Fluid inclusion study of the Sawayardun Au deposit in southern Tian Shan, China: Implication for ore genesis and exploration

Abstract

The Sawayardun gold deposit in southern Tian Shan, China, which was structurally controlled by the faults and hosted by Carboniferous carbonaceous slates, has been reported as the first case of the Muruntau-type Au deposits in China. Ore-hosting structures are shear zones with deformation ranging from ductile compressive to brittle tensional shear. Hydrothermal process includes three stages: the early quartz veins, the middle Au-bearing stockworks of fine-grained poly-metallic sulfides, arsenides and antimonides, and the late veinlets of quartz-carbonate assemblage. Compositions of fluid inclusions are complex, including: type A, CO2-poor inclusions composed of liquid H2O - vaporous H2O; type B, CO 2-bearing inclusions of liquid H2O-liquid CO2-gaseous CO2; and type C, CO2-rich or pure CO2 inclusions of liquid CO2 gaseous CO 2. Homogenization temperatures of fluid inclusions trapped in the early, middle and late stages concentrated at 300°C - 370°C, 200°C - 280°C and 140°C - 185°C, respectively. The salinities of fluids are very low (<5 %) in early stage, and high (up to 17.5%) and divergent in middle stage. Fluid boiling occurred probably at 350°C and 250°C, which might cause the formation of quartz veins and poly-metallic sulfide stockworks. The barren quartz veins show less hydrothermal over-printing of middle and late stages compared to the Au-bearing veins. Decrepitation temperatures of fluid inclusions of pyrites show that most of pyrites deposited in middle stage and then hydrothermally overprinted in late stage. Hence the contents of sulfides and the middle-stage fluid inclusions can be used as criteria to evaluate the prospect of quartz veins. Accordingly, the potential sequence for deep exploration of three important mineralized zones is predicted to be: II > II > XI. The tectonic setting, ore geology and fluid inclusions of the Sawayardun Au deposit are similar to both the Muruntau Au deposit and the orogenic-type Au deposits in the world. It is a typical orogenic-type gold deposit formed in continental collision and its hydrothermal ore-forming process could be interpreted by using the CMF model.