钠交代作用对碱性花岗岩体系中稀土富集成矿的贡献  

Na-metasomatism and its contributions to REE enrichment in alkaline granite systems

作　　者：张东 杨武斌[1] 牛贺才[1] ZHNAG Dong;YANG WuBin;NIU HeCai(CAS Key Laboratory of Mineralogy and Metallogeny,Guangdong Provincial Key Laboratory of Mineral Physics and Materials,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;University of Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院广州地球化学研究所矿物学与成矿学重点实验室,广东省矿物物理与材料研究开发重点实验室,广州510640 [2]中国科学院大学,北京100049

出　　处：《岩石学报》2024年第3期864-872,共9页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42122023、41930424);广东省基础与应用基础研究重大项目(2019B030302013);广东省科技计划项目(2023B1212060048);中国科学院青年创新促进会项目(Y2021095)联合资助.

摘　　要：碱性岩是全球稀土资源的主要来源之一,特别是中-重稀土资源。针对碱性花岗岩体系中稀土(REE)和部分高场强元素(HFSE)超常富集机制及其控制因素等关键科学问题,目前尚缺乏深入系统的研究工作。本文重点关注碱性花岗岩成矿体系中的钠交代作用,对常见的钠长石化、钠铁闪石化和钠辉石化等热液交代过程中的矿物交代反应过程及其稀有稀土元素再活化-迁移过程开展分析和讨论。在碱性岩中,碱性角闪石和辉石被认为是REE和HFSE的重要载体,同时也是岩浆分异演化的有效示踪剂。以中国黑龙江碾子山碱性花岗岩为例,岩浆晚期的热液交代会导致碱性角闪石和辉石从富钙的矿物相向富钠的矿物相转变,在这个相转变过程中会导致REE和HFSE的活化和迁移。特别是岩浆晚期热液富钠霓辉石的形成过程中REE和HFSE会大规模释放到交代流体中,可能是导致这些关键金属元素在岩浆晚期超常富集和成矿的关键控制因素。因此,碱性角闪石和辉石的钠指数[Na^(#)=Na/(Na+Ca)摩尔比]可能是一个潜在的矿物地球化学指标,或将为碱性岩型稀土资源勘查提供新的方法。Alkaline igneous rock is one of the main sources of rare earth resources in the world,especially heavy rare earth resources.Until now,there is a lack of comprehensive and systematic research on key scientific questions such as the super-enrichment mechanism of rare earth(REE)and some high field strength elements(HFSE)in alkaline granite systems and their controlling factors.This paper focuses on Na-metasomatism in the alkaline magmatic-hydrothermal systems,and discusses the mineral replacement reaction processes and the remobilization and migration processes of rare earth elements in the hydrothermal replacement processes,such as albitization,arfvedsonization and aegirinization.In alkaline systems,alkali amphiboles and pyroxenes are considered to be the significant carriers of REE and HFSE,and are also effective tracers of magmatic differentiation and evolution.Taking the Nianzishan alkaline granite in NE China as an example,the late magmatic-hydrothermal metasomatism will lead to the evolution of alkali amphibole and pyroxene from calcium-rich minerals to sodium-rich mineral phases,which will lead to the remobilization and transferring of REE and HFSE in the late hydrothermal stage.In particular,REE and HFSE would be released into the metasomatic fluids,which may be the key controlling factors leading to the super-enrichment and mineralization of these key metal elements in the late hydrothermal stage.Therefore,the sodium index[Na^(#)=Na/(Na+Ca)molar ratio]of the alkali amphiboles and pyroxenes may be a potential mineral geochemical index,which will provide a new proxy for REE exploration in the alkaline-peralkaline plutons.

关 键 词：碱性花岗岩 碱性角闪石 钠交代作用 稀土 钠指数(Na^(#)) 

分 类 号：P588.15[天文地球—岩石学] P618.7[天文地球—地质学]