Mineral Processing in Blue Nile

A Preliminary Proposal

Ahmed Khidir Yagoub Ph. D.

P.O.Box 794, Omdurman, Sudan.

akyagoub@gmail.com

Tel: 249 155260454

Introduction

The mining industry in the Sudan is quite behind even within the standards of the

developing world. Before the country become oil producing in 1999 only a limited

chromite export of 15,000 tons and 4 tons of Ariab gold was contributed by the

mining sector, providing limited revenue of foreign exchange. Additional revenue is

obtained through taxes and royalties and the newly acquired shares made righteous by

the CPA after 2005.

In this mineral industrial investment we are advocating mineral processing side by

side with mining. Mineral processing is essentially chemical and metallurgical

processing. It is well known that chemical processing at a limited scale is rarely

feasible. This is due to the fact that chemical processes are chain and dendrite in

nature i.e. follows serial and branched paths. If the by-products are not utilized as

inputs or cycled the cost shoots up. It is therefore quite advisable to invest in mining

and processing of several of the minerals available at the rich Ingassana locality and

breed the processing towards multiple products for greater marketing degrees of

freedom.

Consider the availability of chromite, magnesite, marble, graphite, asbestos and talc.

Chromite processing require iron for chrome steel making and for chromium

chemicals production, marble is needed. Marble can participate in this input as well as

being itself processed as lime or cement. Marble is also important in asbestos different

products. All these chemicals processes require sulfuric acid, if the latter is

manufactured, its only input is cheep sulfur which can be imported and the production

can thus cover the market which imports sulfuric acid for car batteries. It is also

tempting to think of the paper industry since its backbone is cheep electricity and high

demand for water. Sulfuric acid, sodium hydroxide, lime and talc are inputs in the

paper process.

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Chromium and magnesium salts, lime, cement chrome steel among the many products

expected from this complex chemical industry, are all cash products. They have many

uses and stand as raw material for more sophisticated industries and are easily

marketed and stands as a respectable export that have price index like oil, cereals,

sugar and meat.

This joint venture is expected to be a partnership of three: The state royalty, a financer

and the expert firm. The state will host the business with an agreed upon equity

shares and royalty. The state has to emphasize the high value in the technology

transfer and know-how gains from this joint venture rather than the money gain in

terms of state GDP per capita. This of course is to be adopted by the state through

awareness and development strategies and planning put forward for health, education

and the environment. The financer is to support the infra structure and plant

development. The expert firm is to provide the know-how, manages the plant and set

the production and marketing policy.

The major benefit of course is the uncontested technical skills acquired through

technology transfer and the impact of foreign investment. The great physicist Abdul

Salam noted: No country can opt for creation and diffusion of domestically produced

technology without the import and diffusion of foreign one. At the same time, an

efficient transfer of foreign technology and thus stable technological development can

not be productive unless accompanied by a reasonably high level of domestic research

and development (R&D). The characteristics of importing technology should be taken

into consideration when defining R&D priorities, while the capability in the latter

field should influence the import of technology. To rely only on domestically

produced technology is not rational or feasible, while to concentrate mainly on import

and diffusion of foreign technology leads to technological dependence. Therefore an

adequate balance between them, both on regional and global bases should be achieved

taking into account specific conditions of individual countries.

The above asserts two important points; sound education for the domestic

technologist who will collaborate with the expertise and the latter whom is willing to

disseminate his know-how. High standard young engineers, technologist and scientist

are needed to run this multinational venture. However if they are not available

locally, we should make provision to send nationals abroad to train in accredited

institutes. Some of the highly technological countries do not endorse or even consider

training locals as is happening in the oil sector presently.

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Other benefits of foreign investment on top of the impact of technology transfer in

terms of machinery, skills and know-how is the streamlining of the investment in

directions of marketable production and minimized risk. It is also worth mentioning

that joint ventures are self-protected in this global market jungle against the piracy,

hijacking and containment attitude of large conglomerate and multinational

companies and at occasion governments.

The chemical plant is usually established at places of continuous and sustainable

supply of water. Most chemical processes are done in solvent water with a diminished

cost than if done in gas or solid phase. Water also helps in carrying the effluents

where it is easy to recycle, reclaim or purify the effluents according to standard

pollution abating methods. Modern reactors of the chemical industry including

metallurgical process use electrical supply as a source of energy. Cheep and

efficiently used supply is a prime factor on the success and feasibility of a chemical

plant. The water resources and the hydroelectric potential of the Blue Nile state rates

it high among other states and regions rich in mineral resource but yet with scanty

water and power sources like Red Sea Hills, Beyuda desert, Nuba Mountains and

Hofrat En Nihas.

Survey of Processes and Products Uses

Mechanical processes are needed for size reduction of the mineral depending on the

nature of the occurrence, in a hill, mountain or a quarry. This is achieved by Hammer

mills, jaw crushers and ball mills where the powdered mineral is then carried to the

processing plant by conveyer belts.

Chromite

Chromite is worked by quarrying, open-cast mining and underground mining

according to the type of deposit. The ores usually worked are high grade not to require

further treatment before melting.

Ferrochrome is a high quality steel (stainless steel) made directly from the ore since

chromite contains iron (FeCrO4) by smelting in an arc furnace with other ingredients

like carbon. Pure chromium is obtained by reducing chromic oxide obtained from

chromite ore by aluminium. Chromium compounds are obtained after heating

chromite in a rotary kiln with marble and sodium carbonate and leaching sodium

chromate from the spongy mass obtained by water. Decorative chromium

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electroplating is applied to steel, brass, aluminium and other metals to give a hard

bluish-tinged coating which will take a high polish very resistant to deterioration.

Lime and Cement

Lime and cement are products based on the raw materials limestone or marble and so

are jointly produced. The most important piece of equipment used for both production

of lime and cement is the rotary kiln. The calcium carbonate in the marble or

limestone is to be burnt at 1000˚C to give calcium oxide which when hydrated with

water gives lime in special rotating equipment. The same is done in case of cement

production but here the marble or limestone is mixed with clay usually from the Nile

silt to give the clinker which is then finely divided to give cement. Cement marketing

is at the fore front nowadays and does not need over emphasis. Lime uses are two

many in and industrialized country, but even in Sudan the amount needed by the

textile, sugar and the tanning industry may amount to 100,000 tons annually if these

are working at full capacity. Most of this is imported. Generally, metallurgical, food,

rubber, petroleum, leather, paint and paper industries all use lime.

Mgnesite

The size reduced mineral may be heated to 1000˚C similar to marble to obtain in this

case caustic calcined magnesite, or magnesium oxide. This is used in many industries

including the production of the special cement oxychloride cement. Magnesite or

magnesium carbonate can be used directly with acids to form different magnesium

salts. Mgnesite is direcly converted to the metal magnesium by electrolysis which is

used in many metallurgical processes and in electronics. However, if heated in the

kiln up to1450˚C a dense sintered product called dead-burnt magnesite is formed.

This is used as refractory material in metal smelting furnaces.

Asbestos

Asbestos deposits usually occur near the surface, they are mainly mined in open-pit

mines, or by tunneling into the side of the hills. Recovery of asbestos from the mined

lumps containing up to 15 % of asbestos is based on a crushing process, which

completely remove the adhering rocks without destroying the fibrous structure of the

asbestos. Finally the process is completed in an asbestos mill capable of purifying and

classifying the fiber structures according to their length. Asbestos fiber woven into

yarn or blended with metal wire of brass, lead or copper is used as brake lining and

incase of short fibers mixed with metal chips and glued into a matrix by a resin. They

are several other ways of formulating the fiber into packing sheets, paper and yarn,

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Asbestos cement is used in making pipes and tile as construction material. Generally

high temperature uses are too many in particular gaskets of pipes and machinery

experiencing high temperature. Asbestos is a hazardous material, to minimize human

contact, its working requires several precautions and protection means in automated

procedures according to international standard, which increases its cost of production.

Graphite

Natural graphite occurs near the surface in lumps or vein and as flake graphite. Its

mining procedure is similar to asbestos. However graphite is not fibrous and can be

concentrated from the ore but it is difficult to refine further and because of the widely

varying nature of graphite deposits no method is universal. Its uses are based on its

property of low heat conductivity and high conduction of electricity, making it

suitable as metallurgical crucibles and lining of reacting vessels and as electrodes in

electrolysis cells and electric arc furnaces. It is also used in brake lining, refractory

and lubrication.

Talc

Talc is mined in open-cast and shaft mines. The lumps obtained in the mine are sorted

according to their properties and color. Massive lumps free of cracks are used for

cutting into shapes. Small pieces are powdered in dry form in ball mill. Talcum

powder is used as a carrier in cosmetics and pharmaceuticals. It is also used in

ceramics, porcelain and glazes and as a very important additive in the paper industry.

Complex Layout

One would envisage a complex near Er Roseiris Dam Lake. A plant of chemical

processing units provided with a high supply of electric power and administering its

large water demand directly from a water treatment plant at the foot of the lake. A

collection of plants or an industrial village, then, is developing at this site. This

comprise electric arc furnaces for metal smelting, rotary kilns for cement and lime,

evaporators, dryers, filters, sulfuric acid plant, sodium hydroxide plant, paper and

pulp mill, etc.

