ﺑﺴﻢ اﷲ اﻟﺮﺣﻤﻦ اﻟﺮﺣﯿﻢ Ministry of Minerals Geological Research Authority of Sudan (GRAS) Bentonite Deposits of Omm Ali Area (River Nile State) Sudan By: El Gizouli Ahmed Hamid. February 2011
Abstract The study area is 0.775km 2, (774.99m 2 ). 15 bore holes were drilled to 11.3m for each in semi-grid system using augering method. 52 samples from different boreholes and depths were collected. The collected samples were tested for Atterburg limits, grain-size distribution, and chemically analyzed for main oxides. There are two layers of clays; the upper is grey in color, and the lower one is dark in color. Grain-size distribution ranges for both clays are shown in table below: Grain size Grey clay Dark clay Sand range 2-28% 3-21% Silt range 12 53% 22-60% Clay range 25-78% 27-73 % Limits of dark and grey clays of Omm Ali area. Grey clay Dark clay Shrinkage limit 11-28%, 19-28%. Liquid limit 35-75% 51-78%. Plastic limit 13-27% 18-29%. Plasticity index. 21-50%, 32-54%. Clay activity 0.62-1.08 0.71-2.0 According to grain size distribution, the raw material either sandy clay of low plasticity, or clay of very high plasticity. The raw material is treated by carboxyl methyl cellulose (C.M.C), the optimum properties obtained at 2%. It is noticed that the dark clay gives good properties than the grey one, to reach the standard values it is recommended that the sand percentage must be decreased, and to be ground finer. Now bentonite comes to Sudan from abroad; estimation of the bentonite reserve of Omm Ali area is 5151600m 3. Omm Ali is 298km north from Khartoum. 1
1.1 Location: the study area is located on the right bank of the river Nile, between the railway, and the main national road (Khartoum - Atbara). The area is bounded by coordinates 17 o 01 / 26.5 // N, 33 o 43 / 21.1 // E. 17 o 01 / 41.2 // N, 33 o 43 / 42.5 // E. 17 o 00 / 57.9 // N, 33 o 43 / 56.6 // E. 17 o 01 / 05.5 // N, 33 o 43 / 56.6//E. Fig (1). 1.2 Topography: Omm Ali area is pounded by low hills in north, the whole area is gently slopes towards the Nile course. 1.3 Accessibility: The area can be easily reached by both railway and national tarmac road from Khartoum (298km), or from Atbara (90km). 1.4 Climate: It is hot during summer (40 o C), with rare rainfall, and cold during the winter (15 o C). 2
Geology The geology of the study area is Cretaceous sediments (Nubian Formation). These strata are defined by Whiteman (1971) as Shendi Formation, which deposited by fluvial and lacostrine. Shendi Formation belongs to Nubian cycle which is Late Jurassic Late Cretaceous in age. The formation is composed of interbedded fluvial and near shore facies in north-west Sudan, Klitzsch and Squyres (1990). These sediments are described as predominant of relatively fine grained clastic of braided meandering, and meandering river, floodplain and minor lacostrine environments Bussert (1993). The Paleoclimate during the deposition of Albian- Cenomanian period have been interpreted as tropical with dry seasons. According to all previous works, kaolinitic and smectitic deposits are part of sedimentary fining upward sequence. On the other hand smectite-mudstone represents lacostrine environment. Hence the smectitic clay is strongly related to warm and humid climate. 3
Field and laboratory works Field work: 15 boreholes were drilled in the area in semi grid system. The interval among boreholes varies from 170m to 500m. The total drilled depth is 152.8m, the average depth is 10.18m, all boreholes contain clay except borehole 11 (Fig 1.4). There are two layers of clay, the first one is a grey one, it exposed at the surface, but the other one is not less than 4m deep. These two layers are separated by undesirable layers, (Fig1.3). The reserve estimation is 5151600 m3. 59 samples were collected from different boreholes and depths. The clay is dominant at the centre of the study area, Fig (1.4). The grey clay is of intermediate plasticity, and almost underlain by dark clay or intercalated with it, Fig (1.3), and (1.4). At the eastern part of the study area the dark clay becomes deeper (8m), Fig (1.3) 4
