CO2/碳酸盐在稀有金属花岗伟晶岩成矿中的作用——以川西典型稀有金属矿床为例

The roles of CO2 in the formation of hydrothermal ore deposits were paid much attention in recent years. However, in granitic pegmatite-type rare metal deposits, the roles of CO2 were ignored in some degree, as the formation of pegmatite was ascribed to the roles of H2O, F and other fluxes traditionally. In these years, many kinds of carbonates were distinguished within crystal-rich inclusions in rare metal granitic pegmatite. And our research found the silicates dissolved in the carbonate aqueous solutions during heating the crystal-rich inclusions. Furthermore, the granitic magma that pegmatite melt exsolved from were enriched with C-H-O components, which is different from the CO2-poor features of granite type rare metals deposits. These features indicate the importance of CO2 in the separation of pegmatite melts from granitic magma and the mechanism for silicate to dissolve in pegmatite melts. This preliminary conclusions were consistent with the enrichments of CO2 and carbonate in the typical pegmattie deposits in western Sichuan. But no enough research to supported the conclusions. Therefore, in this project, we plan to take the typical lithium deposits in western Sichuan as a case study, in order to investigate the roles of CO2 in the minerallization of pegmatite, through the research in petromineralogy, melt and fluid incusions and high temperature and pressure experiments. Finally, we will try to conclude the typomorphic characteristics of pegmatite rare metal deposits based on the roles of CO2, and develop the metallogenic theory of rare metal resources.

CO2是热液成矿系统中备受重视的挥发分，但在稀有金属伟晶岩中，因传统上多强调H2O和F等助溶剂，CO2的作用未得到足够重视和深入研究。近年来，多种碳酸盐子矿物被发现于稀有金属花岗伟晶岩中的富晶体包裹体。在均一实验中，这类包裹体的(稀有金属)硅酸盐子矿物溶解于碳酸盐水溶液中；而且，许多稀有金属伟晶岩的母花岗岩浆也富含C-H-O组分，不同于许多花岗岩型稀有金属矿床贫CO2的特点。这些特征暗示，CO2可能是伟晶岩熔体自花岗岩浆分异和容纳大量硅酸盐和成矿物质的关键组分，这与川西伟晶岩矿床富CO2和碳酸盐的特征一致，但该认识缺乏足够的地质资料和实验数据支持。本项目拟在川西选择典型伟晶岩矿床，在野外工作的基础上，开展“岩石矿物学-熔体和流体包裹体原位观测-高温高压实验”研究，揭示CO2在稀有金属花岗伟晶岩成矿中的贡献，建立基于CO2作用的稀有金属伟晶岩成矿和找矿标型特征，发展稀有金属成矿理论。