Open Pit Optimisation and Design of Tabakoto Pit at AngloGold Ashanti Sadiola Mine Using Surpac and Whittle Software

Abstract

This paper demonstrates the application of Surpac and Whittle in open pit optimisation and design. Exploration data on the Tabakoto deposit of AngloGold Ashanti Sadiola Mine (AASM) has established 13 652 661 t of gold resource with an average grade of 1.15 g/t that could be mined using open pit method. The aim of this paper is to optimise and design a pit to mine the deposit safely and profitably using Surpac and Whittle software. The work entailed: block modelling of the Tabakoto deposit using Surpac; importing the block model to Whittle for pit optimisation; and importation of the optimal pit back to Surpac for detailed pit design. In all, 55 nested pit outlines were generated but the one with the highest Net Present Value (NPV) of US$3 185 637 was selected as the optimal pit. The optimal pit contains 446 750 t of ore at an average grade of 1.709 g/t and 2 310 910 t of waste while the designed pit has 444 982 t of ore at an average grade of 1.683 g/t and 2 416 988 t of waste.  It can be seen that using the optimal pit as base, the designed pit has less tonnes of ore, a lower grade and more waste. The difference in values is due to the expansion of the pit bottom and the creation of a ramp and berms in the designed pit which resulted in some ore loss and dilution. Again, the designed pit contains only 32.59% of the gold resource established by exploration, but the ore contained in the designed pit is what, under the current economic and geotechnical constrained, can be mined profitably and safely.

Keywords: Block Modelling, Optimal Pit, Pit Design, Surpac, Whittle