Slope stability analysis at pit 2 of Ghanaian Australian Goldfields Ltd (GAG)

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The Iduapriem mine of the Ghanaian Australian Goldfields Limited (GAG), 10 km southwest of Tarkwa and some 60 km north of the port city of Takoradi in the Western Region of Ghana, is engaged in the mining of low grade gold ores hosted in conglomerates, in open pit operations. Ore grade gold mineralization occurs within five specific areas namely Block 1, Block 2, Block 3, Block 4, and Block 5 (Northern Hills). These have ore zones named A, B, C, and D constituting the Banket Reef Zone. The depth of weathering extends to 15m below surface for Block 1 but shallower in the remaining blocks. At Pit 2 (Block 2) mining operations started at approximately 500m RL and would continue to about 330m RL according to the final pit design considerations. However at the present stage of 474m RL, some micro slope failures have been encountered in the northern (hanging) wall, an indication that the average minimum resistance of the rocks must have been overtaxed. Detailed geologic structural mapping using scanlines and subsequent analysis of the data indicate the presence of four discontinuity sets for Blocks 2 and 3, which both actually constitute one block. Furthermore, the predominant failure mode likely to occur is that of wedge with an isolated case of plane failure. Two rock types, quartzite and dyke to a lesser extent make up the waste rock with the former having strength parameters lower than the latter. Factors of safety computed for the northern wall, though greater than unity were generally lower than most sections of the pit. However it is concluded that the benches will be stable for mining to proceed to the proposed depth.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of Postgraduate Professional Diploma in Mining Engineering, 1996