In-situ trace element and S isotope systematics in porphyry-epithermal pyrite, Limnos Island, Greece

A more sustainable society with CO2 neutral energy production requires substantial amounts of trace metal(loids). However, our understanding about the fractionation processes of these elements between the epithermal and porphyry environment is still limited, but may be essential to secure the future supply of these rare commodities. The porphyry-epithermal mineralization on Limnos (Fakos, Sardes, Kaspakas) show variable Te and related element (e.g., Au, Ag) contents, and therefore represent a natural laboratory to define key fractionation and enrichment processes. Subalkaline to alkaline igneous rocks and siliciclastic sediments host the porphyry-epithermal mineralization on Limnos. Pyrite, magnetite and minor chalcopyrite dominate the porphyry mineralization, whereas the epithermal stage comprises pyrite, sphalerite, galena, chalcopyrite together with minor sulfosalts (e.g. enargite, tetrahedrite-tennantite, bournonite), tellurides and native Au. Pyrite is ubiquitous in most alteration-types and its chemical composition, therefore provides insights into mineralization processes at variable fluid conditions. Epithermal pyrite is enriched in most trace elements (e.g., As, Ag, Sb, Au, Pb, Tl) compared to porphyry pyrite (Se-bearing), most likely caused by a more favorable mineralization process in the epithermal environment. However, Te shows no systematic variation between porphyry and epithermal pyrite, which we refer to its competitive incorporation between pyrite, galena, sulfosalts and tellurides in the epithermal stage. Sulfur isotope variations in pyrite report on the contribution of magmatic and meteoric fluids in variable proportion between different mineralizations on Limnos. We present a hydrothermal model based on the mineralogical and chemical data, defining key fractionation processes for Te and related elements in the porphyry-epithermal environment.