At the Hills the mines and quarries are the complementary plant with the mechanical

machinery necessary for mining, picking and size reduction of rock. This may

include, Hammer mill, jaw crusher, ball mill, sieves and dust cyclones. This site

accesses the complex at the dam lake by a network of electric railway and conveyer

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belts supplied by electric power transmission lines to transport the finished minerals

to the processing plant.

Possible Products

Metals

Chromium, stainless steel, gold, magnesium, nickel, platinum.

Chemicals

Sulfuric acid, sodium hydroxide, chromic oxide, sodium dichromate sodium

chromate, sodium carbonate, sodium sulfate, sodium fluoride, calcium carbonate,

magnesium carbonate, magnesium sulfate.

Materials

Cement, lime, chromite refractory, magnesite refractory, asbestos fiber, asbestos

paper, asbestos tiles, asbestos pipes, asbestos yarn, break lining, talc powder, talc cut

stones, marble cut stones, graphite powder, graphite flakes, graphite blocks and rods,

paper sheet for press, paper sheet for packing, cartoon sheet.

References

Adli Abdel Mageed, Sudan Industrial Minerals and Rocks, Centre for Strategic

Studies, Khartoum, 1998.

De Bussy, J. H., Materials and Technology, Longman, 1971.

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Annex I

The Mineral Potential and geology

The Ingassana Hills lie 80 km south west of Ed Damazin, approximately between

latitudes 11˚ 1 5' - 11˚ 33' N and longitudes 33˚ 54' - 34˚ 10' E, in the southeastern

Sudan. This area, occupying the upper Blue Nile valley, is one of the most attractive

regions of the Sudan for mineral development. The area possesses substantial mineral

resources with reasonable access and logistics as it is traversed by the highway

linking Khartoum and PortSudanl Ed Damazin and by the railway linking PortSudan

with Snnar/Kosti/ Ed Damazin. There is power and water available from the hydro-

electric dam at Er Roseires on the Blue Nile.

1. Chromite

Chromite ore deposits are known to occur in the “greenstone-ophiolite’ belts in the

Sudan. These belts include (1) the Ingassana Hills in the Blue Nile Region (2)

Hamissana-Sol Hamed in the Northern Red Sea Hills (3) the Nuba Mountains in

Southern Kordofan (4) J. Rahib northwest Sudan and (5) J. El Tawil in Central

Butana. In southern Sudan, a full ophiolite section from ultramafic to chenical

sediments has been reported between Juba and Nimule and in Kapoeta area but there

is no information on chromite occurrences in these rocks.

Ingassana Hills Chromite Deposits

The Ingassana Hills form a distinctive massif mainly built of ultramafic-mafic-

granitic complex which extend, discontinuously southwards to Kurmuk. The

watershed crosses the Hills from south to north where Khors Fern, Dom and other

smaller ones drain eastwards into the Blue Nile, while K. Doleib flows westwards into

the White Nile.

Since the discovery of chromite deposits by Kabesh in 1961, the Ingassana Hills have

been the target for numerous researches and specialized surveys. Kabesh published

Bulletin 11 in 1961, "On the Geology and economic minerals and rocks of the

Ingassana Hills”. Hunting Geology and Geophysics (1969 - 1971) carried out a

regional interpretation survey on behalf of the United Nation Development

Programme. Detailed studies were carried out by Shaddad (1974), Babiker (1977),

Vail and others (1986) and many other unpublished reports by the officers of the

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Sudan Geological Survey (1978-1985). The major detailed exploration works on the

Ingassana Hills, were carried out by the technical team of the Government of the

People Republic of China (1975-1977).

The possibility of establishing a ferro-chrome production plant at Ed Darnazin

utilizing the electrical power available from Er Roseires Dam, has been the subject of

several studies. The most interesting study was that carried by Mitsubishi Corporation

and Japan Metals and Chemical Co.Ltd. 1978, which showed that such a development

is technically feaib1e, given the availability of adequate electrical power at Er

Roseires, but the minimum scale for successful operation would have to be in excess

of 50,000 tons per year and would require improvement in the general cost structure

of the area. Therefore such “added value” development wil1 require a substantial

increase in chromite production. possibly gaine by exploiting the large known

reserves of low grade chromite as well as improvement in the rail transport and

general industrial infra structure of the area.

Mining of high grade chromite in the Ingassana Hills started in the early 1960s at Bau

locality. Since then, the number of Sudanese investors, both companies and

individuals, has increased steadily to reach a total of eight by 1980. The location of

147 occurrences of chromite in the Ingassana Hills by the Chinese technical team, the

high quality and salability on the world market, have greatly attracted and encouraged

chromite mining activities. However, the poor mining and loading facilities together

with difficulties in transport and shipping, have greatly affected the continuity and

increase of production. The annual production varies between 5 and 15 thousand tons

and was dominated by the former Sudanese Mining Corporation (public sector) which

was holding leases for the major mines Gam, Romeilik, Gebanit, Kurba, Bau, Chikay

and other smaller ones until 1993.

Local Geology

The Ingassana Hills massif consists of intrusive rocks of metagabbro, ultramafic

masses and the Bau granite stocks (427+5 m.y) intruding the basement gneisses

schists, marble and quartzites older rocks (847+38.3 m.y) (Fig. 4.1). The intrusive

rocks resulted from the multiphase intrusion of magmas under the control of NNE and

NW trending fault structures. Field observations indicated that the gabbro was

intruded first, followed by ultrabasic masses and at last by the Bau granites (Chinese

Technical Team) (1977).

The total exposed area of the ultramafic masses, is about 400 sq.km. It is divided by

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the NNE trending shear fault zone, which passes along Khor Feri, into an eastern part

and a western larger part. The older basement rocks consist of granitic gneisses which

appear in the southwest, schists, marble and quartzites which surround the whole

mountain mass. The schistosity planes strike NNW-SSE. The ultramafic rocks which

originally consist of dunites and peridotites (mainly harzburgite) have been

serpentinised. The structure of the intrusive rocks is of ring distribution, showing a

circular arc, 35 km in total length extending form Gam Mine through Kuker and

Gebanit to Bobuk. Gabbro occurs extensively over a basin to the east of Gebanit

Mine, which lies in the centre of the arc. Along the contact between the gabbro and

the serpentinised dunites, pyroxenites with big crystal aggregates, is found in a dyke-

like shape.

The plutonic rocks consist of serpentinised dunite and peridotites, pyroxenites,

anorthosite, gabbro and granite, and are intruded by lamprophyre dykes, quartz veins,

aplite veins and pegmatites. The ultrarnafic rocks occur in zonal distribution which is

related to the sequence of crystallization from magma. The petrologic description of

these rocks is as follows:

1. Gabbro

The gabbro is hard massive, dark brown in olour, medium grained and has been

subject to saussuritisation. Clinopyroxene has been replaced by actinolite while the

labrodorite plagioclase was altered to zoisite or epidote. Parts of the rock has been

described as epidiorite and meta-dolerite (Hunting geology and geophysics 1969).

2. Pyroxenite

Pyroxenite occurring between gabbro and dunite, is distributed in a belt shape as if

forming the border of the gabbro. The width varies from few metres to more than l00

m. The rock is dark green in color and is formed of big crystals, 5-20 mm in size, of

slightly altered clinopyroxene to tremolite-actinolite.

3. Dunite

Dunite is found between pyroxenite and harzburgite in a belt-shape. It forms a low-

lying ground and has a thickness of 2 to 2.2 km. The dunite is massive, dark green in

color but it exhibits a brown color on the weathered surface. Near the contact with

harzburgite the proxene crystals are aligned along the foliation planes which coincide

with the general arc direction. The dunite which contains veinlets of chromite is

partially serpentinised thus it is relatively more fresh in comparison with the other

rock formations.

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4. Harzburgite

Harzburgite is distributed along the general strike and is surrounding dunite and the

silicified serpentine. It has irregular lenticular shapes which vary in width between

200 and 1000 m. Orthopyroxene makes up more than 20% of the rock and is mostly

altered to serpentine and chlorite. The olivine has been also altered into serpentine.

Spinel chromite is found oftenly enveloping idiomorphic crystals of olivine.

In the western side of the Ingassana Hills, harzburgite and dunite occur as alternating

layers parallel to each other and forming belts 0.5 to 5 m wide. The pyroxene in

harzburgite is arranged in good order of tabular structure thus giving the rock the

banded state appearance with strike varying between north and 30˚ and dip varying

between vertical and 60˚ W. Under the microscope, the olivine has been nearly

completely replaced by serpentine. Serpentine forms in lines with a certain rhythm in

the shape of flagstones, exhibiting texture peculiar to peridotite. Secondary chlorite

formed after pyroxene and reddish brown chromite occurs as accessories.

5. Silicified serpentine

This is a common rock occurring over the whole area of the Ingassana Hills. The rock

is extremely hard and brown in color. Quartz or chalcedony fills all cracks, fissures

and joints. Silicified serpentine forms the mountain tops and ridges on almost the

same level.

