伟晶岩型稀有金属矿床成矿作用研究进展

Research advances on rare metal pegmatite deposits

伟晶岩型矿床是世界上重要的稀有金属矿床类型之一,也是当前国际矿床学研究热点之一。近年来该类稀有金属矿床在分类、成矿流体及成矿物质来源、伟晶岩成岩方式和稀有金属富集机制等方面的研究取得了一些重要进展。伟晶岩通常与母质岩浆具有密切的时空关系,但不少也与母质岩浆无成因关系。伟晶岩稀有金属矿床成矿熔体/流体具有低黏度、富水、高分散性、富碱等性质,可导致P、F和B等元素在伟晶岩中的极端富集,使其与稀有金属组成各类络合物或化合物而迁移与富集。富含Li-Cs-Ta(LCT)型伟晶岩与S型花岗岩关系紧密,成矿物质主要起源于黑色页岩等海相沉积物质,而富含Nb-Y-F(NYF)型伟晶岩常与A型花岗岩联系紧密,属同源岩浆演化和矿化。花岗质岩浆分异结晶和地壳或地幔岩石的部分熔融是伟晶岩两种主要的形成方式。流体不混溶作用、富助熔组分花岗岩浆高度结晶分异和热液交代作用3种富集机制可用于解释伟晶岩型稀有金属矿床的形成。

The pegmatite deposit is one of the most important types of rare metal deposits in the world,and it is also one of the most popular interests in the international deposit research.Significant advances have been made in the latest decades,including the classification,source of ore-forming fluids and materials,pegmatite diagenesis mode and enrichment mechanism of rare metals.Ore-related pegmatites have closely temporal-spatial relationship with parental magmatism in general.However,some pegmatites do not show this relative genetic relationship.Studies indicate that the ore-forming melts/fluids of rare-metal pegmatite deposits have properties such as low viscosity,rich water,high dispersibility,and rich alkali,leading to extreme enrichment of elements such as P,F,and B in pegmatite,which migrates and enriches together with rare metals in various complexes or compounds.Li-Cs-Ta type(LCT)pegmatites are closely related to S-type granites.The ore-forming materials are mainly originated from marine sediments like black shale,whereas Nb-Y-F type(NYF)pegmatites are generally associated with A-type granites,which are all derived from the same magmatism.Granitic magma fractional crystallisation and partial melting of crustal or mantle-derived rocks are the two significant formation modes of pegmatites.Meanwhile,three enrichment mechanisms,including fluid immiscibility,highly crystalline differentiation of the flux-rich granite slurry and hydrothermal metasomatism,are widely used to interpret the formation of rare metal pegmatite deposits.