新疆可可托海矿区小虎斯特91号脉中云母类矿物学特征与地质意义  

Mineralogical characteristics of micas in the Xiaohusite No.91 pegmatite dyke in the Koktokay area, Xinjiang and their geological significances

作　　者：田润 张辉[1] 吕正航[1] 唐勇[1] TIAN Run;ZHANG Hui;LYU Zheng-hang;TANG Yong(Key Laboratory of High-Temperature and High-Pressure Study of the Earth's Interior,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang 550081,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院地球化学研究所地球内部物质高温高压院重点实验室,贵州贵阳550081 [2]中国科学院大学,北京100049

出　　处：《矿物学报》2021年第6期593-609,共17页Acta Mineralogica Sinica

基　　金：国家自然科学基金项目(编号:91962222;41372104;41873030);中国科学院战略性先导科技专项(B类)(编号:XDB18020103)。

摘　　要：以小虎斯特91号伟晶岩脉中的不同结构带及蚀变围岩、交代岩、锂云母细脉中云母矿物为研究对象,通过电子探针(EMPA)和激光剥蚀等离子体质谱(LA-ICP-MS)对各结构带不同产状的云母进行主微量成分分析。研究表明,91号脉从围岩蚀变带、伟晶岩边缘带、外侧带、中间带到核部带,依次发育黑云母、白云母、富锂白云母和锂云母,伟晶岩中云母类矿物显示由白云母向锂云母演化趋势。Li在白云母和富锂云母(锂白云母和锂云母)中的置换机制不同,分别可能为2Si^(Ⅳ)+Li^(Ⅵ)←→3Al^(Tot)和Si+Li←→Al^(Tot)+Fe (Zn,Mn,Mg)(白云母)和3Li^(Ⅵ)←→Al^(Ⅵ)+2□^(Ⅵ) (富锂云母,□代表空位)。小虎斯特91号伟晶岩脉经历了岩浆-热液的演化过程,随着演化进行,云母中K/Rb、Mg/Li比值显著降低,Li、Rb、Cs、F含量显著增大,指示分离结晶作用是晚期熔体相Li、Rb、Cs、F富集的主要机制。但云母类矿物的主、微量元素特征显示小虎斯特91号脉岩浆-热液过渡阶段特征不明显,伟晶岩演化很快由正岩浆阶段转化为热液阶段。In this study,the major and trace elements of mica minerals in different textural zones,altered host rocks,metasomatic rocks,and lepidolite veinlets from the Xiaohusite No.91 pegmatite dyke were analyzed by using electron microprobe analysis(EMPA) and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS),respectively,in order to reveal the magmatic-hydrothermal evolution of the pegmatite system.The results show that Mg-rich biotite,muscovite,Li-rich muscovite,and lepidolite respectively occurred in subsequent zones from the alteration zone of host rock,to edge zone,outer zone,intermediate zone,and the core zone of the Xiaohusite No.91 pegmatite dyke.Chemical features of micas from the pegmatite dyke had shown the evolution trend of micas varying from muscovite to lepidolite.The substitution mechanism of Li in muscovites is obviously different from that in Li-rich micas(Li-muscovite and lepidolite),as the substitution of Li in muscovite could be in form of 2Si^(Ⅳ)+Li^(Ⅵ)←→3Al^(Tot) or Si+Li←→Al^(Tot)+Fe(Zn,Mn,Mg) while the substitution of Li in Li-rich micas could be in form of 3Li^(Ⅵ)←→Al^(Ⅵ)+2□^(Ⅵ)(where □ represents a vacancy).The No.91 pegmatite dyke had experienced the magmatic-hydrothermal evolution process.As the evolution process proceeds,the K/Rb and Mg/Li ratios of micas are obviously decreased but the contents of Li,Rb,Cs,and F in micas are obviously increased,indicating that fractional crystallization is the main mechanism for the enrichment of Li,Rb,Cs,and F in late-stage melt.However,characteristics of major and trace elements of micas show that the No.91 pegmatite dyke has no obvious characteristics of the magmatic-hydrothermal transition stage,as the evolution of pegmatite system could be quickly transformed from the magmatic stage to the hydrothermal stage.

关 键 词：化学组成 微量元素组成 岩浆-热液演化 云母矿物 伟晶岩 

分 类 号：P578.959[天文地球—矿物学] P579[天文地球—地质学]