Mineral Resources Potential - Geothermal Resources
Mineral Resources Potential - Geothermal Resources
Mineral Resources Potential - Geothermal Resources
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<strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong><br />
of Ethiopia<br />
Solomon Tadesse
;;<br />
5<br />
<strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong><br />
i of Ethiopia<br />
Solomon Tadesse
I@&h9969,<br />
I, zs3auozgR<br />
m,:m<br />
tn-ll;niMi<br />
.'ida~.qt@~qPp~<br />
a C.. . fI<br />
Mdis Ethiopia<br />
TCL +
....<br />
Chapter two<br />
'. . -<br />
Geological outline .,. . .......... "..H .... ...*..*...I....H 5<br />
2.1 Geology ....................... . ............................ 5<br />
2.1.1 Precambrian metamorphic<br />
rocks and associated<br />
intrusions ...............................I............. 5<br />
2.1.2 Late-Palaeozoic and Early-<br />
Mesozoic sediments ............................. 6<br />
2.1.3 Cenozoic rocks ................................. .-.. 9<br />
2.1.3.1 Cenozoic sedimentary<br />
rocks ....................................... 9<br />
2.1.3.2 Cenozoic vol~c rocks ......... 9<br />
r 2. I .3.3 The Rift and RiR<br />
volcanic rocks ................... . 10<br />
2.2 An overview of the main<br />
structural features in Ethiopia ........................... 17<br />
2.3 <strong>Mineral</strong> resources .............................................. 22<br />
Chapter three<br />
I<br />
Metallic minerals ............. -.*,. . . .... "..-... 32<br />
3.1 Gold Deposit ........... ....... .....I. ..++........ ............. 34<br />
3.2 Platinum Deposit ............................................. 71<br />
(<br />
3.3 Tantalum (Niobium, FEE, Lithium,<br />
I Beryliium) deposit ......................................... .78<br />
3,4 Nickel (Cobalt) deposit .................................... 95<br />
3.5 Irondeposit I .................................................... 100
3.6 Chromite ....................................................... 109<br />
3.7 Manganese deposit .......................................... f 11<br />
. 8 ~ a s d metals (Copper. Zinc. Lead,<br />
................... .***...<br />
Molybdenum. Wolfram) deposit .+ 113<br />
Radioactive minerals (Uranium. Thorium)<br />
posit ......................................................... 120<br />
ntite 122<br />
.........................................................<br />
.,. ...<br />
{* *" ..'.'"'.."*'*.. 'H w n ' r T41PJ. i ....<br />
.. I<br />
.... Industrial minerals . .....m..w.......~mm.*.mm.....*..m....1* f 23<br />
4.1 Soda ash (sodium carbonate) .......................... 125<br />
4.2 Diatomite ........................................................ 127<br />
4.3 Bentonite ....................................................... 129<br />
4.4 Other clays and kaolin .................................... 130<br />
4.5 Common-sdt ................................................ I33<br />
4.6 Magnesite ....................*.... . ............ 135<br />
4.7 Feldspars (Ceramic and sheet glass raw<br />
materials) ......... . .............. ....... 137<br />
4.8 Talc ........................... . ................................ 139<br />
4.9 Kyanite .................................,..................... i. ... 140<br />
4.10 Graphite ........................................................... 141<br />
4.11 Silica ................... . .......................... 142<br />
4.12 Quartz ........................................................ 1 4 4<br />
4.13 Mica ................... . .................................... 145<br />
4.14 Agrominerals ................................................... 146<br />
4.15 Phosphate ................... . ............................. N<br />
4.16 Gypsum. anhydrite ........................................ 150<br />
4.17 Potash ............................................................. 152<br />
4.1 8 Dolomite and Limestone ................................. 154<br />
4.19 Sulphurs ...................................................... 158<br />
4 -20 Pumicelscoria .................................................. 160<br />
4.21 Natd zeolite ................................................. 161<br />
4.22 <strong>Mineral</strong> waters ................................................ 163
423 Other metallic and industrid <strong>Mineral</strong>s ........... 164<br />
Chapter five<br />
Constraction material and dimension stones 166<br />
Chapter six<br />
..............<br />
5.1 Marble ..................................... . ........................ 167<br />
5.2 Limedone ....................................................... 170<br />
5.3 Granite ............................................................. 173<br />
5.4 Sandstone ....................................................... 178<br />
5.5 Volcanic rocks ................................................ 181<br />
5.6 Cement raw material ....................................... 181<br />
Gemstones and semi-precious stones ........ . ............. 183<br />
.......................<br />
...................................................<br />
...<br />
.....................*....... .<br />
6.5 Garnet ..............................................................<br />
6.6 Qudz ............... i ..............................................<br />
... .- .. ? .<br />
6.1 Corundum (ruby and sapphire) 189<br />
6.2 Opal .... ....... 190<br />
192<br />
6.3 Beryl .............................................................<br />
6.4 Olivine (peridot) . 192<br />
6.7 Diamond .............,. ...>I..<br />
.r......... , ..... WYtW'r'ir****-<br />
...<br />
Chapter seven<br />
Energy resources." .................. .....- ...... ,<br />
193<br />
195<br />
195<br />
.......... 199<br />
7.1 Fossil fuel ....................................................... 199<br />
7.1.1 cod ...................................... 209<br />
7.1.2 Oilandgas ........................... 215<br />
7.1.3 Oil shale ............................... 221<br />
7.2 <strong>Geothermal</strong> resources ..................... . ............ 222<br />
.......................................<br />
7.3 Hydroelectric pqwer' 232<br />
Snmmary and conclmions .............. .+ ...".. " ..........<br />
., .,., ........ 237
. .<br />
,, i,!'!' ,,,, : I , :: , . , ,,<br />
I '<br />
;!' . ., 4 1<br />
mm.1 ,: ,,!,.f~ ;I, i;:, -,I:.) t:. ; , ' , .:, . .<br />
Maj:og..mind. deposits of Ethiopia ('A; 'Ij<br />
:<br />
, ,;I -3:: - 2 '<br />
I 8 , -<br />
8t C ,class) ......................................................... i *. ..256<br />
, .<br />
I<br />
pifi'n&x-2A<br />
M*r mhtral deposits of Ethiopia:<br />
CC1a~s D, E,N/A) ...........................I..r I.!I1.II.i ........I..... 262<br />
.Annex 3 . .<br />
. a . ,<br />
'Defmitiofis of geologicalltechnical terps , ., * , I . j a<br />
. - dinthebook ......................................................... 281<br />
, ,<br />
, &,eq 4 (<br />
., . . L<br />
Techniqws utilized in digit'izing the<br />
geology and mineral map of Ethiopia ............. .L.. ... 285<br />
Apnex 5<br />
Mining law and-investment oppartmities:<br />
in Ethiopia .......................................... l... .;... ........ 289
t<br />
I<br />
Preface<br />
This baok is not the first of its kind. A similar work exists in the<br />
archives of the Ministry of Mines and Energy entitled <strong>Mineral</strong><br />
, Occurrences of Ethiopia (Jelenc, 1966). This work, compiled over<br />
t<br />
forty years ago, does not indude some-of the new developments in<br />
the field. Other works on industrial minds and rocks were<br />
compiled by Magistu and Fentaw (2000). There are also other<br />
unpublished reports, mainly by the Ministry of Mines and Energy<br />
and the Ethiopian <strong>Mineral</strong> <strong>Resources</strong> Development Corporation<br />
(EMRDC), which are technical reports on specific mind<br />
resources of the country,<br />
The author has, therefor&, been encouraged to the<br />
present work to fill the existing gap and the strong need of scholars<br />
and the general public for a comprehensive and up-to-date<br />
reference material. The primary aim and important feature of this<br />
book are the possibilities it provided for a systematic digital<br />
compilation of various studies of the mineral and energy RSO&<br />
of the country in a single volume. The aim of this book is, first and<br />
foremost to provide readers an insight into the principal mineral<br />
' and energy resouroes of the country and to describe these mineral<br />
morns in relation to their geological environments by which an<br />
insight into their present usefulness and the mineral outlook of the<br />
I various parts of the country in the future can be obtained. The<br />
published data are complemented by unpublished information<br />
r<br />
provided by various authors, wjld further updated through<br />
compilation of geological, economic and metallogenic elements<br />
gleaned from recent literature.<br />
This work also presents geo-scientific maps and databases<br />
i for geology and mineral and energy resources of the country in a<br />
digital form at a synthetic scale of 1:2,000,000. The mineral<br />
occurrence maps display a compilation of the spatial distributions'<br />
'<br />
of over 650 data entries. Based on earlier works dating from those<br />
of Jelenc (1966) up to the recent syntheses by, but not limited to, the
ii <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
following authors: Senbeto and de Wit (1981); EMRDC (1985);<br />
Ethiopian Geological Survey (EGS, 1989); Getaneh and Saxena<br />
(1984); Getaneh Assefa (1985, 1991); Wolela et al. (1986, 1987); 1<br />
Wolela (1991, 1992, 1995); Gebre (1991); Meseret Teklemariarn<br />
(1 991, 1993,2000); Befekadu and Senbeto (1993); Abera (1 994);<br />
Ethiopian Ministry of Mines and Energy (1995); Tefera et al.<br />
(1996); Walle (1 996); Solomon Tadesse and Zerihun Desta (1 996);<br />
Solomon et al. (1997); Solomon Tadesse (1999; 2000; 2001);<br />
Meseret et aI. (2000); Selassie and Reymold (2000); Mengistu and<br />
Fentaw (2000); and Solomon Tadesse et al. (1998, 2003); along<br />
with the author's own long and direct experiences and scholarly<br />
research in many localities of Ethiopia.<br />
The author believes that the book is reasonably<br />
comprehensive and systematic in its treatment of topics and hopes<br />
that it will be of interest to both scholars and the general public.<br />
The book is intended as a text of reference for both undergraduate<br />
and graduate students in the field of Economic Geology, Mining<br />
Geology and Exploration Geology in the Department of Earth<br />
Sciences of the Addis Ababa University and other universities in<br />
Ethiopia offering related courses. It is hoped that it will be a useful<br />
guide and encourage potential local and foreign investors in<br />
undertaking mineral exploration activities and perhaps be useful<br />
also in identifying locations likely to produce new occurrences of<br />
minerals in the country.<br />
Chapter one begins with an introduction presenting a<br />
historical review of the country's mining and mind exploration<br />
and development activities. Chapter two comprehensive1 y reviews<br />
the regional geological and tectonic framework ofqhe country with<br />
a summary of a broad stratigraphic unit. The chipter emphasizes<br />
the range of geological processes responsible for the formation of<br />
the enormously diverse resource types found in the country.<br />
Chapter three presents a systematic description of important<br />
metallic mineral resources. Pertinent information on origin,<br />
I<br />
I<br />
i<br />
I
Preface iii<br />
composition, application and production of the commodities are<br />
discussed. The chapter displays geo-scientific maps and a<br />
summw of all known mineral occurrences (location, deposit<br />
types, reserves, etc.) containing key geological parameters.<br />
Chapter four reviews industrial minerals and rocks of the country<br />
describing them in a same patterti as the rnetdlic mineral<br />
resources. Chapter five reviews construction and building mate~ials<br />
in relation to their geological environment. Chapter six discusses<br />
gemstone resources with their geological context. Geological<br />
sources of energy such as natural fossil fuels (coal, oil and gas) and<br />
geothermal energy are considered in chapter seven.<br />
Geologically, Ethiopia lies at the northern end of the<br />
contjnental part of the East Afican Rift. Voluminous piles of<br />
mainly Tertiary volcanic rocks occupy large parts of the country<br />
along the Rift Valley. Proterozoic rocks occur in northern Tigray,<br />
western Wollega, southern Adola, south-western Akobo, and the<br />
eastern Harar part of the country; and Mesozoic rocks occur in<br />
north Mekele Outlier, central Abay Basin and Mugher, south-east<br />
Ogaden. Tewtiary rocks underlie most of the eastern and western<br />
part of the country. The floor of the Rift Valley is filled with<br />
relatively young lacustrine sediments and volcanics. Several<br />
alkaline plugs are known from Ethiopia, but no carbonatite has<br />
been identified as yet. Metallic resources (precious, rare, base and<br />
ferrous-fernalloy metals) are generally related to the 'metamorphic<br />
metavolcano-sedimentary belts and associated intrusives belonging<br />
to'various terraines of the Arabo-Nubian Shield welded together<br />
during the East and West Gondwana collisional orogeny<br />
(Neoproterozoic, 900-5 00 Ma) -a potential greenstone belt.<br />
Industrial mineral and rocks occur in more diverse geological<br />
' environments including the Qoterozoic basement rocks, the Late<br />
Paleozoic to Mesozoic sediments and Recent (Cainomic) volcanic<br />
amnd associated sediments. Energy resources (oil, coal, geothermal
iv <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethimia<br />
mwces) are restricted to Phanerozoic basin sediments and<br />
Cainomic volcanism and rifting ctreas.<br />
In preparing this wbrk, I have, co~ously or<br />
.* unconsciously, been influenced by methods, statements,<br />
illustrations, a. that have appeared in other books or publications.<br />
So, I have tried to acknowledge my indebtedness, in general in<br />
scholarly terms, but, if I have failed to mention all, I wish to<br />
express aplogy and gratitude at the same time.<br />
I am particularly grateful to the Ministry of Mines and<br />
Energy, the Petroleum Operation Department, the Ethiopian<br />
Geological Survey, and the Ethiopian <strong>Mineral</strong> Development Share<br />
Co. for giving me access to their geological and mineral databases.<br />
A Mcular debt of gratitude is owed to Dr. Asfawossen Asrat,<br />
Dqmtment of Earth Sciences, Addis Ababa University, and a<br />
reviewer who undertook the onerous task of reviewing the entire<br />
manuscript. Their comments have helped me to b& to my<br />
, attention certain errors and omissions that were duly corrected.<br />
Finally, I thank the publisher, Addis Abaha University<br />
Press, for all the effort to produce the book in its present form.<br />
Solomon Tadesse (Ph.D.) Professor of Eoonomic Geology and<br />
Exploration Geology, Department of Earth Sciences,<br />
Addis Ababa University<br />
(E-mail: golotade@neol,w.edu.@<br />
March 2008
Chapter One<br />
Introduction<br />
<strong>Mineral</strong> resources play a vital role in the eoonomic development of<br />
a country. The accelerating growth of the world's population<br />
cornbind with an improving standard of living throughout the<br />
world, greatly increases demand for mineral products of all types.<br />
The combination and development of the abilities of the<br />
explorations and of the scholars researchers of mineral sectors can<br />
effectively improve exploration and exploitation of the mineral<br />
resources.<br />
Ethiopia is endowed with a wide variety of minerals and<br />
rocks, some of which are available in large quantities and are of<br />
excellent quality. <strong>Mineral</strong>s such as potash, bentonite, kyanite,<br />
diatomite, graphite, kaolin, marble, granite, limestone, gypum,<br />
sand, etc. occur in sufficiently large reserves that could warrant<br />
medium to large-scale mining. The history of mining in Ethiopia is<br />
comparatively recent. However, some mining activities such as<br />
iron mining and salt extraction were known in Ethiopia since time<br />
immemorial. Ethiopia has been a producer of gold, and such<br />
industrial minerals as brick-clay, diatomite, and feldspar,<br />
gemston-, granite, gypsum, dydrite, kaolin, limestone, pumice,<br />
salt, sand, scoria. The country also produced cements, lime, lignite,<br />
and steel. Ethiopia's main mined export is gold, limestone,<br />
marble, and gem, mainly opal.<br />
Mining for gold in the southern region of Ethiopia dates<br />
back to mid 1930's. Since then nearly 80 tons (EMRDC, 1985) of<br />
gold has been produced 6om placers of the Adola area alone and<br />
nearly 35 tons of gold from the Legadembi primary gold deposit<br />
(Midroc Legadembi) between 1991 and the end of 2007. No record<br />
is available on the gold production of the western and south-<br />
western regions. However, it is believed that local miners are<br />
producing a few kilograms of gold annually. Until' the
2 <strong>Mineral</strong> kurces <strong>Potential</strong> of Ethiopia<br />
establishment of mdern methods for the mining of the primary<br />
gold deposits of Legadembi and Sakaro, mining for gold was<br />
mainly carried out by primitive panning methods, employing<br />
significant number of labourers. The introduction of semi-<br />
mechanized mining methods, such as hydraulic 'monitors and<br />
dredging in the last 2 to 3 decades, has significantly inproved the<br />
production of gold in the Adola area<br />
Current mining activities include the production of tantalite<br />
and soda ash, on a pilot scale; primary gold from Legadembi;<br />
placer gold mining mainly from Adola; and mining of industrial<br />
minerals such as kaolin, dolomite, magnesite, and dimension<br />
stones (limestone, marble, granite, basalt, and sand) as well as<br />
sdl-scale artisanal mining of precious metals, gemstones and<br />
salt. Other undeveloped resources include copper, semiprecious<br />
gemstones (agate, aquamarine, chalcedony, chrysoprase, emerald,<br />
garnet, jasper, obsidian, ruby, sapphire, and spinel), manganese,<br />
molyt&num, mercury, nickel, palladium, platinum, rhdhn,<br />
tungsten, zinc, apatite, bentonite, dolomite, potash, and quartz.<br />
In the mineral industry these activities are dominated by the<br />
private sector. Some of the privately owned mining activities<br />
include the Dalleti Meteke1 marble which was purchased by the<br />
National Mining Corporation (NMC) from the previous Ethio-<br />
Libyan Joint Mining Company; Metekel marble by Tis Abay Plc;<br />
and Legadembi primary goId mine which was also purchased by<br />
Midroc Gold Mine (a subsidiary of Midroc Ethiopia Group).<br />
Mined prospecting and exploration in Ethiopia began<br />
around the end of the 18th century. However, modern minerals<br />
exploration started in 1968 with4fhe establishment of the EGS as a<br />
department within the Ministry of Mines and Energy to undertake<br />
surveys of the geology and potential mineral reserves of the<br />
country. Over the past 25 years, the EGS has carried out<br />
exploration for metallic, industrial and energy resources; the<br />
results of which are made available to investors.
I<br />
t<br />
Introduction 3<br />
A quarter of the total surface area of the country has teen<br />
1 geologicallymappedata~deof1:250,000,ofwhich20%has<br />
been geochemically surveyed at the same scale. Since the<br />
establishment of EGS and EMRDC, the Ethiopian government has<br />
undertaken various mined exploration projects. both<br />
independently and with the assistance of donor organizations. Until<br />
recently, systematic exploration for mine~als and mining activities<br />
have ken limited to parts of the country, principally to the Adola<br />
area (southern Ethiopia), where only a few resources have been<br />
found so far that would warrant large-scale mining.<br />
Surveys were carried out mostly in the Precambrian lowgrade<br />
metamorphic terrains. Exploration activities so far have<br />
outlined priority target areas and the reserve of the Adola placer<br />
gold, the Bombowha and Kombolcha kaolin, the Kenticha quartz,<br />
the Yubdo platinum, the Adola nickel, the Dallol potash, the<br />
Gewane Mille bentonite and the Lakes Region diatomite. Later,<br />
, modern investigation continued' and resulted in the discovery of<br />
important dewsits of gold, (such as Legadembi and Sakaro), the<br />
Keriticha columbotantalite, the Lakes Region soda ash (by<br />
EMRDC), the Bikilal iron and phosphate, the Yayu coal, the<br />
Bombowha and Komblcha kaolin, the Gewane bentonite, the<br />
Chembi kyite, the Dallol potash, the Afdera salt, the Kenticha<br />
magnesite, the Yita opal, the DaIeti and Metekel the Babile and<br />
Hamama granite, marble as well as other deposits.<br />
Although it is believed that there are different mineral<br />
occurrences in different part of the country, integrated explodon<br />
activities were not conducted at the appropriate scale required to<br />
1 assess all the potential areas for the economic deposits that would<br />
eventualIy foster the welI-being of the society. Some of the major<br />
I causes for mineral exploration problems in the country include:<br />
political instability, government policy in the mining sector,<br />
absence of geologicai maps at an appropriate scale, inaccessibility,<br />
unsuitable working conditions, non-integrated investigation and
41 Mhal Rmum <strong>Potential</strong> of Ethiopia<br />
.march works, and shortage of well-trained human resources.<br />
Burthermore, although many mineral deposits exist in Ethiopia,<br />
thick layers of voIcanic lava covers the older ore-bearing mlis,<br />
wbich renders exploration and exploitation difficult. Outcroppings<br />
-of iron, copper, zinc, and lead have been mined since ancient<br />
times, but deeper reserves of these minerals remain largely<br />
unexploited.<br />
The mineral industry, like other sectors such as agricdhue,<br />
contributes significantly to the economic development of the<br />
country. Therefore, effort should be made to explore the county's<br />
mineral aud energy resources by integrating studies and attracting<br />
local and foreign investors to the mind and energy sector.
Chapter 'Two<br />
Geological outline<br />
The main rock types recording the geological history of Ethiopia<br />
illustrated on the general and schematic framework of the geology<br />
of Ethiopia (Fig. I) are:<br />
- The Precambrian metamorphic rocks with associated syn-to<br />
post-tectonic intrusions which form the Basement<br />
Complex;<br />
- The Late-Palaeozoic to Mesozoic marine and continenla!<br />
sediments;<br />
- The Cenozoic 'basic and felsic volcanics and a<br />
volcano-sedimentary and volcanoclolstic rocks<br />
Early Telqiary, Late Tertiary and Quaternary volcanic.<br />
These rocks assemblages represent 23%, 25%, 34% and<br />
18% of the total surface area respectively. Such a diverse<br />
geological set up makes the country wealthy in mineral<br />
;, .--':<br />
resources of various types. The synthetic stratigraphic<br />
column including . . the miin units in p&sented in able 1<br />
! :- y $;
6 Mined <strong>Resources</strong> <strong>Potential</strong> of Ethimia<br />
country (Fig. 1 ). The basement in the south and west of the country<br />
where granitic rocks and gneisses predominate has been more<br />
strongly metamorphosed than the Precambrian sequences in the<br />
north. The highest metamorphic grade (granulite facies) has been<br />
recorded in gneisses of the southem and south-western prt of the<br />
country. Though in many cases strongly folded and foliated, the<br />
rocks in the north, which include the youngest formations (known<br />
in the basement), have generally undergone only very low to low<br />
grade metamorphism. The low-grade Upper Proterozoic rocks are<br />
exposed in the sou^ west, southwest and north forming the<br />
southern, western, the southwestern Akobo and the northern Tigray<br />
Gttenstone Regions, respectively. Most of the known metallic<br />
mineralizations hosted in these low grade metamorphic rocks are<br />
known over a tittle area in the east exhibiting lead and copper<br />
anomdies. A tbfold lithotectonic sequence has ken suggested<br />
for the Precambrian basement rocks of Ethiopia by Kamin (1 975)<br />
and Kazmin et al. (19781, consisting of a Lower, Middle and Upper<br />
Complex. However, recent geochronogical and isotopic studies<br />
suggest that this Precambrian basement (granite-gneiss, volcano-<br />
sedimentary and ophiolitic suite;) is dominantly Neopmterozoic in<br />
age (Aydew et d, 1990; Ghichile, 1992; Telclay et al., 1998;<br />
Gerra, 20001, and that the rocks previously attributed to the<br />
Archereoul or pre-Neopmteromic could be part of pre-<br />
Neoproterozoic continental crustal fragments e.g. Tulu Dimtu<br />
orogenic belt, western Ethiopia, (Tadesse G. ad Allen A., 2002),<br />
including possibly reworked and remobilizsd components, as<br />
indicated by Archaem zircon xenocrysts found by Teklay el a/.<br />
(1 998).<br />
2.13 Late-Pdaeozoic and EariyrMemmic Sediments<br />
The Paleozoic Era in Ethiopia is marked by a regional<br />
unconfonnity due to long period of penepwon. Late Paleozoic-<br />
Triusic sediments are widespread in Ethiopia as a result of the
.<br />
P : tmxgtew1~1a1~~isri. ofithe *a, and cover the Northern,<br />
r~ .W&aIi Eastem 'and Southeastem part of the eountry. The Late<br />
Palaeozoic to Triassic sedimentsx and tillitcis composed of<br />
sandstone, siltstone, shale, rmd.minor oonglommte (Table 1); have<br />
been mapped in several regions, These -sediments comprise the<br />
i Enticho Sandstones (thickness: 160 m; Timy), the Edaga .&bi<br />
I<br />
Glacial Sediments (thickness: 150-180 m; Tigr~y)+ $the Permian<br />
I Sandstone (south-western Ethiopia), the Gura 8andstone (SE<br />
!<br />
Ethiopia), the Middle Abay ~iilite (central E?hiopia)+h,tbe Waju,<br />
I ,Cdub, Gumburo Sandstones and the Bob Shttle (Qgaden, SW<br />
Ethispicd) and Gede Basin Glacial 'Tillites (Tadesse and Melaku,<br />
1 9981;<br />
The Mesozoic rocks were widely deposited in Ethiopia<br />
I during a continuous period of subsidence of the land and migration<br />
of the sea fmm the cast in the Ogaden wards the west and ~ n h .<br />
and covering the central part and northern areas of the country.<br />
. They rest unconformably on the Precambrian metamorphic rocks,<br />
filling channels in the basement rocks. Rocks of Mesozoic age are<br />
mainly sediments such as sandstone, limestone and gypsum. They<br />
cover the whole of the eastern lowlands of Ethiopia and large areas<br />
of Ham, Bale, Borenq and Tigray. They also outcrop in the upper<br />
valleys of the Blue Nile and its tributaries in central Ethiopia.<br />
The Mesozoic sedimenfb comprise:<br />
(i) The Lower or Adigrat Sandstone of Triassic age;<br />
(ii) Jurassic Limeston f Antalo group; and<br />
(iii) Cretaceous Upper andstone with mudstone and marl<br />
intercalations. T<br />
The Adigrat Sandstone' rests unconfomably on the<br />
basement. This sandstone, which varies from a few meters to 800<br />
m in thickness, is typically a yellowish to pink, fine to medium<br />
grained, non-calcareous, weil-sorted, cross-bedded quartz<br />
sandstone with interbedded siltstones and minor conglomerates.<br />
The Antalo Group incorporates the three formations which make<br />
9
up the marine Mmic sequence within the central Plateau. The<br />
type section of the Antalo Group, in the Abay Gorge in the Blue<br />
Nile Bash, totals 880 m (Getaneh, 1991). halo Limestone is<br />
typically developed in the Mekele area, where a 750 m thick<br />
sequence consists of fossiLifmus yellow iimestone and marl,<br />
In chmobgical order, the formations within this group are:<br />
- The Abay Beds (central Ethiopia, Middle Jurassic), which<br />
we mposed of limestones, calcareous sandstones, and<br />
shale and gypsum beds with a total thick of 580 m;<br />
- The Antalo Limestone (localized in different regions, Upper<br />
Jurassic, ("Oolithic Jurassic") consists of fossiliferous<br />
limestone, interbedded marl, calcareous shale and rare<br />
amaceow beds (thickness: up to 1400 m);<br />
- The Agula Shale (Tigray), Upper Jmic (Kimmeridgian) is<br />
connposed of shale, black shale, marl, claystone and minor<br />
limestone and dolomite (thickness: 60-250 m);<br />
- The Upper Sandstone (@retaceous) consists of sandstone,<br />
shale, marl, oolithic and dolomitic limestone and mim<br />
gypsum- andlor aatry drite-bearing beds deposited<br />
conformably on the Jurassic rocks in some mas, as in<br />
Western Ethiopia, and unconfonnably in others, ws in<br />
Tigmy region,<br />
The thickest and most complete succession of Mesozoic<br />
rocks are know in eastem and westem Ogaden and harghe<br />
region including upper Jurassic to Turonian Gabredam (Oolithic<br />
limestone, sandstone, marl, shale, and minor gypsum-bearing beds;<br />
thickness: 400-630 m), KO& (dolomitic limestone, marl, shale<br />
4 minor anhydrite-bearing beds; thickness: 100-500m), M&l<br />
(limestone, shale d marl), Ferfer (dolomite and clayish<br />
limestones; thickness: 100-200 m), Belet Uetl (limestone and<br />
glauconite shale; thickness: 90-230 m) and Amba Aradom<br />
(sandstone, shale, siltstone; thickness: 1 50-600 m) Formations<br />
2000).<br />
(a<br />
4,:
1, '<br />
I;<br />
i wnthmtaI<br />
I '!<br />
. .<br />
Geological outline 9<br />
Tht Mesozoic formation comprising of sandstone,<br />
claystme, &sum, and limestone are important explomtion tafgets<br />
for fossil fuels such as oil and gas and coal; as well as sources of<br />
raw matorials for cement, glass and lime production; industrial<br />
mbrals such as clays, bentonite, diatomite and gpm; and<br />
metallic deposits such as oms of zinc, copper, lead, iron and<br />
manganese are deposited during this period and are to be looked<br />
forinthm mcks.<br />
2.l.3.l Cenomk dlmentary Pocks<br />
Sediments and volcano-sediments me intercalated ih various<br />
pmpor&iond with voldc episodes from the Early Tedq to the<br />
Qllirtemary. Cenozoic sedimentary rocks occur in eastern Ogadea,<br />
the Danakil depression, and the lower Ono Valley. Mark and<br />
sediments in eastern Ogaden, ranging from Palaeocene<br />
to Middle Eocene, have a tototal thickness of up to 1000 rn (Getaneh,<br />
1991), Late Tertiary to Quaternary sedimentary rocks assmiabed with<br />
volcanic rocks include clay, silt, sand, gravel, tuffs, marls and<br />
limestone of the Omo Group (1 5&750 m thick, 13-3 1) and clay,<br />
; siltstone, sandstone and conglomerates of the Hadar Formation (3&<br />
ZMnthieX.Z.M.I)Ma(Tslarnul.I996).S~~ofTdq<br />
.age, which are represented by smdstcmes, limestow, gypsum,<br />
dnhydrites etc., are known to *occur in eastern Ogaden, in the<br />
Danakill depression and in the Omo River valley. Quaternary<br />
sediments wre also widely distributed and genetically belong to<br />
lrtcwhhe and marine origin.<br />
Ir<br />
$<br />
i -<br />
2.1.3.2 Cenozoic volcanic m b<br />
I : cmmzoic volcanic rocks (~athy<br />
to m t l m areassociated<br />
i . with the fonnation of the Main Ethiopian Rift, Afar depkmion and<br />
bae highland volcanic. The unit consists of halt, trolchytes and
10 <strong>Mineral</strong> <strong>Resources</strong> Potmtia! of Ethiopia -<br />
associated dyke swarms, andesites, rhyolite~, igninlbrites at:d<br />
pilrnice as ash. Highland Ethiopia is underlain mainly by Tertiary<br />
volcanic, mostly basalt. The Rifi Valley, which divides the Ell1 iopiarr<br />
highlands into the eastern and western Plateaus, is undel-lain by<br />
Tertiary as well as Quaternary volcanics and sediments. 'There are<br />
also alkaline and acidic intrusive which range in age from<br />
Mesozoic to Late Tertiary.<br />
Tertiary volcanic ("PI ateau volcanic"), the earliest and most<br />
extensive group of volcanic rocks is the "Trap Series". erupted<br />
from fissures during the Early Tertiary (54 Ma to I3 Ma, (Zanet~ir~<br />
B, 1993; Tefera et al., 1996; Hofmann et al. 1997). The Trap Series<br />
consists of piles of flood basalts and ignimbrites. The basalts of ~i IC<br />
Trap Series are transitional from alkaline to tholeiitic in<br />
composition and erupted from fissures. The flows range in<br />
thickness from 500-1 500 rn (Mohr and Zanettin, 1988) to up to 30130<br />
m (Tefera et al., 1996). Shield volcanoes that consist mainly of<br />
porphyritic amygdaloidal olivine basalt overlie these rocks.<br />
2.1.3.3 The Rift and the Rift vohanic rocks<br />
The Great Rift Valley is a vast geographical and geological featurc<br />
that runs north to south for some 5,000 h from northern Syria ro<br />
central Mozambique in East Africa, The valley varies in nicl~h<br />
from 30- 100 km and in depth from a few hundred to sevem!<br />
thousand metres. It has been created through the rifting atid<br />
separation of the African and Arabian tectonic plates that began<br />
around 35 million years ago in the north, and by the ongoing<br />
separation of East Africa from the rest of Africa along the East<br />
African Rift, which began about 15 million years ago.<br />
The northernmost part of the Rift forms the Beqaa Valle><br />
in Lebanon sepprating the Lebanon Mountains.To the south in<br />
Israel, it is khown as the Hula. Valley separating between the<br />
Galilee Mountains and the Golan Heights. Further south, the vuI Ic!<br />
becomes the Jordan River, which flows southward through t':*am
B<br />
?<br />
Geological outline 1 1<br />
Lake Hula into the Sea of ~dilee in Israel, and then continues<br />
south througb the: Jordan Valley into the Dead Sea on the Israeli-<br />
Jordanian border. $Am the Dead Sea southwards, the rift is<br />
occupied by the Wadi Arab& and then the Gulf of Aqaba and the<br />
Red Sea.<br />
The Western Rift, also called the Albertine Rift, is edged<br />
by some of the highest mbuntains in Africa, including the Virunga<br />
Mountains, Mitumba Mountains, and Ruwenzuri Range; and<br />
contains the Rift Valley Lakes, which incfude some of the deepest<br />
- lakes in the world (up to 1470 rneters deep at ]Lake Tanganyika).<br />
Lake Victoria, the second largest area freshwater lake in the world,<br />
[. is considered p~ of the Rift valley system, although it acidly lies<br />
It between the two' biiches, The other Great Lakes are dso formed<br />
,:. bytheRift.<br />
m8 In Kenya the valley is deepest to the north of Nairobi. As the<br />
Lakes in the Eas'tern Rift have no outlet to the sea, these lakes tend to<br />
be shallow and have s high mineral content as the evaporation of<br />
kter leaves the salts behind. The volcanic activity at this site and<br />
unusual concentration of hotspots has produced the volcanic<br />
mountains -Mount KUimanjaro,, Mount Kenya, Mount Karisimbi<br />
'<br />
Mount Nyimgongo, Mount Mcru and Mount Elgon as well as the<br />
Crater Highlands in Tanzania. The 01 Doinyci Lengai volcano<br />
remains active, and is currently the only natrocarbnatite volcano in<br />
j the world.<br />
7.. *.If.<br />
'<br />
,+<br />
-1: l . - 4 - -<br />
.+ fit, :-I - 8 , - ,:>.<br />
. . I.
Map of East Africa showing some of the historically<br />
active volcanoes (the trianglss) and the Afar Triangle<br />
(shaded, center) -a triple junction where three plates<br />
are pulling away from one another: the Arabian Plate,<br />
and the ?wo PG3ftS ofthe African Plate (the Nubian and<br />
the Somalian) splitting along the East African Rifi<br />
Zone (USGS).<br />
The Ethiopian Rift is thi: northernmost extension of the<br />
great East Afrim Rift that extends from Nortb-Eastem Ethiopia to<br />
Mozambique in Southern Africa, with a length of more than 4,000<br />
krn. More than onequarter of the rift system lies in Ethiopia (Fig.<br />
1). The central Main Ethiopian Rift (MER) is a large 1 km deep<br />
graben with an average width of about 70-80 km and e length of<br />
700 krn stretching from the Ethiopian-Kenyan border in the south<br />
to the Afar Depression in the north (Dipaola, 1972). The riR<br />
dissects the highlands of the country into the eastern (Harar) and<br />
western (central Ethiopia) Plateaus and is bounded on two sides by
Geological outline 13<br />
a series of large normal faults. The eastern escarpment of the MER<br />
is chamterized by steep faults with significant throws in its northeastern<br />
sector exceeding 1,500 m between the top of the Pldeau<br />
and the Rift floor. The westem margin is gradational and less<br />
marked thus accounting for the asymmetry of the MER, Active<br />
tectonic movements are confumed by numerous faults affecting<br />
Holocene rock units and by the intense recent seismicity of the<br />
I whole region.<br />
The Ethiopian Plateaus bordering the Rift consist of a-thick<br />
I succession of flood bdts and subordinate amounts of hyolites<br />
! emplaced during Eacene to middle Miocene (54 to 13-1 5 -my)<br />
: (Woldegabriel e6 al., 1990). The floor of the rift is commonly<br />
covered by Plio-Quaternary volcanic products and basin-fill<br />
i<br />
volcanmlastic sediments. Basaltic volcanic rocks (transitional<br />
from alldim to tholeiitic in composition) become progressively<br />
younger northwards to Afar, although young basaltic volcanism of<br />
. minor volume is also common along the axid zone of the<br />
! Ethiopian Rift. The main petrological feature of the MER is the<br />
abundance of felsic peralkaline volcanic (mainly pantellerites)<br />
related both to the fissd activity and to the several volcanoes<br />
rising from the rift floor. It has been suggested that east-west<br />
structures may be an important factor in controlling the locations<br />
of volcomisrn along the rift Thick sediment accumulations of<br />
hamsirhe origin cover large areas of the rift flmr.<br />
The Rift Valley has hen a rich sow of anthropological<br />
discovery, especially in the A h area. Because the rapidly eroding<br />
highlands have filled the valley with sediments, a favourable<br />
I environment for the preservation of remains has been created. The<br />
I bones of several hominid ancestors of modern humans have been<br />
found there, including those of "Lucy", a nearly complete<br />
dopithecine skeleton, which was discovered by<br />
anthm~logist Donald John. Richard and Meave Leakey have<br />
dm done significant work in this region.
~aln-ggrwpll ~lrln<br />
lll~ ~gpb) "complrx" Main<br />
mlckms8 types w<br />
MrW RIFT (cr m n W Om Maln Ethloplan Fwc 3TH . W)<br />
MWena ADEN) (1.3-nl~a) RUI<br />
S<br />
loaulim, -<br />
?5&7m)<br />
peralwne<br />
voleenlc<br />
WndU Fe,Mn)<br />
volePh<br />
n t s<br />
m n s<br />
LU<br />
0 ment5<br />
nlmr haab 311, Gas,<br />
volmnlm bal
Hamanlei Form.
g<br />
8<br />
2<br />
550-500<br />
Ma?<br />
Y7<br />
Pan African omgen<br />
Geological outline 1 7<br />
2.2 An overview of the main structuml features in Ethiopia<br />
The Precambrian<br />
WYEHT<br />
W-udmm<br />
sedimenta~y -<br />
ultlamfk<br />
belts<br />
(Neoproiemzolc<br />
'lhre wries)<br />
Gmnite-<br />
GwW<br />
TmW<br />
possi~.<br />
reworked -<br />
~emoblilred<br />
pm<br />
mqmmb<br />
(1 2 - 0.9<br />
Gal7<br />
Maln bxpo~urer hletamrphic rocks U<br />
ln BYkw<br />
N. pOst-l6dmk<br />
E ~ ~ I ttudvsa O ~<br />
IrIgaY)<br />
, w,<br />
Emiopia<br />
' ponegal<br />
S.<br />
Ethkpla<br />
(Sibwno)<br />
E.<br />
Efiw.<br />
(Hams)<br />
Granuk<br />
fscle~ In S and<br />
Ethiopia<br />
lwgnde blrnodal<br />
ate- votcano<br />
a-lary island.<br />
The Pre-Cambrian basement structures constitute the oldest<br />
structures which also controlIed later stnrctural patterns. Two major<br />
Precmbri an (Neoproterozoic) tectono-stratigraphic units are<br />
recognized in Ethiopia: high-grade gneiss and low-grade meta-<br />
sediments (Fig. l ) . The gneissic *mck consists of polydeformed and<br />
metamorphosed schists and gneisses (biotite-hornblende gneiss and<br />
mphibolites). These rocks are comparable to the predominantly<br />
grreissic terraines of the Mozambique Belt described by Vail(1987,<br />
1988). The low-grade metamorphic volcano-sedimentary units<br />
consist of amphibolite, cmbonaceous quartz-mica schist, chlorite-<br />
arc<br />
W cph~olitZc sultes<br />
~ P W<br />
psammltlc -<br />
M~c met<br />
sediment& mema<br />
Wdle Cornplei')<br />
Hie-<br />
po(YmetamoQhased<br />
h h h a<br />
gnairgm.<br />
mlgrnatites<br />
("Lower Complefl<br />
Au,PGE, Ht<br />
1Co)<br />
Cu, Cr<br />
fe' Ti. (w W)<br />
Ta, (Nb, REE.<br />
s<br />
, .u. m)<br />
3k, Feld,<br />
ya. Qr Kln,<br />
&<br />
TIC,
18 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> or Ethiopia<br />
4<br />
actinolite schist, quartz-feldspar-biotite schist, meta-conglomerate 1<br />
and graphitic quartzite and mafic to ultramafic bodies. The q<br />
ultrabasic mks associated with the metavolcan~sedirnentan; I<br />
sequence form a N-S trending linear zone and occur as structurally<br />
modified and hdined lenses, extensively altered into serpentinite.<br />
talc-schist and talc-tremolite schist. These ophiolitic mafic-<br />
ultramafic belts could be interpreted, in accordance wih the models<br />
developed in the Arabian-Nubian Shield, as Neoproterozoic suture<br />
zones, along which different terranes were accreted during the<br />
Gondwana collision (Shackleton, 1994 and 1996; Stern, 1994;<br />
Abdeisalarn and Stern, 1997, Tadesse G. and Allen A., 2002).<br />
The greenstone sequence appeared correlatable to the<br />
volcano-sedimentary-ophiolite assemblage described for the most<br />
part of the Arabian-Nubian Shield by Vail (1987, 1988). Earlier<br />
a<br />
works (Kdn, 1972; EMRDC, 1985) suggested that the contact<br />
between the high grade gneiss and the low grade metamorphic<br />
volcano sedimentary unit is stratigraphical. However, detailed<br />
i<br />
1<br />
c<br />
I<br />
structural studies regarding the tectonic relationship between the<br />
volcano-sedimentaiand keiss rocks and the cont& between the<br />
4<br />
major lithologic units wi&n the greenstone belt by Beraki et d. 1<br />
1989; Hailu and Yifa, 1992; Gebreab, 1992 and Hailu, 1996<br />
Indicated that the contacts are of regional shear zone and me joined 14<br />
by ductile to brittle-ductile shear zone in a north-south direction.<br />
I<br />
These tectonic zones are characterized by strong development of<br />
schistosity and complexity in strucbwl features i d interking of<br />
different rock types evidenced by shear fabrics, mylonitic zones<br />
d textural variations.<br />
Most of the Precambrian volcano-sedimentary sequences<br />
sible greenstone belts) and associated intrusions have been<br />
ected to several orogenic episodes since their formation, in 1<br />
I<br />
I<br />
1<br />
8
Gmlogical uuliinr: 1 9<br />
Red Sea and the East African -Ethiopian Rift Valley, has resulted<br />
in considerable fracturing and shattering. Major water resowces<br />
are associated with these fracture zones. These ancient rocks and<br />
their minerals are exposed eithe~; because they were not covered by<br />
younger rocks as in northern and southwestern districts, or because<br />
younger rock cover was eroded away during subsequent uplifi and<br />
erosion.<br />
The ~alkmic and Memwic<br />
The Paleozoic Era in Ethiopia is marked by a regional<br />
unwnformity due to long period of peneplanation. Very few<br />
Paleozoic residual deposits (containing Precambrian basement<br />
debris and agglomerates) are observed on the peneplained surface<br />
in northern Ethiopia (e. g., Enticho Sandstone).<br />
Unlike the Paleozoic, the Mesozoic Era in Ethiopia is<br />
, marked by thick marine sedimentation and extensional tectonics,<br />
Several N W to SE striking structural basins have served as active<br />
depositional basins during the Mesozoic. Mesozoic sedimentation<br />
started with the Permo-Triassic to Jurassic deltaic .Adigrat<br />
Sandstone and was followed by a NE to SW marine transgressive<br />
sequence of Middle to Upper Jurassic Antalo Limestone, argillites<br />
and gypsum. It ended with the deposition of upward coarsening<br />
Cretaceous sandstone indicating regression, These Mesozoic<br />
transgressive and regressive sequences mark successive subsidence<br />
and uplift episodes of tectonism in the Horn of Africa between<br />
Permian and Cretaceous times (e.g., Boselini, 1989). Several<br />
extensional basins oriented N W to SE developed in Ethiopia during<br />
the Upper Jurassic to Fretaceous. The present Danakil-Red Sea<br />
region was already a strongly subsiding trough in early Jurassic<br />
time and this heralded the Tertiary breakup the Afro-Arabian plate,<br />
which gave rise to the present Red Sea.
,<br />
20 M i d <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
The Cenozoic<br />
The youngest structural features in Ethiopia are associated with the<br />
Main Ethiopian Rift System and Afar. The Main Ethiopian Rift<br />
(MER) constitutes the northemmost part of the East African Rifi<br />
System (EARS), connecting the Kenyan with the Afar triple<br />
junction.<br />
As it is well known, a rifting cycle begins with the<br />
activation of a hot spot below a craton; this convective movement<br />
of mantle material generates doming of the sialic crust,' fracturing<br />
of this dome along three directions (triple point), and rifting along<br />
these fractures, The three fractures are the M Sea, the Gulf of<br />
Aden, and the Ethio~jan Rift, which meet at the Afar Triangle. The<br />
Ethiopian Rift is lowland W extends from the Afar Triangle.<br />
through the Lakes District encompassing Lakes Zeway and .<br />
Chamo, to Me Turkana at the Kenyan barcierl East of the<br />
Ethiopian Rift (Eastern Highlands), major rivers like the Wabe<br />
Shebele, Weyb, Genale and Dawa flow eastward away from the<br />
if€ rim. West of the Ethiopian Rift valley (westem Highlands),<br />
major rivers like the Tekeze, Dinder, Abbay, and Baro flow<br />
westward away h m the rift rim. The river flow pattern, therefore,<br />
is amevidence of the doming of the region and its dissection by a<br />
riR valley. The three rift systems evolve at different speeds and<br />
degrees, and often at least one of them aborts (aulacogen).<br />
Thermal anomalies beneath the Arabian-Nubian Shield<br />
induced by a rising plume that mechanically and thmdly eroded<br />
the base of the mantle lithosphere and generated pulses of<br />
prodigious flood basalt since -30 Ma (Beyene and Abdelsalam,<br />
2005). Subsequent to the stretching and thinning the Mar Dome<br />
subsided to form the Afar Depression. The fragmentation of the<br />
Arabian-Nubim Shield led to the separation of the Nubian,<br />
Arabian and Somalian Plates along the Gulf of Aden, the Red Sea<br />
and the Main Ethiopian Rift. he southern end of the Red Sea<br />
marks a fork in the rift. The Afar Triangle or Danakil Depression<br />
. 3'
Geological outline 2.1 '<br />
01' hhiopia and Eritrea is the probable location of a triple junction<br />
which is possibly underlain by a mantle plume. The Gulf of Aden<br />
is an eastward cai~tinuation of the Rift -before the rifi opened, the<br />
Arr~bian Peninsula was attached to the Horn of Africa and>from<br />
this point the rift continues as part of the Mid-oceanic ridge bf the<br />
Indian Ocean. In a southwest direction the fault continues as the<br />
Great Rift Valley, which split the older Ethiopian highlands into<br />
two halves: In eastern Africa the valley divides into two, the<br />
Eastern Rift and the Western Rift. . . .<br />
During Pliocene and Quatemar y, , the M ~ progressively R<br />
deepened, evolving through a sequence of interacting half-graben<br />
scgnzents marking the bun- between the Nubia and Somalia<br />
plutcs. The MER is limited by discontinimw boundary faults,<br />
adve from late Miocene ( WoldeGabriel et d, 1990) ad sdiking<br />
between NNE to SSW in the south and NE to SW in the n&.'The<br />
youngest part of the MER is the axial qne (Wonji,~au$&It,<br />
a<br />
( W FB)), mainly formed during the QuateGary (8oo;'etg: or. ol.,<br />
1998). Despite the overall NE to SW uend of thi MBR; the'\3~8 is<br />
characterized by active NNE to SSW trending extension fmctwes<br />
and i~ormal faults. These &e often set in an emechelon<br />
arrangement and are associated with volcanic activity. If ,foll~~s'<br />
that the dome- rifi process is a possible explanation for tl$ great<br />
topographic relief in Ethiopia, which ranges from 0 in the Afar and<br />
the Red Sea coast to about 4,600 meters above sea level at rCas<br />
Das hen.<br />
Tk formation of the Rift Valley continues, *robably &ven '<br />
by mantle plumes and ultimately a result of the African supaswell.<br />
The associated geothermal activity and spreading at the fie has<br />
caused the lithosphere to thin fmr~ a typical I@ km thickness for<br />
continents to a mere 20 km. Within a few~mi1lion yak, thi<br />
lithosphere may rupture and eastern Africa ~ HkpIit - off to hrm a<br />
nzw landmass. If spreading continues, this will 'head 'to ' the .<br />
formation of a new mid-qcean.ridge.
