Abstract:

The Jinchuan ultramafic intrusion in western China hosts the third largest magmatic CuNi deposit in the world, but the emplacement history of the magma and sulfide liquid in the intrusion remains poorly understood. Based on the lithological structure, crosscutting relationships and compositional variations in the intrusion, we propose a fivestage emplacement model: (1) formation of sulfidepoor ultramafic lithology by injection of an olivinerich magma; (2) formation of disseminated sulfide zones by injection of olivinerich magma containing small amounts of suspended sulfide droplets; (3) formation of nettextured sulfide ore zones by injection of sulfide olivinerich magma; (4) formation of massive sulfides zones ore body by injection of sulfide liquid; and (5) formation of CuPtPdrich sulfide veins by injection of fractionated sulfide liquids derived by fractional crystallization from nearby sulfide zones and emplaced into fractures in the intrusion and footwall rocks. Ni, Cu, Pt, Pd, Rh, Ir, Ru, and Co correlate positively with S indicating that they were hosted primarily in sulfides. PtPd enrichment zones are the relic liquid of monosulfide solid solution segregation,and massive ore may represent the accumulation of monosulfide solid solution. The magma conduit of Jinchuan CuNi (PGE) sulfide deposit belongs to dike magma conduit.

Key words: emplacement sequence, sulfide orebearing ultramafic intrusion, Jinchuan