Geochemical and thermodynamical modeling of magmatic sources and processes for the Xiarihamu sulfide deposit in the eastern Kunlun Orogen, western China

Magmatic sulfide deposits in subduction-collision settings are genetically related to oxidized and hydrous magmas, where the degree of partial melting, fractional crystallization, and sulfide saturation are all expected to differ significantly from those in dry and reduced magmas associated with most giant magmatic sulfide deposits in intracratonic settings. This study provides petrological and geochemical data as well as multiple modeling approaches for the post-collisional Xiarihamu magmatic sulfide deposit of the eastern Kunlun Orogen to investigate melting mechanism and magmatic differentiation in an oxidized and hydrous magmatic system. Petrographical observations and whole-rock geochemistry suggest that the olivine orthopyroxenite, orthopyroxenite, websterite and gabbronorite in the Xiarihamu complex were cumulates. Pressures estimated from clinopyroxene and hornblende compositions and oxygen fugacities from hornblende and biotite compositions further suggest that these cumulates crystallized under moderate- to high-pressure, oxidized conditions. The Xiarihamu parental magma was high-MgO basalt as evidenced by multiple modeling methods. This parental magma was generated from a metasomatized mantle peridotite source in the spinel stability field with moderate melting degrees and then experienced a fractional crystallization process with a first iron-enriched and then silica-enriched trend under moderate-high pressures to form the observed crystallization sequence and mineral compositions. Minor amounts of wall rock assimilation during magmatic evolution were supported by Sr-Nd isotopic modeling. Sulfide saturation previously proposed by crustal sulfur addition at Xiarihamu was not straightforward but was likely caused by an oxygen fugacity decrease triggered by magmatic differentiation.