2.3 <strong>Mineral</strong> resouwes -<br />
The term "resource" refers to the amount commodity<br />
particular economic me that is present in an area These estimates<br />
include both extractable and non-extractable amounts of this<br />
commodity.<br />
Earth resohbs covered in this Book include:<br />
- Ore Deposits: which cin be further subdivided into (a)<br />
'<br />
@eci'ous metals (AU, Pt, Ag), (b) non-ferrous metals (as the<br />
' -base metals Pb, Zn, Cu, Sn, and elements like AI), (c) iron<br />
,,J,L and fmalloy metals (as Mn, Ni, Cr, Ti, Mo, W, V, and Co),<br />
(d) minor metals and related non-metals: Sb, As, Be, Bi. Cd,<br />
REE, Ta, Nb, Te, Ti, and Zr, (e) fissionable elements: U and<br />
Th;<br />
- Industrial minerds and rocks -graphite, sob ash, kaolin,<br />
diatomite, quartz, kyanite, gypsum, phosphate, sulfur,<br />
potash, asbestos, marble, granite, limestone, sand, basalt,<br />
etc;<br />
- Gemstones -diamond, ruby, sapphire, beryl, opal, zircon,<br />
garnets, etc;<br />
- Energy resources such as coal, oil, gas, geothermal energy.<br />
It should be pointed out that most if not all of the above<br />
mentioned resources are fairly common, and, indeed, do occur in<br />
many crustal rock types. However, their concentrations (or average<br />
crustal abundances) are so low that they are not easily extracted<br />
from these rocks. For an economic deposit to form, these<br />
"commodities" have to be conceptrated by some natural method.<br />
It is well known that different igneous rocks host ore<br />
deposits with deferent metal associations and that this must be<br />
reW somehow to the environments in which magmas are<br />
generated and the resulting composition-characteristics they inherit<br />
from 1 their various settings. It is widely recognized, for example,<br />
1
24 <strong>Mineral</strong> Resourca <strong>Potential</strong> of Ethiopia<br />
- Placer minerals sorted and distributed by flow of<br />
water (or ice);<br />
- Residual mineral deposits formed by weathering<br />
reactions at the earth's surface.<br />
Ore geumis processes<br />
Internal prmases<br />
These processes are integral physical phenomena and chemical<br />
reactions internal to magmas, generally in plutonic or volcanic<br />
rocks. These include:<br />
Fractional ctystallization, either creating monominerallic<br />
cumulate ores or contributing to the enrichment of ore<br />
minerals and metals;<br />
Liquation or liquid immiscibility, between melts of<br />
differing composition, usually sulfide segregations of<br />
nickel-copper-platinoid sulfides, oxides, carbonate and<br />
silicates.<br />
Hydrothermal proceses<br />
These processes are the physico-chemical phenomena and<br />
reactions caused by movement of hydrothermal waters within the<br />
crust often as a consequence of magmatic intrusion or tectonic<br />
upheavds. The foundations of hydrothermal processes are the<br />
source-transport-trap mechanism. Sources of hydrothermal<br />
solutions include seawater, formational brines (water trapped<br />
within sediments at deposition) and'metamorphic fluids created by<br />
dehydration of hydrous minerals during metamorphism.<br />
Metal sources may include a plethora of rocks. However,<br />
most metals of economic importance are carried as trace elements<br />
within rock-forming minerals, and so, may be liberated by<br />
hydrothermal processes. This happens because of:
Geological outline 25<br />
- Incompatibility of the metal with its host mineral, for<br />
example zinc in calcite, which favours aqueous fluids in<br />
contact with the host mineral underkliagenesis,<br />
- Solubility of the host mineral within nascent<br />
hydrothermal solutions in the source rocks, for example<br />
mineral salts (halite), carbonates (cerussite), phosphates<br />
(monazite and thoriernite) and flllfates (kite); and<br />
- Elevated temperatures causing decomposition reactions<br />
of minerals.<br />
Transport by hydrothermal solutons usually requires a salt or other<br />
soluble species which can form a metal-bearing complex. These<br />
metal-bearing complexes hilitate transport of metals within<br />
aqueous solutions, generally as hydroxides, but also by processes<br />
similar to chelation.<br />
This process is especially well understood in gold<br />
metallogeny where various thiosulfate, chloride and other goldcarrying<br />
chemical complexes (notably tellurium~hloridelsulfate or<br />
antimony-chloridelsul fate). The majority of metal deposits formed<br />
by hydrothermal processes include sulfide minerals, indicating<br />
sulfur is om important metal-carrying complex.<br />
Sulfide depoaition<br />
Sulfide deposition within the trap zone occurs, when 4-<br />
carrying sulfate, sulfide or other complexes become chemically<br />
unstable due to one or more processes: falling ternpatme, which<br />
renders the complex unstable or metal insoluble loss of pressure,<br />
which has the same effect reaction with chemically reactive wall<br />
rocks, usually of reduced oxidation state, such as iron bearing<br />
rocks, mafic or ultramafic mks or carbonate rocks degassing of<br />
the hydrothermal fluid into a gas and water system, or boiling,<br />
which alters the metal carrying ,capacity of the solution and even<br />
destroys metal-carrying chemical complexes. Metal can dso<br />
nminitate when -&re and wessure or oxidation state favour
26 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
Wmt ionic complexes in tlie water, f& instance the change<br />
froin sulfide to sulfate, oxygen fugacity, exchange of metals<br />
Ween sulfide and chloride mplexes, etc.<br />
Metamorphic p m e a<br />
Ore deposits formed by lateral d o n are formed by<br />
metamorphic reactions during shearing, which liberate mineral<br />
constituents such as quartz, sulfides, gold, carbodes and oxides<br />
from deforming rocks and focus these constituents into zones of<br />
redud p~~~ure or dilation such as faults. This may occur without<br />
much hydrothermal fluid flow, and this is typical of podiform<br />
chromite deposits. Metamorphic pmcewes a h control many<br />
physicd processes which form the source of hydrothermal fluids.<br />
Surficial procases are the physical and chemical phenomena<br />
which cause concentmion of ore material within the regolith,<br />
generally by the action of the &nvironment. This includes placer<br />
deposits, laterik deposits ad ~sidud or eluvial deposits. The<br />
physical processes of ore deposit formation in the surficial realm<br />
include:<br />
- Emsiondeposition by sedimentary pmwes,<br />
including winnowing, density separation (e.g.<br />
gold p ~ ~ ) ;<br />
- Weathering via oxidation or chemical attack of a<br />
rock either libemthg rock hgmmts or creating<br />
~hemically deposited clays, laterites or manto<br />
deposits.
Mineml msourowr of Ethiopia<br />
0001ogicaloutliw 27<br />
The -brim crystalline basement of Etbiopia is of particular<br />
interest due ta the fact that it hosts almost all known mined'<br />
commodities of the country (both metallic and industrial m inds<br />
and rocks), notably gold, platinum, rare-metals, nickel, copper,<br />
iron, chromium, kaolin, feldspar, clay, asbestos, talc, etc, Marble,<br />
limestone and granite are also common. Geological mapping and<br />
minerd exploration by EGS (1 989) show that among the crystdine<br />
basement terrain, the most promising areas for gold and base metal<br />
deposits are particulariy linked to the low-grade metamorphic<br />
volcano-sedimentary belts belonging to the 900-500 Ma Arabian-<br />
Nubian Shield terranes.<br />
The Mesozoic sediments are important for their associated<br />
industrial mheds and building material including Iimestones,<br />
sand, sandstones, gypsum and clays. Favomble conditions for oil<br />
and gas we also present. Early Tertiary formations show potential<br />
possibilities for lignite, opal, oil shale and lateritic iron ore.<br />
Bentonites, industrial clay minerals, perlite and pumice are<br />
common. Tertid anq Younger sediments host sulfur, diatomite,<br />
bentonite, potash, common salt, and perlite. Favourable conditions<br />
for oil and gas are also present. Rift volcanic and sediments are<br />
important for geothd energy, soda asb, epithermal gold,<br />
diatomite, bentonite, salt, sulfur, pumice, mineral water, etc.<br />
A flunmary of ore-deposit types (metallic and industrial<br />
minerals, wnstmction and building materiaIs) known to date in<br />
Ethiopia is presented in Table 2. Characteristics of main ore<br />
deposits (Class A: very large deposits; Class B: large deposits;<br />
Class c: medium deposits are summarized in Table 3 while small<br />
deposits (Class D), occurrenca (Class E) and deposits without<br />
available economic data (Class NIA) are presented in Annex 1.<br />
Locations of metallic mineral. deposits are presented in Figure 2<br />
and that of non-metallic mineral deposits in Figure 3.
28 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Mh'm~ia<br />
Table 2: Ore deposit types of Ethiopia
Asmas, lslc or mngncsite ,<br />
-its hcsted by basic and<br />
UltrabaSIcrocks<br />
Volwic-hosted industrial rock G e m Mi,<br />
Cldlch Mad<br />
':guprgene ~ nsediment-~lated d<br />
inddd rock and mineral<br />
, deposits<br />
~Sedlmenr-related industrial<br />
Yrbo(Am@,<br />
Mekdh Mclh<br />
Jddu,&kkr<br />
y~xlks<br />
Valoanic-hosted industrial mk<br />
and mineral deposits<br />
Indu&i@l rock d minerals<br />
related to plutonic rocks,<br />
pegmatites<br />
hb tdon Wdet<br />
I<br />
I<br />
V o l c m idt&ial ~<br />
Yila<br />
dmd mineral dqmh<br />
E v ~ ~ a tW e d SodDbk<br />
raksandmimrrls<br />
Industrid racks lad minerals<br />
datedto~icmcks;<br />
Mqdc<br />
S ~ . M a l m & d<br />
ilij&iAl deposi I<br />
InduslriPl mks and rnMk I CbcPM<br />
P<br />
Ulduslrial mks and mimls<br />
mhkd to plutonic rocks<br />
Slate, marbls and omammtal- DalcH, Morn,<br />
stonedewdts Bnruda<br />
LscuPRine Wits (sebkhs, Lnke Ablynl Lnk<br />
*, alkali& hkd , I ~hsla,LPkCCMlhl<br />
Sdb and gypsum depabits;<br />
lawtrine deposits (sebkha,<br />
dar, alkaline lake)<br />
Volcanic-hmtcd industrial mk<br />
and mineral deposlts<br />
-<br />
Gnluti, Hula - Kuni<br />
Wick Blik -<br />
Bmlba9a<br />
Axum, Adwa<br />
Hasereselm.<br />
Mhr,<br />
Adadikoto, Bissidimo<br />
valley Ramis valley<br />
--<br />
Dire Dma, Cefenq<br />
Kelh, Jemma-<br />
Wdit, Shib<br />
Marecbi.Shebell-i
Geoloaicsll outline 3 1<br />
Sllc Sediment-related industrial<br />
iocka, and minerals; supergene<br />
deposits and minerals : Haghere<br />
Hiwot<br />
Dh-hmM~~k, Kechr,Mi<br />
IWbMmte. w<br />
Gimbicbo
I<br />
I<br />
Chapter Three<br />
Metallic Mineml Deposits<br />
Mttjor metaLIic. o~ , deposits of Etbiopirt include precious metals<br />
(Au, Pt), rare metals fTw) and Ni d Fe; some deposits are'<br />
currently mined for Au and Ta (e.g. Legadembi, Kenticha) or at an<br />
advanced stage of development (e,g. Bikilal project, Fe). To date,<br />
base metals (Zn, Pb, Cu) and &oy metals (Cr, Mo, Mn) are only<br />
knoknown as occurrences or non-economic sd-size deposits.<br />
Metallic resources are mostly genetically linked to the kctonothermal<br />
evolution of the various low-grade metamorphic volcaflosedimentary<br />
belts belonging. to the Upper Proterozoic (900-500<br />
- Ma) Arab-Nubian shield terrms -a potentid penstone hlt.<br />
' Aocording to the rqmtition of these belts, regional distribution of<br />
metallic mineral resources shows three distinct domains (Fig, 2 and<br />
E'ig. 4).<br />
1. A southern domain, including the meta-volcano-sedimentmy<br />
Adola and Kenticha belts (see Fig. 2b). The Adola Belt is one<br />
of the major Neoprobmzoic shear belts within the Pan-<br />
African bgen and this domain hosts major primary gold<br />
deposits (e.g. Lega Dembi mine, Megado, Sakcuo), the main<br />
Elthiopian gold placer deposits (Adola), the pegmatite-hosted<br />
Kenticha tantalum mine and the secondary Mte-dated<br />
nickel deppsits of the Adda district,<br />
Apemaryarn and h Greenstone Region: The<br />
Ageremaryam and the Arero Greenstone regions are located<br />
260 km and 100 km south-west of the town of Kibre Mengist<br />
and hosts: ma-Wc and meta-ultrabasic rocks related<br />
pyrite-bearing Au; meta-ultramafic rocks related Cr, Ni, Co,<br />
V; and Intermediate -to acid alkaline related rocks Bi Sn, W,<br />
Other isolated primary gold deposits in Southern Ethiopia<br />
under rsconnaissance are known in Moyale greenstone<br />
regions 200 krn southwar& close to the Moyale town and the
- Kenya border (e.g. Haramsam, Hasante). The Haramsam<br />
and IIaamte area is located 50 km east of the town of<br />
Moyde. The rocks in the area are, meta-grmodiorite,<br />
amphibolites, gabbro-amphibolite, gabro, and amphibolites<br />
schist. The Haramsam and Hasamte are considered potential<br />
mas for goid.<br />
2. A wide wmtem domain, following the Sudanese border; this<br />
domain can be subdivided into four belts, hosting primary<br />
gold deposits (e.g. Dul, Oda-Godere); the Yubdo platinum<br />
deposit md Meti-Tuludimtu platinum occurrences; the iron<br />
deposits of Bilikai, Chago, Gadma, and base metals<br />
prospects of volcanogenic-volcano sedimentary type<br />
(Abetselo, Kator), The predominant lithologies of the western<br />
Greenstone belt are chlorite, sericite and graphitic schists,<br />
phyuites, quartzites, and h itic to rhyolitic volcanic, iron-<br />
bearing quartzites and congIomerates are also present, The<br />
Akobo greenstone regions are potential areas for pIatinum,<br />
gold, copper and nickel. The area is underlained by mafic<br />
schist, meta-dtramafic rocks, metassdimentary schists and<br />
undifkrentiated schist and gneiss.<br />
3. A northern domain (Tigray) extending northwards in<br />
Eritrea, composed of several meta-volcano sedimentary belts<br />
and sub-belts, bounded by mafic-dEramelfic rocks, hosting<br />
gold and base-metal occurrences (e.g., Adi Zeresenay, Au;<br />
Werri, cu; and Mariam Adi Destra, lead-zinc).<br />
Significant metallic mineral sites located outside of these<br />
domains are scarce; they include the Melka Arba iron deposit<br />
(basic intrusion-related), the Chercher copper occurrence (Red Bed<br />
type in Mesozoic sandstones) and the Enkafala manganese deposit<br />
(Plio-Pleistocene sediments of the Dmakil depression). Therfore,<br />
potential investment areas in the m ind sector are concentrated in<br />
the Adola, Ageremaryarn, Arero, Moyale, western Akobo and<br />
Tigray greenstone regions and are considered as the best locations<br />
;&.
34 Mined <strong>Resources</strong> <strong>Potential</strong> or Ethiopia<br />
of metallic mineral deposits (gold, base metals, rare metals, Ni-Cr-<br />
Co and others), for potential investors to enjoy such rewarding<br />
business opportunities.<br />
3.1 Gold deposit<br />
Occurrence<br />
Due to its relative chemical inertness, gold is usually found as the<br />
native metal or alloy. Occasionally large accumulations of native<br />
gold (also known as nuggets) occur but usually gold occurs as<br />
minute grains. These grains occur between mineral grain<br />
boundaries or as inclusions within minerals. Common gold<br />
associations are quartz often as veins and sulfide minerals. The<br />
most common sulfide associations are pyrite, chalcopyrite, galena,<br />
sphalerite, arsenopyrite, stibnite and pyrrhotite. Rarer mineral<br />
associations are petzite, calaverite, sylvanite, muthrnannite,<br />
nagyagi te and krennerlte.<br />
Gold is widely distributed in the Earth's crust at a<br />
background level of 0.03 g11,000 kg (0.03 ppm by weight) (Boyle,<br />
1987). Hydrothermal ore deposits of gold occur in metamorphic<br />
rocks and igneous rocks -alluvial placer deposits originate from<br />
these sources. The primary source of gold is usually igneous rocks<br />
or surface concentrations. A deposit usually needs some form of<br />
secondary enrichment to form an economically viable ore deposit:<br />
either chemical or physical ,pro'cesses like erosion or solution or<br />
more generally metamorphism, which concentrates the gold in<br />
sulfide minerals or quartz. There are several primary deposit types;<br />
common ones are termed reef or vein. Primary deposits can be<br />
weathered and eroded, with most of the gold being transported into<br />
stream beds where it congregates with other heavy minerals to<br />
form placer deposits. In all these deposits the gold is in its native<br />
form. Another important ore type is in sedimentary black shale and<br />
limestone deposits containing finely disseminated gold and other<br />
platinum group metals. Gold occurs in sea water at 0.1 to 2 mg/t
I 987).<br />
Origin<br />
oed~g~&#&-$hg<br />
f ~ l<br />
W~QW<br />
flpih sm 1 @rectd..&mugh a structure<br />
~ ~<br />
t*;&fmq$g=,%y~w7 @ 31~w c4dcal. wndi4i~ns<br />
@ , ~ ~ f f ~ t h4qmqWda p ~ ~ d ~ ae ~ minerals. @ i ane @ ~<br />
@Y<br />
- - pr~du~e<br />
flm@:;mf<br />
~ m @gmo&&qy ~ c ~ s ~ p g s & g ~ ~ ~ t ~<br />
$ r e 5 5 ~ ~ ~ ~<br />
T@ -pmeqW~~of iqiaqsi~e rooks EUld altatipn associata<br />
, with.&qn .p.ro
36 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
Production<br />
Economic gold extraction can be achieved from ore grades as little<br />
as 0.5 g11,000 kg (0.5 ppm) on average in large easily mined<br />
deposits, typical ore grades in open-pit mines are 1-5 g/1,000 kg<br />
(1-5 ppm), ore grades in underground or hard rock mines are<br />
usually at least 3 g11,000 kg (3 ppm) on average. Ore grades of 30<br />
gl1,000 kg (30 opm) are usually needed before gold is visible to<br />
the naked eye. Therefore, in most gold mines you will not see any<br />
visible gold.<br />
Since the 1880% South Africa has been the source for a<br />
large proportion af the world's gold supply. Production in 1970<br />
accounted 'for 79?? of the world supply, producing about 1,000<br />
tonnes. However, production in 2004 was 342 tonnes (Boyle,<br />
1987). This decline was due to the increasing diaculty of<br />
exbction and changing economic factors affecting the industry in<br />
a that country. Other major producers are Canada, United States,<br />
Russia, and Australia Mines in South Dakota and Nevada sup&y<br />
two-thirds of gold used in the United States. Siberian regions of<br />
Russia also used to be significant in the global gold mining<br />
industry. Kolar Gold Fields in India is another example of a city<br />
being built on the greatest gold deposits in India. Today about one-<br />
quarter of the world gold output is estimated to originate from<br />
ions, southem Ethiopia.
Metallic M W s 37<br />
jewelry, gold is measured in karats (k), with pure gold being 24k.<br />
However, it is more commonly sold in lower measurements of 22k,<br />
18k, and 14k. A lower %" indicates a higher % of copper or silver<br />
mixed into the alloy, with silver being thc more corz~monly used<br />
metal between the two. Gold can be made into thread and used in<br />
embroidery. It pmkrrns critical functions in computers,<br />
communications equipment, spacecraft, jet aircraft engines, and a<br />
host of other products. It is also the form used as gold paint on<br />
ceramics prior to firing. Gold is used as a coating enabling<br />
biological material to be viewed under a scanning electron<br />
microscope (Jensen and Bateman, 1979),<br />
Gdd deposits in Ethiopia<br />
Primary goid deposit<br />
Primary and placer gold deposit and. occurrences have been<br />
reported from the Pan-African volcano-sedimentary sequence in<br />
Southern Ethiopia (Adola gold field), Western Ethiopia (Wollega<br />
region), South-Western Ethiopia (Akobo region), and Northern<br />
Ethiopia (Tigray region). However, at present the Adola gold field<br />
is the only existing active gold producing area except for small-<br />
scale placer gold mining activities by artisanal miners in the above<br />
mentioned regions.<br />
Primary gold sources were discovered in the 1980s during<br />
detailed exploration in the Adola gold field by EMRDC. Such work<br />
resulted in the discovery of the Legadembi and Sakaro primary<br />
gold deposits and many other primary gold occurrences. The<br />
Ethiopian investment company Midroc Gold (a subsidiary of<br />
Midroc Ethiopia Group) operated the Legakmbi gold mine in<br />
Southern Ethiopia; other gold mines that operated in Southern<br />
Ethiopia included the Adola and Sakaro field. Reported gold<br />
production fell to 3,443 kg in 2004 from 3.875 kg in 2003. In fiscal
!<br />
6<br />
i<br />
'14<br />
- 38 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
year 2002-3, exports of gold amounted to about 5,000 kg at a value<br />
?' of $42 million, or 9% of total exports (international Monetary<br />
i -<br />
k<br />
'' Fund, 2005a). Midroc Gold planned to start underground<br />
operalions and to upgrade its processing plant at the Legadembi<br />
mine in 2008 that would increase gold production capacity from<br />
I 1<br />
2,800 kg per year to 4,700 kg. Midroc acquired the mine from the<br />
Government in March for $1 72 million. Midroc planned additional<br />
exploration and eventuaIly to expand the mine's capacity to 5,000<br />
kg per year, Midroc Gold Mine plc also acquired prospecting<br />
licenses for the Adoldkgadembi and Metekel projects, The<br />
company planned to explore for gold and rare-earth elements at the<br />
AdolalLegadembi prospect, which is north of the Legadembi Mine,<br />
and for gold at Metekel, in western Ethiopia.<br />
A global potential of more than 127 tons (Table 3) of<br />
primary gold can be estimated (,resources), based on present stage<br />
of knowledge, including the Adola gold field with Legadembi (62<br />
'<br />
tons Au; open-ended) (Midroc Gold Legadembi), Megado (23.76<br />
tons Au), Serdo (2.85 tons Au), Sakaro (30 tons Au), Wollena,<br />
Kmudu and the Western Ethiopia area with the Dul deposit (2.5<br />
tons Au) (EMRDC, 1985).<br />
There are various types of primary gold deposits (see Table 2):<br />
; (I) the orogenic mesothermal gold deposits being the dominant<br />
L type, (Il) some poorly known gold-bearing volcanogenic massive<br />
b<br />
I<br />
sulphides (VMSs) and secondary gossan-type occurrences and (I1 I)<br />
recently identified epithermal-type mineralization (Solomon<br />
Tadesse, 200 1 ).<br />
I The orogenic maotherma1 gold deposits<br />
Orogenic mesothermal lode deposits form dong, and are localizd<br />
to, major regional fault and fi.acture systems, but are actually<br />
located in secondary or tertiary structures. These vein deposits<br />
form hm hydrothema1 (hot aqueous) fluids, which were derived<br />
deep in the earth's crust at w medium geological temperature (250
Metallic <strong>Mineral</strong>s 39<br />
to 40O0c). The fluids use the fault/fracture zones as permeable<br />
channels along which to tow from their region of origin untii they<br />
reach a point where in any of a number of factors -chemical<br />
reactions with country rock andlor changes. in the temperature<br />
andlor pressure -causes the fluids to precipitate. The gold<br />
precipitates out of solution along with the quartz vein material.<br />
These regional fault systems develop during the waning stages of<br />
continental collision and hence can form at significantly later<br />
periods than the host rocks; as such, they are termed "epigenetic."<br />
The actual host rocks of the orogenic mesotl~ern~al lode<br />
deposits are affected by these fnultlfracture origins and can range<br />
fmn mylonites to fault gouge. Mylonites indicate deformation<br />
under confining pressures sufficiently high that the rock<br />
recrystallizes to a fine grain size. This is plastic or ductile<br />
behavior, and indicates that the vein formed deep in the earth's<br />
am@, Alternatively, if the faultlfrachlre cuts a rock at a level cIose<br />
, to the earth's surface, then it does not have the same confining<br />
pressure and hence will break into fault gouge.<br />
Typical orogenic mesothermal lode gold deposits consist of<br />
quark veins with gold, pyrite andlor arsenopyrite, The gold is<br />
usually pure gold and can be present in textures ranging from<br />
solitary grains to grains intimately ii~tergrown with sulphide<br />
minerals. In some deposits, gold is present as "invisible"<br />
intergrowths with suIphj& minerals such as arsenopycite (that is,<br />
the gold is in the crystal lattice of the sulphide mineral). In other<br />
deposits, the gold is not pure but electnun -a mineral made up of<br />
gold, with 20% to 80% silver. Orogenic mesothermal vein gold<br />
systems are characterized by abundant, typically iron-rich,<br />
hydrothermal carbonate alteration assemblages which spread into<br />
the host rock from the vein. They represent pulses of fluid which<br />
flowed along the hctudfault plane into the surrounding country<br />
lock with which they am not in chemical equilibrium, producing<br />
chemical reactions and the resultant alteration halo.
4 MindResoums <strong>Potential</strong> of Ethiopia ;hcl<br />
:<br />
Alteration associated with gold mineralization also invdlvk?s :'<br />
;srflph.ildbtion (sulphide halos are a characteristic aitmtibs<br />
phgnbmenol~ of most orogenic mesothermal vein gold depasi@)<br />
.:ad potassium metasomatism (potassium is usually enriched in the<br />
alteration halo around the veins). These halos overprint preexisting<br />
alteration assemblages in the host rock. Any rock type can<br />
1. L - host these vein systems, but, at best, they are developed in d c<br />
'fo;cks such as badts, greenstones, gabbros and turbiditic shaky<br />
j.<br />
r<br />
I.<br />
i<br />
sedimentary rocks; this is attributable to the chemical contrasts<br />
between host rock and ore fluids. The ore fluids are silica-rich with<br />
Garbon dioxide and potassium; hence they react best with mafic<br />
rwcks, which-& not contain free silica but which have calciumiron-Magnesium<br />
silicates that can react with carbon dioxide to<br />
- form carbonate alteration minds. Gold abundance are characteristically Iow in most<br />
geological rnakrids, The average crustal abundance of gold is in<br />
, the order of three parts per billion, and generallyno single rock<br />
type is preferentially enriched in gold As a result of the low<br />
background contents of gold, a large mount of. rock must be<br />
affected by the hydrothernld fluids in brder for sufficient deposits<br />
of dissolved gold to be formed. The general model for these<br />
deposits suggests that the associated regional faults have deep<br />
roots that extend down to the lower crust, Hydrothermal fluids,<br />
which contain gold dissolved from a wide region, are formed, and<br />
these are focused up dong the M t s to higher levels in the crust,<br />
where they react with country rock to form lode gold ores. In<br />
temporal terms, orogenic rnesothd vein gold deposits<br />
apparently have ken restricted to specific intervals in the Earth's<br />
history, including the Late Archean, Early Pmterozoic. Early<br />
Paleozoic and Early Mesozoic periods. They are best deveIoped in<br />
Archean greenstone belts within Archean cratonic areas, such as in<br />
northern regions af Ontario and Quebec, Western Australia and<br />
Southern Afiica.
Omgenic mesolhermal gold deposits in Ethiopia<br />
Merallic M inds 41<br />
Most af the known primary orogenic mesothermal goId deposits<br />
and occurrences are related to shear-zone-hosted veins within the<br />
Neoprotmzoic volcan~sedimentary succession of greenschist to<br />
amphi bolite facies metamorphic rocks. They consist of<br />
a<br />
ampbibolite, carbonaceous quartz-feldspar-biotite schist, graphitic<br />
quartzite, me ta-sandstone and conglomerate and associated basicultrabasic<br />
intrusions, common in other greenstone belts of different<br />
ages, such as the Barberton (South Africa) and the Birimian<br />
volcano-sedimentary belts in West Africa (Milesi et d., 1992;<br />
Marcoux and Milesi, 1993; Ledru et a!., 1997), The auriferous<br />
quartz veins and lodes vary in length from a few meters to several<br />
hundred meters. The Kumudu ore occurrence is the smallest, about<br />
400 m in length, while the Legadembi deposit exceeds 3000 m in<br />
strike and 100 m in width. Individual quartz veins (e.g. Sakm)<br />
measure up to 580 m by 2 to 10 m, Most of the quartz veins and<br />
lodes strike confombly with the country rocks. Thus it is doubtful<br />
if they are really veins. Gold [fineness: 350-870 at Legadembi)<br />
occurs in veins as free particles (grains) or is contained within<br />
sulphides such as pyrite, gdena and chalcopyrite. Gold contents in<br />
the ore bodies reach up to 10 glt (e.g. Legdembi). The types oE<br />
wall rock alteration vary depending on the host rock types but are F!;<br />
"<br />
generally represented by sericitization, silicification, chloritization,<br />
sulphidization, carbonatization, serpentinkation and biotitization.<br />
Quartz and carbonates are the most common gangue minerals.<br />
Sulphides are generally associated with the gangues, but do not<br />
exceed 2% of the volume of the veins. The most common sulphides<br />
are galena, chalcopyrite, arsenopyrite, gyrrhotite and pyrite.<br />
Tellurides (petzite, altaite and hessite) are common, e.g. Legadembi<br />
(Solomon Tadesse 2000).<br />
With regard to the gold origin, most of the known primary<br />
gold deposits and occurrences in the region are concentrated within
-11 Minsral Rusourc~~ I'otzntial or Ethiopia<br />
the Megado Belt and partly in the Kenticha Belt which is filled by<br />
volcano-sedimentary (greenstone) rock associations (Upper<br />
Complex). The ore bodies known so far are located within these<br />
units or close to the shear contact with high-grade gneiss with the<br />
only exception of the Digati gold occurrence. Therefore, it is<br />
qbvious that this major structure (the Megado Belt) of the region<br />
served in the emplacement and deposition of the soutcelhost rocks<br />
and provided channel ways for the circulation of hydrothermal<br />
fluids during gold transportation and deposition. Thus, the model<br />
proposed belongs to the syn-orogenic mesathermal type with<br />
significant contributions for the source and trapping of the Pan-<br />
African deformation-metamorphism and magmatism events. The<br />
gold was most probably brought to the surface from a source of<br />
depth in association with basic-ultrabasic magmatism, during the<br />
opening of the Megado Belt (Solomon Tadesse, 2000). Later, due<br />
to metamorphism and defomtion, gold might have been leached<br />
from the protore and trapped at favourable structmI and<br />
lithological sites at various localities within the volcano-<br />
sedimentary sequence and at the contact of these rocks with the<br />
high-grade gneiss formations. Disseminated gold mineralintion<br />
associated with possibly sulphides-bearing veinlets is hosted by<br />
various meta-sediments such as quartzite's and mica-schists of the<br />
Adola Group and meta-conglomerates of the Kajimjti Beds. These<br />
deposits, often confined to Pan-African shear-zones and faults,<br />
probably also belong to the orogenic type mineralization.<br />
The Legadembi primary gold dewit<br />
The Legadembi primary gold deposit located in the Adola Belt,<br />
opia, is one of the major Neoproterozoic shear belts<br />
within the Pan-African Orogen. It is related to the shear zone-<br />
hosted vein system in the Neoproterozoic metamorphosed volcano-<br />
sedimentary succession of greenschist-to amphibolitefacies<br />
. The rocks consist of a sequence of biotite-feldspaf-
Metallic Mincrals 43<br />
quartz schists, carbonaceous mica-schists, amphibolites and basic<br />
to ultrabasic rocks. This unit is separated from footwall biotite<br />
gneiss by a major shear zone. The ore bodies are hosted in the<br />
volcano-sedimentary sequence and colisist of swarms of quartz<br />
veins, lenses, and stockworks that propagated along mesoscale<br />
dude to brittle-ductile shear;zones. The lithology of the facies<br />
occurring in the Legadembi deposit and surrounding area is briefly<br />
described below (Fig. 5).<br />
(i) Quartz-feldspar-mica-schist; gold mineralization at: the<br />
Legadembi mine occurs in quartz0 feldspathic mica-schist, and to<br />
some extent in actinolite-treinolite-hornblende schist. The schists<br />
are bounded to the east by non-mineralized biotite-quartzo-<br />
feldspathic gneiss and to the west by meta-gabbro. All these units<br />
dip at approximately 70" to the best and strike N-S direction. The<br />
quartzo-feldspathic mica-schist is about 1 00 rn thick. pinching out<br />
to the south. In the mine area, it occurs as discontinuous thrust-<br />
nappes units. It is composed of quartz, sericite, graphite, biotite,<br />
and plagioclase with disseminated sulphides. Biotite schist is<br />
dominant, but not the only host for gold mineralization;<br />
(ii) Biotite gneiss; this unit occurs to the east and adjacent to the<br />
eastern side of the Legadelnbi deposit, forming the footwall of the<br />
Legadembi-Sakaro thrust sequence. It is strongly foliated and<br />
contains porphyrodasts of quartz and feldspar. The only alteration<br />
seen in this biotite gneiss unit consists of minor quartz-sericite<br />
along the contact with the ultramafic rocks to the west;<br />
(iii) Ultramafic rocks; these rocks are strongly altered to chlorite-<br />
talc and tremolite-actinolite-talc rocks, with lesser chlorite schist,<br />
tremolite-actindite schist and graphitic quartz-mica-actinolite<br />
schist. They define the major shear zone that separates the upper<br />
greenschist facies meta-volcano-sedimentary sequence of the<br />
Megado Terrain from the upper arnphibolite facies gneisses. The<br />
altered meta-ultramafic rocks locally contain quartz veins that host<br />
gold mineraIization;
- , '''4;<br />
; ,q<br />
- 34<br />
44 <strong>Mineral</strong> <strong>Resources</strong> F~rential of Ethiopia ' < 4<br />
(iv) Metagabbdiamasiive to fol,iad coarse-grained metagabbm<br />
forms the hangfwvuall of the mineralized shear zone. It consists of<br />
basic plag i odd&'(i&adptite to, anorhit e), quartz, hornblende aud<br />
biotite. Nem tb~ontact<br />
of the miheralized zone, it displays fie- to<br />
medium-&&. tkkhms with plagiwlase laths (altered to a fine-<br />
- -<br />
grained &me of saicite, carbonate, chlorite and quartz) in a<br />
ma^^ of chlorite and minor calcite;<br />
(v) hphibolite; this fine-to medium-grained rock contains<br />
hodPde and plagioclase with magnetite por$hyroblasts. It<br />
exhibits a well-developed foliation conformable with the bedding<br />
df lhe regional rook Gentes;<br />
( ~ ) ~ ~ - gbeids:, ! I ? this ~ ~ rock ~ s is ~ medium to coarse grained,<br />
i6~&hgf~f6&ed, h'd mists of plrrgioclase, mono-smphibole and<br />
quark... It" .is. 2;lokel$ ' as-iated with amphibolik and is also<br />
elongated parallel to the 'reg$onal foliation ofthe Adola Belt.<br />
-
Ah Mincml RLWUKCS l'utential or Ethiopia<br />
mum 6 General panomma of he hga Dembi phuy gold deposit ' .
t<br />
,, .<br />
Ore minerals and mintrrml paragenesb<br />
metavolkano-sedimentary rocks in. the<br />
Microscopy and microprobe studies on Legadembi surface and<br />
underground samples indicate a complex mineral association<br />
consisting of gold-electrum accompanied by sulphides, tellurides,<br />
antimonides, and sulphosalts in variable abundances, with quartz,<br />
carbonate and silicates as gangue minerals. The following ore<br />
minerals were observed; pyrrotite, chalcopyrite, galena, pyrite,<br />
arsenopyrite, gold, electrum, altaite, hessite, petzite, cubanite,<br />
ullmanite, tetrahedtite, freibergite, breithauptite, boulangerite,<br />
bournonite, meneghinite, nisbite, gersdorffite and mackinawite.<br />
..- .<br />
. ,<br />
, - .,. r . . . -<br />
, . ': . ..<br />
. .<br />
*' 1.. , '.<br />
., ..*$ ;<br />
8
'-&<br />
-.<br />
,.:&<br />
Metallic Minds 49. -<br />
-<br />
Based on different textural features of ore minerals and gangue.) rrs<br />
well as intergrowth relationships, the paragenetic sequence has<br />
been subdivided into four paragenetic stages. Stage one is<br />
characterized by an assemblages of pyrrhotite, chalcopyrite,<br />
sphalerite, cubanite, gersdofite, ulmanite, pentIandite and<br />
mackinswite. The sulphide minerals mainly occur in the wall rocks<br />
and me inherited as relic in awifmus quartz veins, In stage two,<br />
pyrite replaces pyrrhotite along grain boundaries. Finger-like<br />
protrusion of pyrite in pyrrhotite is common, Stage three is<br />
represented by the last pyrite generation. This pyrite stage occurs in<br />
late quartz veinlets cutting across the schistosity. Stage four<br />
includes gold, electrum, galena and tellurides. These minerals are<br />
confined to laminated or banded quark veins and their wall rocks,<br />
Gold and tellurides always occur as inclusions in galena pig. 9).
50 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethionia<br />
Possible genetic processes of the LDPGD<br />
1 Fofrnation of a volcano-sedimentary sequence, with mafic<br />
gold-bearing horizons interbedded at two main levels (within<br />
the lower most part of quartzo-feldspathic schist);<br />
2 RegionaI metamorphism of the entire sequence up to the<br />
amphibolite facies, with n~obilization and pre-concentration<br />
of ore minerals. Gold occurs as sub-micron to visible<br />
inclusions in and around the edges of galena and as free gold<br />
associated with tellurides, implying that the low temperature<br />
environment was a favorable condition for gold precipitation.<br />
The presence of gold as inclusions in galena, together with<br />
the absence of gold and galena in unmineralized wall rocks<br />
clearly supporls a temporal association of gold and galena;<br />
3 The intimate association between gold mineralization,<br />
metavolcano-sedimentary succession, brittle-ductile shear<br />
zones, lithological contrasts within the Neoproterozoic Pan-<br />
African Adola shear belt is, therefore, similar to most of the<br />
shear-zone-related and greenstone hosted gold deposits like<br />
those described by Robert and Brown, 1986 for Sigma mine,<br />
Canada and Aildrews et al, 1986 for Abitibi, Quebec.
. 46<br />
'&<br />
52 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
*<br />
Volcdc-associated massive sulphide (VMS) deposits qdi .<br />
throughout the-world and throughout the geological time col4 in:-"r<br />
nic domain that has submarine volcanic ~ cks<br />
uent. VMS deposits we major sources of Cu<br />
significant quantities of Au, Ag, Pb, Se, Cd, Bi,<br />
Sn qq We11 as minor amounts of other metals. As a group, VMS<br />
dap6% consist of massive accumulations of sulphide minerals<br />
(&o* than 60% sulphide minhs) which occur in lens-like or<br />
tai6ulm bodies parallel to the vofcanic stratigraphy or bedding.<br />
@ey are usually underlain by a footwall stockwork of vein and<br />
s&r sulphide mineralization and hydrothermal aheration. They<br />
my occur in any rock type, but the predominant hosts are volcanic<br />
rocks and fme-med, clay-rich sediments. The deposits consist of<br />
ubiquitous iron sulphide (pyrite, pyrrhotite) with chalmpyrite,<br />
sphalerite, and galena as the principal economic minerals. Barite<br />
and cherty silica are common gangue accessory minerals.<br />
As to the origin, at divergent boundaries, water from the<br />
ocean floor flows though fractures in the oceanic crust. The<br />
waters are heated by the nearby magma source, producing a<br />
seawater convection cell which reacts with neighboring rocks to<br />
leach out metals. These dissolved metals are transported to the<br />
ocean floor where they mix with cold bottom waters. The sudden<br />
decrease in temperature causes the minerals to precipitate from<br />
solution and they are incorporated into sediments deposited ahng<br />
the ocean ridge system. In Ethiopia, this type of mineralization<br />
warrants further investigations.<br />
III Epithermal gold deposit<br />
Epithermal precious metal mineralization is commonly associated<br />
with Cenozoic or Quaternary geothermal systems in areas of calc-<br />
alkaline volcanism. Much of this voIcanism typically occurs above<br />
subduction zones along continental margins and in Island Arcs as<br />
well as along spreading Mid-Ocean Ridges. Less commonly,
*<br />
western Asfa and continues along the eastern side of Mica. ThG ;, &'<br />
system already includes sectors that represent evolving<br />
basins (the Gulf of Aden and the Rsd Sea), but mostly it comptises<br />
sub-aerial intracratonic rifb, including the Ethiopian Rift Valley.<br />
Sub-aerial volcanism h the Ethiopian Rift Valley %has caused<br />
hydrothermal activity, which is still active in s v d sites being<br />
investigated for geothed energy. Extinct geothd fields are<br />
also quite common. The possibility that these gmthermd systems,<br />
related to the contined rifling, have been .and may be oreforming<br />
systems cannot be discarded a priori.<br />
An epithermal gold deposit is one in which the gold<br />
minerdidon occurs within 1 tp 2 km of surface and is deposited<br />
from hot fluids, The fluids are estimated to range in tempemhm<br />
from less than lOOC to hut 300C and, during the hdon of a<br />
&posit, can appear at the surface as hot springs, similar to those<br />
found in Yellowstone National Park (in northwestern Wyoming,<br />
muthem Montana and e&m Idaho). The deposits are mast often<br />
fomd in areas of active volcanism around the margins of<br />
continents.<br />
EpiEhermal gold mineralization can be formed from two<br />
types of chemical1 y distinct fluids -"low sulphidation' (LS) fluids,<br />
which are qduced and have a na-neu-tral pH (the measure of tb<br />
concentration of hydrogen ions) atld "high sdphidation" (HS)<br />
fluids, which are more oxidhd and acidic. LS fluids are a mixture<br />
of rainwater that has percolated into the subsurface and magmatic<br />
water (derived from a molten m k source deeper in the earth) that<br />
has risen toward the mfke. Gold is carried in ailution and; for LS<br />
waters, is deposited when the water approaches the surface and<br />
boils, HS fluids are mainly derived from a magmatic some a d<br />
deposit gold near the surface when the solution c ds or is diluted<br />
by mixing with rainwater. The gold in solution may come either
54 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
directly from the magma source or it may be leached out of the<br />
host volcanic rocks as the fluids travel through them.<br />
In both LS and HS models, fluids travel toward the s ace<br />
via fractures in the rock, and mineralization often occurs 4within<br />
these conduits. LS fluids usually form large cavity-filling veins, or<br />
a series of finer veins, called stockworks, that host the gold. The<br />
hotter, more acidic HS fluids penetrate Wer into the host rock,<br />
creating mineralization that may include veins but which is mostly<br />
scattered throughout the rock. LS deposits can also contain<br />
economic quantities of silver, and minor amounts of lead, zinc and<br />
copper, whereas HS systems often produce economic quantities of<br />
copper and some silver. Other minerals associated with LS systems<br />
are quartz (including chalcedony), carbonate, pyrite, sphalerite a h<br />
galena, whereas an HS system contains quartz, alunite, pyrite and<br />
copper sulphides such as erwgite. Geochemical exploration for<br />
these deposits can result in different chemical anomalies,<br />
depending on the type of mineralization involved, LS systems tend<br />
to be higher in zinc and lead, and lower in copper, with a high<br />
silver-to-gold ratio. HS systems can be higher in arsenic and<br />
copper with a lower silver-to-gold ratio.<br />
Epithermal gold occurrences in Ethiopia<br />
The Ethiopian Rift Valley in general held little more than an<br />
academic interest in scientific circles for a long period of time.<br />
Detailed geological studies and regional mapping of the rift valley<br />
have been conducted since the last 25 years. These have helped<br />
delineate specific industrial resources (e, g,, diatomite, bentonite,<br />
soda ash and geothermal steam), mainly through the work of the<br />
EGS. A new metallogenic province characterized by epithermal-<br />
type gold mineralization has been recently identified in Ethiopia<br />
(Solomon Tadesse, 200 1 ). Low sulphidation (adularia-sericite<br />
type) occ~cces have been found within Quaternary volcanoclastic<br />
rocks of the MER.
een dfted by intense hydro@errnal albratioq:. p90tassic and<br />
argillic alterations at Gedemsa $nd Tadaho, esqgntidly propylitic<br />
alteratio?.:a CorM. Thw, a lot of oaq and> ,cutting samples<br />
calbated. at various localities (such as Gedemsa, Aluto and<br />
Cbrbetti caldm, Tendaho . graben, Afar and MER) ,hve .revealed<br />
anoms ,wt~e~r~~ging hm ioo to 500 ppb (0.1-0.5 'gp~) gold.<br />
These sc?cuqremes warra4t fqrther investigzjtions. ,A new, field of<br />
inv%t&$gisn on epipithemal ore occmnces wldeb we ,und for<br />
th$ l ~ ~ ~ Ethiopian i a t metallogeflic scenery is .pmb&ly mergbfg.<br />
A,, study, ofl phe~~mena, in , lighl ,of @cent .rqc~ulsitions in<br />
~~a:how19dgeJ d d be, of potl ~Iytifor further<br />
u sci@c stugi but far new pgsib;ili~eq ini~&g activity.<br />
SQ&QO . aimed @ id~fiQjng epifiem&me, pmious metal<br />
$m&d$ gold), resources within the Ethiopian Rift is :relatively<br />
recent. , .. I ,<br />
Geological setting and epithermal gold mineralization<br />
The Corbetti anidera<br />
Corbetti is a Holocene volcanic complex found in the central sector<br />
of the MER. The most abundant volcanic rocks are peralkaline<br />
py roclastics (ignirnbrite and pumice) which are attributed to<br />
central-type eruptions with subsequent volcano-tectonic collapse.<br />
The geometric outline of the resulting caldera is elliptical with its<br />
long axis measuring about 12 km. The wall of the caldera has a<br />
variable height between 50 and 200 m. Post-caldera activity is<br />
represented by the emplacement of two very recent volcanic<br />
4
k<br />
56 <strong>Mineral</strong> Rtsoum <strong>Potential</strong> of Ethiopia<br />
centers (Urji and Chabbi) situated on active faults that parallel the<br />
major structural zone of the rift systeni. The Urji and Chabbi<br />
centers have extended pumice flows and falls with minor obsidian<br />
flows. Both centers are at fumaroles stage.<br />
Several NNE trending minor no& faults cut all the<br />
volcanic rocks except the youngest products of the Urji and Chabbi<br />
centers. Eight shallow temp-grad boreholes have been sunk at<br />
different locations in and outside the caldera ranging in depth from<br />
50-200m. The boreholes were irregularly located but have enabled<br />
constructing shallow subsurface volcanic stratigraphy.<br />
Altered rock forms a roughly north-south elongated area<br />
some two kilometers Iong and several hundred meters wide. Steam<br />
activity is apparent only along the extremities of this zone, but it is<br />
possible that thick soil cover may have Masked the rest of the area.<br />
A low sulpkidation (adularia-sericite type) alteration processes are<br />
indicated by propylitic and advanced argillic assemblages in<br />
ignimbrite, pumice and rhyolite, The alteration is characterized by<br />
the presence of chlorite, kaolin, calcite and quartz. The metallic<br />
minerals found in the shallow &ill-chip samples include Fe- and<br />
Ti-oxides, sulphide minerals including pyrite and chalcopyrite and<br />
possibly Pb-bearing sulphosalts. The propylitic alteration, which is<br />
largely overprinted by later intermediate Wllic alteration,<br />
surrounds an elongated and discontinuous core of potassic<br />
alteration. Advanced argillic alteration is limited to areas in<br />
proximity to the vents. Crusts of salts and silica occur around the<br />
vents; some of these sdts are greenish in colour and appear to be<br />
ferrous iron and copper salts. Weakly developed surface alteration<br />
zones locally occur, with Fe and Ti oxides. Gold content, a1 though<br />
irregular or err&ic, commonly exceeds 150 ppb both in compact<br />
mks and in pumice fragments. The Corbetti caldera appears to be<br />
one of the most economically promising among the newly<br />
discovered occurrences.
p&ducts.<br />
The caldera itself is clearly a composite structure that<br />
requited from repeated collapses following large pliniad pyroclast~c<br />
' empioris?' The geometry of the caldera is almost circular,<br />
mear~whig tabout '1 0 km. The whole caldera structure is strongly<br />
d&&d~ by many large close1 y-spaced WE-SS W-trending fdts,<br />
6peddly at its earn pout. These faults belong to the Wonji Fault<br />
Belt @d manifest active tectonics within the rift Evidence for past<br />
hydrothermal activity is observed in the. north-west caldera ~ l l<br />
*&&'an a mall dome hide the caldera. Occurrema of several<br />
Wv&therind maniftistations are .also known along NNE hult lines<br />
iminediately outside the calderq proper. The fossil hydrothe&<br />
m&festations have oxidid pumiceous deposits with some<br />
&psition of silica. Two. shallow tempemure gradient wells have<br />
ken drilled within the Gedemsa caldera reaching depths of 1W<br />
and 200 m respectively, with rack cutting samples taken every 3m.<br />
Rhyolite Iavas, ignhbrite and pumice deposits represent<br />
rhe'host~rocks. The alteration belongs to the low-sulphidation type.<br />
The alteration forms a roughly NW elongated area some 5 km long
wide. Propylitic dtetatibln,~ which is<br />
tennedhk argillic alteration, surroun@<br />
on. several &in quartz-duiaria ve~irrr<br />
hsic alaon. The occurrences are formed of<br />
,and granular quartz Carbonates and clay<br />
present. The ore-mineral assemblage includes<br />
, iron oxides, epidote, chtorite and<br />
caldera, pyrite occurs in fractured<br />
propylitized rhyolite, with m w mms of ptassic alteration and<br />
development of intermediaie argillic alteration. In the fractures,<br />
i thin veins of cavernous quartz with abundant copper sulphide<br />
dissemination, occur. Gold content ranges hm 100 to 440 ppb.<br />
This area appears to be the most promising among the lowsulphidation<br />
murrences.<br />
Auto volcano<br />
The Aluto volcanic complex is a Quaternevy volcanic center -:<br />
located dong the Wonji Fwult &It in the central seaor of the MER,<br />
' -<br />
The geology of this complex is relatively well-known from surface<br />
mapping supplemented by data on the deep stratigraphy and I<br />
struchue from eight deep exploratory wells that were sunk to ii<br />
depths ranging from 1,300 to 2,500 m<br />
$E!: .<br />
by EGS.<br />
L uj<br />
According .to Govatmi and Mewet Teklemariam (1993) .*. ! ..<br />
the oldest ~utcro~~in~ rocks in the area are found at the adjacent ; ,]eastern<br />
rift escarpment and consist mainly of siiicic volcanic~ . ,: :.L<br />
commonly known as the Tertiary ignimbrite unit. This unit is<br />
overlain by a fisfltral, basaltic unit known as Bofa Basalt, which in gk . I ,. .I :.<br />
turn is covered by sediments of lacustrine origin which also extend "-,<br />
over large areas-of the rift floor. Th volc&c products of duto<br />
volcanic centre itself consist of w succession qf ash-flow tuffs,<br />
silicic tuff breccia$, silicic domes and pumice flows. These<br />
volmic products are very young and are associated with surface<br />
thermal manifestations that consist of hot springs and fumaroles<br />
., I
Metallic <strong>Mineral</strong>s 59<br />
with tempratures up to 95%- steaming grounds, silica sinter and<br />
travertine deposits. The hydrothermal deposit temperatures<br />
measured in the deq cxploratdry wells range from 88 b 335'C<br />
(Solomon Kebede, 1 986).<br />
The alteration observed in the studied samples froin Aluto<br />
includes an upper facies characterized by intermediate 'and<br />
propylitic assemblages. Intermediate argillic facies are typidy<br />
represented by smectite-group clay minerals; alteration intensity is<br />
variable, hm incipient groundmass argillification to almost<br />
pervasive metasomatism. The latter is best developed in rack units<br />
originally very rich in glass. Propylitic alteration includes the<br />
chmcteristic minerals, calcite, chlorite, quartz and epidote. The<br />
metallic minerals found in the studied samples mostly include<br />
oxides and sulphides. The oxides consist of magnetite, ilmenite,<br />
hematite and Ti-oxide. The sulphide minerals are pyrite,<br />
chalcopyrite, and sulphosalts possibly of Pb. Pyrite is the most<br />
abundant. Gold value ranges from few ppb to 100 ppb,<br />
The emd dab graben<br />
This graben is found further north in the Afar depression. It is a<br />
NW-SE trending graben about 50 lun wide and is the southern<br />
extension of the Afar active spreading zones where the active Erta<br />
Ale-Manda Harm volcanic ranges are situated. The A h axial<br />
: ranges are considered to be the exposed equivalents on land of the<br />
Red Sea oceanic spreading ridges (Barberi and Varet, 19771,<br />
The Tendaha graben exposes a thick succession of basalt<br />
flows of Pliocene age (known as the Afar Stratoid Series) at its<br />
borders. The graben is filled with thick lacustrine and alluvial<br />
1 deposits consisting of siltstone and sandstone. Very young basaltic<br />
flows and scoria cones (the Afar Axial Ranges) have be~n<br />
emplaced on top of the graben volcani-cIastic sediments. The axial.<br />
zone is also characterized by the ~resence of open fissms and
60 <strong>Mineral</strong> Rrsources <strong>Potential</strong> of Ethiopia<br />
,-<br />
numerous active faults which as a whole define the sites of active<br />
spreading.<br />
The fissures and faults are evidence of active and fossil<br />
hydrothermal deposits which extend for several kms along strike.<br />
In fact, the most interesting feature of this area is the extensive<br />
hydrothermal activity which is controlled by N W -SE trending<br />
normal faulting. h the Tmdaho rift, the hydrothermal activity in<br />
the area extends for several krns according to a general NW-SE<br />
trend and consists mainly of steaming grounds. Several veins<br />
preferably cut the rocks undergoing potassic altersttion. These<br />
veins, with variable strike mund NW-SE, range from veinlets a<br />
few meters long and a few cehheters thick to bodies several<br />
hundreds of meters long. The quartz forming in these veins may be<br />
chalcedony near the walls, but commonly the central part of the<br />
veins is drusy and colourless mmcrystalline quartz. The<br />
alteration is manifested by the presence of mined assemblages<br />
a including chlorite, smectite, vermiculite, epidote, adularia and<br />
1 . quartz. The sulphide minerals include pyrite, galena, chalcopyrite,<br />
stibnite and covelitt. Sarnples h m drill cores recovered for the<br />
purpose of exploratory geothermal energy have been analyzed for<br />
gold. Analysis of a few samples hrn a core in Tendaho (TDI)<br />
range in value fiom tens of pbb to 400 pbb Au.<br />
I<br />
PetPobgicrrl notes<br />
The volcanic rocks of the above described formations range in<br />
composition from alkali olivine basalts to peralkali rhyolite and<br />
have the following genevpl petrographic features. Ignimbrites:<br />
these rocks show a remarkable uniformity of composition over<br />
large areas. They are porphyritic pdkdine rhyolites with<br />
abundant glassy matrix usually constituted by a very fine glassy<br />
dust. The common phenacrysts are an orthoclase, acmite and<br />
faydite. Xenoliths of foreign rocks are abundant in the ignimbrites.
