An Rs Final Mineral Report

7/23/2019 An Rs Final Mineral Report

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LIMITED CIRCULATION

ANRS Investment Office

Potential Survey, Identification of Opportunitiesand Preparations of Projects Profiles and

Feasibility Studies

Part One: Potential Assessment Survey

Mineral Resource PotentialFinal Report

Development Studies Associates

(DSA) and

Shawel Consult International (SCI)

February 2006Bahir Dar

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Content

Part One: Summary .............................................................................................................1

Part Two: Introduction .......................................................................................................3Part Three: General Geological Setting and Structure ........................................................5

3.1. Precambrian Basement Complex..............................................................................5

3.2. Late Paleozoic to Early Mesozoic Sediments ..........................................................73.2.1. Late Paleozoic ...................................................................................................7

3.2.2. Mesozoic Sediments .........................................................................................7

3.2.2.1. Adigrat Formation (Ja)................................................................................93.2.2.2. Abay Formation (Jb)..................................................................................9

3.2.2.3. Antalo Formation (Jt)..................................................................................9

3.2.2.4. Amba Aradom Formation (Ka)...................................................................9

3.2.2.5. Other Localities ........................................................................................10

3.3. Pre-Rift Volcanic Succession ................................................................................103.3.1. The Ashangi Formation ..................................................................................10

3.3.2. The Aiba Basalt (P3a)......................................................................................103.3.3. The Alajae Formation (PNa)............................................................................11

3.3.4. Tarmaber Gussa Formation (PNtb)/Tarmaber Megezez Formation (Ntb)......11

3.4. Quaternary Plateau Basalts and Associated Sediments .........................................113.5. Post Precambrian Structures ..................................................................................15

3.5.1. The Tana and Chilga Rift Basins ....................................................................15

3.5.1.1. The Tana-Rift Basin..................................................................................153.5.1.2. The Chilga - Rift Basin ............................................................................16

3.5.1.3. The Kombolcha (Borkena Robi) Graben ...............................................16

Part Four: Mineral Resources of the Amhara Region.......................................................184.1. Metallic Minerals....................................................................................................184.2. Non-Metallic Minerals............................................................................................19

4.3. Energy Minerals......................................................................................................21

4.3.1 Petroleum potential of the Abay River Basin ..................................................214.4. Gemstone................................................................................................................25

4.5 Dimension Stone .....................................................................................................26

4.5.1 Precambrian crystalline rocks and associated intrusives ................................274.5.2 Mesozoic sediments as source of dimension stone...........................................28

4.5.3 Volcanic Rocks ................................................................................................29

4.6 Construction Raw Materials ...................................................................................30

Part Five: Exploration ......................................................................................................315.1. Early Exploration ...................................................................................................31

5.2. Recent Exploration .................................................................................................36

5.2.1. Industrial Minerals and Rocks ........................................................................365.2.2. Investigation for Gemstone .............................................................................40

5.2.3. The Bure-Abergele Gold and Base Metals Exploration Project......................41

Part Six: Recommendations .............................................................................................516.1. Immediate Objective Metallic .............................................................................51

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6.2. Long Term Programme ........................................................................................53

6.3. Investigation for Non-metallic Minerals Associated with Mesozoic Sediments....55

6.3.1. Immediate objective .......................................................................................556.3.2. Long Term Objective .....................................................................................57

6.4. Energy Minerals .....................................................................................................58

6.4.1. Immediate Objective ......................................................................................586.4.1.1. Lignite ......................................................................................................58

6.4.1.2. Oil Seepage ..............................................................................................59

6.4.2. Long Term Objective ......................................................................................606.4.2.1. Lignite ......................................................................................................60

6.4.2.2. Oil Shale....................................................................................................60

6.4.3. Gemstone- Immediate Objective ...................................................................60

Part Seven: Mineral Water and Thermal Springs..............................................................617.1. Mineral Water ........................................................................................................61

7.2. Thermal Springs .....................................................................................................62

Part Eight: Mining/Quarrying ...........................................................................................63

Part Nine: Review of Mineral Legislation ........................................................................689.1 Institutional Set-up .................................................................................................68

9.2 Mineral Legislation..................................................................................................689.3 Review of Mining Regulation of the Amhara National Regional State..................73

9.4 Environmental Issues Associated with Mineral Development ...............................74

9.5 Proposed Memorandum of Association for the Establishment of Artisan and Small-Scale Mining Cooperatives............................................................................................75

9.6 Application for Registration of a Cooperative Society (Format) ............................84

Part Ten: Capacity Building ..............................................................................................86

10.1. Facilities ...............................................................................................................8610.2. Training of Personnel ...........................................................................................88

References .........................................................................................................................89

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Part One: SummaryThe review and assessment of the geological and mineral exploration results by the

Consultant revealed that the Geology of the Amhara Region can be broadly divided into

four major groups. These are:-

1.1 The Precambrian Complex, which is further subdivide into the Lower

Complex and the Upper Complex

1.2 The Paleozoic Mesozoic Sediments1.3 Tertiary Volcanic

1.4 Quaternary Plateau Basalts and associated sediments.

With regards to the mineral resources associated with the above formations:-

(a) The low grade metamorphic rocks are the source of placer gold presently being

recovered by artisanal miners in the Sarkayasa area, situated in Kilaj district,Agawi zone.

Through reconnaissance exploration in the Kilaj district primary gold targets have been

outlined in the Sarkayasa and Goder localities. These gold targets in the two localities

have been recommended for further investigation, using among other things, diamond

core drilling. The other primary gold mineralization identified as a result ofreconnaissance exploration within the Upper Complex is in the Abergele area, situated in

the northern part of the Amhara Region, bordering the Tigrai Region. The targets

identified lie between Finarwa and Niraque villages. The entire auriferous zone betweenthe two villages requires further investigation within the framework of short term

programme.

In addition to gold, the Upper Precambrian Complex has great potential, as the geology

indicates, for other metallic and non-metallic minerals, as well as industrial rocks.

According to the existing geological information the Upper Precambrian Complex is

exposed in the west, northwest and the northern parts of the Amhara Region andtherefore, it is necessary to cover this potential complex by general mineral exploration

on long term basis.

Within the Mesozoic sedimentary sequence two specific areas, namely Wenchit and

Jemma areas have been explored in the past. The results have revealed the existence of

commercial deposits of gypsum, silica and limestone in the two areas. These rawmaterials are the source of glass, cement, and lime industries. The sandstone and

limestone are the source of dimension stone, extensively used in the building industry.

With further investigation, these raw materials can be exploited for various industrial

uses. The two areas require immediate attention.

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With respect to energy minerals lignite, (brown coal) is known to occur in a number of

localities within the Amhara Region. However, this important energy source has not been

utilized, in spite of serious energy crisis, as demonstrated by the scale of deforestationwithin the Amhara Region and outside the Region. Further assessment of the lignite

resource on short and long term basis would have significant contribution to the

development of cheap energy for domestic, as well as for industrial uses.

Other indications of energy resources in the Amhara Region are the oil seep and oil shale

occurrences in Mechala Shet and Werekyou areas, in Wello. The oil seep in particularrequires immediate attention, while geological sampling and testing of the oil shale can

be carried out on long term basis.

Opal of gem quality occurs just northwest of Mezezo town in North Shoa Zone of theAmhara Region. Between 1994 and 1998 three occurrences of opal have been

investigated by a private company known as Abay Natural Resources Development PLC.

According to company's report the exploration was carried out up to the stage of reserve

estimation. However, the present status of the project is not known.

The other occurrence of opal is in South Gonder Zone, Farta Wereda, Boda locality.

To date no investigation has been carried out on the occurrence and therefore requires

immediate attention.

With regards to mineral water there are localities in the Amhara Region where such water

is known to occur. However, there are no records of any hydrogeological investigation on

this resource.

From the present state of knowledge there is certainly an underdevelopment with respect

to the mineral resources of Amhara Region, the main constraints being: -

Lack of adequate financial in put on the part of the Regional government to

carry out systematic geological mapping and mineral exploration on a continuousbasis

Lack of an autonomous organization which would be responsible for the above

work, as well as other duties that include promotional, regulatory and monitoringfunctions

The underdevelopment of mineral based industries in the Region.

The present incentives in the mining sector not being attractive to investors.

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Part Two: IntroductionAs the Terms of Reference of the Consultant indicate the objective of the review and

assessment of the available geological and mineral information, pertaining to the Amhara

National Regional State is to solicit public interest in mineral resource developmentwithin the Region. This is certainly a step in the right direction.

Sustainable production of minerals and rocks entails the intensification of the mining

industry with a view to yielding mineral based products.

The linkages that exist between the mining industry and other developmental activities

within an economy is manifested in many ways. With regards to human development therole of minerals is directly relevant to education in terms of educational infrastructure,

such as buildings and equipment.

