As for many commodities, gold mining has relied on economies of scale to allow material to be mined and processed more cost effectively. Lower mining and processing costs, together with increased demand for metals and technological innovation, have resulted in larger deposits at lower grades being exploited. As well, the move to larger scale mining, which is inherently less selective, has increased added dilution in the processing feed. The compounding effects of lower grade deposits and higher dilution have resulted in added waste and lower head grades for downstream mineral processing.
To address challenges in reduced head grades and to generally improve profitability, the heterogeneity of mineral deposits should be considered. All mineral deposits exhibit heterogeneity – some more than others. Gold deposits often possess a high degree of heterogeneity, which can result in small amounts of high-value gold mineralisation remaining economic despite high dilution in process feeds. This paper explores the heterogeneity of gold deposits and introduces the concept of “waste liberation” to gauge when mining scale or particle size is sufficiently small, and mineralisation is sufficiently absent, to preclude further processing. Rejecting liberated waste is key to improving process head grades and for many deposits with head grade – recovery relationships, improved head grades mean improved metal recoveries.
