伟晶岩型锂矿中矿物原位微区元素和同位素示踪与定年研究进展

In situ trace element tracing and isotopic dating ofpegmatite type lithium deposits:an overview

锂是重要的战略性关键金属,伟晶岩型锂矿是锂资源的主要来源之一。伟晶岩的成因及锂等关键金属在花岗质岩浆-热液演化过程中是如何富集成矿的,是人们十分关注的重要科学问题。多种方法可对伟晶岩的成岩成矿年龄进行限定,除锆石外,其他副矿物和矿石矿物如磷灰石、铌铁矿族矿物、锡石等的原位微区U-Pb定年己得到广泛应用,但需根据定年矿物的共生关系、结晶学及矿物化学特征进行系统研究,合理解释所获年龄的地质意义;伟晶岩型锂矿的成岩成矿一般具有同时性,个别存在多期成矿。伟晶岩的地球化学类型主要有LCT型(富集Li-Cs-Ta)和NYF型(富集Nb-Y-F)及它们的混合类型;成因有"母体花岗岩浆的结晶分异"和"源岩直接部分熔融"两种主要模型;多种矿物学和地球化学方法可用于区分这两种成因。伟晶岩型锂矿床的成矿机制研究包括成矿元素在源区的初始富集,成矿元素在岩浆过程中的富集和沉淀,以及在岩浆-热液过程中的行为和富集作用。伟晶岩中贯通性矿物和矿石矿物的原位微区分析是研究锂等关键金属成矿过程的重要方法。

Lithium is an important strategic critical metal of which the pegmatite type lithium deposit is one of the main sources.The origin of pegmatite,and how lithium and other critical metals were enriched and mineralized during the process of granitic magmatic and hydrothermal evolution are important scientific issues that required close investigation.It is difficult to obtain reliable U-Pb isotope dating from zircon in pegmatite as it has high U content and is prone to metamorphism or recrystallization.In situ U-Pb dating of other accessory minerals and ore minerals such as apatite,columbite-group minerals,and cassiterite has been widely used for dating pegmatite and related mineralization.The pegmatitic emplacement and mineralization for pegmatite type lithium deposits are generally simultaneous,and some of them may have multi-stage mineralization.The geochemical types of pegmatites are mainly LCT(Li-Cs-Ta)type and NYF(Nb-Y-F)type,and also their mixed types.The petrogenesis includes two major models of magmatic crystallization differentiation and crustal anatexis;a variety of mineralogical and geochemical methods can be used to distinguish the two types of genesis.The metallogenic mechanism of pegmatite type lithium deposits includes the initial enrichment of ore-forming elements in the magma source area,the enrichment and precipitation of ore-forming elements in the magmatic process,and the behavior and enrichment of ore-forming elements in the magmatic-hydrothermal process.In situ microanalysis of common silicate minerals and ore minerals in pegmatite is an important method to study the mineralization process of lithium and other critical metals.