南岭地区离子吸附型稀土矿床基岩的稀土元素预富集机制探讨  

Mechanism of REE Enrichment in Granitic Bedrocks of the Ion-adsorption REE Deposits in the Nanling Mountain Range,South China

作　　者：豆敬兆 王焰[1,2,3] 谭伟 赵子送[1,4] DOU Jingzhao;WANG Christina Yan;TAN Wei;ZHAO Zisong(CAS Key Laboratory of Mineralogy and Metallogeny,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;Guangdong Provincial Key Laboratory of Mineral Physics and Materials,Guangzhou 510640,Guangdong,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,Guangdong,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,广东广州510640 [2]广东省矿物与材料研究开发重点实验室,广东广州510640 [3]中国科学院深地科学卓越创新中心,广东广州510640 [4]中国科学院大学,北京100049

出　　处：《大地构造与成矿学》2024年第2期200-212,共13页Geotectonica et Metallogenia

基　　金：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(2020B1212060055)联合资助。

摘　　要：南岭地区离子吸附型稀土矿床是目前全球重稀土的主要来源。在岩浆演化及热液蚀变过程中,稀土元素在成矿基岩中的迁移和富集过程受稀土元素的地球化学行为控制。本文对比了离子吸附型轻、重稀土矿床中基岩在矿物组合、岩石化学及主要稀土矿物类型等方面的差异,简要介绍了南岭地区离子吸附型稀土矿床基岩中热液活动与稀土元素富集的相关研究进展。其中富重稀土矿床的基岩主要为高硅碱长花岗岩(SiO_(2)>75%),基岩中硅铍钇矿和氟碳钙钇矿为主要稀土矿物。岩浆期后热液过程中,早期形成的氟铈矿等轻稀土矿物可导致残余流体富集重稀土元素,并形成重稀土热液矿物,稀土氯络合物可能是流体中迁移并富集重稀土元素的主要介质。而富轻稀土矿床的基岩主要为黑云母花岗岩、花岗闪长岩等(SiO_(2)<75%),主要稀土矿物为褐帘石和榍石,为岩浆演化晚期结晶产物,其在后期含F^(−)、CO_(3)^(2−)/HCO_(3)^(–)流体作用下蚀变成氟碳钙铈矿;这一过程导致轻稀土元素在基岩中被重新活化并再次富集。含F^(−)、CO_(3)^(2−)/HCO_(3)^(–)流体可能与南岭地区地下水的贡献有关。The ion-adsorption REE deposits hosted in granite-derived regoliths in the Nanling Mountain Range are the dominant source of the world’s heavy REE(HREE)resources.Identifying the mechanism of REE enrichment in granitic bedrocks can provide a better understanding of the geochemical behaviors of REE during magmatic evolution and hydrothermal alteration.This paper summarizes the differences in the mineral assemblages,chemical compositions,and REE carriers between the bedrocks of ion-adsorption light and heavy REE deposits and provides a brief overview of the recent progress in the mechanism of REE enrichment in granitic bedrocks.The bedrocks of the ion-adsorption HREE deposits are mainly alkali-feldspar granites with SiO_(2)>75%,in which synchysite-(Y)and gadolinite-(Y)are the principal REE repositories.Formation of fluocerite precursors in chloride-bearing deuteric fluids can enrich HREE in residual fluids from which HREE-rich minerals crystallize.In contrast,the bedrocks of the ion-adsorption light REE(LREE)deposits comprise biotite granite,granodiorite,etc.and usually have SiO_(2)contents of less than 75%.Allanite and titanite are the main REE carriers and formed at the late stage of magmatic crystallization.They were subsequently altered into synchysite-(Ce)during F^(−)and CO_(3)^(2−)/HCO_(3)^(–)-bearing fluid infiltration,thereby mobilizing LREE into synchysite-(Ce).The F^(−)and CO_(3)^(2−)/HCO_(3)^(–)-bearing fluid most likely originates from the local groundwater in the Nanling Mountain Range.

关 键 词：南岭地区 离子吸附型稀土矿床 花岗质基岩 热液蚀变 稀土富集 

分 类 号：P612[天文地球—矿床学] P595[天文地球—地质学] P597