The occurrences and geochemical characteristics of thorium in iron ore in the Bayan Obo deposit, Northern China

The Bayan Obo deposit in northern China is an ultra-large Fe–REE–Nb deposit.The occurrences,and geochemical characteristics of thorium in iron ores from the Bayan Obo Main Ore Body were examined using chemical analysis,field emission scanning electron microscopy,energy dispersive spectrometer,and automatic mineral analysis software.Results identified that 91.69%of ThO2 in the combined samples was mainly distributed in rare earth minerals(bastnaesite,huanghoite,monazite;56.43%abundance in the samples),iron minerals(magnetite,hematite,pyrite;20.97%),niobium minerals(aeschynite;14.29%),and gangue minerals(aegirine,riebeckite,mica,dolomite,apatite,fluorite;4.22%).An unidentified portion(4.09%)of ThO2 may occur in other niobium minerals(niobite,ilmenorutile,pyrochlore).Only a few independent minerals of thorium occur in the iron ore samples.Thorium mainly occurs in rare earth minerals in the form of isomorphic substitution.Analyses of the geochemical characteristics of the major elements indicate that thorium mineralization in the Main Ore Body was related to alkali metasomatism,which provided source material and favorable porosity for hydrothermal mineralization.Trace elements such as Sc,Nb,Zr,and Ta have higher correlation coefficients with thorium,which resulted from being related to the relevant minerals formed during thorium mineralization.In addition,correlation analysis of ThO2 and TFe,and REO and TFe in the six types of iron ore samples showed that ThO2 did not always account for the highest distribution rate in rare earth minerals,and the main occurrence minerals of ThO2 were closely related to iron ore types.

Formation of the Giant Bayan Obo Deposit by ca. 1.3 Ga Carbonatitic Magmatism and its Link with Continental Rifting in the Columbia Supercontinent

The Bayan Obo in the northern North China Craton is the world’s largest light rare earth element(LREE)deposit and the largest niobium(Nb)and thorium(Th)deposit in China(e.g.,Wu,2008;Kynicky et al.,2012;Ling et al.,

Metallogenic Correlations for the Fe-Nb-REE Mineralization in the West Mine of the Bayan Obo Deposit, Inner Mongolia, China

The West Mine of the Bayan Obo deposit, located in the northern-central part of Inner Mongolia, China, is enriched in Nb, rare earth elements and iron （Nb-REE-Fe） mineral resources. This paper presents a combined method to explore metallogenic correlation of the Nb-REE-Fe mineralization at the Bayan Obo West Mine. The method integrates factor analysis and Back Propagation （BP） neural network technology into processing and modeling of geological data. In this study, the Nb and REE contents of samples were transformed into discrete values to analyze the correlations among the metallogenic elements. The results show weak mineralization correlations between Nb and REEs. Nb and U are closely related in the geochemical patterns, while Fe is closely related to both Th and Mn. LREEs are an important factor for the mineralization of the Bayan Obo deposit, while Fe and Nb can be considered as the results of passive mineralization. On the basis of a metallogenic correlation analysis, the factors affecting the Fe-REE-Nb mineralization were extracted, and the Nb mineralization model was established by the BP neural network. Based on the BP neural network data computing, the variability of the Nb concentration displays a coupled multi-factor nonlinear relationship, which can be used to reveal the inherent metallogenic elemental regularities and predict the degree of element mineralization enrichment in the mining area.

Fundamental Research on Comprehensive Exploitation and Utilization of Paragenetic Fluorite in Bayan Obo deposit of Inner Mongolia,China

Bayan Obo deposit in Inner Mongolia,China is not only the largest Iron-LREE-niobium deposit known in the world but also a giant fluorite deposit.Banded and streaky fluorite-rich REE-iron ores,bastnasiteapatite -pyroxene-fluorite ores,high-Fe,REEs,and fluorite ores,monazite(bastnaesite)-fluorite(low-Fe, high REE) ores etc.are widely disseminated in the Main and the East ore bodies.In 1985,proven

Carbon and Oxygen Isotopic Characteristics of REE-Fluorocarbonate Minerals and Their Genetic Implications, Bayan Obo Deposit,Inner Mongolia, China