6. Talc-Carbonate

These rocks form lenticular and dyke-like bodies usually found along the peripheries

of some of the serpentine bodies and they are generally light creamy or buff in color,

sometimes with reddish tint. Serpentines and talc carbonate in the Ingassana Hills, are

associated with minor occurrences of chlorite, tremolite and talc rocks which are

genetically related to the serpentine. These mono-mineralic rocks occur in planes

trending NNE-SSW and NNW-SSE and one or more of these rocks are found in one

and the same plane. Usually chlorite forms the innermost zone followed outwardly by

tremolite and finely by talc. The chlorite rocks are dark green to green, fine to

medium grained and with magnetite grains parallel to the linear structure. Talc and

tremolite are pale green to apple green and with soapy touch. Under the microscope,

the talc carbonates consist of talc, carbonate and haematite with or without small

amount of antigorite. The talc is found in fine scaly aggregates or platy crystals

enclosing clusters of haematitised carbonate crystals. The carbonate is present in big

quantities as irregular crystals. Some rounded grains of chromite can be seen with

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deep reddish brown core and black rim. A typical sample of talc carbonate rock

consists of 19.9 % talc. 37.8% carbonate and 42.3% iron oxides ( Kabesh 1961).

7. The Bau Granites

These granites cover about 35 sq. km in the southeastern sector of the Ingassana Hills

and are surrounded in the east, north and west by serpentinites. The contact with

serpentines is intrusive with granitic dykes and apophyses cut the serpentines.

Although there is no direct contact with the metasediments and gabbro, the granites

are considered younger in age. In the southeastern part of the Bau area, the granites

form the high peaks of Jebels Bonuc, Welk, Belik and Bors.

The granites are coarse-to-medium grained, hard, massive and pale pink to whitish in

color. They are quite uniform in composition, unfoliated and un-xenolithic and are

weathered into cuboid blocks. Joints are common especially those along E-W and N-S

directions. In the field, two types of granites were recognised. A medium-grained

porphyritic pink granite which forms the greater part of the rocks and pink granite

which borders the former to the west. There is no sharp contact between the two

granites, but the gradual change between them indicates their same origin.

8. Dykes and Veins

Dykes are of various composition and texture, and quartz veins arc intruding the

granites. the serpentines and the metasediments. Basic dykes are commonly basaltic,

doleritic and gabbro lamprophyre. The ultrabasic dykes are deep green in color and

consisting mainly of orthopyroxenes and amphiboles and occur in serpentinite.

The acid dykes are mainly aplitic and albitophyre made of albite or microcline

phenocrysts in a groundmass mainly consisting of albite with some microcline. Quartz

veins and lenses are common in the metasediments, granites and serpentinites. They

range in thickness from a few centimeters to more than one meter and, in places,

quartz bosses up to 20 m across occur. Some brecciated quartz veins cut serpentinites.

The Chromite Deposits

The chromite deposits are found in many places in the serpentinite or in the associated

talc-carbonate rocks. They usually occur either as lenticular or banded bodies of

irregular shapes and variable sizes as well as veins or disseminated ores. According to

the Chinese Technical Team (1975-1977), the chromite deposits are divided into two

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major genetic types, based on the geological features of various occurrences,

especially the major deposits at Garn, Chikay, Kurba and Gebanit Mines.

A. Deposits of the Orthomagmatic Stage

Most of the orthomagmatic deposits occur within the dunite facies zone as banded ore

bodies, while only few of them are found as lenses or bockets, at the lower part of the

complex facies near its contact with dunite. The contacts between the chromite ore

bodies and the host rocks, are generally gradual and in rare cases, the contacts are

very sharp. The ore bodies are mainly composed of fine to medium, euhedral to

subhedral grains and are generally of medium to low grain where Cr2O3 content is less

than 35% and Cr/Fe ratio below 3. The deposits usually vary in length from 20 to 200

m and in thickness from 0.5 to 8 m. It is clear that, this type of chromite is controlled

by the lithology.

B. Deposits of Late Magmatic Stage

Most of the late magmatic deposits occur within the dunite schlierens in the dunite-

harzburgite complex zone. Few of these deposits are found in the upper part of the

dunite near its contact with the above complex. The chromite ore bodies occur as

veins, lenses or lumps with very sharp contact with the country rocks. They are

mainly massive, compact medium and coarse subhedral to anhedral in texture. The

ores are either compact, hard, high grade and lumpy with Cr2O3 content varying from

48% to more than 50% and Cr/Fe ratio above 3; or medium-grade spotted ores, or

medium-grade combined lump and spotted varieties. The high-grade lumpy ores form

the dominant chromite deposits while the lumpy-spotted ores are less abundant.

The general strike of the chromite lenses and veins coincides with that of the country

rock and in some cases, they are at right angle to the general strike or arranged in

echelon in the same area. They vary in length from 10 to 200 m and the vein width

from 0.5 to 6 m. The form of this type of deposits is extremely complicated and some

of them branch from one vein into two or three. They are mainly controlled by the

lithology and primary structures of the rocks. Examples of this type of chromite are

found at Cam, Chikav, Kurba and Gebanit Mines.

In general the chromite deposits in the Ingassana Hills have the following

characteristics as revealed by the Chinese Technical Team (1975-1977).

1. In plan, the chromite deposits occurrences of the two types exhibit the phenomena

of existing in zones. One zone extends from Gam Mine to Gebanit Mine in the north.

The second type of the chromite deposits, is widely distributed in a sub-north-south

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direction, while in Rumeilik zone area, they are closely-spaced bodies of the first type

with their strike coinciding with the direction of the primary banding i.e. NNW-SSE.

2. The individual ore bodies are generally not big in size. They tend to occur in

groups arranged in en-echelon like manner and they pinch and swell along both strike

and dip directions.

3. The over-all review of the whole area of the Ingassana Hills indicated that the rock

masses in the southern section of the western part of the hills, are more basic and

relatively swelling and are characterized by the frequent occurrences of chromite of

industrial quality. Other sections of similar features are located in the vicinity of

Gebanit Mines.

Geophysical Prospecting Works

in addition to the detailed exploration and drilling works carried out by the Chinese

Technical Team on the chromite deposits, the team carried out, detailed gravity and

magnetic surveys to locate blind ore bodies as well as to reveal the down extension of

the exposed chromite ore. The results of the general gravity survey (40 m x 10 m

grid) and the detailed survey (20 m x 10 m and 10 m x 10 m grids). 53 local gravity

anomalies and two magnetic anomalies have been found. 45 anomalies have been

checked by drilling, pitting and trenching of which 17 anomalies were found to be due

to blind ore bodies near the known occurrences and the other anomalies directly

reflect the extension of the outcropping ore bodies. There are conspicuous density

contrasts 1-2 g/cm3 between the chromite ore bodies and their country rocks, which

would definitely help to locate more hidden chromite bodies.

Chromite Reserves and Quality

Based on the detailed geological and geophysical works, in addition to drilling, pitting

and trenching, a total of 147 chromite ore bodies and occurrences were located. Fifty

seven ore bodies are found in Gam Mine area alone, the total reserves of which are

estimated at more than 500,000 tons of chromite grading 50 - 57% Cr2O3. The

chromite reserves of all the other occurrences, are estimated at more than 100,000

tons grading 35 - 48% Cr2O3.

Further exploration works were carried out by a Japanese Team from Mitsubishi and

Japan Metals and Chemicals Co.Ltd. in 1 978 to evaluate the chromite deposits of the

Ingassana Hills. In their feasibility study report, they estimated the chromite ore

reserves of Gam Mine area, at 655,370 ton with an average grade of 50.17 % Cr2O3

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and Cr/Fe ratio of 3.14. The ore reserves in all the other remaining occurrences are

estimated at 240,000 with Cr2O3 content varying between 41.28 to 48%.

The Japanese Technical team has divided the Ingassana Hills into six areas according

to the distribution of the chromite ore bodies and mineralisation as fllows:

1. Gam Mine area (5 sq.km).

2. Romeilik area (50 sq.krn).

3. Gebanit Mine area (18 sq.km).

4. Komrag area (50 sq.krn).

5. Kurba rea (5 sq.km) all in the western rock block.

6. Eastern area (50-l00 sq.km).

Chromite deposits exist only in dunite and peridotite and are not found at all in

pyroxenite or gabbro. It was also observed that the chromite deposits in dunite

always occur near the contacts with peridotite and when they occur in the peridotite

country rocks, the deposits often exist in schlieren-shaped dunite. More information

on these chromite deposits is given below.

(1) Gam Mine Area

There are five main deposits in Gam Mine area, producing some 15,000-20,000 ton

per year. The mineralised serpentinised country rock, has an area of 200 x 800 sq.m

and an elevation varying between 300 - l000 m above sea level. The biggest deposit

has a continuous length of 200 m and its maximum thickness is more than 6 m. The

second extends for 150 m as lenticular or irregular vein with an average thickness of 6

m.

The other three deposits are smaller and occur as 15 - 20 inclined veins. The ore is

hard, compact lumpy or accompanied by fine-grained spotted ore in part, and is

generally of high metallurgical quality.

Chikay chromite mine lies about one kilometre northeast of Gam Mine and was

mined in two branches. Mining was suspended because of the poor quality of the ore

in the lower part (25 % Cr2O3). The ore occurs as vein of complicated shape.

(2) Romeilik Mine Area

Lies north of Gam Mine and has a length of about 10 km (20 - 30° NW direction) and

a width of 5 km. The area comprises 20 chromite outcrops which occur as banded and

bedded ore deposit in the eastern parts and as lenticular or vein deposits in the middle

and western parts. The total estimated possible reserves of lumpy chromite ore in

Romeilik area, are l63,200 ton grading at 31 – 52 % Cr2O3 (average grade 41.28%

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Cr2O3). Because of the number of chromite deposits and the proximity of Romeilik

area to Gam Mine, it is considered the most promising prospective area.

