Pre-crusher stockpile modelling to minimise grade variability

Abstract

The use of pre-crusher stockpiles to store ore and buffer short-term fluctuations in production processes is generally well recognised and accepted. However, the potential to reduce short-term grade variation of ore entering the crusher is rarely recognised and generally poorly understood. Pre-crusher stockpiles are commonly built and reclaimed in an ad-hoc manner whereas well-designed and disciplined build and reclaim procedures can reduce variability into the crusher at low cost. Design options for pre-crusher stockpiling should consider the four competing roles of storage, buffering, blending and grade control, to produce predictable and uniform crusher feed grades. The selection of alternative grade allocation methods requires careful consideration, as decisions at this early stage of the production process have been shown to flow on to shipping and to the customer. This paper reports conclusions from studies simulating the reduction of grade variability for a range of alternative pre-crusher stockpiling configurations and grade allocation methods. The benefits achievable in reducing grade variance by systematically building stockpiles of appropriate dimension are quantified.