Metallic <strong>Mineral</strong>s 61<br />
Peralkaline Rhyolite; these rocks are represented by some<br />
lava flows, lava domes and pumice flows. Petrographically, they<br />
appear to be always highly glassy, with variable contents of the<br />
following minerals: alkali feldspar, generally anorthoclase, acmite,<br />
alkali amphibole (riebeckite) and me fayalite and quartz. Basalts;<br />
in the studied area, the basalts are usually holocrystalline and show<br />
typical features of allcaline basalts. The mineralogic a1 assemblage<br />
is magnesia olivine, clinopyroxene of augite type, calc plagioclase,<br />
magnetite, ilmenite and rare small apatite crystals.<br />
'HE results obtained so far represent the first phase of<br />
studies on epithermal occurrences within the (MER) and Afar.<br />
Much work has to be done in order to arrive at a reasonably well-<br />
documented synthesis, However, a working hypothesis can be<br />
attempted as a basis for future detailed studies from the obtained<br />
observations and results.<br />
The different associations among ore-mined assemblages<br />
and alterations seem to reflect different levels of mineralization.<br />
This is shown at Corbetti and Gedemsa which are hosted in similar<br />
volcanic systems. At Corbetti the occurrence of base metals is<br />
accompanied essentially by propylitic alteration, while at<br />
Gedemsa, precious metals and quartz addaria occur, in association<br />
with potassic and argillic alterations. Gold is likely to originate<br />
from Precambrian basement, which is presumed to extend under<br />
the rift floor. Hydrothermal fluids rose through a network of<br />
Mum found within and outside the caldera, provided that a<br />
major hcture system was present that should serve as a plumbing<br />
system. In the Corbetti caldera, one possible source of the fluids<br />
may have been the two rhyolite domes near the road just north of<br />
the steaming ground structure which apparently represent an<br />
intedon between the NS structure (fault plane) and a contact<br />
between pyroclastic and a hard, impervious compact rock. This<br />
fluid channel way is marked by the abundant silica encrustation of<br />
the surfaces.
I'<br />
Other sidlar structures ~ b lof e driving solutions might<br />
exist that pdtentially ImaIize sites of gold enrichment. Irregular<br />
fracture system within the caldera cause sporadic aI teration and<br />
discrepant gold values in the same rock unit. The youngest pumice<br />
unit appears fresh (except where fractures offer reactive channels,<br />
e.g. steaming ground areas). Although the gold content is<br />
comparable to that of the underlying rocks, fiis may have resulted<br />
from the fluid supplied from almost neud solutions, because<br />
buffered by alkalis in underlying rocks, but still containing gold,<br />
permeated through the interface of rock-pumice and spread<br />
through the unconsolidated, highly permeable material. A further<br />
expansion, resulting in an adiabatic drop in pressure and<br />
temperature would enhance the precipitation of gold from the<br />
circulating solution. Mixing with surface water might also occur,<br />
that recharges the groundwater body which occurs dong the<br />
interface between the pumice-hard rocks. The high precipitation<br />
characterizing the area, the high permeability of the surface and the<br />
much lesser permeability of the underlying rocks all favored this<br />
model. The wide surface area offered by the pumice and its glassy<br />
nature, allow adsorption phenomena in the entire pumice unit.<br />
As far as the age of epithermal mineralization in the rift is<br />
concerned, no quantitative data are yet available. However, it has<br />
been established that in all areas, where gold occurrence has been<br />
documented, the host rocks are ignimbrites, rhyolite laws and<br />
pumice deposits, with subordinate basaltic rocks. Thus, the<br />
epithermal occurrences are mostly hosted in acidic rocks emitted<br />
from central volcanoes during Late Quaternary times, i.e. younger<br />
than 0.8 Ma in age. The overall characteristics of the known<br />
occurrences and the evolution of the central volcanoes within the<br />
rift and associated epithermal phenomena apparently define an<br />
individual, homogeneous metallogenic province within the rift.<br />
Analyses of a total of 579 core and cutting samples<br />
collected from 18 deep holes from the. studied locgities showed<br />
,. . :;;cy$&;- s ,& .+*t'? y .>;. .,,. Gj, L, .e.- ;=-
I Metallic <strong>Mineral</strong>s 63<br />
gold contents that range from hundreds of ppb to 0.44 g/t.<br />
Concentrations ranging between 120-300 ppb are very common<br />
t<br />
throughout the geological profiles particularly at Corbetti and<br />
Gedemsa calderas and Tendaho graben. The mean gold content<br />
from the above 1ocaIities exceeds the maximum gold values<br />
1<br />
reported in literature i.e. 3 ppb for rhyolite and 5 ppb for the upper<br />
lithosphere. Nearly all the analyzed samples showed high<br />
anomalous values starting from a depth of four meters downwards.<br />
1 Obviously, it is too early to give any economic evaluation, but the<br />
field and analytical data appear encouraging for the development<br />
of exploration and a preliminary estimate for gold, at least in the<br />
t Corbetti, Gedemsa and Tendaho prospects.<br />
A$ simple calculation shows that the overall gold quantity is<br />
huge, For instance, taking an average value of I00 ppb for the gold<br />
I<br />
a<br />
dispersed in the upper uniformIy spread unwelded pumice unit<br />
having an average thickness of 40 m over a surface area of 50 km2,<br />
the total reserve (assuming a specific gravity of 0.9 for pumice)<br />
can be calculated to over 200 tons in just one of the caldera alone,<br />
i,e. a gold reserve level of an important mine. Obviously, at current<br />
mining exercise, 0.1 g/t average gold content is .too low for the<br />
wide pumice layer to be considered as economical. It is to be<br />
noted, however, that the bore holes used for the present evaluation<br />
were strategically located to intersect known fluid-driving<br />
s~ructures nor was it possible to have fdly representative<br />
composite core samples for assay. If systematic geophysical and<br />
exploration drilling directed for gold were done, the subsequent<br />
analysis might enable to identify high-grade gold concentration<br />
target areas even at shallow depth.<br />
IV Gold-bearing placer<br />
Plat gold deposits form as a result of the breakdown and<br />
-ring of existing gold concentrations, erosion of the
64 <strong>Mineral</strong> Resourax <strong>Potential</strong> of Ethiopia<br />
w-eathered material and, ultimately, the concenbration of that<br />
material at a variable distance from its source. The tam "placer" is<br />
derived from the Spanish word for sand bank or stream eddy.<br />
Placer deposits, in the strictest &me, are formed in river systems,<br />
but the tern is typically used to describe deposits formed in- glacial<br />
and beach environments. Placer gold deposits are formed when<br />
gold is carried from its source to its site of deposition and<br />
concentration by a surface erosional force such as rivers, glaciers, -<br />
oceans end (rare1 y) wind.<br />
The formation of gold placers is predicated by two<br />
fundamental physical properties of gold To begin with, gold is<br />
dense, with a specific gravity of 19.3 grrtms per cubic cm-among<br />
the highest for all known minerals or native elements. Also, gold is<br />
a native element rather than a mineral (the latter being a naturally<br />
, occurring inorganic chemical compound), and dws not readily<br />
react with other elements. A corollary of this second pint is that<br />
gold is difficult to dissolve out of rock or minerals. The original<br />
' source of the gold is unimportant, ranging, as it does, bm<br />
mesoaermal lode deposits to massive suiphide deposits to<br />
disseminated sulphides in bedrock to pre-existing placer systems.<br />
Placer deposits depend on an original pre-con&-tion of gold<br />
which can be liberated through weathering. Eluvial, or residual,<br />
placers are a type of placer deposit in which gold has undergone<br />
little transport and actually forrned on, or near, the original source<br />
through the weathering or erosion of host rock. Owing to its<br />
relative chemical inertness, gold remains behind while h<br />
Gold in placer systems is transported as discreet grains as a<br />
the metal's inertness. Such grains are said to be &td, as<br />
derived from the physical weathering and breakdown of
Metallic <strong>Mineral</strong>s 65<br />
material (detritus) carried in the same erosional system, the gold<br />
grains must be transported by erosional agents operating with<br />
~~elatively higher energy than that needed to transport normal rock<br />
detritus. When the energy exerted by the erosional agent decreases,<br />
the gold and other dense detritus will stop moving. In the case of<br />
fluvial (or river) placer systems, detritai gold grains ad<br />
concentrated in those mas where the current of the stream slows,<br />
such as on the slow sides of beds in the river, on the downstream<br />
sides of islands or near sand bars. old grains move when energy<br />
is exerted on them by the -porting medium. The grains will<br />
continue to move until the medium loses sufficient energy,<br />
whereupon the gold grains will settle out of the transporting<br />
medium.<br />
An example of a fluvial placer gold deposit is a mature<br />
stream in a valley floor into which numerous subsidiary streams<br />
'<br />
flow. h glacial tills, gold is transported along with other detrital<br />
&rial until the glacier ceases to move, dropping the gold and<br />
detritus. The driving mechanism for the formation of placer<br />
deposits, therefore, is gravity. Another innate feature of placer gold<br />
deposits is that the material that hosts the gold is unconsolidated<br />
sediment (particulate rock that is not cemented together). The host<br />
sediment can range from gravels to sand in fluvial systems, as well<br />
as to various types of till in glacial deposits or beach sands.<br />
A "pay stre&" is the layer of sediment in a placer deposit<br />
which is enriched in particulate gold. In fluvial examples, the "pay ..<br />
streak" frequently occurs in sediments that lie directly on tap of :i!'l<br />
r: A<br />
bedrock. The "pay streak" will also contain other dense, hard or :<br />
inert minerals, such as magnetite, zircon, garnet or chromite, There<br />
is some debate as to whether nuggets in fluvial systems represent<br />
purely detrital fragments that were rounded in transport or are the<br />
nuclei upon which dissolved gold in the stream precipitated and<br />
grew. In some instances, gold &ns have greater finene<br />
. .
, suggesting either- .prefeferftiti~<br />
most important in the Adda gold field. Dcluvial gold is known to<br />
!' occur on the hillsides of the Legadembi and S&m primary gold<br />
deposits and the Kumudu ore occurrence. In the Adola goldfield,<br />
placer deposits with contents averaging 0.1& or more of gold<br />
and with gold reserves of over 30 kg are classifid as "placer<br />
deposit", while those with lesser gold valws and reserves erre<br />
a termed 'bplacex occurrence". All gold placers are concentrated in<br />
the N-S hending Megado Belt. The economic gold con&ntratim<br />
of the placers occur in gravel, shd, silt and clay sediments of dry<br />
streams, river fl-, old vdIeys, and terraces. They are derived<br />
- from the primary gold deposits (orogenic mesothermal v-, lodedeposits),<br />
and gold-bearing quartzite's associated-with the<br />
rocks of the Adola Group and the conglomerates of the Kajimiti<br />
Beds, that are often confined to Pan-African Shear-Zones and<br />
Fdts.<br />
The largest gold placer deposit has been explored in the<br />
Bore valley with calculated reserves of up to 4.5 tons of gold<br />
(EMRDC, 1 985; $elas;sie and Reimold, 2000). This placer bas been<br />
mined since the late 1950s and its gold production is still in<br />
progress by misd miners. In the Adola area, a total reserve of<br />
13.67 toas of placer gold was @mated in 1985 (EMRDC, 1985;<br />
Selassie and ReimoId, 2000). Other placer gold are mined in a<br />
small scale in Wollega, Akobo 4 Tigray region by local people.<br />
I '
Mttallic <strong>Mineral</strong>s 67<br />
Genetically, the gold placers of the Adola area fall in<br />
three groups.<br />
(i) residual-eluvial (slope placers) at sites of disintegration<br />
primary source, (ii) eluvial-alluvial lacers formed in small valleys<br />
and fans, due to intermittent stre !m activity, and (iii) alluvial<br />
placers formed in the valley floor and on river ' terraces.<br />
Commercially, the potential of the area is linked with the alluvial<br />
placers containing the bulk of the estimated reserves. Residual-<br />
eluvial and proluvial placers are targets for hand mining<br />
operations. The major part of known placers is shallow-lying with<br />
overburden being as thick as 20 m (e.g., Kajimiti).<br />
Based on the mode of occurrence and geology of placers of<br />
the area, the following observations can be madel-the low-order<br />
valleys are rather monotonous in geomotphic aspect along their<br />
~~3<br />
entire length. The Iarger valleys (such as Bore, Kajimiti, ,-, + .-.<br />
Bedakessa, Awata, and Mormora) have contrasting morphologies<br />
at different sections due to locd control by undetlying geology, . .<br />
neotectonics and faults. LOW-or& valleys have no terraces.<br />
Terraces of high-order valleys as a rule have little or no surface<br />
expression in topography. In most cases the terraces are buried<br />
under slope waste.<br />
All placer gold occurrences are discontinuous; they form<br />
isolated grounds and pay-streaks. Gold is concentrated as nests and<br />
as combination of nests and pay streaks. Nest-like concentrations<br />
most frequently occy against distributed gold.<br />
--<br />
Tn conclusion, the regional distribution of placer deposits<br />
and occurrences in the area is characterized by distinct spatial<br />
association with both the Megado and Kenticha primary gold belts.<br />
This emphasises the intimate spatial association of the areas of<br />
placer formations with the primary gold fields. The majority of the<br />
placers are localised in the areas of enhanced erosive<br />
transformation of the relief. Structurally the Adola area consists of<br />
numerous, variously uplifted blocks of the crystalline basement.
68 Minerat Rcsouwcs <strong>Potential</strong> of Ethiopia<br />
Under these circumstances, the spatial distribution of zones of<br />
'weakness exerts direct control on the formation of the drainage<br />
pattern. These zones of weakness include systems of faults of<br />
various ages.<br />
Figure 1 1 Ground sluicing for placer gold by artisanal miners in Adola area
Figum 12 Placer gold minhg by hydra monitor at Ula Ulo,<br />
Adnh p i n l r t h Ethjnniq<br />
Figure 13 Excavating gold-bearing grad in Aodok area
I<br />
Figure 16 Plawrgoldminiihm adoeppit(34m) by artisanal<br />
mima {Adola)<br />
3.2 Platinum deposit<br />
' Occurrence<br />
Platinum and palladium are precious metals generally found in<br />
ultramafic rocks. The source of platinum and palladium deposits is<br />
ultramafic rocks which have enough sulfur to form a sulfide mineral<br />
while the magma is still liquid. This sulfide mineral (usually<br />
pentlmdite, pyrite, chalcopyrite or pyrrhotite) gains platinum by<br />
mixing with the bulk of the magma because platinum is chalcophile<br />
and is, concentrated in sulfides. Alternatively, platinum occurs in<br />
association with chromite either within the chromite mineral itself<br />
or within sulfides associated with it.<br />
Sulfide phases only form in ultramafic magmas when the<br />
magma reaches sulfur saturation. This is generally thought to be<br />
nearly impossibIe pure fraction& crystalliaation; so other<br />
processes are usually required in ore genesis models to explain<br />
sulfur saturation. These include contamination of the magma with<br />
crustal material, especially sul fur-rich wall-rocks or sediments;
72 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
magma mixing; volatile gain or loss. Often platinum is associated<br />
with nickel, capper, chromium, and cobalt deposits. Platinum is often<br />
fbund as native platinum and alloyed with iridium as platiniridium.<br />
The platinum arsenide, sperrylite, is a major source of platinum<br />
associated with nickel ores in the Sudbury Basin deposit. The rare<br />
sulfide mineral cooperite, (Pt, Pd, Ni) S, contains platinum along with<br />
palladium and nickel. Cooperite occurs in the Merensky Reef within<br />
the Bushveld Complex, Transvgal, South Africa. Platinum, often<br />
accompanied by small amounts of other platinum family metals,<br />
occurs in alluvial placer deposits in the Witwatersrand of South<br />
Africa, Colombia, Ontario, the Ural Mountains, and in cemin western<br />
U.S. states (Wolfe, 1984). Platinum is produced commercially as a<br />
by-product of nickel ore processing in the Sudbury deposit. The huge<br />
quantities of nickel ore processed makes up for the fact that pIatinum<br />
is present as only 0.5 ppm in the ore.<br />
Applications<br />
Platinum, platinum alloys and iridium are used as crucible materials<br />
for the growth of single crystals, especially oxides. The chemical<br />
industry uses a significant mount of either platinum or a platinum-<br />
rhodium alloy catalyst in the form of gauze to catalyze the partial<br />
oxidation of ammonia to yield nitric oxide, which is the raw materiel<br />
for fertilizers, explosives, and nitric acid. As a catalyst in the catalytic<br />
converter, an optional componem of the gasoline-bled automobile<br />
exhausts system. As a catalyst in fuel cells. Certain platinum-<br />
containing compounds are capable of crosslinking (or alkylezting) with<br />
DNA and are chemotherapeutic agents owing to this capability. E;or<br />
example, cisplatin, carboplatin and oxdiplatin belong to this class<br />
of drugs (Boyle, 1987). Platinum is also used in. resistance<br />
thermometers, electrodes for use in electrolysis, grills (deuorat ive<br />
plates on the teeth) and as a catalyst in the curing of silicone<br />
elastomers.
Platinum deposits in Ethiopia<br />
Mcmllic Minrrals 73<br />
<strong>Mineral</strong>ized mdc-ultramafic rocks in Ethiopia occur as zoned<br />
Alaskan-ts ultramafic bodies (e.g. Yubdo), ophiolitcs (e.g..<br />
Kenticha) and possibly as xenoliths or dikes within the Trap basalts<br />
covering most of the highlands (Mogessie et al , 2000).<br />
Linear bodies of altered mafic-ultramafic rocks occurring<br />
from Yubdo to the Tulu-Dimtu area were thought: to be part of an<br />
ophiolitic sequence by Kazrnin ef al. (1 978). Recently, Mogessie ef<br />
al., (2000) have suggested that these rocks were intruded into a<br />
magmatic rift or back-arc basin. The main rock units of the Yubdo<br />
area are dunites at the core, surrounded by peridotite and<br />
hornblende-clinopymxenite; an outcrop pattern typical of Alaskan<br />
type deposits.<br />
The Kenticha belt in the Adola granite-greenstone terrain is<br />
dominated by ulmmafic rock6 with subordinate amphibolites,<br />
biotite schists, n~inor graphitic schists, and marbles, Based on<br />
geological field relations, geochemical data and PGElchondrite<br />
normalized plots, the Kenticha ultramafic rocks are considered to<br />
be ophiolites (Mogessie et a/., 2002). Detailed ore reflected<br />
microscope and electron microprobe analyses of chromite rich<br />
layers within the Renticha rnafic-ultqafic units have been made.<br />
PGM's such as laurite (RuS2) with a composition varying between<br />
R~32.390~<br />
I -71 h0.61 S62.12 and RUZ~<br />
99 @I 5 1 Iro.70 S65.42, and ~rflall<br />
concentrations of Rh and Pd have been documented for the first<br />
time. In comparison to the Yubdo m&c-ultramafic rocks, the<br />
Kenticha ultrarnafics are rich in chromite suzd the small PGM<br />
grains are most of the time located at the rims of zoned chromite<br />
grains in contact with chlorite andfor serpentine. Furthermore.<br />
most of the PGM in Yubdo are rich in Platinum whereas the<br />
Kenticha are enriched in Ru, 0 s and Ir.
74 Mind Rcsourccs <strong>Potential</strong> of Ethiopia<br />
Geology of the Yubdo platit~arn deposit<br />
The Yubdo platinum deposit occurs in Western Ethiopia, 540 km<br />
west of Addis Ababa. The deposit was discovered in 1923-1924<br />
and mining started in 1926. The area is underlqin by an ultramafic ,<br />
complex of qmtinized dunite, pyroxenite and peridotite,<br />
bounded by a metamorphic aureole of molite-actinolite-chlorib<br />
talc-serpentine, which is locally schistose, and is surrounded by<br />
metasediments of the Birbir Group. Birbirite appears to be a silicic<br />
alteration product overlying the dunite.<br />
The platinum is associated with ultramafic complexes and<br />
more specifically with the lowemost part of alteration products<br />
(laiterites) of dunite rocks. The average grade of secondary residual<br />
ore from Yubdo mine is 0.005-1.31g pt/rn3. At Yubdo mine, the<br />
average composition of the Pt-Fe nuggets is 79.48% platinum,<br />
0.49% palladium, 0,75% rhodium, 0.8% iridium, 1.41%<br />
osmiridium, and 0.49 % gold. The remaining percentage is iron.<br />
Other metallic minerals include electnun, pentlandite and<br />
/ chalcocite (Clarke, 1978).<br />
Recently, Stanley et al, discovered a new platinum minerals<br />
species Kingstonite, RhjSs, b m the Birbir River, Yubdo District.<br />
It occurs as subhedrsl, tabular to elongate anh& inclusions in a<br />
Pt-Fe nugget with the associated minerals; fernplatinurn,<br />
tetraferroplatinum, a Cu-Mng Pt-Fe alloy, and osmium, enriched<br />
oxide mmmts of osmium, laurite, bwieite, fenorhodsite and<br />
cuprofhodsite. Past production of Yubdo from 1926 is estirnafed at<br />
2.7 tons. Pt. Resource calculations vary in a wide range between 2<br />
and 27 tons Pt, following vario& estimates: 20 tons Pt at 0.4 glm3<br />
by Duval Corp. (1969); 12 tons Pt at 0.34 glt byr Nippon Mining<br />
Co (1974) and 27 tons Pt at 0.2 dm3 (+ 10 tons Au and 9.8 tons<br />
Ag) byr Gilevich (1 980).<br />
There are several localities in Ethiopia where mafic-<br />
ultramafic rocks occur. me Tertiary Trap Mts which.cover most<br />
of the highlands of Ethiopia me also interesting locations to look
Metallic Minwala 75<br />
for mineralized zones. A det&iIed geological, geochemical and<br />
'ecomic gmlological studies of these mcks will undoubtedly<br />
result in finding economic precious metal deposits as is the case in<br />
Yubdo. PGM occurrences have dso ken reported together wjth<br />
gold from se~eral secondary type occurrences in Western Ethiopia<br />
(WolIega) (e.g. Dalleti, Tulu Dimtu, residual and Soddu. placer).<br />
Similar occurrences bve been found southwest dong the belt in<br />
the Omo River region.<br />
As to the origin, Platinum Group Metals (Platinum (Ft),<br />
Palladium (Pd), Iridium ,(Ir), Rhodium (Rh), Osmium (bs), and<br />
Ruthenium (Ru)) have g$etic &mities to both Ni-Cu-sulphides<br />
and chromiies. However, while the fundammtal processes<br />
involved in the formation of mi-Cu and chromite deposits are<br />
relatively simple, the concenktion and depodtion of PGM<br />
appears to k a not too well understood, dverst and multistage<br />
process. S evd lines of evidence indicate that PGM can:<br />
- Fractionated magmatic fluids enriched in PGMS ascending<br />
under the influence of dipIacement by the cumulus phases;<br />
- Deposition h m hydrothermal solutions.,<br />
- Sulfide dmplets pass through turbulent convecting magmas<br />
and scavenge the PGM's from these magmas. Upon<br />
cooling, the sulfides and suspended crystals sink, giving<br />
rise to cumulate layers;<br />
- Contamination of the magma with the coutry mcks<br />
triggers the precipitation of sulfides and their PGM' s.<br />
' F<br />
1 ,,: :$<br />
;& >, -<br />
'--, *sp.: -$<br />
g.'i<br />
Id t.<br />
I*;<br />
. ,+"<<br />
..:<br />
I... ..<br />
;,,
7A <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
Figure 17 -eal sketch map of h YuWo plmum a m<br />
Ethiopia.(afk ee al. 20021
Metallic <strong>Mineral</strong>s 77<br />
Pigrrro 18 A) A rnagmtio droplet of FbPe grain In a ohmmite. B)<br />
Osmium laths IP a WFe grain h n Yubdo (hn, Kebsde ei<br />
d. 2000)
Meidlic <strong>Mineral</strong>s 79<br />
potassium fluorotantalate, reduction of potassium fluorotantalate<br />
with sodium, or by reacting tanhum carbide with tantaIum oxide.<br />
Tantalum is also a byproduct from tin smelting (Cemy, 1990).<br />
Applications<br />
The major use for tantalum, as tantalum metal powder, is in the<br />
production of electronic components, mainly tantdum capacitors.<br />
Tantalum electrolytic apitors exploit the natural tendency of<br />
tantalum to form .a protective oxide surface layer, using tantalum<br />
foil as one plate of the capacitor, the oxide as the dielectric, and an<br />
qledmlytic solution as the other plate. Because the dielectric layer<br />
can be very thin (thinner than the similar layer in, for instance, an<br />
alm~um. electrolytic capacitor), high capacitance can be<br />
=hiex& in a. small space. This size In d weight advantage makes<br />
tantalum capacitors attractive for portable telephones, pagers,<br />
personal computers, and automotive electronics.<br />
Tdum is also used to produce a variety of alloys that<br />
have high melting points, are strong and have good ductility.<br />
Alloyed with other metals, it is also used in making carbide tools<br />
fbr ^metal-working equipment and in the production of superalloys<br />
for jet engine components,' chkical process equipment, nlacleax<br />
reactbrs, and missile parts (Cemy, 1990), It is ductile and cm be<br />
drawn into fine wire, which is used as a filament for evqomting<br />
metals such as aluminium. Because it is totally immune to the<br />
action of body liquids and is none-irritating, it is widely used in<br />
making surgical appliances. Tantalum oxide is used to make<br />
special high refractive index glass for camera lenses. The metal is<br />
also used to make vacuum furnace parts.
80 <strong>Mineral</strong> <strong>Resources</strong> Potentid of Ethiopia<br />
The Tantalitc deposit in the Kenticha area<br />
The Kenticha area is located in Southern Ethiopia within the Adola<br />
gold field. The area belongs to a me-metal metallogenic province.<br />
the only one so far known in the horn of Africa. From this it<br />
follows that a comprehensive study of the different minerals and<br />
rock types of the Kenticha area can provide preliminary evaluation<br />
of future economic potential.<br />
The Kenticha rare-metal pegmatite in the Adola area<br />
was discovered in 1980 by EMRDC during the course of<br />
preliminary and detailed explomlion. Mining in Kenticha started in<br />
1991. Since then the deposit has produced a total of 870 tons of<br />
tantalite concentrates (Ethiopian <strong>Mineral</strong> Development Sh. Co).<br />
Production is now running at about 220,000 lblyear of tantaIum<br />
oxide from weathered pegmatite and alluvial ore (Selassi e and<br />
Rehond, 2000). In 1 988, preliminary reserves were eval uated at<br />
25,000 tons of Tantalite ore at a 0.02-0.03 % Taz05 grade and<br />
hard rock ore reserves are currently under evaluation by Ethiopian<br />
<strong>Mineral</strong> Development Sh. Co. In addition to tantalite, Li, Rb and<br />
Cs could also be commercially recovered in the future from the<br />
pepatites of the district, especially by selective mining.<br />
Furthermore, Colwnbo-tantalite concentrates represent a complex<br />
raw material for the extraction of other rare metals [e-g. Nb, Zr,<br />
and REE). Other significant tantalite occurrences have been<br />
identified in Kilkile, and Bupo, in the same rare-metal field, while<br />
a Nb-Ta and REE - Th pegmatite-related occurrence close to a two-<br />
mica granite was discovered near Meleka (Glenso) in the Sidamo<br />
region.<br />
The existing geological investigations and the hi story of<br />
similar pegmatite fields in the ,world suggest the possibility for<br />
further potential economic me-metal resources within the region.<br />
Tantalum is reported to be present mainly in eastern Africa and<br />
southern Afiica such as in Ethiopia, Nigeria, Congo, Burundi,<br />
Rwanda, Uganda, Tanzania, Zimbabwe, Mozambique, Namibia,
Metallic <strong>Mineral</strong>s 81<br />
and South Africa. Substantial quantities of tantalite pegmatite<br />
north of South Africa have started to be- mined in March 200 1. Of<br />
all these occurrences, remarkably the richest tantalite deposit, more<br />
than 70% of Ta205, is so far known to be present in E!hiopia<br />
(Solomon and Zerihun, 1 996),<br />
Geology af the Kentichi frmntollam-besuing pegmatite depmit<br />
The rare metal occwrences in Kenticha are hosted in a long ma<br />
Ihw Kenticha belt. The Kenticha, belt extends for over 100 lun<br />
[from Katawhicha Mountain on the south to the left bank of the<br />
Genale River on the north). The pegmatites in the Kenticha raremetal<br />
field are genetically related to dome- and lens-shaped<br />
differentiated granitic and pegmatitic intrusions along a discrete N-<br />
$ fault and shear system, including biotite granite, two-mica<br />
granite and daskitic granite. The granitic pegmatite, emplaced by<br />
intruding the ultramafic suite, oc~urs within a large serpentinite hi11<br />
, that covered about 9 km2. m<br />
These post-orogenic intrusive are supposed to be h"e^ parent<br />
rocks of the rare-metal enriched pegmatites occurring within the<br />
field, mged in zonal patterns around the source granite and<br />
following a N-S trending regional fault and shear system. The<br />
post-tectonic granite, =-metal bearing pegmatites and accasional<br />
alaskitic granite are widely developed in the fom of stock or dikes<br />
varying from sevd kilometers to a few meters in width. N-S<br />
trending structure is believsd to have controlled the localization of<br />
the rare metal bearing pegmatite and associated acidic granitoid,<br />
The army of pegmatites follows N-S trending find&. In addition to<br />
the principal N-S trending faults, there are two younger faults<br />
systems trending NESW and NW-SE. The intersection of these faults<br />
with those trending N-S appears to be the most favorab1a site for the<br />
emplacement of the late stage diffemhtes conbhq<br />
concentrations of the memetal ores (Solomon and Zerihun, 1996).
J<br />
I,<br />
i<br />
<<br />
f<br />
82 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
'The Iate to post-Pan-ecan Kenticha pegmatite' is dated<br />
480*50 and 5 1 5k 1 0 Ma (Selassie and Reimold, 2'000): Within athe<br />
granite-pegmatite system, post-magmatic alterations (albithtiw<br />
sericitization, greisenimtion, kaolinization and development of<br />
maimsite and microcline) are widely developed, priicularly in the<br />
late products of granite-pegmatite series.<br />
The mineral associatiods found in the pegmatite rocks<br />
include Columbo-tanlite group minerals, ixiolite, beryl,<br />
lepidolite, staurolite, phosphates (apatite, arnblygonite and<br />
lit hiophilbte), tourmalines (schorl and elbaite), garnets (spessartite<br />
and rnanganian aimandine), rutile, ilrnenite and magnetite<br />
(Solomon and Zerihun, 1996). Othe me metal occurrences were<br />
found in Kenticha, KatawHicha, Dermidm, Ula Ulo, Kilkile,<br />
-<br />
B U and ~ Kotisa. Detailed investigation of the rare metal bearing<br />
pegmatite within the main Kenticha deposit has proved a world<br />
class ore reserve of tantalite with subordinate niobium, lithium,<br />
beryllium kuhg minerals, gemstones (beryl, spodumene,<br />
lepidolite, amazonite, mountain quartz) in addition to high quality<br />
ceramic grade quartz-feldspar and other industrial minerals. The<br />
complex ore is associated with a primary granite-pegmatite body<br />
and to a lateriti~ mantle of weathering developed over the primrrry<br />
pegmatite. In general three typs of ore of the deposit have been<br />
recognized.<br />
- Primary ore, tmtalite bearing granite-pegmatite with<br />
complex Ta-Nb-Li-Be mineralization;<br />
- Lateritic type ore, th~ mantle of weathering developed<br />
over pegamtitie and granite;<br />
- Eluvialdelwial and alluvial placer,<br />
The weathered ore developed over the primary ore of pegmatite<br />
represents the huge rare metal resources of the Kenti* deposit.<br />
This deposit is marked with high quality Ta-Nb and made it one of
, -<br />
Figure 22 Kdnticha Tantalito deposit with lodon of open pit,<br />
pht, waste dm$ and tailing dam.<br />
Metallic <strong>Mineral</strong>s 83
84 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiupia<br />
F ~ L r J a i m u r. e. w (black) in quartz and mixdine (white)<br />
in Kenti&<br />
Fwm 24 betvlfeen d y h g qmthh and underlyii<br />
IqnWiteat Keaticha
Figw 26 Mining fnr caatalite in Kmtidm<br />
Metallic <strong>Mineral</strong>s 85<br />
rn
Figure 28 Tantslite promsing plant; separation of fm bntdih concentr- %m<br />
hmbysltaking*@ntih)
d. fieId .umbhs s series of' barren to rrlre<br />
'&&%&"
88 <strong>Mineral</strong> Resourn <strong>Potential</strong> of Ethionia<br />
The granite body is elongated in north-south dimtion with a<br />
lenticular shape which has 10.5 lun length and 2 km kidth. It is<br />
sunounded bi a swarm of pgmatites &at include the above san<br />
types. The didbution of all the above pegmatite bodies follows a<br />
zoning pattern around the source granites in which the more complex<br />
and fractionated ones are located relatively fix hm the centre (e.g.<br />
Main Kenticha and Bupo I pegmatites) (Figure 30).<br />
Each zone contains pegmatites of similar geological, geochemical<br />
and structutal characteristics. The individual zones with pe&tes<br />
of similar composition, mineralogy and texture are descri&d &low:<br />
~lbite+pwlumene type (Bupo lpegmatite) is found very far hn the center of the source area and the pegmatite M e s in this zone are<br />
hly diffe~ntiatsd. This gegqatite is about 12 km north of the<br />
win Kenticha pegmatite and is deeply affected by weathering. -.<br />
use of the weathering effect and lack of god exposure, it is less .<br />
ed and, therefore, mineral association and intend .<br />
structure are not well known. However, analyses of some '::;<br />
obtained from 1a-e mistant outcrops, suggest that this '.<br />
pegmatite body is rich in Ta and probably belongs to the albite- - ,<br />
spodumene type of Cerny's (1990) classification. ji<br />
C~mplex spodumeue type (Main Kenticha pegmatite), , this ) - I<br />
wnesponds<br />
;-<br />
to the mplex spdumene type described in Cerny's<br />
p-,t<br />
(1989; 1990) classification. The pegmatite in this zone is completely<br />
%r<br />
differentiated, since each one has different mineralogicalochemid<br />
characteristics. ~<br />
ery1-colnmbite type (Ta-rich), this type is represented in th<br />
$a<br />
rrnidama and Kilkile I areas, located south of Wile 111 and north<br />
Klkile I1 pegmatites, respectively. The ore bodies in both areas<br />
m characterized by relatively high-Ta ddization. The<br />
pegrnatites have variable internal zoning, and can be assigned to the<br />
highIy evolved type of the beryl columbite p<br />
) classification.
-WiFrMoaals 89,<br />
Beryl-columbite type (~a-~oorj, this type includes the pgmtites<br />
of Kilkile 11, Kilkile I11 and Bupo I1 areas, which cantah beryl, d<br />
femolumbite. Beryl crystals are of the greenish (aquamarine) type<br />
and tourmaline is of schorl variety. K-feldspar has a graphic texture<br />
and sometimes shows a slight albitization. Small d a r bookmuscovites<br />
form patchy textures in the relatively fresh parts of the<br />
pegmatite blocks. Generally, the single bodies show the outer<br />
xenomorphic zone as a thin layer, whereas the main pegmatite unit' is<br />
mostly formed of muscovite, albite, quark, microcline-perthite<br />
assemblages. Some pegmati- show also a greisens zone (e.g.<br />
Kilklie TI pegmatite). The country rocks include serpentinite, talc,<br />
biotite schist's andor biotite gneiss.<br />
Barren pegmatit- this type is the nearest to the center of the<br />
source region and contains barren and simple pegmatites parallel to<br />
the altitude of the two-mica granite. The majority of these pgmatites<br />
are located in the westem side. On this side, the b n pgmatites<br />
reach the foot of the Kilkile 111 (44.5 km away from the tw-mica<br />
' granite.
SEPI* 3 Km<br />
0-<br />
Figure 30 Geology of part of the Kenticha mmetd field showing<br />
zoning of pegmatites, as well as the location of areas mentioned i<br />
A: area of bamn pgmatiw: B: area of Kilkile [I. Kilkile 111 and Bupo I1<br />
pegmatites (bayl-columbite types): C: area of Kilkile 1 and Dermidama<br />
<strong>Mineral</strong>ogy and internal structure of the pegmatite bodies<br />
The pegmatite unit in the Kenticha rare-rnetal field consists of a<br />
multitude of large and small veins and dykes, most of which display<br />
inward mineralogical and textural changes. The variability of internal<br />
units and textural complexity increases padel to the degree of lim
Metallic <strong>Mineral</strong>s 91<br />
pegmatite fractionation. This type of pegmatite zoning and inward<br />
mineralogical and geochemical change hm border to core zone is<br />
common in most of the rare rnd pegmatites in the world and was<br />
interpreted (Yahns, 1 982; Shearer et al., 1987; Cemy, 1990) to be an<br />
inward crystallization from rim to core from hydrous map. The<br />
observed types of minds in various zones and the gemhemistry of<br />
some elements within the pegmatites indicate the fractional<br />
crystallization in the system. As a whole, the vertical trend of zoning<br />
in these pegmatites is from K-feldspmrich at the top to Na-feldspar-<br />
rich at the bottom. Most of the pegmatites with a large number of<br />
zones consist mentially of a bad dic aplite with m overlying<br />
microcline-quark-albite zone, followed by a quartz-muscovite-<br />
albite-spodumene zone. The innermost part of some of these<br />
pegmatite$ consists of a small lenticular mass that includes greisens,<br />
Iepidolite and quartz core units. Around the quartz zone, cavities or<br />
pockets filled with euhedral crystals are common. The most evolved<br />
, pegmatite so far known in the region is the miin Kenticha pegmatite,<br />
which shows a variety of intd zoning and replacement<br />
phenomena The sequence of zoning in this pegmatite consists of a<br />
border zone, first, second and third intermediate zones, and a core<br />
zone (formed last).<br />
The lower border zone (footwall) of the pegmatite is formed<br />
by W t e granite that grades upWard to aplite. The alaskite granite<br />
is composed of muscovite, K-feldspar, quartz and albite. Mior<br />
phases that make part of the above mineral association include<br />
spessarhe, tourmaline, ilmenite and magnetite. This association is<br />
completed by the columbo-tantalite and Mn-columbite. The first<br />
intermediate zone is made up of muscovite-quw-albite-mimcline<br />
pegmatite. The zone is characterized by a medium-grain texture,<br />
sometimes with giant Microcline crystals. The second intermediate<br />
zone is composed of albite, cleaveldte, quark, spodumene,<br />
microcline and sericite. The characteristic accessory and rare<br />
minerals include apatite, Li-muscovite, tantalite (Mn), cowbite
...k; *.-,<br />
92 <strong>Mineral</strong> Rwurces <strong>Potential</strong> of Ethiopia ,- > La<br />
(Mn), amblygonite, beryl and ixiofite. It is characterized by medium-<br />
to came-grained textwe. The columbo-tmtalite minerals in this zone<br />
contain more Ta and Nb. Next to this zone, the third intermediate<br />
zone continues upward with a major mineral assemblage of albite,<br />
spodumene, ammonite, ambl ygonite, microcline and sericite. The<br />
awewry and ore minerals in this zone include apatite, Li-mica,<br />
tanate, topaz, beryl, pollucite and ixiolite. The central zone is<br />
entirely formed by north-south elongated, discontinuous, Ienticular<br />
quartz and replacement bodies. The replacement bodies include<br />
spherical greisens bodies and fine-wed Li-micas, both of which<br />
replace the microclime-perthite and quartz body, The contact between<br />
the pegmatite and the serpentinite rock is formed by chlorite, talc and<br />
rnonoczinic amphibolite (tremolite actinolite) assemblages resulting<br />
fiom the interaction of pegmatite forming aqueous fluids and the<br />
county rocks.<br />
As to the mechanism of formation of the Kenticka raremetal<br />
bearing-pegmatite-granite in Kentich, a well known and<br />
interesting feature of ore deposit that are genetically associated<br />
with granite intrusions is that the origin and composition of the<br />
magma generally controls the nature of the metal assemblages in<br />
the deposit. This control is almost certainly related in part to the<br />
metal endowment inherited by the magma from the rocks that was<br />
melted to produce it. Where felsic magma is derived from melting<br />
of a sedimentary or s~~racrustal'~roto1ith<br />
(termed S-type granites),<br />
associated ore deposits are characterized by concentrations of<br />
metals such as Ta, Ce, Rb, Sn, W, U, and Th. Where it is derived<br />
from melting of order igneous protoliths in the crust (I-type<br />
granite) the ore association is typified by metals such as Cu, Mo,<br />
Pb, Zn, and Au. The I-type granites tend to be metaluminous and<br />
typified by tonalitic (or quartz dioritic) to granodioritic<br />
compositions, whereas S-type are often peraluminous and have<br />
quartz-monzonitic to granite compositions.<br />
r
Metallic M inds 93<br />
The Kenticha rm-metal pegmatite-granite is typified by<br />
ore mineral associations such as Ta, Nb. Li, Be, Ce. This mineral<br />
association is metallogneticall y very significant suggesting that the<br />
parental rock where feIsic magma derived from melting of<br />
sedimentary or supracrustal protoits. Further more, studies by<br />
Solomon Tadesse and Zerihun Desta on whole rock analyses from<br />
the Kenticha pegmatite granite have shown that an Fe203/FeO<br />
ratio (useful discriminant between I-type with Fe203M.3 and S-<br />
type, with ratio Fe2031Fe0
94 <strong>Mineral</strong> <strong>Resources</strong> PotenIial of Ethiopia<br />
chlorine, phosphorus, and sulfur. This highly fluid, aqueous melt<br />
provided an environment for concentration of chemical elements<br />
with ionic sizes too great to fit into crystalline structures of major<br />
rock forming minds; these elements were thus concentrated in<br />
pegmatite deposits.<br />
The occurrence of pegmatite corresponding to most<br />
plutonic rock compositions gabbros, diorites, syenites, anorthosites<br />
further suggests this possibility. Other pegmatites grade into the<br />
rocks that surround them and show no intrusive relationships. Such<br />
bodies may represent material produced by melting (anatexis)<br />
during metamorphism at high temperatures and pressures. Some<br />
elements and fluids may be literally "sweated out" of a rock<br />
complex during metamorphism, well known because it conrains<br />
crystals of many different minerals. This rock is pushed up as large<br />
veins of magma that was rich in volatile elements, resulting in<br />
large crystals, usuaIly surrounded by grantic rocks.<br />
Pegmatites may be composed of a variety of minerals.<br />
Terms such as granite pegrn'atite, gabbro pegmatite, syenite<br />
pegmatite, or names with any other plutonic rock type as prefix are<br />
used. Compositions in the range horn granodiorite to granite are<br />
common. Large crystals of quartz, potassium feldspar, sodium rich<br />
plagioclase, and micas (e.g., muscovite and lepidolite) may be<br />
abundant. Simple pegmatites contain few, if my, exotic minerals.<br />
The center zones of complex pegmatites, however, may contain a<br />
wide variety of minerds such as tourmaline, topaz, garnet,<br />
spodurnene, scapoli te, ber y 1, apatite, fluorite, zircon, and various<br />
rare minds, some limited to only a few localities in the world.<br />
GEM quality stones are sought in such rocks. Elements such as<br />
tungsten, boron, tantalum, columbium, bismuth, tin, uranium,<br />
radium, sheet mi&, and sulfide minerals of various metallic<br />
elements are among substances obtained from pegmatite deposits.<br />
As to the origin of Tantalum, during fractional<br />
crystallization, water and elements that do not enter the minerals
Metallic <strong>Mineral</strong>s 95<br />
separated from the magma by crystalIization will end up as the last<br />
residue of the original magma. This residue is rich in silica and<br />
water along with elements like the Lithium, Tantalum, Niobium,<br />
Boron, Beryllium, Rare Earth Elements, and Uranium. This residue<br />
is often injected into fractuw surrounding the igneous intrusion<br />
and crystallizes as a rock pegmatite that characteristically consists<br />
of large crystals.<br />
3.4 Nickel (Cobalt) deposit<br />
Occurrence<br />
The bdk of the nickel mined comes hm two types of ore<br />
deposits. The first are laterites where the principal ore minerals are<br />
sickelifexous limonite (Fe, Ni)OIOH) and garnierite, (a hydrous nickel<br />
silicate): (Ni,MghSif15(OH). The second are magmatic sulfide deposits<br />
where the principal ore mineral is pentlandite: (Ni, FebS*. Sulfide type<br />
, nickel deposits are formed in essentially the same manner as<br />
platinum deposits. Nickel is a chdcophile element which prefers<br />
sulfides, so an ultramafic or mafic rock which has a sulfide phase<br />
in the magma may form nickel deposits. The best nickel deposits<br />
pre formed where sulfide accumulates, much like in a placer gold<br />
deposit, in the base of lava tubes or vobanic flows -especially<br />
kornatiite lavas.<br />
Origin<br />
Ni-Cu deposits are the end of a magmatic process known as<br />
"liquid immiscibility". This process involves the separation from<br />
the parental magma of a sulphur-rich liquid containing Fe-Ni-Cu.<br />
Upon cooling, the sulphur-rich liquid produces an immiscible<br />
sulphide phase (droplets of sulphide liquid in silicate liquid, like<br />
oil in water) from which minerals such as pyrrhotite (FeS),<br />
pentlandite (Fe, Nibss, and chalcopyrite (CuFeS2) crystaIize. The<br />
I
96 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Etkionia<br />
sulphide liquids, rich in copper and nickel, are denser, and settle to<br />
the floor of the chamber, where they form copper or nickel ore. Ni-<br />
Cu deposits are found in layered intrusions, stocks and ultrarnafic<br />
sills and flows. The largest deposits are of Archean and<br />
Proterozoic age. Examples of Ni-Cu deposits include the Sudbury<br />
orebodies in Canada (layered intrusion hosted), the Karnbalda ore<br />
bodies in Western Australia (ultramafic flow hosted) and the ore<br />
bodies in the Thompson District of Manitoba, Canada (ultramafic<br />
sill hosted).<br />
Applications<br />
Nickel is used in many industrial and consumer products, including<br />
stainless steel, magnets, coinage', and special alloys. It is also used<br />
for plating and as a green tint in glass. Nickel is pre-eminently an<br />
alloy metal, and its chief use is in the nickel steels and nickel cast<br />
irons, of which there are innumerable varieties. It is also widely<br />
used for many other alloys, such as nickel brasses and bronzes, and<br />
alloys with copper, chromium, aluminium, lead, cobalt, silver, and<br />
gold. Nickel consumption can be summarized as: nickel steels<br />
(60%); nickel-copper and nickel-silver alloys (14%); malleable<br />
nickel, nickel clad and Inconel (9%); plating (6%); nickel cast irons'<br />
(3%); heat and electric resistance alloys (3%); nickel brasses and<br />
bronzes (2%); others (3%) (Jensen and Bateman, 1979).<br />
Nickeliferous deposits in Ethiopia<br />
More than twenty nickeliferous occurrences have been identified in<br />
association with serpentinite bodies belonging to the Adola and<br />
Kenticha Belts (Adola). One third of these occurrences have been<br />
explored in detail by pitting and drilling, leading to a reserve<br />
estimate of 17 Mt of ore grading 1.3% nickel (EGS, 1989). Main<br />
deposits are located at Ula Ulo (4 Mt at 1.33% Ni and 0.01 % Co)<br />
and Tulla (6.6 Mt at 1.28% Ni)'(EGS, 1989). Other similar nickel
Metallic <strong>Mineral</strong>s 97<br />
occurrences have also been reported in Sidamo (e,g, Kilta, 2 Mt at<br />
1.5 % Ni, Big Dubicha, Small Dubicha, Fulanto, Monissa, Burjiji<br />
wnd Lolotu).<br />
All these occurrences are related to ultrabasic rmks,<br />
metamorphosed to serpentinites, almost entirely altered. These<br />
serpentinites formed of lizardite and antigorite, with some<br />
chrysotile stringers, are all enclosed in a "Mo" of talc and bands<br />
of talc schists, tremolite schists, chlorite schists and actinolite<br />
schists, ~hl: nickel mineralization, of residual type, is hosted in<br />
Iaterites capping the serpentinite budies and is apparently mainly<br />
held in a secondary mineral of the garnierite group (pimelite). The<br />
average metal contents for unaltered ultrabasic source rocks are<br />
uneconomical: nickel (0.1-0.3%), cobalt (0.02%), copper (0.998%).<br />
Impregnations of q d t e with pyrite and cobalt with manganese<br />
coating have been reported in Kunni valley. Other cobalt mineral<br />
occurrences have also been reported in the area of Nejo, near Tulu<br />
Bolio and Tula Gotel (Wollega).<br />
The origin of the deposits seems to be similar to that of<br />
silicate deposits in other parts of the world. Nickel concentrates in<br />
the crystalline lattice of ferrornagnesian silicate rock forming<br />
minerals such as olivine and pyroxene during the early cooling and<br />
crystallization history of the magma, in the absence of sulphur.<br />
Fractional crystallization and cumulative process such as gravityinduced<br />
settling of these early crystals on the bottom of the magma<br />
chamber can account for the high nickel and chrome contents in<br />
mnulative ultramafics. Secondary adchment is attained during<br />
iqmtinization and weathering. The following are descriptions of<br />
m e of the beqer known deposits some of which have received<br />
nore attentioh in recent years.
