川西扎乌龙伟晶岩型稀有金属矿床的锂、铍矿物学特征及其对成矿作用的指示  

Mineralogical characteristics and mineralization implication of Li and Be-bearing minerals from Zhawulong pegmatite-type rare-element deposit,western Sichuan,China

作　　者：熊欣[1] 李建康[1] 张珈铭 严清高 王臻 XIONG Xin;LI JianKang;ZHANG JiaMing;YAN QingGao;WANG Zhen(MNR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing 100037,China;China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质科学院矿产资源研究所,自然资源部成矿作用与资源评价重点实验室,北京100037 [2]中国地质大学(北京),北京100083

出　　处：《岩石学报》2023年第7期2085-2100,共16页Acta Petrologica Sinica

基　　金：国家重点研发计划项目(2019YFC06050203);国家自然科学基金项目(41872096、41703048);中国地质调查项目(DD20230034、DD20230289);中央级公益性科研院所基本科研业务费专项基金(KK2211)联合资助.

摘　　要：扎乌龙花岗伟晶岩型稀有金属矿床位于四川省和青海省交界处,其西部矿体被称为青海草陇矿床,是我国西部松潘-甘孜稀有金属成矿带的重要组成。扎乌龙矿床Li 2O资源储量预估高达157万t,最主要的锂、铍矿石矿物为绿柱石和锂辉石。前人以扎乌龙伟晶岩脉内多阶段的流体包裹体为研究对象,着重剖析了其岩浆热液演化过程。然而,迄今为止尚缺乏锂铍矿物学和同位素方面的研究来加深对该矿床岩浆热液演化及成矿作用方面的理解。14号钠长石-锂辉石型伟晶岩脉是扎乌龙花岗伟晶岩型矿床出露面积最大、锂储量最高的伟晶岩脉,也是研究该稀有金属矿床成矿作用过程的理想对象。该伟晶岩脉具有一定的内部分带性,由边部至核部分为:石英-白云母带(Ⅰ带)、微斜长石-钠长石带(Ⅱ带)、钠长石-锂辉石带(Ⅲ带)和石英-锂辉石带(Ⅳ带)。绿柱石和锂辉石矿物结构和化学组成表明,扎乌龙14号脉锂铍矿化主要可划分为两个阶段:第一阶段为岩浆阶段,主要形成均一或振荡环带结构的原生绿柱石和锂辉石;第二阶段为热液阶段,主要表现为流体与原生矿物发生再平衡,原生锂辉石发生蚀变形成云母等矿物,原生绿柱石边部和内部缝隙产出相对富Cs_(2)O或Na 2O含量的次生绿柱石。14号伟晶岩中原生和次生绿柱石的Cs_(2)O含量(0.71%~2.28%)均低于世界上许多其他Li-Ta-Cs伟晶岩脉,表明其岩浆结晶分异程度相对较低。Ⅲ和Ⅳ带原生锂辉石均呈现出不均匀的δ^(7)Li值(-1.70‰~1.67‰),表明锂辉石结晶于流体出溶的环境。次生锂辉石相对略低的δ^(7)Li值(-1.90‰~-0.03‰)表明了热液阶段锂的再活化沉淀对于锂同位素组成产生了一定的影响。次生绿柱石较原生绿柱石的Cs_(2)O含量增加有限,热液作用未形成高度富铯或锂的矿物如铯馏石和锂云母,表明热液作用对于原生稀有金属矿物的改造有限�The Zhawulong granitic-pegmatite type rare-element deposit is located in the junction area of Sichuan and Qinghai provinces,whose tectonic position belongs to the Songpan-Ganze orogenic belt in northwestern China.This deposit includes an estimated 1.75 million tons of Li 2O,and its main ore minerals are beryl and spodumene.Previous studies have focused on the reconstruction of its magmatic-hydrothermal evolution through analysis on the multi-stage fluid inclusions.However,the evolution degree of the magma and crystallization conditions from magmatic to hydrothermal stages remain poorly constrained because of the absence of mineralogical and isotopic evidence.The No.14 albite-spodumene pegmatite is one of the largest pegmatite dikes with a greatest lithium reserve in the Zhawulong deposit.This pegmatite dike could be classified into four centric zones from border to core:the quartz-muscovite zone(zoneⅠ),the microcline-albite zone(zoneⅡ),the albite-spodumene zone(zoneⅢ)and the spodumene-quartz zone(zoneⅣ).Two Li-Be mineralization stages have been identified based on beryl and spodumene mineralogical characteristics.The stage I is characterized by crystallization of magama,forming primary beryl and spodumene with simple textures(homogenous and progressive zoning).The stageⅡis characterized by hydrothermal alteration,forming secondary Cs-or Na-enriched beryl veinlets together with secondary muscovite.The relatively low Cs_(2)O contents(0.71%~2.28%)in beryl suggest the No.14 pegmatite has experienced lower degrees of fractional crystallization than many other Li-Cs-Ta pegmatites in the world.Primary spodumenes from zoneⅢandⅣshow a variableδ^(7)Li values(-1.70‰~1.67‰),indicating both of them are crystallized from a highly evolved aqueous melt immisibile with exsolving fluids.δ^(7)Li values(-1.90‰~-0.03‰)of secondary spodumenes are slightly lower than those in primary ones,suggesting the crystal-fluid interaction only produces a restricted Li isotope fractionation in the closed system.The slightl

关 键 词：花岗伟晶岩 锂辉石 绿柱石 伟晶岩熔体分异 稀有金属 成矿作用 松潘-甘孜造山带 扎乌龙矿床 

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