Porphyry Cu–Au and Cu–Mo Systems as Sources for Critical Metal Resources: A Review and Future Projection

Porphyry systems are considered as low-grade, but high-tonnage, sources of scarce critical metals such as Cu and Mo, but they also host economic by-products of precious metals such as Au and Ag as well as rare trace critical metals such as Se, In, Te, and Re. The latter are of increasing importance as they represent essential components in the manufacture of green energy devices such as solar panels and modern high-tech gadgets. Until recently, the majority of critical trace metals remained in the metallurgical waste streams in most of the large porphyry mines, but several operators in Brazil, China and Japan have already begun to recover them from their mine tailings at an industrial scale. There are two sub-types of porphyry-type deposits: (1) porphyry Cu±Au, and (2) porphyry Mo±Re systems, the former associated with calc-alkaline or alkaline intrusions in continental- or island-arc settings, whereas the latter are normally hosted by more evolved high-K calc-alkaline intrusions derived in post-collisional arc settings. Both sub-types form large S and Fe, rather than Cu and Mo, anomalies in the Earth’s upper crust and are defined by high total sulfide contents with pyrite representing the largest sulfide proportion when compared to the much less abundant directly economic chalcopyrite, bornite, and molybdenite phases. Importantly, pyrite hosts the majority of critical trace metals (Se, In, Te) in porphyry systems and therefore represents a vast untapped resource of these rare critical metals. Understanding the complex deportment of these rare critical elements can facilitate their extraction from pyrite concentrates in the metallurgical processing plants of current and future porphyry mining operations. This can boost their supply at a time when exploration discovery and mining of new porphyry systems have slowed due to a range of geological, governmental, environmental, and social issues and is unlikely to meet demand in the short term.