投稿时间：2021-06-25
修订日期：2021-09-02
网络发布日期：2021-10-22
中文摘要:川西扎乌龙花岗伟晶岩型锂矿床位于甘孜-松潘造山带内，为大型锂矿床。前人基于对扎乌龙系统的流体包裹体研究，认为扎乌龙锂矿形成于500~580℃，压力350 MPa的环境。然而，对于扎乌龙成矿流体的来源及其何种流体挥发分对成矿起主导作用，仍缺乏有效制约。锂辉石型伟晶岩脉是扎乌龙锂矿最富集的类型，脉体内部分带性良好，可划分为4个带：石英-白云母带、斜长石带、钠长石-锂辉石带和石英-锂辉石带。根据地质现象和流体包裹体的岩相学观察，扎乌龙锂辉石型伟晶岩脉可划分为伟晶岩阶段和热液阶段2个主要阶段，锂矿化集中于伟晶岩阶段。文章对扎乌龙成矿流体的来源及成分开展了研究，即对锂辉石型伟晶岩各阶段的流体包裹体进行了激光拉曼光谱、群体包裹体和氢、氧、碳同位素分析。流体包裹体成分揭示，成矿流体由伟晶岩阶段的高温（500~580℃）、低盐度（w （NaCleq）0.8%~8.5%）、富挥发分（Li、P、B等）、弱碱性的硅酸盐水体系，向晚期中高温（300~400℃）、低盐度（w （NaCleq）4.4%~9.6%）、富CO2、弱酸性的盐水体系热液演化。氢、氧同位素组成表明早期成矿流体以岩浆水为主，晚期无明显的大气降水加入。碳同位素分析结果表明，二氧化碳主要来源于岩浆出溶。结合已有的研究成果，笔者认为相对封闭的成矿环境导致挥发组分的大量聚集和弱碱性环境，是扎乌龙锂矿富集与沉淀的主要控制因素。晚期贫F、富Cl的弱酸性热液流体有利于锂辉石的保存。
Abstract:The Zhawulong granitic-pegmatite type lithium deposit is a large deposit located in the west of SongpanGanze orogenic belt. Previous fluid inclusion studies have indicated the spodumene was formed in a condition of 500~580℃ and 350 MPa at Zhawulong. However, the origin and composition of ore-forming fluids remain unclear. Spodumene pegmatite dike, as the main lithium host at Zhawulong, could be classified into four mineralogical-textural zones:quartz-muscovite zone, plagioclase zone, albite-spodumene zone and quartz-spodumene zone. According to geological investigation and fluid inclusions observation, the formation of spodumene pegmatite dikes can be divided into two stages:pegmatitic and hydrothermal stage. The spodumene was deposited during pegmatitic stage. The study of fluid inclusion compositions suggests that the fluid evolved from high temperature (500~580oC), low salinity (w(NaCleq) 0.8%~8.5%), volatile-rich (such as Li, P and B) and weak alkali pegmatitic fluid, to medium-high temperature (300~400℃), medium-low salinity (w(NaCleq) 4.4%~9.6%), CO2-rich and weak acidic hydrothermal fluid. The H-O isotopic compositions indicate that the ore-forming fluids were magmatic origin, without obvious addition of meteoric water at late stage. The C isotopic compositions indicate that CO2 of the fluid is the result of magma exsolution. This study shows that the relatively closed or sealed ore-forming system, resulting in the accumulation of high volatile components and weak alkali conditions, is the main factor for the enrichment and precipitation of Zhawulong lithium deposit. The weak acid hydrothermal fluid with F-poor and Cl-rich at late stage is beneficial to the preservation of spodumene.
keywords:geochemistry enrichment mechanism fluid inclusions composition isotopes granitic pegmatite Zhawulong lithium deposit
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基金项目:本文得到国家重点研发计划（编号：2019YFC06050203、2019YFC06505202）、国家自然科学基金资助项目（编号：41872096、41703048和42002109）和中央级公益性科研院所基本科研业务费专项基金（编号：KK2004）联合资助
引用文本：
熊欣,李建康,李兴杰,严清高,张珈铭.2021.川西扎乌龙花岗伟晶岩型锂矿床成矿作用过程——来自流体包裹体与同位素的证据[J].矿床地质,40(5):997~1012XIONG Xin,LI JianKang,LI XingJie,YAN QingGao,ZHANG JiaMing.2021.Mineralization process of Zhawulong granitic-pegmatite type lithium deposit in western Sichuan: Evidences from fluid inclusion and isotopic studies[J].Mineral Deposits40(5):997~1012
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