内蒙古查干敖包铁锌矿床成矿流体特征及成矿机制

查干敖包铁锌矿床地处二连—东乌旗成矿带东段,为典型的矽卡岩型铁锌矿床。该矿床经历了干矽卡岩阶段(Ⅰ)、湿矽卡岩-磁铁矿阶段(Ⅱ)、石英-硫化物阶段(Ⅲ)、碳酸盐阶段(Ⅳ)等4个成矿阶段。流体包裹体岩相学和显微测温学研究表明:成矿早期,流体为高温(348℃~523℃)、高低盐度(2.89%~60.44%)并存的NaCl-H 2O体系,氢、氧同位素组成指示其来自岩浆热液;在上升过程中,随着温度、压力的减小,成矿流体发生了多期次的沸腾作用,高氧逸度时(成矿Ⅱ阶段)Fe元素大量沉淀成矿,低氧逸度时(成矿Ⅲ阶段)Zn元素大量富集成矿;成矿晚期,大气降水混入残余流体中,成矿流体转变为低温(112℃~234℃)、低盐度(3.21%~7.99%)的NaCl-H 2O体系。

Ore-forming fluids characteristics and ore-forming mechanism of the Qagan Obo Fe-Zn Deposit,Inner Mongolia

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-H 2O 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(stageⅡ),Zn enriches and mineralizes in large amounts under conditions of low oxygen fugacity(stageⅢ).In the late stage of mineralization,meteoric water and residual fluids are mixed,and ore-forming fluids transformed to be NaCl-H 2O system hydrothermal fluids with low temperature(112℃-234℃)and low salinity(3.21%-7.99%).