Abstract: Erdaogou Gold Deposit is one of China’s source areas of gold production,but its physicochemical ore-forming conditions have been insufficiently studied.To further explore the deposit genesis,based on previous research,this study constructed thermodynamic models to analyze the physicochemical conditions during ore formation.Thermodynamic models of temperature and pressure for the main ore-forming stages of Erdaogou Gold Deposit and 3 nearby deposits (Benqu,Sandaocha,and Bajiazi) were established to estimate the physicochemical parameters during the main ore-forming stage of the 4 deposits,which were as follows:pH 4.314-7.186,lg fO2-35.617 to-40.825 for Benqu Gold Deposit; pH 3.04-7.228,lg fO2-40.576 to-49.646 for Erdaogou Gold Deposit;pH 4.041-7.137,lg fO2-36.829 to-42.315 for Bajiazi Gold Deposit; pH 4.405-7.181,lg fO2-43.469 to-39.277 for Sandaocha Gold Deposit.The results indicate that during the main ore-forming stage,the fluid’s pH gradually increased from low to high,evolving from acidic to neutral.The lg fO2 showed a transition from high to low oxygen fugacity.Combined with fluid inclusion and H-O isotope studies,the findings suggest a close relationship between ore-forming fluids and meteoric water.