Transition from open-pit to underground in the case of Chah-Gaz iron ore combined mining

Geological and economic modeling of an ore body and also optimization of the depth at which transition is made from open-pit to underground mining is an important part of the mining design process in large and massive deposits. In this paper, a geological block model of Chah-Gaz iron ore deposit located in Iran was first created based on iron ore cut-off grade. Then with considering the economic parameters in the geological block model an economic model was derived. The economic block model of the deposit was used to determine the transition from open-pit to underground mining. The transition depth determination process was mathematically modelled for the case study. The objective function was chosen to be the maximization of the total profits earned from the combination of both open-pit and underground mining of the deposit. Chah-Gaz transition problem was finally solved by developing MATLAB optimization based code. The results obtained indicate a transition depth of 450 m.