Petrology of the Kuolotong sulfide copper-nickel deposit in northwestern China

The picrite-dolerite ore association was well expressed at the orogenic stage of development of the Hercynides of the Zaisan-Gobi fold belt, separate parts of which are associated with Cu-Ni ore occurrences and deposits. On the example of the Kuolotong deposit (North Xinjiang, China), we show that the fold belt formed as a single ore-magmatic system, from sulfide-silicate liquation in an intermediate chamber to fractional crystallization of a sulfide melt in the ore-hosting intrusion. The fractional crystallization played a leading role in the formation of ores of varying composition (Ni-Fe, Fe-Cu, and abnormally cupriferous). Additional evidence is the partitioning of Pt, Pd, Au, and Ag, enriching the residual sulfide melt. The fact that Au dominates over Pd in the Kuolotong ores suggests considerably advanced fractionation of sulfide liquid during their formation, which corresponds to experimental data for these metals in sulfide systems. The isotope composition of sulfur in the ores is close to the meteorite standard, slightly deviating toward the heavy isotope. Halogen-bearing fluids contribute little to migration and concentration of noble metals. The petrological and geochemical characteristics of the Kuolotong deposits, in combination with mineralogical and geochemical signatures of other ore-bearing intrusions of picrite-dolerite ore association may be used for estimating the ore potential of such intrusions.