祁漫塔格白干湖-戛勒赛钨锡矿带石英脉型矿石流体包裹体及氢氧同位素研究

Fluid inclusions and H-O isotopic compositions of quartz-vein ores in the Baiganhu-Jialesai W-Sn mineralization belts,Qimantage,NW China

对祁漫塔格白干湖-戛勒赛钨锡矿带石英脉型矿石石英中流体包裹体的岩相学特征研究表明,包裹体类型主要分为富液相两相包裹体、含CO2、CH4三相包裹体及单相H2O溶液包裹体3种类型,前2类为原生包裹体,与成矿关系密切;富液相两相包裹体均一温度峰值为220～260℃,盐度为0.88%～20.82%NaCleqv,流体的总密度为0.72～1.06g·cm-3,液相成分主要是水溶液,气相成分含有部分CO2及CH4;含CO2、CH4三相包裹体完全均一温度峰值为260～280℃,盐度为6.63%～15.21%NaCleqv,流体的总密度为0.60～0.91g·cm-3,气相成分以CO2、CH4为主,次为H2S、N2及少量的H2;液相组分以H2O为主,次为CO2及少量的CH4、H2S。各矿区石英脉型矿石的δ18OH2O为4.02‰～6.32‰,δD为-75.5‰～-42.8‰,均显示出岩浆水的特征。总体而言,石英脉型矿体的初始流体主要来自酸性岩浆热液,为中高温(220～280℃)、中盐度(10%～14%NaCleqv)、低密度的NaCl-H2O-CO2体系。钨锡成矿与区内加里东期岩浆作用密切相关,石英脉型矿石形成时流体处于不均匀的状态,成矿流体不混溶作用以及温压条件、pH、Eh、fO2、fS2等的变化是石英脉型钨锡矿沉淀的主要原因。

There are three types of fluid inclusions in the quartz of quartz-vein ores,Baiganhu-Jialesai W-Sn mineralization belts,Qimantage： Liquid-rich two-phase inclusions,CO2 and CH4-rich three-phase inclusions and water inclusions,of which the first two types are primary inclusions and are closely related with W-Sn mineralization.The peak homogenized temperatures and salinity of liquid-rich two-phase inclusions in quartz,with liquid component of H2O and gas component of CO2 and CH4,range from 220℃ to 260℃ and from 0.88% to 20.82% NaCleqv respectively,the total density of fliuds range from 0.72 to 1.06g·cm-3.The peak homogenized temperatures and salinity of CO2 and CH4-rich three-phase inclusions in quartz range from 260℃ to 280℃ and from 6.63% to 15.212% NaCleqv respectively,the total density of fliud range from 0.60 to 0.91g·cm-3.The gas components of CO2 and CH4-rich three-phase inclusions are mainly CO2,CH4 and less H2S,N2,H2,while the liquid components are mainly H2O and less CO2,CH4,H2S.The value of δ18OH2O and δD of quartz-vein ores range from 4.02‰ to 6.32‰ and -75.5‰ to -42.8‰ respectively,both of which indicate that the fluid is significantly magmatic water.In all,the initial fluid of quartz-vein ores is from magmatic hydrothermal fluid,which belongs to NaCl-H2O-CO2 system with middle-high temperature （220~280℃）,middle salinity （10%~14% NaCleqv） and lower density.The W-Sn mineralization is closely related with the Caledonian magmatism,and the uneven fluids are captured when the quartz-vein ores formed.The significant factors of forming of quartz-vein ores are immiscibility of ore-forming fluids,and changes of temperature,pressure and value of pH,Eh,fO2 and fS2.