南岭花岗岩区锂铍铌钽成矿规律与找矿方向

南岭是全球最重要的稀有和有色金属资源基地之一, 以大面积出露的花岗质岩浆岩与大规模的稀有金属矿化而举世瞩目。华南多旋回构造岩浆活动, 造就了广泛发育的各类花岗岩, 并普遍经历了高分异作用, 使得钨、锡、锂、铍、铌、钽等稀有金属不同程度富集成矿。前人对南岭钨和锡的时空分布规律、成矿作用和成矿动力学背景进行了大量研究。本文结合近年矿产调查新进展, 重点总结了南岭花岗岩区锂铍铌钽矿化类型、时空分布规律及其成矿条件, 系统梳理了锂铍铌钽矿化相关花岗岩的成矿专属性。花岗质岩浆体系中源区组成、部分熔融程度、结晶分异程度、岩浆-热液流体的交代作用控制着锂、铍、铌、钽的分配和富集, 铌和钽可在花岗质岩浆熔体演化晚期阶段形成独立矿物, 铍一般在岩浆-热液的过渡阶段富集, 锂在伟晶岩阶段形成锂辉石, 也可富集于流体中交代形成锂云母。南岭地区铌钽矿化主要产出在花岗岩晚期阶段和云英岩中, 铍常与钨锡相伴生产出于石英脉型和接触交代型矿床中, 南岭锂资源以锂云母形式主要产出于富锂花岗岩体的云英岩化带。本文进一步讨论了多期岩浆作用与铌钽成矿关系、岩浆热液体系中铍与钨锡的成矿机理及南岭花岗岩区锂(锂云母)的成矿潜力, 这对下一步南岭地区锂铍铌钽找矿行动部署具有重要的意义。

     

稀有金属矿物微区同位素定年与示踪

作为战略性关键金属矿产资源, 钨、锡、铌、钽、锂、铍、铷、铯、锆、铪、稀土等稀有金属, 在国民经济与国家安全方面有着重要的研究意义。稀有金属矿石矿物微区同位素定年与示踪, 是开展稀有金属矿床成矿作用研究的最直接手段, 具有整体分析无可比拟的优点。近年来, 钨锡铌钽锆铪稀土等稀有金属矿物微区U-Pb定年与Sr-Nd-Hf同位素示踪发展迅速, 而锂铍铷铯等稀有金属矿物微区Rb-Sr/Lu-Hf定年正蓬勃发展。本文综述了黑钨矿、白钨矿、锡石、铌钽矿(铌钽氧化物类矿物的简称)、独居石、磷钇矿、氟碳铈矿等稀有金属矿物微区U-Pb定年与Sr-Nd-Hf同位素示踪技术主要进展, 展望了锂云母、铁锂云母、铯沸石、钾长石(天河石)等微区Rb-Sr定年与磷钇矿、磷灰石、褐帘石、独居石、黑钨矿、白钨矿等微区Sm-Nd和Lu-Hf定年的广阔前景, 获得如下认识: (1)低铀矿物U-Pb定年, 除了采用高灵敏度磁式等离子质谱外, 元素成像技术能很好地揭示微量元素之间相关性, 进而快速锁定高U/Pb区域, 提高低铀矿物U-Pb定年成功率; (2)铌钽矿-锡石激光微区Hf同位素能够直接示踪花岗岩-伟晶岩稀有金属成岩成矿物质源区, 但这方面工作仍需进一步加强; (3)碰撞/反应池等离子质谱的出现, 使高Rb/Sr、Sm/Nd或高Lu/Hf比矿物的同位素定年成为现实, 是未来稀有金属激光微区同位素年代学发展的新方向; (4)实验方法研发与标准物质研制相辅相成、相互促进, 仍是当前迫切需要解决的关键技术难题。随着战略性关键金属日渐成为国内外成矿作用研究的热点, 钨锡铌钽锂铍铷铯锆铪稀土等稀有金属矿物微区同位素定年与示踪方法研究, 必将为我国新一轮稀有金属矿床学研究做出应有的学术贡献。

     

