The genesis of the ores and intrusions at the Yuhai Cu–Mo deposit in eastern Tianshan, NW China: Constraints from geology, geochronology, geochemistry, and Hf isotope systematics

Abstract

The Yuhai porphyry Cu–Mo deposit is located in the eastern Tianshan orogenic belt of the southern Central Asian Orogen Belt, being an economically important porphyry Cu deposit in NW China. The deposit comprises sixteen buried orebodies that are predominantly associated with dioritic and granodioritic intrusions and are structurally controlled by roughly NE-trending faults. LA-ICP-MS zircon U–Pb dating yielded crystallization ages of 441.6±2.5Ma (MSWD=0.03, n=24) for diorite and 430.4±2.9Ma (MSWD=0.04, n=19) and 430.3±2.6Ma (MSWD=0.09, n=24) for granodiorite. In situ zircon Hf isotope data on a diorite sample show εHf(t) values from +8.7 to +18.6, and two granodiorite samples exhibit similar εHf(t) values from +12.6 to +19.6 and +12.6 to +18.9, respectively. The dioritic and granodioritic intrusions belong to a low-K tholeiite series and are relatively enriched in large ion lithophile elements (K, Ba, Pb, and Sr) and are depleted in high field strength elements (Th, Nb, Ta, and Ti). Moreover, these intrusions have high SiO2, Al2O3 and MgO contents, low Na2O, P2O5 and TiO2 contents, low Nb/Ta ratios, and slightly positive Eu anomalies. Re–Os dating of molybdenite intergrowth with chalcopyrite yielded a well-constrained 187Re–187Os isochron age of 351.7±2.9Ma (MSWD=1.5) with a weighted average age of 355.7±2.4Ma (MSWD=0.69) Ma, indicating that the Yuhai Cu–Mo deposit is younger than the intrusion of the diorite and granodiorite. Combined with the regional geological history and above-mentioned data, we suggest that the Yuhai intrusions were most likely derived from the partial melting of mantle components that were previously metasomatized by slab melts formed by the northward subduction of the ancient Tianshan ocean plate beneath the Dananhu–Tousuquan island arc during the Silurian to Carboniferous. Under the subduction-related tectonic setting, the metasomatized mantle magma was emplaced into the shallow crust and induced the formation of the Early Carboniferous Yuhai Cu–Mo deposit, and the hydrothermal fluids of enriched sulfides probably played an important role in the Cu–Mo mineralization.