湘东南太和仙铅锌矿床流体包裹体研究

摘要

太和仙铅锌矿床位于东南地洼区之南岭成矿带中段,为了了解其流体性质及演化,探讨成矿机制,通过现场调查,对矿区不同成矿阶段的矿石进行了流体包裹体岩相学、显微测温和激光拉曼探针分析.该矿区成矿作用分为3个阶段,依次为石英-黄铁矿-毒砂阶段(早阶段)、石英-铅锌多金属硫化物阶段(中阶段)、石英-方解石-黄铁矿阶段(晚阶段).包裹体研究表明:矿床中主要发育富液相水溶液包裹体(Ⅰa型)、富气相水溶液包裹体(Ⅰb型)、CO2包裹体(Ⅱ型)、含CO2的三相水溶液包裹体(Ⅲ型)4类.早阶段中均一温度为235 ～ 349℃,盐度为2.03％～7.44％(NaCleq,质量分数,下同);中阶段包裹体均一温度为159 ～272℃,盐度为1.39％～10.86％;晚阶段包裹体均—温度为128 ～205℃,盐度为1.39％ ～7.58％.激光拉曼探针测试表明,3个阶段中包裹体的组分主要为H2O,其次有少量CO2和还原性气体CH4、N2.早阶段成矿流体在演化过程中发生了不混溶作用,表现为CO2等气相成分的逸失是导致金属元素沉淀富集的主要因素.中阶段成矿流体在演化过程中发生不同流体间的混合作用,表现在以大气降水及层间水的混入是导致大量金属元素沉淀成矿的主要因素.晚阶段流体以大气降水为主,推测可能流体自然冷却致使成矿元素沉淀富集.%The Taihexian Pb-Zn deposit is located in southeastern Hunan Province.In order to understand its fluid properties and evolution and discuss its metallogenic mechanism,the authors conducted field investigation and analyzed the ores of different metallogenic phases by such means as fluid inclusion petrography,microthermometry and laser Raman microprobe.The results reveal the existence of three ore-forming stages in the Taihexian Pb-Zn deposit,characterized by vein cutting relation and mineral assemblages of quartz-pyrite-arsenopyrite (the early stage),quartz-Pb-Zn polymetallic sulfides (the middle stage) and quartz-calcite-pyrite.Four main types of fluid inclusions were distinguished in the hydrothermal quartz,i.e.,liquid-rich inclusions (type Ia),vapor-rich inclusions (type Ⅰb),carbon-aqueous two-phase inclusions (type Ⅱ),and carbon-aqueous three-phase inclusions (type Ⅲ).Microthermometic data show that the homogenization temperatures of the fluid inclusions from the early stage to the late stage are gradually decreased,from 235 ～ 349℃,through 159 ～ 272℃ to 128 ～ 205℃,with the corresponding salinities being 2.03％ ～7.44％,1.39％ ～ 10.86％,and 1.39％ ～7.58％.Raman microspectroscopic studies of the fluid inclusions show that the main component of aqueous inclusions in quartz-pyrite-arsenopyrite,quartz-Pb-Zn polymetallic sulfides and quartz-calcite-pyrite is H2O,followed by CO2,with a little reducing gas CH4 and N2.The metals precipitation resulted from fluid immiscibility caused by CO2 escaping at the early stage,fluid mixing caused by meteoric water and interlayer water at the middle stage and natural cooling of fluid system at the late stage.