98 <strong>Mineral</strong> <strong>Resources</strong> Potmtial of Ethiopia<br />
Tub nickel ocrurrences<br />
The Tulls srrpentinite, one of the smallest (200 x '900 m) of the<br />
serpentinite bodies, forms a conspicuous sparseIy vegetaa hill 23<br />
km south of Megado. The serpcntinitc strikes 1 50' and dips 55' W;<br />
and dip 200-30' east and is ovedain to the west by chlorite schist<br />
whilst quartzites ae adjacent to the eakt The outcrops are highly<br />
weathered and fractured. Gakierite,. light aquamitrine to dark<br />
green, occurs as fdlings in some fiVdcture planes. The<br />
mineralization has been check& by 27 boreholes showing an<br />
average of 1.28% Ni content over an average depth of 54 m. The<br />
prospecting holes in the locality revealed reserves of 6.6 Mt at 1.28<br />
% nickel (EGS, 1989).<br />
Uh Ulo nickel oacummaear<br />
Ula Ulo lies about 18 km SSE of Megado. The mpmtinite is & a<br />
-4- -<br />
approximately 1000 x 600 m in outcrop, strike N-S and dip 75'. G:.<br />
. Altogether 138 test holes totalling h ut 1500 m were dug at llla kc'<br />
UIo in 1963. Garnierib is prominent in the lower slops of the hill; ,.-<br />
:. -<br />
g*<br />
it occurs- as a fmtw in fillings of soapy appearanGI:. Test holei .;<br />
revealed a reserve of 4 Mt at 1.3.3 % nickel (EGS, 1989). Another ?I: ',<br />
!<br />
Big Dubicba<br />
Metallic <strong>Mineral</strong>s 99<br />
Big Dubicha lies 8 h NE of Kibre Mengist. Like many of the<br />
serpentinite bodies it forms a conspicuous feature, rising above<br />
adjacent hills and being barren of trees. The serpentinite is<br />
comparatively well-exposed in numerous outcrops. The strike varies<br />
between 30 and 50' with dips ranging from 25 to 50' W. A few<br />
chromite lenses, 2-3 m long and stringers, have ken observed.<br />
Gmierite mineralization occurs in the usual form of fracture<br />
filling and dissemination in weathered qntinite. Nine to eight<br />
holes were sunk in the ldity revealing 1.6 tons<br />
% nickel (EGS, 1989).<br />
&&&', .<br />
,! k
100 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
contain numerous fine-grained magnetite stingers ranging @bin<br />
0.5 to 1.5 cm in thickness, The sqentinite body and talc-chlorite<br />
rock units are often found to contain small seams of chromik,<br />
1 -2m wide. Serpentinization, silicification, sericitimtion, ~hlaritizathn,<br />
actinolization and carbonatiztition are the major alteration<br />
processes that affected the ultramafic body. The Ni-bearing<br />
mineral is garnierite. It has been prospected by 386 holes, &y<br />
in the northern pwt, and the result revealed rewwes of 3.9 Mt<br />
grading 1 28% nickel (EGS, 1989).<br />
Figurn 3 l Ibe Kenticha q~tw<br />
.$hiit:F.mS.<br />
I;~:, , ,r,~:e;~!;<br />
I<br />
L-&;$; A +.dl . .., &&a,":-<br />
3.5 Iron deposit i;i&<br />
C<br />
,--,,1 OccurrenmILI, :-: , , . -.-; ---. .-u- r--.,-,-i,'<br />
,; .I L.: T??:;.. , -'.. .< , ,-..-- .
- ., , .<br />
Metallic <strong>Mineral</strong>s 10 1<br />
[ . ,hickel alloy. About 5% of the metearites similarly consist of ironi<br />
nickel alloy, Although rare, these are the major form of natural<br />
*%e~llic iron on the e d s surface.<br />
. ,<br />
Origin<br />
Fe-Ti deposits are either "stratifom" or present be injections.<br />
Many small to medium sized magnetite deposits occur in gablamic<br />
intrusions, but the really big tonnages occur in the stratiform<br />
lopoliths. The formation of Ti-Fe deposits may be tentatively<br />
described as follows:<br />
Residual maghatic melts generally become enriched in silica and<br />
water; but certain types of basaltic magmas may become enriched<br />
h iron,and titanium. The basic plagidase magmas may become<br />
enriched! in iron and titanium. The basic plagioclase wystallizes<br />
6rst and Fe-oxides last, the residual liquid may dmh out from the<br />
mush of plagiochse crystals or, in other words, the plagioclase<br />
' crystals may float in the upper parts of the high density iron melt.<br />
By this mechanism stratifel layers of titanomagnetite could be<br />
foped in between anorthosite on top and peridotite at the base.<br />
The residual liquid may also solidify without segregation; this<br />
kuld explain the occurrence of olivine rocks with titano-magnetite<br />
filling crystal interstices. Finally the iron rich residual liquid may<br />
become injected into t e overlying consolidated rocks and solidify<br />
as orebodies; that At the structure of the rook (filter pressing).<br />
Ti-Fe deposits can be broadly divided into ilmenitehematite and<br />
titanifemus magnetite deposits, Both types show ex-solution<br />
Gxtures. The economic vdue of the deposits depends on grade and<br />
- I..<br />
kenability to mechanical ilmenite~~wxide separation. An example<br />
of an economic Ti-Fe deposit is Lac Tho in the AUwrd lake area<br />
(Quebec).<br />
>l
102 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethionia<br />
Applications<br />
Iron is the most used of all the metals, comprising 95 % of dl the<br />
metal tonnage produced worldwide. Its combination of low cost<br />
and high sirength make it indispensable, especially in applications<br />
like automobiles, the hulls of large ships, and structural<br />
components for buildings. Steel is the best known alloy of iron.<br />
Production<br />
Approximately 1,100 Mt (million tons) of iron ore was produd in<br />
the world in 2000, with a gross Market value of approximately 25<br />
billion US dollars (Jensen and Battman, 1979). While ore<br />
production occurs in 48 countries, the five largest producers were<br />
China, Brazil, Australia, Russia and India, accounting for 70% of<br />
world iron ore production. The 1,100 Mt of iron ore was used to<br />
produce approximately 572 Mt of pig iron (Wolfe, 1984).<br />
Irop deposits ia Ethiopia<br />
Iron occurrences were identified, in many areas in Ethiopia: among<br />
others, Wollega (Gordoma, Chago, Worakalu, Dimma, Billa, and<br />
Tulu Bolale) Kaffa (Mai Gudo, GwmmaIucho, Kurkue, Garo,<br />
Dombowa, and Melka Sedi), and Tigray (Adua, Enticho). They<br />
belong to three main types (Table 2).<br />
(i) Precambrian basic intrusion-hosted Fe-Ti type (Bikild, Melka<br />
Arba), (ii) banded iron formation (BIF) type occurrences associated<br />
with Pmambrian fernginow quartzites (Koree, Gordoma, Chago)<br />
and (iii) secondary laterite and/or gossan-related deposits (e.g.<br />
Melka Sedi, Garo, Gato, Billa, Gmbo, Gammalucho).<br />
Among these occurrences with those estimated reserves are found<br />
in: (i) Wollega: Chago (1.2 Mt, 64% Fe), D h a<br />
(0.05Mt, 65%<br />
Fe), Gordona-Korree (0.27 Mt, 63% Fe), Worakalu (0,15 Mt, 62%<br />
Fe), Belowtuist (2.5 Mt), Katta valley (0.1 Mt, 61 % Fe), Yubdo<br />
(0.05 Mt, 70.9% Fe); (ii) Kaffw: Garo (12.5 Mt, Melka Sedi (12.5
Metallic <strong>Mineral</strong>s 103<br />
Mt), Dombova (12.5 Mt), Mai Guda (0.075 Mt, 40% Fe); (iii)<br />
Sihno: Melka Arba (4.63 Mt); (iv) Tigray: Adua, Axurn and<br />
Enticho (5 Mt, 30% Fe) (EGS, 1989).<br />
Other occurrences where total reserves are not yet estimated are<br />
found. in the localities: Aim, Famasari, Billa, Gambo, Gmbella-<br />
Dembidollo, GeiqDaleti (Wollega), Assale, Beliga, Chilachii<br />
I Adi Berbere (Tigray), Bissidimo, Galeti, Kunni, Ujau, Soka<br />
(Ham), Ghimira Bash, Kurkure, Like (Kaffa). Data regarding<br />
these mcmences are just preliminary observations not based on<br />
systematic expioration. The folldwing is a description of the better<br />
known deposit which has received more attention in recent years.<br />
Bikilal i&n deposit<br />
The best known m& Ethiopian iron deposit known to date is the<br />
recently discovered deposit of Bikilal in Wollega. The deposit is<br />
hosted in Precambrian meta-sedimentary rocks (feldspar-<br />
amphiblite schist, quart z-amphi bole schist, quark-feldspar and<br />
mphibk schist, and marble) intruded by basic-ultrahasic rocks<br />
and granitoids. The titanifemus iron ore bodies are confined to the<br />
ultrabasic zone which consists of ore-Mng actinoiite rick dzks,<br />
olivine ppxenite, met a-homblendite, apatitebearing meta-<br />
hornblendite and meta-gabbro. The ultrabolsic zone is about one<br />
kilometre wide and 12 km long. The size of the ore bodies is of<br />
200- 1 400 rn in length, 2-6 m in width and 200-300 m in depth The<br />
d o a t ore minds in the Bikilal titanifcmw iron ore deposit<br />
are magnetite (containing ilrnenite as exsolution lamellae) (40x1,<br />
iImenite (29%) silicate minerals (about 30%). The most ~ m o n<br />
accessory minerals are pyrrhotite and pyrite (2-2.5%), apatite<br />
(0.6%), chalcopyrite and pentlandite (< 1%). Main gangue<br />
minerds are amphiboles, chlorite and rarely phlogopite, olivine,<br />
pyroxene and plagioclase. The titanifemus iron OR is chiefly<br />
compact and disseminated. The Bikifal iron *sit is estimated at
104 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
about 58 Mt tons grading 41% total Fe (EGS, 1989). Zones of<br />
apatite enrichment are currently evaluated through drilling (1 8 1 Mt<br />
of apatite ore at average grade of 3,5% P205, with 2 1.8 % total Fe,<br />
(Fentaw and Mengistu, 2000); (Selassie and Reimold, 2000). Apart<br />
from iron and phosphate, vanadium and titanium are by-product<br />
metals considered to be commercially worthy using magnetic<br />
dressing benefication, \<br />
The origin of the Bikilal Fe-Ti deposits seems to be similar<br />
to that of iron deposits in other parts of the world. The deposit is<br />
typically thought to be dated. to large differentiated intmsiove<br />
complexes made\up mainly of pyroxenite, hablendits and gabbro<br />
mplaced in Prpcambrian meh-sedimentary mks. The Fe-Ti oxide<br />
ore accumulations occur as strati- layers and disseminations<br />
within the intrusion complexes themselves, or as a more massive,<br />
higher grade, cross-cutting or dyke-like bodies. This deposit is<br />
clearly a product of in situ crystal fractionation. Early extraction of<br />
a plagioclaspdo~ crystaI assemblages results in concentration<br />
of Fe and Ti in the residual magmas, which crystallize to form<br />
femgabbm. Titanifemus magnetite or hemo-ilmenite also<br />
crystallizes with disseminated layers formed by crystal settling<br />
accumulation on the chamber floor. The more massive discordant<br />
bodies are considered to be a product of the pressing out (filter<br />
pressing-the processes whereby the residual magma within a<br />
network of accumulating crystals in a *ally solidified chamber<br />
can be pressed out into a regions of lower pressure such as<br />
overlying non-crystalline magma or fractures in the country rock)<br />
;, - of an Fe-Ti oxide mineral slurry -the slurry concentrated to form<br />
an intrusion body often dong the margins of the imgely<br />
. consolidated gabbm-pyroxinite-hornbIendite complexes or into<br />
: fkactures and breccias in the host rocks.
Table 5: Iron ore deposit types ofzthiopia<br />
COMMODITIES<br />
Fe, Ti, (P)<br />
Fe<br />
ORE DEPOSIT<br />
TYPES<br />
Ore deposits<br />
hosted by basic<br />
intrusions<br />
Banded iron<br />
formations (BIF<br />
pp<br />
F'e, (Mn)<br />
Metallic <strong>Mineral</strong>s I as<br />
Table 6: Major Iron ore deposit of Ethiopia (A,B & C class)<br />
NO Dewit<br />
name<br />
Laterite-related<br />
and gossan-<br />
related deposits<br />
Comm.<br />
I<br />
Class<br />
M.41N DEPOSITS<br />
(A, B, C)<br />
(see Table 6)<br />
Bikilal<br />
MINOR DEPOSITS<br />
Melka Arba, Kenticha<br />
Beliga 2, Chago,<br />
Bikilal Gordana, Koree,<br />
--<br />
Dombova<br />
Adua, Entichio Adi<br />
Melka Sedi, Berbere, Chilachikin,<br />
Cam malurho, Di mma, Katta, Billa.<br />
Garo, Gambo, Gato (Mai<br />
Dombova Guda), Melka Sedi,<br />
Tulu Bollate<br />
Tonnage<br />
Range<br />
Other<br />
mmm.<br />
tong.<br />
I Bikilal (Fe) Fe 10-16 Mi Fe<br />
Deposit<br />
Cu, P h(Au, o ~ Co) , T ' i , N i - ~ ~ 9'30 ~ , ~ ~ develop ' under<br />
1<br />
3<br />
-- "--<br />
Galnlnalucho I Fe<br />
Gara Fe<br />
Fe<br />
t<br />
1<br />
/<br />
"<br />
C<br />
- -A<br />
Mt Fe I CO.<br />
10 - 100 1 Me.Au,!I NI-<br />
37 19 7.51<br />
"- M!Fe .!-..Cob. + .. .<br />
I: : I M:-z.R 37 39 7.50<br />
ment<br />
Prospect<br />
--<br />
Pmsprct<br />
5 Dombova Fe 1 C 'LiLr i ' Prmpect<br />
ht<br />
Status<br />
,
106 Minwal <strong>Resources</strong> Potmtial of Ethiopia<br />
. .<br />
Table 7: Iron Ore occumce and depits of Ethiopia
108. <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Elhimia<br />
RESERVE<br />
35.53 9.07 0.05 Mt,<br />
62%Fe<br />
Hematite<br />
4.48 Mt Mawetire.<br />
Magnetite<br />
Hemaire<br />
Formations<br />
(81F "Superior I<br />
stc retared<br />
dqmii: Au.<br />
Ag. Zn<br />
maikdatd<br />
cH-edqUd5:<br />
Fc, Mn. Hi-C&<br />
Aq<br />
CmwdumS.<br />
R E Nb. Pt<br />
-:tYMS,<br />
MVT. Veins<br />
tic*<br />
&qmh: Am,<br />
Agza<br />
baepoJitrin<br />
w w<br />
-- (Ural ard<br />
Akbl5ub<br />
i l d<br />
dEpositsr Ti. Ft.<br />
depoails<br />
kkwuist M i d ZM MI f@mii Firmgimus<br />
(Wobga) oenm*lro kdk, cpmlzils Au,<br />
Limiw REE. Pb. Ni. PI
3.6 Chromite<br />
Metallic <strong>Mineral</strong>s 109<br />
An iron magnesium chromium oxide: (Fe,Mg)CrzOb is an oxide<br />
minerd belonging to the spinel gotip. Magnesium is always<br />
present in variable amounts, also aluminium and iron substitute for<br />
chromim. Chromite is found in peridotite and other layered<br />
ultramafic intrusive mks as well as in metamorphic racks such as<br />
serpentinites. Ore deposits of chromite form as early magmatic<br />
differentiate, It is commonly associatsd with olivine, magnetite,<br />
serpentine, and corundum, The vast Bushveld Igneous Complex of<br />
South Africa is a large layered d c to dtrarnafic igneous body<br />
with some layers, consisting of 90% chromite making the rare rock<br />
type chromitite. Chromite is found in Afghanistan, Iran, Pakistan,<br />
Oman, and Zimbabwe (Boyle, 1987).<br />
Origin<br />
,When dense minerals form early in the crystallisation sequence,<br />
they may sink to nmr the bottom of the magma chamber and<br />
accumulate. This process is called crystal settling. Such settling is<br />
aided by a low viscosity of the magma; so crystal settling is best<br />
developed in basaltic magmas. Chromite is one of the first minerals<br />
to crystallise hm basaltic melts, and may settle out to form dark<br />
bands of nearly pure chromite. Stratiform chromite deposits consist<br />
of laterally persistent chromite-rich layers (a few mm to several m<br />
thick) alternating with silicate layers. The silicate layers include<br />
ulb.amafic and d ~ rocks c such as dunite, peridotite, pyroxenite<br />
vd a variety of others, less commonly gabbroic rocks.<br />
\ Chromite deposits are the end product of the separation of<br />
solid phases (Cr-rich spinets, (Fe, Mg) (Al, Cr. Fe) 204) from a<br />
liquid and their accumulation into chmite-rich layers. The<br />
pmsses involved in the formation of chromite layers are<br />
Mional crystallization and gravity settling. Chromite crystallizes<br />
into mineral grains within the silicate liquid and, because they are
110 Mind <strong>Potential</strong> of Ethiopia<br />
heavier than the liquid, they sink to form a cummulate layer at the<br />
base of the intrusive. They are generally found within bad<br />
portions of mafic-ultramafic layered intrusions of Archaean ageT<br />
such as the Bushveld Complex in South Africa. Most of the world's<br />
chromium ores were formed in this manner by the settling of<br />
chromite.<br />
Chromite, used mainly in chemid and metallurgical industries<br />
(chrome fixtures, etc.), is the chief ore of chromium, but, is also<br />
used as a refkctory material.<br />
Chromite mcurrencess h Ethiopia<br />
Occurrences of good quality chromite me found in Sidamo and<br />
Wollega. The chromite occurrences in Sidamo are associated with<br />
serpentinite rocks and we= found in Kenticha (Fig. 32), Metti-<br />
Gola, hbicha Gudda, Dermidama and Molicha, In these localities,<br />
the mineral occurs as lenticular bodia and pods with varying grain<br />
size (medium to coarse grained). M&c and ultrstmafic bodies<br />
hosting chromite are also found in Wollega. Among these<br />
occurrences, the most significm is the Yubdo-Ddleti-Tdu Dimtu<br />
belt where chmite-platinum mineralization is associated. The<br />
detailed geology and potential economic significance of different<br />
chromite occurrences have not been studied so far. Therefo~,<br />
systematic exploration is required to assess the chromite potentid. 1 I<br />
I 1I
3.7 Manganese deposit<br />
Occurrence<br />
Metallic <strong>Mineral</strong>s 1 I I<br />
Manganese occurs principally as pyroIusite (Mn02) and30 a lesser<br />
extent, as rhodochrosite (MnC03). Land-based resources are large<br />
but irregularly distributed; those of the United States are very low<br />
grade and have potentially high extraction costs (Boyle, 1987).<br />
South Africa and Ukraine account for more than 80% of the<br />
world's identified resources and South Africa accounts for more<br />
than 80% of the total exclusive of China and Ukraine. Manganese<br />
is also mind in Burkina Faso and Gabon. Vast quantities of<br />
manganese exist in manganese nodules on the ocean floor (Jensen<br />
and Bateman, 1 979).<br />
Applications<br />
Manganese is essential to iron and steel production by virtue of its<br />
sulfur-fixing, deoxidizing, and alloying properties (Boyle, 1 979).
112 <strong>Mineral</strong> <strong>Resources</strong> Potmtial of Ethiopia<br />
manganese demand, p~sently in the range of 85% to Wh of the<br />
total demand. Among a variety of other uses, manganese is a key<br />
component of low-oost stainless steel formulations and certain<br />
widely d aluminium alloys. It is also added to gasoline in order<br />
to reduce engine knocking. Manganese (IV) oxide (manganese<br />
dioxide) is used in the original type of dry cell Wry, and is also<br />
used as a catalyst. This element is used to decolorize glass<br />
(removing the greenish tinge that premce of iron pduces) and, in<br />
higher concentration, mala violet-coloured glass. Manganese<br />
dioxide is a brown pigment that can be used to make paint and is a<br />
wmpnent of natural umber. Potassium permangmwte is used in<br />
chemistry as a potent oxidizer and in medicine as a disinfectant.<br />
Manganese phosphate is used for rust and corrosion preventation<br />
on steel,<br />
Mangam deposits in Ethiopia<br />
' The Enkafala area in Tigray (Danakil depression) is responsible for<br />
the small former Ethiopian ,manganese ore production (about<br />
40,000 tons of ore from 1958 to 1963). mrves of the Enkafala<br />
sedimentary Mn deposit are believed to be 75,000 metric tons<br />
(Getaneh, 1985). The thin manganese layer is interstratified in<br />
cldc plio-Pleistocene marine sediments, Ore consists of hard<br />
oxides (psilomelane, pyrolusite) d hollandite. Barium is 1 041 y<br />
present in tbe ore. Other areas in Tigray where manganese mineral<br />
occurrences are hown .are Mussley, Beliga, Handeda, Adi<br />
Berbere, and Adi Chigono. The origin of these occurrences is<br />
poorly known, some of them being at least partly of secondary<br />
origin (gossan-type e.g. Mussley, Adi Berbere), The Melka Sedi<br />
occurrence (Kaffa) is associated with laterites.
Metallic Minalals 1 13 ,.<br />
3.8 Base Metals (Copper, Zinc, Lead, Molybdenum, and<br />
Wolfram) deposit<br />
Copper occurrence<br />
Copper can be found as native copper in mineral form. <strong>Mineral</strong>s<br />
such as the carbonates azurite'(~a(~0&(0~) and maiachite<br />
(CU~CO~(OH)~) are sources of copper, as are sulfid& such as<br />
chalcopyrite (CuFeSz), bornite (CusFeS4), covellite (CuS),<br />
chdcocite (Cu2S) and oxides like cupriti: (Cy20). Most copper ore<br />
is mined or extracted from large open pit mines in copper porphyry<br />
deposits that contain 0,4 to 1.0 % coppe'. Examples include:<br />
Chuquicamata in Chile and El Chino mine in New Me&. The<br />
average 'abundance of copper found within crustal rocks is<br />
ap~mximately 68000 parts per billion by mass, and 22,000 parts<br />
per billion by atoms (Jensen and Batman, 1979).<br />
Copper is found in association with many other metals wnd deposit<br />
styles. Commonly, copper is either formed within sedimentary<br />
rocks, or associated with igneous rocks. The world's major copper<br />
deposits are formed within the granitic porphyry copper style. The<br />
source of the copper is generally considered to be the lower crust<br />
or mantle where the granite melt forms. The copper is enriched by<br />
processes during crystallisation of the granite and forms as<br />
chalcopyrite -a sulfide mined, which is canied up with the<br />
@mite.<br />
Sometimes granites erupt to suface as volcanoes, and<br />
copper minerdisation foms during this phase when the granite and<br />
volcanic mks cool via hydrothd circulation. Sedimentary<br />
. copper forms within ocean basins in sedimentary rocks. Generally,<br />
this forms by brine discharging-hm deeply buried sediments into<br />
the deep sea, and precipitating cupper and often lead and zinc
I 14 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiooia<br />
sulfides directly onto the sea floor. This is then buried by further<br />
sediments. Often copper is associated with gold, lead, zinc and<br />
nickel deposits.<br />
Applications<br />
Copper is used extensively in products such as: Electronics<br />
-copper wire, electromagnets, electrical machines, especially<br />
electromagnetic motors and generators, electrical relays, electrical<br />
busbars and electrical switches, vacuum tubes, cathode ray tubes,<br />
and the magnetrons in microwave ovens, wave guides for<br />
microwave radiation. Household Products +opper plumbing,<br />
doorknobs and other fixtures in houses, roofing, guttering, and<br />
rainspouts on buildings; in cooking-wares, such as fiying pans;<br />
most flatwares (knives, forks, sp~ons) contain some copper (nickel<br />
silver); sterling silver, if it is to be used in dinnerware, must<br />
contain a few % copper; copper was sometimes used by the Inuit to<br />
make the cutting blade for ulus; coinage -as a component of coins,<br />
often as cupronickel alloy, Euro coins contain different copper<br />
alloys; biomedical applications: as a biostatic surface in hospitals,<br />
and to line parts of ships to protect against barnacles and mussels;<br />
chemical applications: compounds, such as Fehling's solution, have<br />
applications in chemistry, as a component in ceramic glazes, and to<br />
colour glass; others: musical instruments, especially brass<br />
instruments and cymbals (Guil bert and Parks, 1 986).<br />
Lead<br />
Occurrence<br />
Native lead does occur in nature, but it is rare. Currently lead is<br />
usually found in ore with zinc, silver and (most abundantly)<br />
copper, and is extracted together with these metals. The main lead<br />
mineral is galena (PbS), which contains 86.6% lead. Other<br />
common varieties are cerussite (PbC03) and anglesite (PbS04).
,3<br />
I<br />
Metallic<strong>Mineral</strong>s 115<br />
I But more than half of the Iead used currently comes from recycling<br />
I (Hutchison, 1983).<br />
Applications<br />
Lead is a major constituent of the Lead-acid battery used<br />
extensively in car batteries. Lead was used as a white pigment in<br />
Lead paint. It is used as a colouring element in ceramic glazes,<br />
notably in the colours red and yellow. Lead sticks were used as<br />
pencils, but has been replaced by graphite for the last 450 years.<br />
The element is used as projectiles for firearms and fishii sinkers<br />
because of its density, low cost verse alternative products and ease<br />
of use due to relatively low melting point. Lead is used in same<br />
candles to treat the wick to enswe a longer, more even burn. Lead<br />
is used as shielding from radiation. Molten lead is used as a<br />
coolant, e.g. for lead-cooled fast reactors. Lead glass is comprised<br />
of 12-2Ph lead. It changes the optical characteristics of the gIass<br />
' and reduces the transmission of radiation. Tetraethyl lead has been<br />
used in leaded fuels to reduce engine knocking; however, this is no<br />
longer common practice in the Western World due to health<br />
concerns. Lead is used as electrodes in the process of electrolysis<br />
(Gilbert and Parks, 1986).<br />
Origin<br />
Lead-zinc deposits are generally accompanied by silver, hosted<br />
within the lead sulfide galena or within the zinc sulfi& sphalerite.<br />
LRad and zinc-deposits are formed by discharge of deep<br />
sedimentary brine onto the sea floor (termed sedimentary<br />
exhalative or SEDEX), or by replacement of limestone, in skarn<br />
deposits, some associated with submarine volcanoes (called ,<br />
volcanic-hosted massive sulfide or VHMS) or in the aureole of<br />
subvolcanic intrusions of granite. The vast majority of lead and
I<br />
I<br />
I<br />
I<br />
1 16 <strong>Mineral</strong> Resoumm <strong>Potential</strong> of Ethiopia<br />
zinc deposits are Proterozoic in age. The immense Broken Sll,<br />
Century Zinc, Lady Loretta, and Mt Isa deposits in Australia, the<br />
Sullivan, Red Dog qd Jason deposib of North America and the<br />
Hindustan zinc ~ l&i t ~h&a are all SEDEX type deposits.<br />
The limestone replacement type of deposit exemplifies the<br />
Mississippi Valley Type (MVT). Some of these occur by<br />
Metallic Minemls 1 17<br />
water colours or paints, and as an activator in the rubber industry.<br />
As an over-the-counter ointment, it is applied as a thin coating on<br />
the exposed skin of the face or nose to prevent dehydration of the<br />
area of skin, It,can protect against sunburn in the summer and<br />
windburn in the winter. Applied thinly to a baby's diap area<br />
(perineum) with each diaper change, it can protect against mh. As<br />
determined in the Age-Related Eye Disease Study, it is part of an<br />
effective treatment for age-related macular degeneration in some<br />
cases. Zinc chloride is used as a deodorant and can be used as a<br />
wood preservative.<br />
Zinc production<br />
There are zinc mines throughout the world, with the largest<br />
producers being Australia, Canada, China, Peru and the U.S.A.<br />
Mines in Empe include Vieille Montagne in Belgium, Tara in<br />
Ireland, and Zirzkgruvan in Sweden (Guilbert and Parks, 1 986).<br />
Moly bdeaum<br />
- Occurrence<br />
Though molybdenum is found in such minerals as wulfenite<br />
(PbMo04) or powellite (CaMoQ), the main commercial source of<br />
mo jybdenum is mo lyklenite (MoS2). Molybdenum is mined<br />
directly, and is also recovered as a by-product of copper mining, It<br />
is present in ores from 0.01% to about 0.5%. About half of the<br />
world's molybdenum is mined in the United States, with Phelps<br />
. Dodge Corporation being a primary provider (Guilbert and Parks,<br />
1986).<br />
Applications<br />
Over % of all molybdenum is used in alloys. Molybdenum is used<br />
to this day in high-strength alloys and in high-temperature steels.
1 18 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
sp&ial molybdenum-containing alloys, such as the Hastelloys, me<br />
notably heat-resistant and corrosion-resistant. Molybdenum is used<br />
in oil pipelines, aircraft and missile parts, and in filaments.<br />
Molybdenum finds use as a catalyst in the petroleum industiy,<br />
especially in catalysts for removing organic sulfurs from petroleum<br />
products. Ma-99 is used in the nuclear isotope industry.<br />
a Molybdenum ranges are pigme'nts ranging from red-yellow to a<br />
in paints, inks, plastics, and rubber<br />
Coppr, zinc, lead, molybdenum murmnees in Ethiopia<br />
Copper most promising occurrences seem to be related to<br />
volcanogenic massive sulphide (VMS type) mineralization<br />
occurring in the meta-volcano-sedimentary belts of Western<br />
Ethiopia (Abetselo, KatPr). Other occurrences are related to basicultrabasic<br />
magmatic rocks and copper is also a common pathfinder<br />
of gold in many shear-zone related "mesothermd" goId deposits<br />
(Table 2). The well-hown Cu-Mu-(Co) Chercher deposit in<br />
Eastern Ethiopia, hosted in Mesozoic sandstones discordant over<br />
the Precambrian basement belongs to the Red Bed type. Recently,<br />
the Ethiopian <strong>Mineral</strong> Development Sh. Co. have discovered<br />
copper occurrencm at localities Wachile and G d e in Arero<br />
Wore&, Borena zone (Southem Etbiopia). The copper minerds<br />
are malachite associated with meta-granite and &randorite. The<br />
localities are currently under intensive gmIogical and geophysical<br />
mmm<br />
Zinc, Lead, as well as other commodities (e.g. Ag, As, Sb, Bi) are<br />
associated with Cu and Au in polpetallic massive and<br />
disseminated sulphides of volcanogenic and volcano-sedimentary<br />
deposits (Kata, Abetselo, Azale-Akendeyu), as well as pathfinders<br />
y primary "lode" orogenic deposits. Other Pb or Pbs<br />
located close to the basal contact of discordant<br />
I<br />
i<br />
II
Metallic Minds 119<br />
sediments over the Precambrian bament (e,g+ Soka, Ijabq<br />
Ramis River in Wolfega and AfFmtu and Grava) may represent<br />
Red Bed type or carbonate-hosted base-metal deposits. This type<br />
of mineralization warrants further investigations.<br />
I<br />
Molybdenum (as molybdenite) occurs in leucocratic quartzplagioclase<br />
acidic rocks at a flank of granite batholiths at Fakusho.<br />
Some granitic pegmatites also contain Mo (Bissidimo valley,<br />
Chiltu). Wolfram occurs with Mo in granitic rocks at Kata<br />
(Wollega); this element is also commonly identified as trace<br />
dement in numemu shear-zone related mesothermal gold deposits<br />
(e.g. Digati, East SWo, and Korkora in Adola), Other<br />
molybdenum occurrences have been reported in Bissidimo River<br />
valley 13 km hm the town of 'Ham. The Mo is associated with<br />
quartz veins. The quartz veins confining Mo mineral occurs in<br />
pegnmites. Similar occurrences has been also found in Dedessa<br />
River (Wollega) associated with pegmatites, The scarcity of<br />
si-cant base-metals deposits in Ethiopia may k due to a lack of<br />
systematic exploration. Therefore, systematic exploration is<br />
required to asses the base-metals potential of the country.<br />
Molybdenum, Tin, and tungsten 4 s generally form in a<br />
certain type of granite, via a similar mechanism to intrusive-related<br />
gold and copper. They are considered together because the process<br />
of fuming these deposits is essentially the same. Skarn type<br />
mindisation related to these granites is a very important type of<br />
tin, tungsten and molybdenum deposit. Slam deposits form by<br />
reaction of minedised fluids from the granite reacting with wall<br />
rocks such as limestone. S h mineralisation is also important in<br />
lead, zinc, copper, gold and occasionally uranium minerahation.<br />
Greisen granite is another related tin-molybdenum and<br />
topaz mineralisat ion style. Greisens are formed by endoskam<br />
alteration of granite during the cooling stages of emplacement.<br />
Greisen fluids are formed by gyanites as the last highly gas- and
120 Mind Reuwrces <strong>Potential</strong> of Ethiopia<br />
water-rich phases of complete crystalisation of granite melts. This<br />
fluid is forced into the interstitial spaces of the granite and pools at<br />
the upper margins, here boiling and alteration occur.<br />
3.9 Radioactive mineral (Uranium, Thorium) deposits<br />
Udum is a naturally occurring element found in low levels<br />
witkin all rocks, soils, and water. This is the highest-numbered<br />
element to be found naturally in significant quantities on earth. It: is<br />
considered to be more plentiful than antimony, beryllium,<br />
cadmium, gold, mercury, silver, or tungsten and is abut as<br />
abundant as arsenic or molybdenum. It is found in many minerals<br />
including waninite (the most common uranium ore), smite,<br />
uranophane, torbernite, and coffinite. Significant concentrations of<br />
~miwn occur in some substances such as phosphate rocks, and<br />
minerals such as tantalite, lignite, and monazite sands also contain<br />
uranium-rich ores (It is recovered commercially from these<br />
sources) (Jensen and Bateman, 1979). The decay of uranium,<br />
thorium and potassium40 in the Earth's mantle is thought to be the<br />
main source of heat that keeps the outer core liquid'and drives<br />
mantle convection, which in tub drives plate tectonics. Uranium<br />
ores, i.e. mks containing uranium mineralisation in concentrations<br />
that can be mined economically, typically give I to 4 pounds of<br />
uranium oxide per ton, or 0.05 to 0.20 % uranium oxides.<br />
Origin<br />
Uranium deposits are usually sourced from radioactive granites,<br />
where certain minerals such as monazite are leached during<br />
hydrothermal activity or during circulation of groundwater, The<br />
uranium is brought into solution by acidic conditions and is<br />
deposited when this acidity is neutralized. Generally, this occurs in<br />
certain carbon-bearing sediments, within an unconformity in<br />
sedimentary strata. Uranium has a large atom that does not "fit"
1<br />
Metallic M inds 121<br />
into most silicate structures, and is therefore concmtmted in the<br />
magmatic fluid afier most of the magma has crystallized, where it<br />
enters the structures of h n and sphene in granites and<br />
pegmatites. For economic deposits of U minerals to form, U has to<br />
be leached out of its host rock, mobilized, then redeposited, as is<br />
the case with vein deposits. Alternatively, the concentration of U<br />
has to reach a high enough level in the residual fluid of magmatic<br />
crystallion, that U mineral can crystallize directly out of the<br />
magmatic fluid and will occur disseminated in granites and<br />
pegmatites.<br />
Applications<br />
The 6 use of urttnium in the civil sector is as fuel for<br />
commd nuclear power plai~ts. Generdly, this fuel is in the<br />
fom of enriched uranium, which has been processed to have<br />
higher-h-nad levels of 235~, sacient to be used for a<br />
variety of purposes relating to nuclear fission. Commercial nuclear<br />
power plants use fuel typically enriched to 2-3% 235~, though some<br />
reactor designs (such as the Candu reactom) can use natural uranium<br />
(unenriched, less than 1% 23S~) fuel (Jensen and Bateman, 1979).<br />
Radhdve 'mined accurm- in Ethiopia<br />
Radioactive mineral deposits of economic class have so far not<br />
ken discovered in Ethiopia Uranium and thorium minerals have<br />
been o h e d in pegmatite veins occurring in gneisses of<br />
Hararghe and Sidamo (Kenticha) regions. Precambrian granite,<br />
Cretaceous and Jurassic sediments in the same regions, particularly<br />
in the Din Dam-Ham district, are also gonsidered to be<br />
fsvourable host rocks for the deposition of radioactive minds.<br />
The scarcity of significant radioactive mineral deposits in Ethiopia<br />
may be due to a lack of systematic exploration.
:In lMi&raI Rwufces <strong>Potential</strong> of Ethiopia<br />
' ' .# 'Udutn deposits are usually s o d hm mdioaatiNe<br />
&mites, where ceitain minerals such as monazite are "l~~hed<br />
i &king hydrothermal activity or during circulation of groundwW~<br />
The 'uranium is bmlight into solution by acidic cohditions and is<br />
de~sitetl when this acidity is neutralised. Generally, this aurs h<br />
i<br />
I o&ain carbon-bearing sediments, within an wmnfbmity in<br />
;<br />
;<br />
i<br />
I<br />
1<br />
se'd&ent&y strata The majority of the world's nuclear power is<br />
murced,hm h u m in such deposits.<br />
Ilmenite (FeTi03) is a d y magnetic iron-black or steel-grey<br />
minerd found in metamorphic and plutonic igneous racks. it is an<br />
ironithim oxide in crystalline form. The majority of the<br />
ilme'hite mid is used as a raw material for titanium oxide, which<br />
is mainly-twd for titanium pigment production (paper, paint,<br />
plastics, rubber, printing inks, cosmetics, soap and phamceuticals).<br />
'<br />
The titanium dioxide is an extremely white substance used as a<br />
base in high quality paint (~enseh and Bateman, 1979).<br />
The gabbroic intrusive rocks,af Melka Arba and Bikilal areas are<br />
important hosts of ilmenite. Tlmenite is fomd intimately associated<br />
with magnetite, hosted by ~dissmbted ore-bring pyroxenite<br />
andlor hornblmdEte8 and massive iron ores. The average grade of<br />
henite for disseminated ore-bearing pyroxenite and iron ores at<br />
Melka Arba area. is 9.100/0 and 17.80% respeotively (Mengistu and<br />
Fentaw, 2000). \
Chapter 4<br />
Industrial minerals<br />
Industrial minerals and rocks are a group of naturally mcurring<br />
materials excluding gemstones, metallic ores, groundwater and fuels<br />
(coal, oil and gas) that are important sources of raw materials for the<br />
chemical, metallurgical, construction, agricultural, and related<br />
industries. A few metallic ores such as chromite, alumina, and<br />
pyrolusite, when used for certain purposes such as refractories in high<br />
temperaturn furnaces, may also be classified as industrial minerals.<br />
Industrial minerals are commonly occurring minerals and<br />
rocks that aE widely used in industry, sometimes undergoing very<br />
little processing. Most are high volume and low unit value<br />
commodities and their economic importance depends on the<br />
availabi 1 ity of markets, market location, transportation costs, their<br />
' physical and che~nical characteristics, and the degree of processing<br />
required for end use, A notable feature of these minerais and racks is<br />
that a single material may form the basis for a wide range of<br />
industries, starting from low technology processes producing low<br />
value products to higher technology industrial units producing high<br />
value products for export markets (McVey, 1989). A developing<br />
country with abundant resoumes and little know-how may start by<br />
producing low unit value products for the home market, followed<br />
eventually by high value products for export markets. A good :,:<br />
example is provided by a resouFe like limestone or dolomite which *r .<br />
initially may be a source of construction material (cement, aggregate<br />
and dimension stone) and later a raw material for agricultural,<br />
metallurgical, and chemical industries. Earnings from foreign trade r!<br />
could be increased by limiting exports of unprocessed raw materials.<br />
For example, a government may decide to export less phosphate rock<br />
while increasing exports of phosphoric acid and phosphatic fettilizers.<br />
How much effort and money is needed to catalog national industrial<br />
minerals and rock is a difficult, costly, but not impossible task,<br />
, '<br />
'
124 <strong>Mineral</strong> Resourm <strong>Potential</strong> of Ethionia<br />
Groups of Industrial <strong>Mineral</strong>s<br />
Industrial minerals may be classified based upon different factors;<br />
on end-use and economic factors. One classification identifies the<br />
following six groupings: construction materials, ceramic materials,<br />
metallurgical and refractory materials, abrasive materials, general<br />
manufacturing materials, and chemical and fertilizer materials.<br />
These six categories can fall into three broad groups. The<br />
first group, known as construction materials, includes sand, gravel,<br />
clays and stone (e-g., limestone, dolomite, granite, serpentinite and<br />
quartzite), Stone is both a source of crushed and dimension stone.<br />
This group is characterized by materials that are valued for their<br />
physical attributes, are very widespread in nature, are very bulky,<br />
and have low unit value, even as they require minimal processing<br />
before use. These attributes have a profound effect on the<br />
economic value of industrial mineral deposits. Commodities with<br />
high bulk and low unit value must be located close to markets to be<br />
economic, while less common materials with unique properties<br />
have a high unit value and may be profitably sold at high prices i<br />
distant markets (McVey, 1989). i 1<br />
The second group, referred to as process materials, includes<br />
a wide range of minerals and rocks possessing special<br />
characteristics that allow them to be used in specialized areas. This<br />
group includes (i) ceramic materials made up mainly of clays but<br />
also silica, limestone, dolomite, feldspar, quarts and bauxite; (ii)<br />
abrasive materiqls like garnet, silica, and especially chalcedony,<br />
chert, quartz, quartzite, sandstone, and silica sand; and (iii)<br />
rehctory and metallurgical materials like magnesite, fire clay,<br />
graphite, bauxite, silica, and dolomite. Materials in the third group<br />
include optical materials like quartz; -absorbent materials like<br />
bentonite and diatomite; fillers like asbestos, bentonite, gypsum,<br />
kaolin, limestone, and vermiculite; glass materials like glass sands,<br />
soda ash, limestone, dolomite, feldspar, borax, and gypsum; and oil<br />
drilling materials fke asbestos: barite, bentonite, limestone and
Industrial <strong>Mineral</strong>s 125<br />
dolomite. Materials in this group are valued mostly for their<br />
physical properties. They are less bulky, have higher unit values<br />
than construction materials, and can be sold on the export market.<br />
Industrial mineral deposits in Ethiopia<br />
Industrial mineral resources occur in various geological formations<br />
from Precambrian to recent and are used in a wide set of industries;<br />
among them, glasses, ceramics and cement industries are<br />
prominent. The main comrnadities available in large quantities in<br />
Ethiopia include soda ash, potash, diatomite, bentonite, clay,<br />
common salt, gypsum, anhydrite, feldspars, talc, kyanite,<br />
mgnesite, dolomite, graphite, quartz, mica, apatite, pumice, silica<br />
sand, kaolin, phosphate, and silica. Despite the availability of<br />
these industrial mineral resources, Ethiopia used to import raw<br />
materials to supply existing local industries.<br />
4.1 Soda ash (sodium carbonate)<br />
Sodium carbonate (also known as washing soda or soda ash),<br />
NA~CO~, is the anhydrous sodium carbonate. The most common<br />
sodium carbonate is heptahydrate, a crystalline substance which<br />
readily efloresces to form a white powder, the monohydrate. The<br />
best sodium carbonate known form is sodium carbonate<br />
decahydrate. Soda ash has a cooling alkaline taste, and can be<br />
extracted from the ashes of many plants. It is often produced<br />
artificially in large quantities from common salt but, commercial<br />
soda ash, is extracted from lake brines or the mineral trona World<br />
soda ash production for 2003 was estimated at 38 million metric<br />
tons (McVey, 1989). Of the 3 1 countries that produce natural and<br />
synthetic soda ash, the United States was the world's largest<br />
producer, accounting for 28 % of total world output. Only the<br />
United States, Botswana, China, Ethiopia, and Kenya produce soda<br />
ash from natural sources -the remainder manufactures soda ash
126 ~in&al <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
through various chemical processes, primarily the Solvay synthetic<br />
soda ash +prpdwtion process. Total world natural soda ash.<br />
production reprebented abut 31 % of combined (bath natural md<br />
synthetic) world sdda ash production, The five leading producers<br />
were the United stab, china, Russia, India, and Germany,<br />
accounting for 71 % of world production in 2003 (McVey, 1989).<br />
Applications<br />
I Domestically it is used as a water softener during laundry. It<br />
competes with the ions magnesih and calcium in hard water and<br />
* prevents them b m bmding with the detergent bein4 used. Without<br />
using washing soda, additiqnal detergent is needed to soak up the<br />
magnesium and dcim iqns. Colled washing soda in the detergent<br />
section of Ares, it effectively removes oil, grease, and alcohol<br />
stains. Sodium carbonate is kidely used in photographic pmcesses<br />
as a pH igulator to main* stable alkaline conditions necessary<br />
for the action of the majority ,of developing agents (McVey,<br />
1989). Sdum carbonate is also used by the brick industry as a<br />
wetting agent to reduce tho amouni of water needed to extrude the<br />
clay. sodium carbonate is used in the mmufmtm of glass, pulp<br />
and paper, detergents, and chemicals such as sodium silicates and<br />
sodium phosphates. It is also used as an alkaline agent in many<br />
chemical industries.<br />
Soda mh depib in Ethiopia<br />
The Ethiopian Rift Valley Lakes, particuiarly, Lakes Abiyata and<br />
Shala, contain huge volumes of tmna brines (460 Mt of sodium<br />
carbonate in solution, at concentmtions ranging between 1.1 and<br />
1.9 % (Mengistu and Fentad, 2000). Soda ash deposits are<br />
localized in major volcano-tectonic depression (calderas) filled by<br />
lacustrine deposits. Prolonged evaporation is responsible for the<br />
ation in concentrations. Lake Shalla and Chitu have high
Induslrid M i d 127<br />
concentration of alkali elements in solution. Lake Abiyata alone<br />
has revealed the presence of 400 Mt ofMnes of soda ash (EGS,<br />
1989). In this locality, 25,000 tons of brines are produced annually<br />
by a small scale pilot plant. Abiyata Soda Ash Enterprise produced<br />
6,444 tons of soda ash in 2004 compared with 4,377 tons in 2003.-<br />
The company was conducting a feasibility study on the<br />
construction of a new processing plant with a capacity of 1.2<br />
Mtlyear. Subject to favorable results of the study; a first-stage<br />
plant with a capacity of 220,000'1/year would be built (Hariman,<br />
2004).<br />
4.2 Diatomite<br />
Diatomaceous earth, also known as diatomite, kieselguhr,<br />
kieselgur, and celite, is a naturally occurring, soft, chalk-like,<br />
sedimentary rock mineral that is easily crumbled into a fine white<br />
to off-white powder. This powder has an abrasive feeling similar to<br />
puhice powder and is very light-weight due to its high porosity. It<br />
is made primarily of silica and. consists of fossilized remains of<br />
diatoms, a type of hard-shelled algae. It is used as a filtration aid,<br />
as a mild abrasive, as a mechanical insecticide, as an absorbent for<br />
liquids, as cat litter, and as a component of dynamite (McVey,<br />
1 989). The most common use (68%) of diatomaceous earth is as a<br />
filter medium, especially for swimming pools. It has a high<br />
porosity, because it is composed of microscopicall y-small? coffin-<br />
like, hollow particles. It is used in chemistry, as a filtration aid, to<br />
filter very fine particles that would otherwise pass or clog filter<br />
paper. It is also used to filter watek and other liquids, such as beer.<br />
It can also filter syrups and sugar. Other industries such as paper,<br />
pints, ceramics, soap and detergents use it as a filling material.
