U–Pb, Re–Os and Ar–Ar dating of the Linghou polymetallic deposit, Southeastern China: Implications for metallogenesis of the Qingzhou–Hangzhou metallogenic belt

Abstract

The Qingzhou–Hangzhou metallogenic belt (QHMB) in Southeastern China has gained increasingly attention in recent years. However, due to the lack of reliable ages on intrusions and associated deposits in this belt, the tectonic setting and metallogenesis of the QHMB have not been well understood. The Linghou polymetallic deposit in northwestern Zhejiang Province is one of the typical deposits of the QHMB. According to the field relationships, this deposit consists of the early Cu–Au–Ag and the late Pb–Zn–Cu mineralization stages. Molybdenite samples with a mineral assemblage of molybdenite–chalcopyrite–pyrite±quartz are collected from the copper mining tunnel near the Cu–Au–Ag ore bodies. Six molybdenite samples give the Re–Os model ages varying from 160.3 to 164.1Ma and yield a mean age of 162.2±1.4Ma for the Cu–Au–Ag mineralization. Hydrothermal muscovite gives a well-defined Ar–Ar isochron age of 160.2±1.1Ma for the Pb–Zn–Cu mineralization. Three phases of granodioritic porphyry have been distinguished in this deposit, and LA–ICP–MS zircon U–Pb dating shows that they have formed at 158.8±2.4Ma, 158.3±1.9Ma and 160.6±2.1Ma, comparable to the obtained ages of the Cu–Au–Ag and Pb–Zn–Cu mineralization. Therefore, these intrusive rocks have a close temporal and spatial relationship with the Cu–Au–Ag and Pb–Zn–Cu ore bodies. The presences of skarn minerals (e.g., garnet) and vein-type ores, together with the previous fluid inclusion and H–O–C–S–Pb isotopic data, clearly indicate that the Cu–Au–Ag and Pb–Zn–Cu mineralization are genetically related to these granodiorite porphyries. This conclusion excludes the possibility that this deposit is of “SEDEX” type and formed in a sag basin of continental rifts setting as previously proposed. Instead, it is proposed that the Linghou polymetallic and other similar deposits in the QHMB, such as the 150–160Ma Yongping porphyry-skarn Cu–Mo, Dongxiang porphyry? Cu, Shuikoushan/Kangjiawang skarn Pb–Zn, Fozichong skarn Pb–Zn and Dabaoshan porphyry-skarn deposits are of magmatic-hydrothermal origin and likely formed in a subduction-related setting. This work provides new insight that these intrusion-related deposits (e.g., porphyry and skarn types) of middle to late Jurassic age can be the most important targets for exploration in the QHMB.