赣西北狮子岭花岗岩型锂-钽矿床的矿物学特征及成矿机制

赣西北狮子岭岩体是九岭地区新发现的一个花岗岩型锂、钽矿化岩体, 前人对其矿物学特征以及锂、钽成矿机制的认识较为薄弱。本文在详细野外工作的基础上, 利用光学显微镜、电子探针(EPMA)和激光剥蚀等离子体质谱仪(LA-ICP-MS)对狮子岭岩体中云母族矿物和稀有金属矿物(铌钽锰矿、钽铌锰矿、细晶石、含铌钽锡石和磷锂铝石)的产状、结构、化学成分以及类型进行研究。结果表明: 从二云母花岗岩、锂(白)云母碱长花岗岩、黄玉锂云母碱长花岗岩到似伟晶岩, 云母的种类发生变化, 云母中K/Rb、K/Cs比值逐渐降低, Li、Rb、Cs、F含量逐渐升高, 部分云母发育成分环带; 铌钽矿物具有较高的Ta/(Ta+Nb)、Mn/(Fe+Mn)值, 发育岩浆成因的成分环带; 含铌钽锡石具有较高的Nb₂O₅+Ta₂O₅含量; 在锂(白)云母碱长花岗岩、黄玉锂云母碱长花岗岩和似伟晶岩中, 细晶石和磷锂铝石常与钠长石及锂云母等矿物共生。据此认为, 狮子岭岩体中的云母族矿物存在两种演化序列, 即铁叶云母→黑鳞云母→铁锂云母→锂云母和白云母→锂白云母(铁锂云母)→锂云母, 二者均向着富Li的方向演化, 且均为岩浆结晶分异的结果; 云母族矿物与稀有金属矿物的类型、成分以及结构特征均表明狮子岭岩体具有高度演化特征; 岩浆体系中Li、F、P等组分的富集有利于狮子岭岩体中稀有金属矿物的结晶; 狮子岭岩体Li、Ta矿化主要由岩浆的结晶分异作用所控制。

     

福建溪源头伟晶岩及围岩中的云母特征

作者对福建溪源头稀有金属花岗伟晶岩及其围岩中的40余个云母样品进行了成分、物性、结构及热性质的综合研究。溪源头伟晶岩之不同组合带中产出的云母均为2M_1型含铷白云母,云母中含铷、铯而贫锂、贫氟。云母斜长变粒岩中的白云母为含铁白云母。其中钛、镁含量偏高。石英云母片岩中之3T铝黑鳞云母的八面体阳离子占位介于二八面体和三八面体之间。该云母以富稀碱元素及挥发分为其特征。溪源头云母的成分及种属反映了形成它的地质环境特点,与围岩性质及成矿类型有关,可作为稀有金属伟晶岩矿床的标型矿物,可以用作找矿标志。     

浙东南吴小垟矿床晚白垩世铌成矿特征及其找矿指示意义

稀有金属铌钽在我国华南存在多时代成矿特征,前人对其最晚成矿期晚白垩世成矿事件报道较少。本文以浙东南的吴小垟铌矿床为研究对象,结合野外调查、岩石学、矿物原位微区分析和同位素年代学等研究,确定矿床铌成矿岩体为细粒黑云母花岗岩,成岩成矿年龄分别为89.2±0.8 Ma和86.5±1.0 Ma,揭示了该区存在晚白垩世花岗岩侵位及其相关铌成矿事件。铌除了以独立矿物的形式赋存在铌铁矿、铌铁金红石、铅烧绿石中,还有部分铌赋存于黑云母中。在岩浆-热液作用下,云母类型发生了从铁云母→黑鳞云母→铁锂云母的变化。铁云母Nb含量最高可达1253×10^-6,黑鳞云母-铁锂云母铌含量最高至794×10^-6,黑云母极度富铌的特征,指示该花岗岩具有非常好的铌找矿潜力,富铌黑云母可以作为一种铌钽找矿指示性矿物。综合上述矿物学特征,得出吴小垟矿床存在两阶段铌成矿事件:岩浆期原生铌铁矿族矿物、原生富铌黑云母和铌铁金红石的形成;以及后期热液作用下铌从岩浆和原生含铌矿物中迁移出形成次生的含铌氧化物。     

珠峰地区锂成矿作用: 喜马拉雅淡色花岗岩带首个锂电气石-锂云母型伟晶岩

喜马拉雅淡色花岗岩具有较好的稀有金属成矿前景。珠穆朗玛峰位于该淡色花岗岩带的中部,其中大量的淡色花岗岩和伟晶岩出露,并成为珠穆朗玛重要的岩石组成部分。近期,我们在珠峰前进沟地区发现并采集了锂成矿伟晶岩,在手标本上可以清晰看到浅褐红色的铁锂云母。进一步的全岩地球化学以及矿物学研究表明,前进沟锂成矿伟晶岩为锂电气石-锂云母型伟晶岩,具有稀有金属元素（Be-Nb-Li）含量高、Rb/Sr比值高、Zr/Hf和Nb/Ta比值低等特征。所有的矿物学和地球化学特征都表明该伟晶岩经历了高度的岩浆分异作用。矿物成分上看,云母由铁锂云母演变为锂云母,电气石由黑电气石演变为锂电气石,Fe、Mg含量降低,Li含量升高,这一特征直接指示着演化过程中岩浆成分的变化。这次发现,是首次在该地区发现锂成矿作用,也是我国喜马拉雅首次报道锂电气石-锂云母型伟晶岩的存在。结合珠穆朗玛峰周围（普士拉、热曲）近期发现的锂辉石-透锂长石型伟晶岩,珠穆朗玛地区很可能成为我国重要的一个锂（Li）成矿远景区。

