Petrogenesis and age of granitoids associated with the Dongshan Cu polymetallic deposit, East Kunlun Orogenic Belt, NW China: Implications for the Middle to Late Triassic tectonic setting and Cu polymetallic mineralization

The Dongshan Cu polymetallic skarn deposit is located in the eastern part of the East Kunlun Orogenic Belt (EKOB), NW China. The EKOB is an important Au-Cu-Fe polymetallic metallogenic belt. The mineralization is spatially-associated with granite porphyry and its contact with the Upper Triassic carbonates. In this paper, zircon UPb dating, whole-rock geochemistry, and zircon Hf isotope analysis were conducted to estimate the timing of intrusion emplacement, and identify magma sources and tectonic setting of the ore-related porphyry granite. Zircon UPb dating indicates that the emplacement ages are 239.6 ± 1.6 Ma and 235.6 ± 1.2 Ma, respectively. They belong to weakly peraluminous high-K calc-alkaline I-type granite, and exhibit significantly negative Eu anomalies (δEu = 0.31–0.39), depletions of high field strength elements and heavy rare earth elements (HREEs), and enrichment of large-ion lithophile elements (LILEs). Zircon Hf isotope compositions reveal that the ε_Hf(t) values range from −2.71 to 0.01, corresponding to T_DM2 of 1265–1437 Ma. These results suggest that the ore-related granite porphyry is originated from the partial melting of lower crust, mixed with the mantle-derived components. Furthermore, the ore-related granite porphyry in the Dongshan Cu polymetallic deposit shares characteristics of syn-collisional granites. Hence, we propose it was formed in a tectonic setting of continental marginal arc related to the northward subduction of the Paleo-Tethys Ocean.