母岩特征对上犹复式岩体中风化壳离子吸附型重稀土矿形成的制约  

Constraints of Parent Rocks on the Formation of Ion Adsorption HREE Deposit in the Weathering Crust of the Shangyou Granite Batholith

作　　者：黄玉凤 谭伟[1,2] 包志伟[1,2] 何宏平[1,2,3] 梁晓亮[1,2] 黄健 王珩[1,2,3] HUANG Yufeng;TAN Wei;BAO Zhiwei;HE Hongping;LIANG Xiaoliang;HUANG Jian;WANG Heng(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,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/广东省矿物物理与材料重点实验室,广东广州510640 [2]中国科学院深地科学卓越创新中心,广东广州510640 [3]中国科学院大学,北京100049

出　　处：《大地构造与成矿学》2022年第2期303-317,共15页Geotectonica et Metallogenia

基　　金：广东省基础与应用基础研究重大项目(2019B030302013);中国科学院地质与地球物理研究所重点部署项目(IGGCAS-201901);国家自然科学基金项目(42022012、41921003);广东省科学技术厅“珠江人才计划”项目(2017GC010578)联合资助。

摘　　要：近年,在赣南加里东期上犹复式花岗岩体风化壳中首次发现了离子吸附型重稀土矿,这一找矿突破受到广泛关注,但其成因机制尚不清楚。本文对上犹复式岩体中产出重稀土的剖面中的基岩开展了岩相学、矿物学、元素地球化学及锆石LA-ICP-MS U-Pb定年研究。结果显示,重稀土矿的风化母岩为中细粒黑云母花岗岩‒强绢云母化黑云母花岗岩,(含)稀土副矿物主要为磷灰石、锆石、磷钇矿等,均富中重稀土元素。新鲜基岩的主量元素具高硅、富钾特征;稀土元素总量(∑REE)为258μg/g,LREE/HREE为0.84,稀土元素配分模式整体以富重稀土为特征,具强烈的Eu负异常;微量元素亏损Ba、Sr、Ti、Nb、P,相对富集Rb、U、Ta、Y,这些特征与上犹复式岩体中的晚期侵入体——陡水岩体的地球化学特征相似。锆石U-Pb年龄结果为412.7±1.2 Ma,成岩时代与陡水岩体一致,也证实重稀土的成矿母岩为上犹复式岩体中的晚期侵入体。对比重稀土剖面的蚀变基岩和新鲜基岩发现,蚀变形成的强绢云母化花岗岩稀土总量显著降低至46~140μg/g,而且主要(含)稀土的副矿物磷灰石发生分解,形成次生的磷钇矿、独居石等耐风化矿物,表明基岩的蚀变不利于后期的风化成矿。通过研究指明了在上犹复式岩体中呈岩株、岩枝产出的晚期侵入体的风化壳为重稀土矿找矿范围。An ion adsorption HREE deposit has recently been discovered for the first time in the Caledonian Shangyou granite batholith in the southern Jiangxi province.In this paper,petrological,mineralogical and geochemical analyses were carried out on the bed rocks of the HREE-rich profiles developed above the Shangyou granite batholith.Accurate U-Pb age of zircon from the weathering crust was analyzed by LA-ICP-MS.The results show that the bed rocks of the HREE-rich profiles are medium fine-grained biotite granite and sericitized biotite granite.The REE-bearing minerals are primarily apatite,zircon,xenotime,etc.The Electron Probe Micro-analyzer(EPMA)analysis shows that all REE-bearing minerals are rich in HREE and MREE.The biotite granite samples are characterized by high silicon and potassium.The total amount of REEs are ca.258μg/g;chondrite-normalized REE patterns show a weak right-inclined of LREEs and flat HREEs,with significant negative Eu anomalies;the LREE/HREE is ca.0.84.The granite rocks are depleted in Ba,Sr,Ti,Nb and P,and relatively enriched in Rb,U,Ta and Y.These characteristics are similar to that of the late stage intrusions of the Shangyou granite batholith.Additionally,U-Pb dating of zircon in the weathered granite yielded an age of ca.410 Ma,which is consistent with the age of the late stage intrusions,which further confirms that the metallogenic bed rocks for the HREE mineralization are the late stage intrusions in the Shangyou granite batholith.By comparison,sericitization resulted in significant decrease of REE contents of the biotite granite,during the sericitization the primary REE-bearing mineral apatite dissolved and formed secondary weathering resistant minerals such as xenotime,monazite,therefore,the alteration of the granite bedrock is not conducive to epigenic REE enrichment in the weathering crust.The research results indicate that the late stage intrusions in the Shangyou granite batholith are the causal bed rocks of HREE mineralization in the weathering crust,and thus are favorable locus

关 键 词：上犹复式岩体 加里东期 花岗岩 离子吸附型重稀土矿 锆石LA-ICP-MS U-Pb年龄 

分 类 号：P612[天文地球—矿床学] P595[天文地球—地质学]