     

滇西地区稀有金属宝石矿床成矿系列成矿规律与找矿方向

本文按矿床成矿系列理论研究方法, 初步厘定了滇西地区与燕山期—喜马拉雅期伟晶岩有关的稀有金属宝石矿床成矿系列及亚系列, 与第四纪表生作用有关的稀有金属矿床成矿系列及亚系列, 研究结果表明本地区在燕山期—喜马拉雅期发生了大规模的中-酸性岩浆侵入活动, 并形成众多的伟晶岩, 发生了重要的岩浆-热液成矿事件, 稀有金属铍、铌、钽、锂、铷、铯等矿产成矿主要与其有关, 构成了特定的稀有金属矿产矿床成矿系列。本文初步总结了滇西地区稀有金属矿产资源及其特征、矿床成矿系列及成矿规律, 分析了找矿潜力, 划分出找矿远景区, 深化了该区稀有金属矿产成矿规律认识。     

稀有金属花岗岩结晶分异过程中铷的富集与成矿:来自江西甘坊岩体的矿物学证据

内容提要:铷的成矿与稀有金属花岗岩密切相关。由于稀有金属花岗岩中普遍存在晚阶段热液蚀变,很难厘清岩浆过程与热液过程,稀有金属成矿起主导作用的是岩浆分异作用,还是热液交代作用,目前的认识尚不清晰。江西甘坊岩体是一个重要的稀有金属成矿区,当前在甘坊岩体内发现了一系列花岗岩型和细晶岩脉型锂铷稀有多金属矿床(点),其稀有金属成矿机制仍不明确。本文选择甘坊岩体内的白果、大港、楠木坑花岗岩型铷矿和富华、同安细晶岩型铷矿为研究对象,采用矿物自动扫描系统、电子探针、LA-ICP-MS等方法对多种花岗岩中的长石类和云母类矿物进行精细结构和成分分析。结果表明:云母类矿物是铷的主要载体(Rb=1683×10^-6～12047×10^-6),长石类矿物中铷含量低,其中钾长石铷含量为1683×10^-6～4051×10^-6,而钠长石几乎不含铷(1.82×10^-6～89.94×10^-6)。富铷锂的云母由白云母经锂多硅白云母和铁锂云母向锂云母转变,其中锂主要通过2Li⁺...     

414富钽花岗岩的蚀变作用及其矿化特征

在毛主席革命路线的指引下,××省冶勘公司地质七队于1969年发现富钽花岗岩矿床.现已查明矿床的主要工业矿物有:富锰铌钽铁矿、细晶石、锂云母、锡石和钠长石;可供利用的元素有:钽、铌、锂、铷、铯和锡.矿床规模较大,品位较高,矿化均匀,可选性良好,适宜露天开采.本文着重介绍矿床蚀变作用及其矿化特征.     

尼日利亚中生代碱性花岗岩和黑云母花岗岩成因及其对锡多金属找矿的指示

尼日利亚中生代环状杂岩中产出丰富的含锡(铌钽)等多金属的花岗岩, 其中与成矿相关且占主体的2种岩石类型是碱性花岗岩和黑云母花岗岩, 前者具有含碱性暗色矿物过碱质特征, 后者具有含黑云母过铝质特征。前人对2种共生的岩石对锡(铌钽)成矿作用可能的制约机制还未深入探讨, 综合分析前人研究资料, 为理解非造山A型花岗岩锡(铌钽)成矿作用提供新视角, 进一步明确找矿方向。2种岩石绝大多数在侏罗纪侵位, 但在同一杂岩体中, 碱性花岗岩锆石结晶普遍稍早于黑云母花岗岩, 且前者分异程度稍弱于后者。碱性花岗岩是起源于富集地幔岩浆在极端分离结晶作用下的产物, 但此过程中有部分地壳物质的混染。过铝质黑云母花岗岩并非与造山型过铝质花岗岩一样来自地壳物质的熔融, 它更可能是来自于碱性花岗岩同一母岩浆演化的另一个混染了更多地壳物质的晚期分支。与俯冲背景的成锡花岗岩一样, 尼日利亚锡多金属富集主要与弱过铝质黑云母花岗岩有关, 受岩浆后期出溶流体的显著影响。碱性花岗岩对锡(铌钽)元素的富集程度, 大致代表了未受出溶流体影响时共生黑云母花岗岩的锡(铌钽)含量。成矿物质来源为泛非基底围岩, 元素的富集成矿主要被分离结晶和流体出溶行为控制。尼日利亚不成矿环状杂岩体中, 黑云母花岗岩和碱性花岗岩的锡(铌钽)含量都偏低, 两者的Sn含量范围为4×10-6~13×10-6; 而对于成矿杂岩体, 两者锡(铌钽)含量基本高于不成矿杂岩体, 但其中与成矿密切相关的黑云母花岗岩锡(铌钽)含量反而较碱性花岗岩偏低, 其中碱性花岗岩Sn含量范围为21×10-6~205×10-6, 黑云母花岗岩Sn含量范围为10×10-6~62×10-6, 表明熔体中成矿元素含量高低及后期流体出溶是决定能否成矿的关键。因此, 高锡(铌钽)含量杂岩体中具有较低Sn含量的黑云母花岗岩是寻找锡多金属矿的第一选择。     

