A New Model for Simultaneous Optimization of Production Scheduling and Cutoff Grades in Open Pit Mines

Optimal cutoff grades calculation in each period under the maximizing the economic outcome of a mining project is an interactive process, including the economic parameters (metal price, mining, and milling cost, etc.), the capacities of stages (mine, mill, and refinery) in the mining operation, mining sequence, and grade distribution of the deposit. Processing decisions of blocks play a principal role in the change of mining sequence. The effect of these changes will be enormous on the cutoff grades of mining operation during the mine life. Essentially, it asserts that the dynamic cutoff grade at any given period is a function of the ore availability and the needs of the mill at that period. Consequently, cutoff grades strategy and extraction sequence should be considered simultaneously. However, existing methods cannot find the optimal cutoff grades because they are independent of the mining sequence. An effort is made for the development of a new model for optimization of cutoff grades which considers mining sequence during mine life. In this paper, a new mixed integer programming model was developed to deal with this objective. Using this model, the optimum extraction sequences in each period are identified based on the optimum processing decisions. The cutoff grades obtained using the suggested model will be realistic and practical.

Keywords:

mining sequence , cutoff grade , optimization , mixed integer programming , net present value (NPV)