Abstract:The Great Xing’an Range hosts many hydrothermal Pb- Zn polymetallic deposits related to magmatism. A study of the characteristics of mineral paragenetic associations and the mechanisms of migration and precipitation of ore- forming elements in these types of deposits is essential for a continued study of mineral deposits. Towards this objective, a typical magmatic hydrothermal deposit in the Great Xing’an Range, the Dongjun Pb- Zn- Ag deposit, was selected. Based on the detailed field geological investigations, microscopic study of mineral assemblages, combined with the study of microthermometry and laser Raman spectroscopy of fluid inclusions, and H- O isotope data, three main metal sulfides: galena, sphalerite, and pyrite, were selected for the calculation of thermodynamic equilibrium. According to the results of microthermometry of fluid inclusions, four temperature sections (473 K, 513 K, 553 K and 593 K) were selected for drawing the phase diagrams of Eh- pH, lg\[Pb 2+ \]- pH, and lg\[HS-\]- pH. Results show that as the evolution of hydrothermal mineralization period progresses, the main metal sulfides and their mineral assemblages are Py(Ⅰ)→Py(Ⅱ)+Gn(Ⅰ)+Sp(Ⅰ)→Gn(Ⅰ)+Sp(Ⅰ)→Gn(Ⅰ)+Sp(Ⅱ)→Gn(Ⅱ)+Sp(Ⅱ)→Gn(Ⅱ). Fluid boiling, fluid mixing and water- rock reaction are the main ore- forming mechanisms of the Dongjun Pb- Zn- Ag deposit, and the resulting changes in temperature, ion activity, Eh and pH play an important role in controlling the migration and precipitation of ore- forming materials and the formation of mineral assemblages. The formation of the main metal sulfide and their mineral assemblages during the hydrothermal mineralization of the Dongjun deposit is the result of multiple factors. This study adds to the current understanding of mechanisms of mineral migration and precipitation and mineral assemblages of typical hydrothermal Pb- Zn deposits in the Great Xing’an Range.