In situ analyses of micas in the Yashan granite,South China: Constraints on magmatic and hydrothermal evolutions of W and Ta–Nb bearing granites

Most rare-metal granites in South China host major W deposits with few or without Ta–Nb mineralization. However, the Yashan granitic pluton, located in the Yichun area of western Jiangxi province, South China, hosts a major Nb–Ta deposit with minor W mineralization. It is thus important for understanding the diversity of W and Nb–Ta mineralization associated with rare-metal granites. The Yashan pluton consists of multi-stage intrusive units, including the protolithionite (-muscovite) granite, Li-mica granite and topaz–lepidolite granite from the early to late stages. Bulk-rock REE contents and La/Yb ratios decrease from protolithionite granite to Li-mica granite to topaz–lepidolite granite, suggesting the dominant plagioclase fractionation. This variation, together with increasing Li, Rb, Cs and Ta but decreasing Nb/Ta and Zr/Hf ratios, is consistent with the magmatic evolution. In the Yashan pluton, micas are protolithionite, muscovite, Li-mica and lepidolite, and zircons show wide concentration ranges of ZrO₂, HfO₂, UO₂, ThO₂, Y₂O₃ and P₂O₅. Compositional variations of minerals, such as increasing F, Rb and Li in mica and increasing Hf, U and P in zircon are also in concert with the magmatic evolution from protolithionite granite to Li-mica granite to topaz–lepidolite granite. The most evolved topaz–lepidolite granite has the highest bulk-rock Li, Rb, Cs, F and P contents, consistent with the highest contents of these elements and the lowest Nb/Ta ratio in mica and the lowest Zr/Hf ratio in zircon. Ta–Nb enrichment was closely related to the enrichment of volatile elements (i.e. Li, F and P) in the melt during magmatic evolution, which raised the proportion of non-bridging oxygens (NBOs) in the melt. The rims of zoned micas in the Li-mica and topaz–lepidolite granites contain lower Rb, Cs, Nb and Ta and much lower F and W than the cores and/or mantles, indicating an exotic aqueous fluid during hydrothermal evolution. Some columbite-group minerals may have formed from exotic aqueous fluids which were originally depleted in F, Rb, Cs, Nb, Ta and W, but such fluids were not responsible for Ta–Nb enrichment in the Yashan granite. The interaction of hydrothermal fluids with previously existing micas may have played an important role in leaching, concentrating and transporting W, Fe and Ti. Ta–Nb enrichment was associated with highly evolved magmas, but W mineralization is closely related to hydrothermal fluid. Thus these magmatic and hydrothermal processes explain the diversity of W and Ta–Nb mineralizations in the rare-metal granites.     

