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Transcript of Chrome Report 4
Mineral Processing in Blue Nile
A Preliminary Proposal
Ahmed Khidir Yagoub Ph. D.
P.O.Box 794, Omdurman, Sudan.
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.
1
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.
2
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
3
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,
4
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.
6
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
7
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
8
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.
9
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
10
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
11
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
12
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
13
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