINING OPERATIONS
is transported to the concentration table for additional cleaning. The middlingproduct is sent for a cycle of spiral separation.
Thus, additional cleaning operations are carried out by three concentrationtables of a similartype and size. Concentratesfrom all the concentration tablesare transported to the dewatering bin and then further processed to obtain amarketable concentrate. The middlingproduct from the concentration tablesis accumulated in the sump and pumped from the sump to the second spiralseparator. The tailings of the concentration tables are directed from thedewatering bin to a 0.2 mm vibrating screen. The product on the screens isclassifiedaccordingto the grain size: to +0.2 mm, sand product, and -0.2 mm,slimeproduct.
Bothproducts are transported to the magnetic separators, where the magneticfraction such as magnetite, etc. is separated from the concentrate and sent tothe dump. The non-magnetic fraction of each magnetic separator is sentseparately on to small-sizeslime andsand concentration tables. Cleaning andproductionof marketabletantalite concentrateswith 35-41% T~Os is completedin the concentration tables. The tailings of the tables are pumped into thesecondspiral separator for processingtogether with the middlingproduct of thelarge-size concentrate tables.
Hand-sorted and coarse-grained concentrates have a much higher grade thanfine concentrate. The different concentratesare kept separate and are mixedto arrive at a marketable concentrate grade of 43% T~Os.
The plant is designed to operate 300 calendar days per year. Tbe basicschedule is 2 shifts per day, 8 hours per shift. Employment at the plant isshownbelow:
Figure 14Kenticha Tantalum Mine and
Plant Employment
Classification Employees Shifts
1
2
2
SOURCE: Regassa Kebede, Mineral OperationsDepartment.
98
Professional 30
Semi-professional 100
Laborers 50
TOTAL 180
99
GRIULY
TROMMEL
SCREEN&mm
m SCREENUNDERSIZE
WET.IIOOINO
JKIIIIDDlING,
ROUGHERSPIR.OL
AOUGHSPIRALF((D
ROUGHER ROUGHI"CONCS MIOS
SANDTABLE
SANDTABLE t I SUMU fABLEtFEED 'EED
SECOND SPIRAL
SECOND SPIRALFEED
SECOHOSPIRAL1110.
I SLIMESTABLE12 I
SUMES TULE 2FEED
SUMES TAILE 2CONC8
SCREENZmm
FINAL2rnmSCREENFEED
CD MADSE' IFEED I
I Fa WAG IREJECTS
COARSECLE.ANUP 'INE CLEANUP
co CLEANUPTAIUFUD --,
CO CUANUPTAU
SECTION X. EXISTING MINING OPERATIONS
D. LAKE ABlYATA SODA ASH OPERATION
This semi-industrial soda ash operation is situated on the shores of Lake Abiyata inthe Ethiopian Rift Valley, approximately 200 kilometers south of Addis Ababa. Theplot plan of the soda ash plant is shown in Figure 17 and the process flow diagram inFigure 18.
1. SODAASH RESOURCE
The waters of Lakes Abiyata, Shala and Chitu have medium to high salinity andcontain sodium-chloride-carbonate. Their brines are amenable to the extractionof trona and other salts.
2. RESERVES
Studies indicate that these lakes contain 460 million metric tons of sodium
carbonate at concentrations ranging from 1.1% to 1.9%. Lake Abiyata issufficient for the current production level. Lake Shala, with a larger storagecapacity, is considered the prime source of brines for future industrial produc-tion.
3. BRINE COLLECTIONANDEVAPORATIONOPERATION
Two pumps are used to pump 2 million cubic meters of brine out of LakeAbiyata into two reconcentration ponds. These ponds are nearly 6 kilometerslong and provide an evaporation surface of over 1 million square meters.
4. PLANT
A 20,000 m~tric ton per year capacity treatment plant has been in operation atthe site since 1990. The latest production figure is 14,700 metric tons ofproduct per year. Soda ash is produced by solar evaporation and fractionalcrysta11ization,followed by washing, classifying, centrifugal solid liquid separa-tion and calcination. In the liquid separation and calcination stage, impuritieswhich discolor the salts are removed, resulting in a 99 percent pure product.
Of the current production, 1000 metric tons is used for testing export potentialand the balance is shipped to Addis Ababa for use by domestic industries. Inthe future, 12,000 metric tons will be sent to a new caustic soda plant beingbuilt in the town of Ziway.
