桂东北越城岭大源-小源地区伟晶岩磷灰石矿物化学特征及其成矿潜力  

The mineralogical characteristics of apatite from the Dayuan-Xiaoyuan pegmatite in Yuechengling and its implication on mineralization

作　　者：招传 付伟[1,2] 刘希军[1,2] 寇东平 许成 冯梦[1,2] ZHAO Chuan;FU Wei;LIU Xijun;KOU Dongping;XU Cheng;FENG Meng(Collaborative Innovation Center for Mineral Resources Exploration and Efficient Utilization of Nonferrous Metals,Giuilin University of Technology,Guilin 541006,Guangxi,China;Guangxi Key Laboratory of Subsurface Metal Mineral Exploration,Guilin University of Technology,Guilin 541006,Guangxi,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]桂林理工大学有色金属矿产勘查与资源高效利用协同创新中心,广西桂林541006 [2]桂林理工大学,广西隐伏金属矿产勘查重点实验室,广西桂林541006 [3]北京大学地球与空间科学学院,北京100871

出　　处：《地球化学》2025年第2期248-262,共15页Geochimica

基　　金：国家自然科学基金面上项目(42173067);广西自然科学基金创新研究团队项目(2020GXNSFGA297003);广西研究生教育创新计划项目(YCBZ2022122)联合资助。

摘　　要：桂东北越城岭地区发育2000多条伟晶岩脉,是开展伟晶岩型稀有金属找矿勘查的重要目标区,然而有关区内伟晶岩的成岩演化机制及成矿潜力仍不清楚。基于磷灰石矿物成分记录了岩浆源区性质、岩浆演化和热液流体活动等地质作用重要信息,本文选取桂东北越城岭大源–小源地区伟晶岩中的磷灰石为研究对象,通过磷灰石微区原位分析探讨伟晶岩的岩浆演化过程及其稀有金属成矿潜力。EPMA分析显示,磷灰石F含量(3.22%~6.43%)高、Cl(低于检测线)、FeO(<0.34%)、MnO(<0.32%)、SiO_(2)含量(<0.97%)低,表明其为岩浆成因的氟磷灰石。LA-ICP-MS分析显示,随着Eu/Eu^(*)值增高,Ce/Ce^(*)值未有明显变化,表明磷灰石形成于还原环境。磷灰石的(La/Yb)N、(Sm/Yb)N值和Sr含量呈正相关关系,具有较低的Sr含量和强烈的Eu负异常,说明在岩浆演化过程中经历了长石→磷灰石→褐帘石和独居石的分离结晶作用。磷灰石的Ce/Pb和Th/U值呈负相关关系,Nb/Ta(0~21.2)和Zr/Hf值(0~37.1)较低,且在磷灰石边缘发育次生的稀土矿物(如褐帘石和独居石等),表明岩浆演化后期遭受了热液流体交代作用,促使磷灰石溶解–再沉淀形成新的含稀土矿物。研究表明,在伟晶岩形成过程中经历了高度的结晶分异作用,后期又遭受了热液叠加活动,结合野外勘查,表明研究区伟晶岩具有一定的稀有金属成矿潜力。然而,磷灰石形成于还原环境,又呈现弱稀土元素四分组效应,判别伟晶岩成富矿的这两指标似乎不太乐观,其成矿潜力需要开展进一步的研究。More than 2000 granitic pegmatite dikes have been documented in the Yuechengling district,northern Guangxi,which represents an important area for pegmatite-type rare metal exploration.However,the genetic evolution and mineralization potential of these pegmatites remain poorly constrained.The mineral composition of apatite serves as an effective recorder of the magma source,magmatic evolution,and post-crystallization hydrothermal activity.In this study,we present the geochemical characteristics of magmatic apatite from the Dayuan-Xiaoyuan pegmatite to explore their potential implications in petrogenesis and mineralization investigations.The high F content(3.22%-6.43%),low Cl(below detection limit),FeO(<0.34%),MnO(<0.32%),and SiO_(2)(<0.97%)revealed by EPMA analyses indicated that the apatite belongs to fluoroapatite.LA-ICP-MS analysis showed that the Ce/Ce^(*)values of the apatite did not change the increasing of Eu/Eu^(*)ratios,indicating that the apatite might have been formed in a reducing environment.The positive correlations between(La/Yb)N and(Sm/Yb)N ratios and Sr contents,coupled with the low Sr contents and strong negative Eu anomalies of the apatite,indicated that mineral phases such as feldspar,apatite,allanite,and monazite crystallized during granitic magma evolution.Based on the negative correlation of Ce/Pb with Th/U,low Nb/Ta ratios(0-21.2)and Zr/Hf ratios(0-37.1),and the fact that secondary REE-bearing minerals occur around apatite,it is inferred that a late-stage hydrothermal alteration resulted in the formation of allanite and monazite around apatite.Combined with field exploration,the pegmatite might have undergone highly crystallization differentiation and late-stage hydrothermal activity,indicating the potential for rare metal mineralization.However,based on the premise that apatite is formed in a reducing environment with a weak REE tetrad effect,it is inferred that the Dayuan-Xiaoyuan pegmatite may not be a bonanza for rare-metal mineralization,and further research is required to assess its

关 键 词：伟晶岩 磷灰石 稀有金属 越城岭 成矿潜力 

分 类 号：P597[天文地球—地球化学]