Similarly the use of mechanized agriculture and the utilization of fertilizers lead toincreased food production, as is presently the case. In this regard minerals are the raw

materials used for the manufacture of modern agricultural machineries, as well as thesource of the three nutrient elements, namely nitrogen, potassium and phosphorus.

With respect to basic services the role of minerals in the provision of clean water and

medical services is long known.

In short the contribution of minerals to socio-economic development is beyond question.

Even though the Amhara Region is endowed with a variety of mineral resources, ranging

from metallic to energy minerals, the mineral industry in the Region is at a very low levelof development, as compared, for instance, to the Oromia Region.

Therefore, in order to transform the Regions economy from purely agrarian to a more

balanced and integrated economy, and to lay the foundations for industrial scheme, the

Amhara National Regional Government should give greater emphasis to the mineralsector.

This assessment report contains a reasonably complete digest of the information, relatedto the basic geology and mineral resources of the Amhara Region. The report also

includes recommendations on future exploration of the Regions mineral resources on

short and long term basis.

The geological and mineral information utilized for data review and assessment was

drawn from the Ministry of Mines, which is the main custodian of earth scienceinformation, the Ministry of National Water Resources, in Addis Ababa, as well as from

the Office for Minerals and Rural Energy Development of the Amhara National Regional

State in Bahir Dar.

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The Consultant had also a number of useful discussions with some senior geological and

mineral exploration professionals who have in the past worked in the Amhara Region.

Finally the Consultant wishes to thank those government officials and staff members of

the institutions mentioned above for their cooperation and valuable assistance.

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Part Three: General Geological Setting andStructure

3.0. The geology of the Amhara Region consists of:-

Precambrian Basement Complex

Paleozoic-Mesozoic Sedimentary Succession

Tertiary Volcanics

Quaternary Plateau Basalts and Associated Sediments

3.1. Precambrian Basement Complex

The Precambrian Basement Complex, exposed in the Amhara Region is part of a long

belt of crystalline rocks, extending from southwestern Ethiopia to the northern part andbeyond.

On the basis of differing lithologies, structural style and grade of metamorphism the

Basement Complex is divided into two litho-tectonic units and these are:- (a) high gradeand (b) low-grade metamorphic rocks and associated intrusives.

(a) Lower Complex (High Grade Metamorphics)

According to the available geological data the high grade metamorphic rocks of generally

north-south orientation are mainly exposed in the southern part of the Amhara Region

along the Blue Nile Basin, geological map of Ethiopia,1996

From the information available to date the high grade metamorphic rocks are generally

barren in terms of metallic minerals concentration. However, these rocks could be thesource of non-metallic, industrial minerals, such as feldspar and mica, which normally

occur within the complex as pegmatites of late magmatic phase.

High-grade metamorphic rocks could also be the source of such gcm minerals as garnets.

The Lower Complex within the Amhara Region is represented by the Alghe Group (ARi)(Mengesha et. al 1996), previously termed by V.Kazmin as the Alghe Gneiss. The

formation was named after the Alghe Village, which is the type locality situated inBorena Zone of Southern Oromia, Kazmin (1972, 1975).

Lithologically, the Alghe Group of rocks are banded, grey to dark, maffic gneisses and

migmatites, constituting the main facies of the Lower Complex. These rocks are well

foliated and consist of mafic layers, containing biotite and/or hornblende and occasionalpinky garnet, which alternate with grey, quartzo-feldspathic bands.

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Concordant layers of pinky gneissose type pegmatites and aplites are commonly present,

in places these rocks also occur as late stage cross cutting veins, not tectonised.

The leucocratic components of these gneisses have a composition of granodiorite or

quartz diorite.

(b) The Upper Complex (Low-grade Metamorphics)

The Upper Complex:- within the Amhara Region the Upper Complex is represented bywhat is referred to as the Tulu Dimtu Group (PR2td), named after the locality of Tulu

Dimtu, situated south of the Blue Nile, in the Beneshangul-Gumuz Region. This complex

is relatively a narrow belt that extends from south of Yubdo in western Welega to the

west and southwestern parts of the Amhara Region.

Within the Tulu Dimtu Group a number of lithological units have been identified that

include meta-ultramafic and gabbroic rocks, mafic metavolcanics and various

metasediments. The main rock types of the Tulu Dimtu Group are metamudstone,graphite schist, meta-conglomerate, quartzo-graphite schists, quartzites and chert,

marbles, mafic metavolcanics (greenstones, and amphibolites), Kazmin, 1978.

A thick sequence of sediments, grading from fine graphitic schists to coarse

conglomerates occur within the Tulu Dimutu Group of rocks.

Meta-mudstone is one of the most common rock types in the Group. This rock is dark-

grey, fine grained with relict bedding and poorly to well developed foliation. They are

intercalated with dark grey psammite rocks. The psammites consist of bands ofrecrystallised quartz and plagioclase grains, alternating with biotitic or sub-rounded

clasts.

The graphitic and quartz-graphitic schists within the Tulu Dimtu Complex are dark in

colour, thinly foliated, ranging in thickness from few meters to tens of meters. They

occur as both softer and harder, silicifid varieties; silicifed graphitic schists formprominent ridges that could be traced for a number of kilometers. This particular

lithologic unit is associated with massive, grey and brown quartizites and thinly banded

cherts which together form discountinous bands and some of them are several kilometers

in strike length. The quartzites are essentially made up of mosaic of quartz with minorbiotite and hematite. The cherts display greater degree of deformation and grain

orientation.

The greenstones within the Tulu Dimtu Group are commonly pyritiferous,, dark green in

colour, nearly massive and strongly jointed. Relict of porphyritic textures are common.

The primary minerals are pale green amphibolites, chlorite, epidote and sericite. Thegreenstones have been mostly derived from basaltic rocks, but some form rocks of

andesitic composition.

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Amphibolites are common within the Tulu Dimtu Group. These rocks are dark grey, fine

to coarse grained, well to poorly foliated. The fine grained and well foliated varieties

have been possibly derived from mafic volcanics, whereas the coarse grained varietieshave been derived from mafic intrusives.

Numerous concordant lenses of serpentinites, talc-serpentinite and talc-carbonate rocksoccur within the metasedimentary succession of Tulu Dimtu Group. Kazmin (1978)

interpreted these rocks as representing concordant, foliated and serpentinized bodies of

dunite. They are composed of flaky antigorite and talc with accessory magnetite andchromite.

The Structure of the Basement Complex In the past the grade of metamorphism has

been the principal criteria used by investigators to classify the Precambrain terrains ofEthiopia.

As noted earlier the Lower Complex in the Amhara Region is represented by the Alghe

Group while the Upper Complex is represented by the Tulu Dimtu Group.

The major deformation, which is characteristic to the Lower Complex is the tightisoclinal fold with axial surfaces steeper than the foliation.

Another characteristic feature of the Lower Complex is the existence of the more openfold.

Regarding the Upper Complex the strike is generally north-south with variations from

northwest to northeast.

3.2. Late Paleozoic to Early Mesozoic Sediments

3.2.1. Late Paleozoic

The oldest sedimentary formation within the Amhara Region is considered to be late

Paleozoic, possibly Permian. The formation is exposed in the southern most part of the

Region, in the Blue Nile gorge and consists of sandstone, siltstone and shale, (Jepsen et.al 1961).

3.2.2. Mesozoic Sediments

During the Mesozoic period marine transgression from the east and northeast hadextended to certain parts of Ethiopia. Northern Ethiopia is one of the Regions that

marine transgression had extended, resulting in the deposition of sediments.

In the Amhara Region the main exposure of Mesozoic Sediments is along the Blue Nile

River and its catchments in which the sequence starts in the eastern part of Gojam at the

confluence of the Blue Nile and Baschilu rivers and extending downwards up toDembecha area in the southwest (Geol. Map of Ethiopia, 1996).

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The succession from bottom to top are as follows:-

3.2.2.1. Adigrat Formation (Ja)

The Adigrat Formation is the basal unit of the Mesozoic sequence, whose age is usually

considered to be Upper to Middle Triassic, (Danelli, 1943). The formation is thesandstone sequence which includes the whole succession of clastic rocks, and essentially

consisting of sands, with minor horizons of shale, siltstone and conglomerate (Garland,

1972).

The sandstone within the Adigrat Formation is commonly yellowish to pink, fine to

medium grained, well sorted and cross-bedded. The Adigrat Formation lacks fossils forage dating, however, based on the age of overlying formation an early Liassic Age and

fluviatile to shallow marine environment of deposition have been inferred, (Buscaglian

et. al 1993).