一种特殊类型的云英岩:湘南香花岭地区癞子岭云英岩成岩成矿特征

癞子岭岩体具有极好的垂向分带性,从下部到顶部包括了花岗岩、云英岩和伟晶岩,其中云英岩以其厚度巨大,云母类型属于铁锂云母,黄玉含量高,W-Sn-Nb-Ta含量高,而区别于其他地区云英岩。通过对癞子岭云英岩进行岩石学、地球化学和矿物学的研究,本文得出:癞子岭云英岩是高硅的强过铝质岩石类型,全碱含量低(3~4.3 wt%),富集挥发组分,全岩Zr/Hf(~8)和Nb/Ta(~1.7)比值低。造岩矿物铁锂云母中Nb(~74×10~(-6))、Ta(~66×10~(-6))、W(~23×10~(-6))、Sn(~75×10~(-6))等成矿元素含量较高。副矿物锆石自形且成分均一,含有HfO_2约10 wt%,Zr/Hf比值最低为5,与云英岩下部的癞子岭钠长花岗岩中的锆石成分有连续过渡的关系。这些特征与南岭地区高演化稀有金属花岗岩或伟晶岩相当,体现了相近的演化程度。癞子岭云英岩中有明显的Nb-Ta-W-Sn成矿作用发生,主要形成铌铁矿族矿物、锡石和黑钨矿,成分和结构均具有岩浆成因特征。花岗质熔体中含有大量挥发组分Li和F,结晶出黄玉和Li-F云母,F在稀有金属的成矿作用和云英岩的成岩过程中发挥了非常重要的作用,成矿作用发生在岩浆演化的晚期并伴随有流体作用。因此,云英岩可能是钠长花岗岩高度分异演化之后的特殊产物,这为研究花岗岩岩浆-热液体系成岩成矿过程提供了新的窗口。     

New data on REE and rare-metal mineralization in pegmatites of the Slyudyanogorsk muscovite deposit in the Southern Urals

The Slyudyangorsk muscovite deposit in the southern Urals was explored and mined in 1926–1957. By the mid-1950s, 104 veins of quartz–feldspar pegmatites including 21 muscovite-bearing veins have been found. Pegmatites with giant black Y-bearing epidote crystals are crosscut by veins with giant muscovite crystals, which, in turn, are intersected by veins of two-mica–quartz–two-feldspar pegmatites with rare-metal and REE mineralization. Microprobe data on compositions of complex Ti–Ta–Nb oxides [fergusonite-(Y), samarskite-(Y), euxenite-(Y), polycrase-(Y), columbite-(Fe), pyrochlore supergroup] are characterized, as well as of uraninite, ilmenorutile, scheelite, Y-bearing epidote, certain sulfides and rock-forming minerals from the Slyudyanogorsk deposit. The morphology and interrelation of minerals indicate that they are the result of crystal growth in cavities rather than of metasomatic replacement of gneisses, as has been suggested earlier. Thus, it is more promising for rare-metal and REE minerals in the Slyudorudnik area to be found in igneous rocks (granitic muscovite–quartz–feldspar pegmatites with the Nb–Ta–Ti–Y–U–W–Mo mineralization) than in metasomatic rocks.     

Rare-metal pegmatites of Wamba,central Nigeria - their formation in relationship to late Pan-African granites

he Sn-(Nb, Ta) mineralization of the Wamba field (central Nigeria) occurs in muscovite-quartz-microcline pegmatites, which are related to the late-orogenic Pan-African (f 550 Ma) "Older Granites". The emplacement of granites and pegmatites was controlled by late Pan-African shear tectonics. The granitoid magmatism was multiphase and has produced peraluminous biotite granite, biotite-muscovite granite, and muscovite granite plutons. Sodic metasomatism has altered highly evolved granite cupolas and many of the pegmatite dikes. The pegmatitic mineralization of predominantly cassiterite is closely associated with albitization. Chemical data of granites and granitic and pegmatitic muscovites show that Rb, Cs, Sn, Nb, and Ta are enriched during both magmatic and postmagmatic evolution, with highest contents of these elements in early muscovites of the albitized and mineralized pegmatites. Trace-element chemistry of the pegmatitic muscovites reveals a chemical zonation of the pegmatite field related to the late-orogenic shear system.     

伟晶岩型锂矿床研究现状及其在中国西部的找矿前景

锂现为全球战略性关键金属矿产,花岗伟晶岩型锂矿是锂资源的重要类型之一,也是当前国际矿床学的研究热点。花岗伟晶岩划分为LCT（Li–Cs–Ta）、NYF（Nb–Y–F）及二者混合的LCT+NYF型,其中LCT型伟晶岩富集稀有元素Li、Rb、Cs、Be、Ga、Sn、Ta、Nb及B、P、F等助熔剂,通常与伸展背景下的晚造山和造山后阶段过铝质S型花岗岩具有成因联系。笔者分析了全球伟晶岩型锂矿床的时空分布特征,发现锂矿成矿事件主要发生在超大陆会聚造山作用的中晚期。研究表明中国花岗伟晶岩型锂矿空间分布相对集中,主要分布在9个锂成矿带,成矿期以三叠纪为主。花岗质岩浆结晶分异和下地壳物质低程度的部分熔融是伟晶岩两种主要的形成方式。稀有金属伟晶岩的成矿机制主要有分离结晶作用、岩浆不混溶、超临界流体和组成带状纯化。总结分析了中国西部西昆仑、川西松潘–甘孜、阿尔泰等3个典型伟晶岩型锂矿带的的成矿特点、分布特征、研究进展及找矿前景,并提出了构造–岩浆–变质–成矿的耦合关系是制约锂成矿过程和富集规律的关键科学问题。     

