Genesis of the giant Zhaoxian gold deposit in the Jiaodong Peninsula, China: Constraints from geochronology, fluid inclusion, and H-O-He-Ar isotope

• First reported mineralization age of the giant Zhaoxian gold deposit is ca. 120 Ma. • Ore fluid is CO 2 -rich, medium temperature, and low salinity metamorphic fluid. • Ore fluid and metal derived from metasomatized subcontinental lithospheric mantle. • Fluid immiscibility and water–rock reaction together control gold deposition. The Zhaoxian gold deposit is an important deep-exploration discovery in the Jiaojia goldfield of the Jiaodong Peninsula, with orebodies extending to depths exceeding 2000 m. To assess whether its genesis differs from that of shallow gold deposits, this study conducted a systematic investigation involving petrography, fluid inclusions, geochronology, and isotope geochemistry. Four stages of hydrothermal veins were identified: pre-ore veins containing milky quartz and minor disseminated pyrite; main-ore veins consisting of gold-bearing pyrite, quartz, and minor muscovite; late-ore stage veins consisting of (gold-bearing) pyrite, galena, chalcopyrite, and quartz; and post-ore veins characterized by calcite, quartz, and minor pyrite. Gold mineralization primarily occurred during the main-ore stage, with minor mineralization in the last-ore stage. Hydrothermal monazite and apatite U-Pb dating constrain the timing of gold mineralization to approximately 120 Ma. The ore-forming fluid was a CO 2 -H 2 O-NaCl ± CH 4 system with salinity of 1.0–12.2 wt% NaCl equiv. and temperatures of 195 °C–372 °C. Fluid immiscibility during the main- and late-ore stages, coupled with water–rock interaction led to gold precipitation. The δ 18 O and δD values of fluids from the pre-ore, main-ore, and post-ore stages range from 2.7 to 6.3 ‰ and −83.3 to −78.1 ‰, respectively while pyrite from the main-ore stage exhibits 3 He/ 4 He values of 1.45–2.16 Ra. These isotopic characteristics indicate that the Zhaoxian deposit shares a common fluid source with other deposits in the Jiaojia goldfield and across the Jiaodong Peninsula, likely derived from devolatilization of the metasomatized subcontinental lithospheric mantle. Overall, these results suggest that the Zhaoxian deposit follows the same genetic model as shallow gold deposits in the Jiaojia goldfield, and formed in a transpressional setting driven by Paleo-Pacific plate rollback at approximately 120 Ma.