I28 Mind <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
Occurreltlce<br />
Because diatomite forms from the remains of water-borne diatoms,<br />
it is found close to either current or former bodies of water. It is<br />
generally divided into two categories based upon soqrce;<br />
freshwater and saltwater. Freshwater diatomite is mined+om dry<br />
lake beds and is characteristically low in crystalline silica wntent,<br />
Salt water diatomite contains high crystalline silica content,<br />
making it a useful material for filters, due to the sieve-like feams<br />
d<br />
of the crystals (Noetstaller, 1988).<br />
Applications<br />
Diatomite is used as filler (paint, pulp, rubber, pharmaceuticals,<br />
etc), toothpaste, and polish-<br />
Diatomite depits In Ethiopia<br />
'<br />
Most of the diatomite depofits are located within the MER and the<br />
A k depression and more than 12 diatomite occurrences have been<br />
identified by EGS. Deposits of relatively good quality are found in<br />
Gade Mota, Adamitulu, Chefe Jilla and Abiyata located in the<br />
central part of the rift, The high-grade ores in the above localities<br />
have Si02, A1203, F-O3 and CaO in the range of 84.=6.5%, 3.1-<br />
3.7a0, 1.5-2.4%, and 0.1-1 .Ph, ~spectively (Mengistu and<br />
Fentaw, 2000). The diatomite deposits are located in lacustrine<br />
deposits of Tertiary to ~lejstoeene age, interbedded with<br />
volcaniclastic rocks, ignimbrite, t@-and pumim, Total geological<br />
potential- of the Lakes Region District (Mota, Adamitulu, Chefe<br />
Jilh and Abiyata) is estimated at $0 Mi of diatomite of which<br />
about 85% is contributed by Gade Motta diatomite (EGS, 19891,<br />
These--d,eposits have Si02, Al2O3, FezOs and CaO in the range of<br />
84,S86.$0/'0,
43 Bentonite<br />
Industrial <strong>Mineral</strong>s 129<br />
Bentonite is an absorbent aluminium, generally impure clay<br />
consisting of phyllosilicate mostly of montmorillonite, (Na,<br />
Ca)3(Al,MghSi40 dOH)z*nH20 with several other types. Two<br />
types exist: swelling bentonite, which is also called sodium<br />
bentonite, and non-swelling bentonite or calcium bentonite. It<br />
forms h m weathering of volcanic ash, most often in the presence<br />
of a water body. Bentonite expands when wet-sodium bentonite<br />
can absorb several hundred % of its dry weight in water<br />
(Noetstaller, 1988).<br />
Applications<br />
It is commonly used in drilling fluids. used to make slurry walls,<br />
and to form impermeable barriefs (i.e. plug old wells, as a linerin<br />
the base of landfills to prevent migration of leachate into the soil);<br />
several other minor uses (medicine, agriculture, etc.) also exist.<br />
Bentonite is used as absorbent, animal. feed, foundary sand,<br />
catalyst (oil refining), waterproofing and sealing, etc. (Noetstalier,<br />
1988).<br />
Bentonite deposits in Ethiopia<br />
Huge deposits of bentonite occur in the Afar region at several sites<br />
(e,g. Wakisa Mi, Gewme area, Hararghe) and at Gidicho Island<br />
(Lake Abaya) in Sidarno. In the Afar region, the total resources<br />
have been estimatsd at 170 Mt of bentonite (EGS, 1989). The<br />
chemical composition is in the range of 5040% silica, 11-14 %<br />
alumina, 7-9% iron and less than 1.3% sodium and potassium<br />
(Mengistu and Fentaw 2000). The deposits are part of the thick<br />
sequence of lacustrine and reverine clays, silts sands and<br />
calcareous grits, grad conglomerates and Mites interbedded with<br />
basalt and ash beds. The sediments were deposited near the<br />
western margin of the southern part of Afai Depression which
1 30 <strong>Mineral</strong> Rqmm <strong>Potential</strong> &Ethiopia<br />
throughout are late Tertiary and Quaternary. The largest deposit h<br />
situated about 17 km north-east of the town of Gewane (lati*<br />
10~14' 30"N and longitudes*40~ 35'40"E and #*35'30"~)<br />
mupying an area of 6.5 km2. The reserves at this site have been<br />
estimated at 77 Mt by EGS. The average thickness of the bentonite<br />
cl L y is about 13.8 m. The second largest deposit is Wolrseisa<br />
si ted 1-3 krn north of DessisAssab highway been the<br />
Badona River and Warseisa. The bentonite deposit occupies an<br />
area of about 127 ktn2. The reserves have been athated to be<br />
over 7 Mt and the average thickness is about 5.6 m.<br />
The Ledi deposit is situated dong the Addis-Assab<br />
highway about 30 km south of the Dessie junction, It is bounded<br />
by latitude l.lO1O'OO"-1 1'1 3'20" and longitudes 40~42'00'"-<br />
40°47~". In the area, east and west of the highway, the clay is<br />
calculated to outcrop over an area of 557,000 m2. At Ledi, the<br />
average thickness of the bentonitic bed is estimated to 3.2 m and<br />
, reserves have'been calculated to 1.78 Mt; the total reserves in the<br />
&a-have been estimated to 7 Mt (Mengistu and Fentaw 2000).<br />
Much-higher-qdity deposits of bentonite Rave been found<br />
at Lake Abaya in Sidamo. ~ hk 'bentonite-bearing beds are part of<br />
lacustihe sediments, which consist of clays, salt-bearing beds,<br />
sandstones, calcareous sandstones, conglomerates aud interbedded<br />
volcaniclastic rocks, They result, following Mengistu and Fentaw<br />
(20001, fiorn the dieration of glassy magmatic materials. The<br />
s in the ~idioho Island (Lake Abaya, Rift Valley) are<br />
ed to be 6.4 Mt (EGS, 1989).<br />
-4 Other clays and kaolin<br />
Clay deposits are formed h m the weathering of feldspar bearing<br />
ocks, such as granites, pegmdtes, gneiss or sandstone and<br />
olcanics, volcaniclastics and sediments. Kaolin results from the<br />
weat hering of granite and gneiss feldspar-related rocks and from
alteration (hydrothermal and weathering) of felsic and intermediate<br />
volcanics and volcaniclastics.<br />
Kaolinite is a mineral with the chemical composition<br />
A12Sif15(0H)+ It is a layered silicate mined, with one tetrahedral<br />
sheet linked through oxygen molecules to one octahedral sheet of<br />
alumina mtahedra, It is a soft, earthy, usually white mineral<br />
(doctahedral phyllosilicate clay), produced by the chemical<br />
weathering of feldspar, Natural deposits of kaolinite mixed with<br />
other clays and silica, are known as lraolinite or china clay, In<br />
I !many parts of the world, it is coloured pink-orange-red by iron<br />
oxide, giving it a distinct rust' hue. Lighter iron concentrations<br />
i<br />
! yield white, yellow or light orange colours. Alternating layers are<br />
? sometimes found, as at Providence, Canyon State Park, in Georgia,<br />
r:<br />
P .<br />
I<br />
I'<br />
. 1<br />
@<br />
USA (Noetstaller, 1988),<br />
' Kaolinite is one of the most common industrial mifierclls, it is<br />
mined in Brazil, France, Britain, Germany, India, Australia, Japan<br />
(Amakusa), Chin% and the South-eastern U.S. states of Georgia,<br />
Florida, and, to a lesser extent, South Carolina (Hmben and Bates,<br />
r 984).<br />
Applications<br />
LI-,, 9Due to its extremely fine nature (her than silt), it is mixed with<br />
'water and transported in tanks as a liquid slurry. It is used in<br />
8, ceramics, medicine, bricks, paper, as a food additive, in toothpaste,<br />
' and in cosmetics. A recent use is as a specially formulated spray<br />
applied to fruits, vegetables, and other vegetation to repel or deter<br />
d damage. A traditional use is to soothe an upset stomach,<br />
similar to the way parrots (and lam, hums) in South America<br />
1; originally use it. The largest use is in the production of paper, as it<br />
is a key ingredient in mating 'glossy' pap (but calcium
,<br />
Kaolinldepwits in Ethiopia<br />
Refractory bond. clays and clays suitable for cement manufachuing<br />
occur, in Gonder (Chelga) and Shewa (Koka). Alluvial clay<br />
deposits for brick, tile, pottery and pipe industry occur in Shewa<br />
(Addis Abah w), near Debre Zeit, Akaki, Kaliti and Suhlw<br />
between Debre Sina and Debre khan, and Zega W&l, Ka&<br />
(Bebeka), Adola (Kibre Mengist ma), Wollega milla), Hararghe<br />
(Dire Dawa area), Abay River Valley and the Rift Valley Lake<br />
Regions. The main sources of kaoIin for the ceramic industries are<br />
the weatbering products of granites and pegmatites. Clay materials<br />
for the manufacture of pigments occur in Gondar and Kaffa.<br />
Ceramic clays are common in Ambo, Shewa, Harar arid Adola<br />
(Bombowha or Bombweha). According to Mengistu and Fentaw<br />
(2000), Kaolinite is the predomimt clay mineral of the<br />
Kombolcha (Harar) and Bombowha (Adola) areas with quartz-<br />
&Idspar and illite/muscovite occuring as subordinate minerals,<br />
Alumina is generally above 35% in the Bornbowha kaolin with<br />
,impurity elements such as iron (< 1%) and total alkali rind titanium<br />
accounting for less than 3%. On the contrary, the Kombdcha<br />
kaolin bears a relatively lower alumina (33.24%), and higher total<br />
alkali and iron, averaging 2.54% and 2.63% respectively. Reserves<br />
of kaolin at Bombowha are edhkd to over 0.5 Mt (EGS, 1989).<br />
The Bombowha kaolin mining is supplying the main ceramic raw<br />
materid to the oniy one ceramics factory of Ethiopia, known as<br />
Tabor Ceramics Factory, located in Awassa, south Ethiopia.<br />
Kaolin is an mential constituent of cups, saucers, plates, including<br />
ather porcelain wares including porcelain electrical insulators, In<br />
recent years, domestic output of kaolin and sulfuric acid has been<br />
inhibiid by limited domestic demand: caustic soda, by import<br />
competition and shortages of lime need& as raw material: and
silica sand, by the capacity of the country's only glass and bottle<br />
factory.<br />
4.5 Common salt<br />
Sodium chloride, also h wn as common salt, table salt, or halite,<br />
is a chemical compound with the f'omuIa NwCI, Sodium chloride<br />
is the salt most responsible for the saliity of the ocem and of the<br />
extmelhdar fluid of many muiticellular organisms. As the main<br />
ingredient in ediblesalt, it is commonly used as a condiment and<br />
food preservative. Sodium chloride is essential to life on earth.<br />
Most biological tissues and Imdy fluids contain a varying amount<br />
of salt. The concentration of sodium ions in the blood is dkdy<br />
related to the regulation of safe body-fluid levels. Propagation of<br />
nerve impulses by signal transduction is regdated by sodium ions.<br />
(Potassium, a metal closely related to Sdium, is also a major<br />
component in the same bodily system). 0.9% sodium chloride in<br />
water is called a physiological solution because it is isotonic with<br />
blood plasma It is known medically as normal saline moetstaller,<br />
EvapmOn of lake water or sea water results in the loss of water<br />
, and thus conceatrates dissolved substances in the remaining water.<br />
When the water becomes saturated in such dissolved substance<br />
they precipitate hm the water. Deposits of halite (table salt),<br />
gypsum (used in plaster and wall board), borax (used in soap), and<br />
sylvite (potassium chloride, h m which potassium is extracted to<br />
use in fertilizers) result from this process.
134 <strong>Mineral</strong> <strong>Resources</strong> Potwial of Ethiopia<br />
Applications<br />
Whik most people are familiar with the many uses of salt 'in<br />
cooking, they might be unaware that salt is used in a plethora of<br />
applications, from manufactwing pulp and paper a d dyeing<br />
textiIes and fabric to producing soaps and detergents. In most of<br />
Cam& and the northem USA, large quantities of rack sdt are used<br />
to help clear highways of ice during winter, although "Road Wtn<br />
loses its melting ability at temperatures blow -1 5°C to -20°C<br />
(5OF to 4OF). Salt is a h the raw material used to prodchlorine<br />
which itself is required for the production of many<br />
modern materids including PVC and pesticides used in human and<br />
animd diet, food seasoning and food presewations, to prepare<br />
sodium hydroxide, soda ash, cawtic soda, hydrochloric acid,<br />
chlorine; metallic sodium in ceramic glazes; metallurgy, cuijng of<br />
hides, mhmd wafers, soap mufwcture, home water softeners,<br />
highway de-icing, photography qnd in scientific equipment for<br />
optical parts. Single crystals are used for spectroscopy, ~Itraviolet<br />
and inhd transmission.<br />
Rock salt is produced hm the Danakil depression, which covers w<br />
dace of many thousands of square kilometres with reserves<br />
estimated at 3 Mt of salt (Getaneh, 1985). Common salt occurs<br />
both as brine and rock salt. Rock salt commonly occurs as thin<br />
stratified layers; gmerally less than one meter thick assaciated<br />
with marl and gypsum beds.<br />
Many salt water sources are exploited far salt in saIines<br />
which are located in Bale (e.g. Kalamis, Otrada, Creen, Dol,<br />
Hocdu, Eldere), Gojjam (50 km south-east of Debre Markm) and<br />
Sidamo, near Mega (e.g. El Sod). Ogaden, Afar and Sidamo me the<br />
most potential source areas. The potential salt resources of Afar<br />
are Bu&,Gekim, Afdm and Assale arm. The resources are
&ted at ksevd. hundnL million .tons wjlh,.a:jgqde; af =<br />
NiCl- The Afdera.salt plain done has a xwmwue. offatma 3%<br />
million tons (Magistu and Fentaw 2QQO). mer. minor somw<br />
imlude dty springs o~~ from wldc. cl.aters ia-many<br />
subordinate ponds of Afder, Ed, =me, eta, in: the Southm<br />
Ethiopia and munt for a small portion of artisanal mining of<br />
edible salt. Afar Salt plc, Bashenfer Sdt plc, and Gea A&on
136 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethio~ia<br />
fireproofing, fire extinguishing compositions, cosmetics, dusting<br />
powder, and toothepaste. Other applications are*-as filler material,<br />
smoke suppressant- in plastics, a -reinforcing agent in neoprene*<br />
rubber, a drying agent, and calm retention in floods. In addition,<br />
high purity magnesium wbonate is used as anti-acid and as an<br />
additive in table salt to keep it free flowing (Noetstrlller, 1988),<br />
Magnesium carbonate, most often referred to as 'chalk', is used in<br />
rock climbii as a drying agent for hmds.<br />
\<br />
Magmesite deposits in Ethiopia<br />
wesite is found with dolomitic marble in Kenticha (Adoh<br />
Belt), as white, fine to medium grained crystalline rock. lt occurs<br />
-as linear belts extending for tens of kilometers. It is mainly<br />
associated with graphite schist. The width of the occurrence varies<br />
from few meters to about 50 m. Other occurrences of magmite<br />
me reported in H m (k Jak, Kunni), Sidamo, Moyale,<br />
WoIlega and .Assom in close 'on with basic and ultrabasic<br />
EGki rocks as yeins; ,Systematic e=n activities are required to<br />
assess the ecummic :potential of the magnesite mmmnces.
I FIm 33 Magtmite block from ~h magnosite deposit in of K4cb Adola<br />
4.7 1 Feldspar (ceramic and sheet glers raw materials)<br />
1 Feldspar is the m e of an important group of rock-forming<br />
minerals which make up perhaps as much as 60% of the Earth's<br />
crust. Feldspars crystallize b m magma in both intrusive and<br />
extrusive rocks; they occur ssLcompact minerals, as veins, and are<br />
also present in many types of metamorphic rock. Rock formed<br />
entirely of plagioclase feldspar is known as anorthosite. Feldspars<br />
are also found in many types of sedimentary rock. This group of<br />
minerals consists of framework or tectosilicates:<br />
orthoclase a potassium-aluminium silicate;<br />
microcline also a potassium-aluminium silicate; and
138 M i d Resoutces <strong>Potential</strong> of Ethiopia<br />
plagioclase a sodiutpdtqidum silicate to.: a-cdq<br />
aluminium silicate isomorphous ' sdb:<br />
oligoclase, andesine, labradorite, bytownih, d d .<br />
Feldspar is a common raw material in the production of ceramics;<br />
feldspars are used for thennoluminescence dating and optical<br />
dating in earth sciences and mhaeology; feldspar is an ingredient<br />
in Bon Ami brand household cleaner; it is used as a glazing<br />
material. Feldspar is also industrially important in glass and<br />
cemic industries; patter and enamelware; soaps; bond for<br />
abrasive wheels; mrnen@ and insulating compositions; fertilizer; 1<br />
tarred roofmg materials; and as a sizing, or filler, in textiles and<br />
paper. A warsg greyish-gkn talc has been called soapstone or<br />
steatite gql @# been used for stoves, sinks, electrical switch<br />
boards, e&m:(%hy, 1989). 1<br />
Feldspar deposit in ~thiopia<br />
-<br />
Feldspar occurrences have been reported in a number of localities tij<br />
in Ethiopia, the most irnportaAt of which are in Sidamo (e.g.<br />
;,p<br />
Kenticha and Neghele) and Hmrghe (Babile-Bombasa). 6-<br />
Generally, in all of these localities, feldspars are associated with<br />
pegmatite dykes. The feldspar mineral is of microcline or albite<br />
type, The mserves in the Kenticha pegmatite deposit have been<br />
dm&d to 0.46 Mt (Ethiopian <strong>Mineral</strong> Development Sh. Co) and<br />
the pegmatite dykes in Babile-Bombasa contain abossible reserve<br />
of 0.15 Mt of feldspar (EGS, 1989). Presently !he feldspar useful<br />
for industrial application in Ethiopia comes from the Kenticha<br />
pegmatite which is produced ss'bypmluc't to the primary tantalum<br />
concentrate mining. The feldspar in Kenticha pegmatite usually<br />
forms large pure white crystals with intergrowth of quartz and<br />
qodumene.
4.8 Talc<br />
Occurrence<br />
Industrial M inds 139<br />
Talc is a mineral composed of hydrated magneim silicate with<br />
the chemical formula HzMg3(Si03)4 or Mg3Si401dOHh, It occm<br />
as foliated to fibrous masses, its monoclinic crystals being so rare<br />
as to be host unknown. It has a pfect b d cleavage, and the<br />
folh are non-elastic, although slightly flexible, It -is sectile and<br />
very soft, with a hardness of 1 (t'alc is the softest of the Mohs' scde<br />
of mineral hardness). It has a pific gravity of 2.5 -2.8, a waxlike<br />
or pearly luster, and is translucent to opaque. Its colour ranges h., 1::<br />
133<br />
from white to grey or green and it has a distinctly greasy fed and<br />
its streak is white.<br />
Applidions<br />
Talc finds use as a cosmetic (talcum powder), as a lubrimt, and as<br />
fdler in paper manufacture. Talc is used in baby powder, an<br />
astringent powder used for preventing rashes on the area covered<br />
by a diaper (Nmtstdler, 1 988). -<br />
Ta.k deposits of Ethiopia<br />
Talc minedimtion is widespread in Sidamo (Negele,<br />
Agremariam, Uh Ul, Shakisso, Megado, kenticha, Moyele<br />
greenstone belt, and Tulia), Tigray, and in many parts in Wollega<br />
(Yubdo). The talc deposits are generally of two types: those<br />
occuring in schists and those associated with serpentinite rocks. A<br />
resource of about 0.1 Mt of talc has been identified at Anno, 80 km<br />
north of Kibre Mengist in Adola (Mengistu and Fentaw, 2000). For<br />
all that, however, there has been no systematic investigation on talc<br />
for commercial purposes. Hence, dudy is recommended to make<br />
the best of such important resources of the country.<br />
-
' b~ k, alternative<br />
I<br />
140 <strong>Mineral</strong> Rtsou- <strong>Potential</strong> of Ethidpia<br />
4.9 Kyanite<br />
Kyanite is a typically blue silicate mineral, commonly found in<br />
aluminium-rich metamorphic pegrnatites and/or sedimentary rock.<br />
Kymite is a diagnostic mineral of the Blueschist Facies of<br />
metamorphic rocks. K yanite is a member of the duminosilicate<br />
series, which includes the polymorph andalusite and the<br />
polymorph sillimanite. Kyanite is strongly anisotropic, in that its<br />
hardness varies depending on its crystallographic direction. While<br />
this is a feature of almost all minerals, in kyanite this anisotropism<br />
can be considered an identifying characteristic. Kyanite has several<br />
names, including dirthcnc, rnunkrudite and cyanite.<br />
White-grey kyanite is also cdled heticite (Noetstaller, 1988).<br />
Applications<br />
Kymite is used primarily in pfractory and ceramic products,<br />
including porcelain plumbing fixtures and dinnerware. It is also<br />
wed in electrical insulators and abrasives. Kyanite has also been<br />
used as a gemstone, though this use is limited by its anisotropisrn<br />
and perfect cleavage. Finally, as with most minerals, kyanite is a<br />
collector's minerztl. i1<br />
Kyanite deposits in Ethiopia<br />
The north-eastern part of the AdoIa Belt hosts a thin belt of<br />
kyanite-quartz schist and kaolinized kyanite-quartz mica schist<br />
extending for more than 30 km; modal compositions of these<br />
kyanite-bearing rocks range between 21-26 % kyanite, 7 1-75 %<br />
quartz and 2-5 % other minerals. In the Chembi area, detailed<br />
mapping and geologic inference by Fentaw and Mengistu, suggest<br />
a resource of more than I0 Mt of high quaIity kyanite. The Chembi<br />
kyanite is hosted by quartz-kyanite schist having a regional strike<br />
direction of nearly N-S for more than 30 km and dipping at about<br />
20' to the east. Keolitlized quartz-kyanite-mica schist occurs as
~<br />
.. -<br />
Industrial <strong>Mineral</strong>s<br />
..<br />
14 1<br />
intercalation within the quart z-kyanite schist. Graphite schist,<br />
amphibole schist, quartz-kyanite schist, quartz-feldspathic schist,<br />
and granitic intrusive characterize the area. Quartz and kyanite<br />
constitute about 95% of the bulk mineralogy with kaolin,<br />
illite/muscovite and naile occudng as subordinate minerals.<br />
4.10 Graphite<br />
Graphite is one of the allotropes of carbon. Unlike diamond,<br />
graphite is a conductor, ,and can be used, for instance, as the<br />
material in the electrodes of an electrical arc lamp. Graphite holds<br />
the distinction of being the most stable form of solid carbn ever<br />
discovered. It may be considered to be the highest grade of cod,<br />
just above anthracite, although - it is not normally used as fuel<br />
because it is hard to ignite.<br />
Applicaf ions<br />
Most people first encounter graphite as pencil lead (in fact it is not<br />
lead, it is graphite). In its pure glassy (isotropic) synthetic forms,<br />
pyrolytic graphite and carbon fiber graphite is an extremely strong,<br />
heat-resistant (to 3000 "C) material, used in reentry shields for<br />
missile nosecones, solid rocket engines, high temperature reacto~s,<br />
brake shoes, electric motor brushes and as electrodes in EDM<br />
electrical discharge machines. Imescent or expandable graphites<br />
are used in firestops, particularly plastic pipe devices, as well as<br />
gaskets, fitted around the perimeter of a fire door. During a fire,<br />
the graphite intumesces (expands and chars) to resist fire<br />
penetration and reduce the likelihood of the spread of fire and<br />
hes. A typical start expansion temperature (SET) is between 150<br />
and 300 degrees Celsius. Cartmn fikr and carbon mnotubes are<br />
also used in graphite reinforced plastics, ad in heat-resistant<br />
composites such as reinforced carbn-carbn (RCC). Products<br />
made from carbopfiber graphite composites include fishing rods,
142 <strong>Mineral</strong> Resourocs <strong>Potential</strong> of Ethiopia<br />
golf-clubs, and bicycle frames, and have been successfully<br />
employsd in reinforced concrete (Noetstaller, 1 98 8).<br />
Graphite deposits in Ethiopia<br />
The meta-sedimentary rocks in Sidarno, Haramghe, Wollega and<br />
Tigray are potential sources for graphite. A series of Iong belts of<br />
graphitic schist extends for tens of kms through the Kenticha and<br />
Kibre Mengist areas of the Adola Belt and in Soka, and Kunni<br />
valley of the Chercher Mountain with large greenschist series. The<br />
graphite in Moyale area is hosted by quartz-feldsp-mica schists<br />
and quartzites which gendl y form continuous bodies extending<br />
for hundreds of meters, The .Moyale graphite deposit has an<br />
estimated reserve of 0.46 Mt of graphite (Mengistu and Fentaw,<br />
2000).<br />
- - 4.11 Silica<br />
The chemical compund silicon dioxide, also known as silica, is<br />
the oxide of silicon, chemical formula Si@. Siliceous is an<br />
adjective meaning "referri6 to silica". Silica is found in nature in<br />
( aB$; several forms, including quartz and opal. In fact, it has 17<br />
I . .I'<br />
crystalline forms. The most oornmon constituent of sand in inland<br />
continental settings and non-mpical coastal settings is silica,<br />
usually in the form of quartz because the considerable hardness of<br />
this mineral resists erosion, However, the composition of sand<br />
varies according to local rock sources and conditions. Variants<br />
found in high-pressure impacts are mite and stishovite. Many<br />
rrns of life contain silica structures (Biogenic Silica), including<br />
icro-organisms such as diatoms, plants such as horsetail, and<br />
mds such as hexactinellid sponges. It is present in the cell walls<br />
virious plants (including edible ones) to strengthen their<br />
ctural integrity. '
hx several. fum incldiing ;, glass (a<br />
form is called fwd silica), synthetic<br />
@I (used e.g. as desiccants in new &Xhes '<br />
ca is also -used as a food additive, primarily as a flow<br />
n.pow;ded foods, or to absorb water (Nogtaller;"l.~IB~ : j f I<br />
4- 8 -<br />
.r . .<br />
occurs in #he .MU@W valley, in 'the Penmaand<br />
in Enticho units df Adigrdt-Ump of<br />
rig@$ lk dca d deposits of Enticho area are grouped within<br />
sediments that form lower part of<br />
Gnurp. The silica deposits afilhticho Sd~&kf the<br />
= g&y a t e to grey*<br />
in* tw,aqpne grained gnd at ~Lors kaolinid The thickness<br />
oft&md$$pne ranges from IS30 m. Other good quality sand<br />
is hewn to O& in Eci'ug9 . >< valley*<br />
7T.T<br />
qpql*<br />
,?' 1 .<br />
-<br />
' II<br />
. .<br />
'.
144 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethionia<br />
4.12 Quartz<br />
Occurrence<br />
Quartz occurs in hydrothermal veins and pegrnatites. Well-formed<br />
crystals may reach several metres in length and width hundreds of<br />
kilometers. These veins may bear precious metals such as gold or<br />
silver, and form the quartz ores sought in mining. Erosion of<br />
pegrnatites may reveal expansive pockets of crystals, known as<br />
"Cathedrals." Quartz is a cpnmon constituent of granite,<br />
sandstone, limestone, and many other igneous, sedimentary, and<br />
metamorphic rocks. Trid y mite and cristobalite are high<br />
temperature polymorphs of SiOz which occur in high silica<br />
volcanic rocks. Lechaklierite is an amorphous silica glass SiOz<br />
which is formed by lightning strikes in quartz sand,<br />
Applications<br />
Many varieties of quartz are used in jewelry and for ornamental<br />
purposes. Agate and chalcedony are used in scientific instruments,<br />
chemical and radio apparatus. Ground and crushed quartz are used<br />
in wood filler, ceramics, glass, polishing soap and as an abrasive. It<br />
is also used as a flux in metallurgical work and in making<br />
refractory bricks.<br />
Quartz deposits in Ethiopia<br />
Quartz occurs widely in the basement rocks, in the form of veins<br />
and as a component of pegmatites. Several quartz vein and quartz-<br />
bearing pegmatites occur in the Kenticha area, with estimated<br />
resource of 0.26 Mt (Ethiopian.'<strong>Mineral</strong> Development Sh. Co) of<br />
good quality that can be used for glass and ceramics factories.
Itldwtrial Minds 143<br />
Specific varieties of mica include; biotite, muscovite, lepidolite~@~~<br />
phlogopite, illite. Muscovite, also known as potash mica, is a<br />
phyllosilicate minemi of aluminium and potassium with formula<br />
KAl2(A1Si3Ol o)(F,0H)2. Muscovite is the most common mica,<br />
found in granites, pegmatite, gneisses and schists, and as a contact<br />
metamorphic rock or as a secondary minerd resulting from the<br />
alteration of topaz, feldspar, kyanite, etc. Biotite is a common<br />
phyllosilicate minerd whose chemical formula is<br />
K(Mg,Fe++)3AlSi301 O(F,0H)2 and has a molecular weight of<br />
+. .<br />
43 3,53g/mol. kpidolite (KLi2A1(A1, Si)30 lo(F,0H)2) is a lilac or<br />
rose-violet colored phyllosilicate rriinerd of the mica group that is<br />
a secondary source of lithium. It is associated with other lithiumbearing<br />
minerals like spodumene in pegmatite bodies, It is one of<br />
the major sources of the rare dkdi metals, rubidium and cesium.<br />
I<br />
I Puogopite is a yellow, greenish or reddish brown member of the<br />
mica family of phyllosilicates. It is also known as magnesium
I<br />
I<br />
144 <strong>Mineral</strong> Resourcm IWdd of Ethiopia<br />
mica. It occurs in contaqt metamorphic zones around intrusives<br />
into magnesium rich limestones, dolostone, and in WM~ ultmmiic<br />
igneaus rocks. Illite is a none- clay-sized, mica~eous<br />
minerd. Illite is a phyllodicate or kyd silicate, Typical<br />
applications are plastic, paint, jhper, fire extinguisher, insulaters<br />
mid cosmetics (NoWer, 1988).<br />
I Mica depmits in Etbiopir<br />
Mia is known to o q in H m (Jijiga, Cmma, and Asebeteferi);<br />
Sidamo (Chembi, Mde& and Bornbo,wha) and Wollega ma All<br />
Imown occmce3 PC 'BSSOC& ~ith pegmatitic veins in the<br />
.Went rocks. The pegmatites commonly host columbo-tantalite<br />
group mind, ixiolite, berylJ s&urolite, phosphate (apatite,<br />
k mblygonite and lithiophillite), tourmaline (&rl and elbaite),<br />
spodumene, garnet (spessarite and manganian almandine), rutile,<br />
ilmenite and magnetite.<br />
4.14 Agwaminerrrls (Phosphritm, potash, Iim~~neldobmite,<br />
gypsum lanhydrftel suhr, natural zeolite, scoria/<br />
pumice)<br />
!<br />
Apminerals are minerds of importance to agriculture and<br />
horticulture, and are usually essential plant nutrients. The study of<br />
agrominerds is termed agmgeology, and wgrogeologists are<br />
concerned with issues such as the replenishment of soil fertility in<br />
r areas where-ggrominerals have been mined out or depleted by<br />
i unsustaimble farming methods.<br />
! 4.15 Phosphate<br />
[<br />
Aptite is a group of phosphate minerals, usually referring tb<br />
hydroxylapatite, fluorapatite, and chlorapatite, named for high<br />
concentrations of OK, I?, or C1' ions, respectively, in the crystal.
I ndusttial <strong>Mineral</strong>s 147<br />
The formula of the admixture of the three most common species is<br />
written as COlj(PO&(OH, F, Cl).<br />
Applications<br />
Apatite is one of few minerals that are produced and used by<br />
biological systems. H ydrox ylapatite is the major component of<br />
tooth enamel, and a large component of bone material. Fluorapatite<br />
is slightly stranger than hy,droxyapatite; thus, fluoridated water,<br />
which will allow exchange in the teeth of hydroxyl ions for<br />
fluoride ions, slightly strengthens the teeth (Noetstaller, 1 988).<br />
Origin<br />
Immense quantities of phosphate rock mur in older sedimentary<br />
basin, generally formed in the hteromic. Phosphate deposits are.<br />
thought to be sourced from the skeletons of Dead Sea creatures<br />
which accumulated on the seafloor. Similar to iron ore deposits<br />
and oil, particular conditions in the ocean and environment are<br />
thought to have contributed to these deposits within the geological<br />
past. Phosphate deposits are also formed from alkaline igneous<br />
rocks such as nepheline sye&tes, carbonatites and associated rock<br />
types. The phosphate is, in this case, contained within magmatic<br />
apatite, monazite or other rare-earth phosphates.<br />
! Phmphate dapadb in Ethiopia<br />
Considerable efforts have been made by EGS over the last few<br />
1<br />
decades to discover phosphate deposits in Ethiopia. The<br />
exploration efforts of the EGS showed the potentid of finding<br />
phosphate accumulations in various geological settings of Ethiopia<br />
Based on paleo-environmentah and lithologicd considerations<br />
1 dong with findings from borehole evidence, the late Cretaceous<br />
(Coniacian-Campmian) rock Series of Eastern. Fthiopia , has great<br />
I potential for phosphate accumulations. The Upper Cretaceous
148 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
represents a phospho-genic period in which many phosphorites<br />
have been discovered worldkide. Unfortunately, the Upper<br />
Cretaceous sediments do not crop out at the surface.<br />
<strong>Potential</strong> areas in Ethiopia with the greatest chance of<br />
finding large quantities of sedimentary phosphates are in the<br />
eastern part of the country, in Tertiary sedimentary sequences<br />
associated with transgressions and regressions in the Somalia-<br />
Ogaden embayment. The Auradu sequence in particular has the<br />
potential of bearing phosphates as these sediments were deposited<br />
under conditions favourable for phosphate accumulation. These<br />
characteristics include a favourable palmgeographic setting, cyclic<br />
transgressive-~gressive sequences, a typical chert-limestone-marl<br />
association and deposition during a major phosphogenic time<br />
interval, the Eocene. Other potential areas for finding phosphates<br />
are the carbonatite-peralkaline ring structures of Cenozoic age.<br />
To date, phosphate mineral resources in Ethiopia (Wollega,<br />
= Bale, and Borena areas) are related to intrusive rocks. Layered<br />
gabbro, gabbro-pyroxenite, and alkaline gabbro plutons host<br />
apatite-ilmenite mineralization. The gabbroic intrusions of Bikilal<br />
( Wollega) and gabbro-pyroxenite rocks emplaced in the basement<br />
rocks of biotite-amphibole gneisses and quartzo-feldspathic<br />
gneisses of Melka Arba are currently regarded as the most<br />
promising potential phosphate resources. Apatite, ilmenite and<br />
magnetite are the main minerals of economic interest in the area.<br />
Apatite is mainly hosted by disseminated apatite-oxide-bearing<br />
pyroxenite and gabbro pegmatites. The ore occurs as lenses and<br />
interlayering with gabbro and have width ranging from stringers to<br />
several meters. The average grade of P205 for Melka Arba area is<br />
about 3.75% (Mengistu and Fentaw, 2000).<br />
Small amounts of mitridatite, a very rare Ca-Fe-Mn<br />
phosphate mineral with the formula c%(H~ 0) [(~e* 8.2<br />
0.8)06(P04)9].3H20 has been found in lacustrine sediments in the<br />
Shungura Formation near Kelem north of Lake Turkana, in
InaustrialMbemls 149<br />
southwestern Ethiopia (Rogers and Brown, 1979). These minerals<br />
mcur together with hydrox y -apati te, following partial dissolution<br />
of carbonate substituted apatite (fish scales and bones). The latdral<br />
extent of these lacustrine phosphatic beds is not known, These<br />
phosphate finds are important as they indicate biogenic phosphate<br />
mineralization in a lacustrine rift-related environment, similar to<br />
that in which the Minjingu phosphate deposit in the Tanzanian riff<br />
valley has been found. Other potential phosphorite accumulations<br />
could be expected in the black shale-chert-limestone associations<br />
of another major phosphogenic period, the Neopmtemzui~~ In<br />
Ethiopia these sequences occur in the Tulu Dimtu metasedimentary<br />
sequence of Wollega region, in the .Adigrat area of<br />
Tigre region, and in various other geological formations (Assefa,<br />
1991).<br />
The Bikilal phosphate deposit<br />
The only igneous phosphates discovered to date, are at Bikild, 24<br />
km north-northeast of Ghimbi in Wollega Administrative Province<br />
and Melka Arba (Sidamo). The phosphate mineralidon is<br />
relatively unusual, as it is associated with a Proterozoic layered<br />
gabbro-anorthosite intrusion. Low-grade phosphates (34% P205,<br />
mean 4.56% P2O5) have been encountered in the apatite-magnetite-<br />
iImenite mineralization that is spatially and genetically associated<br />
with the intrusive complex. The apatite-magnetite-ilmenite<br />
mineralization in hornblendites occurs in a zone about 15 km long<br />
and 0.7 to 1.2 km wide. Several apatite-bearing hornblendites have<br />
been delineated in steeply dipping bands. The crystallographic<br />
unit-cell a-value of the Bi kilal apatites is a = 9.394 A (Abe~y el a/.,<br />
1 994), indicative of a relatively unreactive fluor-apatite.<br />
Reported reserve estimates of apatite-bearing material in<br />
the Bikilal area, to a depth of 200 m, are 127 million tones at 3.5%<br />
P205, 23.8% Fez& 7.3% TiOz (Yohannes, 1994, Mengistu and<br />
Fentaw, 2000). The phosphate resource in Bikilal which is
IS0 M i d <strong>Resources</strong> Potentld uf Ethiopia<br />
composed of apatite, ihenite and magnetite has the following<br />
compositions and mums: 3.59% PzOs, 6.04% TiOz, 0.09%V205<br />
and 2 1,87% total iron. The nm-surface, Iow-grade igneous<br />
phosphates from Bikilal have been evaluated on their suitability for<br />
upgrading through siezing and magnetic separation (Abera, 1 988;<br />
Abera et a!., 1994). Apatite concentrates up to 36% P2O5 were<br />
produced using simple processing techniques. However, the<br />
recovery rate was low at only 40-5 8% (Abem, et al., 1994).<br />
4.16 ~y~surn, anhydrite<br />
Occurrence<br />
Gypsum is a very common mineral, is thick and extensive<br />
evaporitic beds in association with other sedimentary rocks. The<br />
largest deposits known occur in strata from the Permian age.<br />
Gypsum is deposited in lake yd sea water, as well as in hot<br />
springs, from volcanic vapors, and sulfate solutions in veins.<br />
Hydrothermal anhydrite in veins is commonly hydrated to gypsum<br />
by groundwater in near surface exposures. It is often associated<br />
with the minerals halite and sulfur. Because the gypsum from the<br />
quarries of the Montmartre district of Paris has long furnished<br />
burnt gypsum used for various purposes, this material has been<br />
called plaster of Paris (McVey, 1989).<br />
Production<br />
Commercial quantities of gypsum are found in Germany, Italy,<br />
England, in British Columbia, Manitoba, Ontario, Nova Scotia and<br />
Newfoundland in Canada, and in New York, Michigan, Iowa,<br />
Kansas, Arizona, New Mexico, Colomdo, Utah and Nevada in the<br />
United States. There is also a large mine located at Plaster City,<br />
California in Imperial County (McVey, 1989).
Applications<br />
Industrial <strong>Mineral</strong>s 15 1<br />
Blackboard chalk, cement, drywall, plaster, a construction<br />
material, dental modes, surgical casts, paint filler, toothpaste,<br />
gesso, molds for casting metals, agricultural soil amendment,<br />
solidifying earth (cast earth construction), tofu coagulation,<br />
improving mineral content of brewing water, dietary calcium<br />
additives in breads and cereals, pharmaceuticals, 'dessicant.<br />
Anhydrous calcium sulfate (anhydrite) is sold under the brand<br />
name Drierite (Noetstaller, 1988).<br />
Gypsum, anhydrite deposits in Ethiopia<br />
Very large deposits of gypsum and anhydrite are known to occur in<br />
the sedimentary forrf;ations of Danakil depression, Ogaden, Shewa,<br />
Gojjam (Abay), Tigray and Hararghe. Extensive gypsum and<br />
anhydrite resources are known from the Mugher (Sodoble) valley,<br />
the Abay beds, Jemma River, Ferefer, Dewalle, Adi Guddem and<br />
Hagere Selam. The Adi Guddem and Hagere Selam gypsum has a<br />
resource potential of about 410,000 tons (Mengistu and Fentaw,<br />
2000).<br />
These occurrences are mainly associated with the Mesozoic<br />
sedimentary rocks and occur at many localities as htercalation<br />
with calcareous strata. Total reserves are enormous because the<br />
thickness of the gypsum deposits is many hundreds of metres and<br />
the formations are known to extend laterally for hundreds of<br />
kilometres. Gypsum and anhydrite are associated with salt and<br />
potash at the upper part of the Quaternary evaporites of the<br />
D&il depression in association with Quaternary salt and potash<br />
deposits. Others occurrences are hosted by Mesozoic sedimentary<br />
formations as intercalations within calcareous rocks. Patches of<br />
gypsum also occur in the lacustrine beds of lower Awash River<br />
valley near Asaita, in southern Afar region.
152 M i d hums P d a l of Ethiopia<br />
4.17 Potash (Fertilizer mw materials)<br />
Potash is an impure form of potassium carbonate (K2C03) mixed<br />
with other potassium salts. Potash is used as a fertilizer, while the<br />
pwe carbonate is used in medicine, in the chemical industry and to<br />
produce decorative colour effects on brass, bronze and nickel.<br />
Production<br />
The worId's largest potash producer is the Potash Corporation of<br />
Saskatchewan (North America). Many other mas, however, have<br />
the resources for potash production. Today, 14 countries produce<br />
the world's supply of potash. The main producers are North<br />
America (mainly Saskatcbewa, with two-thirds of the world's<br />
recoverable potash located there), Russia, Belarus, Germany, Israel<br />
and Jordan, (the later two both using solar mporaPion pans at the<br />
Dad Sea to produce camallite from which potassium chloride is<br />
' produced). In Ethiopia, some 3,578 short tons and 2,500 short tons<br />
were mined by small-scale extraction techniqua in 1917 and 1927<br />
respectively (EGS, 1989).<br />
Potash deposits h Ethiopia<br />
There are large potash resources in Ethiopia in the extremely hot<br />
and arid Danakil depssion near Dallol. The potash deposit is par?<br />
of a Quaternary evaporite sequence that covers an area of about<br />
1,150 km2, of which only a small portion has been explored.<br />
Exploration work by the US-based Ralph M. Pmns Company<br />
included drilling of more than 300 lmreholes, seismic work and<br />
shaft sinking to 100 m depths, as well as approximately 600 m<br />
underground openings (EGS, 1989). The company delineated two<br />
ore bodies in the Dallol area; the Crescent ore body and the Mudey<br />
ore body. In this area the evaporite sequence is greater than 1,000<br />
m thick and includes Iarge potagh reserves. Most of the potassium<br />
salt is in the form of sylvite (KCI), but carnallite and kainite are
,+<br />
Industrial MimlS : -153 977<br />
also reported. The main sylvite-bearing zone ranges :frop 1 5<br />
in thiclu~ess.<br />
Potash reserves are located mainly in th(: ~&il<br />
depression (Salt Valley). Dallol @anakil) is s niajoi ' d&j&it<br />
hosting Mite, sylvite, and other potassium salts reserves<br />
shallow marine evaporitic sediments that also contain gyps&-alnd<br />
anhydrite. The salt formation is composed of a thick evapohte<br />
succession of gypsum, anhydrite, inter stratified halite, potash salts<br />
and shales. New indications surfaced out recently that three<br />
I borehole were drilled M e r to the east in the Danakil depression<br />
1<br />
I<br />
and encountmd two layers of potash at 680 rn and 930 m and<br />
presumed to be stratigraphically continues with the Musely ore<br />
body, Therefore, the total potential reserve of potash within the salt<br />
plain alone is estimated to reach several billion tons. The tonnage<br />
of recoverable potash product in the Musley ore zone, based on, 85<br />
drill hoIes, is 30,021,000 short tons (Arkin 1969). The whole<br />
a depression contains at least 1 60,456,000 short tons of ore with 3 1-<br />
34% KC1 (Arb, 1969, Mengistu and Fentaw, 2000). Reserve<br />
estimates by Abera (1 994) exceed 60 million tonnes of recoved1e<br />
KCI.
Figure 35 Rock salt in the Danakil Depression worked out by<br />
traditional miners, Northern Ethiopia<br />
. 4.18 Dolomite and Limestone<br />
Dolomlte is the name of both a carbonate rock and a mineral<br />
consisting of calcium magnesium carbonate (c~tMg(C0~)~) found<br />
in crystals. Dolomite rock (also dolostone) is composed<br />
predominantly of the mineral dolomite. Limestone which is<br />
partially replaced by ,dolomite is referred to as dolomitic limestone,<br />
or as magnesian limestone. Dolomite mineral crystallizes in the<br />
trigod-rhombohedd system. * It forms white, grey to pink,<br />
commonly curved crystals, although it is usualry massive. It has<br />
physical properties similar to those of the mineral calcite, but does<br />
not rapidly dissolve or effervesce (fizz) in ilute hydrochloric acid.<br />
3.5 to 4 and the specific gra&y is 2.8
I<br />
I<br />
I<br />
ApplCcp1tio1~~<br />
Indudrial <strong>Mineral</strong>s I55<br />
Dolomite is used as an omentai stone, as a raw material for the<br />
manufiadme of cement, and as a source of magnesium oxide. It is<br />
an important petroleum reservoir rock, and serves as the host rock<br />
for large strata-bound Mississippi Valley-Type (MVT) ore deposits<br />
of base metals (that is, readily oxidized metals) such as lead, zinc,<br />
and copper. Where calcite limestone is uncommon or tcw, costly,<br />
dolomite is sometime used in its place as a flux (impurity remover)<br />
for the smelting of iron and steel. In horticulture, dolomite and<br />
dolomitic limestone are added to soils and soilless potting mixes to<br />
lower their acidity ("sweeten" them) (Noetstaller, 1 988).<br />
Dolornitellimestone depits in Ethiopia<br />
There is several million tons of dolomite as large in quantity as<br />
limestone is all over Ethiopia. Soil surveys of Ethiopia show that<br />
. the soils of large areas of western and southwestern Ethiopia are<br />
acid, with pH levels below 5.5 (Schlede, 1989). The largest<br />
volumes of limestone are located, however, in the eastern part of<br />
the country. Exceptions are the extensive and thick Mesozoic<br />
limestone and gypsum sequences in the Blue Nile River arka in<br />
Cend Ethiopia.<br />
Proterozoic limstoneldo~omite deposits in Western and<br />
Southwestern Ethiopia have considerable potential as they are<br />
located close to the acid soils. Dolomitic limestones and marbles<br />
helve been reported from many places in western Ethiopia,<br />
including Daletti, near Mendi. Liming material cm be found in<br />
Ethiopia within three major geological units:<br />
- In Proterozoic rocks, mainly as marble;<br />
- In Mesozoic sedimentary sequences, main1y as limestone,<br />
dolomite, and marl;<br />
- In Caenozoic sediments, as limestones, dolomites, and<br />
marls.
I<br />
156 <strong>Mineral</strong> <strong>Resources</strong> Pbtential of Ethiopia<br />
Proterozoic liming matelriala Roteromic marbles occur in<br />
northem Ethiopia (Tigray), in the west (Gojam, Wollega, Illubabor,<br />
Ma), southern (Orno, Sida.) and eastern (lharghe) parts of<br />
Ethiopia. A general observation is that these resources occur in<br />
areas where strong to moderately acid soils (pH< 5.5) sre<br />
dominant.<br />
Mesozoic liming materials, Mesozoic limestone, dolomitic and<br />
marl deposits in westem and rmrthern Ethiopia occur in Tigray, in<br />
the Danakil Alps and in the Blue Nile (Abay) valley. They also<br />
outcrop over large areas on the Somali Plateau. Smaller outcrops<br />
of Mesozoic liming materials occur in the central PIateau area near<br />
Ambo town, in the Didessa valley. Smaller deposit occurs in the<br />
Kella area south of Addis Ababa. The Jurassic Ando Group with<br />
sequences of limestone, dolomites and marls occur in the Blue Nile<br />
(Abay) valley and the Mekele (Tigray). In the Mekele area the<br />
Anterlo limestone is about 750 rn thick (Getaneh, 1985). In general,<br />
the Mesozoic limestone, dolomite and marl ~ESOW are located<br />
further away from m s with strong to moderate ?id soils<br />
I (pH
I<br />
.. '<br />
- ,<br />
. . -. .-..- -<br />
, , , ,,.-,A,<br />
. A Industrial Minemls 157<br />
named Madern Building Industry PK., lacated in Awash, which is<br />
engaged in processing a dolomitic marble' in order to manuf..~<br />
a standardized filler mineral at the required micro sizes. At t$gJ<br />
moment this company is supplied with the dolomitic marble from*<br />
the Kenticha Precambrian racks. The application of gypsum as a<br />
soil amendment for ahline soils on S-deficient soils and for<br />
groundnut production should be agronumically t d . Gypsum<br />
deposits should also be tested on the acid soils of westem Ethiopia,<br />
especially in acid soils with high Al-toxicities.<br />
Local resources of agricultural limestones and dolomites, as<br />
well as gypsum, should be investigated for their potential to<br />
ameliorate acid and Al-toxic soils, As in many countries, these<br />
morns of 'aglime' and dolomite have largely been overlooked.<br />
Research should be carried 'out to determine cost-effective<br />
extraction and low-cust crushing and grinding technologies<br />
I followed by demonstration of the apnomic effectiveness of<br />
liming materials and gypsum on acid soils. Further exploration and<br />
' testing of their suitability and agronomic effectiveness are neded.<br />
In addition, it is important to demonstrate the benefits of using<br />
I local lirnestone/dolomite and gypsum to farmers.
