Design of optimal slope parameters for the proposed Kobeda Pit at Gold Fields Ghana Limited, Tarkwa Mine

Abstract

Tarkwa Gold Mine (TGM) is depleting its reserves to the east of the mine. It has, as a result embarked on vigorous near mine exploratory work to the west of the concession for reserve generation. Results indicate gold mineralisation of economic interest. TGM seeks to provide slope design that would satisfy shareholders and employees in the context of safety, ore recovery, and financial returns for the proposed Kobeda Pit. Rock Mass Rating (RMR) and subsequent adjustment to obtain the Mining Rock Mass Rating (MRMR) was done for rock mass characterisation. The rock mass ratings for the various geotechnical zones ranged from 40.91 to 67.72 and rated from fair to very good. Kinematic stability analyses were performed for all the three design sectors using stereographic techniques to determine the failure modes that are kinematically possible in bench and/or multi-bench scale slopes. Multi-bench scale planar and wedge failures are kinematically possible in all sectors. Limit equilibrium analysis gave factors of safety that exceeded the minimum acceptable factor of safety of 1.05 for completely weathered material and 1.20 for fresh rock. The probability of failure was however less than 5%. Pit wall architecture for the geotechnical domains were 8 meters, 18 meters, 75 degrees for the berm width, bench height, and bench face angle respectively. Indicative overall slope angles fell between 50.02 to 59.21 degrees and rated from fair to very good.