(3) Gebanit Mine Area

It has a N-S length of 9 km and E-W width of 2 km and comprises 4 small deposits

with the operating Gebanit Mine located in the centre. The possible estimate reserves

amount to 22,600 ton of massive chromite containing an average of 43.35% Cr2O3.

(4) Komrag Area

Eight medium-to high-grade chrornite bodies varying in size from 1500 ton to about

11000 ton, are scattered in an area extending for 12 km from Gebanit to Komrag

village and has a width varying between 3 and 6 km. The total possible chromite

reserves are estimated at 48,300 ton grading at 38-50% Cr2O3 ( average grade 43.78 %

Cr2O3).

(5) Kurba Area

J.Kurba, an independent mountain mass lies to the SW of the Ingassana Hills find

covers an area of 5 sq.km. The two chromite deposits found in Kurba were mined out

several years ago. There are still present several small lenticular or vein chromite

deposits of high-grade lumpy quality but the reserves are not estimated.

(6) The Eastern Area

The ultrabaic rocks east of the Ferri fault are intruded by the Bau granite and contain

few, small chromite deposits of total estimated reserves of 5,900 ton with an average

grade of 43.59 % Cr2O3.

The grand total of the chromite ore possible reserves at Romeilik, Gebanit, Komrag

and the Eastern area, amount to 240,000 ton classified by grade as follows 104,100

ton at more than 45 % Cr2O3, 67,800 ton at 40-44 % Cr2O3, 3,900 ton at 35-39 %

Cr2O3 and 32,200 ton below 35 % Cr2O3.

In general, the chromite deposits of the Ingassana Hills belong to the spinal type of

mineralization and are mostly lumpy but sometimes, are pisolitic or fine grained. The

chromite is black with metallic luster, brown streak and mostly in well developed

idiomorphic crystals. The complete chemical analyse of the typical representative

samples of Gam massive ore and Romeilic banded ore, are shown in Table 1.

15

Table 1

Chemical Analysis of typical Chromite Deposits, Ingassana Hills

2. Gold

The part of the Blue Nile region adjacent to Ethiopia. that extends from longitude 34°

eastwards to the border and latitudes 8° to 2° can he considered as one of the most

attractive areas of the Sudan for mineral development. The area possesses substantial

mineral resources within reasonable access and logistics, as the area is traversed by

both the main highway linking Khartoum with PortSudan and Ed Damazin and the

railway linking PortSudan with Sennar, Kosti & Ed Damazin. Power and water are

available from the hydro-electric dam at Er Roseires on the Blue Nile and the annual

rainfall of about 800 mm with higher rainflill in the Ethiopian Highlands immediately

to the east sustain a strong agricultural sector.

Regional Geology

The area is mainly underlain by the basement complex rocks which are mostly

concealed under the Quaternary-Recent sediments. Reconnaissance geological

mapping revealed that the area lies close to the eastern margin of the Sudan craton

Massive ore % Banded ore %

Cr2O3 51.22 31.21

FeO 14.38 14.81

SiO2 8.04 18.24

Al2O3 5.68 8.17

CaO 0.70 0.84

MgO 16.83 19.24

S 0.007 0.010

P 0.006 0.007

lg. loss 2.54 5.21

Cr/Fe 3.13 1.85

16

with the orogenic volcano-sedimentary greenschist assemblages of the Nubian Shield

to the east (Vail & others,1986). The ontact between the two terrains is sinuous and is

interpreted as highly tectonised, ophiolite, draped suture zone, on each side of which,

characteristic stratigraphic sequences have been recognised. (Fig. 9.22).

The lower basement complex known as the Tin Group comprises two formations,

Selak Formation made up of strongly deformed and intensely migmatised quartz

felspathic gneisses & amphibolites, and Gonak Formation of supracrustal sediments

occurring within the above gneisses. These metasediments include substantial

psammitic, pelitic to semi-pelitic lithologies with coarse crystalline marble horizons

and clacsilicates.

The Uffat Group, (upper basement complex), overlies the Tin Group and is made of

low grade, predominantly green-schist facies extending into Ethiopia. The group is

sub-divided into three zones:

1. Marafa Formation : Low grade metasediments with volcanogenic materials.

2. Central discontinuous belt of mafic and ultramafic rocks (ophiolite affinity).

3. Kurmuk Formation of volcano-sedimentary rocks with gabbro and granite plutons.

The Marafa Formation consists of two distinct sequences separated by tectonic

boundary.The lower sequence comprises pelitic-semipelitic, arkosic quartz mica

schist, slate and phyllites interbanded with variable coloured banded marbles.

Quartzite is sparse but minor concordant lenses of basic-intermediate metavolcanic

and amphibolites are characteristic. Pegmatites, aplites and quartz veins up to 45 cm

thick, are present in the lower sequence, especially near the shear zones where

silicification occurs. The upper sequence is spatially confined to the vicinity of the

ultramafic masses of the Ingassana Formation and not seen anywhere else. These

rocks comprise a massive chaotic melange unit with exotic blocks several kilometers

in extent. These rocks are enclosed in undeformed arenaceous matrix or in places

within sheared serpentinite matrix. The blocks are predominantly poorly sorted

sandstones with thin beds (l-2 m) black marble, chert, graphitic phyllite, pebbly and

conglomeratic sandstones, oolitic ironstones, brecciated quartzites and minor basic

tuffs.

In Queissan area, clastic metasedimetns occur. The rocks comprise thick slaty

phyllites with scattered andesitic lenses overlying the gneissic basement along

tectonic contact. Most notable is a wide band of conglomerate, several kilometers in

length and up to 2 kilometers wide. The clasts in the conglomerate, include basic

17

volcanic, metasediments, granite and mafic detritus embedded in a pelitic and

calcareous matrix.

The Ingassna Formation occurs as discontinuous mafic-ultramafic masses along the

western side of the volcano-sedimentary greenschist assemblages with the Uffat

Group. The ultramafic rocks are chromitiferous serpentinites with unaltered but

deformed dunite, harzburgite and pegmatitic pyroxenites. The mafic rocks are mainly

formed of altered meta-gabbro, basic dykes and pillow basaltic lavas.

The Kurmuk Formation comprises mainly meta-volcanics associated with volcani-

clastic materials. The predominant units are mafic schist and phyllites of basaltic

andestic composition with some rhyolitic and subordinate volcaniclastic rocks and

thin metasedimentary units towards the top. The succession is folded into a series of

isoclinal folds and is metamorphosed into the greenschist facies of regional

metamorphism. In Queissan region, meta-basic rocks commonly intercalated with

metasediments. They are usually fine grained, dark green and locally pyritiferous.

The synorogenic to late orogenic intrusive rocks are widespread in the area

neighbouring Ethiopia. They penetrate the volcanosedimentry greenschist

assemblages and the high-grade gneisses. They are foliated granitoid plutons mainly

occupying the cores of major anticlines and apparently they are aligned along

structural belts. At Queissan, numerous syn-to post-tectonic orogenic masses of

granites, granodiorites, diorites, homblendites and gabbros are intruded into both the

gneisss and the low grade volcano-sedimentry rocks.

Late tectonic gabbro-granite complexes either as large plutons or ring complexes are

intruding the metavolcanic sequences of Kurmuk Formation with sharp cross-cutting

contacts, chilled margins and metamorphic aureoles. Other intrusions in the area, are

the post orogenic granites, e.g. at Bau, syenite at J.Mufwa together with gabbros and

basic dykes.

Gold Mineralisation

Gold has been mined in the upper Blue Nile valley by local inhabitants for at least 200

years. Artesanal gold workings are developed on old river terraces along the Blue Nile

and also extend in a narrow belt along the foothill of the Ethiopian Highlands from

Fazugli to Daga Post, a distance of about 200 km (Fig. 9.23). Virtually, all these local

workings are alluvial and are worked only during the rainy season when water is

available. Some recent work has located extensive gold-bearing quartz veins at

Queissan which are reported to have potential of 800,000 tons at a grade 6 g/t. The

18

quartz veins form a stockwork zone up to 70 m in width with individual veins up to

20 m wide. The full extent of the veins along the strike is not known owing to the

extensive soil and talus cover in the area. Minor auriferous quartz veins have been

reported over an area of 70 x 20 km between Kurmuk and Queissan associated with

the contact zone between pyritic basic volcanics and the overlying volcano-clastic

sediments.

The UNDP survey of the Ingassana Hills (1968-1971) located widespread gold values

in heavy minerals stream sediment samples (22 out of 133 samples). The best gold

values were associated with anomalous copper values in the southeast of the survey

area, near Bau. This anomaly yielded samples with maximum assay values up to 0.42

% Cu, 0.8 g/t Au and 0.5 ppm Ag. The source of the anomaly was not located.

