喜马拉雅东段库曲岩体锂、铍和铌钽稀有金属矿物研究及指示意义  

Li-Be-Nb-Ta mineralogy of the Kuqu leucogranite and pegmatite in the Eastern Himalaya,Tibet,and its implication

作　　者：周起凤 秦克章[2,3] 何畅通 吴华英 刘宇超 牛向龙 莫凌超 刘小驰 赵俊兴[2] ZHOU QiFeng;QIN KeZhang;HE ChangTong;WU HuaYing;LIU YuChao;NIU XiangLong;MO LingChao;LIU XiaoChi;ZHAO JunXing(Institute of Mineral Resources Research,China Metallurgical Geology Bureau,Beijing 101300,China;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;State Key Laboratory of Lithospheric Evolution,Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing 100029,China)

机构地区：[1]中国冶金地质总局矿产资源研究院,北京101300 [2]中国科学院矿产资源研究重点实验室,中国科学院地质与地球物理研究所,北京100029 [3]中国科学院大学地球与行星科学学院,北京100049 [4]岩石圈演化国家重点实验室,中国科学院地质与地球物理研究所,北京100029

出　　处：《岩石学报》2021年第11期3305-3324,共20页Acta Petrologica Sinica

基　　金：第二次青藏高原综合科学考察研究项目(2019QZKK0802、2019QZKK0806);国家自然科学基金项目(41602095);中国科学院重点部署项目(ZDRW-ZS-2020-4-1)联合资助.

摘　　要：稀有金属矿物记录了花岗伟晶岩成岩成矿的重要信息。喜马拉雅是全球著名的淡色花岗岩带,库曲岩体位于喜马拉雅东段的特提斯喜马拉雅岩系中。本文调查了库曲岩体的二云母花岗岩、白云母花岗岩、电气石花岗岩和花岗伟晶岩,其中,花岗伟晶岩涉及花岗岩的伟晶岩相和独立伟晶岩脉。库曲岩体产出的稀有金属矿物包括锂辉石、锂绿泥石、绿柱石、铌铁矿-钽铁矿、钇铀钽烧绿石和细晶石,它们主要赋存于似文象伟晶岩、石英-钠长石-白云母伟晶岩、块体长石-钠质细晶岩、块体长石-电气石钠质细晶岩、锂辉石-块体长石-细晶岩、白云母花岗岩的伟晶岩相以及电气石花岗岩内。显微镜观察、电子探针和LA-ICP-MS测试结果显示锂辉石具有四种产状,包括粗粒锂辉石自形-半自形晶、细粒锂辉石-石英镶嵌晶、中细粒锂辉石-钾长石-钠长石-云母镶嵌晶以及发育锂绿泥石的粗粒锂辉石,揭示了其形成时复杂的熔流体动荡结晶环境。绿柱石背散射电子图像(BSE)下呈均一结构和不均一结构(蚀变边、不规则分带和补丁分带),元素替代机制包括通道-八面体替代、通道-四面体替代以及通道中碱金属阳离子间的置换。铌铁矿族矿物包括原生、蚀变边和不规则分带结构,部分被钇铀钽烧绿石和细晶石交代。与原生铌铁矿相比,蚀变边和不规则分带铌铁矿族矿物总体上富钽贫锰,显示了结晶分异、过冷却引起的过饱和以及流体作用。根据稀有金属矿物揭示的成因信息,独立伟晶岩脉(似文象伟晶岩)、白云母花岗岩的伟晶岩相和电气石花岗岩在岩浆分异程度、经历的演化过程、以及流体活动方面存在差异,很可能是不同期次岩浆活动的产物。库曲岩体绿柱石的Rb和Zn含量、以及铌铁矿族矿物的Sc_(2)O_(3)、SiO_(2)和PbO含量,与已有指示标志存在相关性,作为潜在指示标志仍需开展The rare-element minerals record important information of rock-forming process and metallogenesis.Himalaya is a famous leucogranite belt.The Kuqu intrusion is located in the Tethys Himalayan sedimentary sequence in the Eastern Himalaya.This study investigated two-mica granite,muscovite granite,tourmaline granite and granitic pegmatites in the Kuqu intrusion.The granitic pegmatites refer to either the pegmatite rocks that are included in and related to granite or the pegmatite zones that make up a single pegmatite dyke.The rare-element minerals identified in the Kuqu intrusion include spodumene,cookeite,beryl,columbite-tantalite,Y-hatchettolite and microlite.They are distributed in quartz-feldspar-muscovite pegmatite,quartz-albite-muscovite pegmatite,blocky feldspar-aplite,block feldspar-tourmaline aplite,spodumene-blocky feldspar-aplite,pegmatite rock in muscovite granite,and tourmaline granite.The EMPA and LA-ICP-MS analytical results indicate that spodumenes show four occurrences which consists of coarse-grained subhedral to euhedral spodumene,fine-grained symplectitic reaction border composed of spodumene and quartz,middle to fine-grained mosaic structure of spodumene,K-feldspar,albite and muscovite,and coarse-grained spodumene filled by cookeite veins.These occurrences of spodumene reveal a complex and fluid-rich unstable crystallization environment.There are homogeneous and heterogeneous beryl crystals in the intrusion.The internal zonation patterns for heterogeneous beryls are alteration border,patches and complex irregular zoning in BSE images.The substitution mechanisms of beryl in the Kuqu intrusion are channel-octahedral,channel-tetrahedral and alkali cations in channel.The columbite-group mineral crystals are composed of primary part and alteration border or display irregular zoning pattern,some of which are altered by Y-hatchettolite and microlite.Compared with primary parts,the alteration border and irregular zoned crystals have higher Ta/(Nb+Ta)values and lower Mn/(Fe+Mn)values,indicating fractional

关 键 词：库曲淡色花岗岩和花岗伟晶岩 锂辉石-绿柱石-铌铁矿族矿物 东喜马拉雅 找锂意义 

分 类 号：P588.131[天文地球—岩石学] P618.7[天文地球—地质学]