新疆东天山小白石头钨（钼）矿床流体包裹体及稀土元素地球化学对成矿作用的指示

The indicating significance of fluid inclusions and REE geochemistry for mineralization of Xiaobaishitou W-(Mo) deposit, East Tianshan Mountains, Xinjiang

东天山小白石头中型钨(钼)矿床分布于三叠纪黑云母花岗岩与中元古界灰岩接触带的矽卡岩中。成矿过程经历了早期矽卡岩阶段、退化蚀变阶段、石英硫化物阶段和碳酸盐阶段,其中退化蚀变阶段是白钨矿的主要形成阶段,石英硫化物阶段是辉钼矿和白钨矿的形成阶段。白钨矿成矿温度为254~376℃,盐度w(NaCleq)为3.06%~6.74%;石英硫化物阶段成矿温度为138~371℃,盐度w(NaCleq)为1.40%~11.70%。结合前人研究成果表明,4个成矿阶段成矿温度从高温演化到低温,尽管各阶段流体盐度均为低盐度,但最晚阶段盐度最低。从早期矽卡岩阶段到石英硫化物阶段再到碳酸盐阶段,成矿流体的成分存在明显差异,呈现出规律性变化。稀土元素特征表明不同矿物组合的矽卡岩具有演化关系,含白钨矿矽卡岩为正铕异常,形成于较强氧化环境,温度相对较高;不含白钨矿的矽卡岩为负铕异常,形成于低氧化环境,温度较低。流体沸腾作用是石英硫化物阶段矿质沉淀的主要机制。

The Xiaobaishitou deposit in the East Tianshan orogenic belt is a medium skarn W-(Mo)deposit characterized by the development of orebodies along contacts between Triassic biotite granite and Mesoproterozoic carbonaceous rocks.At least four paragenetic stages of skarn formation and ore deposition have been recognized:prograde skarn stage,retrograde stage,quartz-sulfide stage and calcite stage.The scheelite was mostly precipitated during the retrograde stage and quartz-sulfide stage,whereas the molybdenite was widely precipitated during the quartz-sulfide stage.The fluid inclusions of scheelite are characterized by temperatures of 254~376℃and salinities w(NaCleq)of 3.06%~6.74%.The fluid inclusions of the quartz-sulfide stage are characterized by temperatures of 138~371℃and salinities w(NaCleq)of 1.40%~11.70%.These data and previous researches indicate that the mineralization temperature of the four metallogenic stages evolved from high temperature to low temperature.Although the fluid of each stage is of low salinity,the salinity of the last stage is the lowest.From the skarn stage,quartz-sulfide stage to the calcite stage,the compositions of the ore-forming fluid are also significantly different with a regular change.The characteristics of rare earth elements suggest that the scheelite-bearing skarn was formed in a strong oxidization and high temperature environment with positive Eu anomalies,the barren scheelite skarn was formed in a low oxidization and low temperature environment with negative Eu anomalies.In addition,the petrography and temperature measurement results of fluid inclusions reveal that the fluid of the quartz-sulfide stage underwent the boiling process,which provided the suitable physical and chemical environment for precipitation of tungsten and molybdenum.