The economics of extended pre-strip stripping

Waste stripping involves the most costly processes for any given open cut coal mining operation, As such, it is fundamentally important to optimise material scheduling and the sequences involved in excavating and hauling waste material. In situations constrained by fleet capacity and productivity. The only viable option to potentially yield further cost gains is to modify current mining methods. In the case of many Australian coal mines, truck-shovel systems excavate the initial overlying waste, known as pre-strip, down to a predetermined level known as the pre-strip horizon. This paper provides and analyses a simulation model to derive the optimal strip width for pre-strip activities. Case study data obtained from an established leading coal producer in the Bowen Basin was implemented into a pit simulation model to assess the effect of pre-strip width on the overall pit economics. Pre-strip widths of 60 to 120 m in 10 m increments were assessed whilst keeping dragline and coal stripping widths constant at 60 m. The simulation revealed the potential for cost reductions to be significant when a 90 m pre-strip case is adopted as opposed to the base case of 60 m. The paper presents the simulation findings for each case and discusses the key drivers behind the cost variations for each case.