Role of chalcophile element fertility in the formation of the eastern Tethyan post-collisional porphyry Cu deposits

Abstract

Post-collisional porphyry Cu deposits are genetically related to the magmas generated by partial melting of sulfide-bearing lithosphere fertilized by subduction components. The ore-forming magmas are suggested to be enriched in chalcophile elements compared to the barren magmas. However, the chalcophile element contents in the post-collisional magmas and its role in controlling the porphyry ore formation remain unclear. Platinum-group element (PGE) geochemistry has been used as a proxy for Cu and Au. In this study, we report PGE concentrations of representative post-collisional ore-associated and barren suites in the eastern Tethyan metallogenic domain. The ore-associated suites have moderate Pd and Pt contents ranging from ~ 0.05 to 0.5 ppb, which are comparable to those associated with giant porphyry systems in continental arc settings. In contrast, most of the barren suites have systematically lower Pd and Pt concentrations below ~ 0.1 and 0.05 ppb, respectively. Numerical models show that the ore-forming magmas, derived from partial melting of subduction-modified lithospheric mantle, have precipitated a small amount of sulfide phases during magma differentiation, leading to the moderate depletion of Pd and Pt in the ore-associated suites. Although the sulfide segregation has depleted highly chalcophile element contents, the ore-forming magmas contain sufficient Cu to form porphyry Cu deposits. This contrasts with the barren suites, which mainly originated from partial melting of the lower crust and contain about five times lower Cu contents, unfavorable for porphyry Cu mineralization. We suggest that moderate chalcophile element contents in the ore-associated magmas have increased the porphyry ore-forming potential in the eastern Tethyan domain.