In Qala En Nahl area, gold has been reported at J. Ghanain and spectacular outcrops

of copper sulphide mineralization occur at Nafa El Keib and J. Salmin in rocks

described as base metal schist (Ruxton, 1957). Although the geology of this area is

poorly known, it is apparent that most of the reported gold and copper occurrences are

found in close proximity to the upper contact of the basic volcanics, (Kurmuk

Formation) with meta-sediments containing ferruginous cherts, carbonates and minor

acid volcanics. This is a similar geological setting to that of the massive sulphide

deposits in the Ariab area further north. The gold mineralisation and the copper

occurrences are very strongly indicative of stratabound volcanogenic sulphide

mineralisaion on the upper contact of the basic volcanics similar to that which occurs

in the Ariab area.

This auriferous zone extending over a distance of 200 km between Daga Post and the

Blue Nile (Fig. 9.23) is a high priority target for oxidation zone (gossan) type gold

deposit in volcanogenic base-metal sulphide deposits. Systematic exploration along

this favorable geological horizon possibly using the limestone-marble beds as

stratigraphic marker horizons, may result in the discovery of gold, copper, zinc &

silver sulphide deposits. This could provide the capital investment required to the

transport and infrastructure of the area and provide a window of opportunity enabling

some of the presently marginal or sub-economic industrial mineral deposits to be

profitably developed.

Description of Prospective Areas

The gold placers are found within beds of ancient and modern streams draining the

Ethiopian-Sudanese territory along the frontier. The most important centres of native

19

gold mining, are Jurut (near Kurmuk), Adula, Amido, Mias (near El Keily) as well as

around Queissan and at Amoro in Khor Sumba where the placers are buried (Fig.

9.24). The natives make holes up to 8 meters deep through the alluvial deposits in

order to mine the gold-bearing deposits which are utilised to mine gold bearing

gravel.

Primary gold is found in quartz veins near abangharu, Belagola and Wadeka. They are

usually large veins of milky white quartz. The rich veins are generally thin, not

exceeding a few centimetres in width. These veins were reported to have yielded good

quantities of gold at Mufo and Wadeka. They could not be sampled directly since the

natives had mined out the first 15 meters of the veins.

A. Buried Alluvial Placers in River Beds

These are the placers of Khors Jurut, Amido, Adula, Mias in Kurmuk area and Khors

Aghunfeg, Funtun and Orung, a tributary of K. Sumba in Queissan area. They are

found either as raised terraces in mountainous area (Queissan) or as buried river beds

followed closely by the present streams. The overburden is black cotton soil up to 8

meters thick. The sediments are composed invariably of a mixture of cobbles,

pebbles, sands and clays with the gravel size forming the predominant part. This type

of placers is the richest one and is the only place being exploited by the natives.

B. Recent River Alluvium

This is the alluvium deposited by the present river system which was formed after the

cotton soil. The parts of those river systems within the Sudan, display a more

advanced stage of deposition. Therefore, the river alluvium in the Sudan is of better

sorted material of sandy composition (Khors Jurut and Sumba). Although large rivers

like Tumat are not yet sampled they belong to the same category. This type of

alluvium is relatively poor in gold content. The more concentrated occurrences of

gold are confined to the outermost part of the sediments. The thickness of the sand

layer is usually 2-3 metres. They have the advantage over the first type by the absence

of the overburden, a fact which makes them less costly to operate.

The most important placer gold areas are:

A. Kurmuk Area

1. K.Jurut

The gold placers of K. Jurut are found 5 km south of Kurmuk. They are in the form of

buried streams running E-W along the course of K. Jurut. The area is about 4 km long

and has a width of 60 meter. The thickness of the overburden and of the gold bearing

20

sediments was measured in several pits and they showed an average thickness of 5-7

m for the overburden and 80 cm for the gold-bearing sediments. Gravel and large

pebbles (1-7cm or more in diameter) constitute about 40-60 % of the volume of the

sediments. The gold is found in the form of grains and flakes ranging in diameter

from 0.5 to 3 cm. Seven samples of the gold-bearing sediments were collected and

gave the following assay values:

Sample No. 1 2 3 4 5 6 7

Gold gm/cm3 1.29 0.47 0.51 2.58 1.98 7.51 2.8

If all the 4 km of K. Jurut deposits are exploited and if the natives have worked out

only 50 % of the gold values, then one would expect that some 96,000 cubic meter of

gold-bearing gravel exist. Assuming an average content of 4 gm/m3, a reserve of 396

kg of gold can be estimated.

2. Adula

There are two small khors crossing Kurmuk-Mufwa road, 15 miles southwest of

Kurmuk. The first, Khor Adula proper is a small gully about 40 m wide and flanked

by rocky outcrops and numerous veins of white quartz which seem to have supplied

the placer gold. The second Khor, known as K. Abazy, lies 2.5 miles away from the

first and is not so extensively worked by the local people. The Khor is about 50-60 m

wide and is a trough running through bare rocky outcrops. The ancient sediments lie

in the Khor bed below a cover of clay, 50-180 cm thick. The thickness of the

sediments as disclosed in two pits was 20 cm in one and 50 cm in the other. The

sediment is heterogeneous with predominantly gravel size material. Gold value of

samples taken from the two pits gave assays of 0.9057 gm/m3.

3. Belila El Dawala

South of Belila village near Wadika and about 142 km west of Kurmuk, an ancient

Khor with no visible topographic expression is located. It is difficult to find its width

and direction, but it was disclosed by a few pits dug by the local people for gold there.

The gold placer lies below a clay overburden of about 3-5 m and has a thickness of

50-65 cm. The sediments heterogeneous with a dominant gravel size fraction. Two

samples taken from abandoned pits assayed 0.27 and 1.1 6 gm/m3.

B. Queissaia Area

1. Khor Aghunfeg

This Khor drains the mountains 16 km east of Queissan where the gold-bearing placer

is a raised terrace on the left side of Khor Aghunfeg. It occupies an area of 500 m x

21

600 m and occurs under an overburden of clay 3 m thick. The sediments are of a

heterogeneous composition with a predominant rounded gravel fraction. Samples

from an abandoned pit showed only traces of gold.

2. Khor Golli

An old Khor bed was found running parallel to the present stream of Khor Golli, 17.5

km to the southeast of Queissan. The ancient Khor is 60- 80 m wide and was pitted by

natives for a distance of 1.5 km. The sediments are heterogeneous and gravelly.

Samples collected from 3 pits showed traces of gold.

3. Amore

The gold-bearing placers in Amore area are connected with the upper reaches of Khor

Sumba. They occur in two types the first is a buried khor which occurs parallel or

sometimes crossing Khor Sumba and can be followed for five kilometers in an eastern

direction up to the village of Amore Yassin. It has a width of 60-70 m and occurs

under an overburden of 4 m. The gold bearing sediment is usually 1- 1.5 rn thick and

is composed of typical khor sediments ; a heterogeneous mixture of sand, clay and

rave1 which constitutes 40 % of the sediments. It is overlain by a 1.5 m thick pebbly

clay. Samples collected from the gold - bearing sediments gave only traces of gold.

The second type of the gold-bearing horizon, is the sands of Khor Sumba which is 30-

50 m wide. A pit was dug 1.8 m down to the khor bed. The sands are coarse and

pebbly with some clay. The gold content is negligible in the upper 90 cm as well as in

the lower most 20 cm and the interval 80-120 cm. Samples taken from the interva1

120-160 cm and 40-80cm assayed 1.8 & 3.93 gm/m3 respectively.

4. Jebel Mias

This hill is located about 4.8 km northwest of the village of EL Keily which lies on

the Kurmuk-Ingassana Hills road. The gold sediments are found in the bed of a buried

khor lying paralel to Khor Zigon which is a tributary of Khor Orob. Khor Zigon like

its predecessor is a small stream draining low hills 3.2 km away from Khor Orob.

The gold-bearing sediment lies under an overburden ranging from 25 to 160 cm and is

20-60 cm thick. The sediment is heterogeneous and is distinctly reddish in color. Four

samples collected from this sediment showed a gold content varying between 0.17

and 0.093 gm/m3.

Water Supply

The Kurmuk-Queissan area is crossed by numerous large khors with water running in

them only during the rainy season. In summer, water is obtained from wells dug in the

22

beds of the khor. Large tracts of country covered by thick cotton soil are almost

deserted in summer time because of the shortage of water. This factor contributed

towards a restriction of native mining operations which are usually carried out in the

rainy season except for areas near large khors such as Khors Jurut and Sumba.

3. Nickel

Nickel deposits of economic significance have not yet been located in the Sudan

However, encouraging high values of nickel were recorded at the following localities

A. In the Ingassana Hills

Geochemical exploration by the UNDP of the ultrabasic rocks at the Ingassana Hills,

has revealed several areas of highly anomalous nickel- bearing birbirites with nickel

values up to 2.87 %. These geochemical nickel anomalies were related to ferruginous

capping along the crests of narrow ridges within the ultramafic rocks. It was

concluded by the UNDP that the nickel enriched zones have resulted from the

secondary enrichment of nickel values in an old laterite weathering profile on a

former land surface now dissected by the present drainage system. Such lateritic

nickel, occurring only as minor ridge top remnants, has no economic potential.

However, no detailed investigations of these nickel anomalies were carried out and

the source of the anomalies remains to be identified.

Therefore, it would be worthwhile to investigate these anomalies for the possibility

that they might have been derived from copper-nickel sulphide gossans. Any copper-

nickel sulphide gossan would be very difficult to recognize in the deeply weathered

ultrabasics of the Ingassana Hills and would require multi-element geochemistry to

distinguish a gossan from a laterite. The generally high level of metal content in the

Ingassana ultramafic rocks, with known copper, nickel, gold, chromite and platinum

minerals, suggest the likelihood presence of copper-nickel mineralization there.

