A new model for open-pit production and waste-dump scheduling

An open-pit mine schedule defines the optimal sequence of mining valuable (ore) and waste material with the objective of maximizing the value of the project. Given this production schedule, a waste-dump schedule is then developed to determine the optimal waste-rock allocation in waste dumps. Thus, production and waste-dump schedules are managed separately, which leads to an inappropriate consideration of the material haulage cost, suboptimal schedules generating less value, and the incorrect classification of ore and waste. This article proposes a mixed-integer programming-based model that determines the optimal production and waste-rock dumping schedule concurrently with the objective of maximizing the discounted cash flow [net present value (NPV)] of the project. An implementation of the proposed model on a gold-mining operation outperforms the two existing methods [traditional and two-step mixed-integer programming (TSMIP) model] in the context of project NPV as well as its practicality.