adjusted over the longer term: adding balls is straightforward but removing them is more difficult. Natural fluctuations in ore hardness and coarseness typically exceed the operating flexibility of the circuit. Sites experience these fluctuations despite rigorous process control. The next level of process stability is not in the process control, but in the geometallurgy through ore blending and ore domaining. • Ore blending. The capability to identify the softest and hardest materials to SAG milling through an effective ore characterisation, will put sites in a much better position to improve the blending practices. With better data quality coming from an effective ore characterisation, ore blending can be implemented to narrow down the variations in feed hardness and coarseness bringing stability to the operation and hence producing a more consistent final grind size and flotation recovery. • Differential blasting. Tailored blast designs, informed by established ore domains, provide another means of controlling variability, i.e., narrowing down the particle size range feeding the comminution circuit. More aggressive blasting is applied to the most competent ores to debottleneck SAG mills, while less intensive blasting is applied to the softer ores—leading to significant savings in D&B costs —to promote higher mill fillings and increased SAG mill power draw. As with ore blending, the success of differential blasting depends critically on robust ore characterisation. 1.5 Monitoring SAG Mill Performance Figure 41 compares key comminution circuit performance metrics between two plant trials, Trial 1 and Trial 2, to illustrate the effect of ore hardness and coarseness on circuit performance. Trial 2 processed overall finer and softer material than Trial 1, as confirmed by multiple analyses, including image analysis and measured Run-of-Mine (ROM) particle size distributions. Each trial consisted of 12 hours of continuous operation, and performance metrics were extracted from PI data at one-minute intervals for the respective time windows. The finer and softer feed in Trial 2, captured by the image analysis system in SAG mill feed, resulted in slightly higher throughput and lower pebble recycles; shorter residence time in SAG feed causing lower SAG mill fillings as captured by the JK Mill Filling Inference Tool (JKMillFIT). The lower mill fillings in turn resulted in lower SAG power utilization and reduced fines generation due to decreased abrasion breakage, ultimately resulting in a coarser final product size negatively affecting flotation recovery. These results highlight that more aggressive blasting is not always the optimal strategy; feed characteristics and ore competency must be considered to maintain efficient comminution and downstream recovery.
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