新疆阿尔泰柯鲁木特112号钠长石-锂辉石伟晶岩脉的岩浆-热液演化与Nb-Ta成矿过程:来自云母成分变化的启示  

Magmatic-hydrothermal evolution and Nb-Ta mineralization process of the Kelumute No.112 albite-spodumene pegmatite,Altai,Xinjiang:Insights from mica compositional variation

作　　者：罗耀清 冯浩轩 申萍[1,2,3] MENUGE Julian Francis 白应雄 曹冲 武阳[1,2] LUO YaoQing;FENG HaoXuan;SHEN Ping;MENUGE Julian Francis;BAI YingXiong;CAO Chong;WU Yang(Key Laboratory of Mineral Resources,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China;College of Earth and Planetary Sciences,University of Chinese Academy of Sciences,Beijing 100049,China;Innovation Academy of Earth Science,Chinese Academy of Sciences,Beijing 100029,China;Irish Centre for Research in Applied Geosciences(iCRAG),Dublin D04 N2E5,Ireland;School of Earth Sciences,University College Dublin,Dublin D04 N2E5,Ireland;College of Mining Engineering,North China University of Science and Technology,Tangshan 063210,China)

机构地区：[1]中国科学院地质与地球物理研究所,中国科学院矿产资源研究重点实验室,北京100029 [2]中国科学院大学地球与行星科学学院,北京100049 [3]中国科学院地球科学研究院,北京100029 [4]爱尔兰应用地球科学研究中心(iCRAG),都柏林D04 N2E5 [5]都柏林大学地球科学学院,都柏林D04 N2E5 [6]华北理工大学矿业工程学院,唐山063210

出　　处：《岩石学报》2023年第11期3369-3391,共23页Acta Petrologica Sinica

基　　金：国家自然科学基金重大研究计划重点支持项目(91962213);新疆维吾尔自治区区域协同创新专项项目(2020E01043);中国科学院国际合作局国际伙伴计划项目(132A11KYSB20190070)联合资助。

摘　　要：伟晶岩岩浆-热液演化中流体出溶时间和铌钽矿化过程还存在争议。针对上述科学问题,本文选择了中国新疆阿尔泰造山带柯鲁木特112号钠长石-锂辉石型伟晶岩脉作为研究对象,在野外观察和室内岩相学研究的基础上,以云母的结构和主量成分为切入点,为该伟晶岩脉的结晶演化和铌钽矿化过程提供了一些新约束。112号脉主要发育以下5个结构单元:钠化微斜长石-石英带(I)、白云母-石英-钠长石集合体(II)、钠化块体微斜长石带(III)、石英-钠长石-锂辉石带(IV)和糖晶状钠长石集合体(V)。它具有弱的分带:I和II多出现在脉体边缘或外侧,是贫矿的伟晶岩的“壳”;III是贫矿的富巨晶微斜长石的中间上部带;IV是富巨晶锂辉石的中间下部带;V是富铌铁族矿物(CGM)的晚期岩浆残余相。在不同的分带/集合体中共识别出3类白云母:Type A,原生成分均一白云母;Type B,原生被改造的成分变化白云母(BSE下具有亮暗分带);Type C,次生成分均一白云母。研究结果表明,112号脉历经了3个演化阶段:(1)早期流体出溶和流体-围岩(二云母花岗岩)相互作用;围岩发生云英岩化,围岩中黑云母分解产生的部分Fe进入伟晶岩岩浆(围岩混染)。(2)熔体内部分离结晶与钠长石化;外侧I带中部分Type A白云母和所有Type B白云母的亮部具有全脉最高的FeO^(T)含量(5.20%~5.73%),反映了一阶段的云英岩化过程中围岩Fe的贡献;而从I带至V集合体,Type A白云母和Type B白云母的亮部的FeO^(T)和MgO含量整体递减,指示分异演化程度增强。(3)二次流体出溶;晶体-流体相互作用导致Type B白云母中的Fe、Mg和F释放进入流体,形成了亮暗成分分带;同时,致使FeO^(T)、MgO和F含量较低的Type C白云母以交代的形式生长在原生矿物内部。最后,本文认为:一阶段中围岩混染Fe的加入为CGM的沉淀提供了Fe源;二阶段中磷灰石的分离结晶对熔体中F的消耗促�The timing of fluid exsolution and the processes that control the niobium-tantalum mineralization during the magmatic-hydrothermal evolution of a pegmatite are still not well understood.This paper focuses on the Kelumute No.112 albite-spodumene pegmatite,Altai orogen,Xinjiang,NW China,to address the above scientific issues.Based on field observation and petrographic study,we present new constraints on the No.112 pegmatite evolution and related Nb-Ta mineralization process from a perspective of mica texture and major element composition.Five textual units are developed in the No.112 pegmatite:albitized microcline-quartz zone(I),muscovite-quartz-albite assemblage(II),albitized blocky microcline zone(III),quartz-albite-spodumene zone(IV),and saccharoidal albite assemblage(V).It is weakly zoned:I and II mostly occur at the border or wall of the pegmatite,they can be viewed as the poorly mineralized "shell";III represents poorly mineralized upper intermediate zone that contains abundant mega-crystal microcline;IV is lower intermediate zone that contains abundant mega-crystal spodumene;V represents the residual of the pegmatitic melt that contains abundant columbite-group minerals(CGM).Three types of mica were identified:Type A,primary compositionally homogeneous muscovite;Type B,primary but altered by fluid,compositionally heterogeneous muscovite(showing bright and dark zoning in BSE images);and Type C,secondary compositionally homogeneous muscovite.A three-stage model for the magma evolution of the pegmatite is suggested as follows:(1) Stage I,early fluid exsolution from the pegmatitic magma and fluid-country rock(two-mica granite) interaction took place,which resulted in the greisenization of the country rock,and some iron was also released to the pegmatitic magma through the breakdown of biotite from the country rock(contamination) at the same time.(2) Stage II,represented by an internal fractional crystallization process of the melt that was followed by albitization.During this stage,part of Type A muscovite and t

关 键 词：岩浆-热液演化 铌钽矿化 钠长石-锂辉石伟晶岩 柯鲁木特 阿尔泰 

分 类 号：P578.959[天文地球—矿物学] P588.131[天文地球—地质学] P618.7