REE-fluorocarbonates as major REE minerals in the Bayan Obo deposit, the largestREE deposit in the world, were analyzed for their stable isotopic compositions. The δ13C andδ18O values of huanghoite, cebaite and bastnaesite from late-stage veins vary in the ranges of -7. 8 - - 4. 0‰ and 6. 7 - 9. 4‰ respectively. These data are relatively similar tO those ofbastnaesites from banded ores: δ13C - 5. 6 - - 5. 2‰ and δ18O 3. 6 - 5. 5‰ The REEfluorocarbonates from both late-stage veins and banded ores are characterized by lower δ13C andδ18O values, especially the δ18O values of bastnaesites from banded ores. Compared with them,the disseminated bastnaesits the dolomite-type ores possess rather high δ13C and δ18O values, i.e., - 2. 1 - - O. 4‰ and 8. 6 - 12. 9‰ respectively. The high values are typical of thesedimentary host dolomite rocks as well as of the dolomite-type ores. The carbon and oxygenisotopic characteristics of REE fluorocarbonate minerals provide new evidence for the hypothesison the origin of Bayan Obo deposit-epigenetic hydrothermal metasomatism.

The giant Bayan Obo REE-Nb-Fe deposit,China:Controversy and ore genesis

Bayan Obo ore deposit is the largest rare-earth element（REE） resource,and the second largest niobium（Nb） resource in the world.Due to the complicated element/mineral compositions and involving several geological events,the REE enrichment mechanism and genesis of this giant deposit still remains intense debated.The deposit is hosted in the massive dolomite,and nearly one hundred carbonatite dykes occur in the vicinity of the deposit.The carbonatite dykes can be divided into three types from early to late：dolomite,co-existing dolomite-calcite and calcite type,corresponding to different evolutionary stages of carbonatite magmatism based on the REE and trace element data.The latter always has higher REE content.The origin of the ore-hosting dolomite at Bayan Obo has been addressed in various models,ranging from a normal sedimentary carbonate rocks to volcano-sedimentary sequence,and a large carbonatitic intrusion.More geochemical evidences show that the coarse-grained dolomite represents a Mesoproterozoic carbonatite pluton and the fine-grained dolomite resulted from the extensive REE mineralization and modification of the coarse-grained variety.The ore bodies,distributed along an E-W striking belt,occur as large lenses and underwent more intense fluoritization and fenitization.The first episode mineralization is characterized by disseminated mineralization in the dolomite.The second or main-episode is banded and/or massive mineralization,cut by the third episode consisting of aegirinerich veins.Various dating methods gave different mineralization ages at Bayan Obo,resulting in long and hot debates.Compilation of available data suggests that the mineralization is rather variable with two peaks at～1400 and 440 Ma.The early mineralization peak closes in time to the intrusion of the carbonatite dykes.A significant thermal event at ca.440 Ma resulted in the formation of late-stage veins with coarse crystals of REE minerals.Fluids involving in the REE-Nb-Fe mineralization at Bayan Obo might be REE-F-C02-NaCI-H20 system.The presence of REE-carbonates as an abundant solid in the ores shows that the original ore-forming fluids are very rich in REE,and therefore,have the potential to produce economic REE ores at Bayan Obo.the Bayan Obo deposit is a product of mantle-derived carbonatitic magmatism at ca.1400 Ma,which was likely related to the breakup of Columbia.Some remobilization of REE occurred due to subduction of the Palaeo-Asian oceanic plate during the Silurian,forming weak vein-like mineralization.

Re-interpretation of zircon date in a carbonatite dyke at the Bayan Obo giant REE-Fe-Nb deposit,China

Recent ce-valuation of the dating of the carbonatite dykes associated with the REE-Re-Nb giant deposit at Bayan Obo

Proterozoic anorogenic magmatic rocks and their constraints on mineralizations in the Bayan Obo deposit region, Inner Mongolia

The Proterozoic anorogenic magmatic rocks are well developed in the Bayan Obo deposit region. They are composed of trachyte, magnesioarfvedesonite-feldspatite, potash-rhyolite, dacite, rhyolite, quartz porphyry and trachy basalt. A lot of high-K diabase veins (dykes) are also found. These anorogenic magmatic rocks are derived from the mantle. They have lowerεNd (t) (4.52-5.88) with T(Nd DM)=1.54-1.92 Ga. Their Nd isotopic compositions and T(Nd DM)are consistent with those of ores, implying that the ore-forming materials were derived from these anorogenic magmatic rocks. The zircon U-Pb ages of the rocks are 1.8 Ga. Research results indicate that the Bayan Obo Group was replaced by the hydrothermal solution related to the anorogenic magmatic rocks, resulting in the formation of the deposit.

