Assessing the role of tectono-magmatic setting in the precious metal (Au, Ag, PGE) and critical metal (Te, Se, Bi) endowment of Porphyry Cu deposits

Abstract

Porphyry Cu deposits commonly contain critical and precious metal by-products, including the chalcophile and siderophile elements, Au, Pd, Pt, Ag, Te, Se, and Bi. These elements partition into residual sulfides during the partial melting of mantle wedge peridotite during subduction, potentially depleting the source magma for subduction-related porphyry Cu deposits. The chalcophile-rich residual sulfides in subduction-modified sub-continental lithosphere are thought to be the source of metals in postsubduction porphyry Cu deposits, and as such these deposits may be more enriched in chalcophile and siderophile elements than subduction-related porphyry deposits, although many postsubduction deposits have low Au grades. We test this by presenting whole-rock assay and PGE data with in situ LA-ICP-MS trace element data from sulfide minerals from three porphyry Cu deposits. The Skouries Cu-Au-(PGE) porphyry deposit, Greece, and the Muratdere Cu-Au-Mo porphyry deposit, Turkey are both postsubduction; these are contrasted with the El Teniente Cu-Mo porphyry deposit, Chile, which is a classic subduction-related system. By comparing these results with a newly compiled global dataset of trace element concentrations in sulfides from 18 other porphyry Cu deposits we show that postsubduction porphyry Cu deposit sulfides are relatively enriched in Bi, Sb, Te, and Se compared to sulfide minerals from subduction-related deposits. However, although some critical and precious metals (Ag, Bi, and Se) mainly reside in primary sulfide ore minerals, others (Au, Te, Pd, and Pt) are predominantly hosted in minor accessory minerals. Whole-rock data from mineralized samples show that although the Skouries and Muratdere deposits are enriched in Au compared with El Teniente, globally both subduction-related and postsubduction deposits can be precious and critical metal enriched, with metal endowment independent of tectonic setting. PGE-enriched porphyry Cu deposits are also enriched in Bi, Te, and Au, and semimetal melts are suggested to play an important role in PGE transport and concentration in porphyry Cu deposits.