A mixed integer linear programming framework for optimising the extraction strategy of open pit - underground mining options and transitions

The decision to exploit a mineral deposit that can be extracted by open pit and/or underground mining involves consideration of the following options: (a) independent open pit extraction; (b) independent underground extraction; (c) simultaneous open pit and underground (OPUG) extraction; (d) sequential OPUG extraction; and (e) combinations of (c) and (d). This paper investigates the extraction strategy for deposits using Mixed Integer Linear Programming (MILP) optimisation framework to maximise the net present value and determine the schedules for mining, processing, underground capital and operational developments, and 3D crown pillar position. The MILP framework is implemented for a gold deposit. The results showed a combined sequential and simultaneous open pit and underground (OPUG) mining with crown pillar as the optimal extraction option generating NPV that is 11% and 13% better than independent OP or UG mining, respectively.