I<br />
158 <strong>Mineral</strong> Remums Fbtential of Ethiopis<br />
I<br />
i<br />
t~gure ;?o A large out-crop of dolomrt~c marble wnnln grapnlte<br />
Kenticha, Adola<br />
. Eleinental sulfur can be found near hot springs and volcanic<br />
regions in m y parts of the world. Such volcanic deposits are<br />
currently exploited in Indonesia, Chile, and Japan (Noetstaller,<br />
1988). Significant desposits of elemental sulfur also exist in salt<br />
domes along the coast of the Gulf of Mexico, and in evaporites -in<br />
Eastern Europe and western Asia. The sulfur in these deposits is<br />
believed to come hm the action of anaerobic bacteria on sulfate<br />
eerals, especially gypsum. Such deposits are the basis for<br />
commercial production in the United States, Poland, Russia,<br />
Turkmmistan, and Ukraine (Noetstaller, 1988).<br />
Common naturally occurring sulfur compounds include the<br />
metal .sulfides, such as pyrite (iron sulfide), cinnabar (mercury<br />
sulfide), galena (lead sulvex sphalerite (zinc sulfide) and stibnite<br />
(antimony sulfide); and the rnd sulfates, such as gypsum<br />
cium sulfate), aiunite (potassium aluminium surfate), and barite
1 I<br />
Industrial Mjnorah '1 59<br />
(barium sulfate). Hydrogen sulfide is the gas respomible for the<br />
odor of rotten eggs. It accurs naturally in volcanic emissions, such<br />
as from hydrothemat vents, and from bacterial action ofl decaying<br />
sulfur-containing orgauic matter.<br />
Applications<br />
Sulfur has rnany industrial uses. Through its major derivative,<br />
sulfuric and (&SO4), sulfur mpks as one of the more important<br />
elements used as an industrial raw material. It is of prime<br />
impo&ce to every sector of the world's economies, Sulfuric acid<br />
I<br />
I<br />
production is the major end use for sulfur, and consumption of<br />
sulfuric acid has been regarded as olie of the best indices of a<br />
nation's industrial development. More sulfuric acid is produced in<br />
the United States every year than any other industrid chemical.<br />
Sulfur is dso used in batteries, detergents, the vulcanimtion of<br />
rubber, fungicides, and in the manufacture of phosphate fertilizers.<br />
Sulfiks are used to bleach paper and as a preservative in wine and<br />
dried hit. Because of its flammable nature, sulfur dm finds use in<br />
matches, gunpowder, and fireworks. Sodium or ammonium<br />
thiosulhte is used as photographic fixing agents (Noetstaller,<br />
I 1988).<br />
There are small and scattered occurrences of native sulfur in the<br />
sediments and associated volcanic activities of the Rift Valley and<br />
in Danakil Depression. All are solfhtara-type associated with<br />
fmambs and crater deposits. The Danakil Depression resource at<br />
Zariga, north of Dallol, and on-mlol hill are estimated at 0.36 Mt<br />
at a grade of 5&55% sulfur. Anothk resource west of Dallol, on<br />
the road to Musley and Chebret Ale-crater, was reported to contain<br />
0.2 and 7 million tons at a &e of I&20% and 900? sulphw<br />
' respectively (EGS, 1989). There are various sulfur deposits in the wfl<br />
D-l Depression and mud Dofan deposit in the central rift
160 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
are$ and most of them are of volcanic odgin formed by gasous or<br />
hmlic activity around volcanic crater and hot springs.<br />
Localities of sulfur occurrences:<br />
- Sulfur occurs in Zariga (20 km north of Dallol) on the road to<br />
Mersa Fatirna and in two other localities in Dallol area and<br />
Cheberet Ale deposit (spring deposit due association with a<br />
crater) is 60 km south east of Dallol;<br />
- Sub also occurs in the Dofan vobano in the central rift<br />
valley at (8021'27"N and 40' 07'09"E). It is fomed by<br />
continuous fumerolic activity having impregnated a limited<br />
amount of element. sulfur by sublimation within the porous<br />
pumice and scoria layers and dso along fmtwes;<br />
- Manda is also known for sulfur deposits which are still<br />
exmcted by l ad ppIe.<br />
In addition, &bent exploration activities by EGS, at DofaR west of<br />
Awash River, revealed a deposit of 2,900 tons with sulfur grade at<br />
626%.<br />
4.20 Pumicdscoria<br />
Pumice is a highly vesicular pyroclastic igneous rock of<br />
intermediate to siliceous magmas including rhyolite, trachyte and<br />
phonolite. Mice is usually light in colaw ranging from white,<br />
yellowish, grey, grey brown, and a dull red. Pumice has an average<br />
porosity of W/o. Pumice is formed as pyroclastic material is<br />
ejected into the air as a froth containing masses of gas bubbles or<br />
vessicles; the lava solidifies and the vessicles are contained in the<br />
rock. The basaltic version of pumice is horn as scoria and has<br />
m y differences due to mineralogy.<br />
Pumice is widely used to make lightweight concrete and as an<br />
abrasive, especially in polishes and cosmetics exfoliants. When<br />
used as an additive for cement, a hie-graid version of pumice
Industrial <strong>Mineral</strong>s 161<br />
called p omb is mixed with lime to form a light-weight, smooth,<br />
plaster-like cbncrete.<br />
Pumice deposits in Ethiopia<br />
Large resources of volcanic scoria and pumice have accumulated<br />
within and along the margins of the rift valley. These resources can<br />
be used in soil moisture conservation techniques, called rock<br />
mulching. Experiences from other parts of the world, especially the<br />
Canary Islmdq have shown that rock mulch can considerably<br />
reduce evaporation from soil surfaces.<br />
Pumice occurs in several localities of the Rift Valley as<br />
recent shore sediment of lakes and also as older lacustrine<br />
sediments. Pumice =ewes are located near Nazareth railway<br />
station and in the Mojo stxea. Other deposits occur as shore<br />
sediments at Debrezeit, Langano, Awassa and other Rift Valley<br />
Lakes, Rock mulch field experiments using local scoria and<br />
pumice resources fiom near Naareth were carried out in the<br />
wework of the Ethiopia-Canada agrogeology project (Woldeab<br />
ei al., 1 994). The results of field experiments illustrated the effects<br />
of scoria and pumice mulches in the Rift Valley of Ethiopia. The<br />
application of 3 to 5 crn scoria or pumice mulch on top of the soil<br />
swfim resulted in effective soil moisture conservation, as well as<br />
grain yield increase of maize by as much as 4 he (Wold& et<br />
al., 1994). The main constraints to this system are availability of<br />
mulching materids in the close vicinity to soils with moisture<br />
stress, and economics.<br />
4.21 Natural zeolites<br />
Zeolites are the aluminosilicate members of the family of<br />
microporous solids known as "molecular sieves". Zeolites are<br />
widely used as ion-exchange beds in domestic and commercial<br />
water purification, softening, and other applications. In chemistry,<br />
zeolites are used to separate molecules (only molecules of certain
162 M i d <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
sizes and shapes can pass through), as traps for molecules so they<br />
can be andyzed. Zeolites have the potentid of providing precise<br />
and specific separation of gases including the removal of H2Q,<br />
C02 and SO2 from low-grade natud gas streams. Other<br />
separations include: noble gases, N2, freon and formaldehyde.<br />
However, at present, the true potential to improve the handling of<br />
such gases in this manner remains unkmwn.<br />
Currently, the world's annual production of natd zeolite<br />
is about 4 million tons. Of this quantity, 2.6 million tons' are<br />
shipped to Chinese markets to be used in the concrete industry.<br />
Eastem Eumpe, Western Europe, Australia, and Asia are world<br />
leaders in supplying the world% demand for natural zeolite, By<br />
comparison, only 57,400 mettic tons (wurce: U.S. Geological<br />
Survey, 2004) of zeolite (only 1% of tke world's cmmt<br />
production) is produced in North America+<br />
Natural zeolites form where volcanic rocks and ash layers<br />
m t with alkaline groundwater. Zeolites also crystallized in postdepositional<br />
environments over periods ranging from thousands to<br />
millions of years in ~Ilow marine basins. Ndly occurring<br />
zeolites are rarely pure and are contaminated to varying degrees by<br />
other minerals, metals, quartz or other zeolites. For this m o ,<br />
naturally occurring zeolites are excluded from many important<br />
commercial applications where uniformity and purity are essential.<br />
Natural eeolite deposits in Ethiopia<br />
Several million tonnes of high-grade zeolite deposits (mordenite<br />
and clinoptilolite) were discovered by geologists of the Ethi*<br />
Canada agrogology project in rift valley sediments nmr Nmth<br />
and Boru, west of N mth, Muger and Gondar (Fig. 37). Zeolites<br />
have high cation exchange capcities and, specifically, high<br />
ammonium selectivities. There we many applications of zeolites in<br />
agriculture and horticul~, among them are applications of<br />
zeolites in chicken houses that can reduce the losses of
ammonium-nitrogen by ion dchange and adsorption lht~ t?~<br />
channels of zeolites, These ammonium-charged zeolites could be<br />
used as an effective slow-release of soil amendment The extent ~f<br />
the natural zeolites in the Rift VdIey should be surveyed, and the<br />
zeolites need to be characterized mineralogically and chemichlly.<br />
Pradcal. applications for the natural. or mdifid. zeolites of<br />
Ethiopia in aaiculture and horticulture have to be assessed,<br />
FIgm 37 Acfcuh zealits (mt~) crystal w<br />
4<br />
'4.22 <strong>Mineral</strong> waters<br />
<strong>Mineral</strong> water is water containing minerals or other dissolv<br />
1 substances that alter its taste or give it therapeutic value. Salts,<br />
1<br />
i<br />
sulficr compounds, and gases are among the substances chat can be<br />
dissolved in the water. <strong>Mineral</strong> water can often Ix effervescent.<br />
Muaal warn bc prepared em occur naturally.
I<br />
I Humasa,<br />
Traditionally mineral waters would be used or consumed at their<br />
source, often refeked to as taking the waters or taking the cure and<br />
such sites were referred to as spas, baths or wells. Spa would be<br />
P<br />
used whh the water was consumed and bathed in, bath when the<br />
water was not generally consumed and well when the water was<br />
not generally bathed in. Often an active tourist centre would grow<br />
up around a mineral water site (even in ancient times). Such tourist<br />
development resulted in spa towns and hydropathic hotels (often<br />
shortened to Hydros). In modern times, it is far more common for<br />
mineral waters to be bottled at source for distributed consumption.<br />
Mlneml watem deposits in Ethiopia<br />
More than 130 thermal springs are known in Ethiopia of which<br />
about 70 are situated within the Rift System (Nech Sar, Abaya,<br />
Matigola, Blate, Cherico Gidabo, Grabs Quhe, Wondo<br />
Genet, Kike, Dubicha, south lake Shda, east lake Shala, Tub<br />
Gudo island, Bole graben, Edo Laki, Oitu Bay, Alemtena and<br />
Koka, Gumare pool, Sodere, lake Beseh, Wasero, Bilen, lake<br />
Hertde, Erer Gota, Meleka, north Gewane, Issa graben, Wanuf,<br />
KiIelu, Danab (Maru), Teo, Gamma, Muluke, Chachetu,<br />
Allalobeda, Kio Derayta, Dobi, Seha, Mantebo, Uluye, Gugubdo,<br />
lake Afdm, Ain Allah, lake Bakilli, lake As'ale, Dalol, Black<br />
Mtn, Musley and the rest on the Plateau, mostly in the Lake Tana<br />
Basin (Getahun, 2002).<br />
4.23 Other metallic and industrial minerals<br />
A wide variety of other metallic and industrial minerds is known<br />
to occur in various geological environments (Table 2); among<br />
them mention can be made of mercury, wolframite, vanadium, tin,<br />
tungsten, asbestos, pozzolane, pyrite, and vermiculite. Most<br />
promising sites hosting rocks and industrial minerals are the
Industrial <strong>Mineral</strong>s 165<br />
Moyale graphite deposit (0.46 Mt), the Garibaldi Pass (Nazareth)<br />
pozzoline deposit, the Kenticha area for high-quality quartz (0.26<br />
Mt) and the big fumaroles sulfur deposit of Chebret Ale (6.5 Mt of<br />
S) (EGS, 1989). Investigations have been made regarding several<br />
of these commodities, but little published information is available,<br />
and qmtity, quality and economic considerations have not been<br />
studied in any detail.<br />
Role of Iodustrlal <strong>Mineral</strong>s in the National Economy<br />
Worldwide it is estimated that sand, gravel, limestone, clay, sulfur,<br />
salt, and phosphate make up 90% of the total tonnage of all<br />
industrial minerals and rocks produced and 60% of total value. The<br />
widespread use of industrial minerals and rocks is in large part due<br />
to two characteristics of these materials. Firstly, the use of a single<br />
mineral in one production process often involves the use of several<br />
others. For example, the production of glass from silica sands may<br />
require the use of soda ash, limestone, dolomite, feldspar, borax,<br />
1 gypsum and fluorspar. Secondly, a single mineral or rock may<br />
form the basis for a large number of industries. A very good<br />
example is limestone which may be used in the construction,<br />
metallurgical, agricultural, and chemical industries. Lime, a<br />
product derived from limestone, is itself a raw material used in the<br />
production and processing of a myriad of products such as glass,<br />
steel, chemicals, paper, sugar, paint, water and food. Other major<br />
industries like chemicals, fertilizers, ceramics, and metallurgy<br />
depend on industrial minerals and rocks as a source of raw<br />
materials. Above all, these minerals and rocks provide the raw<br />
materials for infrastructure development in which large volumes of<br />
sand, gravel, clay, crushed and dimension stone are consumed.
Chapter 5<br />
Construction materials and dimension stones<br />
+<br />
Using stones as an ornamental material for beauty and durability in<br />
all kinds of construction dates back to the dawn of civilization<br />
Almost every variety of rock has been used as dimension stone, as<br />
the suitability of a particular stone for dimension stone is governed<br />
primarily by its physical properties m_d its specid appeal to<br />
humans. The ornamental dimension stone is becoming very<br />
popular for the basic reason that it renders a romantic beauty to the<br />
fascinating architects of modern buildings.<br />
Stone that is linished to specific dimension and shape is<br />
considered as dimension stone. Other stones, referred as building<br />
stones, me sold in either natural or broken sizes and shapes and are<br />
sorted into size ranges but not finished or dressed to specific<br />
n dimension. The term "dimension stone" is defined as naturally<br />
murring rock material cut, shaped or selected for use in blocks, I<br />
slabs, sheets or other construction units of specified shapes or sizes<br />
and used for external or interior parts of buildings, foundations,<br />
curving, paving, flogging, bridges, revetments, or other<br />
architectural or engineering purposes. The term is dso applied to<br />
quarry blocks from which piqep of fixed dimensions may be cut.<br />
Marble, granite, limesthe, md sandstone provided the bulk of<br />
dimension stone, although slate, diorite, basalt and diabase are<br />
included.<br />
The classification of dimension stone is not strictly adhered<br />
to sedimentary, igneous and metamorphic puping of geology, as<br />
the stone trade name under "granite" refers to all true granite and<br />
gabbro, norite, and syenite. Likewise all crystalline limestone,<br />
travertine, sandstone and serpentinite that are capable of taking a<br />
polish are grouped under marble in addition to the true marble. As<br />
the distribution of rocks is governed by geologic factors, the<br />
diverse geological environment of Ethiopia has ultimately formed
1 '<br />
".:-' 168 :@inaal .Reso~r&:PotmtinI 6f Ethiopia<br />
cdidrless aTp P wry .pn. a of @oi+<br />
whiih "is *-in ,a wide variq of idustries Finely pro<br />
pb6der is a con@pge.nt in paints, toothpaste; and p~astics;<br />
&n& can . also<br />
, -<br />
. be radw ugder high h d to cslciuni<br />
(a& kn'ovh as %&), which has many applications inc<br />
mg a primary compnqpt of most merits.<br />
Marbles are widespread in the bademat r&ks df Ethiopia, in<br />
particular the Pmterozoic calcmus schistg, Same of these have<br />
beem exploited by the cement industry and the Nafid Mhhg<br />
Company. The late Pmterozoi~ to early Pdaeomic marbles< pf the<br />
Tsalient and Tmbitn pups am known not to have complete<br />
mqsEallkWnmn .han$don of the parent limestone to<br />
die. PLU& rnriditjdm of -bib are very .ideal .for dimension<br />
stones and l$hey~w w&onlp~ found in northem -Ethiopia. These<br />
mcts +W 'biotb; ~ ~ s t iof c+ne s mi die, although<br />
ireftmdmmpsi~e hhk Jimstane, K e d l~imestone (800,m<br />
thic&),md &em ~li~estone ,(3QO n ck) ad commonly loccur in -<br />
Y<br />
r<br />
Ddjdepressj~n.~ , 1 ,<br />
4<br />
.<br />
miation with intmbwls of slate, mhfble./and dolomite. In this<br />
combdon, ' bi ~~&ilihm. formatidn, 'the youngest of the<br />
, btmzoic mck, (1,S0,0 m. tk~k). MC, 2003) consists of<br />
- mish -to white. dolomite. This unit h dso found txpd in the<br />
r 8<br />
13. the- hi-ry, of conshyctiorxt in Ethiopiq marble is th<br />
most ension ion stone. For instame, some of the Addis<br />
, Abba's;~oldip high gtmey, building% e. g. the, :National Bank ,of<br />
' EtBioph.were buiIt'afmwb1e:fur inmd and extnal application.<br />
The highly exclusive and- luxurious, ,five star hotels, Sheraton<br />
Addis, has been the most modern and recently built commercial<br />
I 'building in Addis A W. Thia hotel is the fi& building to have<br />
I
1 74 <strong>Mineral</strong> Reswrces <strong>Potential</strong> of Ethiopia<br />
crystals larger than the groundmass forming a rock known as<br />
porphyry. Wtes can be pink to dark grey or even black,<br />
depending on their chemistry and mineralogy. Occurrence of<br />
granite is currently known only on earth where it forms a major<br />
part of continental crust. Granik occurs m relatively small, less<br />
than 100 km2 stock-like misses and as large batholiths often<br />
associated with orogeaic mountain ranges ar;d is frequently of<br />
great extent. Small dikes of granitic composition called aplites are<br />
associated with granite margins. In some locations very coarsegrained<br />
pegmatite masses occur with granite.<br />
mite has been intruded into the crust of the earth during<br />
all geologic periods; much of it is of Precambrian age. Granite is<br />
widely distributed throughout the continental crust of the earth and<br />
is the most abundant h e n t rock that underlies the relatively<br />
thin sedimentary veneer of the continents. Despite being fiairly<br />
common throughout the world, the areas with the most commercial<br />
W t e quarries are located in the Scandinavian Peninsula (mostly<br />
in Finland and Norway), Spain (mostly in the Gdicia ma), Brazil,<br />
India and several countries in the South end of the Afiican<br />
continent, namely Angola, Namibia, Zimbabwe and South Africa.<br />
Origin<br />
Granite is an igneous rock and is formed from magma. Granite<br />
magma has many potential origi*ns, but it must intrude other rocks.<br />
Most granite intrusions are emplaced at depth within the crust,<br />
usually greater than 1.5 km and up to 50 km depth within thick<br />
continental crust. The origin of granite is contentious and has led to<br />
varied schemes of classification. Classification schemes are<br />
regional. There is a French scheme, a Bnu scheme and an<br />
*?<br />
American scheme. This confusion arises kcause the classification<br />
schemes define granite by different means. Generally the 'alphabet-<br />
soup' classification is used hause it classifies based on genesis or<br />
origin of the magma.
w;i;y<br />
Gems~ones and Semi-precious Stones 187<br />
to the surface by the basaltic magmas. Most of the world's<br />
emeralds are mined from low-grade carbonaceous schists in<br />
Colombia, South America. In Australia, emeralds occur within<br />
biqtite schists found in Western Australia, and within pegmatites in<br />
the New England region of New South Wales. Other gemstones<br />
which occur in metamorphic rocks include ioUte (the gemquality<br />
lilac-purple variety of cordierite), timite and kyanite. Jade is a<br />
term given to tough compact aggregates of two minerals, i.e.<br />
jadeite (a pyroxene) and nephrite (a term given to a group of<br />
amphibole minerals, not a minerd).<br />
Sedimentary deposit<br />
By far the most valuable gemstone formed in sedimentary<br />
envirqnments is precious opal. The largest deposits of this occur<br />
throughout central Australia in the far western New South Wales;<br />
muth-west Queensland; and central to northern South Australia in<br />
what is known as the Great Artesian Basin. Most of these opal<br />
deposits occur in fine-grained rocks of Cretaceous age.<br />
Placer deposit<br />
Because of their toughness and resistance to weatherin<br />
erosion, gemstones arerelativeli abundant in some placer deposits.<br />
Most of the sapphires from eastern Australia occur in placer t<br />
deposits where they have become concentrated by alluvial<br />
processes. Other important gemstones which commonly awur in<br />
placer-type deposits include diamond, zircon, topaz, ruby, garnet,<br />
agates and petrified wood.<br />
Gemstone deposits Io Ethiopia<br />
It is known that Ethiopia is endowed with suitable geol<br />
m<br />
environments to host all varities of gemstone, although not yet -., ,<br />
been well investigated in detail. Nevertheless, miner s o z-<br />
I
188 <strong>Mineral</strong> <strong>Resources</strong> Potentid of Ethiopia<br />
gemdtones (e.g. beryl, aquamarine, tourmaline, pet, spinel,<br />
top~z, chalcedony and agate, jasper, petrified wood, chrysoprase)<br />
are reported to occur in Sidamo (Kenticha, Kibre Mengist area),<br />
Harm (Babile, Jijiga: amethyst, garnet), and Tigray (Axum and<br />
Adwa area: amethyst, agate, chalcedony). Primary occurrences are<br />
related to pegmatite-granite rocks; the gravels of some of the major<br />
rivers of Ethiopia host some secondary alluvial occurrences.<br />
Besides, there are plentiful indications suggesting the presence of a<br />
variety of gemstones in Ethiopia, including ruby (Kibre Mengist),<br />
sapphire @ills area), emerald (Cheri, Fularia, Moyale), and<br />
diamond (Turmi, Moyale). Gemstone is, therefore, regarded as one<br />
of the rich mineral resources of the country, which deserves proper<br />
investigation.<br />
Artisanal and small-scale miners produced a variety of<br />
gemstones. Opal was found at Mezezo in Amhara Regional State;<br />
garnet, at Harshitmi; sapphire, at Bonga; aquamarine, at Chembi,<br />
Kenticha, and Kilkile; emerald, at Chembi; and peridot, at<br />
Chewbet, Gofa Gedo, Mega, Megado, and Tbsy. Other gemstones<br />
produd included amazonite, amethyst, quartz, and tourmaline. In<br />
fiscal year 2003-04, -the production of opal increased to 370 kg<br />
from 187 kg in fiscal year 2002-03; md garnet, to 1 1 kg from 6 kg.<br />
Presently there is a very widespread illegal transactions of<br />
gemstones largely smuggled out of Ethiogia. According to the<br />
<strong>Mineral</strong> Operation Department, the gemstones involved in illegal<br />
transactions include opal, bwyl, corunddum (ruby and sapphire),<br />
garnet, and peridot. It is also lemt that many gemstone bearers<br />
were not willing to locate where the gem came from. Therefore,<br />
this seems so crucial considering the urgent -need required to<br />
reduce illegal trading and smuggling out unprocessed gemstones,
6.1 Corundum (ruby and sapphire)<br />
Sapphire is the single-crystal form of aluminium oxide (A1203), a<br />
mineral known as corundum. It can be found naturally as<br />
gemstones or manufactured in large crystal bodes for a variety of<br />
applications. The corundum group consists of pure aluminium<br />
oxide. Trace amounts of other elements such as iron and chromium<br />
give sapphires their blue, red, yellow, pink, purple, orange or<br />
greenish color. Sapphire includes any gemstone quality varieties of<br />
the minerd corundum including the red variety, which is also<br />
known as ruby. Ruby is a red gemstone, a variety of the mined<br />
conmdum (aluminium oxide). The color is caused mainly by<br />
chromium. Its name comes hm ruber, Latin for red. Natural<br />
rubies are exceptionail y rare, but synthetic rubies (sometimes<br />
called created ruby) can be manufactured fairly cheaply. Other<br />
varieties of gemquality corundum are called sapphires. It is<br />
considered one of the four precious gems together with sapphire,<br />
the emerald and the diamond.<br />
Rubies are mined in Africa, Asia, Australia, and Greenland.<br />
They are most often found in Myanmar (Burma), Sri Lads<br />
Kenya. Madagascar, and Thailalld, but they have also been found<br />
in the U.S. states of Montana, North Carolina and South Carolina,<br />
The Mogok Valley in Myanmar has produced some of the finest<br />
rubies, but in recent years very few good rubies have been found<br />
there. In central Myanmar the area of Mong Hsu also produces<br />
rubies. The latest ruby deposit to Lx found in Myailmar is situated<br />
in Narn Ya. In 2002 rubies were found in the Waseges River area<br />
of Kenya. Rubies are being mined at Audilamena in northeastern<br />
Madagascar. Sometimes spinels are found dong with rubies in the<br />
same rocks and are mistaken for rubies. However, fine red spinels<br />
may approach the average ruby in value. Rubies have a hardness of<br />
9.0 on the Mohs scale of minerd hardness. Among the natural<br />
gems oqly diamond is harder.
- -<br />
.;>*F,-<br />
190 MInehl Resourns <strong>Potential</strong> of Ethlopi<br />
Ruby and sapphi w occurrencess in Ethiopia<br />
'<br />
Ruby gem is known to occur in southern Ethiopia (Kibre Mengist,<br />
and Dilla ldity) (Fig, 39, 40). The occurrences are associated<br />
with marble, gneiss and schists in the basement rock. Sapphire<br />
gems are reported to occur in Dilla area associated with volcanic<br />
rocks (bmlts). There is a great illegal market of ruby and sapphire<br />
gem in the country. Therefore, systematic exploration is required<br />
to assess the ruby and sapphire potential of the region.<br />
6.2 Opal<br />
The mineraloid opal is amorphous SiOz*nH20; hydrated silicon<br />
dioxide, the water content sometimes being as high as 20%. On the<br />
basis of the interplay of colour, opal ranges from colorless through<br />
white, milky blue, grey, red, yellow, green, brown' and black. The<br />
high vdk of precious opal is adversely &ected such. that it<br />
becomes lower when the contrast between the iridescent patches<br />
and the background colour is less pronounced. It has also lower<br />
value if the colour patches are less clearly defined, Opal is a<br />
mikraloid gel which is deposited at relatively low temperature.<br />
Opal is normally found in association with effusive magmatic rock<br />
deposited in cracks and cavities by aqueous fluid at low<br />
temperature. It may also be found in siliceous sandstone where<br />
hydrous silica has been precipitated perhaps due to strong<br />
alteration of feldspar by percolating water; and is most commonly<br />
found with limonite, sandstone, rhyolite, and halt.<br />
Opal deposits in Ethiopia<br />
Recently, opal was discovd at Yita ridge in the 'b enz Gishe<br />
district of Shewa province. The opal site is located about 140 km<br />
north-west of Addis Ababa The opal-behg rock is a nodular<br />
rhyolite which is ~iocene in age. This opal occm within the<br />
hyolitic rock overlain by thin ~orltinwus bands of 3 to 30 m thick<br />
L.
I<br />
1<br />
b<br />
Gemstones and Semi-precious Stones 191<br />
pitchstone (vitric tuff) of the Algae Formation. The territory where<br />
opal is found is quite vast, The concession areas cmot be kept<br />
under permanent surveillance. The opal is found as spherical or<br />
elliptical nodule with the gem opal resting inside, It is possible to<br />
find as many as eight nodule of opal within one square meter. A<br />
slowly cooled siliceous fluiaava upon differentiation when<br />
extruded the thin continuous rhyolitic horizon. The gem variety<br />
opal accounts for the formation of a densely scattered<br />
ellipticdsphere nodules. The gem field has been estimated to<br />
extend over an area of at least 7 x 7 km. The opal nodules average<br />
about 10 cm in diameter. Rock with opal nodules, particularly<br />
visible on the collapsed block, height of the level, 4m.<br />
Recently, an opal nodule weighing 4-5 kg has been found<br />
by local people (Fig. 41). The opal from northern Shewa shows the<br />
internal interplay of colours, xeGealing various base colours; clear,<br />
translucent white lavender, red or anger yellow-green and blue<br />
- wlours (Fig. 42, '43). Such quality of precious opal is exceeded<br />
only by the four principal and highly priced gemstones (diamond,<br />
emerald, ruby and sapphire). Contrary to Australian opals, the red<br />
ones are 'the most common and the blue ones the rarest. The highland<br />
inhabitants collect the nodules, which are for sale in the<br />
capital city later on, It is in the nature of things; but it is forbidden<br />
to non-natives. There are seven concessions, but only three of them<br />
are king exploited. The precious opal is currently mined by a<br />
private company in small-scale, at Mam in northern Shew<br />
Amham National Regional State. The precious opal mined in north<br />
Shewa is exported largely semi-processed nodules. However, it is<br />
recommended that precious opal be exported being cut, shaped wnd<br />
finished here within the country. Other occurrences of precious<br />
opal are reported in Warder, Ogaden, and Dire Dawa, and Me;<br />
thus it is believed to be available in many parts of tbe country.
1 92 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
63 Beryl<br />
The mineral beryl is a beryllium aluminium cyclosilicate with the<br />
chemical formula Be3Al2(SiO3b. Varieties of beryl have been<br />
.;considered gemstones since prehistoric times. Green beryl is called<br />
emerald, red beryl is bixbite or red emeraid or scarlet emerald; blue<br />
r-Beryl is aquamarine, pink bryl is rnorgmite, white beryl is<br />
goshenite, and a clear bright yellow beryl is called golden beryl.<br />
Other shades such as yellow-green for heliodos and honey yellow<br />
are common. Beryl is found most commonly in granitic<br />
pegmatites, but also occurs in mica schists. Massive beryl is a<br />
primary ore of the metal beryllium.<br />
Beryl occurrenaes in Ethiopia<br />
Beryl is reported to occur in Chembi village, located 35 km north<br />
of Kibre Mengist, Southern Ethiopia The area is underlain by<br />
' various gneisses, meta-sediments and intrusive. The intrusive rocks<br />
are represented by ultrabasic rocks, granite and pegmatites and are<br />
exposed along the Genale River and Ababa vaIIey. The pegmatites<br />
are 1-2 m thick and 200 m long. The granites and pepatites are<br />
course and often host e nite and substantial amount of garnets,<br />
spodurnene, green spinel, apatite, malachite and beryl. Gem quality<br />
of greenish to bluish has been identified in this locality (Fig. 44,<br />
45). In the pegmatite, a beryl cr&al as large as 4 cm long has been<br />
found. Aquamarine and white beryl, emerald, ammonite, topaz are<br />
found in Kenticha and are associated with pegmatites.<br />
6.4 Olivine (peridot)<br />
Peridot is the gem quality variety of forsterite olivine. The<br />
chemical composition of peridot is (Mg, Fe)2Si04. Peridot is<br />
found in Arizona, Hawaii, Nevada, and New Mexico, in the US,<br />
and in Australia, Brazil, China, Kenya, Mexico, Myanmar
Gemstones and Semi-~wious Stones 193<br />
@ma), Norway, Pakistan, South Africa, Sri Lanka, and<br />
Tanzania.<br />
Olivine deposits in Ethiopia<br />
The precious olivine, peridot, occurs in Mega, 720 km south of<br />
Addis Ababa. There are also a number of localities, nameiy Gofa,<br />
Gofa Gedo. Tassy, Megado and Chewbet, that bear the gem quality<br />
olivine (peridot) (Fig. 48). All the localities lie within 30 km radius<br />
from Mega town and are associated with thick basaltic flows<br />
characterized by poor-phyritic olivine-bearing basalt near volcanic<br />
cone. <strong>Potential</strong> areas of peridot bve been delineated by EMRDC at<br />
the localities of Bulgendo and Alabora enclosed with in dark grey<br />
olivine basalt. It is also interesting to note that the gem quaiity<br />
olivine occurs within large xenoliths of dunite and peridotite<br />
engulfed within the young yet olivine bearing trachitic basalt<br />
indicating the depth of formation and transportation which may be<br />
good indication for others such as diamond. A regional geologicd<br />
mapping and detail mapping in specific localities had been<br />
conducted in the area by EMRDC resulting in delineating potential<br />
areas for peridot at Bulgendo and Alabora. In Bulgendo the gem<br />
quality is enclosed within the dark grey olivine basalt, covering an<br />
area of 22 km2. The gem quality of the peridot in these localities<br />
are reported to be rated of high and medium with estimated reserve<br />
of 2457 kg (EMRDC, 1985).<br />
Six wmmon varieties of garnet are recognized based on their<br />
chemical composition. They are .pyrope, dmandine or arbuncle,<br />
spessartite, giossularite (varieties of which ate hessonites or<br />
cinnamon-stone and tsavorite), ,uvarovite and andradite, Gmets<br />
are most commonly red in color but can Be found in a variety of<br />
colors, including purple, red, orange, yellow, green, brown, black,
194 <strong>Mineral</strong> <strong>Resources</strong> htential of Ethimia<br />
or colourless. Garnets are very abundant in the lower crust and<br />
mantie and thus play an important role in geochemical<br />
understanding of the Earth. The garnet is the birthstone for<br />
January. It is a symbol of faith and trust and when given as a gift is<br />
a tolken of devotion and loyalty.<br />
Applications<br />
Pure crystals of garnet are used as gemstones. Garnet sand is a<br />
good abrasive and a common replacement for silica sand in sand<br />
blasting. Mixed with very high pressure water, garnet is used to cut<br />
steel and other materials in water jets. Pyrope varieties are used as<br />
kimberlite indicator minerals in diamond prospecting.<br />
Garnet occurrence3 in Ethiopia<br />
Deep red garnet (almandine) crystal is reported to occur in<br />
Harshitmi locality, about 20 krn east of Moyde town. The garnets<br />
are rlssociatd with high grade metamorphic rocks (quartzmuscovite<br />
schist). The crystals are up to 4 cm long (Fig. 49). Baya<br />
Corelli and Bow in southern Ethiopia are other localities where<br />
red garnet accurrence is reported. In these localities, dmandine<br />
garnet is present in the residual deposit derived from the<br />
underlying gn iss and schist. Garnet (almandine) occurs in large<br />
\<br />
quantities along the mica of the Carrara deposit to the east of the<br />
Harar-Jijiga road where small-scale operation by local inhabitants<br />
takes place. Baya Corelli in southern Ethiopia, is another locality<br />
where red garnet occurrence is reported. In this locality, almandine<br />
garnet is present in the residual deposit derived, from the<br />
underlying gneiss and schist. Similarly in Bonga deep red<br />
porphyroblatic garnet as large as 5 crn in diameter have been found<br />
within gmet-silIimanite gneiss. Garnet is made up 4040% of the<br />
rock mass and is considered as an important deposit for abrasive<br />
manufacturing. Other gamer occurrences are reported to occur in
Gemstones and hi-&ws Stones 195<br />
Babile (Harm) and Adols area. An occurrence of this gem quality<br />
gamet is well known by the local people in southem Ethiopia,<br />
6.6 Quartz<br />
The precious quartz crystals reveal various mlours. Amethyst, the<br />
clear purple or bluish violet variety, and rose q w rose-red or<br />
pink are found in Ethiopia (Fig. SO, 5 1, 52, 53). The colorless<br />
quartz, as o h is the case, is popularly known as rock crystal and<br />
used for mdhg cheap jewelry. It is also utilized to manuoptical<br />
glass. Although the source is not yet known, rose and >tke<br />
colokless quartz are illegally sold in the black 'market in Addis<br />
Ababrr.<br />
6.7 Diamond<br />
The occ~ces of diamond have been reported in Tmmi, Moyale<br />
area of the southern Ethiopia. The quality ad quantity is yet<br />
unknown, There is a great illegal market of diamond in the area by<br />
I d people. Therefore, systematic exploration is required to<br />
assess the diamond potential of the ~gion.
196 <strong>Mineral</strong> Podcntlal of Ethiopia
1 Gemstones and Semi-prmious Stones 197
198 Mined Remums Patential of Bthiopia
7.1 Fossil fuels<br />
Chapter 7<br />
Energy <strong>Resources</strong><br />
There are three major forms of fossil fuels; coal, oil and natural<br />
gas. All three were formed many hundreds of millions of years ago<br />
before the time of the dinosaurs -hence the name fossii fuels. The<br />
age they were formed is called the Carboniferous Period. It was<br />
part of the Pdeomic Era "Carboniferous" gets its name from<br />
carbon, the basic element in coal and other fossil fuels.<br />
The Carboniferous Period occurred from about 360 to 286<br />
million years ago. In that period, the land was coveflwith<br />
. swamps filled with huge trees, ferns and other large leafy plants. -<br />
The water and seas were filled with algae -the green stuff that<br />
forms on a stagnant pool of water. An algae is actually millions of<br />
very small plants.<br />
Some deposits of coal can be found during the time of the<br />
dinosaurs. For example, thin carbon layers can be found during the<br />
late Cretaceous Period (65 million years ago) -the time of<br />
Tyrannosaurus Rex. But the main deposits of fossil fuels are from<br />
the Carboniferous Period (MaCabe, 199 1). As the trees and plants<br />
died, they sank to the bottom of the swamps of oceans. They<br />
formed layers of a spongy material called peat. Over many<br />
hundreds of years, the peat was covered by sand and clay and other<br />
minerals, which 'turned into a type of rock called sedimentary.<br />
More and more rock piled on top of more rock, and it weighed<br />
more and more. It began to press down on the peat. The peat was<br />
squeezed and squeezed until the water came out of it and it<br />
e*ntually, over millions of years mimed into coal,. oil or<br />
petroleum, and natural gas.
200 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
7.1.1 Coal<br />
Coal is a naturally occurring combustible material consisting<br />
primarily of the element carbn, but with Iow percentages of solid,<br />
liquid, and gaseous hydrocarbs)ns and other materials, such as<br />
compounds of nitrogen and sulfur. Coal is usually classified into<br />
the sub-groups known as anthracite, bituminous, lignite, and peat.<br />
The physical, chemical, and other properties of coal vary<br />
considembly from sample to sample.<br />
Coal forms primarily from ancient plant material that<br />
accumulated in surface environments where the complete dscay of<br />
orgaaic matter was prevented, For example, a plant that died in a<br />
swampy area would quickly be covered with water, silt, sand, and<br />
other sediments. These materials prevented the plant debris from<br />
reacting with oxygen and decomposing to carbon dioxide and<br />
water, as would occur under normal circumstances. Instead,<br />
v b i c bacteria (bacteria that do not require oxygen to live)<br />
' . attacked the plant debris and converted it to simpler forms:<br />
primarily pure carbon and simple compounds<br />
hydrogen (hydroarbom). Because of the way it<br />
(along with petroleum and natural gas) is often<br />
fossil fkl. The initial stage of the decay of a<br />
woody material known as paf. In some parts of the world, peat is<br />
still co1Iected from boggy areas and used as a k l. It is not a good<br />
fuel, however, as it burns poorly and with a great deal of smoke.<br />
If peat is allowed to remain in the ground for long periods<br />
of time, it eventually becomes compacted as layers of sediment, as<br />
overburden, collect above it. The additional pressure and heat of<br />
the overburden gradually converts peat into mother form of coal<br />
known as lignite or brown coal. Continued compaction by<br />
overburden then converts lignite into bituminous (or soft) coal and<br />
finally anthracite (or hard) coal. Coal has been formed many times<br />
in the past, but most abundantly during the Carboniferous Age<br />
(hut 300 million years ago) and again during the Upper
Energy Kesoams 20 1<br />
CreWus Age (about 100 million years ago). Today, coal formed<br />
by these processes is often found in Iayers between layers of<br />
sedimentary rock. In some cases, the cod layers may lie at or very<br />
near the earth's surface. In other cases, they may be buried<br />
thousands pf feet ,of meters under ground. Cod seans range from<br />
no more than 3-1 97 A ( 140 m) or more in thickness. The location<br />
and confqpation of a coal seam determines the methud by which<br />
the coal will be mined.<br />
Cod is regarded as a non-renewable resource, meaning that<br />
it was fomed at times during the Earth's history, but significant<br />
amounts are no longer forming. Large supplies of coal are known<br />
to exist (proven reserves) or thought to be available (estimated<br />
resources) in North America, the fonner Soviet Union, and parts of<br />
Asia, especially China and India. According to the most recent data<br />
available, Chim produces the Cargest amount of coal each year,<br />
t about 22% of the world's total, with the United States 19%, the<br />
brmer members of the Soviet Union 16%, Germany 10% and<br />
' PoM 5% following. Chins is also thought to have the world's<br />
largest estimated resources of coal, as mu& as 46% of dil that<br />
exists. In the United States, the Iargest coal-producing states are<br />
Montana, North Dakota, Wyoming, Alaska, Tllinois, and Colorado<br />
(MaCabe, 1491).<br />
Cod is still used in industries such as paper production,<br />
cement and ceramic manuf&ture, iron and steel production, and<br />
chemical manuf~chm for heating and for steam generation,<br />
I<br />
Another use for coal is in the manufacture of coke. Coke is newly<br />
pure &n produced when soft coal is heated in the absence of<br />
air. A number of processes have been developed by which solid<br />
coal can be converted to a liquid or gaseous form for use ws a fie!.<br />
Conversion has a number of advantages. In a liquid or gaseous<br />
form, the fuel may be mier to transport, and the conversion<br />
process removes a number of impurities from the original cod
202 <strong>Mineral</strong> <strong>Resources</strong> Potmtial of Ethiogia<br />
(such as sulfur) that have environmental disadvantages. One of the<br />
conversion methods' is known as gasification. In gasification,<br />
crushed coal is reacted with steam and either air or pure oxygen.<br />
The coal is converted into a complex mixture of gaseous<br />
hydrocarbons with heat values ranging fiom 100 Btu to 1,000 Btu.<br />
One suggestion has been to construct gasification systems within a<br />
coal mine, making it much easier to remove the coal (in a gaseous<br />
I form) hm its origid seam.<br />
In the process of liquefaction, solid coal is converted to a<br />
petroleum-like liquid that can be used as a fuel for motor vehicles<br />
and other applications. On the one hand, both liquefaction and<br />
gasification are attractive technologies in the United States because<br />
of our very large coal resousccs. On the other hd, the wide<br />
availability of raw cod means that rmew technologies have been<br />
unable to compete ecunomically with the mtud product. During<br />
the last century, coal oil and coal gas were important sources of<br />
fuel for heating and lighting homes. However, with the advent of<br />
natural gas, coal distillates quickly became unppula~, &since they<br />
were somewhat smoky and foul-smelling.<br />
Types of coal<br />
As geological processes apply pressure to peai over time, it is<br />
transformed successively into:<br />
- Lignite also referred to as brawn coal, is the lowest rank of<br />
coal and used almost exclusively as fuel for stearn-electric<br />
power generation, Jet is a compact form of lignite that is<br />
sometimes polished and has been used as an ornamental<br />
stone since the Iron Age;<br />
- Sub-bituminous cod whose properties range fiom those of<br />
lignite to those of bituminous coal and are used primarily as<br />
fuel for stearn-electric power generation;<br />
- Bituminous coal, a dense coal, usually black, sometimes<br />
dark brown, often with well-defined bands of bright and
, m<br />
Enwgy <strong>Resources</strong> 203<br />
dull material; used primarily as fuel in steam-electric power<br />
generation, with substhial quantities also used for heat and<br />
power applicitions in manufacturing and to make coke;<br />
Anthracite, the highest rank, used primarily for residential<br />
and commercial space heating.<br />
Major coal producing regions<br />
China is the biggest producer of cod i~ &e world, while the United<br />
States and Russia contain the world's largest coal reserves. Europe<br />
Coal fields in South Wa(es, Yorkshire, other parts of the United<br />
Kingdom and Australia used to be major mining areas. .,. -',t ?.<br />
?.
' !<br />
I<br />
I<br />
: I'<br />
I I - ,<br />
'<br />
204 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
more energy-efficient way of using coal far eldcity production<br />
would be via solid-oxide fuel cells or molten-carbonate fuel cells<br />
(or any oxygen ion tramport based fuel cells that do not<br />
discriminate between fuels, as long as they consume oxygen),<br />
which' would be able to get 60%-85% combined efficiency (ditect<br />
electricity + waste heat steam turbine), compared to 3540%<br />
normally obtained with steam-ody turbines.<br />
Coal degasits in Ethiopia<br />
Geological Mng of coal dccumnc~~ of Ethiopia<br />
The coal occurrence of Ethiopia has been studied by several<br />
geologists and a number of reviiws, classifications and summaries<br />
have been published (Jelenc, 1966, Getaneh, 1985, Getaneh and<br />
Ssxena, 1984, Wolela, 1991,1995 and others). Most of the Ethiopian<br />
coals fall in the category of lignite. he& coal seams are f&<br />
associated and interbedded with the Cenozoic volcanics of the<br />
Northern Ethiopian F lateau. Some are associated with sediments that<br />
occur between the Mesozoic continental clastics and the Cenozoic<br />
volcanics, or sandwiched between the Precambrian hasement rocks<br />
and the Cenozoic volcanics (Getaneh, 1985, Getaneh and &err,<br />
1984). The lignite seams differ greatly both in their vertical<br />
thickness and lateral extent, and- the nature of their occurrence.<br />
Whereas some of them have relatively good lateral extension, the<br />
eeds about 1.4 m, though some may<br />
locally attain greater thicknesses. Table 10 lists the major lignite<br />
seams and the areas where they are found. According to Getaneh,<br />
199 1, depending upon their geological setting, the lignite deposits<br />
of Ethiopia can be broadly grouped into the following types:<br />
. 1. Inter-Trappean Lignite (Chilga Type);<br />
2. Infka-Trappem lignite (Arjo type);<br />
I, . . +<br />
--I<br />
4. I<br />
i'<br />
.
P<br />
. ,<br />
Ug&e (CbilgiType)<br />
hrw mrces 20s<br />
$ @::of iig&'te occmnce, of which Chilga is the best<br />
example,, is found as .fluvatile andlor lamtrine intercalations<br />
within the volcilllios (Tmp Series) of Northem Ethiopian<br />
Plateau Lignite seams of Delbi: Moye, Meteso, Lalo-Sapo, Debre<br />
~ i ~ o~hida, s , Beressa, Mush Vdley, Soyoma, Wda, Chida<br />
Ankober, Sululta, Kindo, Wuchalle, kie, Dills, Jiren, dl belong<br />
to this group and occur under similar geological settings to those st<br />
Chilga. The lignite bearing are characterized by the presence<br />
of vol~clasts irregularly alternating with wyhg thickness of<br />
carbonaceous shale's with thin lignite seams, and qresent<br />
deposition during the periods of quiescence in between the<br />
volcanic eruptions.<br />
d<br />
G-eneraW stratigraphy of the Inter-Trappean type lignite<br />
Cen'bmic-volcanic rocks' with intercalations of continental<br />
volcaniclasts and shales with lignite seams<br />
. I .<br />
Mesozoiic - contitid and marine sedimentary mks<br />
, .<br />
Thea deposits, as the name makes clear, always occur below the<br />
Cenozoic volcolnics (Tmp Series), between the Mesozoic<br />
continental clastia and volmics, generally intermed with<br />
sedimentary rocks. Such deposits are few compared with Inter-<br />
Trajpan type. Examples of this type of occurrence include Arjo,<br />
Diddessa and Hun& Blesuma.
206 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Wliopia<br />
Generalized stratigraphy of the Infra-Trappean type lignite<br />
Cenozoic-volcanic rocks<br />
Shales with lignite seams<br />
Mesozoic - continental clastic sedimentary rocks<br />
-. ' . " ,<br />
-. .' -. . +'.! ;:d&-;<br />
Nejo type lignite<br />
oj.:*- .&S<br />
,. These are found to occur between the Precambrian rocks and the<br />
Cenozoic vulcanik's (Trap Series). Some of them are not only<br />
covered by the vulcanite'si but also occur interbedded with them.<br />
Generalized stratigraphy of the Nejo type lignite<br />
Interbedded shales, mwls, sands and conglome<br />
with lignite seams<br />
Precambrian - basement mks
General characteristics of the coal deposits in Eth-<br />
Energy <strong>Resources</strong> 207<br />
Coal in general are assessed and classified on the basis of the<br />
amount of fixed carbon, percentage of volatile matter, ash content<br />
and calorific value. With favorable burial conditions (i.e. long<br />
periods of accumulation of vegetation, thick sediment cover, depth<br />
of burial, etc.) the deposits mature and there is a gradual increase<br />
in the fixed carbon content and other properties. Most of the<br />
Ethiopian coal, irrespective of their stratigraphic position and<br />
occurrence, fhll in the category of lignite that have been deposited<br />
under conditions lacking all these favorable factors and are,<br />
therefore, chmcbrkd by comp&atively low maturity and<br />
evolution (Getaneh, 1985, Wolela, 1991, 1995). Generally, they<br />
are thin bedded, less mature and with quite high mineral content.<br />
Consequently, most of the coal in general consists mainly of lignite<br />
that is of high ash content (2.4% to 65%), which fulfil the<br />
categories of soft coal, low fixed carbon (20% to 60.2%), low<br />
calorific values (range from 900 to 6,900 callkg) and average<br />
moisture and volatile content (fall under the categories of lignite to<br />
I medium-high volatile bituminous coal). However, there are coal<br />
seems having low ash contents and high calorific values (heating<br />
value) in the acceptable range for utilization in the energy sector.<br />
Since there are lignite with high calorific values (up to 6,400<br />
calkg) and low ash contents (e.g. as little as 1%) these could be<br />
blended with low calorific value and high ash-content lignite's to<br />
reach an optimum acceptable minimum (Getmeh and Saxena,<br />
1984). All these calls for a reassessment and =valuation of<br />
important lignite occurrences and W e d study of their economic<br />
I<br />
i<br />
I<br />
feasibility.
I<br />
208 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
Coal distribution in Ethiopia<br />
The following are descriptions of some of the better known<br />
deposits, some of which have received more attention in recent<br />
years.<br />
Yayu coal deposit (Illubabur)<br />
The Yayu area is located (8" 15'-8" 30'N and 35" 42L-36" 05' E).<br />
564 km from Addis Ababa along the Jima-Bedele-Gambella, or<br />
500 km along Nekemt-Bedele-GambeUa road. The sequence of<br />
coal and oil shale-bearing clastics is exposed around-Yap area in<br />
the eastern part of Geba River within the Geba Basin. Middle<br />
Oligocene to Early Miocene sediments are laying on a<br />
metamorphic basement floor with rernnants of older Tertiary<br />
basalts. The lithology of the succession comprises:' conglomerate,<br />
sandstone, siltstone, mudstone, oil shale, cod and tuff. The<br />
thickness of the coal seams ranges from 0.1 to 4 m. chemically;<br />
they are of high ash and medium sulfur content.<br />
Mush Valley coal depit<br />
Carbonaceous lignite deposit of the Mush Valley is situated 40 km<br />
from Debre Berhan in the direction of Dessie falling between the<br />
coordinates (9'45' 9" N and 3Y 40' 7" E). The lignite bearing<br />
sedimentary succession of Mush Valley area lie upon the Mio-<br />
Pliocene volcanic rocks of rhyolite composition. The Inter-<br />
Trappean sedimentary formatipn consists of an association of<br />
sandstones, sil tstones and shale's irreguIar1 y alternating with<br />
carbonaceous shale strata showing thin lignite seams. According to<br />
Getaneh, 1985, these rocks are as thick as 384 m, and are overlain<br />
by 134 m of tuff that occasionally interbedded with basalt and<br />
palaeosoils. Two coal bearing formations exposed at the banks of<br />
the Mush Valley (Babu and Getaneh, 1984) estimated the overall<br />
thickness of the two seams to be 1 m covering an area of 200,000<br />
sq m. This volcano-clastic sedimentary rocks crop out in the<br />
valleys of Mush River and its tributaries.
I<br />
I<br />
I<br />
t<br />
!<br />
a<br />
Five principal tmigenous rock types occur within the<br />
sections; sands and sandstones (20%), conglomerati~ siltstones<br />
(BOO! of the total sequ-) and gravely silt (9%), shale and'<br />
mudstones 66%) d carbonaceous shale and shale (5%). From the.<br />
natw and mode of murrence, the coal bearing stmta seems td be<br />
of fluvide origin deposited on the basalt substratum (Jelenc,,<br />
1966; Getmbh, 1'985; Wolela, 1991, 1995). Petrographical and<br />
chemical studies conducted by Babu eb al., 1980, revealed that the<br />
coal in Mush Valley has high moisture (19.3-2 1.34%) and ash<br />
content (52.1-54.2 % in hsh and 22.2% in dry), low carbon<br />
content (1.343.09 in fresh and 38,53 in dry) and low calorific<br />
value (3,82Q-4,020 cdkg in fresh and 4,552 W g in dry).<br />
Cbilga cod depodt (Gondrmr)<br />
The Chilga coal deposit is by f& the best known lignite deposit in<br />
Ethiopia It is situated northwest of Lake Tam (7'1 0'-T15'N and<br />
36O45'-36"55'E); not very fm from the capital of Gondar, and has<br />
' drawn artention since 1 93 0s. A total of 98 sq km was gedogically<br />
mapped by Heeman Wolfgang, Minye Behu and ~~leia in 1988.<br />
The area consists of Trap volcmics and sedimentmy rocks. The<br />
sedimentary sequence lies on a basaltic substratm which is<br />
Oligocene in age. The fluvial-lacustine coal bearing is mainly<br />
composled qf terrigenous clasts of (argillaceous and maceous<br />
maWs), orgamgenic deposits of cod ad mbmgillites. The<br />
thickness of the coal seams mge between 0.5-2.5 m.<br />
Delbi maat deposit (Ulubab~r)<br />
The Inter-Trappean fluvial-hdne coal and oil W e bearing<br />
sediment of Delbi is situated within the geogqhic coordinates 7'<br />
21 '-7" 24'N and 36" 5'-36" 53'E. Delbi is located 390 km southwest<br />
of Addis Abbq and 50 km south of Jimma. The Delbi cod<br />
and shale occurrence is one of the best studied coal deposit in<br />
Ethiopia using bore holes by Water well drilling project, 1983;<br />
Woleh er a]., 1991; Wolela et al., 1995; and others. The a m<br />
. .<br />
-<br />
- 4
2 10 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
consists of two major rock type!: Trap volcanies euid sedimentary<br />
rocks. The fluvid-lacustrine Delbi cod and oil shale-bring.<br />
formation is composed of mudstone, ~ ~ r ~ clay, o silt, u clay, s<br />
sand, sandstone, coal, organic shale and pyroclastic sediments. The<br />
thickness of the coal seam ranges 0.5-2.2 m. Petrographical and<br />
chemical studies conducted by the above authors revealed that the<br />
coal in Delbi has low moisture content (3.98-10.4%) and ash<br />
content 12.1-54.2 %) in fresh and 22.2% in dry), low carbon<br />
content (1,343.09 in fresh and 38.53 in dry) and low calorific<br />
value (4,000-5,000 cal/kg in fresh and 4,552 callkg in dry)<br />
(Wolela, 1 99 1 ).<br />
-<br />
Maye cod deposit (Illubabur)<br />
The Inter-Tappean continental fluvial-lacustrine sedimentary<br />
sequence of Moye is situated within the geographic coordinates 7" 1<br />
19'45" - 7' 24'7" N and 36' 48'21 " - 36" 5 1' E. It is located 59<br />
km southwest of Jimma and 14 km west of Delbi. Moye is one of<br />
the best studied coal deposit in Ethiopia by Wolela et a/., 1987; F;'7<br />
Assefa Aklilu et ul., 1987; ~inyk et al., 1988; Korean lignite<br />
exploration group, 1988. The area consists of volcanic kd I<br />
sedimentary rocks. The sediments are composed of mudstone,<br />
graded sandstone, sand y-bmcias conglomemte, carbonaceous<br />
4<br />
clay, coal and oi! shale. The volcanic rocks consist of basalt, tuff,<br />
pyroclastics and tuff breccias. The coal seams at Moye are grouped<br />
under humic coal (lignite-sub bituminous).<br />
Nejo-Meckeke coal deposit (Wollep)<br />
The fluvid-lacustrine lignite deposit of Nejo is located 9" 27'-9"<br />
33'N and 39" 19'-35" 29'E, 190 km west of the town of Nekemte.<br />
The area consists of three major lithological units: Precambrian :.-<br />
i ; c .<br />
c'-.*, 5 ..<br />
basement, pre-basaltic sediment and Trap volcanics. The basement $ :,: i, '<br />
consists of schist, phyllite, and metasediment, metavolcanic and . 13<br />
dioritic intrusion. The pre-basaltic sediment overlies the basement $ :<br />
- and cupped by trap vdcanite's. The sedimentary sequence<br />
6'4<br />
:: ,<br />
, x m , .<br />
*,*..<br />
&:,:<br />
" .