4. Platinum

The scarcity of surface water and the generally small size of the he ultrabasic rocks in

Sudan, make alluvial platinum of very limited occurrence. The only areas which could

be prospective and where water is available would be the Ingassana Hills, Qal En

Nahl, Kapoeta, Nuba Mountains and Hamissana area in the western Red Sea Hills

(rare water).

In the Ingassana Hills, platinum is known to occur in chromite as well as in the

alluvial deposits. 41 stream sediment samples, 100 kg each, were collected along

23

drainage courses descending from the mountainous area between Gebanit

chromite Mine and its eastern surrounding. The heavy fractions of these samples

were analyzed for platinum in China and gave the following result.

8 samples contain 1 to 3 grains of platinum

5 samples contain 3 to 8

9 samples contain 7 to 8

19 samples contain no platinum.

Five samples were analyzed by Electron Probe Method to examine the

composition of the platinum group elements. The results are shown in Table

31.5.

Table 2: Composition of the platinum group in the stream sediments, Ingassana

Hills

sample No Os% Ir% Pt% Ru% Rh%

1 51.0 38.8 trace 3.6 trace

2 44.5 35.4 2 8.2 -

3 49.6 37.5 trace 8.2 -

4 46.2 36.1 1 5.1 2

5 45.4 46.4 - - -

Four chromite samples collected from Gam Mine, each weighed 200 grams were

analyzed for the platinum group elements as shown in Table 31.6.

Table 3 Platinum group elements content of chromite, Gam Mine.

Os Ru Rh Ir Total Pt content

1 0223 0.243 0.013 0.215 0.711

2 0.310 0.250 0.016 0.255 0.861

3 0.082 0.180 0.011 0.056 0.349

4 0.130 0.215 0.012 0.109 0.376

It was observed that the content of platinum in chromite increases with the content of

Cr203. Osmium, radium and iridium are the most important elements.

5. Asbestos

Asbestos is known to occur in several localitie in the Sudan, but major chrysotile

deposits proved to exist in two localities, (1) Qala En Nahl area and (2) Ingassana

24

Hills. In both localities, asbestos is associated with sheared and altered zones in the

ultrabasic rocks. There are four significant asbestos deposits in Qala En Nahl, (El Fau

Hill, 2 localities), Utash Hill and Umm Sagata (Fig. 2.1). These deposits were

investigated by exploratory shafts and adits by the Sudan Geological Survey (1960-

1961) and were evaluated in 1962 by the Italian Asbestos Mining Corporation. At the

Ingassana Hills, two main asbestos deposits were investigated, at Fadamiya in the

eastern margin and Kukur in the western margin (Map 2.2). Fadamiya includes J.

Gasbel asbestos deposit and Dufur asbestos deposit. These deposits were explored in

details by UNDP and the Sudan Geological Survey between 1969-1973 and a

feasibility study was carried out by the Canadian Johns Manville Company ltd (1975-

1978).

Anthophylite and actinolite-tremolite asbestos, were found mainly

in the Red Sea Hills but no details were given on their quality and quantity.

Asbestos Deposits of Qala En Nahl Area

Chrysotile asbestos deposits occurring in Qala En Nahi area, are situated at J. El Fau 6

km NW of Qala En Nahl village (two localities), Umm Sagata 48 km SE of it and J.

Utash east of Umm Sagata.

El Fau Asbestos Deposits

Jebel El Fau is an arc shaped hill standing out about 520 m above sea level. The high-

most sharp tops attain 120 m above plain level. The valleys are generally oriented

according to the axis of the hill arc and transversal to it and are covered with rock

detritus. According to the occurrence of asbestos, El Fau Hill, is divided into El Fau

north and El Fau South.

Local Geology

Jebel El Fau is made up of basic-ultrabasic rocksmainly composed of serpentinite

with gabbro and talc schist intruded by quartz veinlets. The following is a brief

description of these rocks (Fig 2.3).

1. Serpentinites

Four types of serpentines were distinguished.

A. Green Serpentinite white speckled

This type of serperitinite occupies the main part of the hill as large Continuous band.

When freshly fractured, this serpentine has a green colour with large white specks, but

25

when weathered, it is altered to reddish yellow serpentinite with brown specks. The

serpentinite is sometimes schistosed in two directions, NW-SE and from inward to the

periphery of the hill. In the extreme southeast part, it is intensively foliated. This type

of serpentinite does not carry any asbestos mineralization except in the extreme

southeast of the hill arc at the contact with the red silicified serpentinite

B. Red Silicified Serpentinite

Silicified serpentinite occurs mainly in the north eastern slope of the hill, at El Fau

South, El Fau Central Valley and El Fau North. The rock is irregularly crossed by thin

quartz veinlets, coloured red on the surface and shows some traces of asbestos

C. Green Serpentinite

This is the type of serpentinite which carries the main asbestos mineralization and

occurs as four outcrops of limited extension at both El Fau North and El Fau South

(Fig. 2.3). The green serpentinite is also crossed by rnagnesite and pyroxenite

veinlets.

D. Dark Bluish Green Serpentinite

This very hard serpentinite appears only at the extreme north of Jebel El Fau where it

forms numerous small outcrops scattered either at the foot of the hills or in the valley.

It has a spongy appearance with sharp corner- edges and shows reddish shades on

weathered surface. The serpentinite carries rarely small and thin asbestos veins.

2. Gabbro

Gabbro appears in the southeastern parts of J. El Fau South as two main hills and

numerous small outcrops in the valley and extends up to the edges of the hill where

they form irregular contacts with the talc schist. The rocks are generally weathered

and foliated especially near the contact with serpentine. In El Fau North they occur as

small dykes intruding the serpentine.

3. Talc Schist

Talc carbonate schists with some chlorite schists, are found in the southeastern side of

the hill at El Fau South. The talc schists are bordered in the west by the dark bluish

green serpentine type where a hypothetical contact was drawn Fig (2.4 ). Bodies of

this serpentine together with gabbro, magnesite and lenses of dolomitic rock, are

found enclosed in the talc schists. The colour of the talc schist is pale green or creamy

and the schistosity planes strike N 20°E.

4. Quartz

Fragments of quartz are scattered throughout the area and most probably come from

26

the quartz veinlets in gabbro or the big quartz vein intruding the talc schists.

Pegmatite and granite fragments were also noted in the area and are believed to

belong to acid veins in the basic rocks ( M. Carlesi 1962 ).

According to Tyler (1932), the intrusion of J. Beila granite, west of J. El Fau, had led

to the serpentinisation of the older J. El Fau ultrabasic rocks. This was later followed

by regional metamorphism which resulted in the schistosity of both the Beila granite

and El Fau serpentine. The intrusion of the granites of J. Ban and J. Balos south of

Gala En Nahl (Fig 2.1) caused the silicification of serpentinites and quartz veinlets

crossing the schists and basic rocks. A long period of erosion took place which

resulted in the deposition of the vast cotton soil in the surrounding plain. The talc

carbonate rocks were formed through local contact metasomatism processes on

serpentine along structural lines. Because of the heavy covering of the rocks forming

J. El Fau by detritus, it was difficult to trace faults and contact lines in the field as

well as in the aerial photographs. However, based on the trenches dug in the hill, the

geologists of the Italian Asbestos Mining Corporation (1962 ), believed that, the

contacts between the different serpentine types are gradual except the contact between

the white speckled green serpentinite and the red silicified serpentinite and that

between the serpentinite and talc schist which are structural contacts.

Asbestos Mineralization

Asbestos mineralization occurs mainly in the green sepentinite, type (C) and to some

extend in the dark bluish green serpentinte, type (D). The red silicified serpentinite

type (B) carries traces of asbestos mineralization while the white speckled

serpentinite, type (A), is completely barren of mineralization. The asbestos

mineralization at El Fau South is more important than that at El Fau North as regards

the extension, intensity of asbestos veins and the length of the fibers.

In El Fau South, the asbestos can be traced to 30 m high up the slopes of the hill. It is

bound in the west by the silicified serpentinite and in the east by a band of talc schist,

where the contact is gradational from schistosed serpentinite to talc schist (Fig 2.4).

The asbestos is of the chrysotile type. It occurs in small veins as cross fibers,

sometimes as slip fibers and considerably extends along different directions, but

mainly along NW-SE and are vertical or subvertical. The thickness of the

asbestos veins varies from 4 to 15 mm but the thickness of the majority of the small

veins, is 4-6 mm.

In El Fau North, only three types of serpentinites exist. The red silicified serpentinite

27

type (B), which is barren, appears at places and forms the uppermost top of the hill.

The green serpentinite which is soft and with asbestos mineral, is revealed by one

trench to extend from north to south. The hard dark bluish green serpentinite Type (D)

is the dominant rock where it appears in many places. It has spongy appearance with

sharp corner edges and is frequently mineralized with longitudinal fiber aggregates of

asbestos. The thickness of the asbestos veins varies between 6 and 9 mm.

