Rock-to-Metal Ratio: A Foundational Metric for Understanding Mine Wastes

Abstract

The quantity of ore mined and waste rock (i.e.,over burden or barren rock) removed to produce a refined unit of amineral commodity, its rock-to-metal ratio (RMR), is an importantmetric for understanding mine wastes and environmental burdens. Inthis analysis, we provide a comprehensive examination of RMRs for25 commodities for 2018. The results indicate significant variabilityacross commodities. Precious metals like gold have RMRs in therange of 105-106, while iron ore and aluminum are on the order of101. The results also indicate significant variability across operationsfor a single commodity. The interquartile range of RMRs forindividual cobalt operations, for example, varies from 465 to 2157,with a global RMR of 859. RMR variability is mainly driven by oregrades and revenue contribution. The total attributable ore minedand waste rock removed in the production of these 25 commodities sums to 37.6 billion metric tons, 83% of which is attributable toiron ore, copper, and gold. RMRs provide an additional dimension for evaluating the impact of materials and material choice trade-offs. The results can enhance life cycle inventories and be extended to evaluate areas of surface disturbances, mine tailings, energy requirements, and associated greenhouse gas emissions.