3.2.2.2. Abay Formation (Jb)

The Abay Formation refers to the former Abay Beds and the lower unit of the formerAntalo Group, (Kazmin, 1972, 1975), resting on the Adigrat Formation and overlain by

Antalo Limestone. From bottom to top the Abay Formation is made-up of sandy

limestone and calcareous sandstone, gypsum, and interlaying of shale and limestone. Thewhole formation has a total thickness of about 600 meters.

The inferred age of Abay Formation is middle Jurrasic.

3.2.2.3. Antalo Formation (Jt)

This formation was formerly known as the Antalo Limestone (Blanford, 1870) named

after the type locality Antalo in Tigray. The formation was described in detail by Mohr

(1963), Beyth (1971), Kazmin (1972, 1975) and Merla (1973, 1979). It is essentially

made up of fossiliferous limestone, with lenses of marl and calcareous shale andarenaceous bands near to the top.

3.2.2.4. Amba Aradom Formation (Ka)

The Amba Aradom Formation, formerly termed as the Upper Sandstone, Mehadi (1968),

Beyth (1971), Arkin et. al (1971), Kazmin (1972, 1975) is exposed in several localities in

Ethiopia, including the Blue Nile Basin. The formation which was named after the typelocality Amba Aradom in Tigrai is made-up of sandstone, shale, marl, and

conglomerate.

Lithologically the Amba Aradom Formation is similar to the Adigrat formation with a

thickness in the range of 300 to 600 meters.

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3.2.2.5. Other Localities

Tekeze River Basin In addition to the Blue Nile River Basin, the Adigrat Formation is

exposed along the Tekeze River Basin, in the northern part of the Amhara Region.

Occurrence West of Lake Tana This occurrence of Adigrat Formation is situated westof L. Tana. The Formation is oriented north-south, and is about 120km (air distance) in

strike length and the width varying from 4 to 16km.

3.3. Pre-Rift Volcanic Succession

3.3.1. The Ashangi Formation

Within the Amhara Region fissural and central type eruptions have taken place on an

extensive scale during the pre-Tertiary period. These eruptions have produced a thicksuccession of basalts referred to as the Ashangi Group, after the type locality Ashangi.

Presently the term Ashangi Formation is used to describe several hundred of meters thick,highly weathered, alkaline and transitional basalts of the Ethiopian Plateau, (Zanettin,

1993).

It is now generally accepted that within the Ethiopian Plateau the Trap basalts wereformed in the course of two clearly separate cycles of eruptions, namely the Ashangi

cycle (35-50 My) and post-Ashangi cycle (15-32 My) (Zanettin, 1993).

The Ashangi Formation occurs in an old, northwesterly trending rift system, now buried

under younger volcanics and partially eroded away, (Zanettin et. al 1978, Zanettin, 1993).

This formation consists mainly of several hundred of meters thick, strongly weatheredand titled basalts, with rare trachyte and ryholite and containing some pyroclastic

intercalations. This formation is commonly intruded by dolerite sills and dykes.

Texturally the Ashangi Basalts are either aphyric or porhyric, containing olivine orplagiodase phenocrysts or both.

3.3.2. The Aiba Basalt (P3a)

The Aiba Basalts represent the second major cycle of fissural basalt volcanism in the

northwestern Ethiopian Plateau after the Ashangi Formation (Zanettin & Visentin, 1973).

This new cycle began with the eruption of huge volumes of lavas, flooding the peneplainsurface of the Ashangi Formation.

The Aiba Basalts, whose age is 25-36 My old are typical transitional basalts and very

homogenous in composition. The Aiba basalts are commonly jointed, aphyric or

porphyritic with plagioclase or olivine phenocrysts.

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3.3.3. The Alajae Formation (PNa)This formation consists of aphyric flood basalts, associated with rhyolites, ignimbrites

and subordinate trachyte. The formation ranges in age 13-36 My, Kazmin (1979),

Zannetin et. al (1980), (in explanation of the Geological Map of Ethiopia, 1996).

Within the Amhara Region the Alajae Formation rests uncomformably on the Aiba

Basalts. This formation contains basalts transitional to tholeiitic in character and an

increase in alkalinity is observed in the younger members of the Formation.

3.3.4. Tarmaber Gussa Formation (PNtb)/Tarmaber Megezez Formation

(Ntb)

The above formations represent Oligocone to Miocene basaltic shield volcanism and

occupy much of the central and southern parts of the Amhara Region.

The term Tarmaber Gussa Formation (PNtb) refers to the shield volcanoes with anabsolute age range of 16-26 My, while Tarmaber Megezez Formation (Ntb) refers to the

younger shield volcanoes with an absolute age range of 13-16 My. These formationswere named after volcanisms that brought about Tarmaber Gusa and Tarmaber Megezez

mountains.

The Tarmaber Formations, the former Shield Group of Mohr (1968) are represented by

various basalts, erupted from central shield volcanism and range in composition from

femic pyroxene-olivine porphyritic varieties to leucocratic plagioclase porphyritic types.

In contrast to the tholeiitic and mildly alkaline nature of the underlying fissural basalts,

the Tarmaber Basalts are typically alkaline in nature (Kazmin, 1981).

In general the Tarmaber Basalts and their equivalents have much fresher appearance than

the underlying stratoid basalts of Alajae Formation.

3.4. Quaternary Plateau Basalts and Associated Sediments

The Quaternary basalts within the Amhara Region are characteristically alkaline and are

believed to be the final phase of basaltic volcanism on the Ethiopian Plateau.

The eruption of Quaternary alkaline basaltic and trachytic volcanism took place along

pre-existing structures. However these rocks have not as yet been dated. Nevertheless,their relatively unmodified geomorphological features, such as the prevalence of

prominent cinder cones and small collapse craters indicate their recent age. According toV.Kazmin (1979), Merla et. al (1973) alkaline basalts and trachytic lavas prevail in the

Tana Graben. It was further noted that volcanic cones and flows of scoriaceous basalts

are also well preserved in the L. Tana Graben.

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In the north and in the eastern side of L. Tana, Quaternary alluvial and lacustrine deposits

are well developed. These deposits have originally been formed by simultaneous

process:-

(a) Formations of grabens or half grabens in the Chilga area, which is closely related

to east-west tension, giving rise to north-south fractures.(b) Flooding from the L. Tana, resulting in the formation of lacustrine shaly deposits,

which occur mainly within the graben, as for example the Chilga basin.

Recent (Quaternary) deposits in the northwestern and eastern parts of the Amhara

Region.

In addition to the occurrence of recent (alluvial and lacustrine deposits (Q) around thepresent Lake Tana area, there are occurrences of these deposits in Metema, Abderafi and

Quara areas, in the northwestern part of the Region, as well as in the eastern part, in the

Raya area, northern Welo.

According to the geological Map of Ethiopia, 1996, the alluvial and lacustrine deposits

identified by the symbol Q, in general, consist of sand, silt, clay, diatomite, limestoneand beach sand.

From the information available to date, the diatomite associated with recent sediments isrestricted to the main Ethiopian Rift, Laks District, where deposits of diatomite are

known to occur in the localities of Abiyata, Chefe Jila and Adauni Tulu, in the Eastern

Shoa Zone of Oromia Region, (Bekele Megersa, 1979, Aklilu Asefa et.al, 1983,

Knoth,w,et.el, 1981).

It is possible that similar diatomite deposits may occur within Tana-Chilga Graben,

accumulated under ancient lakes. With regards to the limestone associated with recentsediments, it may not be bedded limestone, per se, but rather hot spring precipitate

(travertive), as far instance, in the case of travertine occurrence in the Mojo area, l

locality underlain by recent sediments

Generally speaking, the Quaternary deposits in Ethiopia, in general, display regional

diversity. Therefore, considering this regional diversity the deposits underlying the

Metema, Anbderafi and Quara areas in the northwest and Raya area in the eastern part ofthe Amhara Region may possibly be composed of sand, silt and clay. This is also the

observation of Belay Mengistu et. al, (2005) in the course of reconnaissance geological,

transverse of the Metema area .

Depositional environment From the presently available information (Geological Map

of Ethiopia, 1996) the recent sediments in the Raya area are bounded by two major faults,which strike nearly north-south and extending into Tigray. It appears that the sediments

have accumulated in faulted basin, possibly under lacustrine environment.

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With regards to the northwestern part of the Amhara Region there are three major river

systems presently draining the Quara, Metema and Abderafi areas, namely Dinder in the

south, Atbara in the central part and Angereb in the north.

It is quite probable that during the early part of the Quaternary Era the northwestern part

of the Amhara Region had experienced high rainfall under very humid climatic condition,thus resulting in the extensive flooding of the low lying areas of Quara, Metema, and

Abderafi. In other words, the flood plains covering the above areas are composed of

classic sediments. This is simply an assumption which has to be proved bygemophological and geological investigations in the future.