J. El Fau Asbestos Reserves

On the basis of the geological work, drilling and digging of 6 trenches by the

Geological Survey of Sudan 1961, and 9 trenches and 56 pits aligned along 21

profiles 25-35 m apart, by the Italian Asbestos Mining Co. 1962, the reserves of

asbestos estimated at J. El Fau, amount to 16,200,000 ton of ores containing 2.7%

fiber with fiber length of 3-20 mm.

Asbestos Deposits of J. Umm Sagata and J. Utash

J. Umm Sagata and J. Utash lie about 48 km southeast of Gala En Nahl village (Fig

2.1). Asbestos bearing serpentine occupies the southern slope of an isolated hill and

extends in an east-west direction for a long distance. The serpentinite is well compact

and the asbests mineralization is good as regards its average content in the rock as

well as the length of the fiber. Three trenches and two adits were dug which revealed

the extension of the mineralization, where asbestos veins attain thickness of 3 to 5

mm and its average content is rather high. The western slope is formed of red

metamorphosed basic rock devoid of asbestos.

The asbestos ore reserves estimated by the Sudan Geological Survey, at Umm Sagata

amounted to 550,000 ton containing estimated l.77 % fiber (fiber length 3.5 mm) and

at J. Utash, 3,5.00,000 ton of ore containing 1.73 % fiber (fiber length 5-20 mm ) i.e.

a total of 4,050,000 ton of ore containing an average of’ 1 .75 % fiber or 70,280 ton

asbestos fiber. The Canadian Johns Manville Company estimated the asbestos ore at

these two localities at 3,926,764 ton containing 1.7932 fiber or 70.415 ton asbestos

fiber.

Ingassana Hills Asbestos Deposits

Chrysotile asbestos has been found in the serpentinised ultramafic rocks on both the

western and eastern flanks of the Ingassana Complex. There are definitely potential

sources of chrysotile asbestos suitable for use in asbestos cement products in the

Ingassana Hills. Tests have shown that the quality is good. The major asbestos

occurrences lie at Fadamiya and Gasbel on the eastern margin of the Ingassana Hills

28

and at Kukur in the western margin of the Hills (Map 2.2). These occurrences are

described as follows (I. M. Babiker 1975 ).

1. Fadamiya Asbestos Deposits

Fadamiya village lies on a narrow valley between two serpentine hills and can be

approached by a motorway track branching out of kurmuk-Er Roseires main road.

Asbestos occurs at three localities.

1. In a serpentine hill just south of Fadamiya village, asbestos occurs as single 2 cm

wide veins and smaller veins. The predominant direction of these veins is 355˚ which

coincides with the strike of the foliation planes in serpentine. The width of the

asbestos-bearing serpentinite outcrop is about 30 m and can he traced for 250 m in

north-south direction. Uphill, magnesite veins appear instead of asbestos.

2. Another asbestos-bearing serpentine occurs 800 m north of the first occurrence. At

this locality, the asbestos veins are narrow in width, but larger single veins are found.

Because of the heavy rock debris cover, the exact dimension of the mineralized area

could not be measured. At places, magnesite replaces asbestos.

3. A third asbestos-bearing serpentinite, lies about 300 m uphill east of locality two.

The asbestos veins are similar to the above occurrence, but at some places, the

asbestos is either silicified or replaced by magnesite.

2. Gasbel Asbestos Deposit

Asbestos-bearing serpentine outcrops at the foot of a small hill north of Gasbel village

which lies about 2.7 km north of Fadamiya. The width of the mineralize zone, is about

l00 m and extends in N-S direction for 750 m which coincides with the general

foliation strike 355˚. Large asbestos veins of up to 3 cm wide, are frequent but the

main bulk of the deposit is of narrower stockwork form.

The deposit was the subject of detailed exploration between 1969-1973 by the UNDP

and Sudan Geological Survey. A feaibility study was carried out in 1975-1978 by the

Canadian Johns Manville Limited which concluded that on the basis of estimated

reserves of 13 million ton at 1.6 - 1.8 % cement grade fiber content, the deposit is

technically capable of supporting a mining project, initially open-pit later by

underground mining methods. The asbestos is mostly of Grade 3 and 4 quality and

well suited to the manufacture of cement products.

The small asbestos deposits at Bogal and Dufur, have to contain 1.92 million ton at 3

% fiber content and 200,000 ton at 10 % fiber respectively.

3. Kukur Asbestos Deposit

29

This deposit occurs in the western margin of the Ingassana Hills and extends over an

area of one kilometer in length and 100 m in width. The deposit was partially

explored. The asbestos mineralization zone is parallel to the contact of highly altered

rocks . The chrysotile reserves have been estimated at 4 million ton of ore containing

1.94 % fiber by the Sudan Geological Survey or 2.043 million ton of ore containing 2

% fiber by the Canadian Johns Manvile Co. Ltd.

6. Graphite

Graphite occurs as disseminations or streaks in schistose rocks almost in all

basement complex outcrops in the Sudan. Graphite schists as a member of the

metasedimentary group of rocks have been lithologically and petrographically

described in many geological reports in different localities. They are generally

mixed or intercalated with quartzites, carbonates rocks, shale, chlorite or mica

schists and meta-chert.

Interesting graphite deposit occurrences in some parts of the country, were

preliminarily investigated and in some cases appraised for detailed exploration

and evaluation in order to identify their industrial suitability. These occurrences

include : the graphite deposit of Babaras SSW of Kurmuk in the Blue Nile

Region, the graphite deposit of El Kuhliat in Central Butana area, the graphite

deposit at Kabus and J. Kurun in NE Nuba Mountains and some occurrences in

Bayuda Desert.

Babaras Graphite Deposit

The graphite-bearing rocks of Babaras area crop out mainly between, latitudes

10° 18' 36”- 10° 21' 18” N and longitudes 34° 12' 42" - 34° 15' E . They lie about

31 km south of El Kurmuk town, (Fig. 10. 1) which is connected to Ed Damazin

by a motorable road except during the rainy season (May-October). The area is

generally flat with ridges and dome-like granitic hills of which the highest stand

115 m above the surrounding plains. The area is dissected by numerous dendritic

drainage system flowing southwestwards.

Local Geology

The area of Babaras and its surroundings is underlain by basement complex

rocks (Fig. 10.2). The oldest rocks, gneisses amphibolites, appear in the eastern

part of the area and they comprise strongly deformed and intensely migmatised

30

quartzo-felspathic gneisses. The rocks are medium-grained with distinct mineral

banding and contain abundant biotite with sub-ordinate hornblende, muscovite

and garnet. The accessory minerals include sphen, apatite, zircon and opaque

minerals. The potassic felspar in the granitic and migmatitic gneisses is mainly

microcline, while orthoclase dominates in the granodioritic varieties. The

amphibolites are medium to coarse grained and are composed of oligoclase-

andesine, hornblende, diopsite, clinozoisite with some biotite, garnet, quartz,

sphene and opaque minerals. The gneisses and amphibolites, have, been given

the lithostarigraphic name “Selak Formation" (A. Magid, A. Rahman 1981).

The second major group of rocks, the metavolcanic-metasedimentary sequences

occupy the western sector of the area. They are preiominantly composed of basic

schists and phyllites of basaltic and andesitic composition with some

metarhyolites and are overlain by graphitic schists, thin marble bands, minor

horizons of ironstone, siltstone and quartzites.

Syn to late orogenic intrusions are found penetrating the gneisses and

metavolcanic- metasedimentary rocks. Late to post tectonic gabbro-granite

complexes have been intruded into the metavolcanic rocks where they form large

plutons or ring complexes with sharp cross cutting contacts, chilled margins and

metamorphic aureoles (Vail 1978).

The Graphite Schists

The graphite schists occur as extensive ridges and patches in an area of about 5

sq.km. east of Babaras village. They form the major rock unit in the

metasedimentary sequence and overlie the gneisses. The thickness of the graphite

beds ranges from few centimetres to more than l00 m. Remnants of chlorite and

mica schists on top of the graphite are found in many localities as scattered

rubble, especially at J. Abi. The schists are intruded by aplite dykes, pegmatites,

basic dykes and quartz veins, veinlets and stringers which caused the

silicification of the graphite schists.

The petrographic studies carried out on Babaras graphite schists has resulted in

the identification of the following mineral assemblages (GMRD 1983).

Quartz - graphite

Quartz - graphite - muscovite

quartz - graphite - fuchsite

Quartz - graphite - tourmaline

31

Quartz - graphite - muscovite - tourmaline

Quartz - graphite - muscovite - fuchsite

Quartz - graphite - fuchsite - talc

Quartz - graphite - sericite

Quartz - graphite - thchsite - tourmaline

Quartz - graphite - muscovite - iron oxides

Quartz - graphite - sericite - tourmaline.

Quartz and graphite are the main constituents while the frequency and

distribution of the other associated minerals is irregular. Graphite occurs either

as disseminations in the form of minute grains or flakes all over the rocks or as

dense bands of flaky graphite. Micas in the graphite schists are represented by

muscovite, sericite and fuchsite. The green fuchsite type of mica imparts its color

to the graphite schists where the content of the mineral is high. Prisms of

tourmaline (schorlomite) are well developed in some varieties of the graphite

schists. Talc is present only in graphite schists in contact with chlorite schist.

