西藏嘎波伟晶岩型锂矿中电气石组成、硼同位素特征及其地质意义  

Characteristics of tourmaline composition and boron isotope from the Gabo pegmatite-type lithium deposit in Xizang and their geological significance

作　　者：郭伟康 董随亮 张松浩 李光明 付建刚[1,2] 张林奎 张志[1,2] GUO WeiKang;DONG SuiLiang;ZHANG SongHao;LI GuangMing;FU JianGang;ZHANG LinKui;ZHANG Zhi(Chengdu Center,China Geological Survey(Geosciences Innovation Center of Southwest China),Chengdu 610218,China;Research Center for Tibetan Plateau Geology,China Geological Survey,Chengdu 610218,China;Chengdu University of Technology,Chengdu 610059,China)

机构地区：[1]中国地质调查局成都地质调查中心(西南地质科技创新中心),成都610218 [2]中国地质调查局青藏高原地质研究中心,成都610218 [3]成都理工大学,成都610059

出　　处：《岩石学报》2025年第3期804-819,共16页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2023YFC2908400、2021YFC2301903);中国地质调查局地质调查项目(DD20242104、DD20240069);第二次青藏高原综合科学考察研究项目(2019QZKK0806)联合资助.

摘　　要：西藏洛扎地区是喜马拉雅成矿带重要的稀有金属富集区,电气石在该地区的花岗岩中广泛富集。本文对洛扎地区的白云母花岗岩、锂辉石伟晶岩、锂电气石伟晶岩和电气石石英脉中的电气石进行系统的岩相学、矿物组成和硼同位素分析,来探讨伟晶岩体系的演化、源区性质、岩体-围岩的相关作用等问题。分析结果表明,所有电气石均属于碱性电气石,除电气石石英脉和锂电气石伟晶岩中的电气石为镁电气石外,其余都是黑电气石。随着岩浆分异演化程度的增加,电气石中Li、Be、Nb、Ta等元素逐渐富集,电气石中(R1+Al)(Na+R2)_(-1)、(Al+O)(R+OH)_(-1)、(Na+Mg)(Al+X_(vac))_(-1)和(X_(vac)Al)(NaR^(2+))_(-1)的替代关系则记录了伟晶岩岩浆逐渐富集Al,亏损Na、Ca、Mg的过程。白云母花岗岩、锂辉石伟晶岩、锂电气石伟晶岩和石英脉中电气石的δ^(11)B平均值分别为(-14.77±0.22)‰、(-11.89±0.34)‰、(-10.94±0.37)‰和(-7.71±0.24)‰,与大陆地壳平均δ^(11)B值(-10‰±3‰)一致,表明物源主要为高喜马拉雅变质岩系;同时,电气石的δ^(11)B值也是逐渐变重的,说明岩浆演化晚期流体出溶是导致硼同位素分馏的主要原因。因此,岩浆-热液过渡阶段对于锂等稀有金属的成矿具有重要意义。The Lhozhag area in Xizang is an important rare metal enrichment area in the Himalayan metallogenic belt,where tourmaline is widely enriched in the granites.In this paper,we systematically investigate the petrography,mineral compositions and B-isotopes of the tourmalines from muscovite granite,spodumene pegmatite,elbaite pegmatite and tourmaline-quartz veins in this area to explore the evolution of the pegmatite system,the properties of the source,and the correlation between the intrusion and country rock.The analysis results indicate that all tourmalines belong to alkaline tourmaline,except for the tourmaline in the tourmaline-quartz veins and elbaite pegmatite,which are magnesio-tourmaline,while the others are schorl tourmaline.With the degree of magma differentiation and evolution increasing,elements such as Li,Be,Nb and Ta are gradually enriched in tourmaline.The substitution relationships of(R1+Al)(Na+R2)_(-1),(Al+O)(R+OH)_(-1),(Na+Mg)(Al+X_(vac))_(-1) and(X vac Al)(NaR^(2+))_(-1) in tourmalines record the process of gradual enrichment of Al and depletion of Na,Ca and Mg in pegmatite magma.The averageδ^(11) B values of tourmalines in the muscovite granite,spodumene pegmatite,elbaite pegmatite and quartz veins are within the values of(-14.77±0.22)‰,(-11.89±0.34)‰,(-10.94±0.37)‰,and(-7.71±0.24)‰,respectively,which are consistent with the averageδ^(11) B value of the continental crust(-10‰±3‰),indicating that the high-Himalayan metamorphic rocks are the main source for these rock units.At the same time,theδ^(11) B value of tourmaline is gradually getting heavier,indicating that the main reason for the boron isotope fractionation in the late stage of magmatic evolution is the exsolution of fluids.Therefore,the magma-hydrothermal transition stage is of great significance to the mineralization of rare metals such as lithium.

关 键 词：稀有金属 电气石 矿物组成 岩浆-热液演化 嘎波 

分 类 号：P578.953[天文地球—矿物学] P588.131[天文地球—地质学] P597.2