Open pit transition depth determination through global analysis of open pit and underground mine production scheduling

Abstract

This paper presents an iterative Net Present Value (NPV) maximization method to determine the optimum surface to underground transition depth for an ore body to be mined by multiple open pits and an underground mine. The determination of transition depth from open pit to underground mining is based on global production scheduling optimization of open pit and underground mines using Mixed Integer Linear Programing (MILP). The method is applied to a case study coming from a gold mining complex with six open pits and a large under- ground mine using long hole open stoping. The results indicate potential improvements of the NPV of global operations when compared to the traditional techniques based on independently optimized open pit first, followed by the underground mining.