Recent applications of operations research and efficient MIP formulations in open pit mining

Mixed integer programming (MIP) models are used for long-term production scheduling of open pit mines. However, formulations based on binary variables for mining blocks require too many variables and are often difficult or impossible to solve. This paper presents and tests alternative MIP scheduling models that have reduced the number of binary variables and solution times, thus increasing efficiency. The results serve as a guide in selecting the approach that will provide the best solution for mining any given deposit. A case study is presented to illustrate how, in the different formulations proposed, the time required for solving MIP models is reduced. In addition, proposed formulations are found to decrease the gap of feasible solutions when exact optimal solutions are difficult to obtain.