Algorithmic approach to pushback design based on stochastic programming: method, application and comparisons

Abstract

Pushback design affects the way a mineral deposit is extracted. It defines where the operation begins, the contour of the ultimate pit, and how to reach such ultimate contour. Therefore, different pushback designs lead to differences in the net present value (NPV) of a project. It is important to find the optimal pushback design which maximises the NPV. Conventional approaches to designing pushbacks lead to not meeting production targets and NPV forecasts. This is mainly due to the lack of integrating uncertainty into the process. Recent efforts have shown that the integration of uncertainty into production scheduling results in NPV increases in the order of ∼25%. The purpose of this research is to make use of a stochastic integer programming model to integrate uncertainty into the process of pushback design. The approach is tested on porphyry copper deposit. Results show the sensitivity of the NPV to the design of starting and intermediate pushbacks, as well as the pushback design at the bottom of the pit. The new approach yielded an increment of ∼30% in the NPV when compared to the conventional approach. The differences reported are due to different scheduling patterns, the waste mining rate and an extension of the pit limits which yielded an extra ∼5500 t of metal.