喜马拉雅东段库曲锂辉石伟晶岩铌钽矿物特征及指示意义  

The feature of Nb-Ta-bearing minerals in the spodumene-bearing pegmatite dykes in Kuqu,eastern Himalaya,and its significance

作　　者：周起凤 秦克章[2,3] 何畅通 刘宇超 施睿哲 赵俊兴 陈彤[1] 莫凌超 ZHOU Qifeng;QIN Kezhang;HE Changtong;LIU Yuchao;SHI Ruizhe;ZHAO Junxing;CHEN Tong;MO Lingchao(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)

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

出　　处：《地质学报》2024年第5期1473-1488,共16页Acta Geologica Sinica

基　　金：第二次青藏高原综合科学考察研究项目(编号2019QZKK0802,2019QZKK0806);国家重点研发计划青年科学家项目(编号2023YFC2908400);国家自然科学基金项目(编号42272101)联合资助的成果。

摘　　要：铌钽矿物是花岗伟晶岩中重要的稀有金属矿物,记录了伟晶岩岩浆分异演化过程。喜马拉雅中段和东段新近取得伟晶岩型锂矿重要找矿发现。本文针对东段库曲岩体中三处含锂辉石伟晶岩脉和白云母花岗岩产出的铌钽矿物(铌铁矿族矿物和细晶石)进行内部结构和化学组成研究。含锂辉石伟晶岩脉中的铌铁矿族矿物(CGM)为铌锰矿-钽锰矿,产出均一、核-边、补丁、不规则分带、振荡环带和复合结构,分为三个形成世代(CGM-I、CGM-Ⅱ、CGM-Ⅲ),由CGM-I至CGM-Ⅱ,铌铁矿族矿物向富Ta、Fe和略贫Y方向演化,体系经历了含Nb、Mn和Y矿物的结晶分异作用,形成了富Ta和Fe的富挥发分熔体或流体,由CGM-Ⅱ至CGM-Ⅲ,铌铁矿族矿物Ta/(Nb+Ta)和Mn/(Fe+Mn)值变化不一,反映了复杂的矿物-流体相互作用。含锂辉石伟晶岩脉和白云母花岗岩中的细晶石产出均一、核-边和不规则分带结构,分别揭示了富Ta和Ca流体作用、边界层效应或富Nb流体交代、以及动荡结晶环境下流体扰动。细晶石的TiO2、UO2、F含量以及Ta/(Nb+Ta)值可作为岩浆分异演化程度的潜在指示标志,但需考虑晚期热液流体对细晶石化学组成的影响。铌钽矿物研究揭示了库曲不同含锂辉石伟晶岩脉的岩浆特征与分异演化过程。1号含锂辉石伟晶岩脉岩浆相对富Fe,依次经历了含Fe矿物、含Nb和含Mn矿物、以及含Ta和含Mn矿物的结晶作用,局部伴随边界层效应或含Fe矿物结晶,晚期存在富Ta和Ca流体活动,并受边界层效应影响。2号含锂辉石伟晶岩脉岩浆就位后首先经历了含Nb和含Fe矿物结晶,之后经历了含Mn和含Y矿物结晶以及含Nb和含Ta矿物结晶耦合作用,晚期发育富Ta和Ca流体活动,随后发生富Nb流体作用。3号含锂辉石伟晶岩脉岩浆相对富挥发分,就位后经历了含Nb、Mn和Y矿物的结晶作用,以及复杂的矿物-液相介质相互作用,体系晚期存在富Ta和Ca流�The Nb-Ta-bearing minerals are important rare-element minerals in granitic pegmatite and record the magma evolution process.Significant progress has been made in exploring lithium deposits in the middle and eastern regions of the Himalayas,China.This study focuses on examining the internal structures and chemical compositions of Nb-Ta-bearing minerals,namely columbite-group minerals(CGM)and microlite,from three spodumene-bearing pegmatite dykes and muscovite granite in the Kuqu pluton.The CGM samples obtained from the spodumene-bearing pegmatite dykes are columbite-(Mn)to tantalite-(Mn)with homogeneous,core-rim,patchy,irregular,oscillatory,and complex structures.These CGM samples can be categorized into three generations:CGM-Ⅰ,CGM-Ⅱ,and CGM-Ⅲ.The transition from CGM-Ⅰto CGM-Ⅱshows an enrichment of Ta and Fe in columbite-Mn,coupled with a depletion of Y.This evolution suggests that CGM-Ⅱcrystals were crystallized from a Ta-and Fe-rich fluxed melt or fluid,subsequent to the crystallization of Nb-,Mn-,and Y-bearing minerals.The evolution from CGM-Ⅱto CGM-Ⅲdoes not exhibit consistent trends in Ta/(Nb+Ta)and Mn/(Fe+Mn)values,reflecting complex interactions between minerals and fluids.Microlite samples from both spodumene-bearing pegmatite dykes and muscovite granite display a variety of internal structures,including homogeneous,core-rim,and irregular-zoned crystals.These variations suggest the influence of a Ta-Ca-rich fluid activity,a boundary effect or Nb-rich fluid activity,and fluid disturbances in an unstable crystallization environment.The chemical composition of microlite,specifically the TiO2,UO2,F contents,as well as Ta/(Nb+Ta)value,may serve as potential indicators for magma evolution.However,late fluid activity that could change the chemical composition of microlite should be considered.The study of Nb-Ta-bearing minerals provides valuable insights into the magma features and evolution processes of the three spodumene-bearing pegmatite dykes in the Kuqu intrusion.The first spodumene-bearing

关 键 词：铌铁矿族矿物 细晶石 岩浆分异演化 库曲含锂辉石伟晶岩脉 喜马拉雅 

分 类 号：P618.7[天文地球—矿床学]