The Economic Potential of Recent (Quatemory) Sediments -Recent, unconsolidated

sediments in general, are good acquifers. Therefore, the sediments around the Lake Tanaarea, as well as sediments occurring in the northwestern and in the eastern parts of the

Amhara Region could be potential source of ground water which can be utilized for

developmental purposes, as well as for human consumption. Hence, these sediments

should on, long-term basis be investigated for their ground water potential usinggeological and hydro-geophysical method and also test drilling.

Consolidated Sediments The reconnaissance geological traverse undertaken in the

Metema area by a team from the Petroleum Department of the Ministry of Mines, (Belay

Mengistru et.al, 2005) shows the occurrence of consolidated sediments, exposed atseveral places within the Quaternary unconsolidated cover. Certainly, such consolidated

sediments were exposed by erosion of the overlying cover.

As to the age of the consolidated sediments the study undertaken suggests as being eitherMesozoic or late Paleozoic.

According to the report the sediments are yellowish gray (buff), reddish brown to darkbrown, poorly sorted and essentially coarse grained.

In was noted in the report that in the course of field work some exposed sections werelogged, the summery of which is given below

1. Bermel Section The thickness of this section is reported to be 30m,

characterized by rounded pebbles of granite, measuring 2-5 cm across, andcemented by clay.

2. Central Section Located between Bermel Section and Mehdid section and is

30m in thickness. This section is conglomeratic in character at places. Thin bedsof siltstone and mudstone, variegated, have also been observed within the section.

3. Mehdid Section- has an estimated thickness of about 65m.

The lower part of the Section (20m) is light gray, medium to coarse grained andpoorly sorted sandstone. The rest of the section is made up of coarse to very

coarse sandstone, poorly sorted and cross-bedded.

4. Gelegu Section- According to the investigation report the thickness of this Section

is 45m. The most lower part of this section(5m) is poorly sorted, coarse grained

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sandstone. This is followed by a thin clastic bed (conglomeratic layer). On top of

the conglomerate is a 3-meter thick sandstone (gray, coarse grained) with slight

cross-bedding. This is followed by a 4-meter thick, whitish gray, coarse grainedlaminated sandstone. The rest of the section (30m) consists of alternating beds of

fine to coarse grained (pebbly) sandstone:

The Depositional Environment - According to the study undertaken the depositional

environment of the consolidated sediments within the Metema Basin represents

fluviatiale environment, where the deposition took place by river action, in which theprocess of weathering, transportation and deposition played a dominant role.

Gravity Survey of Metema and Bahir Dar areas- This study was also undertaken by

the petroleum Department of the Ministry of Mines in the above areas, (Teferi, Negashet. al,2005)

The initial survey involved the localities of Shehedi, Shinfu, Gelegu and Mahdeed

Instrumentation:- Lacoste & Romberg gravimeter was utilized to measure the

difference in gravity between sites.

Data acquisition:-In order to conduct gravity survey, two secondary base stations were

established for each area of operation, namely:

1. Shehedi Secondary gravity base station located in front of the Metema Customs

Office cafeteria (Shehedi town). This station is tied with Seraba elementary

school compound base, considered as the primary gravity base station of knowngravity value.

In addition second base stations of Shinfu and Gelegu towns were established and

tied with Shehedi gravity base station to make the survey more convenient2. Bahir Dar secondary base station-Located at the gate of Bahir Dar towns water

pump station which is tied with Dangla gravity base station, which is one of the

Ethiopian National Net Gravity Station, established in 1964/65(1381st GodeticSurvey Squadron) located at Dangla shell petrol station.

Survey Procedure

Gravity survey started by taking dial reading at the secondary base station

Subsequent dial readings were taken for sequential stations along the surveyroute

Final dial reading at the secondary base station, which completed the daily

reading

Data Processing- For this stage of work GRAVPAC software, which is an (MS-DOS)

program was used for the automatic data processing

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GPS Survey:- TribMble. (4000 si) Receiver was used to acquire coordinates and

elevation for the observed gravity stations

Interpretation and conclusion

(a) Dangla- The intensity of Bouguer anomaly near Dangla town is less thanits surroundings. This indicates that the Precambrian basement at this

point is deeper and that the overlying formation is possibly of lower

density rock(b) Bahir Dar- The Bouguer anomaly in the eastern part of Bahir Dar

decreases and this phenomen might be due to the existence of low density

rock in the area.

(c) Metema-Sehedi:- May represent the basement structure with theinfluence of the surrounding Ashangi Formation.

The Bouguer anomaly near Metema town decreases deeply showing more

negative values. This indicates that the basement rocks in the Metema area

lie very deep and that the overlying formation is possibly sedimentarylayer, which, according the Geological Map of Ethiopia, (1996) is made

up of alluvial (Quaternary) deposits.

(d) The Musabadima Dubba- Bermal- Salia route Represents anomalies

similar to that showing the deepening of the basement rock from westtowards east towards east.

3.5. Post Precambrian Structures

3.5.1. The Tana and Chilga Rift Basins

The Tana-Chilga Rift basin and the Kombolcha (Borkena-Robi) graben are the major

post-Precambrian structures within the Amhara Region.

3.5.1.1. The Tana-Rift Basin

With regards to the Tana Rift Basin two hypothesis have been advanced for the origin ofthe tectonic break, (M. Yebyo, 2002). The first hypothesis, suggested by Minucci (1938),

P. Mohr (1971), states that the Tana Basin had resulted from the uplift of the

Northwestern Ethiopian Plateau by mantle pluming, followed by extensional faulting

and development of monoclinal warping at the westerm margin of the Tana Basin.

Yebyo notes that P. Mohr (1971) mapped a NNE-SSW rift trends and cross-rift faults,with ENE-WSW, and N-S trends. Yebyo further notes that the structures are visible on

the North-Western Ethiopian Plateau and in the Tana Basin itself. Yebyo agrees with the

idea that the Tana as well as the Chilga Rift Basins are the results of extensiveextensional faulting that preceded the Oligocene pluming.

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On the other hand, Bosworth (1989) proposed the presence of Oligocene age NW-SE

trending central African Rift System that encompasses the Tana Basin and extending to

the western Sudan. Yebyo notes that the Oligocene age NW-SE trending Central AfricanRift system extends far beyond the region affected by the Oligocene mantle pluming and

that the structural grains of the rifting have induced the formation of the Tana Basin.

As to the NE-SW rift trend of the Tana Basin, which also encompasses the Chilga Basin

and the present day Lake Tana, Yebyo remarks that the origin of the Lake Tana is a

combination of the two hypothesis stated earlier, in which Lake Tana is perpendicular tothe Central African Rift trend. With respect to the change in the direction of the Rift trend

Yebyo notes that this change was the effect of mantle pluming resulting in the regional

uplift, doming and formation of extensional faults, thus changing the direction of the

previous NW-SE rift trend of the Tana Basin to NE-SW direction.

3.5.1.2. The Chilga - Rift Basin

According to M. Yebyo (2002) the Chilga Rift basin is a continental rift basin withisolated outcrops of sedimentary and volcanic basin-fill, separated by faults related to rift

processes.

Yebyo further notes that sediments filling the Chilga basin are rich in volcanic ashes,

lignite beds, silty sandstones and claystones and flora rich sandstones. Based onpetrographic and x-ray diffraction analysis of the fine grained Chilga Sediments Yebyo

suggests that the Chilga sediments were deposited in alluvial-lacustrine environment with

a nearby fine grained sediment source.With regards to the tectonic activity within the Chilga Rift Basin, Yebyo, (2002) notes

that the identification of normal faults that cut the oldest Chilga sediment and the tectonic

growth fault-sets that cut the entire Chilga sediment succession indicate that the Chilgabasin was tectonically active both during and after sediment deposition.

In conclusion Yebyo notes that the regional low which is now called the Tana Basin

accommodates the present day L. Tana and the Chilga Basin, the latter located 100 kmNW of Lake Tana.

3.5.1.3. The Kombolcha (Borkena Robi) Graben

This graben is another important post-Precambrian structure within the Amhara Region.

According to V. Kazmin (1972) the graben is 60km long and 5-15km wide. The generaltrend is north-northwest, but according to P. Mohr (1967a) the southern part is closer to

north-south. The southern part is bordered by parallel opposite dipping, but in the

northern part these faults converge and so the graben pinches out near Kombolcha.The western escarpment of the graben is a very sharp flexure, faulted at the foothills by a

major synthetic fault.

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In the western escarpment of the graben Tertiary volcanics are horizontal, but further to

the east they form a number of blocks tilted towards Afar. Further to the south the

Plateau-Afar border zone is of the same type with clear down-warping towards the Afarand antithetic faulting.

Kazmin remarks that all tectonic elements in the Borkena-Robi Graben have north-northeast strike instead of north-south or north-northwest, thus reflecting transition from the

Plateau-Afar to the Plateau-Rift margin.

