Origin of the Permian Baimazhai Ni-Cu-(PGE) sulfide deposit, Jinping, Southern Yunnan Province, SW China

Abstract

The Baimazhai Ni-Cu-(PGE) sulfide deposit is hosted in a concentric maficultramafic intrusion at Jinping, SW China. The intrusion is composed of an inner peridotite core surrounded by pyroxenite, which in turn, is rimmed by gabbro. The peridotite and pyroxenite occupies -50 volume % of the intrusion and is almost totally mineralized. The mineralization comprises a disposed massive ore body (-20 volume %) surrounded by nettextured and disseminated ores. Geochemical data demonstrate that the parental magmas were Mg-rich, S-undersaturated melts that became S-saturation before emplacement. The deposit was formed by emplacement of an olivine crystal mush rich in sulfide melts. Due to their highly different densities, the immiscible sulfide melts were concentrated at the bottom of the staging; magma chamber while olivine-rich silicate melts above the sulfide melts. When the melts were squeezed up along a magma conduit under regionally compressive setting, immiscible sulfide melts tend to concentrate in the center of the conduit in response to higher velocity as the magma flows. Eventually, the magma was heavily loaded with cumulus olivine crystals in addition to sulfide droplets on emplacement, and finally the massive sulfide ore body formed in the center surrounded by silicate rocks.