EMRDC has considered commercial scale plants ranging from 200,000-1,000,000 metric tons per year output capacity, subject to successful marketdevelopment, adequate inland transportation, and availability of project financ-ing. The Ministry envisions increased production in the future for caustic sodaand other products of commercial value. If and when domestic demand justifiesit and export markets are developed, an industrial scale plant of 200,000 metric
\100
_.
SECTIONX. EXISTING MINING OPERATIONS
tons per year or larger designcapacity might be economicallyviable. Produc-tion mightthen be increased in successivesteps up to 1,000,000metric tons peryear.
Employment at the Lake Abiyata operation is shownbelow.
Figure 16Lake Abiyata Soda AshComplexEmployment
SOURCE: Kebede Regassa Feyessa,Mineral Operations Department.
101
-- -- ---
Classification Employees
Professional 15
Journeymen 80
Laborers 55
TOTAL 150
----
EIt)co
enWen-w11:_
we!::u~zi:i:a::wLLO:E°m«
:5~
GATEHOUSE
ATHLETIC FIELD
P t 9
Figure 17Plot Plan of Lake Abiyata Semi-Industrial
Soda Ash Plant L? -z.
170m
---I ,Io
PRODUCTSTORAGE
SODA ASHREFINING &
DRYINGSECTIONS
~dUTlliTIESI I
RESERVED FORI
CAUSTICSODAIL~LANT_J
WORKSHOP
-----------------
102
RAWMATERIAL
PILES
-
Figure 18Process Flow Diagram of Lake Abiyata
Semi-Industrial Soda Ash Complex
CJZZNU::,..Wza:ox-<1)1-<tfrl<t<l)Co<I)
r------------------.I PONDS SYSTEM I .. II SECTION11 T'III,
III
-~II,
IIII
effluent
lime
---"1". -- ---
I WASHING t-t. W~M I
'fueT---
---.......I CAUSTICSODA-., waste CaC03
L__ "rNT__J.'Udge ·1I
" ... un , II'U Iz a~ I>M Ia:....C Z
o GRINDINGx_ 1<1)1-
I<to<tW Ig <I) 1000 mt/year > 99.3% 7000 mt/year > 97% I<I) II_ _ __ J
8700 mt/year 30% NaOH solution
SOURCE: Ethiopian Minerai Resources Development Corporation; drawing by Glulunl Chemle Gmbh.Note: The caustic soda plant shown above Is In the planning stage.
-
103
SECI10N X. EXISTING MINING OPERATIONS
E. PROFILES OF OTHER EMRDC OPERATIONS
1. ADOLAGOLD DEVELOPMENTENTERPRISE
AGDE is responsible for the exploitation of the placer gold deposits in theAdola Greenstone Region. During the last 50 years, over 37 metric tons ofgold have been recovered fromthe riversflowingthrough the region. In recentyears, mechanized mining methods, including hydraulic mining, have beenincreasingly used and many formerly inaccessible deposits are now beingexploited. AGDE is currentlymining fiveplacer deposits. Each year AGDEmoves nearly 2 million metric tons of overburden and produces about 300kilograms of gold.
2. ADOLAMINERALEVALUATIONANDDEVELOPMENTPROJECT
The Adola Gold Exploration Project (AGEP) was established in 1978 withSoviet technical assistance. In just twelve years, AGEP geologists mapped anarea of nearly 7500 square kilometers and identified 40 primary gold sources,numerous alluvial deposits and a range of other rare metals. Among theirdiscoveries are the North gold deposit at Lega Dembi and the Kenticha tanta-lum deposit.
Later AGEP was transformed into the Adola Mineral Evaluation and Develop-ment Project (AMEDP), which is responsible for the exploration and evaluationof mineral deposits and prospects. AMEDP has seven drilling crews operatingin the region. A well equipped analytical laboratory based in Shakiso backs upthe field workers.
3. BOLE BULBULACONSTRUCTIONSTONEPRODUCTION ENTERPRISE
The Bole Bulbula Construction Stones Enterprise is situated 10 kilometersoutside Addis Ababa. The biggestcrushingfacilityof its kind in Ethiopia, it hasthe capacity to produce more than a millionmetric tons of material a year andcurrently produces 300,000metric tons of crushed basalt each year for aggre-gate. EMRDC plans to increase the plant's capacity.
