Geology, Fluid Inclusion and Stable Isotope Constraints on the Fluid Evolution and Resource Potential of the Xiadian Gold Deposit, Jiaodong Peninsula

Abstract

AbstractThe Xiadan gold deposit from Jiaodong Peninsula contains more than 200 t of gold, and is one of the representative largest deposits within south part of the Zhaoping Fault zone. The gold orebodies consist of auriferous altered rocks that show disseminated and stockwork mineralization. Mineralization and alteration are structurally controlled by the NE‐ to NNE‐striking Linglong detachment fault. Mineralization can be divided into three stages: (K‐feldspar)–sericite–quartz–pyrite, quartz–gold–polymetallic sulfide, and quartz–carbonate, with the majority of the gold being produced during the middle stage. Based on a combination of petrography, microthermometry, and laser Raman spectroscopy, three types of fluid inclusion were identified in the vein mineral assemblages: NaCl–H2O (A‐type), CO2–H2O–NaCl (AC‐type), and pure CO2(PC‐type). Quartz crystals in veins that formed during the early stage contain mainly AC‐type primary fluid inclusions, with rare PC‐type inclusions. These fluid inclusions homogenize completely at temperatures of 253°C–408°C and have medium–low salinities (1.62–11.89 wt.% NaCl equivalent). Quartz crystals that formed during the middle stage contain all three types of fluid inclusion, and these fluid inclusions homogenize completely at temperatures of 176°C–335°C and have salinities of 0.70–14.73 wt.% NaCl equivalent. In contrast, quartz that formed during the last stage contains only A‐type fluid inclusions; these inclusions have homogenization temperatures of 108°C–253°C and salinities of 1.73–11.60 wt.% NaCl equivalent. The above data indicate that the ore‐forming system evolved from a CO2‐rich mesothermal fluid into a CO2‐poor fluid as a result of an influx of meteoric water. Fluid immiscibility is an essential prerequisite for metals precipitation in Xiadian. The characteristics of fluid inclusions, combined with H–O–S isotopes suggest that the ore‐forming fluids might be of metamorphic origin. Based on the immiscibility of AC‐type fluid inclusions, trapping pressures have been estimated at 88–339 MPa during ore formation, with a depth of metallogenesis of 8.8–12.6 km. The depth of erosion of study area has been calculated as about 10.3 km between 130 Ma and the present. Considering the gold mineralization occurred at around 130 Ma, the space with deep gold exploration is expectable at Xiadian.