1. MINE-TO-MILL The original Mine-to-Mill concept focused on more aggressive blasting to debottleneck SAG mills, thereby creating capacity for increased concentrator throughput. This has since led to the common misconception that Mine-to-Mill is primarily about increasing powder factors in blasting. In reality, more aggressive blasting is only effective when the value chain is constrained by the SAG mill, which was often the case in the 1990s when the concept gained popularity. SAG mills are often the most capital-intensive asset in the value chain, the hardest to expand, and the dominant energy consumer. This creates a strong economic incentive to design and operate the Mine-to-Mill system such that the SAG mill is fully utilized. Operations cannot afford to have high-capex equipment underloaded while cheaper upstream or downstream units become the constraint. The most competent ores are likely to enter the SAG mill at coarser sizes, and it is these ores that may benefit from more aggressive blasting. Conversely, softer ores do not require such blast intensification. The objective is to tailor blast designs to ore competency: producing finer fragmentation for the hardest materials to alleviate SAG mill constraints, while allowing coarser fragmentation for softer materials that can sustain higher mill fillings and power draw. In all cases, the goal is to maximize SAG mill power consumption. Achieving this level of integration relies heavily on the ability to identify the hardest and softest ores in advance, which in turn depends on an effective and reliable ore characterisation methodology. 1.1 SAG Milling Operation Effective Mine-to-Mill process integration requires a clear understanding of how the comminution circuit responds to both ore competency and blast fragmentation. This, in turn, demands a solid grasp of the fundamental operating principles of SAG mills. Unlike ball mills, SAG mills are equipped with a grate discharge mechanism, meaning that particles can only exit the mill once they are small enough to pass through the discharge grates. This feature imposes both a classification function and a finite discharge capacity on the mill. Two primary breakage mechanisms operate within a SAG mill (Napier-Munn et al., 1996), as illustrated in Figure 1: high-energy impact breakage, which occurs through a limited number of events, and low-energy abrasion breakage, which occurs through a very large number of events and is the dominant source of fines generation. High SAG mill fillings favour abrasion breakage at the expense of impact breakage, Height Shoulder Impact Zone (Toe of the charge) Abrasion Zone (kidney-shape region) Ball Rock Figure 34 – Main Breakage Mechanisms in SAG Mills
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