Early Cretaceous adakitic magmatism and contrasting mineralization-related and evolved intrusive facies at the Shangfeng Cu–Mo deposit, Zhejiang Province, SE China

Abstract

Along the northeastern Qin–Hang metallogenic belt in coastal Zhejiang, Cu–Mo occurrences are generally small and discontinuous, and the role of late Early Cretaceous granitoid magmatism in porphyry-style mineralization remains poorly constrained. The Shangfeng Cu–Mo deposit, hosted by a composite intrusive system along the Lishui–Yuyao Fault, provides an opportunity to evaluate whether Cretaceous arc-related magmatism was associated with mineralized intrusive facies in this part of SE China. We integrate deposit geology, drill-core observations, SIMS zircon U–Pb geochronology, whole-rock major- and trace-element geochemistry, and regional geochronological and isotopic compilations to constrain the emplacement age, petrogenesis, and tectonic setting of the ore-hosting granitoids. Zircon from the ore-hosting granitoid yields a weighted-mean 206Pb/238U age of 101.2 ± 0.8 Ma (95% confidence; MSWD = 1.20; n = 15), indicating late Early Cretaceous emplacement. The intrusive suite is high-K calc-alkaline, weakly to strongly peraluminous, and I-type, with negative Nb–Ta–Ti anomalies and positive Pb anomalies typical of a continental-arc setting. Whole-rock data distinguish adakitic, mineralization-related samples with high Sr/Y (55–241), low Y–Yb, and weak Eu anomalies from evolved non-adakitic samples with low Sr/Y (1.9–7.8) and stronger negative Eu anomalies. We interpret the adakitic signature as a working model for melting of thickened lower crust during Paleo-Pacific/Izanagi plate subduction, followed by magma ascent along the Lishui–Yuyao structural corridor. Because direct ore dating is not yet available, the zircon age is treated as an emplacement age and a possible upper temporal constraint on Cu–Mo mineralization. The Shangfeng data indicate that late Early Cretaceous intrusions in coastal Zhejiang should not be discounted in Cu–Mo exploration, and that Sr/Y–Eu–HREE systematics may provide candidate screening criteria for fertile intrusive facies within composite plutons, pending tests from direct ore geochronology and local Sr–Nd–Hf–O isotope data.