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Part Four: Mineral Resources of the Amhara RegionOne of the characteristic features of the minerals industry is the need to explore for new

minerals while the known resources are being exploited. Although not adequately

explored the Amhara Region is well endowed with a variety of minerals, which arecategorized into the following groups:-

4.1. Metallic Minerals

Gold As elsewhere in Ethiopia, gold within the Amhara Region occurs both as nativegold and primary gold (lode gold).

Native Gold

By virtue of its insolubility and high specific gravity gold occurs unaltered andconcentrated in alluvial or placer deposits, and auriferous gravels. In Ethiopia this has

been the primary source of gold until the discovery of commercial deposit of lode gold in

the Legedembi area, Adola, in the latter part of 1980s.

In the Amhara Region the reported occurrence of placer gold is in Agewawi Zone,

Chagne district, where according to ARDCO (1999), local artisanal miners are active,producing the mineral by the traditional method.

Primary Gold (Lode Gold)

Vein type gold mineralization in the localities of Sarkayasa and Goder, both situated in

Agewawi Zone in the southwestern part of the Amhara Region became known as a resultof reconnaissance exploration by the Ethiopian Geological Survey between 1996-1997.

Similar type of gold mineralization has been detected in the northern part of the Amhara

Region, (Finarwa- Niraque auriferous zone), Abergele area, bordering the Tigrai Region.The above auriferous zone was also outlined during 1996 - 1997 exploration by the

Ethiopian Geological Survey.

Detailed information on the primary gold in the above localities is given under a separatechapter on exploration.

Associated Minerals

According to the exploration report there are sulphide minerals (pyrite, chalcopyrite)

associated with the lode-gold occurrence both in the southwest and in the northern part of

the Amhara Region.

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Such mineralogical association plus the general geological setting of the two Precambrian

areas are indications that in addition to gold there are possibilities for economic

concentration of a wide range of metallic minerals.

4.2. Non-Metallic Minerals

Silica Within the Amhara Region the sources of silica are the Upper and Lower

Sandstone layers of the Mesozoic Sediments.

Silica sand is employed extensively in mortar and cement, as a flux in the metallurgical

industry, in the manufacture of glass and silica brick, as abrasive and for numerous other

uses.

The Mesozoic Sediments within the Amhara Region occur extensively along the deeply

incised Blue-Nile River and its catchments.

Other major occurrence of the Mesozoic Sediment is within the Tekeze River Basin, inthe northern part of the Amhara Region, as well as in the west. The sequence occurring in

both areas is the Adigrat Sandstone.

Kaolin Apart from being an important raw material for ceramic industry kaolin is the

chief filler in the pulp to produce the body of the paper and its smooth surface. Kaolin isalso used very extensively in the rubber industry as a filler, as well as having an

increasing application in paint industry.

In Ethiopia ceramic raw materials of economic importance are associated with two

geological formations and these are:-

(a) The Mesozoic Sediments

(b) The acid plutonic bodies associated with Precambrian Basement

Mesozoic Sediments The source of kaolin in the Mesozoic Sediments are the Upperand the Lower Sandstones.

The main mineralogical component of these sediments is quartz, with subordinatefeldspar, kaolin and mica.

In the Amhara Region the reported occurrence of kaolinitic sandstone is in the Wenchit

area in North Shoa Zone.

Laboratory test by the Ethiopian Geological Survey on limited number of samples from

the above area gave kaolin in the range of 6.6 13.5% in the rock mass.

In terms of mineral content the above value is comparable to the value of kaolin obtained

from kaolinitic sandstone in the Mukarba locality in North Shoa, Oromia Region. The

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kaolinitic material from this locality is currently utilized by the Addis Ababa Ceramic

Plant in the production of sanitary ware.

Acid plutonic bodies associated with Precambrian ComplexWithin the PrecambrianComplex kaolin is formed by the decomposition of feldspars in granites which are

associated with the Precambrian complex. This decomposition or kaolinization is effectedin two ways:-

(a) By ascending gases and vapours, which emanate from a deep-seated acid igneousmagma.

(b) Downward percolation of surface waters containing carbon dioxide, organic acidsand other substances which like the ascending vapors, leach out the potash in the

feldspar and leave a reside of kaolin (W. R. Jones, 1955).

In addition to the Mesozoic Sandstones the acid plutons associated with the Precambrian

Complex in the west, southwest and northern parts of the Amhara Region are potentialsource of high quality kaolin raw material.

Feldspar rich volcanic rocks The results of investigation undertaken in 1986 indicate

that the altered and weathered sections of the feldspar rich volcanic rocks in South

Gonder Zone, (around Debre Tabor town, as well as Awzet and Kerker localities) couldbe the source of porous ceramic production.

Gypsum Is a chemical sediment naturally occurring as hydrated calcium sulphate. Theprincipal use of gypsum is in the production of Portland Cement in which gypsum is used

to retard and control the time of setting. Gypsum can also be used as soil fertilizer, as

insulator against heat and cold in modern homes, as well as a filler in paints, etc.

Within the Amhara Region extensive deposits of gypsum occur in association with

Mesozoic sediments in the Blue-Nile Basin.

Presently the major use of gypsum is in the cement industry.

In the building trade gypsum is also used by individuals in the form of hard wall plastersand for stucco work.

According to the East African Group (1998), the Ministry of Education operates a small

gypsum quarry in the Belbelit area of North Shoa Zone, Amhara Region, in which thegypsum is used for the production of chalk.

Bentonite is the commercial name for a substance specified to contain not less than85% of the clay mineral known as montmorillonite, (a hydrated silicate of aluminum,

with calcium and magnesium), W.R. Jones, 1955.

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Bentonite is derived from weathered volcanic ash and deposited as clay in lacustrine

basin.

The most important use of bentonite is its application as drilling mud in oil-well drilling

and oil refining.

Because of its capacity for absorbing water to a far greater degree than ordinary clay

minerals, bentonite can also be used as soil conditioner.

Other applications of bentonite is in foundry and pelletizing.

According to the investigation undertaken by the Mines and Rural Energy Resources

Development Office of the Amhara National Regional Government, bentonite occurs inthe Chilga area, situated in the western part of Gonder.

4.3. Energy Minerals

a) Lignite - within the Amhara region the occurrence of lignite (brown coal) is

known in a number of localities since early times. The various occurrences havebeen investigated at different times, details of which are given under the chapter

on exploration.

The localities where lignite is known to occur are:

a) Gondor Zone- in the Chilga areab) North Shoa Zone in Mush valley and near the town of Debre-Birhan

c) Welo-near Wuchale

b) Oil Seep Occurs in Welo, situated 60km south southwest of Dessie

c) Oil Shale Also occurs in Welo, located 10kms southwest of Mersa, which is in

turn 90km north of Dessie.

4.3.1 Petroleum potential of the Abay River Basin

Potential Reservoir (According to BEICIP, 1998, the potential reservoir corresponds

to the Upper sandstone of Amba Aradom formation (alluvial plain environment) the

potential reservoir corresponds to the Upper Sandstone, of the Amba Aradadom

formation (alluvial plain environment) in which porosity and permeability expected to be

fairly goods.

The oolitic and reefal sequences of the Antalo Limestone (equivalent to the UpperLimestone in Ogaden)may constitute another good reservoir.

The Adigrat Sandstone, which is medium grained and well sorted is also possibleexcellent reservoir.

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Potential source rocks:- The best potential source rocks, according to BETCIP, (1998)

are shale, marl and mudstone of the Autalo Formation that could be the equivalent of the

Urandab source rock of the Ogaden Sedimentary Basin.

The organic matter is of the type II and according to the analyses carried out by BEICEP

FRANLAB, their petroleum potential is relatively high (16-60kg HC/ton). Fieldsamples are immature, but more deeply buried equivalents are the probable source of the

Mechala seep in the Wereilu district.

No equivalent of Bokh sources in Ogaden has been identified. It is probable that they

may exist toward southeast and east of the basin.

Traps

The field sections show homocline with a maximum dip of few degrees towards the east

(i.e with counter dips). According to Beicip no structural traps can be defined at present

within the Basin, due to the lack of seismic data.

Stratigraphic traps, such as pinch-out of sandstone reservoirs and permeability barrierswithin the carbonates could occur

Conclusion

With respect to petroleum potential of the Abay Basin BEICIP-FRANLAB, (1998)

concludes as follows:

The presence of potential source rocks and reservoirs and the presence of an oil seep

show that the Abay River Basin has non negligible petroleum interest. However, the

stage of exploration (no seismic, no well) does not allow more details to be given onpossible plays and no prospect can be defined at present

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Mechela Shet river bottom hosting oil seep (s)After BillSt. John, 1981

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Crossbedded probable Cretaceous Upper sandstoneAfter BillSt. John, 1981

Probable Cretaceous Upper Sandstone beneath Tertiarybasalt

After BillSt. John, 1981

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4.4. Gemstone

Opal Is the known mineral of gem quality within the Amhara Region. The name opal

has been derived from opallios, which in Greek means precious stone.

