Geochronology, petrology and Sr-Nd-Hf isotope geochemistry of the newly discovered Narenguole magmatic Ni-Cu sulfide prospect, Eastern Kunlun Orogenic Belt, Qinghai Province, NW China

Abstract

Since the discovery of the giant Xiarihamu magmatic Ni-Cu-Co sulfide deposit in the Eastern Kunlun orogenic belt (EKOB) in 2011, more and more mafic-ultramafic intrusions containing sulfide mineralization has been found in this area, indicating that the magmatic sulfide deposit has great exploration potential. Recently, magmatic sulfide mineralization of economic significance has been found in the I intrusion of the Narenguole (NRGL) magmatic sulfide prospect in the eastern segment of EKOB, with Cu grade of 0.59 wt% and Ni grade of 2.07 wt%, showing great prospecting potential.

However, the age, the nature of source area and the geodynamic background of its formation have not been studied. In this paper, the petrography, geochemistry, chronology and Sr-Nd-Hf isotopic composition of NRGL I intrusion are reported for the first time. The petrographic observations show that the lithology of the NRGL I intrusion is olivine pyroxenite, which is mainly composed of olivine and orthopyroxene, with a small amount of hornblende and phlogopite. The ore minerals are mainly composed of disseminated to net-textured pyrrhotite, pentlandite and chalcopyrite. Zircon laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating is 258.7 ± 1.4 Ma, suggesting that the intrusion was formed in the Late Permian. The ultramafic rocks are enriched in light rare earth elements (LREE) and large-ion lithophile elements (LILE), depleted in high-field strength elements (HFSE), indicative of arc geochemical affinities. They have low Ce/Pb (10.18–17.30) and Nb/Th (2.02–3.27) ratios, indicating a certain degree of crustal contamination. The ε_Hf(t) values of zircon range from −1.38 to +1.20, with an average value of −0.17. The initial ⁸⁷Sr/⁸⁶Sr ratios and ε_Nd(t) values of the whole rocks range from 0.707633 to 0.708737 and from −3.9 to −4.3, respectively, which are close to the isotopic composition of the enriched mantle (EMII). It is also similar to the contemporary mafic dikes and mafic microgranular enclaves (MMEs) in EKOB. These data suggest that the parental magmas of the NRGL I intrusion has undergone a certain degree of crustal contamination and originated from an enriched mantle source that had been metasomatized by slab-derived fluids. Our results, combined with regional geological constraints, indicate that NRGL I intrusion formed in an Andean-type active continental margin environment. More importantly, a Late Permian magmatic sulfide mineralization event occurred in the EKOB.