陕西丹凤富铷伟晶岩中褐钇铌矿矿物学及地球化学特征

东秦岭的商南—丹凤地区分布着众多含稀有金属矿化的花岗伟晶岩,在该地区的富铷花岗伟晶岩中首次鉴定出褐钇铌矿,其主要产出于富石榴子石的微斜长石花岗伟晶岩中,多与石榴子石、锆石、磷钇矿、铌钽铁矿等副矿物伴生,为花岗质岩浆晚期结晶产物.电子探针分析表明,褐钇铌矿除了含有Y、Nb、REE、Ta、Ti等主要元素,还含有较高含量的放...     

The Zr/Hf ratio as a fractionation indicator of rare-metal granites

The Zr-Hf geochemical indicator, i.e., the Zr/Hf ratio (in wt %) in granitic rocks is proposed to be used as the most reliable indicator of the fractionation and ore potential of rare-metal granites. It was empirically determined that the fractional crystallization of granitic magma according to the scheme granodiorite → biotite granite → leucogranite → Li-F granite is associated with a decrease in the Zr/Hf ratio of the granites. The reason for this is the stronger affinity of Hf than Zr to granitic melt. This was confirmed by experiments on Zr and Hf distribution between granitic melt and crystals of Hf-bearing zircon (T = 800°C, P= 1 kbar). The application of the Zr/Hf indicator was tested at three classic territories of rare-metal granites: eastern Transbaikalia, central Kazakhstan, and the Erzgebirge in the Czech Republic and Germany. The reference Kukul’bei complex of rare-metal granites in eastern Transbaikalia (J₃) is characterized by a uniquely high degree of fractionation of the parental granitic melt, with the granites and their vein derivatives forming three intrusive phases. The biotite granites of phase 1 are barren, the leucogranites of phase 2 are accompanied by greisen Sn-W mineral deposits (Spokoininskoe and others), and the final dome-shaped stocks of amazonite Li-F granites of phase 3 host (in their upper parts) Ta deposits of the “apogranite” type: Orlovka, Etyka, and Achikan. The Kukul’bei Complex includes also dikes of ongonites, elvanes, amazonite granites, and miarolitic pegmatites. All granitic rocks of the complex are roughly coeval and have an age of 142±0.6 Ma. The Zr/Hf ratio of the rocks systematically decreases from intrusive phase 1 (40–25) to phases 2 (20–30) and 3 (10–2). Compared to other granite series, the granites of the Kukul’bei Complex are enriched in Rb, Li, Cs, Be, Sn, W, Mo, Ta, Nb, Bi, and F but are depleted in Mg, Ca, Fe, Ti, P, Sr, Ba, V, Co, Ni, Cr, Zr, REE, and Y. From earlier to later intrusive phases, the rocks become progressively more strongly enriched or depleted in these elements, and their Zr/Hf ratio systematically decreases from 40 to 2. This ratio serves as a reliable indicator of genetic links, degree of fractionation, and rare-metal potential of granites. Greisen Sn, W, Mo, and Be deposits are expected to accompany granites with Zr/Hf < 25, whereas granites related to Ta deposits should have Zr/Hf < 5.     

Geochemistry of lepidolitic granitoids from the Mungutiyn Tsagaan Durulj occurrence (central Mongolia)

We studied the geologic position, geodynamic setting, petrology, and geochemistry of veined lepidolitic granitoids from the Mungutiyn Tsagaan Durulj (MTD) occurrence (central Mongolia), found within the area of Mesozoic intraplate rare-metal magmatism. It has been established that their trace-element enrichment resulted from the intense effect of fluids rich in F, K, Li, Rb, Cs, Sn, Be, and W, which arrived from a deep magma chamber of rare-metal granitic melts, on leucogranites with originally weak rare-metal mineralization. Very high contents of F, rare alkali metals, Sn, Be, and W, characteristic of MTD granitoids, are close only to those in greisens of rare-metal granites and topaz-lepidolite-albitic pegmatites. The difference from the greisens in each case might be due to the features of the original rocks. The difference between the greisenized MTD leucogranites and the topaz-lepidolite-albitic pegmatites is more radical: Along with evident petrographic distinctions, it includes an evolution trend toward the albite norm decrease, not typical of Li–F igneous rocks; rock shearing and gneissosity, which must have contributed to their chemical transformation according to this trend; and stably lower contents of Nb and Ta (trace elements which usually accumulate during crystallization fractionation of F–Li granitic melts and are poorly soluble in magmatic fluids). The greisenized MTD granitoids are not only high-grade rare-metal ores of Li, Rb, F, and Sn but are also regarded as an indicator of a deep concealed pluton of rare-metal granites.     