4. GEM STONE DEVELOPMENTPROJECT
Established in 1989,the Gem Stone Development Project trains technicians tograde, cut and polish the semi-precious stones found throughout Ethiopia.
5. CERAMIC RAWMATERIALSSTUDYANDDEVELOPMENTPROJECT
The kaolin, feldspar and quartz required for the production of ceramics arefound in abundance in Ethiopia. To help develop this industry, EMRDC hasset up a project to develop exploitable ceramicdeposits. In 1990work beganon an operation to produce 14,000 metric tons of washed kaolin per year.
104
REFERENCES
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Abenet Zekewos. Reporton Gold and MetalMineralization,Kurmuk. EIGS internalreport, 1991.
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Ahmed Mohammed. Report on Kurmuk-Geissen Integrated Mineral Exploration Project.EIGS internal report, 1986.
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Ayele et al. ProspectingReportof HaramsamArea. Internal report, 1989.
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1
REFERENCES AND BmLIOGRAPHY
REFERENCES
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Getinet Mewa et al. Report on Detailed Geophysical Survey in Central and Eastern Oda-Godere Area. EI GS internal report, 1989.
GeologicalReport prepared for R. M. Parsons Potash Exploration Company, 1965.
Getenehe Assefa, "Mineral Industry of Ethiopia: Present Conditions and Future Prospects,"Journal of African Earth Sciences, Vol. 3, No.3, pp 331-345, 1985.
Grechanik et al. Report on Detailed Exploration of the Bedakessa, Kajimiti and Dermi- DamaPlacers, with Reserve Calculations. EMRDC, 1984.
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Japan Overseas Technical Cooperation Agency. Report on the Geological Survey of WollegaArea, Western Ethiopia. (Plate I & II). October 1974.
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Senbeto Chewaka and M. J. de Wit (editors). PlateTectonicsand Metallogenesis:SomeGuidelinesto EthiopianMineralDeposits, Chapters 8-18. EIGS Bulletin No.2, July 1981.
2
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Serguienko, V. N., and Aklilu Assefa. Reconnaissance Survey to Assess Apatite OrePotential of an Anorthosite-Gabbroic Intrusive and Alkaline-ultrabasic Ring Complexes inEthiopia. EIGS internal report, 1988.
Shelekhov et al. Regional Geological and Exploration Work for Gold and Other Minerals inthe Adola Goldfield. EMRDC, 1986.
ShiferawDemissie, Yu, Marchuk, V. Evdokimov. Summaryof the Geologyand MineralPotentialof the Adola Area. EMRDC, 1987.
Solomon et al. The Geology and Structure of MoyaleArea. 1991.
Taye Habtewold et al. Report on Alluvial Gold Prospectsof Chamo Creek, Karl, Kandibabaand Middle Akobo River. EIGS,1993.
Teferi Birru and E. P. Zhbanov (compilers). GeologicalProspecting and Exploration forPrimary Gold and other Minerals in Ageremariam, Arero and BulBul Areas (SouthernEthiopia), Volumes 2 and 3. EIGS, 1991.
Tolessa Shagi and Tefera Eshete. The GeologyandStructureof Haramsamand Hassamte,Moyale.April 1991.
UNDP. Report on the Mineral Survey of Two SelectedAreas of Ethiopw. 1971.
Wollie Sheka. Geology and Mineralization of Dul and Azale-Akendeyu. EIGS internalreport, 1991.
NOTE: Ethiopian authors and editors are listed under their given names since in Ethiopiathe last name is not a surname but the given name of one's father. References werepublished in Addis Ababa unless otherwise noted.
3
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From Database of the U.S. GeologicalSurvey LibraryReston, Virginia, United States
SilverPlatter 3.00 and 3.1GEOREF Disc 3
Serpentinites as a Possible Source of the Adola Placer Gold, Sidamo, Ethiopia.Clark, A. M. S.Can. Lake Explor., Calgary, Alberta, CanadaMiner. Deposita. 14. (1). p. 119-122. 20 Refs.1979.