Depending on the interplay of colours three types of opal are known commercially, (Min

of Mines 2002). These are:-

(a) White opal

(b) Black opal

(c) Common opal (fire opal)

The first two types are considered as precious opal while the third is less worthy.

Precious opal is valued in carat in which one carat is equivalent to 0.2 gm by weight (Minof Mines, 2002).

Within the Amhara Region the occurrence of opal are known in two zones.

(a) North Shoa Zone Opal in North Shoa Zone occurs northwest of Mezezo town.

The opal in this locality has been classified by the Ministry of Mines (2002) as

precious opal.

In order to get to the occurrence one drives 7 km from Mezezo town along the

main road leading to Mahal Meda. The occurrence is west of this point, in thevicinity known as Kobastil. The exploratory work carried out on opal by Abay

National Resources Development PLC is discussed under the chapter on

exploration. According to the Mineral Operations Department of the Ministry ofMines the precious opal in North Shoa Zone occupies a wide area.

(b) South Gonder Zone The other occurrence of opal in the Amhara Region is

situated in South Gonder Zone, Farta Wereda in the locality of Boda, bounded bythe following coordinates:-

Latitude 100, 54', 00'' 110 56', 30''Longitude 380, 05', 00'' 380, 10', 00''

Source: (1) Eng. Gari Fufa, formerly Head of the Geophysical Dept. of the

Ethiopian Geological Survey and presently a Private Consultant.

(2) Geologist Said Ali, post-graduate student at Addis Ababa

University.

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4.5 Dimension Stone

According to the definition of the United States Bureau of Mines the term dimension

stone refers to naturally occurring rock materials, cut and shaped for use as blocks, slabs,

sheets or other construction units of specified size.

The term is also applied to quarry blocks from which pieces of fixed dimensions may be

cut.

As the distribution of rock types is governed by geologic factors, the diverse geologic

environment in the Amhara Region gave rise to the formation of a wide variety of rocksthat can be used as dimension stone.

The main sources for good quality dimension stone in the Amhara Region are:

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4.5.1 Precambrian crystalline rocks and associated intrusives

Marble Commercially marble is defined as metamorphosed limestone and dolostone,

in which the original rock texture has been obliterated due to intensive recrystallization.

In the Metekel Zone of Beneshangul-Gumuz Regional State, adjacent to the southwesternpart of the Amhara Region good quality marble occurs in such localities as Baruda, Mora

and Bulen.

Commercially the price of marble is dependent on the colour and texture, in which the

fine grained variety is highly priced.

As can be seen from the published geological map of Ethiopia, (1996) the Precambrian

formation underlying the Metekel Zone is similar to the western and south western parts

of the Amhara Region.

The results of integrated mineral exploration by the Ethiopian Geological Survey in 1996and 1997 in the Bure district, (southwestern part of the Amhara Region) indicates that

lenses of marble occur in the Kilaj area in association with the Precambrian complex.Hence there is a good chance of locating commercial deposits of marble in this part and

possibly other parts of the Amhara Region underlain by Precambrian complex through

further geological mapping, systematic sampling and testing of the marble occurrences.

Intrusives

The Granite Group

The granite group includes all rock types that genetically fall within rocks of acidiccomposition.

The most common rock types used as source of dimension stone are:

Granites of all varieties

Granodiorite

Alkaline plugs (Phonolite, Trachyte)

Rhyolite

Leucocratic porphyries

In the Amhara Region the most notable occurrence of the granitic group of rocks(Geologic Map of Ethiopia, 1996) are:-

a) Granite (Gt4) This plutoric body occurs about 60km (air distance) west-southwest of Bure, just north of the Blue Nile. In this area two isolated bodies,

sub-circular in shape are enclosed by the Alghe Gneiss.

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The granitic rocks are characterized by massive to moderately foliated features, generally

bearing large phonocrysts of feldspar.

b) Granodiorite This plutonic body is located 180km (air distance) west of Bahir

Dar. It is a body which is about 100km in strike length and 20km in width. It is

possible that within this large plutonic body the association of granite is possible,in which the contact between the two bodies may possible be gradational

The Gabbro Series with respect to the gabbro series the most significant rock typesfalling into this category and quarried as dimension stone are:

Diorite

Diabase

Gabbro

Norite and,

Ultramafics

Commercially the rocks of the gabbro series are dull or dark coloured.

Tonalite (Quartz diorite) With respect to the Amhara Region the most significant

occurrence among the rocks of the gabbro series is tonalite or quartz diorite.

This platonic body is located about 50km (air distance) west of Chagni. The body is

enclosed by the Tulu Dimta Precambrian complex and oriented north-south, measuring

about 48km in strike length and 20 km wide, (Geologic map of Ethiopia, 1996)

4.5.2 Mesozoic sediments as source of dimension stone

With respect to Mesozoic sediments the possible source of dimension stone are thelimestone and sandstone.

Limestone As seen from the geological map of Ethiopia, (1996) there are two types oflimestone series within the Blue Nile basin of the Amhara Region namely:

a) The Antalo Limestone (Upper Unit)b) The Abay Formation (Lower Unit)

Physical and chemical tests conducted in the Wenchit and Jema areas of North Shoa Zone

of the Amhara Region have confirmed that the limestone in the two areas meets thestandard for the production of dimension stone.

The sandstone The sandstone occurrence within the Amhara Region is more extensivethan the limestone. In addition to the Blue Nile Basin this formation occurs within Tekezi

Basin in the north, as well as in the western part of the Amhara Region. The latter

occurrence is oriented north-south, measuring 120km in strike length and the widthvarying from 4 to 16 km.

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The available geological and exploration data indicates that in addition to the crystalline

and intrusive rocks the Mesozoic sediments are also important source of dimension stone

in the Amhara Region.

4.5.3 Volcanic Rocks

IgnimbritesPresently ignimbrites are the major source of construction materials in the

central region of Ethiopia, including Addis Ababa, where the materials are being used as

dimension stone

The term ignimbrite has been initially suggested by Marshall, meaning fiery cloud rock

or fiery spray rock, ( in A. Holmes, P 112-113). However, the term has now a wider

meaning and is in general use to describe pyroclastic rocks, whether geologically old(Pre-Rift) or recent (Post Rift)

Moorhouse, W.W (1959) defines ignimbrites as volcanic rock fragments, welded

together, and because of which they are also known as welded tuffs.

Since ignimbrites are well jointed they are commonly used as dimension stone in thebuilding industry. Depending on their texture (close texture) and density about 2gm/cm3,

( Karsteadt, H. , 1985) ignimbrites can also be used as aggregates

According to Karsteadt, et. al, (1986), who carried out geological investigation of

ignimbrites occurring in and around Addis Ababa the size of feldspar phenocrysts in the

rocks varies from 1 to 3 mm.

Based on the currently available geological information the ignimbrites occurring in theAmhara Region can be grouped into:

a) Pre-Rift and b) Post-Rift

Pre-rift- Ignimbrites of pre-Rift origin are associated with the Salic members of AlajaeFormation (PNa). This formation widely occurs in the east and southeastern parts of the

Amhara Region, for instance, in the vicinities of Dessie, Kombolcha, Debrebirhan and

many other towns.

Post-Rift Within the Amhara Region Post-Rift ignimbrites are associated with what is

known as the Nazret Series ((Nn), Geological Map of Ethiopia, 1996. In the central

Ethiopia Rift the Nazret Series form the western margin of the Rift, extending from EastShoa Zone of Oromia Region to the southeastern part of the Amhara Region.

Thus, with systematic geologic mapping of the Amhara Region at the standard scale theAlajae Formation and the Nazret Series occurring in the east and southeastern parts of the

Region could become potential source for ignimbrites.

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4.6 Construction Raw Materials

Basalts among the volcanic rocks the occurrence of basalts within the Amhara Regionis widespread. These basaltic rocks, which are of pre-Rift and post-Rift origin are the

primary source of construction raw materials, involving major construction projects in the

Region.

It may be noted that because of their fine grained nature basalts have extra-ordinary

physical and technological properties. On average basaltic rocks have a density of about

3gm/cm3 and mainly used as raw materials for the production of crushed aggregates.

Scoria is a vesicular basaltic agglomerate related to post-Rift volcanism.

The occurrence of scoria is observed in and around Bahir Dar and therefore ideally

located for construction purposes

Besides road construction, scoria is used for the production of hollow blocket, whenmixed with sand, crushed aggregates and cement.

Clay Since pre-historic times clay has been widely in use in Ethiopia for building and

pottery making and to a lesser extent for ornamental purposes.

With respect to modern construction industry the principal use of clay is in makingbricks, roof tiles, drain tile, conduit ... etc.