Geochemistry of K‐feldspar and Muscovite in Rare‐element Pegmatites and Granites from the Totoral Pegmatite Field,San Luis,Argentina

The geochemistry of K‐feldspar for K, P, Sr, Ba, Rb, Cs, Ga, and of muscovite for the same elements plus Nb and Ta, was used for proving the parental relationships of S‐type granites and LCT (Li, Cs, Ta) rare‐element pegmatites in the southernmost pegmatitic field of the Pampean pegmatite province in Argentina. The variation of K/Rb‐Cs, K/Cs‐Rb, K/Rb‐Rb/Sr, K/Rb‐Ba in K‐feldspar from the granites and pegmatites show that they form an association with the evolutional sequence: granites → barren‐ to transitional pegmatites → beryl type, beryl‐columbite‐phosphate pegmatites → complex type of spodumene subtype pegmatites → albite‐spodumene type → albite type pegmatites. This sequence reflects the regional distribution of the different magmatic units. The Ta‐Cs diagram for muscovite reveals that none of the studied pegmatites exceed the threshold established in previous studies for being considered with important tantalum oxide mineralization. The granites and pegmatites constitute a rare‐element pegmatitic field in which different magmatic units form a continuous fractionation trend, extended from the less evolved granitic facies to the most geochemically specialized pegmatites     

Mineralogical and chemical evolution of tantalum–(niobium–tin) mineralisation in pegmatites and granites. Part 2: Worldwide examples (excluding Africa) and an overview of global metallogenetic patterns

