喜马拉雅夏如淡色花岗岩-伟晶岩的矿物学特征  

Mineralogical characteristics of the Xiaru leucogranite-pegmatite in the Himalayan oregen

作　　者：程飞越 谢磊[1,2] 陈小明[1] Cheng Feiyue;Xie Lei;Chen Xiaoming(State Key Laboratory for Mineral Deposits Research,School of Earth Sciences and Engineering,Nanjing University,Nanjing,210023,China;Frontiers Science Center for Critical Earth Material Cycling,Nanjing University,Nanjing,210023,China)

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学与工程学院,南京210023 [2]关键地球物质循环前沿科学中心,南京大学,南京210023

出　　处：《南京大学学报（自然科学版）》2022年第6期1087-1106,共20页Journal of Nanjing University（Natural Science）

基　　金：第二次青藏高原综合科学考察研究(2019QZKK0802);国家自然科学基金(91855209,42222202);关键地球物质循环前沿科学中心“科技人才团队”项目;中央高校基本科研业务费专项资金(2022300192)。

摘　　要：喜马拉雅夏如岩体出露大量淡色花岗岩-伟晶岩,主要包括(含电气石-石榴子石)白云母花岗岩和花岗质伟晶岩,局部岩石与铌钽钨等稀有金属成矿作用相关,包含富含铌钽钨的氧化物,如铌铁矿族矿物、骑田岭矿、黑钨矿、铌铁金红石等.为了查明夏如稀有金属矿化花岗岩-伟晶岩的岩石学、矿物学特征,更好地了解夏如岩体稀有金属成矿特征,对夏如岩体中出现矿化痕迹的样品进行研究,包括含黑钨矿的白云母花岗岩、含有铌钽钨氧化物的白云母花岗岩和含有铌钽氧化物的伟晶岩作为研究对象,同时还选取典型的未出现稀有金属矿物的白云母花岗岩(简称未矿化白云母花岗岩)进行对比研究.研究主要通过全岩地球化学主量和微量元素成分,造岩矿物和副矿物的产状、主量和微量元素成分特征进行对比.随着样品中铌钽氧化物矿物含量的出现/增加,电气石和石榴子石的含量也明显增加.这些花岗岩-伟晶岩富集SiO_(2)(72.29~75.53 wt.%),富Al_(2)O_(3)(13.17~15.94 wt.%),富碱(K_(2)O+Na_(2)O 8.0~9.8 wt.%),贫CaO,MgO和FeO,它们微量元素含量接近,含铌钽伟晶岩具有较高的Nb和Ta含量.花岗岩-伟晶岩的稀土配分曲线相似,具有明显的Eu负异常,但三种具有矿化痕迹的花岗质岩石中的稀土总量(平均21×10^(-6))明显低于未矿化白云母花岗岩的稀土总量(平均98×10^(-6)),且具有更明显的四分组效应.矿物学研究工作显示,未矿化白云母花岗岩与含钨白云母花岗岩中的主要组成矿物成分相似,含铌钽钨白云母花岗岩与含铌钽伟晶岩中的主要组成矿物成分相似,其中白云母的Al_(2)O_(3)和FeO含量,石榴子石的Mn/(Mn+Fe)比值和Eu负异常、电气石的Mg/(Mg+Fe)值都显示了含铌钽钨白云母花岗岩和含铌钽伟晶岩比未矿化白云母花岗岩和含钨白云母花岗岩具有更高的岩浆演化程度.出现铌钽氧化物的花岗岩-伟晶岩中锆石的结构�A large number of leucogranites and pegmatites occurred in the Xiaru pluton,Himalayan oregen,mainly including(tourmaline-garnet) muscovite granite and granitic pegmatite.Granite and pegmatite which are related to Nb-Ta-W rare-metal mineralization locally, contain Nb-Ta-W oxide minerals, such as columbite-group minerals, qitianlingite, wolframite, and ilmenorutile. In order to investigate the petrological and mineralogical characteristics of the Xiaru granite-pegmatite related rare-metal mineralization,and gain insight of the rare-metal mineralization metallogenisis of the Xiaru pluton,the samples with rare-metal mineralization are selected,including muscovite granite with the occurrence of wolframite,muscovite granite with Nb-Ta-W oxide minerals and pegmatite with the occurrence of columbite-group minerals. Meanwhile,the typical muscovite granite without any rare-metal minerals(barren muscovite granite hereafter) is selected for comparison. Major and trace elements of whole rock geochemistry, the occurrence, major and trace elements of rock forming minerals and accessory minerals are comparable. The abundances of tourmaline and garnet increase significantly with the occurrence/increased abundance of Nb-Ta oxide minerals in the samples. The Xiaru granite-pegmatite are rich in SiO_(2)(72.29~75.53 wt.%),Al_(2)O_(3)(13.17~15.94 wt.%), total alkali(K_(2)O+Na_(2)O 8.0~9.8 wt.%), but poor in CaO, MgO and FeO. The trace elements concentrations of the granite-pegmatite are similar,and the Nb-Ta-bearing pegmatite is rich in Nb and Ta. The shapes of normalized REE patterns are similar,with obvious negative Eu anomalies. However,the mineralized granite-pegmatite have significantly lower total REE concentrations(~21×10^(-6)on average) than the barren muscovite granite(98×10^(-6)on average),and they have more obvious REE tetrad effect. Mineralogical works show that the mineral compositions of barren muscovite granite are similar to that of W-bearing muscovite granite,while the mineral compositions of Nb-Ta-W-bearing muscovit

关 键 词：淡色花岗岩 造岩矿物 花岗岩演化 矿物学指标 

分 类 号：P574.2[天文地球—矿物学] P578.94[天文地球—地质学]