The proper blending of clays and improved firing procedure would improve the quality ofbricks.

According to H.Karstaedt (1985), who made a survey of various brick factories in thevicinity of Addis Ababa, the proportion between white clay and red clay is 3:1, as well as

1:1.

With respect to the Amhara Region the Geological Survey of Ethiopia (2003) reportedoccurrences of clay deposits between DebreBirihan and Debresina in North Shoa Zone.

Other occurrences reported in the Region are in Debre Tabor, South Gonder Zone, in the

localities of Awzet and Kerker.

Through a survey conducted in 1999 by Water, Mines and Energy Resources

Development Bureau of the Amhara Region, deposit of red clay suitable for brickproduction has been located in the Chilga area, situated 50km west of Gonder town.

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Part Five: ExplorationThe geological/mineral exploration within the Amhara Region can be divided into early

exploration and recent exploration.

5.1. Early Exploration

Blanford (1870) was the early geological explorer of the Amhara Region. Because of thewider extent of the Tertiary Volcanics in the Region, much of Blanfords geological work

had concentrated on this rock formation, which he subdivided into:

(a) Magdala Group

(b) Ashangi Group

Blanfords geological investigation was later continued by Daneilli, resulting in the

production of the geological map of the Horn of Africa.

With regards to mineral investigation the available records indicate that early attentionwas directed to lignite (brown-coal) which occurs in several localities in the Amhara

Region.

Exploration Undertaken in North Shoa Zone

Mush Valley

According to D.A Jelenc (1966) the lignite deposit in Mush Valley is situated 40km

northeast of Debre Birhan, centered approximately at 90 45' latitude and 390, 40'longitude.

Mudrock (1944) remarked that the exposed thickness of the lignite seam varies from 2 to

4 meters, thus making the deposit attractive. Mudrocks field observations has beenconfirmed by D.A. Jelenc, who put the length of the exposed section as 300 meters and

seam thickness between 3.5 4m.

Jelenc also noted that the lignite deposit of Mush Valley has in the past been exploited for

local use, as well as a source of fuel for the then Ethio-Franco Railway. Regarding the

reserves, exploratory work undertaken in 1959 by a French Mission from the Bureau

Minier had established a surface area of 262,000m2, seam thickness 1.75 meters andpossible reserves of 300,000 tons. However, this estimation was based on near surface

exploration. No deep drilling was carried out and hence the estimation should be

considered tentative.

Regarding the quality of the lignite the laboratory ''de l' Office Central de Chauffe

Rationnelle in Paris carried out analysis of samples and gave the following results:-

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1. Calorific value for wet samples = 3975 cal/g

2. Calorific value for dry samples = 4552 cal/g

3. Volatile matters = 39.25%4. Ash content = 22.22%

5. Fixed carbon = 38.53%

The number of samples involved in the analysis not known.

Lignite deposit near Debre Birhan

According to D.A Jelenc (1966), Kitachew et. al (1978) the lignite occurrence near the

town of Debre Birhan is situated about 2 km northeast of the town on the eastern side of

Beressa River.

The occurrence is centered at latitude 90, 40' and longitude 390, 30' at an elevation of

2600-2700 meters within Ankober sub-district.

From the town of Debre Birhan access to the lignite occurrences is by dry-weather road,

which leads to the top of Abo-Gedam Gorge, where the lignite occurrence is situated.

The observed occurrence of the lignite at Abo-Gedam Gorge is exposed in a stream along

both banks.

According to Kitachew the lignite seam runs for about 40 meters along the banks, being

concealed in places by large boulders of basalts and bush.

In the course of field work 8 samples were collected and analyzed for ash and moisture

contents.

Sample Designation Moisture Content (%) Ash Content (%)

100393 5.1 78.40

100394 5.4 82.5

100395 4.3 75.3

100396 7.5 3.4

100397 5.5 64.5

100398 7.5 76.2

100399 4.4 78.2

100400 3.9 81.7

As can be seen from the above results, which, of course, are not complete analyses, theash content is unacceptably high in all but one sample, (100396). Nevertheless the

number of samples involved in the analysis is too limited and may not represent the

potential area.

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Lignite Mine Near Wuchale

According to T.G. Mudrock, 1944 the lignite mine near Wuchale is locatedapproximately 5.5 km S 400 W of Wuchale town, which is in turn located 61.3 km north

of Dessie.

Mudrock, who examined the mine noted in his report about the underground mine

development, running approximately S 450 W. Mudrock further noted that the hauling

wall near the portal shows a straight dip to the southeast adding that the drift is about 2meters high and 3 meters wide. Referring to the official Italian records, Mudrock stated

that coal production during the first half of 1939 averaged about 40 metric tons per

month.

With regards to the method of mining, Mudrock remarked that operation was by pick,without the use of explosives.

According to Mudrocks account a 2300 meter cableway was installed in order to

transport the coal, with three intermediate stations, which, Mudrock considered thesystem to be of a gravity type, where loaded buckets were going down, pulling the empty

ones.

Mudrock remarked in his report that it was not possible to make any definite estimation

of the reserves, adding that the mine was apparently developed but not mined out, thepast production being developmental work.

With regards to the quality of the lignite the following are the analytical results by the

Italians.

Analyses ResultsMoisture content 6.13

Fixed carbon 47.98

Volatile matters 32.03

Ash content 13.86

Sulphur 4.7

One of the important criteria in determining the quality of brown coal is the ash content.With respect to the above analysis the ash content of Wuchale lignite is low and therefore

making the prospect a target for further evaluation.

The Chilga Lignite Deposit

The Chilga Lignite deposit is situated 50 km west of Gonder town, close to the Chilga

village. It is bounded by latitude 120, 25' 120, 38', longitude 370, 03' 370, 11'.

Overland access to the area is through Gonder-Metema road.

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The Chilga lignite deposit is known since 1879. According to J. Astrup the deposit was

first examined by A. Sadebeck, who refers to lignite beds situated in Sar Wuha near the

village of Guang in his book entitled Geologie Von Ost Africa, published in 1879.

The last exploratory work on the deposit was carried out by the Ethiopian Ministry of

Mines and Energy, through its Geological Survey in early 1980s. The work involvedsurface geological mapping and deep drilling.

The exploration was carried out over an area of 300 sq. km, using 1:50,000 scale aerialphotographs as a base.

According to Belachew Tezera et. al (1982), who led the exploratory team, the Chilga

lacustrine sediment is composed of alternating layers of clay, silt, ash, shale and lignite.Tezera notes that the whole sedimentary sequence is covered by Pleistocene Sediment,

made up of brown to red-brown loam.

With regards to deep drilling, the initial phase, according to the report, involved 4 drillholes spaced 3,000 meters apart.

During the second phase 8 additional holes were drilled. All the drill holes were plotted

on the topographic map at the scale of 1:10,000.

A total of 90 lignite samples were collected and analyzed at the laboratory of the

Ethiopian Geological Survey in Addis Ababa. The results are summarized below.

Range of ash content (%) Number of Samples

0-32 25

32-50 43> 50% 22

The average ash content of all samples was calculated as 40.2%. The average moisture

content at 1100C was found to be 8.78%.

A second investigation on 83 of the above samples was carried out at the ChemistryDepartment of the Addis Ababa University, where the ash content and the calorific values

were determined.

The values are summarized below:-

Range of calorific value = 1178 6205 cal/g

The average calorific value involving 83 samples was found to be 3347 cal/g.

With regard to the ash content the values range 10.3 63.44%.

Results of individual samples have not been appended in the report.

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Reserve Calculation

The area for the estimation of reserves was based on six drill holes, (DDH-6, DDH-9,DDH-27, DDH-30, DDH-31, and DDH-32), divided into three blocks.

Taking the total surface area as 3.9 sq. km or 3,900,000 sq. m, the total linear thickness oflignite seem as 4.23 m, and density as 1.2, a reserve of 19.7 mil. tons has been estimated.

The ratio of lignite to over burden was calculated as 1:12.6.

It was concluded that the deposit is not minable.

Exploration for other energy resources

Oil seep According to J. Kovacik (1974) oil seepage occurs within Mechala Shet,

situated 60 km south-south west of Dessie town in Welo. Kovacik noted that the altitude

of the oil seep is 2600 meters and the vertical drop-down to the floor of the Canyon about

300 meters.

During the latter part of February, 1992, Bill St. Johns from Hunt Oil Company visitedthe oil seep. In his report Bill St. Johns mentions of five seeps over 50 meters of river

bed. The writer further mentions that the seeps are all located in vertical fractures or

joints, striking approx. N600W.

In the course of the field visit B. St. Johns had photographed two seeps, including one

with the Magalan Unit, which indicated the geographic position by the following

coordinates. Latitude 100, 39', 37'N, and longitude 390, 22', 17'E.