Enagy Resou- 2 1 1<br />
commenced with quartz conglomerate which fines to silty clay and<br />
changed to black carbomwous material. The coal seams attain<br />
maximum thickness of 1.2 m. The ash content ranges 19.7% to<br />
72.9%. The calorific value ranges 3,937-3274 cabkg (Woliela,<br />
1991).<br />
Wucbale awl deposit (Wollo)<br />
The Inter-Trappean cod bearing lacustrine sediments of Wuchale<br />
is located 62 km hrn Dessie along the Addis Ababa-Asrnara<br />
rod. The area belongs to the Central Plateau of Ethiopia which is<br />
largely covered by volcanic &s of trap series (olivine basalt,<br />
porphyritic pyroxene basalt), The Inter-Trappan coal bearing<br />
lac-e sedimentary sequence is composed of argillaceous shale<br />
and clay, menac8ous material (silty sand, sandy silt, sandstone),<br />
organogenic deposits of (carbonaceous shale, carbonaceous clay<br />
and cod seams). The sedimentary formation deposited on a<br />
basaltic substratum bounded by faulted block graben.<br />
Coal occurrences, mainly lignite vdetim are known to occur in<br />
m y areas in Ethiopia So far known lignite deposits are located<br />
in (Gonder, Wollega, Shewa, Ma, Wollo, Tigray and Ham):<br />
among these, occurrences with esti.nated cod reserves are found<br />
in: Yayu, Moye, Delbi (1llubabur); Chelga (Gonder, 1 9.7 Mt), Nejo<br />
(Wollega, 3 M), Wuchale (Wollo, 23 Mt) and Mush Valley<br />
(Shewa, 0.3 Mt) and are relatively extensive, The available data<br />
indicate that Yayu, Delbi and Moye coal deposits are more ,<br />
economical than other deposits in the country, with resources<br />
estimated at about 32 Mt, 20 Mi, and 40.5 Mt respectively (EGS,<br />
1989). Other coal occurrences where total resewes are not yet<br />
estimated are found in the lohities: Chida, Jiren, LalwSapo,<br />
Meteso, Sayoma (Illubabur); Ankober, She, Debre Berhm- Abo-<br />
Gedam, Debre Libanos, Muger, Mojo, Mojo-Anchano (Shewa);<br />
Arjo-Kolati, Arjo-Sembo-Nedo, Mendi, Nejo-Kersa, Neja-Koya,
212 Mind Resoufces <strong>Potential</strong> of Ethiopia<br />
Nejo-Mecheke (Wollega) and Kindo-Halale, Waka (Omo). Data<br />
regding these occurrences are just prelhhy obmaiions not<br />
based on systematic studies and mapping, an; with little<br />
information about their thicknkss depth extension, lateral<br />
extension and exploitable m e s .<br />
Table 10: Important coal deposits of Ethiopia
" ' le 1 ' Other cod (lignite) occurmnces of Ethiopia<br />
.*' I
2 14 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
Sayoina<br />
Sehui<br />
.. ? , . , , , 3 , , , , ,, ,, ? . . ' A : Prospwt j d ~ s i.-Stra!if~m t<br />
, ,, A A 1
I<br />
-<br />
7.13 Oil and gas<br />
Energy Reso- 21 5<br />
Natural wits of oil are most commonly found d e d with<br />
natwal gas (which is itself derived from the heating-up of the oil),<br />
salt water, and sometimes, sotid hydrocarbons. The process of.<br />
petroleurn formation involves several steps :<br />
Organic matter from organisms must be produced in<br />
great abundance.This organic matter must be buried<br />
rapidly before oxidation take place;<br />
Slow chemi-cd reactions -form the organic<br />
material into the hydrocarbons fourad in petroleum.<br />
As a result of compaction of the sediments containing the<br />
petroleum, the oil and natural gas are forced out and migrate into<br />
permeable rock. Migation is similar to groundwater flow.<br />
The petroleum must migrate into a reservoir rock<br />
that is in some way capped by impermeable rocks to<br />
prevent the petroleum from leaking out to the<br />
surface of the Earth. Such a geologic structure id<br />
called atrap.<br />
All of these processes must occur within a spific<br />
t range of tempem!mes and pmm.' If higher<br />
pressures and temperatures are encounted as a<br />
result of metarnprphism or igneous activity, the<br />
I<br />
petroleum will be broken down to other non-useful<br />
forms of hydrogen and carbon.<br />
&cause oil and natural gas have a low density they will<br />
migrate upwards through the Earth and accumulate in a reservoir<br />
only if a geologic structlrre is present to trap the &roleurn.<br />
'<br />
I<br />
Wlogic structures wherein impermeable rocks occur above the<br />
permeable reservoir rock are requid. The job of Wleum<br />
geologists searching for petroleurn moirs is to find conditions<br />
1 near the Earth's surface where such traps might occur.<br />
I
,<br />
2 t6 <strong>Mineral</strong> R m m <strong>Potential</strong> of Eihiopia<br />
Oil traps can be divided into those that form as a result of<br />
geologic structms like folds and fhults, called structural traps, and<br />
those that form as a result of stratigraphic relationships between<br />
rock units, called stratigraphic traps. 'If petroleum has migrated<br />
into a memoir formed by one of these traps,lt-is important to note<br />
that the petroleum, like groundwater, wiII occur in the pore spaces<br />
of the rock. Natural gas will occur above the oil, which in turn will<br />
overly water in the pore spaces of the reservoir. This occurs<br />
because the density of natural gas is lower than that of oil which in<br />
turn is lower than that of water.<br />
Oil recovery<br />
The process of ail recovery is essentially the proc,gs of getting oil<br />
from the places where oil exists in the ground (whether onshore or<br />
offshore) and into processing plants for rehing so that oil is<br />
suitable for industrial and residential purposes. The ways to<br />
recover oil through a conventional well-bore are known as<br />
p-y, wndary, and tertiary (enhanced), but some<br />
unconventional methads are dm becoming popular,<br />
Oil, which is usudly called crude oil in its most basic form,<br />
is a valuable fuel whose chemical makeup is a mixture of<br />
hydrocarbon fuels: kerosene, dissolved n W<br />
gas, naphtha, Iight<br />
and heavy heating oils, diesel fuel, tars, beme, bd gasoline. It is<br />
formed over millions of years by the action of heat and pressure on<br />
organic material buried deep within rock, and typically exists in<br />
combination with salt water, natural gas, and soil. Most of the<br />
world's oil comes h m huge, seemingly inexhaustible subterranean<br />
patches of p us, oi2-permeated rock. The oil is confined to a<br />
certain location, or "trap," by other layers of impermeable rock<br />
(usually types of shale) andlor faults.
Top petroleum-produchg countries<br />
Enerp <strong>Resources</strong> 2 1 7<br />
In order of the mount ( hls per day) produced in 2004) top<br />
petroleum producers are: Saudi Arabia, Russia, United States,<br />
hq Mexico, C U .Norway, Canada, Venezuela, United Arab<br />
Emirates, Kuwait, Nigeria, United Kingdom and Ira. Ordered by<br />
amount exported in 2Q03, top exporters are: Saudi Arabia, Russia,<br />
Norway, Iran, United Arab Emirates, Venezuela, Kuwait, Nigeria,<br />
Mexico, Algeria, and Libya.<br />
Oil and gas deposits in Ethiopia<br />
The most promising wreas where indicatiom of hydrocarbon have<br />
been found andlor sedimentary conditions are fhvomble for the<br />
existence of oil and natural gas includes five main basins; the<br />
Ogaden, the Gambella, the Ahy (Blue Nile), the Mekele and<br />
Southprn Rift Basins. Hydrocarbons (oil and gas) have been<br />
generated in Paleozoic (Bokh shale), Jwic (Urandab Formation)<br />
an& Cenozoic ~cks (WaW Fmnatioq) and the &entary<br />
~olurnn-8tfl~ounts over 5,000 m (Getaneh, 1985). Many reservoirs<br />
are known, bth in Jurassic particularly &&iddie and<br />
Upper H d e i<br />
formations, - consisting of grahtone-, packstone,<br />
bioclastic wackestone and dolomite beds and in pre-Jurassic clastic<br />
rocks (e.g. the Triassic Adigrat Sandstone and the late Paleozoic-<br />
early Mtsomic Calub Sandstone), consisting of quartzo-mnite-or<br />
feldspathic sandstone and mine shale beds. (Getmeh, 1985). The<br />
followings ar6 description of same of the .better known deposits,<br />
some of which hot received more attention in recent years.<br />
Tbe Oga&m Basin<br />
The Ogaden Basin is located in south-eastern part of the country<br />
and covers an are of over 350,000 km2 containing over 5,000 m<br />
thick sediments. The sediments are composed of non-marine to<br />
deepmarine &tics; thick shallow to deep-marine carbonates and<br />
evaporates (Ethiopian Ministry of Mine.8 md Energy, 1995). The
'<br />
2 18 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
most likely oil ,and gas source mks in the sedimentary sequence<br />
of the OgadekBasin are the BokR Shale and the Hamanlei and<br />
Uamdab Formations (Getaneh, 1985). The Bokh Shale comprises<br />
black shale, siltstone and silty sandstone with a few dolostone,<br />
coarse sandstone and conglomgate intercalations. Its thickness<br />
changes towards the NE h m 30 m to 690 m. Bokh Shale is<br />
thought to .represent a deltaic environment. The Hamanlei<br />
Fodon is a Wlow-marine to lagoonal and deltaic deposit that<br />
cqnsists of organic-rich carbonate and evapoks with subordinate<br />
shale and mdstone. The Uwandab Formation is interpreted to be<br />
a neritic deposit. All three formations, and specially the Bokh and<br />
Hmantei Formation, contain organic-rich clays, deposited in<br />
deltaic, neritic and estuarine environments. According to Getaneh,<br />
the three formations thw meet the general criterion that fine-<br />
grained sediments deposited in the above mentioned environments<br />
could be converted to source materials for oil and gas. The Permo-<br />
Triassic Formation of the Karoo System is known to contain<br />
mature to over mature shale source rock. Large gas discoveries in<br />
the Calub and Adigrat Sandstone reservoirs of eastern Ogaden owe<br />
their origin to the Bokh shale. The Jurassic carbonate particularly<br />
the Middle and Upper hanlei Formations which are composed<br />
of grainstone, packstone, bioclastic wackestone and dolomite beds<br />
have good reservoir.<br />
A total of 34 deep wells have .been drilled in the basin of<br />
which 10 are expiomtory, k5 are stratigraphic and 8 are<br />
development wells of the Calub Gas Condensate Field. As a results<br />
of the efforts of Ethiopian Ministry of Mines d Enqgy, a<br />
commercial gas condensate field have been discovered at Calub in<br />
the Ogaden Basin with enormous reserves estimated over two<br />
trillion cubic feet or 35 billion metric tons of gas (Ministry of<br />
Mhm anct Energy, 1995). At the end of 2005, Ethiopia was totally<br />
ependent upon imports to meet its demand for petroleum. Natural
Enew <strong>Resources</strong> 2 19<br />
gas resources in the Calub Field in the Ogaden Basin remained<br />
undeveloped. Small amounts of lignite were reportedly prduced.<br />
Petronas Carigali Overseas Shd. Bhd. of Malaysia explored<br />
for crude petroleum at Block G in the Gambella Basin. In August<br />
2005, the company was awarded three concessions in the Ogaden<br />
Basin. Wal-Wal and Wader covered 36,796 square kilometers<br />
(km); Kelafo, 30.61 1 krn2; and Genale, 25,571 krn2. Petronas<br />
planned to spend $15 million on exploration in the Ogaden Basin<br />
starting in 2006 (Ministry of Mines and Energy). In October 2005,<br />
Pexco ExpIoration of Malaysia was awarded a concession that<br />
covered 29,865 kmt at Abred and Ferfer in the Ogaden Basin.<br />
Pexco planned to spend $5 million on exploration over 4 years<br />
beginning in 2006. In October, 'Afar Exploration Company of the<br />
United States was negotiating with the Government over a<br />
concession and production-sharing agreement that covered 1 8,000<br />
km2 in northern Afar Regional State.<br />
The Cambetla Basin<br />
The Gambella area is the south-eastern extension of the Melut<br />
Basin where two discoveries (Adar and Yale, Sudan) have been<br />
found. The sediment thickness in the Gambella is estimated at 4.5<br />
to 5 km. The source interval for hydracarbons in Sudan Basins<br />
(including the Megulad Basin to the southwest) is Lower<br />
Cretaceous sediment consisting of predominantly of shale with<br />
subordinate sandstone. Upper Cretaceous fine to coarse-grained,<br />
moderately to.poorly sorted sandstone is the main reservoir rock in<br />
Gambella Currently, the Gambella area is under extensive<br />
investigation by Petronas Share Co. (Malaysia).<br />
The Abay Blue Nile Basin<br />
The ~bay'hsin, which covers a large area over the central northwestern<br />
Plateau, consists of a thick Mesozoic succession<br />
exceeding 1,600 m in thickness (Ministry of Mines and Energy,<br />
1995). Beds of marl, variegated shale and mudstone interbedded
a<br />
220 <strong>Mineral</strong> Rwurces <strong>Potential</strong> of Ethiopia<br />
with carbonates, and marl limestonecdornimted beds in the lower<br />
part of a thick limestone unii are potential some rocks in the<br />
Abay Basin. The most potentid reservoir rock in the Abay Blue<br />
Nile Basin is the Upper Sandstone which consists of fine to<br />
medium grained, friable, moderateIy to well-sorted sandstones,<br />
associated within beds of conglomerates and claystones. Laterally<br />
restricted oolitic-reefal limestone facies in the lower and upper-<br />
most parts of AnMo Formation and dolomite beds within the<br />
mudstone-dominated unit overlying the Antalo Pamation might<br />
also be considerd as potential intervals in the Mesozoic Sequence.<br />
The Adipt Sandstone remains a potential reservoir in the Blue<br />
Nile Basin with characteristics similar to those found in the<br />
Ogaden Basin,<br />
The Mekele b i n<br />
The Mekele Basin has an areal coverage of h ut 8,000 sq km in<br />
the northern part of the country. The thick Mesozoic sedimentary<br />
succession of the k in comprises sediments ranging from fluvial-<br />
lacustrine to deep marine origin. The whole sedimentary sequence<br />
reaches 2,000 m in thickness. The Upper Jurassic Agula Shale<br />
Formation, predominantly comprising of shale, rnarlstone and<br />
variegated clay beds (with limestone and gypsum interbeds) is<br />
presumed to have good source rock potential for hydrocarbon. The<br />
Agda Formation (Agula Shale) is thought to be correlative to the<br />
Madbi and put of the Ndh fmmations of the Yemen Gulf of Aden<br />
region. The tramgresive to braided-fluvid sandy Adigrat<br />
Formation, with a thickness ranging between 150 m to 600 m of<br />
medium- to course-grained, greyish-white to pink-red sandstone is<br />
a potential reservoir; as it is in the Ogaden and Blue Nile Basin.<br />
The Southern Rift Basin<br />
The Omo and Chew Bahir Basins lie within the broadly rifted zone<br />
of Southem Ethiopia bordering Northern Kenya. The possible<br />
existence of sediments of a Jurassic-Cretweous riR system
underneath the Tertiary rift strata is also possible. Organic-rich oil<br />
shale with an average oil yield of 8 lidton. occurs in a regionally<br />
WSW-ENE extending Tertiary basin in the northern part of the<br />
Southern Rift basins (Ethiopian Ministry of Mines and Energy.<br />
1995). Other basins are less explored and have scarce data with<br />
. respect to hydrocarbon potential. The whole Ogaden Basin (S-E<br />
Ethiopia) has both potential for oil and gas.<br />
\<br />
-<br />
Qwo 55 hqwdvo sadimsnEary bins ofEtbioph ((Etbpb of Mines<br />
7.1.3 Oil shale<br />
Oil shale is considered to l>e formed by the deposition of organic<br />
matter in lakes, lagoons and restricted estuarine areas swll as<br />
t ard 8neagy, 1995).
222 Mind <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
oxbow lakes and muskegs. Generally, oil shales are considered to<br />
Ix formed by accumulation of algai debris.<br />
Oil can be extracted from oil shale, but they must be heated<br />
to high enough temperatures to drive the oil out. Since this process<br />
quires a lot of energy, exploitation of oil shale is not currently<br />
cost-effective, but may become so as other sources of petroleum<br />
become depleted. Known deposits of oil shale are extensive,<br />
Unlike coal, oil shale does not necessarily require low mineral and<br />
ash content, as it is not used for burning, and mineral waste in oil<br />
liquefaction plants is easier to deal with. Eventually, and usually<br />
due to the initial onset of orogeny or other tectonic events, the<br />
algal swamp-forming environment is disrupted and oil shale<br />
accun~ulation<br />
ceases. Oil shale is known as 'rock that bums'.<br />
Oil shale occurrenm in Ethiopia<br />
Oil shale is said to occur in the south western P h u of the<br />
a country and between Lake Ziway and Lake Abyiata in the valleys<br />
of the Bulbul River and its tributaries. The fluvid-lacustrine oil<br />
shale bearing formations of Delbi, Mefeso, Lalo-Sapo, Solo,<br />
Soyoma, and Mojo-Anchema are an Inter-Trappean continental<br />
sedimentadon on the south western Plateau of Ethiopia. The<br />
deposits occur intercalated within Cenozoic volcanics. The oil<br />
shale is characterized by high ash contents, low calorific value and<br />
low fixed carbon. The Pelbi oil shale has a fixed carbon ranging<br />
from 27.6%83,0% and a calorific value r&iging from 58 1-6,165<br />
kcalkg. Recent drillidg data proved the presence of 1W120<br />
million tons of oil shale deposits at Delbi (Wolela, 199 1 ; 1995).<br />
No details are known for the Bulbul River deposits.<br />
7.2 <strong>Geothermal</strong> raources<br />
<strong>Geothermal</strong> energy resources result from complex geologic<br />
processes that lead to heat concentration at accessible depths. The<br />
different forms of gmthermd energy resources-hydmthed, hot
En- Resowlew ~3<br />
dry rock, geopressd, magma, and earth heat-all result from this<br />
concentration of earth's heat in discrete regions of the subsurface.<br />
Temperature within the earth increases with increasing depth.<br />
Highly viscous or partially molten rock at temperatures between<br />
650 to 1 ,2W°C is postulated to hist everywhere beneath the earth's<br />
surface at depth of 80 to 100 kms, and the temperature at the<br />
earth's center, nearly 6,400 kms deep, is estimatsd to k 4,000°C or<br />
higher. Heat flows constantly from its sources with the earth to<br />
the surface.<br />
Three sources of internal heat are most important; (I) Heat<br />
released hm decay of Murally radioactive elements; (2) heat of<br />
impact and compression released during the original formation of<br />
the earth by accretion of in-falling meteorites and (3) heat released<br />
fiom the sinking of abundant heavy metals (iron, nickel, and<br />
copper) as they descended to form the earth's core. An estimated<br />
45 to 85 % of the heat escaping from the earth originates from<br />
a radioactive decay of elements concentrated in the crust. The<br />
remainder results from slow cooling of the earth, with heat being<br />
brought up from the core by convection in the viscous made.<br />
The different forms of geothermal resources have different<br />
characteristics that are important to geothermal energy<br />
development:<br />
- Hydrothermal resources are steam or hot water reservoirs<br />
that can be tapped by WlIing to deliver heat to the surface<br />
for t hed use or generation of electricity. Technologies to<br />
tap hydrothermal resources are proven commercial<br />
processes. Dry steam resources are relatively rare;<br />
- Hot dry rock resources are defined as heat stored in largely<br />
impermeable. Access to these resources involves fhcturhg<br />
rock injecting cold water through one well, circulating it<br />
through the hot fractured rock, and drawing off the now<br />
hot water from another well. Since the current technologies
124 R.1 incral <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
-<br />
are entering a developmept phase, this is not a commercial<br />
process at this time;<br />
Geopressured resources consist of deeply buried brines at<br />
moderate temperature that contain dissolved methane.<br />
Three sources of energy are available: thermal,<br />
'<br />
I<br />
a mechanical, and chemical (methane gas). While<br />
I<br />
technologies are available to tap geoprwsured brines, they<br />
I<br />
I<br />
-<br />
are not currently economically competitive. No funds are<br />
currently being directed toward accessing these resources;<br />
Magma (molten rock) resources offer extremely hightemperature<br />
geothd opportunities, but existing<br />
technology does not allow recovery of heat from these<br />
-<br />
ra0UtT:es;<br />
M h heat itself can b used as the source and/or sink of<br />
heat for the operation of geothermal heat pumps-a proven<br />
technology.<br />
<strong>Geothermal</strong> -11- in Ethiopia<br />
<strong>Geothermal</strong> systems produce inexhaustible aatural steam in<br />
contrast to coal-fired plants or nuclear plants that generate steam<br />
by heating water in large boilers. The pressure of fast flowing<br />
water or steam released against the blades of a turbine rotates its<br />
shaft which is also connected to an electric generator. In the<br />
generation of electricity, mechanical energy is transformed into<br />
electrical energy, The transformertion makes use of the ability of a<br />
rnovi~lg magnet to induce electricity in a conducting wire.<br />
Basically, a magnet around which a copper wire is wound is<br />
attached to the shaft of a turbine. When the turbine rotates, the<br />
magnet is moved and electricity is induced (generated) in the wire.<br />
The electrical energy can be distributed to perform mechanical<br />
tasks, via suitable motors, such as pumping water for irrigation,<br />
drilling tunnets for roads, railroads, etc., and, of course, for<br />
producing light.
Y<br />
I<br />
<strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
htbemal explor6~tion and dwelopment in Ethiopia<br />
Ethiopia started longterm geothermal exploration undertaking in<br />
1969. Over the years, a good inventory of the possible resource<br />
areas has been built up and a number of the more important sites<br />
have been explored. Of these areas, about sixteen geothermal<br />
1 pros- areas are judged to have potentid for high temperatrire<br />
steam suited to electricity generation (Meseret et al., 2000). A<br />
much larger number are capable of being developed for non-<br />
electricity generation applicatiois in agriculture, agro-indw, etc.<br />
Exploration work peaked during the early to mid-1980s when<br />
exploration drilling was carried out at the Auto-Langano<br />
geothermal field. Eight exploratory wells were drilled, of which<br />
four are potentially productive. During the early 199Os, exploration<br />
drilling was also &ed out at Tendaho. Three deep and three<br />
shallow wells were drilled at the Tendaho geothermal field, and<br />
. proved the existence of high temperature and pressure fluid (EGS,<br />
1989). Based on the results of the investigations, Ethiopia could<br />
possibly generate more than 1,000 MW of electric power hxn<br />
geothermal resources alone. This is substantially in excess of its<br />
d requirement of around 700 MW hm all energy sources for<br />
current Inter-connected and Self Contained Systems (Mesera<br />
zF<br />
The followings are descriptions of the better known deposit<br />
hich has received more attention in recent years.<br />
lu to-Langano geothermal fleld<br />
he Aluto-hgano geothermal field is located on the oor of the<br />
thiopian Rift Valley about 200 km south-east of Addis Ahba.<br />
e Aluto volcanic complex "i a Quaternary volcanic center<br />
ted along the Wonji Fault Belt in the central sector of the MER.<br />
geology of this complex is relatively well-known from surface<br />
supplemented by data on the deep stratigraphy and<br />
from eight deep exploratory wells that were sunk to
R- 227<br />
depths ranging from 1,300 to 2,500111 by EGS. In the Alum-<br />
Langano geothermal field, eight deep exploratory wells were<br />
Med to a maximum depth of 2,500m Mmen 1981 and 1985,<br />
out of which four are potentially productive. The maximum<br />
memoir temperature encountered in the productive wells is about<br />
350°C. A feasibility study was conducted by an Italian fmn;<br />
Electro Consult, between 1983 and 1986 (BE, 1986). The study<br />
revesried tbat in the Aluto-Langmo, the capacity of the existing<br />
deep wells is close to 30 MWatt; the energy potential of the field is<br />
estimated between 10-20 Mwekm-3 for over 30 yews (EGS,<br />
1989). A 7.3 MW pilot geothermal plant was installed in 1999<br />
utilizing the exploration wells that had been drilled.
228 <strong>Mineral</strong> P O W of Ethiopia
!<br />
The M aha geothermal field<br />
Energy <strong>Resources</strong> 229<br />
The Ten- graben is found further north in the Afar depression.<br />
It is a NW-SE trending graben about 50 km wide and is the<br />
southem extension of the Afar active spreading zones where the<br />
active Erta Ale-Man& Hararo volcanic ranges are situated. At<br />
Tendaho, between 1993 and 1998, three deep (to a maximum depth<br />
of 2100 m) and three shallow explotatory wells (up to 500 m) were<br />
drilled that found a temperature of over 270°C. The capacity of the<br />
existing producing wells in Tendaho is about 5 MWatt (Aquater,<br />
1996).<br />
Corbetti geothermal prospect arq<br />
The Corbetti geothermd prospect area is located about 250 km<br />
south of Addis Ababa. Corbetti is a Holocene volcanic complex<br />
found in the central sector of the MER. The most abundant<br />
volcanic rocks are peralkaline pyroclastics (ijyimbrite and pumice)<br />
which are attribuFd to central-type eruptions with subsequent<br />
volcano-tectonic collapse. Corbetti is a silicic volcano system<br />
within f 2 km wide caldera that contains widespread thermal<br />
activity such as fumaroIes and steam vents. Detail geological,<br />
geochemical and geophysical investigations conducted in ~o&tti<br />
area indicated the presence of potential geothermal reservoirs with<br />
ternperatwe in excess of 250°C. Six temperature gradient wells<br />
have been drilled to depths ranging from 93- 178 m, A maximum<br />
temperature of 94°C was recorded,<br />
Abaya geothermal pmpect area<br />
Abaya is located on the northwest shore of Lake Abaya, about 400<br />
kms south by road from Addis Ababa, The Abaya prospect<br />
exhibits a widespread thermal activity mainly characterized by hot<br />
springs, haroles and dtered gmunds. Spring temperatms are as<br />
high as 96OC with a high flow rate. Integrated geoscientific studies
230 <strong>Mineral</strong> Rwurces <strong>Potential</strong> of mhiopia<br />
(geology, geochemistry and geophysics) have identified the<br />
existence of a potential geotha reservoir with temperature in<br />
excess of 2M°C (Ayele et al., 20021,<br />
Tulu MoyWemsa geothermal prospect area<br />
The area is characterized by volcanism dating from Recent (0.8-<br />
0.08 Ma) to historical times. The area is highly dfkcted by<br />
hydrothermal activity with the main hyhtheml mmifkstdon<br />
h g<br />
weak fumaroles, active steaming grounds (60-80°C) and<br />
altered grounds. The weakness of the hydrothermal manifestations<br />
is explained as being the result of the relatively high altitude of the<br />
prospect area and the considerable depth to the ground water table.<br />
Dofan geothermal prrwspect area<br />
The area is locat4 about 40 km distance from the high voltage<br />
substation in Awash town. T'he presence of several hydrothermal<br />
manifestations (fumaroles and hot springs) within the graben<br />
' together with an impervious cap needs to be regarded with high<br />
priority for further detail exploration and development.<br />
Fantale geotbed prospect area<br />
The Fantale geothermal prospect is characterized by recent summit<br />
caldera collapse felsic lava exbusions in the caldera floor and<br />
widespread of fumaroles activity suggesting the existence of s<br />
shallow magma chamber. Prospects of geothermal energy at<br />
recomahame level include Kone, Meteka, Dmab, Teo and Lwke<br />
Abe geothermal prospects.<br />
Prospects at mconnabanw Level (Kone, Meteka, Danab, Teo and<br />
L. Abhe geothermal pmpds)<br />
During the 1 980s, reconnaissance geological, geochemical and<br />
geophysical investigations had been conducted in these areas and<br />
revealed the existence of young volcanic features and active<br />
s& thermal manifestations. Me@a-md Teo hold promise for<br />
the discovery of economically exploitable g eothd resources at
1<br />
Energy <strong>Resources</strong> 231<br />
high temperature and warrant detailed surface investigation,<br />
followed by exploratory drilling.<br />
Current <strong>Geothermal</strong> Activities in Ethiopia<br />
b<br />
The status of on-going geothermal activities in the Geological<br />
Swey of Ethiopia (GSE) is: (i) Monitoring (geochemical and<br />
mervoir engineering) of the Tendaho geothermal field (Dubti); (ii)<br />
Detailed geologicd mapping, geochemical and geophysical studies<br />
of the Southern Afar area (e.g. Dofan and Fantale etc.); (iii)<br />
Collection of water samples for isotope, chemical and gas analysis<br />
hm surface geothermal manifestations mmd Main Ethiopian<br />
Rift, Southern Afar and Northern Afar regions.<br />
Detail integrated geoscientific studies of the Lakes District<br />
area, particularly in the Corbetti and in the southern Afar<br />
geothermal prospect areas of Tdu Moyffiedemsa have confirmed<br />
the existence of exploitable geothermal resource and delineated<br />
a target areas for further deep exploratory wells. Currently, detailed<br />
geological, gemhemid and geophysical studies are underway in<br />
the Dofan-Fantale geothermal prospect areas of the Southem Afar<br />
region. Other prospect areas of this region (Kone, Meteka, Teo,<br />
Danab and Abhe, etc.) and in the Northem Afar (Ddlol, etc.) are<br />
yet to be explored in detail.<br />
Future programs of geothermal exploration and<br />
I development shall be based on considerations of logistic and socio-<br />
I economic framework of each prospect. Therefore, each of the<br />
prospects is qualified with respect to the probability of having an<br />
I<br />
economically viable geothermal resource. Acoording to Mesat,<br />
p 1991, other than Aluto-Langanb and Tendaho geothermal fields,<br />
the following are a list of prospects in order of the level of<br />
exploration:<br />
- Advance exploration stage; Tulu-Moye, Gedemsa and<br />
Corbetti;<br />
- Detailed investigation Completed, Abaya;
232 Mind <strong>Resources</strong> Potentid of Ethiopia<br />
- Detailed investigation ongoing; Dofan and Fantale;<br />
- Reconnaissance stage; Kone, Meteka, Danab, Teo and<br />
Abhe.<br />
Energy is an important element in Ethiopia's development strategy,<br />
because it could be a source of foreign excbge and is a catalyst<br />
for industrial progress. Ethiopia has a diversity of modern energy<br />
sources (hydro, geothermal, solar, natural gas, etc.), but still relies<br />
on imported petroleum and petroleum products, Energy<br />
consumption in Ethiopia is made up of less than 1 % electricity,<br />
about 5.4% hydrocarbon fuels and the balance, traditional biomass<br />
fuels (EEPCO Data File). Currently, about 90% of the rural<br />
population still relies on traditional biomass fuel (wood) as their
238 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethimia<br />
Gordma, and hemetal prospects of volcanogenicvolcano<br />
sedimentary type (AbetseIo, Kata);<br />
- a northern domain (Tigray) extending northwards towards<br />
Erika, composed of several metamorphic metavolcanosedimentary<br />
belts and sub-belts, bounded by m&cuItramafc<br />
rocks, hosting gold and base-metal occurrences<br />
(e-g., Adi Zeresenay, Au).<br />
Significant metallic mineral sites l o w outside of these domains<br />
are rare, and include the Melka Arba iron deposit (basic intrusionrelated),<br />
the Chercher copper deposit (Red Bed type in Mesozoic<br />
sandstones) and the Edcafah manganese deposit (Plio-Pleistocene<br />
sediments of the D 4 depression).<br />
Industrial minerals and rock resources occur in more<br />
diversified geological environments, including the Proterozoic<br />
basement rocks, the Late Paleozoic to Mesozoic sediments and<br />
recent (~zoic) voIcanics and assooiated sediments. The<br />
occurrences of energy resources (oil, mtmd gas, coal, geothermal<br />
resources) are restricted to Phaneromic basin sediments and<br />
Cenozoic volcanism and rifting areas.<br />
The discovery of the primary gold deposit at Legadembi<br />
(Southern Ethiopia), which has mched a production stage, can be<br />
cited as the best example of the significance of systematic<br />
exploration conducted in the recent years. Furthermore, the recent<br />
discovery of eluvialdeluvial gold in western Tigray (Adi Daro,<br />
Asgede and Daro Techi) and fie Werri gold and base metals by<br />
Wemi Gold Project (NMIC); discoveries of gold and base-metals at<br />
1dities Gale Repwr, Awm, Epbo (Bden, Benishangd<br />
Gumuz) and Boseti locality (Adola); gold deposit at Okote (Dawa<br />
Digati area; currmtly under intensive exploration by bore holes) by<br />
Midroc Lega Dembi mineral exploration project; and base-metals<br />
(copper) and gold occurrences of WacRile and Gewle in Arero<br />
Womda, Borena zone (Southem Ethiopia) by the Ethiopian
Summary and concludons<br />
The aim of this book is to cumpile in one volume a digital<br />
geoscientific database with maps for geology and mineral and<br />
energy resources of the country. The book is comprehensive but<br />
general in its treatment of topics, and it is hoped that it will be of<br />
wide interest to both scholars and general public. This synthesis<br />
gives an up-- compilation of Ethiopian mineral resources<br />
(location, description) in their geologid context (metallic<br />
minerals, industrial minerals, construction and building materials,<br />
gemstones, and energy resources).<br />
The metamorphic metavolcano-sedimentmy belts and<br />
associated intnrsives belonging to various terrain of the Arabo-<br />
Nubian Shield, welded together during the East and West<br />
Gondwma collisional orogeny (Neopmteromic, 900-500 Ma), host<br />
.yarious metallic resources (precious, rare, base-and ferrousf~aloy<br />
metals). According to the repartition of these belts,<br />
regional distribution of metallic mind resources shows three<br />
distinct domains:<br />
- a southern domain, including the metamorphic<br />
metavolmo-sedimentary of the Adola and Kenticha belts;<br />
this domain hosts major primary gold deposits (e.g.<br />
Legadembi gold mine, Megado, Sakaro, Okote-Dwwa<br />
Digati), the main Ethiopian gold placer deposits (Adola), -<br />
the pegmatite-hosted Kenticha tatlute mine and the<br />
mndary laterite-related nickel deposits of the Adola<br />
district. Other isolated primary gold deposits under<br />
reconnaissance are known 200 km southwards, close to the<br />
Moyale town and the Kenyan border (e.g. Haramsam,<br />
Hasamte);<br />
- a wide western domain, following the Sudanese border;<br />
this domain can be subdivided into four belts, hosting<br />
'primary gold deposits (e.g. Dul, Oda-Godme), the Yubdo<br />
platinum deposit, the iron deposits of BiliKal, Chago,
<strong>Mineral</strong> Development Sh. Co are g d<br />
Summary and conclusions 239<br />
indicators of the mineral<br />
potential sf the country for gold, h-metals and other deposits.<br />
In this &, a wide range of mineral distribution in the<br />
basement d of the southern, western, and northern periphery of<br />
the country invites finma -mematic exploration walr to locate and<br />
deli- different minerd reso-. Furthermore, recent discovery<br />
of strong gold anomalies in the Ethiopian Rifi in the localities of<br />
Tend&, Corbetti, Gedemsa and Aluto suggests the possibility for<br />
further potential economic mineral resources within the rift floor.<br />
A new field of investigation on epithermal ore occurrences which<br />
are unusual for the present Ethiopian metallogenic picture is<br />
emerging. A study of these phenomena, in light of recent<br />
acquisitions of metallogenic knowledge, could be of interest not<br />
only for further scientific studies but also for new possibilities in<br />
mining activity. The unique situation of the East African Rifts, not<br />
yet considered as a possible site for this kind of mineralization,<br />
'should be carefully tested. A fascinating field of mineral<br />
prospecting can be envisaged in these wide volcanic areas of<br />
Ethiopia and other East African countries. All these ment<br />
discoveries in different parts of the colmtry confirm that the<br />
metallogmy of Ethiopia has a significant and potential importance,<br />
greater than the small recorded mineral production wodd suggest,<br />
and justifies Wer work which will contribute to unraveling the<br />
complex geology of the country and its associated mineral potential.<br />
Following the above, the Adola area belongs to a me-<br />
metal metallogenic province, the only one so far known in the<br />
horn of Africa. However, this rich mineral wealth has not yet been<br />
fully explored and utilized. The pment knowledge about the<br />
Kenticha rare-metal belt is limited to a previous economic<br />
evaluation, which was largely based on preliminary geological<br />
approaches, Hence it is necessary to carry out a detailed<br />
investigation to understand the genetic aspects as well as the<br />
pattern of rare-metal enribkt for each area including the
@ G;' 240 Mind Resou- <strong>Potential</strong> of Ethiopia<br />
regional distribution of the tant&m min&dization. Development<br />
of exploration strategies and identification of reserves should be<br />
done on a continuing basis.<br />
It is known that Ethiopia is endowed with suitable<br />
geological environments to host all varieties of gemstone, although<br />
this has not yet been investigated in detail. Nevertheless,<br />
gemstones (e.g, beryl, stquamarine, tourmaline, garnet, spinel,<br />
tom chalcedony, agate, jasper, petrifa wood, chrysoprase) are<br />
reported to occur in Sidamo (Kenticha, Kibre Mengist area),<br />
Harrar (Babile, Jijiga: amethyst, garnet), and Tigray (Axum and<br />
Adwa area: amethyst, agate, chalcedony). There are plentiful<br />
indicators of the presence of a variety of gemstone deposits in the<br />
countq, including ruby (Kibre Mengist area), sapphire (Dilla<br />
area), emerald (Cheri, Fulana, Moyale), and diamond (Turmi,<br />
Moyale). Gemstones are, therefore, regarded as one of the rich<br />
mined resources of the country, though little is known about their<br />
occurrence. Therefore, systematic exploration is required to assess<br />
the gemstoms potenti J of the counEry.<br />
-<br />
presently, there is a very widespread illegal trade in<br />
gemstones which are being smuggled out of the country. The<br />
gemstones involved in illegal transactions include opal, beryl<br />
(emerald, aqdne), conmdm (ruby md -1, garnet,<br />
tourmaline, @te, @dot and even diamond. It is also known<br />
that numy smugglers were not willing to give any<br />
indication as to where the gem came from, which is crucial,<br />
considering the urgent requirement to reduce illegaI trading and<br />
smuggling of unprocessed gemstones, particularly opal, ruby,<br />
sapphire aquamarine and others.<br />
.Ethiopia posseses dl the requirements of a pehliferous I<br />
region. Hydrocarbons (oil a d natural gas) have been identified in -8~<br />
Paleozoic (bkh Shale), Jurassic (CJrandab Formation) and<br />
Cenozoic rocks (Habab Formation); and the sedimentary column<br />
mounts to ova 5,000 meters. Many reservoirs are known, both in @;<br />
,
Summary and conclusions 24 1<br />
&nates (Lower Hamanlei Formation), and clastic rocks<br />
(Adigmt Sandstone and Kalub Sandstone), and various types of<br />
traps are probably present. However, detailed s ubshe studies<br />
combined with geophysical methods are essential to further<br />
success in the discovery of commercial accumulations of<br />
hydrocartans in Ethiopia.<br />
The diversification of energy resumes is essential in order<br />
to ensure sustainable energy supply. Therefore, geothermal power<br />
needs to be developed to help' replace import of fossil fuel; to<br />
provide a major backup to ari uncertain availability of hydropower;<br />
and for use in arid and semi-arid anas of the country where<br />
hydropower is unavailable. Furthermore, emphasis should be<br />
p k d on exploitation of geothermal energy, afforestation of<br />
drainage basins, and improvement of agricultural methodologies.<br />
To conclude, most of the country's mineral mource<br />
occurrences have been examined by local wnd foreign geologists,<br />
but it would be premature to say that there are no further deposits<br />
of useful mineral resourca awaiting discovery, A comparatively<br />
small part of the country has been geologically mapped<br />
systemeltical1y. Geological maps at scales between 1:100,000 to<br />
1 :25,000 should be prepared for areas where mineral occurrences<br />
elre to be prospected for, and where known deposits are to be<br />
developed or exploited. S ystqatic organization of the available<br />
geological database is needed as well as the establishment of an<br />
easily accessible National Geological Data Bank (NGDB), which<br />
wodd aid the discovery of economic deposits within reasonable<br />
time-frame. The relevant authoritied institutions should put more<br />
investment to promoting the mi@ wealth of the country, as the<br />
minerals industry is a highrisk and capital-intensive sector that<br />
cannot be developed by local capacities.
References<br />
Abdelselam, M.G., Stm, R.J. (1997). Sutures and shear-zones in<br />
the Arabian-Nubian Shield. J Afr. Earth SCI: 23: 289-310.<br />
Abera, S. (1994). Review of Industrial <strong>Mineral</strong>s of Ethiopia AGID<br />
Report Series Geoscience in International Development, vol.<br />
18, pp. 173-1 80.<br />
. "The evaluation of Bikild Apatite-Magnetite-<br />
Ilmenite deposit with particular reference to apatite as a<br />
potential phosphate resource." M.Sc. thesis. (1988).<br />
University of Hull, UK.<br />
Abera S, Woldeab A, Assefa A, van Straaten, P. and Chesworth,<br />
W. "Report on the results of the Ethiopia-Canada<br />
Agrogeology Project-Igneous phosphates." Report to IDRC.<br />
(1 994). University of Guelph, Guelph, Canada.<br />
Alemayehu, Shearer, C.K., Papike, JJ and Laul, CJ. (1987).<br />
<strong>Mineral</strong>ogical and chemical Evolution of rare-element granitepegmatite<br />
system: Harney Peak Granite, Black Hills, South<br />
Dakota. Geo. Chem. Cosmchim. Acta 5 1 :473-456.<br />
Arkin, Y. "Potash in Ethiopia." Ministry of Mines, Geological<br />
Survey. Report ( 19691, Addis Ababa, Ethiopia.<br />
Anonymous (200 fa). Tantalum demand soars. Mjn. J 336 (8635):<br />
398.<br />
. (March 200 1 b). Africa, Ethiopia, Kenticha. T.I.C.<br />
Bulletin no. 105. p. 2.<br />
Assefa, A., Getahun, B. "Preliminary geological report on coal<br />
occurrences of Wuchale and Dessie area." Ministry of Mines<br />
and Energy. ( 1 987) Addis Ababa.<br />
Assefh, A., Wolela, A. "Report on lignite occurrences of Geterna,<br />
Aqo (Wollega)." Ministry of Mines and Energy. (1986).<br />
Addis Ababa. pp. 6 1 7.<br />
Assefa, A., (1991). Phosphate exploration in Ethiopia Feri. Res.<br />
301155-163.
'<br />
244 <strong>Mineral</strong> Rmrces <strong>Potential</strong> of Ethiopia<br />
Aquater. ( 1 996). Tenduho <strong>Geothermal</strong> project. Italian Minishy of<br />
Foreign Aflairs. vol. 1, Final report.<br />
Ayalew, T., Bell, K., Moore, J.M., Parish, R.R. (1990). U-Pb and<br />
RbSr geochemistry of the western Ethiopian Shield. Geol.<br />
Soc. Am. Bull. 102: 1309-1316.<br />
Bae, G.J., Minye, B., Getahun, B., WoIela, A., Yirga, T.,<br />
Asmamaw, T. "Report on geology and subsurface<br />
exploration for coal and oilshak occurrences at Delbi and<br />
surrounding area, Keffa administrative region." Ministry of<br />
Mines and Energy. ( 1989). Addis Ababa. pp. 1-65.<br />
Befekadu, B., Senbeto, C. "The marble deposits of Mai Dm,<br />
Filafil, Nohal Ebini and Adi Hatsiro localities, Northern<br />
Tigray, Ethiopia" WOR-EE marble and granite industry share<br />
company. (I 993).<br />
Belachew, T., Heeman, W. "Report on the lignite of Chilga area''<br />
Ministry of Mines. (1 984). Addis Ababa. pp. 1-65.<br />
Belete. K.H., Mogessie, A., Hoinkes, G., Hettinger, K. (2000).<br />
Platinum-group minerals and chrome-spinels in the Yubdo<br />
ultramafic rocks, western Ethiopia. J Afi Earth Sci. 30:<br />
1011.<br />
Beraki. W.H, Bonavia, F.F., Getachew, T., Schmerold, R. and<br />
Tarekegn, T. (1 989) The Adola fold and thrust belt, southern<br />
Ethiopia: a re-examination with implications for Pan-African<br />
evolution. Geol. Mag. V. 126: 647-657.<br />
Beyene, A. and Abdebalam, M.G. 2005. Tectonics of the Afar<br />
Depression: A review. Jour. Afr. Earth Sci. 41 (2005): 41-<br />
59.<br />
Boccaletti, M., Bonini, M., Mazzuoli, R., Abebe, B., Piccardi, L.<br />
and Tortorici. L. (1998). Quaternary oblique extensional<br />
tectonics in the Ethiopian Rift (Horn of Africa).<br />
Tec~onophysics 2 87: 97- 1 1 6.<br />
t3uccaletti M.. Mazzuoli, R., Bonini, M., Trua, T. and Abebe, B.<br />
l c19c) ). Plio-Quaternary Volcano tectonic activity in the
!J ;<br />
northem sector of the MER: relationships with Oblique<br />
J. Afr. Emth Sel., 29: 679-698.<br />
Bosellini, A, 1989, The continental margins of Somalia: their<br />
structural evolution and sequence stratigraphy. Mem Sci.<br />
Geol., 101: 373458.<br />
Boyle, RW. (1979). The Geochemistry of gold anb its deposits.<br />
Geol. Surv. of Can. Bull. pp. 280 - 584.<br />
. (1987). Gold: History and Genesis of deposits.<br />
Geol. Surv. WCm. Ottawa: Untario, Canah. p. 676<br />
Cmy, P. (1989). Characteristics of pegmatite deposits of tantalum.<br />
In: Lanthanides, Tantalum and Niobium, pp. 195-239,<br />
(Moeller, Cerny and Saupe, eds). Springer Verb.<br />
Clark, A.M.S. (1 978). Chemical and mineralogical development of<br />
the Sidamo nickliferous serpentinites (Ethiopia). Miner.<br />
Deposira 13:221-234.<br />
Cottard, F., AWulhay, G.J., Mgnan, D., G-elot, J.L., Roubichou,<br />
Ph, Trinquard, R, Vadala, P. (1993). The A1 Bajar gold<br />
deposit (Kingdom of Saudi Arabia): a newly-discovered<br />
example of supergene enrichment fKIm a massive sulfide<br />
deposit of Late Proterozoicage. Chron. Rech. Min. 5 10: 1 3--<br />
24.<br />
Cottard, F,, Braux, C., Cortial, Ph., Deschamps, Y., El Samani, Y.,<br />
Hottin, A.M., Ornar Younis, M. (1986) Lu .ma sulfures<br />
polymetdliqu~s et les mindisations aurifaes du d i d<br />
%I i d'Ariab (Red Sea Hills, Soudan): Historique de la<br />
dacouverte, cadre geologique et principaux caracteres des<br />
gisements. Chrom Reek. Miw, 483: 19 - 40.<br />
Di Paola, G.M. (1972). Geology of the Corbetti. caldera area (Main<br />
Ethiopian Rift). Bull. Volcan. 35 (2): 497 - 506.<br />
Duval Corporation, USA. (1969). Yubdo evaluation report. In:<br />
Fields, E. D. (Ed). WolZegu Province. Ethiopia4<br />
Edwads, R. and Alkinsoa, K. .(1986). Ore Deposit geology.<br />
London: Chapman and Hwll.
246 <strong>Mineral</strong> hurces <strong>Potential</strong> of Ethio~ia<br />
Electroconsult (ELC) (1 986). Geothemral &ploration Project-<br />
Ethiopian Laks District EEPCO Data file: Edhibpian Electric<br />
Paver Corporation m a File fiploitation of LmgamAluta<br />
Geotheml <strong>Resources</strong>. Feasibility report. ELC, Milano,<br />
Italy.<br />
Ethiopim M iid Resowces Development Corporation (EMRDC).<br />
"Results of geological prospecting and exploration<br />
forprimmy gold in the Bedakaa, upper Bore and kga ,+:<br />
Dembi area.'" 1985). t:<br />
Ethiopian Ministry of Mines and Energy. "Petroleum potential of 1 ~1. ':I ii .!<br />
Ethiopia." Petroleum Operation Department. (1995). -.. I<br />
--P '<br />
Ethiopian Institute of Geological Survey (EIGS), ''Genedid ,-<br />
geological and mineral occurrences of Ethiopia." Ministry of i;:f :- f<br />
Mines and Energy. (1989). :I$ $8 , '.-5-<br />
Evans, A.M. (1993). Ore Geology and Industrial minerals-An :' . , ,<br />
introduction. Blackwell Scientflc publications. Oxford.<br />
$;:<br />
I Fentaw, H.M., Mengistu, T. (19981, Comparison of Bombowha :-..<br />
:I 'r<br />
and Kombelcha kaolins of Ethiopia. J. Appl. Clay Sci. 13: .. -<br />
149-164, :F<br />
;<br />
I<br />
, (2000). The kyanite deposit of Chembi, Ethiopia.<br />
t<br />
!I<br />
Chrort. Rech. Min, 540: 47 - 52, - 44.: - I<br />
I-<br />
Fentaw, H.M,, Mohammed, S. (1999), Geology arad economic<br />
;y ;<br />
aspect of the MoyuIe graphite deposit: Ethio-Norwegian<br />
Report. 99402, EIGS, Addis Ababa. F'T fe ;:i A:,<br />
Gebreab, W., Yohes, E. wnd L.W. Giorgis, (1 992) The Lega 8 -<br />
Dembi gold mine: an example of &ear zone-hosted in .<br />
mineralization in the Adola greenstone belt, southern #' ;.<br />
I<br />
:$,A<br />
Ethiopia. J Afi. h f h Sci. Y, 1 5: 489-500,<br />
. -42<br />
Gebreab, W. (1992) The geological evolution of the Ado% :$-<br />
Precambrian gemstone belt, qiouthern Ethiopia. J A@. Earth<br />
Sci., V. 14: 457+69.<br />
::,& * _<br />
Germ, S. (2000). A short intduction to the geology<br />
+'<br />
of Ethiopia.<br />
Chon Rech Mia 540: 3-10.
