Abstract: Xiaoyuzan gold deposit is an epithermal deposit in the Yeliemodun basin in Western Tianshan, Xinjiang Province. The ore bodies are hosted by volcanic rocks of the Late Paleozoic Dahalajunshan Formation and mainly consist of altered tuff and quartz veins. The hydrothermal alterations include intense silicification, beresitization, illitization and propylitization. The ore-forming process can be divided into three stages: quartzpyrite, quartzchalcedonypyrite and quartzcarbonatepyrite. Hydrothermal quartz from the three stages contains only aqueous fluid inclusions of liquid-rich, vapor-rich and pure liquid types, respectively. Fluid inclusions in the three stages were homogenized in temperatures of 130190, 115161 and 110138 ℃, respectively, with salinities of 0.188.0, 0.703.4 and 0.183.4 wt.% NaCl equivalent, respectively. Homogenization temperatures decreased from early to late stages implying the presence of fluid boiling. LA-ICP-MS U-Pb dating of zircons from tuff breccia yielded an Early Carboniferous age (weighted average) of 353.8±1.8 Ma, while the ore bodies were covered by the Aqialehe Formation constraining the age of deposit between 353.8±1.8 Ma and Visean age. The positive zircon εHf(t) values (4.18.4) and young two-stage Hf model ages (TDM2, 8221095 Ma) suggest a minor juvenile continental crustal involvement. Based on geological evidence including geological and fluid inclusion characteristics and mineralization age of the deposit, we propose that the Xiaoyuzan gold deposit is an LS type epithermal deposit formed in the Early Carboniferous.

Key words:  ore geology, fluid inclusion, zircon U-Pb age, epithermal gold deposit, Xiaoyuzan gold deposit, Western Tianshan