矽卡岩中石榴子石在示踪热液流体演化和矿化分带中的研究现状及其展望

热液型矿床形成过程中流体的组成、运移、演化及其矿质沉淀机制是矿床学研究的重点内容和难点。矽卡岩矿床中具有震荡环带结构的石榴子石完整记录了热液流体的性质、组成及演化过程,这种震荡环带的出现暗示了不同成分系列的石榴子石对不同阶段热液流体成矿物化环境的特定选择性。石榴子石晶体元素化学分带现象是流体运移和矿物再沉淀过程周期性循环再现的结果,对指示早期矽卡岩阶段热液流体中主、微量元素化学分带机制具有重要意义。不同成分系列、不同期次石榴子石的Fe_2O_3和Al_2O_3含量差异显著,其对热液流体演化过程中氧化还原环境的变化具有较好的示踪作用;相对主量元素而言,微量元素在流体演化过程中具有更好的探针作用,钙铝榴石常富集Al、Ti、Zr、HREE元素,而钙铁榴石常富集As、W、Mo、Fe、LREE元素。借助EMPA和LA_ICP_MS技术对具震荡环带结构的石榴子石进行主、微量元素(包括稀土元素)的微区和原位分析是探讨成矿过程中流体组成和性质演化的重要手段,其有可能揭示矿物生长机制、成矿环境以及成矿流体组成与性质的演化,而这一地质信息对于全面理解矽卡岩型矿床的矿化分带及成矿作用非常重要。

The current status and prospects of the study of garnet in skarn for hydrothermal fluid evolution tracing and mineralization zoning

The composition, migration and evolution of hydrothermal fluids as well as the precipitation mechanism are the essence and main difficulties in the study of hydrothermal deposit. Skarn deposit has long been one of the most important hydrothermal deposits in that hydrothermal fluid in this kind of deposit has complex evolution process with multiple stages. Diopside and garnet are the most typical minerals in skarn deposit. Garnets with oscillatory zoning have recorded the property, composition and evolutionary process of the fluids completely in skarn deposits, which suggests that the compositions of garnets of different series have a specific selectivity for physical and chemical environments of hydrothermal fluids at different stages. Chemical elements zoning of gar_ net result from periodic emersion between fluid mobility and mineral reprecipitation, which could indicate the mechanism of major and trace elements zoning in prograde skarn fluid. The values of Fe₂O₃ and Al₂O₃ in differ-ent garnets vary remarkably, which plays an important role in tracing redox environment at the process of fluid evolution. In addition, trace elements constitute a more sensitive probe for detecting fluid evolution to some extent, which could reflect an important process in petrogensis and metallogeny. The grossular is often enriched in Al, Ti, Zr and HREE; however, the andradite is enriched in As, W, Mo, Fe and LREE. In-situ electron microprobe analysis and LA-ICP-MS technology have played an important role in major and trace elements(including REE)analysis of garnets having oscillatory zoning in the process of ore-forming fluid evolution, which can reveal garnets growth mechanism, ore-forming environment and fluid property.