Zircon U–Pb ages and geochemical characteristics of granites in the Yaoertu deposit: Implications for Pb–Zn–Ag mineralization in the southern Great Xing’an Range, NE China

Abstract

Abstract The newly discovered Yaoertu Cu–Pb–Zn–Ag deposit in the southern Great Xing’an Range (SGXR), NE China, is spatially associated with late Yanshanian intrusions. The Cu mineralization occurs within a fine-grained granite, whereas the Pb–Zn–Ag orebodies are developed within country rocks of the Linxi Formation, and are spatially associated with monzogranite or fine-grained granite. The monzogranite and fine-grained Cu-bearing granite have zircon ages of 137.1 ± 0.4 and 137.4 ± 0.5 Ma, indicating that mineralization occurred in the Early Cretaceous, consistent with the formation of extensive skarn or hydrothermal Pb–Zn–Ag deposits in the SGXR. The monzogranite is enriched in SiO2 (69.91–67.87 wt%) and Na2O + K2O (8.43–7.92 wt%), contains 15.20–14.85 wt% Al2O3, and has a mean A/CNK value of 1.01, indicating the monzogranites are weakly-peraluminous high-K calc-alkaline granites. The fine-grained granites contain 77.18–75.14 wt% SiO2, 5.44–4.73 wt% K2O, 13.14–12.16 wt% Al2O3, 0.62–0.52 wt% CaO, and belong to the high-K calc-alkaline series. The monzogranite is enriched in light rare earth elements (REEs), exhibits fractionation of light over heavy REEs (LREE/HREE = 10.58–9.78), and has Eu/Eu* values of 0.74–0.61, whereas the fine-grained granite has LREE/HREE of 8.34–7.07 and more marked negative Eu anomalies (Eu/Eu* = 0.17–0.11). Zircon δ18O values in the monzogranite range from 6.61‰ to 6.87‰, and from 6.67‰ to 7.14‰ in the fine-grained Cu-bearing granite. The chemical composition and zircon Hf–O isotopic data suggest that the Early Cretaceous granites are formed by mixing between the juvenile crust and mantle-derived materials. Post-orogenic extensional settings related to the closure of the Mongol–Okhotsk Ocean resulted in extensive magmatism and large-scale mineralization.