Open-pit transition depth determination through global analysis of open pit and underground mine production scheduling.

An iterative net present value maximisation method is presented to determine the optimum surface to underground transition depth for an orebody to be mined by multiple open pits and an underground mine. The determination of transition depth from open pit to underground mining is based on global production scheduling optimisation of open pit and underground mines using mixed integer linear programming. The method is applied to the case study of a gold mining complex with six open pits and a large underground mine which uses longhole open stoping. The operation is modelled as a large-scale, multimine, multitime period scheduling problem with multiple material types, grade intervals and mining capacities. Costs used in the NPV estimates include all open pit mining, transportation, stockpiling, handling, processing and underground capital and operating costs. The results indicate potential improvements of the NPV of global operations when compared to the traditional techniques based on independently optimised open pit first, followed by underground mining.
An iterative net present value maximisation method is presented to determine the optimum surface to underground transition depth for an orebody to be mined by multiple open pits and an underground mine. The determination of transition depth from open pit to underground mining is based on global production scheduling optimisation of open pit and underground mines using mixed integer linear programming. The method is applied to the case study of a gold mining complex with six open pits and a large underground mine which uses longhole open stoping. The operation is modelled as a large-scale, multimine, multitime period scheduling problem with multiple material types, grade intervals and mining capacities. Costs used in the NPV estimates include all open pit mining, transportation, stockpiling, handling, processing and underground capital and operating costs. The results indicate potential improvements of the NPV of global operations when compared to the traditional techniques based on independently optimised open pit first, followed by underground mining.