1

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.

2 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.

3 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

4 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 1000C 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 1000C 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 to1450C 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,

5 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

6 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.

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 hydroelectric 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-maficgranitic 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

8 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

9 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 dykelike 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 lowlying 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.

10 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

11 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

12 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 duniteharzburgite 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

13 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

14 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%

15 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.

16

Table 1 Chemical Analysis of typical Chromite Deposits, Ingassana Hills Massive ore Cr2O3 FeO SiO2 Al2O3 CaO MgO S P lg. loss Cr/Fe % 51.22 14.38 8.04 5.68 0.70 16.83 0.007 0.006 2.54 3.13 Banded ore % 31.21 14.81 18.24 8.17 0.84 19.24 0.010 0.007 5.21 1.85

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 hydroelectric 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 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

17 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 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

18 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 volcaniclastic 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 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

19 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 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

20 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 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

21 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. Gold gm/cm3 1 2 3 4 5 1.98 6 7.51 7 2.8 1.29 0.47 0.51 2.58

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 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.

22 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 3050 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 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

23 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 coppernickel 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 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.

24 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% 1 2 3 4 5 51.0 44.5 49.6 46.2 45.4 38. 8 35. 4 37. 5 36. 1 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 1 0223 2 0.31 0 3 0.08 2 4 0.13 0 Ru 0.24 3 0.25 0 0.18 0 0.21 5 Rh 0.01 3 0.01 6 0.01 1 0.01 2 Ir 0.21 5 0.25 5 0.05 6 0.10 9 Total Pt content 0.711 0.861 0.349 0.376 Pt% Ru Rh% trace 2 % trace 3.6 2 8.2

trace 8.2 1 5.1 -

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.

25

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 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 (19601961) 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 (19751978). 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 highmost 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

26 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 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

27 found enclosed in the talc schists. The colour of the talc schist is pale green or creamy and the schistosity planes strike N 20E. 4. Quartz Fragments of quartz are scattered throughout the area and most probably come from 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

28 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 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

29 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 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

30 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 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

31 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 quartzofelspathic 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 metavolcanicmetasedimentary 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

32 quartz - graphite - fuchsite Quartz - graphite - tourmaline 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 1 2 3 4 5 6 Carbon % 5.285 3.441 5.051 6.302 8.259 11.060 Sulphur % 0.004 0.003 0.016 0.003 0.004 0.006

33 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 A: Indicted Possible B: C: Indicated Possible D: Indicated Possible E: Indicated Possible F: Indicated G: Indicated H: Indicated I: Indicated F+G+H+I Possible

Area/m2

Height/m (H) Depth/m (D)

Volume/106m3 Cone (C), Rectangle (R)

Tonnage/ 106 ton

670,000 670,000 Not Calculated 2,420,000 2,240,000 670,000 670,000 259,000 250,000 215,000 124,500 237,500 117,00 695,000

74.3 (H) 9.0 (D) 50 (H) 9 (D) 102 (H) 9 (D) 12 (H) 9 (D) 19 (H) 3 (H) 3 (H) 3 (H) 9 (D)

16.6 (C) 6.03 (R) 40.3 (C) 20.78 (R) 22.78 (C) 6.03 (R) 1 (C) 2.25 (R) 1.38 (C) 0.125 (C) 0.238 (C) 0.118 (C) 6.26 (R)

40.16 14.59 . 97.57 52.69 55.10 14.59 2.42 5.44 3.34 0.30 0.576 0.285 15.14

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

34 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.

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

35 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 % 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

36 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 J. Surug J. Hamoriat J. Qerein Reira W. Gadir W. Rauwiyan Qala El Mara CaO% 47.01 25.60 48.13 53.16 44.77 53.72 40.29 MgO% 2.25 12.00 1.66 N.D 4.97 N.D 0.72 SiO2% 1.50 19.12 2.16 1.85 0.31 1.50 14.18 LOI% 42.07 32.29 38.85 41.72 42.83 42.21 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 cemnt 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). 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

37 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.

Annex II

38

Geological Maps