The Woxi Au- Sb- W deposit, located in the Jiangnan orogenic belt, represents a typical case where W, Sb, and Au mineralization occur within a large- scale single deposit. The native gold produced in the Woxi deposit is characterized by extremely high gold fineness (>998). This paper, focused on the gold mineralization, uses ICP- MS analysis and microthermometric analysis of fluid inclusions to determine geochemical features in mineralogy and characteristics of ore- forming fluids, and investigates the indication of gold fineness and Au/Ag ratios for the gold mineralization. The ICP- MS analysis shows Au/Ag ratios are higher in scheelite (103~520) and pyrite (69~673) and lower in stibnite (6~65) and host rocks (0. 3~35), while Au/Ag ratios vary within a large range in quartz (6~199). Based on results of the microthermometric analysis (200~350℃), this paper uses thermodynamic modelling to simulate ore- forming fluids of the native gold associated with pyrite and sericite, demonstrating that the gold solubility is easier to be decreased by the sulfur concentration than the temperature, and the gold fineness has a positive correlation with the temperature and a negative correlation with the sulfur concentration. The native gold in the Woxi deposit is more likely to precipitate in the fluid with a higher temperature and a lower sulfur concentration, and is thus associated with pyrite and scheelite. This paper is expected to provide a new method to study other gold deposits.