滇东南南秧田超大型钨矿床流体包裹体及H、O同位素研究

滇东南南秧田钨矿床位于老君山钨锡多金属成矿区内,大地构造位置位于扬子板块、华夏板块与三江褶皱系的结合部位。钨矿体主要呈似层状赋存于南秧田组,根据不同的矿物组合及穿插关系,可划分出三种矿石类型,即矽卡岩型矿石、石英脉型矿石和碳酸盐型矿石。对南秧田不同矿化类型白钨矿中流体包裹体的岩相学观察后发现该矿床主要发育4类流体包裹体:富液相两相包裹体(Ⅰ类)、富气相两相包裹体(Ⅱ类)、含子矿物三相包裹体(Ⅲ类)和纯气相包裹体(Ⅳ类)。矽卡岩型矿石白钨矿中流体包裹体的均一温度变化于176~311℃,盐度变化于0.2%~10.9%NaCleqv。石英脉型矿石白钨矿中流体包裹体的均一温度变化于200~395℃,盐度变化于0.4%~11.3%NaCleqv。碳酸盐型矿石白钨矿中流体包裹体的均一温度和盐度分别变化于201~395℃和2.6%~11.3%NaCleqv。显微测温结果表明成矿流体属中高温度、中低盐度流体。激光拉曼探针分析表明,白钨矿中流体包裹体组分主要为H2O,含少量的CH4。矽卡岩阶段成矿流体δD值范围为?80.2‰~?78.3‰,δ18O水值为6.8‰,石英脉阶段成矿流体的δD和δ18O水值分别为?93.7‰~?79‰和6.5‰~7.1‰,表明成矿流体主要来自于岩浆水,并可能经历了强烈的去气作用,或者存在不同程度地层有机质、大气降水和孔隙水的混入。流体包裹体均一温度和盐度呈正相关关系及H、O同位素特征综合分析,本研究认为岩浆水与大气降水混合是引起白钨矿沉淀的主要因素。

Fluid Inclusion and Hydrogen-Oxygen Isotope Study of the Nanyangtian Super Large Tungsten Deposit,Southeastern Yunnan Province

The Nanyangtian tungsten deposit is located in the Laojunshan tin-tungsten polymetallic metallogenic area in Southeastern Yunnan province,and geotectonically the contiguous area of the Cathaysia,Yangtze,and Sanjiang blocks.The orebodies occur mainly as layers or veins that hosted in the Nanyangtian Formation.Three ore types have been recognized on the basis of mineral assemblage and intersection relationships:skarn-scheelite type,quartz-vein scheelite type,and carbonate-scheelite type.Detailed petrographic study of fluid inclusion in different types of scheelite samples revealed that there are four types of fluid inclusions:liquid-rich two phase inclusions(typeⅠ),gas-rich two phase inclusions(typeⅡ),daughter mineral-bearing three phase inclusions(typeⅢ),and pure vapor phase inclusions(typeⅣ).Homogenization temperatures of fluid inclusions in scheelite from the skarn type ore vary from 176℃to 311℃,with salinities from 0.2%NaCleqv to 10.9%NaCleqv.The fluid inclusions in scheelite from the quartz-vein type ore have homogenization temperatures of 200℃to 395℃and salinities of 0.4%NaCleqv to 11.3%NaCleqv.The fluid inclusions in scheelite from the carbonate type ore have homogenization temperatures of 201℃to 395℃and salinities of 2.6%NaCleqv to 11.3%NaCleqv.Fluid inclusion observations and microthermometric results show that the ore-forming fluids are medium-high temperature and medium-low salinity.Laser Raman microprobe analysis of the fluid inclusion show that H2O is the dominant component,with a small amount of CH4.The oxygen and hydrogen isotopic compositions of the fluids in the skarn-scheelite and quartz-vein ore types are in ranges of 6.8‰and?80.2‰to?78.3‰,and 6.5‰to 7.1‰and?93.7‰to?79.0‰,respectively.The isotopic characteristics indicate that the ore-forming fluids were mainly derived from magmatic water,and mixed with meteoric water.Meanwhile,the positive correlation between the homogenization temperatures and salinities for fluid inclusions also show a mixing of two different fluids.Combined isotopic and microthermometric results,we believe that scheelite precipitation is caused by the mixing of magmatic and meteoric water.