贵州都匀撒朗重晶石矿床流体包裹体及H-O-C同位素地球化学研究

Fluid Inclusion and H-O-C Isotope Geochemistry of the Salang Barite Deposit in Duyun,Guizhou Province,China

贵州都匀撒朗重晶石矿床位于江南造山带西南段都匀陆缘盆地区之都匀南北向构造变形区,矿体主要呈层状、似层状、脉状或囊状产于层间破碎带及构造交汇部位,受构造控制明显。本文在野外矿床地质调查的基础上,进行了流体包裹体岩相学、显微测温和群体包裹体成分及H-O-C同位素研究,结果显示:撒朗重晶石矿床的成矿流体为具有中低温(95~240℃)、峰值温度(140℃)为低温、低盐度(均值4.9%~9.1%NaCleqv)、中等密度(均值0.95~0.97 g/cm^(3))特征的Ca^(2+)-Na^(+)-Cl−-SO_(4)^(2−)类型水;重晶石流体包裹体水H同位素组成为−48‰~−38‰、O同位素组成为0.55‰~12.05‰,显示成矿流体水来源于大气降水或与围岩水岩反应后的演化大气降水;矿石中与重晶石共生的方解石C同位素组成为−1.9‰~−1.0‰、O同位素组成(SMOW标准)为20.40‰~21.01‰,指示碳来自于海相碳酸盐岩的溶解;矿床的形成晚于围岩,是在围岩地层形成之后,为后期构造及热液活动使其中的成矿物质活化迁移并在相应构造部位富集而形成。

The Salang barite deposit is located in the Duyun north-south tectonic deformation area of the Duyun continental margin basin in the SW section of the Jiangnan orogenic belt.The ore bodies occur in the interlayer fracture zone or at the junction of structures,showing layer,layer-like,vein or capsule shapes.Based on the field geological investigation,samples were collected for laboratory study.The petrography,microthermometry,and composition of the fluid inclusions,H-O-C isotope compositions of barite and calcite of the main metallogenic epoch of the deposit were studied.The results showed that the ore-forming fluid of the Salang barite deposit is of Ca^(2+)-Na^(+)-Cl−-SO_(4)^(2−)type which has the characteristics of low to medium temperature(95~240℃,with a peak temperature of 140℃),low salinity(averages=4.9%−9.1%NaCleqv),and medium density(averages=0.95−0.97 g/cm^(3)).The fluid inclusions in barite haveδD values of−48‰to−38‰andδ18O of 0.55‰to 12.33‰,which indicate that the ore-forming fluid was originated from meteoric water or evolved meteoric water because of water-rock reaction.Carbon and oxygen isotopic compositions of calcite separated from the ores vary from−1.9‰to−1.0‰and 20.40‰to 21.01‰(relative to SMOW)respectively,which reflect that the carbon was likely derived from the dissolution of marine carbonate rocks.It can be inferred that the Salang barite deposit is of epigenetic,formed during the late tectonic and hydrothermal activity while ore-forming materials were derived from the surrounding rocks.