Genesis of the Katbasu gold deposit in the western Tianshan, NW China: Constraints from fluid inclusions and H-O, S, and Pb isotopes

The Katbasu gold deposit, located in the western Tianshan tectonic belt of Xinjiang, China. The genesis of this deposit remains controversial. This study conducted field geological investigations, fluid inclusion (FIs) studies, and stable isotopes (H-O, S, and Pb) analyses. The results indicate that the host rocks exhibit pyritization, the ore minerals are dominated by pyrite with minor chalcopyrite, sphalerite, galena, and native gold. The hydrothermal mineralization period can be divided into three stages: quartz-pyrite veins (early stage), native gold-polymetallic sulfide-quartz veins (middle stage), and quartz-carbonate veins (late stage). The homogenization temperatures of FIs for the early, middle, and late stages are 296.6–344.4℃, 206.4–297.7℃, and 146.7–199.2℃, respectively. The corresponding salinities range from 9.74–12.55 wt%, 5.26–11.61 wt%, and 3.71–5.56 wt%, with densities of 0.76–0.85 g/cm³, 0.77–0.90 g/cm³, and 0.90–0.95 g/cm³. The δ¹⁸O_fluid values range from 3.2 to 3.6 ‰, while the δD values range from −93.4 to −98.1 ‰. The H-O isotopic indicates that the ore-forming fluids were primarily derived from metamorphic water, with involvement of meteoric water. The δ³⁴S_H2S values range from 7.08 ‰ to 9.78 ‰, with ²⁰⁶Pb/²⁰⁴Pb ratios of 18.26 to 19.38, ²⁰⁷Pb/²⁰⁴Pb ratios of 15.60 to 15.65, and ²⁰⁸Pb/²⁰⁴Pb ratios of 38.17 to 38.49. The S and Pb isotopic suggest that the metamorphic stratigraphy played a significant role. Based on previous studies, FIs data, and isotopic compositions of H-O, S, and Pb, the Katbasu gold deposit is classified as an early skarn-type magmatic-hydrothermal deposit and was subsequently overprinted by an orogenic-type gold deposit.