喜马拉雅吉隆花岗伟晶岩中锂矿物的研究

The study of Li-minerals in granitic pegmatites from Gyirong,Himalaya

喜马拉雅造山带中部的吉隆岩体出露有大量淡色花岗岩和花岗质伟晶岩,已有文献报道该岩体英雄沟和扎龙沟淡色花岗岩和伟晶岩中有铁锂云母、锂云母、锂辉石等锂矿物产出。本次研究对吉隆岩体北部扎龙沟的伟晶岩进行了岩相学和矿物学研究,厘定了锂辉石伟晶岩和锂云母-锂电气石伟晶岩(含细晶岩)两种类型的富锂伟晶岩。研究结果显示,在锂辉石伟晶岩中主要的富锂矿物除了已知的锂辉石和锂云母,还发现了透锂长石,同时锂云母的边部出现的铯锂云母((Cs,K)Li_(2)Al[Si_(4)O_(10)]F_(2),Cs/(Cs+K)原子比>0.5)中Cs_(2)O含量达16.9%,该矿物首次在喜马拉雅发现,推测是由锂云母与后期富Cs流体作用后形成。在锂云母-锂电气石细晶岩中主要的富锂矿物包括锂云母和锂电气石,锂云母中的Li_(2)O含量为0.9%~6.7%;锂电气石中Li_(2)O含量最高可达2.4%,且FeO、MgO和CaO含量较低(分别<1.1%、<0.01%和<2.6%),接近锂电气石端元成分。结合吉隆扎龙沟含锂伟晶岩中大量产出铯沸石和细晶石,确认这些伟晶岩是典型的LCT(Li-Cs-Ta)型伟晶岩,矿物组成和成分显示它们具有极高的分异演化程度。

Massive leucogranites and granitic pegmatites were exposed in the Gyirong region,the middle of Himalayan orogen.Recent studies reported that the Li minerals,such as zinnwaldite,lepidolite and spodumene,were found in the leucogranites and granitic pegmatites from the Yingxionggou and Tsalung district in Gyriong pluton.In this study,two-type lithium-rich pegmatites from the Tsalung district were identified by the detailed petrographic and mineralogical studies,including spodumene pegmatite and lepidolite-elbaite pegmatite(aplite included).The major Li-rich minerals in spodumene pegmatites are spodumene,lepidolite and petalite which is new-found in this study.Especially,sokolovaite((Cs,K)Li_(2)Al[Si_(4)O_(10)]F_(2),Cs/(Cs+K)atomic ratio>0.5),Cs-analogue lepidolite,is firstly discovered in the Himalayan orogen,with the marginal occurrence adjacent to the lepidolite and Cs_(2)O content up to 16.9%.It is suggested that sokolovaite is the product of lepidolite reacting with late Cs-rich fluids by the mineral texture.In the lepidolite-elbaite aplite,the main Li-rich minerals include lepidolite and elbaite.Lepidolite contains 0.9%~6.7%Li_(2)O content.Tourmaline contains Li_(2)O content up to 2.4%,and low FeO,MgO,and CaO contents(<1.1%,<0.01%and 2.6%,respectively),close to the end-member of elbaite.Combined with abundant pollucite and microlite found in the Tsalung Li-mineralized pegmatites in Gyirong pluton,it is confirmed that the Tsalung pegmatite is typical LCT(Li-Cs-Ta)-type pegmatite,and the mineral constitution and their chemical compositions demonstrate that the pegmatite is extremely high-evolved.