Conventional Method and Digitally Enhanced Landsat Imagery for GroWldwaterExploration in the Main Rift Valley of Ethiopia.Aberra- Tilahun; Wihuri-HeikkiUniv. Helsinki, Dep. Geol., Helsinki, Finland; Univ. Tex. at Austin, United States;Finn. Int Dev. Agency, FinlandSimpson, Eugene S., Sharp, John M., Jr. Selected papers on Hydrogeology from the28th International Geological Co~gress. Univ. Ariz., Dep. Hydrol. and WaterResour., Tucson, AZ, United States.Hydrogeology, Selected Papers. 1. p. 473-487. 6 Refs.1990
28th Intemational Geological Congress, Washington, DC, July 9-19, 1989
Ethiopian Red Sea Petroleum Geology and Regional Geophysical Evaluation.Assefa, A.; Tadesse, K.; Worku, T.; Tsadik, E.G.Ethiopian Inst. Geol. Surv., Addis Ababa, EthiopiaAnonymous. AAPG International Conference; abstracts. AAPG Bulletin. 75. (8).p. 1402-14031991
AAPG International Conference, London, Sept 29-0ct. 2, 1991
AC Effects in Resistivity Data from Geothermal Prospects.Caldwell, Grant; Hochstein, M. P.; Olurna, BefedakuUniv. Auckland, Geotherm. Inst, Auckland, New Zealand; University of AucklandGeothermal Institute, Auckland, New Zealand; Minist Mines, Energy & WaterResour., EthiopiaProceedings of the Pacific Geothermal Conference 1982; incorporating the 4th NewZealand Geothermal Workshop; Parts 1 and 2. University of Auckland GeothermalInstitute, Auckland, New Zealand. Proceedings of Pacific Geothermal Conference.4. p. 151-155. 10 Refs.1982
Pacific Geothermal Conference 1982; incorporating the 4th New ZealandGeothermal Workshop, Auckland, 1982
SOURCE: The publications from GeoRef listed in this bibliography are from the GeoRef database of theAmerican Geological Institute, and are used with AGI's permission.
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Chemical Grouping of Tephra from the Turkana Basin, Northern Kenya andSouthwestern Ethiopia.Haileab, Bereket; Brown, Francis H.University of Utah, Department of Geology and Geophysics, Salt Lake City, UT,United States.
Anonymous. Society of America, 1993 annual meeting. Abstracts with programs.25. (6). p. 327-3281993
Well Testing Results in Aluto-Langano Geothermal Field.Wale, Abatnen; Melaku, Markos; Birhan, Yihezis A.Geotherm. Explor. Proj., Addis Ababa, Ethiopia; Geotherm. Resour. counc., Davis,CA, United StatesCombs, Jim. Transactions, 1990 International Symposiwn on Geothermal Energy.Geotherm. Resour. Counc., Davis, CA, United States.Transactions, Geothermal Resources Council. 14. (1-2). p. 993-997. 7 Refs.1990
Geothermal Resources Council 1990 Annual Meeting, Kailua, Kona, HI, Aug. 20-24, 1990
Status of Geothermal Energy in Ethiopia.Endeshaw, Abebaw; Belaineh, MollaEthiop. Inst. Geol. Surv., Addis Ababa, Ethiopia; Geotherm. Reseur. Counc., Davis,CA, United StatesCombs, Jim. Transactions, 1990 International Symposium on Geothermal Energy.Geotherm. Resour. Counc., Davis, CA, United States.Transactions, Geothermal Resources Council. 14. (1-2). p. 47-531990
Geothermal Resources Council 1990 Annual Meeting, Kailua, Kona, HI, Aug. 20-24, 1990
Late Eocene-Recent Volcanism and Faulting in the Southern Main Ethiopian RiftEbinger, C. 1.; Yemane, T.; Woldegabriel, G.; Aronson, J. L.; Walter, R. C.University of Leeds, Department of Earth Sciences, Leeds, United Kingdom;Ethiopian Institute of Geological Surveys, Ethiopia; Los Alamos NationalLaboratory, United States; Case Western Reserve University, United States; Instituteof Human Origins, United States.Journal of the Geological Society of London. 150 (Part I). p. 99-1081993
Stratigraphic and Structural Relationship of Ethiopian and Gregory (Chew-Bahir)Rifts, Southern Ethiopia, East AfricaYemane, Tesfaye; Vondra, Carl F.Iowa State University, Department of Geological and Atmospheric Sciences, Ames,IA, United States.Anonymous. Geological Society of America, North-Central Section, 27th AnnualMeeting. Abstracts with programs. 25. (3). p. 91-921993
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Neoproterozoic Structures in the Mozambique Orogenic Belt of Southern Ethiopia.Bonavia, F. F.; Chorowicz, 1.Universite Pierre et Marie Curie, Departement de Geotectonique, Paris, FrancePrecambrian Research. 62. (3). p. 307-322. 34 Refs.1993
