巴尔哲锆-铌-铍-稀土矿床成矿精细过程研究  

A study of the fine Zr-Nb-Be-REE mineralizing processes of the Baerzhe deposit,China

作　　者：吴鸣谦[1,2,3] 马甲栋 邓军 刁习[1] 裴磊 邱昆峰[1,3,4] WU MingQian;MA JiaDong;DENG Jun;DIAO Xi;PEI Lei;QIU KunFeng(School of Earth Science and Resources,China University of Geosciences(Beijing),Beijing 100083,China;School of the Environment,University of Windsor,Windsor N9B 3P4,Canada;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences,Beijing 100083,China;Frontiers Science Center for Deep-time Digital Earth,China University of Geosciences(Beijing),Beijing 100083,China)

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]加拿大温莎大学环境学院,温莎N9B 3P4 [3]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [4]中国地质大学(北京)深时数字地球前沿科学中心,北京100083

出　　处：《岩石学报》2024年第6期1817-1836,共20页Acta Petrologica Sinica

基　　金：国家重点研发计划(2023YFF0804201、2023YFC2906702);国家自然科学基金项目(91962106);高等学校学科创新引智计划(BP0719021);深时数字地球前沿科学中心项目(2652023001)资助.

摘　　要：巴尔哲碱性花岗岩型关键金属矿床拥有世界级Zr、Nb、Be、REE资源量,其成矿具有多期次、多阶段特征。Zr矿化(Ⅰ阶段)发生在岩浆期,表现为多锆相(agpaitic)界熔花岗岩熔体结晶出原生钠锆硅酸盐(斜钠锆石),在该阶段,多锆相界熔花岗岩经历钠质交代,斜钠锆石原位分解为锆石-石英假象,假象中锆石U-Pb年代学表明锆成矿发生在123.9±0.6Ma。随后,Nb-Be-REE矿化以多种矿物形式、分三个连续的阶段(Ⅱ、Ⅲ、Ⅳ阶段)、呈浸染状分布于遭受赤铁矿化的界熔花岗岩中,重稀土为主的矿物普遍形成于以轻稀土为主的矿物之前。Ⅱ阶段是巴尔哲矿床中Nb、Be和重稀土矿化的主要阶段,大部分界熔花岗岩均遭受了不同程度的赤铁矿化,并伴随钇兴安石、铈兴安石、钇易解石、铌铁矿等稀有稀土金属矿物的形成,主要形成以石英为主的假象(Nb-Be-REE假象),Nb-Be-REE假象的前体矿物并非某种Nb-Be-REE矿物。Ⅲ阶段主要形成黑稀金矿、独居石及氟碳铈矿,热液独居石U-Pb年代学指示该阶段热液成矿活动发生在122.8±0.6Ma。氟铈矿和氟碳钙铈矿部分交代氟碳铈矿构成了Ⅳ阶段的矿物组合。Nb、Be和REE在热液过程中的多阶段分配和富集,是造成巴尔哲矿床中复杂矿石矿物组合以及高品位Nb-Be-REE矿化的重要原因。Nb-Be-REE矿石矿物组合中不存在锆石,且其分布与雪球石英、钠质交代和锆石-石英假象的分布没有时空关联。此外,巴尔哲角闪石中Nb、Be、REE的含量低,表明原生锆硅酸盐矿物和角闪石不是Nb、Be和REE等关键金属的物质来源。结合各岩相中角闪石元素含量的变化与熔体包裹体成分特征,笔者提出Nb和REE的富集可能是氟化物-硅酸盐熔体不混溶耦合岩浆期后热液富集的结果。因此,巴尔哲矿床中需要开展精细的熔体/流体包裹体成分研究,针对关键金属尤其是Be的来源、熔-流体演化历程以及矿化精�The Baerzhe alkaline granite-hosted rare-metal deposit represents world-class resources of Zr,Nb,Be,and REE(rare earth elements),which experienced multi-stage ore-forming processes.Zr was concentrated during magmatic stage,manifested by fractionation of primary elpidite in an agpaitic transsolvus granite that always suffered Na metasomatism.In stage I,Zr was redistributed,but not reconcentrated,during the breakdown of sodium zirconosilicates(elpidite)into zircon-quartz pseudomorphs along Na-metasomatism.U-Pb chronology of hydrothermal zircon in zircon-quartz pseudomorphs indicates that the stage I mineralization occurred at 123.9±0.6Ma.Nb-Be-REE mineralization occurs as a variety of minerals that are disseminated through all the hematized transsolvus granites and were precipitated in three sequential stages(stages II-IV),the formation of HREE-dominant phases generally preceding LREE-dominant phases.Specifically,stage II is characterized mainly by Nb,Be and HREE mineralization accompanied by hematite alteration.The stage II mineralization,represented by hingganite-(Y/Ce),aeschynite-(Y)and columbite-(Fe),occurs mainly as quartz-dominant,Nb-Be-REE-rich pseudomorphs,the precursor minerals of which are not Nb-Be-REE-bearing minerals.The following stage III is defined by euxenite-group minerals,monazite and bastn site crystallization.U-Pb chronology of this hydrothermal monazite indicates 122.8±0.6Ma of stage III.Stage IV is represented by fluocerite and synchysite that partially replaced bastn site.The multi-stage hydrothermal redistribution and enrichment of Nb,Be and REE are important factors for the development of a variety of rare-metal mineral associations and high-grade Nb-Be-REE mineralization at Baerzhe.That the Nb-Be-REE-rich pseudomorphs do not contain zircon,and their distribution is independent of the occurrence of snowball quartz,Na metasomatism and zircon-quartz pseudomorphs,in conjunction with the low contents of Nb,Be and REE in amphiboles at Baerzhe,preclude leaching of preexisting sodium zirconosil

关 键 词：巴尔哲 碱性花岗岩 关键金属 岩浆-热液过程 

分 类 号：P588.121[天文地球—岩石学] P618.7[天文地球—地质学]