The genesis of the Ni-Cu sulfide mineralization of the carboniferous Haibaotan intrusion, Eastern Tianshan, Central Asian Orogenic Belt

The large to middle-sized magmatic Ni-Cu sulfide deposits are spatially situated in the eastern portion of Eastern Tianshan, whereas those in the western portion have been poorly understood due to their quantity and scale. The Haibaotan Ni-Cu sulfide occurrence is newly discovered in the western portion of Eastern Tianshan, which provides an opportunity for understanding how its magmatic conduit system was generated and evolved. The Haibaotan mafic-ultramafic intrusion is dominated by peridotite, pyroxenite, olivine gabbro, and gabbro, and sulfide orebodies occur mainly within gabbro. Gabbro from the Haibaotan intrusion is dated at 315.5 +/- 1.9 Ma, which suggests that the Haibaotan intrusion is generated in a subduction evironment. The age is much earlier than the emplacement of other mineralized mafic-ultramafic intrusions (similar to 280 Ma) in Eastern Tianshan. High zircon epsilon Hf-(t) values (+7.09 to +18.44) indicate that the parental magmas of the Haibaotan intrusion have been derived from a metasomatized mantle source. Additionally, mafic-ultramafic rocks in the Haibaotan intrusion exhibit enrichment of large ion lithophile elements (LILE) and light rare earth elements (LREE), together with a depletion of Zr, Ti, and Nb, which is indicative of a subduction-modified mantle source. Core-rim variations of olivine forsterite (Fo) and Ni contents imply that the Haibaotan intrusion resulted from successive magma pulses, and the variable PGE tenors reflect that the sulfide droplets scavenged metals from multiple magma pulses. The low Se/S ratios of sulfide mineralization suggest that the addition of crustal sulfur triggered sulfide segregation in the shallow magma conduit system. The evolution history of the Haibaotan magma conduit system meets the requirements for generating a magmatic Ni-Cu deposit. This study highlights that the subduction environments are favorable for the formation of magmatic sulfide deposits in Eastern Tianshan.