Possibility of Geophysical Research in East African Metallogenic Zone in Respectof Detecting Non-ferrous and Precious Metal DepositsZboril, L.; Filo, M.; Hovorka, D.Geofyz., Brno. Czechoslovakia;Comm. Recent Crustal Movements Afr., AddisAbaba, Ethiopia; Comenius Univ., Bratislava, CzechoslovakiaWassef, A.M. Proceedings of the First International Symposium on CrustalMovements in Africa. Comm. Recent Crustal Movements Afr., Addis Ababa,Ethiopia. P. 458-483. 56 Refs.1981First International Symposium on Crustal Movements in Africa, Addis Ababa, May5-16, 1981United Nations Beon. Commission Africa, Addis Ababa, Ethiopia
The Geophysics and the Structural Behavior of the Earth's Crust.Thomas, Jr.Comm. Recent Crustal Movements Afr., Addis Ababa, EthiopiaWassef, A. M. Proceedings of the First International Symposium on CrustalMovements in Africa. Comm. Recent Cmstal Movements Afr., Addis Ababa,Ethiopia. p. 430-440. 4 Refs.1981
First International Symposium on Crustal Movements in Africa, Addis Ababa, May5-16, 1981United Nations Beon. Commission Africa, Addis Ababa, Ethiopia
Precambrian Crustal Evolution and Its Significance in Mineral Exploration inEastern and Southern Africa Subregion.Banerjee, A. K.Comm. Recent Crustal Movements Afr., Addis Ababa, EthiopiaWassef, A. M. Proceedings of the First International Symposium on CrustalMovements in Africa. Camm. Recent Crustal Movements Afr., Addis Ababa,Ethiopia. p. 104-126. 24 Refs.1981First International Symposium on Crustal Movements in Africa, Addis Ababa, May5-16, 1981United Nations Beon. Commission Africa, Addis Ababa, Ethiopia
An Outline of the Metallogenic History of Ethiopia.Getaneh, A.; Pretti, S.; Valera, R.Univ. Addis Ababa, Dep. Geo!.,Addis Ababa, Ethiopia; Univ. Cagliari, ItalyAnonymous. GeoSom 87; International Meeting; Geology of Somalia andSurrounding Regions; abstracts. p. 72Somali Nat!. Univ., Magadishu1987
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GeoSom 87; Geology of Somalia and Surrounding Regions, Mogadishu,Nov. 23-30, 1987
Distribution of Precious Metals in the Tulu Dimptu Ultramafic Body (Welega,Ethiopia).Sighinolfi, G. P.; Abena, G.; Gorgoni, C.; Valera, R.Univ. Modena, Inst. Mineral. and Petrol., Modena, Italy; Univ. Addis Ababa,Ethiopia; Univ. Cagliari, ItalyAnonymous. GeoSom 87; Geology of Somalia and Surrounding Regions; lateabstracts. p. 17Somali Nat!. Univ., Dept Geol., Mogadishu1987
GeoSom 87; Geology of Somalia and Surrounding Regions, Mogadishu, Nov. 24-Dec. 1, 1987
Tectonometamorphic Evolution of the Moyale Region, Southern Ethiopia.Alene, Mulugeta; Barker, Andrew, 1.University of Southampton, Department of Geology, Southampton, United KingdomPrecambrian Research. 62. (3). p. 271-2831993
Magma Genesis in An Ongoing Rifting Zone; the Tadjoura Gulf (Afar Area).Barrat, 1. A.; Jaben, B. M.; Fourcade, S.; Joron, 1. L.Universite de RelUles I, Geosciences Rennes, Rennes, France; CEN Saclay, FranceGeochimica et Cosmochimica Acta. 57. (10). p. 2291-23021993
Mineral Paragenesis in the Au-Ag-Cu-Zn-Pb-Te Deposit of Lega Dembi (Ethiopia).Fiori, M.; Garbarino, C.; Grillo, S.; Solomon, T.; Valera, R. G.1st Giacimenti Miner. Univ., Cagliari, ItalyGoode, A. D. T., Smyth, E. L., Birch, W. D., Bosma, L. I.BicentelUlialGold 88; extended abstracts; poster programme.Abstracts, Geological Society of Australia. 23. (1-2). P. 184-1861988
BicentelUlialGold 88, Melbourne, Victoria, May 16-20, 1988
Potential Hydrocarbon-generating Rock Units Within the Phanerozoic Sequence ofthe Ogaden Basin, Ethiopia; a Preliminary Assessment Using the Lopatin Model.Assefa, GetanehAddis Ababa Univ., Dep. Geol., Addis Ababa, EthiopiaJournal of Petroleum Geology. 11. (4) p. 461-472. 19 Refs.1988
Current Status (1987) of Geothermal Exploration in Ethiopia.Endeshaw, AbebawEthiop. Inst. Geol. Surv. Geotherm. Project, Addis Ababa, Ethiopia; Int. Inst.Geotherm. Res., Pisa, ItalyBarbier, E., Dickson, M. H., Fanelli, M. Small geothermal resources; Part 2,Geothermal Projects in Developing Countries. Int. Inst. Geotherm. Res., Pisa, Italy.Geothermics. 17. (2/3). p.477-488.
