Experimental investigation of sulfide-sulfate equilibria in silicate melts

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Sulfides largely control the geochemistry of chalcophile and siderophile elements in the Earth¿s mantle and crust. Therefore, understanding the factors affecting sulfide stability is essential to the understanding of the behavior of sulfur and chalcophile and siderophile elements. In magmatic systems sulfur is thought to be present dominantly as sulfide species. However, some magmas contain sulfates, either as crystalline phases (e.g., anhydrite, nosean, hauyne, apatite, silvialite) or as dissolved species in the melt. To date there are very few data to evaluate the extent of sulfide oxidation in magmatic processes. In sufficiently oxidized magma sources, sulfides may not be present during partial melting. In addition, theoretical models indicate that silica activity and melt alkalinity may affect sulfide-sulfate equilibria, stabilizing sulfates at lower fO2. This project will generate experimental data to constrain these models. In this context the main goals of this project are: (1) To constrain sulfide-sulfate equilibria in silicate melts as a function of fO2 and melt composition, (2) To determine if there is a fO2 range in which both sulfide and sulfate species coexist, (3) To establish whether other sulfur species (e.g., sulfite) are present. The results will provide information relevant to the use of siderophile elements as tracers of magmatic processes, the causes of high-sulfur volcanic degassing, and the genesis of magmatic-hydrothermal ore deposit.