南秦岭-大巴山地区下寒武统沉积层状钡矿床成因机制研究  

The genetic mechanism of lower cambrian sedimentary bedded barium ore deposits in the South Qinling—Dabashan Region

作　　者：彭不同 付山岭 韩涛 路志通 PENG Bu-tong;FU Shan-ling;HAN Tao;LU Zhi-tong(State Key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院地球化学研究所,矿床地球化学国家重点实验室,贵阳550081 [2]中国科学院大学,北京100049

出　　处：《矿物岩石地球化学通报》2023年第6期1318-1328,共11页Bulletin of Mineralogy, Petrology and Geochemistry

基　　金：贵州省高层次人才创新创业择优基金资助项目(2021-12);中国科学院“西部之光”人才培养计划项目;国家自然科学基金资助项目(41873056)。

摘　　要：为理清沉积层状重晶石、毒重石矿床成因机制及其差异成矿的控制因素,对南秦岭-大巴山地区下寒武统地层中不同成矿特征的钡矿床开展了矿物学和碳-硫-氧-锶同位素地球化学分析。结果显示,该区内沉积钡矿床有以重晶石为主或以毒重石为主的类型;矿石中碳酸盐矿物具有负的碳同位素组成(δ^(13)C_(Carb)为-26.1‰~-6.3‰),重晶石具有非常大的硫、氧同位素分馏(δ^(34)SBrt为25.1‰~62.2‰,δ^(18)O_(Brt)为12.2‰~18.9‰和δ^(18)O/δ^(34)S≈0.1),反映成矿时有强烈的甲烷驱动微生物硫酸盐还原作用;毒重石等碳酸盐矿物和重晶石的锶同位素组成较为一致,都具有宽的^(87)Sr/^(86)Sr变化范围(0.7070~0.7103)和低的^(87)Sr/^(86)Sr值(~0.7070),指示成矿流体可能是与基性-超基性岩有关的富金属热液,热液流体在运移过程中与碎屑地层相互作用使其^(87)Sr/^(86)Sr值变大。综合研究认为,南秦岭-大巴山地区下寒武统沉积层状钡矿床的形成是富钡等热液流体引入缺氧盆地的结果,甲烷驱动的硫酸盐还原作用导致局部水体中硫酸根和碳酸根浓度的变化是钡离子以重晶石和/或毒重石形成的主控因素。In order to understand the genetic mechanism of sedimentary bedded barite and witherite ore deposits and controlling factors of differential mineralization characteristics among them,several lower Cambrian sedimentary rock-hosted barium ore deposits with different metallogenic characteristics in the south Qinling-Dabashan region have been studied on their mineralogies,and carbon,sulfur,oxygen,and strontium isotopic geochemistries in this paper.The results show that the sedimentary barium deposits are mainly barite or witherite ore deposits in this region.The negative carbon isotopic compositions of carbonate minerals in ores(δ^(13)C_(Carb)=-24.7‰~-6.3‰)and the very large fractionations of sulfur and oxygen isotopes of barites(δ^(34)SBrt=25.1‰~62.2‰,δ^(18)O_(Brt)=12.2‰~18.9‰andδ^(18)O/δ^(34)S≈0.1)indicate that the intensive methane-driven microbial sulfate reduction had been involved in the barium mineralization of those deposits.The strontium isotopic compositions of carbonate minerals including witherite are consistent with those of barites,with a wide range of^(87)Sr/^(86)Sr values varying from 0.7070 to 0.7103 and an extremely low^(87)Sr/^(86)Sr value of about 0.7070,indicating that the ore-forming fluid could be the metal-rich hydrothermal fluid related to basic-ultrabasic rocks.The interaction between the hydrothermal fluid and the clastic rocks could further lead to the increase of^(87)Sr/^(86)Sr ratios in the fluid migration process.Consequently,this study proposes that the formation of lower Cambrian sedimentary bedded barium deposits in the south Qinling-Dabashan region was resulted from the introduction of barium-rich hydrothermal fluids into the anoxic basin.The temporal and spatial variations of sulfate and carbonate concentrations in local waters caused by the methanedriven sulfate reduction are main controlling factors for the precipitation of barium ions in forms of barite and/or witherite.

关 键 词：重晶石 毒重石 寒武纪 南秦岭-大巴山地区 微生物硫酸盐还原作用 

分 类 号：P536[天文地球—古生物学与地层学] P595[天文地球—地质学]