Geochemistry and geochronology of the Qingshanjiao granites: Implications for the genesis of the Dongguashan copper (gold) ore deposit in the Tongling ore district, Eastern China

Abstract

The Dongguashan copper (gold) ore deposit, which is located in the central region of the Middle–Lower Yangtze Cu–Fe–Au–Mo metallogenic belt, Eastern China, is one of the largest stratabound skarn copper (gold) deposits in the Tongling ore district, Anhui Province. The Qingshanjiao quartz monzodiorite is associated with the copper (gold) mineralization in the Dongguashan mining district. Vein-like and disseminated sulfide mineralization are developed within the Qingshanjiao pluton, with the thicknesses of the orebodies increasing closer to the pluton. The LA–ICP–MS zircon U–Pb analysis of the Qingshanjiao quartz monzodiorite yielded a weighted mean 206Pb/238U age of 136.7 ± 2.3 Ma (MSWD = 0.37, n = 10), which is approximately consistent with the previously published molybdenite-related copper (gold) mineralization Re–Os model ages of ca. 140–137 Ma. Based on whole-rock major and trace element data, as well as zircon Lu–Hf isotope data, the Qingshanjiao quartz monzodiorite is a high-K calc-alkaline, metaluminous I-type granite, which is characterized by the relative enrichment of LREE, Cs, K and Th, relative depletion of HREE, Nb, P, Ti and Ta, and εHf(t) values of magmatic zircons ranging from −1.7 to −31.7.Based on these results, combined with those of previous studies, we suggest that the Qingshanjiao quartz monzodiorite may be a mixture of mantle-derived basaltic magma and crust-derived granitic magma and that the Dongguashan copper (gold) ore deposit formed during the tectonic transition from compression to extension ca. 140 Ma.