Graphite Grade and Reserves

The surface area occupied by the graphite schists was roughly estimated at 5

square kilometres and the heights of the ridges between 10 and 115 m. Samples

were collected at intervals of 50 m along 45 profiles, each 5 km long. About 20

trenches and pits were dug across the strike in the graphite schist ridges as well

as in the flat plains between them. Out of the nine channel samples from the

trenches and 14 chip samples from selected areas, only 6 samples were analysed

for carbon ard sulphur in Germany. The result is shown in Table No. 10.1.

Table 4 Carbon and sulphur contents of graphite schists from Babaras area

Sample No Carbon % Sulphur

%

1 5.285 0.004

2 3.441 0.003

3 5.051 0.016

4 6.302 0.003

5 8.259 0.004

6 11.060 0.006

32

The calculation of the reserves, was based on the assumption that all the graphite

schist ridges at sites A, B, C, D, E, F, G, H and I (Fig. 10.2) are conical in shape. The

indicated reserves were calculaed for ridges above the surface and the possible

reserves were estimated down to a depth of 9 m (rectangular in shape) as follows

(sp.gr of graphite 2.419).

Reserved

Area Symbol

Area/m2 Height/m (H)

Depth/m (D)

Volume/106m3

Cone (C),

Rectangle (R)

Tonnage/ 106

ton

A:

Indicted

Possible

670,000

670,000

74.3 (H)

9.0 (D)

16.6 (C)

6.03 (R)

40.16

14.59

B: Not Calculated … … ….

C:

Indicated

Possible

2,420,000

2,240,000

50 (H)

9 (D)

40.3 (C)

20.78 (R)

97.57

52.69

D:

Indicated

Possible

670,000

670,000

102 (H)

9 (D)

22.78 (C)

6.03 (R)

55.10

14.59

E:

Indicated

Possible

259,000

250,000

12 (H)

9 (D)

1 (C)

2.25 (R)

2.42

5.44

F:

Indicated 215,000 19 (H) 1.38 (C) 3.34

G:

Indicated 124,500 3 (H) 0.125 (C) 0.30

H:

Indicated 237,500 3 (H) 0.238 (C) 0.576

I:

Indicated 117,00 3 (H) 0.118 (C) 0.285

33

F+G+H+I

Possible 695,000 9 (D) 6.26 (R) 15.14

Inspite of the detailed sampling of the Babaras schists, the only analysed six samples,

showed that the graphite content of the schists, is low and varyingf between 3 and

11% C. In addition, the petrographic studies indicated the high contents of quartz and

micas.

Butana Graphite Deposits

Graphite-bearing schists are widespread in the metasedimentary rocks of central

Butana area. They are associated with marbles, quartzites, phyllites and slates. The

different layers, streaks or lenses of graphite schists, range in thickness from a few

centimetres to several metres (J. Tukl El Afarit north of Es Subagh village) or they

form high continuous elongated hills, like the occurrences of graphite-bearing schists

at J. El Kuhliat and Khemeiriya village.

J. El Kuhliat Graphite Occurrence

Graphite schists mainly making up El Kuhliat chain of moderate to high hills, occur

about 47 km southeast of Es Subagh village. The strike of the schistosity is 30˚ and is

steeply dipping to southeast. The graphite is flaky, soft, dark grey to black in color,

greasy in touch and with black streak. It is generally resistant to weathering where it

blackens the soils in the surrounding plains. The graphite schists are intercalated with

thin layers of quartzites and calcareous rocks.

The total surface area of the graphite schists as measured from aerial photographs is

1.7 sq.km (Fig. 10.3) and the height ranges between 25 m and more than l00 m above

the local flat plains. Although no chemical analysis was carried out, the graphite

seems to be physically of good quality.

Khemeiriya Graphite Occurrence

This graphite occurrence lies about 31 km SW of J. El Kuhliat. Very rich graphite -

bearing schists are scattered as low hills striking E-W. The graphite seems to be

widely spread as all the wells dug in the area penetrated graphite layers. No chemical

analysis was carried out and detailed investigation of this deposit is strongly

recommended.

34

7. Marble

Er Roseires Area

Steeply dipping beds of marble, striking NE, have been quarried near Er Roseires.

The marbles are of various colours and are cut by granites and pegmatites. The

marbles quarried at Abu Ramad, 9.6 km north of Er Roseires consist of white and

pink varieties containing 87% CaO.

Marbles have also been quarried at Natig, 2.5 km north of Er Roseires and at Ganiz,

6.4 km south of Er Roseires. The Natig marble showed considerable variation in

chemical composition, the CaO content ranges from 41 to 52% and the magnesium

oxide from less 1 to l0 %. At Ganiz, a coarse grained white marble showed a content

of 97 % CaCO3 while a fine grained variety contains 56 % CaCO3 and as much as 42

% Mg CO3.

Ed Damazin Area

A band of white marble striking ENE and dipping SSE, occurs 1.5 km south of Ed

Damazin. This marble is a fairly course-grained, yellow or creamy in colour and is

associated with granites and pegmatites. Another band of white grey marble occur

further south of Ed Damazin rapids and crops out on both banks and on an island in

the midstream. It has a width of 90 m and dips gently to the north and is also

associated with granites and pegmatites

Ingassana Hills-Fadamiya Area

Marbles with other meta-sediments occur in contact with the ultrabasic rocks of the

Ingassana Hills at Fadamiya area about 65 km SE of Ed Damazin. The regional strike

of the marble, is N-S and is folded along NNE axial trend. The CaO content of the

marble is 42 %. Part of the deposit has a high MgO content ranging between 4.12 &

6.5 % and the other part shows a MgO content ranging between 0.02 and 2.93%. The

average silica content is 56.6 %

Sennar Area

Marble bands, striking NNE-SSW and interbedded with gneissic rocks, have been

quarried north of the railway in Segadi -Mashata area as a source of lime for use in

the construction of Sennar Dam. The marbles have a very low MgO content while the

CaO content attains up to 97 %. Marble has also been quarried at Umm Alog south of

the railway line and about 2 km SW of Jebel Dud station. The calcium carbonate

content of this marble, is 93.6 % and the magnesium carbonate is 0.42 -2.95 %

35

Qala En Nahl Area

At Jebel El Gir, 8 km ENE of Qala En Nahl railway station, marble is utilised for the

production of lime. No information on this deposit is available.

Butana Area

Marbles occur at many places in central Butana, as low-lying ground bands running

continuously or discontinuously along their strike, or as moderate to high ridges. The

major marble deposits were preliminarily investigated and representative samples

were collected to check their chemical composition at the localities shown in Table 6.

Table 6 Chemical composition of major marble deposits in central Butana

Location CaO% MgO% SiO2% LOI%

J. Surug 47.01 2.25 1.50 42.07

J. Hamoriat 25.60 12.00 19.12 32.29

J. Qerein 48.13 1.66 2.16 38.85

Reira 53.16 N.D 1.85 41.72

W. Gadir 44.77 4.97 0.31 42.83

W. Rauwiyan 53.72 N.D 1.50 42.21

Qala El Mara 40.29 0.72 14.18 30.21

It is clear rom the above table, that the marble deposits of J. Surug, J. Gerein, Reira

and W. Rauiyan are of good quality and can be used in the manufacturing o cemçnt

and lime. Wad Gadir marbles are of lower quality, but the little content of silica (0.31

%) together with the beautiful variegated colors, rank these marbles as excellent high

polishable ornamental and decorative stones.

8. Magnesite

In the Ingassana Hills, southeast of the Blue Nile region, magnesite occurs as small

lenses, pockets, veins and veinlets along fractures and joints planes in serpentinitic

rocks and in most cases, it s associated with chromite (Kabesh 1961). These different

magnesite occurrences together with its wide scattered scree and debris are common

features in the hills slopes and the wadis. They are mainly concentrated along the bed

of Khor Feri, west and southwest of Fadamiya and north of J. Jegu. (Fig. 16.2) shows

the general distribution of magnesite occurrence numbered 1 to 5 were described to

contain exploitable quantities (Kabesl 1961).

36

The result of the chemical analysis of 9 samples collected from the different

magensite occurrences (the exact samples location not given)

were as follows:

SiO2 = 0.6-4.5 % (5 samples below 1 %)

Fe2O3 = 0.7-2.4 % (5 samples 1.19 %, 1 sample 9.79 %)

CaCO3 = 0.25-29.78 % (2 samples 19.17 % & 29.78 %, 5 samples 1-3.7 %)

MgCO3 = 65.2-97.65 % (6 samples above 96 °/o).

Based on the above results, Kabesh considered that the magnesite ore is relatively

pure, with low iron and is rather free of silica. He believed that the magnesite was

formed as a result of carbon dioxide metasomatism with watery fluids which reacted

with serpentine.

9. Talc-Carbonates

The largest talc carbonates deposit found in the Ingassana Hills area, is located at the

southern edge of J. Jequ at about 5 km west of Er Roseires motor road and at a spot

lying at latitude 11˚ 30' and longitude 34˚ 4'. Talc-carbonates are always found at the

margins of chromite lenses especially at the southern peak of J. Edom, which lies

about 5 km east of Soda village.

The talc-carbonates are formed by the metasomatic attack of serpentinite by carbon

dioxide. They are generally creamy to buff in color with soapy touch and white streak.

The rocks consist of talc and carbonate with iron oxide and chromite. One sample was

analysed and found to contain 20 % talc and 42.3 % iron oxides.

37

Annex II

Geological Maps

38