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    刚果（金）Manono–Kitotolo含锂−铯−钽伟晶岩地质与矿化特征研究

    Geological and mineralization characteristics of Manono–Kitotolo Li−Cs−Ta pegmatite in the Democratic Republic of Congo

      摘要
    • 摘要:
      研究背景 Manono–Kitotolo伟晶岩位于刚果（金）中元古代Kibaran稀有金属成矿带，属于锂–铯–钽伟晶岩（LCT），主要由含锂辉石伟晶岩（40%~70%）构成。通过野外地质调查发现：伟晶岩在横向上由外至内依次发育有：花岗细晶岩带（Ⅰ）—白云母长石石英带（Ⅱ）—石英钠长石带（Ⅲ）—锂辉石带（Ⅳ）—石英内核（Ⅴ）。
      研究方法 通过电子探针（EPMA）法测试，获得伟晶岩中云母、锂辉石、锡石和铌钽铁矿的主量成分，对伟晶岩的分异演化特征、锂矿化、铌钽矿化和锡矿化特征进行了讨论，并对Manono–Kitotolo伟晶岩型稀有金属矿床的成矿作用进行了分析。
      研究结果 白云母由外向内Rb、Li和F含量逐渐升高，K/Rb值逐渐降低，锂云母石英带（Ⅴ−1）中产出的锂云母FeO和Rb2O含量相对高于白云母，表明伟晶岩由外向内结晶的分异演化程度较高。
      结论 锂矿化主要分布在锂辉石伟晶岩（Ⅳ）中，锂辉石粒度呈巨晶—粗粒—中粒变化，主量成分较稳定，但近地表的氧化淋滤作用与黏土化、云英岩化等蚀变作用造成锂元素发生流失；锡矿化分布于Ⅲ—Ⅳ带中，锡石Nb和Ta含量相对较高，属于稀有金属伟晶岩成因，但粗粒锡石主要形成于云英岩化阶段；铌钽矿化分布于Ⅱ—Ⅳ带中，根据元素含量比值显示其为铌铁矿–钽铁矿–锰钽铁矿系列，随着分异作用的进行，铌钽矿物中的钽和锰的含量增加，铌、铁和钛的含量降低，形成富钽、富锰的铌钽铁矿。

       

      Abstract:
      This paper is the result of mineral exploration engineering.
      Objective The Manono–Kitotolo spodumene (40%−70%) pegmatite, one of the lithium−cesium−tantalum pegmatite (LCT) in the world, is located at the Mesoproterozoic Kibaran rare metals metallogenic belt in the Democratic Republic of Congo (DRC). The field works revealed that the symbiotic minerals of pegmatite gradually evolved from outside to inside: granite aplite zone(Ⅰ), muscovite−feldspar quartz zone (Ⅱ), quartz albitite zone (Ⅲ), spodumene zone (Ⅳ) and quartz kernel (Ⅴ).
      Methods In this study, the composition of major elements of mica, spodumene, cassiterite and columbite−tantalite are analyzed by Electron probe X−ray micro−analyzer (EPMA) to bring light on Li−Nb−Ta−Sn mineralization and pegmatitic crystallization differentiation.
      Results The results show that the content of Rb, Li, and F in muscovite gradually increased from outward (Ⅰ) to inward (Ⅴ), meanwhile the K/Rb gradually decreased. The content of Fe and Rb in lepidolite (V−1) is relatively higher than in muscovite(Ⅱ), which indicating highly fractionated pegmatite inside. Li mineralization mainly occurs in spodumene pegmatite (Ⅳ).
      Conclusions The grain size of spodumene varies from macro−crystal to coarse grain and medium grain and its principal components keep consistent except Li lost by oxidative leaching, argillation, greisenization and other alterations. Cassiterite with high Nb and Ta is generally formed by greisenization in zone Ⅲ–Ⅳ. Nb−Ta is mineralized in the form of the columbite−tantalite−manganotantalite isomorphism in the zone Ⅱ–Ⅳ, with the development of differentiation, the content of Ta and Mn in minerals increases, while the content of Nb, Fe and Ti decreases and formed Ta−rich and Mn−rich Columbite−tantalite.

       

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