In contrast, the least competent ores—generally softer and finer materials—exhibit shorter residence times, leading to lower mill fillings and reduced power draw. In such cases, the throughput constraint is more likely to lie outside the SAG milling stage. Blast designs therefore need to be tailored to ore competency, with the objective of maximizing SAG mill power utilization. This involves debottlenecking the SAG mill when processing the most competent ores, while promoting higher mill fillings and increased power draw when treating less competent materials. 1.2 Ore Characterisation Ore characterisation is fundamental to any Mine-to-Mill process integration initiative. Its primary objective is to capture ore competency variability across the deposit. To be effective, ore characterisation results should show a clear relationship with both blast fragmentation outcomes and mill throughput. If this is not achieved, either the test used is unsuitable, or the number of measurements is insufficient. A key requirement of an effective ore characterisation method is the robustness of its test procedure, particularly in minimizing operator-related bias and ensuring reproducible results. For example, if a single sample is split and submitted to two independent metallurgical laboratories, the tests should return comparable results. Only under such conditions can the method be confidently applied across a broader sample set to reliably quantify ore competency variability. The JK Drop Weight Test (JKDWT) (Napier-Munn et al., 1996) and the SMC Test® are widely recognized as bankable, industry-standard methods for ore characterisation over the past 40 years (Weier, 2023). These tests were specifically designed to replicate the breakage mechanisms and energy levels that rocks experience in crushers and SAG mills. The very high control on the energy applied, and particle size selection, minimize the test bias making the test results more reproduceable. To maintain consistent standards, JKTech conducts regular global round-robin programs as part of its QA/QC framework (Weier, 2019) to ensure that the same result is generated from any JK Drop Weight Tester. Figure 4 presents both a schematic and a photograph of the JK Drop Weight Tester used to conduct the JKDWT and SMC Test®. The apparatus is mounted on a concrete foundation and consists of a drop-weight head of known mass, which is pneumatically raised to a predetermined height and released to impact a rock particle positioned on a steel anvil. A clear enclosure surrounds the unit to ensure operator safety, contain broken fragments, and minimize material loss during testing. Figure 36 – Frequency Distribution of SAG Mill Power Draw Readings over a 6month Period
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