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19881st UNITAR/UNDP Workshop on Small Geothennal Resources, Pisa, May 11-22,1987
Assessment of Undiscovered Conventionally Recoverable Petroleum Resources ofNorthwestern, Central, and Northeastern Africa Oncluding Morocco, Northern andWestern Algeria, Northwestern Tunisia, Mauritania, Mali, Niger, Eastern Nigeria,Chad, Central African Republic, Sudan, Ethiopia, Somalia, and SoutheasternEgypt).Peterson, 1. A.U.S. Geol. Surv., Missoula, MT, United StatesOpen File Report U.S. Geological Survey. 28 p.U.S. Geological Survey, Reston, VA1983OF 83-0598U.S. Geol. Surv., Open File ServoSect, West. Distrib. Branch, Denver Fed. Cent,Lakewood, CO, United States
Sedimentologicaland Palynological Implications of a Tertiary Lignite Occurrencein an Ancient Rift Lake (Chilga, Ethiopia).Yemane, Kedamawit; Bonnefille, R.; Taieb, Maurice; Faure, H.C.R.S.S., Lab. Geol. Quaternaire, Marseilles, FranceBogdanov, N. A. Tezisy; 27 y Mezhdunarodnyy Geologicheskiy Kongress,Abstracts; 27th International Geological Congress.International Geological Congress. 27. (2). p. 2321984Mezhdunarodnyy Geologicheskiy Kongress; 27, Moscow, Aug. 4-14, 1984
Precambrian Geology of the Gore-Gambela Geotraverse, Western Ethiopia.Moore, 1. M.; Morgan, 1.; Teferra, M.; Teklay, M.Ottawa Carleton Cent Geosci. Stud., Ottawa, ON, Canada; Ethiop. Inst. Geol.Surv., Ethiopia; Addis Ababa Univ., EthiopiaNewsletters bulletin UNESCO. 5. p. 101-113. 12 Refs.1986
Application of Remove Sensing to Tectonic and Metallogenic Studies in NE Africa.Berne, Seife M.Open Univ., Dep. Earth Sci., Milton Keynes, United KingdomCook, Jerald 1., Rogers, Robert H. Proceedings of the Fifth Thematic conferenceon remote Sensing for Exploration Geology; Mineral and Energy Exploration;Technology for a Competitive World; Volume 1. p. 383-391. 25 Refs.Environ. Res. Inst. Mich~,Ann Arbor, MI1987
Fifth Thematic Conference on Remote Sensing for Exploration Geology; Mineraland Energy Exploration; Technology for a Competitive World, Reno, NV, Sept 29-Oct. 2, 1986
Applied Visual Landsat Inventories for Water Resources Development; anEthiopian Case Study.Larsson, R. A.; Hanson, G.
