Abstract: The Songjianghe gold deposit is located in the middle of the Jiapigou-Haigou gold metallogenic belt. The ore bodies are mainly hosted in the bottom of the middle lithologic member of the Neoarchean Seluohe Group. The hydrothermal mineralization can be divided into three stages: quartz-pyrite, polymetallic sulfide-quartz, and quartz-carbonate. Petrographic studies of fluid inclusions show that the polymetallic sulfide-quartz stage mainly develops gas-liquid two-phase inclusions, CO₂-bearing three-phase inclusions, and a small amount of pure CO₂ inclusions. Microthermometric results indicate that the ore-forming fluids are characterized by low salinity (1.38％~6.81％Na Cl_eqv), low density (0.41~0.86 g/cm³), and the ore-forming temperature is concentrated at 260 ℃~390 ℃, with ore-forming pressure of 70~106 MPa and ore-forming depth of 6.8~8.7 km. During the mineralization process, the fluid underwent immiscibility of the H₂O-CO₂-Na Cl system, which led to a decrease in the solubility of gold in the ore-forming fluid, resulting in precipitation and enrichment to form the gold deposit.