白云鄂博主、东矿三个剖面地球化学特征及其研究意义

近年来关于白云鄂博Nb-REE-Fe矿床H8岩体火成水成归属的争论已渐息,而矿床成矿过程以及REE富集机制仍是学术界关注的热点。文章对白云鄂博矿床白云石碳酸岩体、霓长岩化蚀变带、尖山组板岩3个典型剖面开展系统的岩石地球化学工作,发现赋矿碳酸岩、霓长岩、铁矿石微量与稀土元素配分模式具有相似性,靠近H8岩体的尖山组板岩往往有着更高的稀土元素含量,以及与成矿碳酸岩相近的微量元素配分模式。区内各类岩石单元稀土元素分馏明显,全岩La_(N)/Nd_(N)比值的变化规律显示,H8岩体内部比边缘更富La,边缘比岩体内部更富Nd。通过岩(矿)石薄片BSE图像结合矿物电子探针分析显示,H8岩体内的稀土元素矿物(主要是独居石、氟碳铈矿等)可分为2组,一组相对富La,呈半自形-他形,星点状分布;另一组相对富Nd,呈他形细粒,脉状分布。两组矿物中不同元素的富集特征可能代表了结晶过程中流体环境的改变。上述实验结合地质勘查结果表明,白云鄂博矿床初始成矿物质的起源与H8碳酸岩一致,均来源于中元古代碳酸岩岩浆活动,而不同类型的稀土元素矿物对应了白云岩成岩阶段与萤石矿化阶段两个不同的稀土矿化阶段。

内蒙古白云鄂博矿床年代学特征及其地质意义

内蒙古白云鄂博矿床是世界罕见的特大型REE-Nb-Fe多金属共生矿床,由于经历了复杂的区域地质演化历史,至今仍对稀土成矿时代认识不一。基于前人的同位素年代学研究成果,结合矿床地质特征对稀土成矿时代进行讨论。研究表明,白云鄂博矿区经历了华北克拉通2.5~1.8 Ga的前寒武纪构造演化过程;哥伦比亚超大陆裂解的最后阶段,约1.3 Ga在白云鄂博裂谷形成了巨型稀土矿床,与同期碳酸岩墙形成时代一致;受后期华北克拉通北缘古亚洲洋俯冲碰撞造山的影响,白云鄂博地区引发热液交代活动,形成了晚期稀土矿脉和原有稀土矿物的重结晶,导致H 8赋矿白云岩同位素系统受到扰动,呈现出多期次(1.0~0.2 Ga)的同位素年龄结果。总之,白云鄂博是一个在约1.3 Ga裂谷成矿并叠加了加里东和海西2期热扰动事件的巨型稀土矿床。

白云鄂博中元古代铌成矿特征及可利用性评价

铌是我国被“卡脖子”的战略性矿产资源,铌资源找矿和综合开发利用迫在眉睫。白云鄂博是我国最大的伴生铌矿床,占我国铌资源储量的95%。但由于白云鄂博Fe-REE-Nb矿床多元素共伴生,其矿石类型复杂,铌矿物种类众多,嵌布粒度较细,单体解离度低,分散程度高等的特殊性,导致铌资源综合利用率较低。

白云鄂博矿床钍富集过程及空间分布规律

白云鄂博矿床为一特大型Fe-REE多金属矿床,同时伴生有巨量的钍资源。然而,目前开发利用的矿种主要是铁和稀土资源,钍资源利用率几乎为零。查明矿床中钍资源的赋存状态和分布规律及揭示钍资源的富集过程及机制是今后钍资源开发利用的重要基础。本文依托近些年的系统采样及分析测试成果,对白云鄂博主、东、西矿区570个样品进行了详细的矿物学观察和全岩化学分析,在不同类型矿石中识别出以硅钍石为主的独立含钍矿物,硅钍石除少量呈现被稀土矿物包裹现象外,通常以细脉状穿插于稀土矿物内部,显示其明显滞后富集的特点。矿区ThO_(2)平均品位达0.0322%,高出地壳钍克拉克值(9.6×10^(-6))30多倍,各种矿石类型中ThO_(2)含量具有明显的差别,在云母型、闪石型、霓石型和萤石型矿石中具有高含量Th O_(2),而白云石型矿石中ThO_(2)含量较低,指示矿区钍矿化主要形成于碱性热液交代和萤石化阶段。此外矿区随深度增加钍矿化作用加强,显示出矿床具有良好的钍资源成矿潜力。