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Precambrian Podifonn Chromitites from Kenticha Hill, Southern EthiopiaBonavia, F. F.; Diella, V.; Ferrario, A.Universite Pierre et Marie Curie, Departement de Geotectonique, Paris, France;C.N.R., Italy; Universita degli Studi di Milano, ItalyEconomic Geology and the Bulletin of the Society of Economic Geologists. 88.(1). p. 198-202.1993
GEOREF Disc 2
Preliminary Investigation Results on the Pozzolanic Properties of Local ScoriaBerhane, z.Addis Ababa Univ., Fac. Technol., EthiopiaSinet 4. (2). p. 83-93. 10 Refs.1981
The Mineral Industry of Ethiopia; Present Conditions and Future Prospects.Assefa, G.Addis Ababa Univ., Dep. Geol., Addis Ababa, EthiopiaJournal of African Earth Sciences. 3. (3). p. 331-345. 23 Refs.1985
Seismic Exploration in the Ethiopia Red Sea.Sengbush, R. L.Colo. Sch. Mines, Golden, CO, United StatesWilliams, L. M. Proceedings Offshore Technology Conference. 17 (Vol. 2). p.309-3151985
1985 Offshore Technology Conference, Houston, May 6-9, 1985
Geothermal Exploration Drilling at Lake Langano (Ethiopia).Demissie, G.SINET Newsletter. 5. (1). p. 1-41982
Plate Tectonics and Metallogenic Processes in Ethiopia (preliminary Report)Assefa, G.; Di Paola, G. M.; Valera, R.Addis Ababa Univ., Geol. Dep., Addis Ababa, EthiopiaRendiconti della Societa ltaliana di Mineralogia e Petrologia. 37. (2). p. 861-867.3 p. Refs.1981Convegno di Salice Terme, Pavia, June 2-4, 1981
The Mineral Industry of Ethiopia; Present Conditions and Future Prospects.Assefa, G.Addis Ababa Univ., Dep. Geol., Addis Ababa, Ethiopia
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Kogbe, C. A. Geology for Development; Mineral Resources and ExplorationPotential of Africa. Journal of African Earth Sciences. 1. (3-4). p. 3561983Sixth General Conference on African Geology; Geology for Development; MineralResources and Exploration Potential of Africa, Nairobi, Dec. 11-19, 1982
Analogy Between Natural Gas Found in Lakes of Rift Valley System of East Africaand Its Allied Gas in Japan.Fukuta, O.Geol. Surv. Jap., Ibaraki, JapanAnonymous. Wallace E. Pratt Memorial conference on Future Petroleum Provincesof the world; abstracts. AAPG Bulletin. 68. (9). p. 12021984 .
Wallace E. Pratt Memorial Conference on future Petroleum Provinces of the World,Phoenix, AZ, Dec. 2-5, 1984
Drilling of Temperatures Gradient Roles With Aerated Auids, and TemperatureSurvey of the Aluto Geothermal Prospect (S. Lakes District, Ethiopia).Hochstein, M. P.; Jepsen, P. L.; Collis, S. K.Univ. Auckland, Geotherm. Inst, Auckland, New ZealandAnonymous. Proceedings of the 5th New Zealand Geothermal Workshop, 1983. p.133-137. 11 Refs.Univ. Auckland, Auckland1983Fifth New Zealand Geothermal Workshop, Auckland, Nov. 9-11, 1983
Role of Borehold Geophysics in Mineral Resources Exploration in Africa.Mdala, C.Univ. Zambia, Sch. Mines, ZambiaAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 163-166. 14 Refs.Inst. Min. Metall., Rertford. U.N. Econ. Comm. Africa, Addis Ababa1981
First Regional Conference on the Development and Utilization of MineralResources in Africa, Arusha, Feb. 2-6, 1981
CobaltUnited Nations, Economic Commission for Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 291-298. 75 p. Refs.Inst. Min. Metall., Rertford. U.N. Econ. Comm. Africa, Addis Ababa1981
First Regional Conference on the Development and Utilization of MineralResources in Africa, Arusha, Feb. 2-6, 1981
Bauxite and Development of the Aluminium IndustryUnited Nations, Economic Commission for Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 283-290Inst. Min. Metall., Hertford. U.N. Econ. Comm. Africa, Addis Ababa
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TWlgsten, Columbium and Tantalum.United Nations, Economic Commission for Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 271-282.Inst. Min. Metall., Hertford. U.N. Econ. Comm. Africa, Addis Ababa1981
First Regional Conference on the Development and Utilization of MineralResources in Africa, Arusha, Feb. 2-6, 1981
TitaniumUnited Nations, Economic Commission for Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 264-270. 28 Refs.Inst. Min. Metall., Hertford. U.N. Econ. Comm. Africa, Addis Ababa1981
