Geochronology and Geochemistry of the Granite Porphyry in the Zhilingtou Au-Mo-Pb-Zn Polymetallic Deposit, SE China: Implication for Mineralization Mechanism

The Zhilingtou Au-Mo-Pb-Zn polymetallic deposit is located in the southwestern Zhejiang Province, NE China, and is tectonically situated in the Shaoxing-Longquan uplift belt. Although previous studies have indicated that Au mineralization in this area occurred between 135 Ma and 145 Ma, evidence for coeval intrusive rocks has been lacking. Furthermore, it remains controversial whether the Au mineralization and (~113 Ma) Mo-Pb-Zn mineralization belong to the same magmatic-hydrothermal system. This study conducted comprehensive high-precision geochronological, petrochemical, and Sr-Nd isotopic analyses on the newly discovered granite porphyry intrusion in the mining area. The aim is to constrain the emplacement age of the intrusion, reveal the petrogenesis and source of ore-forming materials, and further discuss the mineralization mechanism. LA-ICP-MS zircon U-Pb dating results indicate that the granite porphyry was formed at 137.8 ± 0.95 Ma, which is broadly consistent with previously reported ages of Au mineralization. It is inferred that this intrusion may be related to a Au mineralization event at around 138 Ma. Geochemical characteristics show that the rock is peraluminous I-type granite, enriched in light rare earth elements (LREEs) and large ion lithophile elements (LILEs) and depleted in high field strength elements (HFSEs) such as Nb, Ta, and Ti, indicating an “island arc-type” geochemical signatures. Sr-Nd isotopic compositions (initial 87Sr/86Sr = 0.712364–0.712711; εNd(t) = −13.9 to −13.4; two-stage Nd model ages TDM2 = 1877–1908 Ma) suggest that the magma was derived from ancient crustal materials with the addition of mantle-derived components. Integrating existing geochronological, isotopic, and fluid inclusion evidence, it is proposed that the Zhilingtou deposit may have experienced two mineralization events: an early event (~138 Ma) involving Au-Ag mineralization related to the granite porphyry and a later event (~113 Ma) comprising Mo-Pb-Zn mineralization associated with a porphyry–epithermal system. Together, these events form a composite mineralization system. This study has important implications for refining regional metallogenic theories and guiding future ore exploration.