Geochronological, mineralogical and geochemical studies of sulfide mineralization in the Yueyawan mafic intrusion in the East Tianshan orogenic Belt, NW China

Abstract

The Yueyawan Cu-Ni sulfide deposit, located in the northern part of Dananhu island arc, is a new case of Cu-Ni mineralization related to Early Permian mafic magmatism in the East Tianshan orogenic belt, NW China. Olivine gabbro, hornblende gabbro, and gabbro are the major rock types of this complex. Disseminated sulfide mineralization with a pentlandite + pyrrhotite + chalcopyrite assemblage occurs in olivine gabbro. Zircon crystals from olivine gabbro yielded a U-Pb age of 275 ± 2 Ma, almost contemporaneous with the postcollisional extension-related Cu-Ni deposits in the East Tianshan nickel belt (e.g., Tulaergen, Xiangshan, Huangshan, Tudun, and Baixintan deposits). The Yueyawan olivine gabbro is characterized by light rare earth element enrichment, pronounced negative Nb-Ta anomalies, low initial 87Sr/86Sr ratios from 0.703282 to 0.703420, positive εNd(t) values from 3.4 to 7.2, zircon εHf(t) values from + 15.5 to + 18.5, indicating that the parental magma of the Yueyawan intrusion was derived from a metasomatized mantle source, similar to other contemporaneous mafic–ultramafic intrusions in the region. The δ34S values of sulfide of the Yueyawan deposit are similar and vary from 0.60 to 1.85 ‰, which are within the range of typical mantle values as well as that of the country rocks, providing no direct evidence for addition of external sulfur. However, the negative correlation between Se/S (54.01 to 77.56 × 10−6) ratios and sulfur contents in the disseminated sulfides indicate crustal contamination played a critical role for sulfide segregation of the magma. The olivine Fo and Ni contents from sulphide-bearing mafic rocks show a negative correlation. Olivine chemistry and Sr-Nd-Hf-S isotope data indicate that fractional crystallization and crustal contamination played a role in triggering sulfide saturation in the Yueyawan mafic magma.