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Fig (1.3) section through BH 4, 2 and 10 Fig (1.4) section through BH 6, 7 and 11 6
Laboratory work: the raw material was chemically analyzed, and the following tests were carried out: grainsize distribution, consistency, limits, plasticity, density, viscosity, gel strength, filterate loss, mud cake, sand content, and PH value detected. The dark clay is high to very high plasticity; it contains less SiO 2, K, Ca, and L.O. I (loss on ignition), but the grey one shows relatively high content of Al 2 O 3, Na, and Fe, table (3). Table (4) shows correlation between Omm Ali clay and international clays. Table (1) Grain size distribution Type of clay Average of grain size Gravel % Sand % Silt % Clay % Classification Grey clay 3 24.5 38.5 39 Clay of intermediate plasticity Dark clay 1.3 11.3 41.1 46.2 Clay of high plasticity. Table (2) Atterburge and clay activity Clay type Atterburge Limit Clay L.L% P.L% P.I% S.L% activity Grey 53.45 14.35 39.1 18.5 1.0 dark 66.0 22.7 43.8 23.2 1.02 Table (3) Average oxides and elements of grey and dark clay Clay Classification Average percentage of main elements SiO 2 Al 2 O 3 Na % K % Ca % Fe % L.O.I % Dark clay High to very high plasticity Grey clay Intermediate plasticity 66.02 12.36 0.43 0.13 0.07 2.5 8.87 67.90 10.38 0.36 0.27 0.41 2.36 9.03 7
Table (4) Correlation between Omm Ali Clay and International Specification Sample Main oxides % SiO 2 Al 2 O 3 Na 2 O K 2 O CaO Fe 2 O 3 1 54.34 19.92 1.965 0.373 0.235 0.863 2 49.91 17.20 0.103 0.232 1.651 1.687 3 66.015 12.358 0.434 0.131 0.072 2.48 4 67.90 10.38 0.46 0.27 0.41 2.36 1. Bentonite blue grey spur bed, Bell Fourche, S.D. Foster (1953). 2. Bentonite, chambers, Ariz, cheto (Kerr et al 1950). 3. Omm Ali dark clay. 4. Omm Ali grey clay. Treatment: Two samples of grey and dark clays each were grinded. Two samples (grey and dark) were treated by carboxyl methyl cellulose (CMC) 2%; the two other samples were tested without treatment. It is noticed that the treated samples improved their properties, and the dark clay shows more good properties, see table (5), Fig (4.4), and Fig (4.5). Table (5) Properties of natural and treated clay. Properties Untreated sample Treated Sample recommended Values (API) Grey Dark Grey Dark Mud density Lb/gal 8.7 8.7 8.7 8.7 9.0 Viscosity 32 33 36 36 38 Second/quart (march funnel) Gel strength a/ initial lbs/100/ft2 b/after 10 minutes lbs/100ft2 10 Filterate loss c.c API 146 120 24 20 20 30 miniuts) Mud cake mm 4.0 1.0 1.0 2 4 Sand content % 2.0 4.0 2.0 4.0 P.H value (litmus paper) 2.0 2.0 2.0 2.0 8
Fig (4.4) untreated and treated dark and grey clay 35 30 25 dark clay grey clay 20 15 10 5 0 density viscosity gel stren mud cake Fig (4.5) treated clays of Omm Ali and standard values 40 35 30 25 20 15 10 5 0 dark clay grey clay stan val mud dens viscosity gel streng mud cake filter loss The table below shows imported bentonite through customs authority, whereas all bentonite for oil companies do not pass through it, so that it is not included here. Table (6) Quantity and values of bentonite imported through customs in period (1996-2000). Year 1996 1997 1998 1999 2000 Quantity in 350.3 462.6 998.3 655.6 570.1 tons Values in US$ 81735.0 112877 146100.5 133703 71970.9 9
REFERENCES 1. Abdellatif O. M. (1997). Lacostrine Deposits and Fluvial of the Upper Cretaceous, Omm Ali area. Central Sudan. 2. Whiteman A. J. (1971). The Geology of Sudan republic, Oxford Claredon University press. 3. Klitzsch, E. and Squyres, C. H. (1990). Paleozoic and Mesozoic geological history of northeastern Africa based upon new interpretation of Nubian strata: - Amer Ass. Petr. Geol. Bull. 74, 1203 1211, Tulsa. 4. Cassangrade (1977), Method of test for soil for civil engineering purposes; British Standards Institution. 5. Deposits of the Central and Western Gulf of the Mexico Coastal plain, U.S. Geological Survey Bull. 1558 c. U.S.A. 6. Bussert, R. Brasse, H. Radic, T, and Reynold, P, O. (1990), Sedimentary and Structural Style of a ruft structure in northern Sudan: The Humar Basin: - Berliner geowiss, Abh (A), 120.1, 89 108, Berlin. 7. Sudan Customs Authority. 10