Rock-to-metal ratio: A foundational metric for understanding mine wastes

Environmental Science & Technology
By: , and 



The quantity of ore mined and waste rock (i.e., overburden or barren rock) removed to produce a refined unit of a mineral commodity, its rock-to-metal ratio (RMR), is an important metric for understanding mine wastes and environmental burdens. In this analysis, we provide a comprehensive examination of RMRs for 25 commodities for 2018. The results indicate significant variability across commodities. Precious metals like gold have RMRs in the range of 105–106, while iron ore and aluminum are on the order of 101. The results also indicate significant variability across operations for a single commodity. The interquartile range of RMRs for individual cobalt operations, for example, varies from 465 to 2157, with a global RMR of 859. RMR variability is mainly driven by ore grades and revenue contribution. The total attributable ore mined and waste rock removed in the production of these 25 commodities sums to 37.6 billion metric tons, 83% of which is attributable to iron 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.

Publication type Article
Publication Subtype Journal Article
Title Rock-to-metal ratio: A foundational metric for understanding mine wastes
Series title Environmental Science & Technology
DOI 10.1021/acs.est.1c07875
Volume 56
Issue 10
Year Published 2022
Language English
Publisher ACS Publications
Contributing office(s) National Minerals Information Center
Description 12 p.
First page 6710
Last page 6721
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