Stope Optimisation Tools for Selection of Optimum Cut-Off Grade in Underground Mine Design

In feasibility studies, the selection of the optimum cut-off grade is often determined through the analysis of tonnage grade curves and manual stope design at one or two cut-off grades. Traditionally, stope designs within the industry hinge on break-even cut-off grades; however, there is a notable absence of consensus regarding the appropriate cost and price assumptions to factor in. This study introduces a novel tool for automated stope design, capable of generating diverse stope shapes for a specified range of cut-off grades or values derived from net smelter return calculations based on block modeling. The developed procedure integrates constraints related to stope and pillar geometries tailored to the specific mining methodology, enabling the evaluation of sublevel intervals and the sensitivity of various design parameters in the pertinent geological and geotechnical context. These unique 'nested stopes' serve a parallel function to 'nested pits' in open-cut designs and play a crucial role in the 'hill of value' methodology that aids in determining the optimal cut-off grade for underground operations. Our findings indicate that the break-even cut-off grade is not necessarily the most advantageous. Importantly, the design principles established during feasibility studies can be replicated for consistent application during mine production.