Where to make the transition from open-pit to underground? Using integer programming

Abstract

The transition from open pit (OP) to underground (UG) operation is one of the challenging mining engineering issues. Mines that have the potential to transition from OP mining to UG mining will eventually come to a 'transition point' where the decision needs to be taken whether to extend the pit or switch to UG mining. In this paper we present a new integer programming (IP) formulation to obtain the optimal transition point from OP to UG mining. The proposed model is implemented on a threedimensional (3D) gold deposit and a two-dimensional (2D) case study is used to demonstrate the validity of the model. Due to the large number of variables, strategies are proposed to shorten the solution time. The proposed model has successfully determined the optimal transition point and generated a significantly better undiscounted profit than that of the traditional approach.