Geochronology, geochemistry and Sr-Nd isotope compositions of the Niubiziliang mafic-ultramafic complex in the South Altyn orogen, NW China: Implications for Ni-Cu mineralization and tectonic setting

The Niubiziliang mafic-ultramafic complex with Ni-Cu mineralization is a rare example of magmatic Ni-Cu deposits formed in an orogenic setting, specifically the South Altyn orogen in Northwestern China. We report a baddeleyites U-Pb age of 452±12 Ma for the complex, which is consistent with the eclogite exhumation ages in the orogen and suggests a rift-related magmatism triggered by slab break-off. The complex shows geochemical and isotopic features indicative of a mantle-derived origin with 10% crustal contamination. The magmatic evolution involved extensive fractional crystallization, assimilation, and crustal contamination (AFC) processes. Fractional crystallization enhanced sulfur saturation in the early stage of magmatic evolution, while crustal contamination was the main factor for sulfide saturation and Ni-Cu mineralization in the later stage.