白云鄂博超大型矿床锆石地球化学和成矿学综合研究

The Bayan Obo is the largest REE deposit in the world, characterized by multi-stage, multi-resource and multi-origin. Previous research focus on the process and origin geologically and geochemically. In this study, advanced in situ and microbeam analytic techniques would be applied to research zircons of carbonatitic and hydrothermal origin, geochemically and systematically. EMP and Laser Raman will be used to detect the internal structure and micro mineral inclusions in zircon. SHRIMP will be used to determine the U-Th-Pb ages of zircon. LA-ICPMS will be used to analyse trace element composition, temperature and O2 fugacity while crystallization would be possibly derived. Hf isotopes will be obtained by MC-LA-ICPMS, as for geochemical property of zircons would be investigated. Datas will be intergrated to comfirm the origin of zircons and geological events during the Bayan Obo deposit formed, ore forming process would be synthesized.

白云鄂博是全世界最大的稀土矿床，具有多期次、多来源、多成因的特点，其成矿机制一直备受关注。本项目拟运用多种原位、微束分析技术，对白云鄂博矿床矿体和火成碳酸岩中的岩浆和水热锆石进行系统的地球化学和矿物学研究。利用电子探针和激光拉曼研究锆石内部结构、主微量元素分带性及其中的细微矿物包体成分。利用SHRIMP测定不同结晶域的U-Th-Pb同位素年龄，LA-ICPMS测定锆石原位的微量元素含量，估算其结晶温度和氧逸度。使用MC-LA-ICPMS测定其Hf同位素，探讨其地球化学属性和结晶环境。综合运用这些数据讨论白云鄂博锆石的成因和成矿过程，即该矿床形成过程中经历的地质事件及地球化学机制。

本项目的工作得到白云鄂博矿体中极高Th/U比锆石平均Th-Pb年龄1286 ± 14 Ma（MSWD = 1.7），Hf-O同位素研究表明其为原始地幔源区特征。鉴定出极高Th/U比锆石中简单矿物包裹体包括白云石、方解石、萤石、独居石、氟碳铈矿、毒重石、氟碳铈钡矿、钠闪石。复杂相包裹体成分近似磁铁矿、钛铁矿、钙钛矿、烧绿石、铌铁矿、金红石、铌铁金红石，这些包裹体的结构还不清楚，甚至是否为结晶矿物尚有待研究。矿体锆石的研究表明中元古代白云鄂博发生典型原始地幔源区的火成碳酸岩侵位事件。.对白云鄂博矿体周边四条火成碳酸岩中的锆石定年显示较大范围的年龄分布，从古生代至古元古代，集中的年龄为古生代300-400 Ma。元古代锆石的Hf-O同位素特征基本显示捕获岩浆岩锆石特征，而古生代年龄锆石则显示壳源热液特征。.根据以上研究，我们认为白云鄂博中元古代火成碳酸岩为地幔源区，并且富集了大量的稀土、钍和铌元素，而古生代的碳酸盐热液活动为白云鄂博地区广泛深入的壳源事件，对白云鄂博进行了深入的改造，以至部分重置了同位素地球化学体系。