Geotechnical Modeling of Optimal Pit: West Limb of the Tarkwaian of Ghana

Abstract

Tarkwa Gold Mine is depleting its reserves to the east of the mine, on the Tarkwaian paleo placer deposit. It has, as a result embarked on vigorous near mine exploratory works to the west of the concession for reserve generation. Results indicate gold mineralisation of economic interest. The Mine seeks to provide optimal slope design that would satisfy shareholders and employees in the context of safety, ore recovery, and financial returns. Rock Mass Rating (RMR) and subsequent adjustment to obtain the Mining Rock Mass Rating (MRMR) was done for rock characterisation. The 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 kinematically possible in bench and/or multi-bench scale slopes. Multi-bench scale planar and wedge failures were 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.