Oil Shale Oil Shale occurrence in Welo is located approximately 10km. (air-distance)

on a magnetic bearing of 2400 from the town of Mersa, which is situated 90 km north ofDessie. The occurrence is found at an altitude of 2275m near the village of Werekeyou on

the bank of Buki River.

The occurrence became known in 1956, when a sample was first examined by J. Astrup,

who described the sample as dark, brownish grey in color, finely laminated, showing

distinct darker parallel bands with specific gravity of 2.18. Astrup further remarked that

when heated for some time in gas flame the sample evolved volatiles which sustained asooty flame for some time, the combustion produced having a characteristic smell of

mineral oil.

Astrup further noted that in the course of chemical test in the laboratory the sample

evolved a notable volume of black smoke of characteristic petroleum odor, the loss on

ignition being 8.36%.

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5.2. Recent Exploration

The geological and mineral investigations undertaken within the Amhara Region since

early 1980s to 2002.

5.2.1. Industrial Minerals and Rocks

Kaolin Investigation for kaolin, Abinet Yematawork, (1986) was carried out in Gonder

province with an aim to make an assessment of kaolin raw materials for small scale

ceramic industry. According to the available report the survey was of a reconnaissancenature lasting two weeks, during which several kaolin occurrences were examined in the

localities of Awzet, Debre Tabor, Iyesus Mountain and Kerker.

From the above localities a total of 24 bulk samples (each weighting 5kg) were collectedfor chemical and physical tests. The chemical analysis involved a complete silicate

analysis by the laboratory of the Ethiopian Geological Survey in Addis Ababa.

The physical tests included:

Density

Free swell test

Grain size analysis

Attenberg plasticity limit and;

Dry shrinkage limit

The first three physical tests were conducted by the Ethiopian Geological Survey

Laboratory while the last two by the Building College Laboratory, in Addis Ababa.

The source of kaolin occurrences investigated are volcanic rocks enriched in feldspars.

Results Chemically the majority of the samples tested were found to contain iron and

other undesirable constituents above the acceptable limit.

The occurrence at Awzet, situated east-southeast of Debre Tabor town, off the main

Debre Tabor- Dessie road has been recommended for further investigation.

Exploration for gypsum and limestone - The areas explored are Wenchit and Jemma

River areas in North Shoa Zone of the Amhara Region.

Overland access to both areas is through Muketuri, which is connected to Alem Ketemaby gravel road of all-weather standard. The exploratory work in both areas was carried

out in 1993 by a team from the Ethiopian Geological Survey.

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The work undertaken is summarized in the following table.

Unit Locality

Wenchit Jemma Total

Geological mapping, scale 1:10,000 sq. km 7.79 8.17 15.96

Section described in no. 2 2 4Channel samples collected 10 9 19

Block sample 3 3 6

Hand specimen 2 2 4

Results of chemical analysis of limestone samples (analysis by the Ethiopian GeologicalSurvey)

Locality Results

SiO2 (%) Al2O3 (%) CaO (%) Fe2O3 LOI (%)

Jemma 1.62 0.35 52.38 0.30 43.3

Wenchit 1.82 0.36 52.68 0.25 43.3

In addition to silicate analysis dry density test was also carried out on limestone samples,in which the values ranged from 2.64 gm/cm3 to 2.65gm/cm3. These values fit the

theoretical value for dimension stone which is 2.7 gm/cm3.

No definite reserve estimates have been made for the areas explored. However, it has

been concluded that in Wenchit and Jemma areas there are sufficient reserves of

limestone which can be exploited for dimension stone.

The study undertaken by Abay River Basin Integrated Master Plan Project -

According to Project Report (1998), the Wenchit limestone deposit has been geologicallyinvestigated, in which bulk samples over an area of 7.8 sq. km have been collected onboth sides of Wenchit River Bridge.

The chemical analysis of 15 bulk samples gave the following results:-

CaO = 52.68%

SiO2 = 1.82 %Al2O3 = 0.36%

L.O.I = 43.30%

Density = 2.64 gm/cm3 (on dry basis)

The above results are comparable with the Geological Survey results.

The project report states that limestone blocks were split and polished in plate and cubeforms at Ethio-Marble Plant with the result that the samples tested showed smooth and

shiny surfaces without scratches, holes or flakes and with very clear edges and angles.

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The Project Report concludes that in terms of quality the Wenchit limestone deposit is in

conformity with the standard for dimensional type material.

Exploration of Jemma Limestone

During the Abay River Basin Integrated Master Plan Project the Jemma limestone deposithas also been investigated for use as dimension stone. The deposit investigated is located

near the confluence of Jemma and Welale Rivers, down stream.

A total of 14 rock samples tested chemically gave the following results:

CaO = 52.38%

SiO2 = 1.62 %Al2O3 = 0.35%

Fe2O3 = 0.30%

L.O.I = 43.37%

The project report concluded that besides the normal chemical content the Jemma

limestone deposit has been physically tested and proved to possess good cutting andpolishing characteristics. Hence the deposit meets the standard for use as dimension

stone, (no maps on the investigated areas have been attached).

Investigation for glass sand in Jemma and Wenchit valleys This investigation was

carried out by Geologists Aklilu Asefa and Leon Gumarov, from the Ethiopian

Geological Survey.

Jemma Valley The sedimentary formation chemically tested in the Jemma Valley is

the Upper (Cretaceous Sandstone), in which the content of Fe2O3 range from 0.3% - 1%

and TiO2 from 0.2% - 0.4%.

Two lenses in the Amber and Berbersa Wuha, were found of interest with Fe2O3 and TiO2less than 0.1%.

It was concluded that after beneficiation the sandstone could be used for glass and

foundry industries.

Wenchit In Wenchit River Basin sections of two streams namely Folfolit and

Ambagenen were investigated for glass sand. Lenses of light grey to whitish sandstone

were delineated.

At location 100478 (no location map attached) the lense is 50 meters thick and 400

meters in strike length. The content of Fe2O3 is less than 0.1% and the TiO2 contentranging from 0.1 0.4%.

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At locations 100480 and 100491 the content of Fe2O3 is above 0.1% and the TiO2 content

ranging from 0.3 0.4%. The lenses are 10-150 meters thick and 750 meters in strike

length.

It was concluded that after beneficiation the section examined could be used for glass

production.

Beto River area in the Beto River area the exposure examined range in thickness from

25m 30m with the following results.

Fe2O3 0.1% - 0.3%

TiO2 0.2% - 0.5%

It was concluded that the exposure does not warrant further investigation.

Other mineral reported by Aklilu Asefa and Leon Gumarov is light grey gypsum (10-15meters) in thickness and interbedded with limestone below the sandstone near the

confluence of Bersina and Jemma Rivers. It was further stated in the investigation reportthat some lenses of gypsum contain translucent, white and pink alabaster, which can be

used for decorative purposes.

The report prepared by Aklilu Asefa et. al concluded that the sandstone with low iron

(Fe2O3) outlined in the Folfolit, Ambagenen and Bersina rivers should be further

examined to prove sufficient reserves of high grade silica.

It was also recommended that the unlimited reserves of limestone in the Jemma and

Wenchit valleys can be used for the production of cement and dimension stone.

Investigation for brick and tile raw material In 1999 the Water, Minerals and Energy

Development Bureau of the Amhara National Regional Government has carried out

geological investigation for brick and tile raw material. The location of the survey area isapproximately 50 km southwest of Gonder town, bounded by the following coordinates,

latitude 120, 25' 120, 39', longitude 370, 04' 370, 12'.

Overland access to the area is through Gonder Metema road. Geologically the area ofinterest is underlain by basalt and tuff.

The maximum reported thickness of the residual cover investigated is 4 meters and theaverage thickness 2.5 meters.

The investigation was carried out using the following data as standard for brickproduction.

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Chemical standard

1. SiO2 - 53 81%2.Al2O3 - 7 23%

3. Fe2O3 - 2.5 8%

4. CaO - 1 15%5. MgO - 0.5 2%

6. K2O - 1.8 4%

7. SO3 - 0.02 1.8%

Physical standard

1. Loss on ignition (L.O.I) - 3 4%2. Linear air shrinkage - < 12%

3. Water absorption (after firing at 1000C) - 8.0 20.0%

Based on the above chemical and physical standards the red, laterite soil was found to besuitable for brick production.

Accordingly the Wagamit area has been recommended for further follow-up, using

shallow bore holes (up to a depth of 20 meters). Further investigation has also been

recommended on bentonite soil, occurring in the survey area, which, according to thereport the bentonite is associated with lignite bed. The reported thickness of the bentonite

layer is up to 6 meters, commonly overlying the lignite seam, and described as cream in

color, easily friable and highly soluble in water.

5.2.2. Invest

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An Rs Final Mineral Report

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