【摘要】 铌(Nb)、钽(Ta)作为关键性战略金属，其在稀有金属花岗岩中的富集机制，长期以来是矿床学和岩石学领域亟待厘清的核心问题。本文以大兴安岭南段台莱花铍-铌-钽矿床的成矿岩体白云母钠长花岗岩为研究对象，系统开展了铌铁矿族矿物微观结构、U-Pb年代学以及矿物地球化学研究，旨在揭示其成矿时代、岩浆-热液演化过程以及Nb、Ta富集机制。白云母钠长花岗岩中铌铁矿族矿物U-Pb定年结果显示，其年龄为144.9～146.6Ma，表明台莱花矿床的成矿时代为晚侏罗世。根据背散射图像，铌铁矿族矿物的结构可划分为环带型(核部CGM-1a，边部CGM-1b)、均质型(CGM-2)和补丁型，补丁型按产出状态与结构特征可进一步分为增生边型(CGM-3a、CGM-3b)和单颗粒型(CGM-4a、CGM-4b)，其中CGM-3a与CGM-4a为少孔洞-亮度均一型，CGM-3b与CGM-4b为多孔洞-亮度不均型。地球化学分析结果表明，所有铌铁矿族矿物均属于铌铁矿-钽锰矿系列，除CGM-3b与CGM-4b部分属于钽锰矿，并具有高Sn、Sc、W含量外，其余类型均为铌锰矿系列，Sn、Sc、W含量普遍较低;各类型铌铁矿族矿物稀土元素配分模式显示为轻稀土亏损、重稀土富集，并具有强烈的负Eu异常，其中补丁型铌铁矿族矿物较其余类型表现出更为显著的负Eu异常与更强的“M”型四分组效应，暗示其受流体改造作用较强。综合铌铁矿族矿物微观结构和地球化学特征揭示了台莱花矿床Nb、Ta成矿过程可分为两个阶段:岩浆阶段以分离结晶作用为主，形成均质型与环带型铌铁矿族矿物，实现了Nb、Ta初步富集;岩浆-热液过渡阶段则先后经历了熔-熔体不混溶与熔-流体相互作用，形成补丁型铌铁矿族矿物，其中CGM-3a与CGM-4a主要受熔-熔体不混溶作用控制，分离出的富水盐熔体进一步富集Nb、Ta，而CGM-3b与CGM-4b则主要受熔-流体相互作用控制。从富水盐熔体中出溶的流体在运移过程中通过交代云母等矿物，萃取Fe等流体活动性元素，随后与富Ta残余熔体发生熔-流体反应，最终促成Ta的高度富集。本研究成果不仅进一步揭示了铌铁矿族矿物不同结构与岩浆-热液演化过程间的成因联系，更为深入理解Nb、Ta在岩浆-热液演化中的富集机制提供了重要依据。更多还原

【Abstract】 Niobium( Nb) and tantalum( Ta),as critical strategic metals,have long been a focus in the fields of mineral deposit geology and petrology,with their enrichment mechanisms in rare-metal granites urgently needing clarification. This study selected the ore-bearing muscovite-albite granite of the Tailaihua Be-Nb-Ta deposit in the southern Great Xing’an Range as the research object,and conducted systematic investigations into the microstructure,U-Pb dating,and mineral geochemistry of columbite-group minerals to constrain the mineralization age,magmatic-hydrothermal evolution,and Nb-Ta enrichment mechanisms. U-Pb dating of columbitegroup minerals from the muscovite-albite granite yields an age of 144. 9 ～ 146. 6Ma,indicating Late Jurassic mineralization. Based on backscattered electron imaging, columbite-group mineral textures are classified into zoned( core CGM-1a and rim CGM-1b),homogeneous( CGM-2) and patchy types,with the latter further subdivided into overgrowth-rim( CGM-3a and CGM-3b) and singlegrain( CGM-4a and CGM-4b) subtypes. CGM-3a and CGM-4a display limited voids and uniform brightness,whereas CGM-3b and CGM-4b are characterized by abundant voids and heterogeneous brightness. Geochemical results indicate that all columbite-group minerals belong to the columbite-tantalite series. While CGM-3b and CGM-4b are partly classified as tantalite and show high Sn,Sc,and W contents,the other types are predominantly manganocolumbite and generally show low Sn,Sc,and W concentrations. Rare earth element( REE) patterns consistently show light REE depletion,heavy REE enrichment,and pronounced negative Eu anomalies.Patchy-type columbite-group minerals exhibit more significant negative Eu anomalies and stronger “M”-type tetrad effects relative to other types,suggesting significant fluid alteration. Integrating the microstructural and geochemical characteristics of columbite-group minerals reveals that the Nb-Ta mineralization process at the Tailaihua deposit can be divided into two stages: An initial magmatic stage dominated by fractional crystallization,producing homogeneous and zoned columbite-group minerals and facilitating preliminary Nb-Ta enrichment; and a subsequent magmatic-hydrothermal transition stage involving melt-melt immiscibility and melt-fluid interaction,leading to the formation of patchy columbite-group minerals. Among these,CGM-3a and CGM-4a are primarily controlled by melt-melt immiscibility,where the separated hydrosaline melts further enriches Nb-Ta. In contrast,CGM-3b and CGM-4b are mainly influenced by melt-fluid interaction. Fluids exsolved from the hydrosaline melt extracted fluid-mobile elements( e. g., Fe) through the metasomatism of micas and other minerals during migration. Subsequently,the fluids underwent melt-fluid reactions with Ta-enriched residual melts,ultimately facilitating the high-degree enrichment of Ta. This study not only clarifies the genetic links between columbite-group mineral textural types and magmatic-hydrothermal evolution,but also provides key insights into the enrichment mechanisms of Nb-Ta in magmatic-hydrothermal systems.更多还原