THE IMPORTANCE OF MINERALOGY IN EVALUATING RECOVERY OF CRITICAL MINERALS AND OTHER METALS FROM MINE WASTE: AN EXAMPLE FROM A PORPHYRY CU MINE

Critical minerals and other commodities in mine waste can pose environmental risks or be valuable resources. In this study, we examine the chemical and mineralogical deportment of mineral commodities into mill output streams at an active porphyry Cu-Mo mine in the U.S. Mass-balance calculations of bulk chemistry of concentrates and waste streams reveal nearly half of the Ag, Au, Sb, and Zn, and the majority of Co, Ge, Ga, In, Pd, Te, W, REEs, and Zr in the ore are lost to tailings. Developing recovery strategies for these elements from the tailings requires knowledge of their mineral hosts.

In tailings, critical minerals and other commodities can occur as discrete minerals (e.g., Te in tellurides or sulfosalts, Ge in Cu-Ge sulfides such as catamarcaite, REEs in monazite, or native metals such as Au or electrum). The discrete minerals can be present as liberated particles or inclusions, often at micrometer or nanometer scale. Additionally, these elements may occur in solid solution within the lattice of a particular mineral. For example, pyrite, a gangue mineral found in the tailings, may be enriched in elements such as Au, Co, Ni, and Te. The association of these elements with pyrite in tailings, both as discrete mineral inclusions and within the mineral structure, suggests that generating a pyrite separate could concentrate them. Extracting a pyrite concentrate would also have the added long-term environmental benefit of removing an acid-generating mineral. In contrast, REEs and Zr occur in the tailings as monazite and zircon, respectively, both of which could be concentrated using density separation.

Additional research will quantify the distribution of critical elements within the minerals found in mine waste and their liberation potential. This information will provide insights into economically viable recovery approaches, ideally, ones that result in more environmentally stable waste products.