白云鄂博矿床磁铁矿成分标型与深部富铁矿体预测

白云鄂博稀土-铌-铁矿床蕴藏着大量的铁资源,其中磁铁矿作为矿石矿物被广泛研究。磁铁矿的矿物标型特征可以指示矿床成因、成矿规律以及深部找矿,但磁铁矿标型矿物学尚未在白云鄂博矿床中普及与应用。本研究使用了22条勘探线全铁数据,利用扫描电镜能谱和电子探针的矿物微区成分测试方法,测试了覆盖600 m×600 m,纵深800 m范围内10条勘探线的45件样品,将白云鄂博矿床中的磁铁矿分为岩浆型和热液型,表明岩浆和热液在白云鄂博矿床中均形成或改造磁铁矿。结合磁铁矿温度计得知,岩浆型磁铁矿,尤其是高温磁铁矿富集的区域,矿床全铁成分更加富集,更容易形成富铁矿体,磁铁矿形成的温度为350~650℃。因此推测,12、13号线的深部东部方向有很大可能形成富铁矿体,可能在深部连接东矿,值得进一步研究与开采。

拉曼Mapping研究霓石型稀土独居石矿物分布特征和取向相位

在地球科学等研究领域自动化分析,逐步取代了传统的光学观察法。然而,这些方法获得结果,过于依赖元素组成到矿物组成的转换。同时,也会破坏掉完整描述矿物材料来源和蚀变历史所需的重要信息。因此,利用合适的检测手段,对分析矿物成矿规律及成因具有重要现实性意义。研究利用拉曼Mapping、光学显微镜、自动矿物分析仪(TIMA)三种技术做对比。对具有代表性霓石型稀土矿物分布特征、化学成分、矿物结构及晶体取向等方面进行研究。通过TIMA与光学显微镜研究结果分析可知,独居石矿物多呈自形-半自形不等粒结构,粒度大小不均约为100~500μm之间,部分颗粒有被磷酸盐溶液交代痕迹,可初步判断独居石矿物经多期成矿;氟碳铈矿物呈细粒状分布较散以不规则颗粒包裹在其他矿物中,具有明显的早期成矿特征;易解石矿物以不规则团块状或放射状集合体,具有明显方向性与方解石形成时间一致。利用拉曼光谱技术在微区进行Mapping扫描,通过数据分析得到独居石矿物[PO4]3-的P—O对称伸缩模式(ν1)与P—O对称弯曲振动模式(ν2)所在峰位面积比值,得到独居石矿物不同生长取向相图。经与独居石矿物光镜特征相结合,进一步证明了浸染状霓石型铁稀土矿石中独居石矿物是多期成矿的事实,成矿期数最少为三期。该发现也为白云鄂博矿床多阶段成矿提供有力证据支撑。此外,该技术也可作为一种快速判断磷酸盐矿物不同生长取向的图像方法。该技术对于碳酸矿物、硫酸盐矿物也同样适用。由此可扩展到多种矿物类型,成为判断矿物多期成矿事实提供了重要依据。也为拉曼Mapping技术应用于复杂矿物的矿物学研究矿物的赋存特征奠定基础。

白云鄂博矿床白云岩的Sm-Nd、Rb-Sr同位素体系

白云鄂博矿床的年龄和成因长期争论。本文报道了白云鄂博矿床白云岩及其组成矿物的Sm-Nd、Rb-Sr同位素分析结果。采自该矿床主、东矿等地的15个白云岩样品的Sm-Nd同位素分析结果呈现一条等时线,等时年龄1273±100(2σ)Ma,INd=0.510919±36(2σ),MSWD1.01。全岩Rb-Sr同位素分析结果分散,不构成等时线。87Rb/86Sr 0～2.092×10-2,87Sr/86Sr 0.70341～0.70541。白云岩矿物的Sm-Nd同位素分析结果给予了与全岩类似的Sm-Nd等时年龄,t=1250±210(2σ)Ma,INd=0.510914±77(2σ),MSWD 0.56。白云鄂博矿床可能是中元古代末期大离子亲石微量元素略为富集地幔源区部分熔融岩浆活动产物。

白云鄂博矿区赋矿“白云质大理岩”成因的稳定同位素证据

内蒙古白云鄂博铁、稀土、铌矿床是举世闻名的超大型稀土矿床。其矿床地质特征和成矿地质环境十分独特 ,在国内外引起广泛注意。关于矿床的成因争论很多 ,其中 ,赋矿“白云质大理岩”的成因最为人们所关注 ,成为争论的焦点。本文在前人工作的基础上补充了S、C、O同位素研究。综合现有资料得出 :“白云质大理岩”的高REE和Nb含量 ,REE分布型式 ,低87Sr/ 86Sr初始比值和接近岩浆岩的Si同位素组成 ,为其岩浆成因提供了证据。“白云质大理岩”中碳酸盐和硅酸盐矿物的高δ18O值及全岩和重晶石硫的δ3 4 S值表明 ,岩石与海水发生过明显的交换作用 ,进一步为岩石的海底火山成因提供了证据。“白云质大理岩”中碳酸盐矿物的δ13 C值也可以用碳酸岩受到海水碳酸盐混染加以解释。由此看来 ,“白云质大理岩”

