Effect of stope size on sustainable steady-state production rates in a sub-level open stoping system

Abstract

An orebody utilising sub-level open stoping can have an intrinsic constraining limit in the production rate achievable that relates to the number of stopes that can be in some phase of the stope cycle at any one time. This constraining limit, the number of stopes, can be changed by decreasing the cut-off grade or by decreasing the stope size. Examples of the effects of using both methods are presented, but in particular the effects of changing the stope size. While smaller stopes will result in a lower average production rate per stope and a higher cost per tonne operating cost, the production rate for the mine when considered as a system can increase. Potentially, this can result in a higher NPV for the operation. The nature of the production rate increase has been investigated and reported for an idealised orebody. For example, for the orebody investigated, the 8-year sustainable steady-state production rate can be increased by 20% by reducing the stope size from 40 m × 40 m (in plan) to 34 m × 34 m (including consideration of pertinent size scaling effects). The orebody example investigated illustrates the need for the production limits of the physical mining system to be understood before making production level assumptions for mine infrastructure.