GENETIC MECHANISMS OF THE JINCHUAN ULTRAMAFIC INTRUSION AND ASSOCIATED SUPERLARGE SULFIDE DEPOSIT, NORTHWEST CHINA

Superlarge sulfide deposits are hosted in the Jinchuan ultramafic intr usion. The central and west segments of the intrusion may represent ma gma conduits along which petrological phases are symmetrical zones. Th e ores are associated with the dunite and Iherzolite in the central pa rt of the intrusive body. The east segment of the intrusion is more ge ntly titled, showing vertical zonation of rock phases with ores locali zed at the base. Cumulate texture is common in various types of rock. Petrological and geochemical studies indicate that flow-differentiatio n may have dominated in the central and west segments while gravity di fferentiation was important in the east. The original magma was believ ed to be tholeiitic in composition. The massive ores were the result o f filter pressing. Ore metals were supplied for the most part by progr essive influx of new magmas. The segregation of sulfide liquid from th e silicate melt was controlled to a large extent by volatiles. Necessa ry conditions for the formation of such superlarge sulfide deposits ar e discussed.