First Regional Conference on the Development and Utilization of MineralResources in Africa, Arusha, Feb. 2-6, 1981
NickelUnited Nations, Economic Commission for Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 255-263. 46 Refs.lost. Min. Metall., Hertford. U.N. Econ. Comm. Africa, Addis Ababa1981
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Manganese.United Nations, Economic Commission for Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 240-254. 88 Refs.lost. Min. Metall., Hertford. U.N. Econ. Comm. Africa, Addis Ababa1981
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First Regional Conference on the Development and Utilization of MineralResources in Africa, Arusha, Feb. 2-6, 1981
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United Nations, Economic Commission for Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 195-206. 64 Refs.lost. Min. Metall., Hertford. U.N. Beon. Comm. Africa, Addis Ababa1981
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United Nations, Economic Commission for Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 175-193.Inst. Min. Metall., Hertford. U.N. Beon. Comm. Africa, Addis Ababa1981
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Petroleum Potential of Africa and Prospects for its DevelopmentUSSR, Ministry of Geology, USSRAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 155-160. 26 Refs.Inst. Min. Metall., Hertford. U.N. Beon. Comm. Africa, Addis Ababa1981
First Regional Conference on the Development and Utilization of MineralResources in Africa, Arusha, Feb. 2-6, 1981
Processing and Utilization of Mineral Raw Materials in African CountriesUnited Nations, Economic Commission for Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 43-51. 2 Refs.lost. Min. Metall., Hertford. U.N. Beon. Comm. Africa, Addis Ababa
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1981First Regional Conference on the Development and Utilization of MineralResources in Africa, Arusha, Feb. 2-6, 1981
Exploitation of Mineral Resources and Development Trends in the Mining Industryin Africa.United Nations, Economic Commissionfor Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p. 26-42.Inst. Min. Metall., Hertford U.N. Beon. Comm. Africa, Addis Ababa1981First Regional Conference on the Development and Utilization of MineralResources in Africa, Arusha, Feb. 2-6, 1981
Major Mineral Resources of Africa.United Nations, Economic Commission for Africa, SecretariatAnonymous. Proceedings of the First Regional Conference on the Developmentand Utilization of Mineral Resources in Africa. p.7-25. 19 Refs.Inst. Min. Metall., Hertford. U.N. Beon. Comm. Africa, Addis Ababa1981First Regional Conference on the Development and Utilization of MineralResources in Africa, Arusha, Feb. 2-6, 1981
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Comments on the Development of the Awash Valley, Ethiopia.Winid, B.Warsaw Univ., Fac. Georgr. and Reg. Stud., Warsaw, Poland; Univ. ColI. Swansea,Cent. Dev. Stud., Swansea, Wales, United Kingdom
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International Colloquium on River Basin Planning, Swansea, Wales, 1980
The Geology, Geochemistry and Origin of Sulphide Mineralization in Katta,Wollega Administrative Region.Mammo, TelahmtSinet; Ethiop. 1. Sci. 3. (1). p. 771980
The Geology of Sacaro Goldfield (Adola, Sidamo, S. Ethiopiai).Gabriel, Giday WoldeSinet; Ethiop. 1. Sci. 3. (1). p. 76-771980
Geothermal Study in Northwest Lake Abaya Area (southern Ethiopian Rift)Yirgu, GezahegnSinet; Ethiop. 1. Sci. 3. (1). p. 75-761980
On the Textures and Treatment of the Sylvinite Ore from the Danakil Depression,Salt Plane (Piano del Sale), Tigre, EthiopiaAugustithis, S. S.Chern. Erde. 39. (1). p.91-95. 4 Refs.'1980
Seismic Investigation of the Ogaden Basin, Onshore Ethiopia.Alazar-TesfalulColorado School of Mines, United States; Master's95 p.1987
Regional Hydrocarbon Source Rock and Thermal Maturity Evaluation of OgadenBasin, Ethiopia.Cayce, P. W.; Carey, B. D., Jr.Tenneco Oil Co., Houston, Tex., United StatesAm. Assoc. Pet Geol., Bull. 63. (3) p. 4311979
AAPG-SEPM Annual Meeting, Houston, Tex., April 1-4, 1979
11
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