Abstract: Qagan Obo Fe-Zn Deposit is a typical skarn-type Fe-Zn deposit,located in the eastern segment of the Erenhot-Dongwuzhumuqin metallogenic belt.The mineralization can be divided into 4 stages:dry skarn stage(Ⅰ),wet skarn-magnetite stage(Ⅱ),quartz-sulfide stage(Ⅲ)and carbonate stage(Ⅳ).The study on petrography and micro-thermometry of fluid inclusions indicates that the fluids were NaCl-H2O system with high temperature (348 ℃-523 ℃) and high and low salinity (2.89 %-60.44 %) at the same time in the early stage of mineralization.The H and O isotopes imply that they originated from magma hydrothermal fluids.During the ascent,with decreasing the temperature and pressure,the ore-forming fluids boiled in multiple periods.While Fe precipitates and mineralizes under conditions of high oxygen fugacity(stage Ⅱ),Zn enriches and mineralizes in large amounts under conditions of low oxygen fugacity(stage Ⅲ).In the late stage of mineralization,meteoric water and residual fluids are mixed,and ore-forming fluids transformed to be NaCl-H2O system hydrothermal fluids with low temperature(112 ℃-234 ℃) and low salinity(3.21 %-7.99 %).