Timing of magmatic–hydrothermal activity and gold mineralization at the Jiudian Gold Deposit, Jiaodong Peninsula, Eastern China: Constraints from integrated U–Pb and Rb–Sr geochronology

The Jiudian gold deposit, a fault-controlled quartz–sulfide vein system hosted mainly within the Linglong granite, represents one of the largest gold accumulations along the southern segment of the Zhaoping Fault in the Jiaodong gold province, eastern China. However, the timing of gold mineralization and its relationship to local magmatism remain poorly constrained, hindering a comprehensive understanding of the deposit’s metallogenic evolution. To address this issue, we integrate detailed petrography with in-situ geochronological and geochemical analyses, including zircon U–Pb dating of granitic pegmatites, garnet U–Pb geochronology and trace-element analyses of newly recognized barren skarns, and Rb–Sr dating of hydrothermal muscovite and sericite from auriferous quartz veins. Petrographic observations, SEM–EDS imaging, and mineral chemistry reveal two generations of hydrothermal garnet (Grt-1 and Grt-2) within the skarns. Zircon U–Pb analyses of pegmatites yield weighted mean 206 Pb/ 238 U ages of 145.9 ± 1.6 Ma and 145.0 ± 1.1 Ma, whereas garnet U–Pb dating produces indistinguishable lower-intercept ages of 145.8 ± 1.2 Ma and 145.0 ± 1.1 Ma for Grt-1 and Grt-2, respectively. These results demonstrate that skarn formation was coeval with pegmatitic magmatism at ∼145 Ma. In contrast, hydrothermal muscovite and sericite intimately associated with electrum, the principal gold-bearing phase, yield Rb–Sr isochron ages of 119.8 ± 8.6 Ma and 119.2 ± 2.7 Ma, constraining the timing of gold mineralization to ∼120 Ma. Combined with previously published geochronological data, our results indicate that the ∼145 Ma skarn-forming event represents a gold-barren magmatic–hydrothermal episode genetically related to emplacement of the Linglong granite, whereas economically significant gold mineralization occurred ∼25 Myr later during an independent hydrothermal event. The ∼120 Ma mineralization age is synchronous with the widespread intrusion of mafic dikes in the Jiudian area and the broader Jiaodong gold province, implying that mantle-derived magmatism likely played a key role in triggering gold mineralization. This study provides robust evidence for the temporal decoupling between early granite-related hydrothermal activity and late gold mineralization in the Jiudian deposit, and further supports a multi-stage metallogenic model involving discrete magmatic-hydrothermal events for the Jiaodong gold province.