An evaluation of the effect of blast-generated fragment size distribution on the unit costs of a mining operation, using modeling and simulation techniques

This research was undertaken to investigate the impacts of finer rock fragmentation (arising from higher energy blasting) on the unit costs of a hard-rock surface mine. The investigation was carried out at a copper operation in southern Utah, which exploits its deposits by conventional methods, including drilling, blasting, loading, and truck haulage. The run of mine is processed in a three-stage crushing circuit and a two-stage grinding circuit, which feed a flotation plant that produces a copper concentrate. The research was carried out using modeling and simulation techniques. Fifty-five blast designs in total were developed for ore and waste units, with energy inputs ranging from 100 kcal/st to 400 kcal/st. For each design, fragmentation was predicted using the Kuz-Ram method. Crushing of the predicted ore fragment size distributions was simulated using MODSIM^TM. Data from pit face imaging and timed motion studies were collected and analyzed for the influence of fragmentation on shovel and truck productivity. Analyses indicated that fragment size distribution alone does not significantly impact this productivity. From simulation of the crushing circuit, it was found that the impact of differences in the blast-generated fragment distribution on the crusher energy is limited to the primary crusher, where a vast range of feed size distributions are introduced. No such relationships were evident at the secondary and tertiary crushers. Energy savings from increasing blasting intensity proved negligible and would not justify the costs of higher energy blasting. There was no evidence from this work that any beneficial influences of blast-generated fragment size distribution reach the grinding mill. Costs were estimated for drilling, blasting, and crushing, which were the principal unit operations inferred to be affected in some meaningful way by the varying intensities of blast energy input. The research shows that, principally as a result of jaw crusher gape restrictions and the significant unit costs of secondary reduction for both ore and waste, the net of all breakage (primary blast, secondary reduction, and crushing) does reduce to a transient minimum before they begin to ramp up again, thus fitting a classical mine-to-mill curve.