A mixed integer programming based cut-off grade model for open-pit mining of complex poly-metallic resources

The mineral supply chain in an ideal open-pit mining operation constitutes a set of sequential stages including a surface mine or an open-pit, a processing plant and a refinery or market. Cut-off grade defines the flow of materials from the mine to subsequent stages within this mineral supply chain. This underlines the significance of cut-off grades in establishing the economic viability of an operation. However, only heuristic methods are available for defining the cut-off grade policy for complex mineral resources (orebodies) that constitute multiple economic minerals. This article proposes a new mixed integer programming based mathematical model that generates an optimal cut-off grade policy for open-pit mining operations that mine, process and refine or market multiple metal products. An implementation of the new method in three separate case studies reflects better performance (i.e., 24%, 36% and 27% higher net present value) against available heuristics.

Automated summary

The mineral supply chain in an ideal open-pit mining operation includes sequential stages such as a surface mine, a processing plant, and a refinery or market, with the cut-off grade playing a significant role in material flow. This article introduces a new mathematical model based on mixed integer programming to optimize the cut-off grade policy for mining multiple metal products, showing better performance compared to existing heuristic methods in three case studies, with a higher net present value.