Getaneh, A,, Saxena, G.N. (1 984). A review of Ethiopian lignite<br />
occurrences, prospects and possibilities. Energy Explop:<br />
PEE) 3 (1): 3642.<br />
Getaneh, A. (1985). The mineral industry of Ethiopia: Present<br />
conditions and future prospts. Joarrn. A@. Earth Sci. 3 (3):<br />
33 1-345.<br />
. (1 991). Lithostratigraphy and environment of<br />
deposition of the Late Jurassic Early Cretaceous sequence<br />
of the central part of north-western plateau, Ethiopia. Njb.<br />
Paluent. Abh. 182 (3): 255-284.<br />
Gebre, W.M. "Construction raw materials in Ethiopia: A surnmaty<br />
from previous works. EIGS," <strong>Mineral</strong> Exploration<br />
Department. (1 99 1 ).<br />
Gianneli, G. and Meseret Teklemmnism. (1993). Water-rock -5<br />
interaction processes in the Aluto-Langano geothermal field<br />
(Ethiopia). Jour. Volcano. petherm. Rese. 56: 429 - 445.<br />
, Gichile, S. (1992), Granulites in the Precambrian basement of<br />
southern Ethiopia: Geochemistry, P-T conditions of<br />
metamorphism and tectonic setting. J Afr. Earth Sci. 15 (2):<br />
251-263.<br />
.<br />
>. .-, :,2<br />
r< > -:<br />
3;. -7<br />
.Gilevich, A.L. (1980). Report on exploration and mines . ,.;<br />
- ,.<br />
development operations at ~ubdo platinum deposits, . .<br />
Wollega, Ethiopia, Geological survey, Addis Ababa, ,- . . + -t<br />
Ethiopia . , , , . . ,<br />
Goossens, P.J. (2000), Chronique africaine: Egypte, Lybie . ,, '<br />
Erythree, Ethiopie, Somalie, Djibouti. Les Techniques de !4i: ,$<br />
1 'Indusfrie Minerule, suppl. au no. 8. :. 3<br />
Guilbert, J.M. and Parks, C.F.Jr. (1986). The geology of ore !?.: - :? .;<br />
deposits. New York: Dreeman. 1, ., -. ; r:<br />
Guatnab, H. (1997). A brief ptmgraphicstudy of Moyale graphite. . .<br />
Now. Geol. SWV. Report 97 - 005.<br />
i; , . ,.<br />
Gummv, L., Asefa, A., "An evaluation of cement raw materials or ,; , -,<br />
the 5th cement plant. EIGS." (1981) Addis Ababa.<br />
:. . . d .<br />
. F', ;r . '2<br />
.- !,:.=!<br />
-.<<br />
+-
248 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
Hofmmm, C., Courtillot, V., Feraud, G., Rochette, P., Yirgu, G,,<br />
Ketefo, E., Pik, R, (1997). Timing of the Ethiopian flood<br />
h l t 3 12 event and implications for plume birth and global<br />
change, Name 389: 83 8-84 1.<br />
Holwerda, JOG. and Hutchinan, R W. (1 968). Potash-bearing<br />
evaporites in the Danakil area, Ethiopia. Econ. Geol. 63:124-<br />
150.<br />
Hutchison, C.S. (1983). EEommic Deposits and their tectonic<br />
setting. Wiley: New York.<br />
Jelenc, D. A. (1 966). <strong>Mineral</strong> Occurrences of Ethiopia. Ministry of<br />
Mines and Energy. Addis Ahba .<br />
Karmin, V. "Geology of Ethiopia: Explanatory Note to the<br />
Geological Map of Ethiopik" Scale 1 :2,000,000. (1 972).<br />
UNDP.<br />
. (1975). The Fkcambrian of Ethiopia and some<br />
aspects of the geology of the Momnbique belt. Bull.<br />
Geophys. Obs. 1 5:27-43. Addis Ababa.<br />
b i n , V., Shifmw, A,, Balcha, T. (1978). The Ethiopian<br />
Ebement: Stratigraphy and possible manner of evolution.<br />
Geol. Rdsch. 67: 53 1-546.<br />
Kitachew, W,T., Tesfhye, B. "Report on lignite occurrences near<br />
Debre Birhan." Ministry of Mines and Energy, (1979).<br />
' Addls Ababa. pp. 1-4.<br />
Knot, W and Abera, S , "Report on diatomite elnd bentonite clay on<br />
Gidicho Island, Lake ~bah." EIGS. (1 983). Addis Ababa.<br />
Ledru, P., Milesi, J.P., Johan, V., Sabat-e, P., Maluski, H. (1997).<br />
Foreland basins and gold-bearing conglomerates: a new<br />
model for the Jacobina Basin (S-ao Francisco province,<br />
Brazil). Precambrian Res. 86: 155-1 76.<br />
Mdish, E., Dejene, G, "The Dalleti marble deposit." EIGS. (1 983).<br />
Addis Ababa.
hkC~ux, E., Milk&, J.P.) (1993). Lead isotope sipahre of Early<br />
proterazoic om deposit in Westem Africa: comparison with<br />
gold deposits in French Guiana. Ewn Geol, 88: 1 862-1 879.<br />
McCth, PJ. (1991). Gsology of coal: Environment' of<br />
deposition. In Gluskoter, H.J., Rice, D.D. aed Taylor, RB.<br />
(&I, Ecommic Geology, US. Vol, p-2 of the geology of<br />
North America, 469-482. Cieo. Soc. Amer., Boulder:<br />
Colorado,<br />
Mcvey, H, (1989). hdustrial <strong>Mineral</strong>s-cm we live without<br />
them? Indwz@*ul <strong>Mineral</strong>s, 259; 745.<br />
Mengktu, T. fcFE+ldOn on bentoniticc lay in hmghe and<br />
Wollo administrative repiom.'' EIGS. (1 987). Addis Abaha.<br />
Me@* T., S.,'Tthtiiw, H.M., Esuyawkal, T., Tadele, EL,<br />
%Uidh, H.~.;\wall;"H,, Te"sfaye, I., Masnmo, W, Mcka, T.<br />
"Wsment of cement riw riiatwials in the munding of<br />
' ~~&le to&dk~1€3fl. (1-993). Addis Abah<br />
: Mmgik~, T' Fentaw, H.M. (1993). "ECaolin resources of<br />
-&'a. granites near Kombelcha, eastern Hararghe."<br />
EIGS. (19931, Addis A h .<br />
. (1 994). Natw an&-economic potentid ofkombelcha<br />
@ih?opia) kaolin. In: Proc. 2nd S E G i<br />
Int. C O Karachi, ~ .-<br />
pp. 2&29. -.<br />
. (2000). The industrial mineral and rock resource<br />
r. htential of Ethiopia Chn. Rech. Min. 540: 3 34. .. :<br />
- Ma&t Teklemarim, Amdebah, Y., Beyene, K, and<br />
Gebreegziabheir, 2. (2000). G e d d Exploration and<br />
Development in Ethiopia. Proceedings in the World.<br />
<strong>Geothermal</strong> Congress, WGC 2000, Kyushu, Tohaku, Japau.<br />
.Milesi, J.P., Ledm, P., Feybesse, J.L., Dommanget, A., Marcoux,<br />
'<br />
E. (1992). Early Proterozbic ore deposits and tectonics of the<br />
Birimim orogenicblt. Precambrian Res. 58: 305-344.<br />
I +<br />
>. ,-,<br />
, - 0.<br />
8 m<br />
.<br />
:.._<br />
1.<br />
'I , -<br />
. .<br />
-;H'. .<br />
, ,.:!<br />
--' <<br />
- 8<br />
t' -<br />
I . ' .<br />
, . -<br />
. . , A'<br />
:i<br />
. <<br />
,.-<br />
. -<br />
I.. I . , . .<br />
. ..*:<br />
?J-,<br />
w<br />
3
250 Minml <strong>Resources</strong> <strong>Potential</strong> of Ethiowia<br />
Million, H.M. (1989). Diatomite exploration in the Main Ethiopian<br />
Rift. In: 2nd World Cdngr, on Non-Metallic Mnerds.<br />
Beijing, China. pp. 5M2.<br />
iny ye, B., Daniel, H.s., ~eselm, T. "~eport on coal occurrences of<br />
Debre Lebanos." Ministry of Mines and Energy. (1985)<br />
Addis Ababa. pp. 3-1 1.<br />
Mogessie, A,, Belete, K.H. (2000). Platinum and gold<br />
mineralization in the Yubdo mafic-ultmdic rocks, western<br />
Ethiopia: historical perspective and some new results. C h.<br />
Rech Mjn. 540: 53-62.<br />
Mohr, P. A. (1 963). The geoIo&v of Ethiopia. Haile Selassie I Univ.<br />
Addis Abah<br />
Mohr, P., Zanettin, B. (1 988). The Ethiopian flood W t province.<br />
In: MacDougall, J.D. (Ed.). Continental Flood Basu~~s.<br />
Kluwer Acad. Publ, pp. 63-1 10,<br />
Mumpton, F.A. (1984). Natural zeolites. In: Pond, W.G. and<br />
Mumpton, F.A. (eds.) Zeo-agricuiture: Use of natural<br />
zeolites in agriculture and caquacul~e. Westview Press<br />
Boulder: Colorado. 247-254.<br />
National Mining Co.PLC. (2003). Dimension stones for a<br />
sustainable economic devtdopment of Ethiopia: Proceeding<br />
of ihe fourth EGMEA Congress. Dec. 19-2 1, 2003. Addis<br />
Ababa, pi '<br />
;
-= 251<br />
Reinhardt, P., Sisay, D. "Evaluation of lignite occurrences in<br />
Ethiopia." VEB Geologischc Forschung and Erkundug.<br />
(1 98 1). Halle: Germany.<br />
Rogers, R.J. and Brown, F.H. (1979). Authigenic mitridatite from<br />
the Shungura Formation, southwestern Ethiopia. Am.<br />
<strong>Mineral</strong>ogist 64: 1 69- 1 7 1.<br />
Sabov, Y .V., Mohammed, S., Walle, H. "Bombowha blin and<br />
Kenticha feldspar, quartz deposits," EIGS, (1983). Addis<br />
Ababa.<br />
Schlede, H. "Distribution of acid soils and liming miterials in<br />
Ethiopia," Ethiopian Institute of Geological Surveys. (1989).<br />
Note 36.<br />
Selassie, M.G., Reimold, W,U, (20001, A review of the<br />
polymetallic mineral resource potential of Ethiopa. Chron,<br />
Rech. Min. 540: 1 1-32.<br />
Shackleton, R.M. (1994). Review of the Late Proterozoic sutures,<br />
ophiolitic melanges and tectonics of Eastern Egypt and<br />
.NorthernSudm.Gesl~undschau83:537-546.<br />
Shkleton, R.M. (1996). ?'he final collision zone between East<br />
and West Gondwana. 5. Afr. Earth Sci, 23 : 27 1-287.<br />
Sheldon, RP. "Phosphate resource potential of Ethiopia based on<br />
available geologic data." Unpubl. Rep. UNlDTCD ETW83-<br />
025. (1984). UN: New York.<br />
Stem, R.J. (1994). Arc assembly and continental collisions in the<br />
Neoprotmzoic East African Orogen: Tmplication for the<br />
consideration of Gondwanolland. Anrn Rev. Earlh Planet. Sei.<br />
23: 319-351.<br />
Solomon K., (1986). "Results of temperature gradient swey and<br />
geophysical review of Corbetti geothermal prospect." (1 986).<br />
EIGS .<br />
Solomon T., Fiori M., and Valera R. (1 988). <strong>Mineral</strong> paragenesis<br />
in the Au-AkCu-Zn- Pb-Te deposit of Legadembi.<br />
Bicentennial Gold 88. Melbourne.
252 <strong>Mineral</strong> Potentid of Ethiopia<br />
Solomon T., Russo, A., Fantozzi, P.L. (1 997) Geological map of<br />
Mekide Outlier. Sheet: 1: 100,000. Italian Cooperation-<br />
Addis Ababa University.<br />
Solomon T,, Alfonso Bosellhi, Antonio Russo, and Getaneh<br />
Assefa. (1997). The Mesozoic succession of the Mekele<br />
outlier (Ti gray Province, Ethiopia). Estrutto da Memorie Di<br />
Scieme Geologiche. Vol. 49.<br />
Solomon T., (1 9981, Structure of Pegmatitic bodies of the Kenticha<br />
deposit, Adola gold field, southern Ethiopia. Africa<br />
Geoscience Review, vol. 5. no. 4, pp. 527-532.<br />
. (2000). The ~nvibnmental Impact of The <strong>Mineral</strong><br />
Mining Industry of Ethiopia: The state of Development and<br />
related problem, Environmental Policy in Mining: corporate<br />
Strategy and Planning for Closure. A contribution to<br />
published book. ISBN 1 -56670-365-4. Editors (A1 yson<br />
Wanrrst and Eigia Noronha). Pp. 4 15-422.<br />
. (2000). The effect of Artid Mining in Ethiopia-<br />
froceedings of Workshops of Intergovernmental<br />
Oceanographic Coxnmission. WorRskop report no. 165.<br />
UNES_CO.<br />
-1<br />
(2000). Genesis of the shear zone-related gold vein<br />
minMization of the Legadembi Primary Gold Deposit<br />
(Adola goldfield, Southern Ethiopia). Gud'wma Research:<br />
Jwnal of International Geoscience, Japan, vol 7, no 2: p.<br />
481-488.<br />
. (1999). Geology andgoid mineralization in the Pan-<br />
African rocks of Southern Ethiopia. ~ournul Gondwana<br />
Research: J o d of International Geosclefice. Japan,<br />
volume 2, no 3: Pp. 43947.<br />
. (2000). origin of the LRga Dembi primary gold<br />
deposit, Adola gold field, southem Ethiopia. Afica Geosci.<br />
Rev, 7 (1): 83-90.
254 <strong>Mineral</strong> Resouroes <strong>Potential</strong> of Ethiopia<br />
Walle, H. "Major dimension stone potential of Ethiopia" EIGS.<br />
(1996). Addis Ababa.<br />
deab A., Assefa A., Yematawork A,, Abera S., Van Straaten<br />
P., Groenevelt, P. and CheswortR, W- Report on the results of<br />
the Ethiopia-Canada Agrogeology Project Rock Mulch. . .<br />
!I<br />
Report." University of Guelph. (1 994). Guelph Canada.<br />
Woldegabriel, G., Aronson, J.L., Walter, R.C. (1990). Geology,<br />
l7 geochemistry, and rift basin development in the mtral sector<br />
Main Ethiopian Rift. Geol. Soc. Am Bull, 102: 439-<br />
Wolela, A. "Highlights on cod and oilshale occurrences of<br />
Ethiopia (catalogue)." Ministry of Mines and Energy. (1 89 1).<br />
Addis Ababa. pp. 67, 14-1 88.<br />
. "Significant coaI deposits and their economical and<br />
mining possibilities in Ethiopia" Ministry of Mines<br />
Energy. (1992). Addis Ababa. pp. 1-47.<br />
. (1 995)- An overview of the geographical distribution,<br />
geological setting and chemical characteristics of Ethiopian<br />
coals. SNET: Ethiopian J Ski 1 8: 27-29.<br />
Wolfe, J.A. (1 984). <strong>Mineral</strong> resources; a World review. Lon<br />
Chapman and HA.<br />
ku, H. (1993). Structural geology and tectonic setting of<br />
Adola Belt (southern Ethiopia). Zn: U, Thorweihe md H.<br />
Schandelmeier (Eds.). Geoscierace Research in Northemi<br />
ica Balkema: Rotterdam, pp. 139-144.<br />
H. and Yifa, K. (1992). The tectonic evolution of the<br />
Precambrian metamorphic rocks of the Adola Belt (southern<br />
Ethiopia). J Afi. Earth Sci., V. 14: 37-55.<br />
ku, H. (1996). Structural control and metamorphic setting of<br />
the shear zone-related Au vein mineralization of the Adola<br />
Belt (southern Ethiopia) and its tectono-genetic dev<br />
Jowt oJA&F Egr&Sci.%.V.23 No. 3: 383-409.<br />
L-' r j ..&L;jg.Tdt:svn ++~=;,J:~@+#~~<br />
;g ~ 3 ~ q ~ , r ~<br />
3<br />
. b- -;3&? =- w<br />
w<br />
f'q*<br />
rL xL,
Rtfmnces 255<br />
Worku, H and Schandelmeier, M. (19%). Tectonic evolution of the<br />
Neoproterozoic AdoIa belt of southern Ethiopia: Evidence for<br />
a Wilson Cycle process and implications for oblique plate<br />
collision. Precmbrian Res: V. 77: 179-2 1 0.<br />
Yahns, R.N., (1982). The study of pegmatites Econ. Ged, 5Oh<br />
Anniv. vol. pp. 230-248.<br />
Yohannes, W.W. (1994). Ethiopia. Mining Annual Review.<br />
Mining JoaffnaI Ltd London p. I 43.<br />
Zanettin, B. (1993), On the evolution of the Eth~op~an volcaruc<br />
province. In: Geology and <strong>Mineral</strong> <strong>Resources</strong> ofSomdiu and<br />
Stirrotding Regions. Ist. Agron. Oltremare, Firenze, Relm<br />
E Mo~gogr. V. 1 1 3: 279-3 10.
Annex 1. Major mineral deposits of Ethiopia (A, B & C Class)
258 <strong>Mineral</strong> kurces P o t d of Ethiopia
260 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia
262 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
' Annex 2. Minor mineral deposits of Ethiopia (Class D, E, NIA)-<br />
I NAME I IDENTIF. I SUBSTANCE I CLASS I X-LO~ I Y-L*~ I<br />
Arero Town I ETH-00028 I U I E 1 38.80- 1 4.70<br />
Wadera ETH-00030 u, I'Ph E 36.35 5 67<br />
Sun~ppa ETH-00031 U E 38-35 5.17<br />
- Sernbaba ETH-00032 U E 38.85 5.85<br />
ppp --<br />
: helm ETH-00033 U E 35.35 f.35<br />
Harm ETH-00036 Nb, Th,U A 42.01 9.35 .<br />
Wellega ETH-00038 Fe D 35.11 8 71
I<br />
1<br />
NAME<br />
Afa (Dabw Insin)<br />
Ahtu<br />
Aflata placer (Au)<br />
AM8 - b wa<br />
A & m m<br />
Agheremarism (Au)<br />
IDENTIP.<br />
ETH-00229<br />
ETH-00230<br />
ETH-0023 I<br />
-<br />
ErHd0233<br />
ETH-ooull<br />
ETH-00235<br />
SUBSTANCE<br />
Alanp 1 mH40242 1 Au I NIA ] 35.09 1 6.80<br />
A0<br />
Pb<br />
Au<br />
All<br />
Tlc, Asb<br />
A% cn<br />
' C W<br />
AWa<br />
ETH44236 An NIA 34.41<br />
A h ETH.oM37 Ft MA 35.36 ----a<br />
ITH-MDD Au, Cu D 33.21<br />
AkOb (a)<br />
ETH60239 1 AuCu.Pb, Zn<br />
Alaltu I ETH-OOZ41 I Au 1 D 1 3 5 3 1 9.51<br />
Alfe (Birbirl basin<br />
Ankh<br />
As8edo<br />
Aslwliim<br />
b k Akendayu<br />
-<br />
ETH-OLI244<br />
ETH-46<br />
ETH-aO247<br />
ETH-00250<br />
ETH4025 1<br />
NIA<br />
NIA<br />
N/A<br />
N/A<br />
WA<br />
NIA<br />
%&<br />
3839<br />
NIA I 35.22 1 5.99<br />
Awata Terrace 1 ETH-OD254 I Au 1 E 1 38.82 1 5.%<br />
Babik - Bob<br />
hda knwda<br />
I'WI~U<br />
AU<br />
Fel d<br />
Cu<br />
Au<br />
l3II40255 Au NrA<br />
kmwo I ETH40256 I Ti I MIA<br />
Bnlr<br />
m<br />
Bam<br />
Bedakesna<br />
: - p l - ,,, L-. .;<br />
I<br />
Belawch<br />
Bdet w~rm<br />
ETH40251<br />
ETH-00258<br />
nli-00159<br />
EM-00261<br />
ETHm162<br />
ETHm63<br />
ETH-00267<br />
ETH-<br />
ETHm-<br />
- . ..4$%~3?Xi$:;.<br />
i ,- : ,*,. t&., :' .- -!4&,-.;. - - i,: L-i * -L. . Y.>, , ; 0.. .g. : ', -.<br />
Au<br />
Au<br />
** ~Cu.Co.<br />
W<br />
Ni<br />
Au<br />
Au<br />
Au<br />
Pah<br />
E<br />
WA<br />
NIA<br />
NIA<br />
NIA<br />
D<br />
NlA<br />
WA<br />
WA<br />
E<br />
NIA<br />
E<br />
NIA<br />
MIA<br />
3825<br />
35.44<br />
39.67<br />
M.29<br />
38-13<br />
Annex 263<br />
5.23<br />
5.23<br />
5.55<br />
10.00<br />
9.07<br />
6.46<br />
k.99<br />
9.59<br />
14.41<br />
14.07<br />
34.43 10.49<br />
35.62<br />
34.36<br />
33QI<br />
/<br />
38s'<br />
34.41<br />
4,8t<br />
11.02<br />
9.69<br />
8.25<br />
5.8 1<br />
lo.%<br />
4.98
266 Miml b u m <strong>Potential</strong> qfj Ethippia , .<br />
NAY E IDEWnP. ' SUaffAMCC ClAS. ~ih Y-M<br />
Ebircha - Okde 5+08<br />
El Sod l3H-00368 Au NIA 3&40 4.20<br />
E k ~r~00369 Say NIA 41.81 . 3.14<br />
Eloda Gamm ETH-00371 Salt Plla 39.56 14.23<br />
Eaidio (Ft) ETH-00372 M MA 39.12 1423<br />
E~iticl~o (BM) . ETH.00373 Fe NIA 39.15 14.48<br />
Eniclo{Cu) - li3lMO374 BM WA 38.% 14.24<br />
--<br />
Entoto ETH-73 s Cu NIA 38.77 8.97<br />
Erm Rim 1 ETH-376 I Ft<br />
ETH - X-35<br />
Fena Mah!o ETH-00381<br />
Gq~wnr - Fm403tf Few, SIC E 38.80 536<br />
Galsdi 1 ETH-00388 ! Au NIA 1 46.28 I 6.82<br />
-ti ETH40- Pen I3 40.79 &58<br />
Gaktli Valley (Cy NI, Co) ETH403W hl I D 10.92 4.07<br />
Wmi Vnlky (FBI ETHWI Cn,Ni,Co 'NIA 41.14 9.01<br />
Gmbeln Mournin ETH-00392 Fe NIA 34.41 10.66<br />
Gambo ETl.00393 Au NIA 35.51 9,SO
Gaada<br />
GLidmol<br />
a i i 2<br />
Gbimira bkn<br />
Gima '<br />
Ell-MMOS<br />
lillwM07<br />
ETH.00408<br />
E T M<br />
ETH-OQIO<br />
GmAu<br />
Salt<br />
G&NI ,<br />
ETH.OWI 1 P#r NIA<br />
Oddare<br />
E'tH-00412 U<br />
E ------<br />
Oodioho<br />
ETH4M13<br />
Au NIA<br />
Goma (EM) 1 ETH-00414<br />
Gm<br />
-<br />
n G,uba (Mrbl)<br />
ETH-004 17<br />
G&a (Fe) ETH-004 19<br />
Ouk ETH-23<br />
Au<br />
3~ '<br />
GwdPma (Au) I ETH-00418 I Au I NIA 1 35.54 1 8.96<br />
Gudba Valley<br />
ETH90424<br />
Fa<br />
SdI<br />
NIA<br />
NIA<br />
NIA<br />
WA<br />
All<br />
E 35.54 8.77 ----<br />
35.28 10.27<br />
Fa<br />
Mrbl<br />
NIA<br />
41-44<br />
35.31<br />
35.21<br />
%at<br />
AU E 38-87<br />
Oudubsa 1 ETH-00425 I Be I A 1 38.12 1 5.36<br />
Fe<br />
NIA<br />
D<br />
N/A<br />
NIA<br />
36.74<br />
41.93<br />
35-17<br />
37.76<br />
35.69<br />
37.27<br />
636<br />
9-15<br />
632<br />
7.02<br />
7.5 1<br />
864<br />
1.43<br />
6.22<br />
8.8<br />
3.74<br />
7.59<br />
38.89 5.68<br />
An NIA 40.09 5.66
268 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
Hiniali<br />
Hocdu<br />
Hola bridge<br />
NAME<br />
IDEATIF.<br />
~$~-00441<br />
ETH-004.12<br />
ETH-00443<br />
SUBSTANCE<br />
Hala - Kuni I ETH-00444 I Mrbl, Do1 I D 1 42.20 ] 9.10<br />
Hunk-Blesnma 1 ETH-00115 I Coal I N/A 1 41.48 1 9.52<br />
Ijabuna I ETtI-00446 I Pb,Cu ( NIA 1 41.88 9.56<br />
Imei<br />
Jaja Valley (Cu)<br />
ETH-0044 7<br />
ETH-OW8<br />
Jaj- Valley (Gr) 1 ETH-00419 I Gr NIA 1 38.70 1 9.05<br />
Jibota I ETH-00450 I Au I E 1 34.05 1 5.83<br />
Jire~i<br />
Kajimiti I<br />
Kajimiii 2<br />
Kalamis<br />
Katawicha<br />
Kebre Me~~gist (ClyC)<br />
Kebre Me~~~ist (Coal)<br />
Kelecha<br />
Kenticha (Fc)<br />
ETH-00451<br />
ETH40454<br />
F.TH-00455<br />
ETH-00.156<br />
ETH404M<br />
ETH-00466<br />
ETH-00467<br />
ETH-00468<br />
ETH-00469<br />
Cu<br />
Salt<br />
Silc<br />
Salt<br />
Cu<br />
Coal<br />
Au. Zn. Co<br />
Au, Zn, Cu<br />
CLASS<br />
NIA<br />
NIA<br />
NIA<br />
NIA<br />
NIA<br />
X-Lon<br />
41.49<br />
39.38<br />
41.1 1<br />
41.17<br />
41.15<br />
k'-Lat<br />
Korkoro ] ETH40483 I Au. Pb, A& W I E 1 38.88 1 5.71<br />
Kumtidu I ETH-00485 I Au I NIA 1 38.90 1 5.70<br />
Kunni<br />
Kunni Valley (CL Ni, Co)<br />
Kun~ii Valley (Gr, Dol)<br />
ETH4048G<br />
ETH-00487<br />
ETH-00488<br />
Salt<br />
Ni<br />
C1$+ Silc, Mica-<br />
I<br />
Coal<br />
Au<br />
Fe<br />
NlA<br />
NIA<br />
D<br />
NIA<br />
NIA<br />
N(A<br />
NtA<br />
E<br />
N/A<br />
38.76<br />
38.81<br />
41.40<br />
35.01<br />
38.88<br />
38.84<br />
38.84<br />
39.18<br />
-----<br />
Fe<br />
Cy Ni, Co<br />
Gr, Do1<br />
NIA<br />
D<br />
N!A<br />
35.49<br />
14.43<br />
5.62<br />
4.80<br />
6.56<br />
9.20<br />
7.70<br />
5.59<br />
5.49<br />
6.55<br />
5 29<br />
5.75<br />
5.90<br />
5.90<br />
5.19<br />
40.94 8.94<br />
40.84 9.06<br />
80.79 8.74
- -<br />
NAME IDEhTlF. SUBSTANCE<br />
Lake nbrOg (GTH)<br />
Id8 Giulieh<br />
L~P hH<br />
Lega Dima t<br />
Le Dima 2<br />
, LegaG-2<br />
WGwhe I<br />
ETH4W489<br />
ETH-004W<br />
ETH40500<br />
ETH-WIO<br />
ETH-005 14<br />
ETH9M 15<br />
ETH.005 16<br />
ETH4D5 17<br />
GTH<br />
Au<br />
Au<br />
CLASS<br />
Likt ETH905 19 Ft NIA 37 -29 1.49<br />
Maji I ETH-OM23 ) ClyC I NIA ) 35.10 ] 6.54<br />
Salt<br />
NIA<br />
NIA<br />
NIA<br />
NIA<br />
35.51<br />
38.86<br />
Lena Gaa 1 ETH-WS!S I Au I NIA 1 38.83 1 5-37<br />
Malca Ho~na<br />
Maldu-.4l&<br />
Marism A& hs&i<br />
Mmwa<br />
MeMm, Adi Hay<br />
ETHM1524<br />
ETH-00525<br />
ETH-00328<br />
ETH-00529<br />
ETHbOS3 I<br />
Au<br />
Au<br />
Au<br />
Cu<br />
Au<br />
Zn. Pb<br />
Asb<br />
Au. BM<br />
E<br />
E<br />
NIA<br />
NIA<br />
NIA<br />
NIA<br />
NIA<br />
NIA<br />
38.11<br />
41.01<br />
38.80<br />
38.68<br />
58.80<br />
38.76<br />
38.83<br />
39.49<br />
40.68<br />
3B.11<br />
6.70<br />
13.40<br />
8.97<br />
5.76<br />
5.76<br />
5.83<br />
5.79<br />
5.32<br />
5.93<br />
13.98<br />
14,M<br />
14.70
270 Miml <strong>Resources</strong> <strong>Potential</strong> of Ethioaia<br />
Mellu A h ETW0053B Ft, Ti, h s D<br />
k Guhb 1 Par1 I ETH-l I h I NIA<br />
Matefinfin {-) EllUHB42 Au.Cn.W NIA<br />
Mct~m ETH40.543 C d NJA<br />
Md ETH 40544 Au NIA<br />
Mag Ial EM.00545 Aab MA<br />
*(w) ETH-00546 CIS NIA<br />
*(Coal) ETH-7 Coll WA<br />
M o j o - A ~ ~ mH-O(H48 Cml WA<br />
Fmio m~a0552 h MIA<br />
McumlmkTankua ETHoM53 Cad NIA<br />
Mayale pmpcrty (Chnmuk,<br />
Lwo Riw ~~~-00578 Ti, V, W<br />
ETH90579<br />
m a r ETHa81<br />
ETH.00382 Au, Cu WA
NAME I<br />
Sam (Ni)<br />
Ss-w<br />
IDENTIF. SUBSTANCE CLASS X-ton<br />
ETl.CODj83 N1, Co, Cu E 39.1 1 -----<br />
E m & Au. BM FUA 39.14<br />
Sawana ETH-OOSSS<br />
--<br />
Au E<br />
*ma ETH4058G Coal NIA<br />
. ..<br />
Sebeaa mH-589 0s NIA<br />
Sdni ETH-00588 Coal NIA<br />
Shski<br />
ETH-0059 1<br />
Fe NIA' ------<br />
%<br />
ETH-92<br />
Au D<br />
Shebdli<br />
Shlnlle<br />
Shirgtlo<br />
S~OOU~<br />
Srmll rhhkha<br />
Gem<br />
ETH40M<br />
ETH-00595<br />
ETH-[X)S%<br />
-597<br />
ErH4599<br />
ETH-006W<br />
Wdu I ETH-00601 I PWAu I D 1 35.49 I 9.08<br />
M r o I ETH-00602 I ClyC ( NIA 1 N.19.59 1 8:10<br />
-(PC)<br />
Sdcll (Gr, MDd)<br />
Subaha<br />
(Pb, Q)<br />
iTH-00603<br />
lXKOD60Q<br />
Taw Riwr ETH40607<br />
Tdid Rim<br />
' T W W<br />
Tsslfa nnd Ulak<br />
lZTH4nM5<br />
ETH-00606<br />
Mi=<br />
LtC, M;bl<br />
Au<br />
Au<br />
Ni<br />
Au E<br />
Annex 271<br />
Y-ht<br />
13.1<br />
Tlllu Gokl 1 ITH-aoa21 I Co I NIA 153.67 1 9.43<br />
. --<br />
Tulu Kmi - Njo<br />
ETH--2 Ail, Be MIA 35.50 9.70<br />
Ft<br />
Or, Ool<br />
Fb, Cu<br />
NJA<br />
NIA<br />
NIA<br />
NIA<br />
NIA<br />
38.63<br />
38.91<br />
42.42<br />
41.F<br />
34.44<br />
3468<br />
39.05<br />
38.01<br />
3.59<br />
Au NIA 37.46 14.14<br />
T& I lTH40609 I Au I E 1 38.m 1 5.63<br />
ETHQ061I<br />
ETH-12<br />
ETH-00613<br />
Asb<br />
Cu<br />
Cu.Zn<br />
Au<br />
-<br />
WA<br />
NIA<br />
HIA<br />
WA<br />
WA<br />
NIA<br />
NIA<br />
41.4s<br />
' 41.32<br />
41.33<br />
39.69<br />
38.94<br />
38.47<br />
34.44<br />
5-22<br />
5.79<br />
9.01<br />
9.73<br />
9.88<br />
10.60<br />
5m<br />
552<br />
9.14<br />
9.17<br />
9.26<br />
14.36<br />
13.81<br />
13.73<br />
9.77
272 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
NAME<br />
Tdu Kspi (Birbir k in)<br />
IDENTIF.<br />
ETH-23<br />
SUBSTANCE<br />
Au, Ag, Cti<br />
CLASS<br />
Wdm ErllauCl Coal NIA 37.13 7,M -----<br />
W m E T W I An A 38.%j 5.68<br />
Wari R i -2 Am, BM NIA 39.16 13.91<br />
Wrandab liTH.00648 Pw WA 43.93 7-23<br />
Yam ETH-(10650 Au E 35.60 9.05<br />
Yubdo (Ah) ETH-53 Asb NIA 35.M 8.86<br />
ZW~, Hargets ~H00657 Au NIA 38.31 14.54<br />
Zariga (Asb) ETHJIMSI Ah NIA 40.35 14.30<br />
Zelpl W&l (ClyC) -*?' clYc N/A 38.21 9.W<br />
Zega W&l (Coal) ETH-00660 Cam1 NIA 3813 9.89<br />
Ze~nbaba Woha ETH-00661 Ti NIA 39.28 5.83<br />
Abadida ITnvissa) I ETH-00662 I Au 1 E 1 38.88 1 5.71<br />
T~habe Embn ETH-00779 CII D 3831 14.20<br />
Agere Maryam (Ni) ETH-00791 MI NIA 38.10 5.44<br />
Apn Maryam (Ta) ETH-00792 Ta NIA 38.M 535<br />
Apero Maryam (Mo)<br />
E<br />
X-Lon<br />
35.65<br />
Y-Lat<br />
9.06<br />
ETI.I.00791 Mo N/A 38.11 5.57
I NAME<br />
Kanticba (Au)<br />
Ogaden (htr, Oas)<br />
IDENTLF. SUBSTANCE - CLASS x-Lon -<br />
Y-Lat<br />
ETH-0079s NtA 34.04 S,55<br />
ETH-00796 Gas D 43.64 5.75<br />
Red Sea I (ETH) ETH-00797 Pea. Gas D 41.~0 l5,OU<br />
Bombowlu 1 E"rH-00801 ! Kln E 1 38.73 I 6.15<br />
Kombelclra ETHWOR ~ ---- l n E 42.13 9.1<br />
Anno 'aHm TIC D<br />
Adigudom EEHmIO GP E 3932 l f 25<br />
-----<br />
Nesash ~-00811 M~bl NIA 39.61 1 %w<br />
Ham Sslm ~-00818 '3b A 39.17 1363<br />
S ! J = [ N ~ ) -rnaOBtg Sik MA 39.80 8.53<br />
EldkhD (Sib) ETH-OO%M btm WA 39.U 14 28<br />
- --<br />
North Mi+m r -27 I A~ - r<br />
N~A -I 5.80 r y3
I<br />
~bbnyfi*rmn*~q<br />
(tower. 2) IrrH-ml I **r I N/*<br />
I~5,ll ( la,,<br />
Abclselo ETH-44882 Za, Pb, Cu, Au MA 34.64 10.74<br />
' .: . . - A<br />
Annex 275 :. . :. -<br />
... . - .. .<br />
:>-,.:3<br />
.* -,!a<br />
Ab- (Upper1 ETH-@#13 Au NIA' 35.39 10.70<br />
-<br />
Abumarc (River) ETH-00884 Au<br />
80.67<br />
A 34.74<br />
Ab- [West, East) ETHm85 A"*As' MA 34.15 10.68<br />
Ni. W - -<br />
(soh)<br />
A- ETH4Wl 9 N/A 38.77 9.85<br />
Afdm (Umk Ondofiok €lll#893 Au E 349 10.24<br />
Agar K ac 1 ETH-00894 Au NIA 35.48 9.5 1<br />
Andm I ETH- ] S~%%CI~C 1 NIA 1 3763 1 8.9%<br />
Ambo I ETH.00896 1 Trav I NIA 1 37.85 1 9.00<br />
Arm- ETH#BW Au MA 35.33 10.30<br />
&jo (Hurls) D W 9 8 ' Coel WA 36A7 8.93<br />
Arjo (Kdati) ETH-OOS~ Cd NIA 36.60 8.88<br />
Atp (hbo-m AleItu)<br />
~~~-00901 11.75<br />
w(hj ETH W 35.42<br />
Bascia ~~~-00904 Ail NIA 34.75 IO.0S<br />
Belm ETN- Mhl NIA 35,03 10.16
276 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethimb<br />
1 NAME I IDMIF- I SUBSTANCE I CLASS [ X-h I I'-b<br />
Belfude (Lower. Upper):<br />
Sirkde (Am)<br />
Bila<br />
ETH-0091 I<br />
ETH-009 14<br />
Au<br />
Fe<br />
NIA<br />
NIA<br />
34.77<br />
35.63<br />
r0.59<br />
9,37
NAME 1 IDENTIF. [ SUBSTANCE I CLASS I X-LO~ I Y-LU~ I<br />
Debre Libnos, Coal<br />
(Gur,S Gongit R.)<br />
Debre Tabor<br />
Dila Amuent<br />
Dila, 1g0<br />
ETH-00943<br />
I<br />
ETH-00914<br />
ETHd0946<br />
ETHd09.17<br />
Dila 1 ETH-00948 I Au I NIA 1 35.31 1 9.24<br />
Dila I ETH-00949 I Pt I NIA ] 35.35 ] 9.19<br />
Dilla (ClyC) I ETH-00950 I ClyC I NIA 1 35.55 1 9.45<br />
Dilla (Upper)<br />
Dura (Lower)<br />
ETH-0095 I<br />
ETH-00652<br />
Coal<br />
Kln<br />
Au. Pltd<br />
Dura Aebin ETH-00953 AII NIA<br />
(Lower) ETH-00954 Au NIA<br />
Dmi (Middle) I ETH-00955 I A I NIA 1 34.60 1 10.65<br />
Ebilcha (Bekuji-Motish)<br />
Ejoba (North)<br />
E~nbukneya<br />
Fare (Lower, Upper) ;<br />
Mesa ; GBbo (Middle) ;<br />
Oda<br />
Fasio (Mount)<br />
Gmm (Lower P)<br />
An<br />
Au<br />
Ao<br />
NIA<br />
NlA<br />
MIA<br />
NIA<br />
N/A<br />
NIA<br />
ETH-00956 Au NIA<br />
ETH-00957 AU NIA<br />
ETH-Om58 AU NtA<br />
ETH-00959 Au NIA<br />
--<br />
ETH-OW60 MO<br />
ETH-00961 Au N/A<br />
Gaza~~(Middle, Upper) I ETH-00964 I Au I N/A<br />
Geb (Middle)<br />
38.82<br />
38.01<br />
35.41<br />
35.24<br />
35.39<br />
35.47<br />
9.73<br />
1 1.83<br />
I I r I I<br />
1NIA ] 34.80 10.64<br />
Gih (Uppar)<br />
Gomi (Amuent), Gomi<br />
(her)<br />
Gotni (Head Waters), Roro,<br />
G~liso (North)<br />
ETH-00969<br />
ETH-00970<br />
ETH-0097 1<br />
AII<br />
Au<br />
Au<br />
NIA<br />
NIA<br />
MIA<br />
34.87<br />
35.44<br />
35,48<br />
6.23<br />
9.28<br />
9.38<br />
10.15<br />
10.58<br />
9.13<br />
9,18 -<br />
ETH-00973 LstC NIA 37,75 8.97
278 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
Mendi (Gerba)<br />
Mendi (KoII~)<br />
Menp (Upper, Middle)<br />
Milendu (Belkwcl)<br />
ETH-01001<br />
ETH-0 1002 Coal NIA 34.98<br />
-----<br />
ETH-01003<br />
Au NIA 34,75<br />
FTH-01004<br />
Coal<br />
Mrbl<br />
NIA<br />
NIA<br />
35.09<br />
35.14<br />
9.72<br />
9.81<br />
10.37<br />
10.33
NAME SUBSANCE CLASS<br />
*(-) FCH-01029<br />
Sirkoltpled Wllrcrs),<br />
Sirkole (Lower) ; Tuma-<br />
ETHQlOM 34.52 10.23<br />
Sirkd~ Junction; Tuma mM)1031 MA 34.77 10.62
280 Minerd Remmxs <strong>Potential</strong> of Ethiopia<br />
Tsoli (SW)<br />
Tdi (West)<br />
Tsoli.<br />
NAME<br />
Twli, G ha (Upper)<br />
Tulu Boli I ETH911W I ah I NIA I 11.39 I 9.51<br />
TUIII Di~ntu EM41011 Ni, Co, Cr, R<br />
TuluHasi (SW) ETHDIO12 Mo<br />
Tuner (Lw)<br />
fTH41038<br />
ETH-01039<br />
Twncl (Uppm) FM41W Au<br />
T-t IUpw) FM.01045 AII<br />
Turn, Hdm, De~nba<br />
Ube (Wube)<br />
wowu<br />
aceem WWr)<br />
Weka (Gran)<br />
Mai Dao<br />
Axam<br />
Mua(h)<br />
IDENTIF.<br />
TKO1036<br />
EW1037<br />
ETH41086<br />
ETH+1047<br />
--<br />
ETH-01055<br />
ETH-01056<br />
SUBSTANCE<br />
Cu<br />
CII<br />
FC<br />
All<br />
Am<br />
Mo<br />
.-<br />
Au<br />
Gran<br />
CLASS<br />
NIA<br />
A<br />
NIA<br />
A<br />
WA<br />
NIA<br />
X-h<br />
35.05<br />
35.06<br />
33.08<br />
35.09<br />
34.79<br />
34.69<br />
Y-LPt<br />
10.23<br />
10.28<br />
10.28<br />
103<br />
I I<br />
NIA 35.25 10.06<br />
NIA<br />
NIA<br />
38.01<br />
38.82<br />
ETH4IOW Mtbl D 3838<br />
-----<br />
ETH41061 Amt PUA 38.72<br />
ETH41062 Amt NIA 38.90<br />
10.09<br />
10.59<br />
1 1.83<br />
6.05<br />
14.30<br />
14.13<br />
14.17<br />
: '
285<br />
Annex 4. Techniques utkd in digitizing the geology and<br />
mineral map of Ethiopia<br />
The folIowing are the steps involved in developing the digital<br />
database for Geology and mined map of Ethiopia.<br />
Data input<br />
k-,., . .<br />
thiopia was first scanned to derive a raster<br />
56 cohurs in TIF format<br />
the project projection that will serve as a base for all<br />
works were performed using Mercator<br />
Projection-Datum NAM7-Ellipsoid Clarke 1 866;<br />
Ektracting contour lines, Political boundaries and drainage<br />
from DC W (Digital Chart of the Worid) were performed.<br />
Microstation and MS Geocoordinator, grids were cteated in<br />
ect all vector data (topographic, drainage,<br />
and boundaries data) onto the he.<br />
ion DescarW, gemeferencing raster geological<br />
map to the Mercator base cartographic map with grid and<br />
hic data were done.<br />
d labeis edited under Microstation using a<br />
on: hydrographic data (blue), politid<br />
boundaries (black) c) grid (magenta) on transpent suppo<br />
ew grid on paper;<br />
and an WP Plotter (HP25OO). printing raste<br />
i mapat1:2,000,000scale,<br />
:
286 Miml <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
Adding informatiori and apgmdhg:<br />
Hand, drawing (in black) was performed to simpli@ the<br />
geology on transparent output (by matching the hydrographic<br />
network and grid between the two supports). Drawing the<br />
geological contacts, faujts, symbols and placing a label point<br />
for each geological unit was done;<br />
Scanning the drawing (in binary) to remove hydrographic and<br />
grids (blue and magenta);<br />
Under MicroStatioa, I/RASB and IIGEOVEC, gareferencing<br />
the raster data; md interactive vectorizing the geological<br />
boundaries (one layer for each object category: contact, fault,<br />
etc.) was perfumed;<br />
Placing interactively the label points and transferring the data<br />
to ArcInfo (twundaries and label points) was done.<br />
Final editing and preparing layouts far printing<br />
With Archfo, generating the polygon topology; batch pmcess<br />
to were. performed to calculate the intersectioris between the<br />
line network and creates the polygons (by chaining the lines<br />
around each label points);<br />
Detects the errors (polygons without label and polygons with<br />
dmnt lakls).<br />
If there are errors<br />
Importing the errors in Microstation for correcting running<br />
&Info process until all the errors are corrected.<br />
When aU the errors are corrected<br />
Under Microstation, imparting the polygons created with<br />
ArcInfo. Function the label points, the polygons may be fill4<br />
with a colour andlor a pattern); a specific colour chart has been<br />
E#l! defined for the Africa R&D project;<br />
Under Excel, creating the le&nd;
g faults, titles, logos,). At this stage, the<br />
~cgeological<br />
map was finalid.<br />
. <strong>Mineral</strong> resources data<br />
Scanning all available documents of Ethiopia (black and<br />
white) on AN ATECH scanner {with grey level);<br />
Under Microstation Descartes, georeferencing (warping)<br />
raster data in Mercator with grid and topographic data;<br />
Under MapInfo, calculating the coordinates (longitude and<br />
I latitude) for, each occurrence and transferring the results in<br />
I<br />
Updating of the data by introducing in the database,<br />
complementary information extracted from recent publications<br />
and b m economic journals;<br />
Under MicroStation, creating the legend for minds. At this<br />
stage, the synthetic digital mineral map was finalia,<br />
3<br />
Under Microstation, printing the map was done using HP<br />
plotter (HP25OO). Kg;.<br />
3q.:'<br />
, (6:'<br />
b .,, , '<br />
. :.?<br />
.,. 'A'
283 <strong>Mineral</strong> <strong>Resources</strong> <strong>Potential</strong> of Ethiopia<br />
3. CD-ROM ,t . -<br />
8, -<br />
.;A:,<br />
* Tmfmhg_the-<br />
data to MapInfo (layers: topography, geology,<br />
hults, symbols and mineral deposits) h m Microstation;<br />
Under Descartes, creating the map viewer from the geological' '<br />
and minerd map;<br />
Creating CD-ROM (using HP CD Writer Plus 7200).<br />
4. Software used<br />
The following software was used to make the digital database of<br />
the map:<br />
Microstation (editing vector data);<br />
Descartes (editing raster data, colour and blackhvhite);<br />
Micros tation geocoordinator (used to manage projection<br />
systems).<br />
Infergraph software (which runs on MicroStation)<br />
I/MSI3 (editing raster data, only blacklwhite);<br />
UGEOVEC (interactive vectorizin~transfom raster to vector);<br />
ESRI software;<br />
ArcInfo (CIS);<br />
AD.D.E software,<br />
MapInfo (GIs).<br />
ANATECH Software<br />
Scansmith scan and Scansmi* view 9 to wan @ visualize<br />
the raster.
Fa, -w<br />
0: Annex 2g9<br />
Annex 5. Mining law and invwtment opportunities in Ethiopia<br />
Policy<br />
The economic policy of Ethiopia envisages the need for the<br />
participation of national as well as international investors in<br />
different economic sectors including mining. The government<br />
realizing the unique nature of mining activities and to encourage<br />
investem in area opted to regulate the mining activities through<br />
laws specifically applying to mining as opposed to other areas of<br />
investment being regulated by the investment laws.<br />
Inveatmea t opportunities<br />
The country is endowed with a variety of mineral resources. All<br />
interested pasons and groups are invited to invest in the mining<br />
industry of Ethiopia.<br />
The Federal Republic of Ethiopia issued a new Mining<br />
Pmla~nation and Mining Tax Proclamation in June 1993. These<br />
laws are the outcome of vigorous research in the field of mining<br />
investment. They replace Mining Proclamation No, 282 of 1971<br />
which governed mining activity in Ethiopia for the last 22 years.<br />
The main objective of the new mining law is to improve the<br />
legal framework for mining investment in the country. Realization<br />
of the shortcomings of earlier laws and policies was very important<br />
in taking the subsequent corrective measures. The future of the<br />
mining sector is now firmly allied to private investment. The<br />
: preamble to the new mining law states that the law recognizes the<br />
significant role of private investment in capital formation, !<br />
technology acquisition and wketing of minds. The Mining<br />
Tax Proclamition No.. 53/1993 is legislation complementary to the<br />
i<br />
Mining Proclamation. The Tax Proclamation fully recognizes the<br />
high risk nature of mining investment and provides a liberal reward<br />
I<br />
for those who venture into the sector. This can be demonstrated<br />
from the following benefits stipulated in the law: 1<br />
1<br />
1<br />
i I<br />
I<br />
I I
I exploration<br />
ZBO Mind <strong>Resources</strong> <strong>Potential</strong> of Ethioaia<br />
- 35% tax on taxable income generated from mining<br />
operation;<br />
- 10% dividend tax;<br />
- 2% optional state free equity;<br />
- Ten year losses carry fbmd;<br />
- Generous deductions and calculations of expenditure;<br />
- Reinvestment deduction;<br />
- Right to sell the produced minerals locally or abroad<br />
without obtaining other licenses;<br />
- Exemption from customs duties and taxes on equipment,<br />
machinery, vehicles except Seda cars and spare parts<br />
necessary for mineral operations;<br />
- Provide for dispute settlement through negotiation and<br />
international arbitration;<br />
- Write off of investment within four consecutive years;<br />
- Low royalty and tax rate;<br />
- Fair exchange control arrangements, with no restrictions<br />
on repatriation of profits and dividends in the currency of<br />
investment or in an approved currency;<br />
- The right to hold a foreign currency account in Ethiopia;<br />
- The right to dispose of the- produced minerals locally or<br />
abroad without obtaining other licences;<br />
- require environmental impact study.<br />
The calcuIations for det,mination of taxable income are<br />
devised so that the investor will get .a fair reward for his effort and<br />
investment in finding and producing the minerals.<br />
The Mind Operations Department of the Ministry of<br />
Mihes is the focal point to receive, facilitate and process<br />
and mining applications presentd by foreign<br />
company's joint venture with local companies and.sdl to large<br />
sale mining activities to be carried out by l d companies.