Columbite-group minerals (CGM) account for the majority of the production of tantalum, an important metal for high-technology applications. Along with other Ta–Nb oxides such as tapiolite, wodginite, ixiolite and pyrochlore supergroup minerals, CGM are recovered from rare-metal granites and granitic rare-element pegmatites. In this paper mineralogical and geochemical data with a focus on CGM, tapiolite, wodginite and ixiolite are presented for rare-element granites and pegmatites from worldwide occurrences except Africa that has been covered in a previous contribution (Melcher et al., 2015). Major and trace element data of the Ta–Nb oxides are presented and compared for a total of 25 granite/pegmatite provinces, and one carbonatite for comparison. Based on CGM compositions, the data allow to distinguish between various subgroups of Li–Cs–Ta (LCT)-family pegmatites, Nb–Y–F (NYF)-family pegmatites, mixed LCT–NYF pegmatites, and rare-element granites.Each period of Ta-ore formation in Earth history is characterised by peculiar mineralogical and geochemical features. Some of the largest and economically most important rare-element pegmatite bodies are located within Archean terrains and intruded ultramafic and mafic host rocks (e.g., Tanco/Canada, Wodgina and Greenbushes/Western Australia, Kolmozero/Kola). They are highly fractionated, of LCT affinity throughout and yield complex mineralogical compositions. The variety of minor and trace elements incorporated attests to a rather insignificant role of the immediate host rocks to their geochemical signature and rather points to the significance of the composition of the underlying crustal protoliths, internal fractionation and the processes of melt generation. Many of the Archean pegmatites carry significant Li mineralization as spodumene, petalite, and amblygonite, and all of them are also characterised by elevated Li in CGM. In addition, Sb and Bi are important trace elements, also reflected by the occasional presence of stibiotantalite and bismutotantalite. REE_N patterns of CGM are dominated by the MREE or HREE, and range from very low to high total REE concentrations. Negative Eu anomalies are omnipresent. Scandium contents are also highly variable, from very high (Tanco) to very low concentrations (Wodgina, Kolmozero).A second period of worldwide pegmatite formation was in the Paleoproterozoic. All CGM analysed derive from LCT-family pegmatites except samples from the Amazonas region where Ta is mined from rare-metal granites at Pitinga. Pegmatites intruded highly variable lithologies including metasediments, metabasites, gneiss, granite and quartzite within a variety of structural and paleogeographic settings; however, most of them are syn- to post-orogenic with respect to major Paleoproterozoic orogenic events. Minor and trace element signatures are similar to CGM from Archean pegmatites. Some are characterised by considerable REE enrichment (São João del Rei/Brazil; Amapá/Brazil; Finnish Lapland/Finland), whereas others have normal to low total REE concentrations (Black Hills/USA, Bastar/India). Examples with high REE commonly are enriched in Sc and Y as well, and are often transitional to NYF-family pegmatites.The Mesoproterozoic period is comparatively poor in rare-element pegmatites and rare-metal granites. Mineralogical and chemical attributes of ixiolite–wodginite, tapiolite, CGM and rutile from placer material in Colombia point to an unusual pegmatite source of NYF affinity, yielding high total REE, Sc and Th at low Li and Bi. REE patterns have typical negative Eu and Y anomalies.A third major period of pegmatite formation was the Early Neoproterozoic at around 1 Ga, documented in the Grenvillian (North America), the Sveconorwegian (northern Europe) and the Kibaran in central Africa. CGM are present in numerous, mostly small pegmatites, although larger examples also occur (e.g., Manono in the D.R. Congo; Melcher et al., 2015). Pegmatite fields often display a zonal arrangement of mineralised pegmatites with respect to assumed “fertile” parent granites. They intrude metasediments, metabasites, gneiss and granite of middle to upper crustal levels and display a variety of mineralogical and chemical characteristics. Pegmatites of the Sveconorwegian and Grenville domains are usually of the NYF type and CGM are characterised by elevated Y, REE, Th and Sc. In contrast, the pegmatites of central (Kibara Belt) and southwestern Africa (Orange River Belt) are commonly of LCT affinity carrying spodumene, beryl and cassiterite (Melcher et al., 2015). These CGM have elevated conce ntrations of Li, Mg, Sn and Hf. Total REE concentrations are low except for the Sveconorwegian, and exhibit a variety of shapes in normalised diagrams.The fourth major pegmatite-forming event coincides with amalgamation of Gondwana at the Neoproterozoic/Paleozoic boundary around 550 Ma ago. This event is omnipresent in Africa (“Panafrican”) and South America (“Brasiliano event” documented in the Eastern Brazilian pegmatite and Borborema provinces). Pegmatites often intruded high-grade metamorphic terrains composed of metasediments including schist, marble, quartzite, as well as gneiss, amphibolite, ultramafic rocks, and granite. Within the Neoproterozoic, rare-metal granites of NYF affinity are locally abundant. Pegmatites show both LCT and NYF affinities, and mixed types occur in Mozambique. The Alto Ligonha and Madagascar provinces are characterised by abundant REE and Sc both within Ta–Nb-oxides and as separate mineral phases. Notably, some pegmatite provinces are almost devoid of cassiterite, whereas others carry cassiterite in economic amounts.In the Phanerozoic (younger than 542 Ma), pegmatites formed at all times in response to orogenetic processes involving various continents and terranes during the long-time amalgamation of Pangea and the Alpine orogenies. Whereas some activity is related to the Pampean, Acadian and Caledonian orogenies, the Variscan/Hercynian and Alleghanian orogenies are of utmost importance as manifested in pegmatite formation associated with Sn–W mineralised granites in central and western Europe as well as in the Appalachians. Most of the Variscan and Alleghanian pegmatites are of LCT affinity, although NYF and some mixed types have been described as well. Variscan pegmatite formation culminated at ca. 330 to 300 Ma, whereas Alleghanian pegmatites range in age from about 390 Ma to about 240 Ma. Most are syn- to post-orogenic and were emplaced at different crustal levels and into a variety of host rocks. Degree of fractionation as well as minor and trace element geochemistry of Ta–Nb oxides are rather variable and cover the complete field of CGM compositions. REE patterns are characterised by prominent negative Eu anomalies.Some Mesozoic and Cenozoic pegmatites and rare-metal granites from Southeast Asia and the Russian Far East are included in the compilation. Rare-metal granites of the Jos Plateau (Nigeria) were previously investigated (Melcher et al., 2015). The proportion of NYF pegmatites and rare-metal granites in the Mesozoic is striking, i.e. illustrated by Jos, Orlovka, Ulug Tanzek as well as the southeast Asian deposits related to tin granites. CGM from these areas are invariably rich in REE, Sc, Y and Th. In all rare-metal granites, Ta–Nb oxides are characterised by high total REE concentrations and both, negative Eu and Y anomalies in chondrite-normalised REE diagrams.Although constituting a vastly different magmatic system compared to rare metal pegmatites and granites, we included the Upper Fir carbonatite from the Canadian Cordillera, for comparison, because it is characterised by unusal high Ta contents. As expected, the CGM differ from the pegmatitic CGM by having high Mg and Th, and low U concentrations in columbite-(Fe) and lack an Eu anomaly. However, they also show similarities to primitive CGM from rare metal pegmatites of the NYF family in terms of the REE pattern and the increase in #Ta and #Mn towards the margins of the CGM. Our findings support recent results presented in Chudy (2014) indicating that the Ta enrichment in some carbonatites might be attributed to magmatic processes and conditions that are similar to the pegmatitic systems.