白云鄂博矿床成因——矿体内霓长岩化成矿作用与赋矿白云岩的联系

通过对组成赋矿白云岩的白云石矿物系统的显微结构和化学成分的研究表明,赋矿白云岩是碳酸岩质次火山岩,因此白云鄂博矿床是与火成碳酸岩有关的矿床。赋矿白云岩属于镁质碳酸岩(MgO>FeO+MnO)和铁质碳酸岩(MgO<FeO+MnO)系列,FeO、MnO和SrO含量高,这与FeO、MnO和SrO含量很低的沉积碳酸岩完全不同。赋矿白云岩的这一特点还表明它来自经历过分异结晶后的白云质碳酸岩浆而不是初始白云质碳酸岩浆。赋矿白云岩复杂的矿物组合表明,其母岩浆是富含F、Cl、P和S这些挥发分以及REE,Na、K和Fe这些元素的。在碳酸岩浆上升和侵位的过程中由于温度压力的降低,碳酸岩浆释放的含上述组分的流体会向上部地壳集中并对其接触的围岩进行交代,这就形成了矿体内呈不对称带状分布的霓长岩化矿石带。在大量的萤石和稀土氟碳酸盐矿物形成以后(其对应于萤石-稀土条带状矿石),流体的成分仍相对富钠和CO_2,钠可以和围岩中的硅结合形成钠辉石,流体较高的比值,有利于稀土的富集,此时形成的钠辉石型矿石的稀土含量是相当高的,仅次于条带状矿石。随着流体继续迁移和交代,流体中CO_2浓度下降而H_2O含量增加,温度也有所下降,但是流体中的钠依然活跃,所以出现了含有结构水的钠闪石,形成了钠闪石型矿石。流体中H_2O的增加,比值的下降,不利于稀土的大量富集,因此,钠闪石型矿石的稀土含量明显低于钠辉石型矿石。这说明,从碳酸岩浆中外逸的流体,在迁移交代围岩的过程中其成分、温度和氧逸度都是有变化的。从初期富CO_2,温度和氧逸度较高,到后期富H_2O,温度和氧逸度都有所降低。不同矿石类型的形成与这种变化有直接的关系。不同矿石类型中的磁铁矿的生成方式虽然不同于白云岩中的磁铁矿,但前者的氧同位素继承了后者的特点,表明了它们的亲缘关系和成因上的联系。稀土分布型式表明,不同矿石类型的稀土分布型式与赋矿白云岩的大体一致,有明显的LREE富集和明显的HREE亏损,且总稀土含量越高,轻重稀土分离程度越高。但是,不同矿石类型在轻稀土含量上有一定程度的差别,表明在霓长岩化过程中轻稀土活动性更强。总之,氟、钠和铁的交代作用在主东矿最强,稀土、铌和铁资源也最为富集,这里的白云岩厚度也最大,表明白云鄂博矿的霓长岩化成矿作用与赋矿白云岩衍生的流体的大量聚集以及流体对围岩广泛强烈的交代作用直接相关。

白云鄂博矿床研究若干问题的探讨

白云鄂博巨型稀土-铌-铁矿床是与火成碳酸岩(即H8)有关的矿床。在碳酸岩岩浆阶段,在其蚀变围岩(霓长岩)中以及晚期的热液阶段都有稀土、铌和铁等的富集。因此,白云鄂博矿床不是单一矿床类型,其涵盖了稀土-铌-铁碳酸岩岩浆型矿床、稀土-铌-铁交代蚀变岩型和热液型矿床,这种复合类型的矿床是十分罕见的,可称之为白云鄂博式矿床。根据已发表的年代数据,白云鄂博大规模碳酸岩的形成时代和伴随的稀土矿化的高峰期在1.3～1.4Ga。加里东构造热事件对本区的影响广泛和强烈,不仅有广泛发育的大型褶皱、冲断层和韧性剪切作用,并伴有广泛的流体交代作用和局部的热液活动,某些稀土矿物的同位素体系受到重置,表现为其Sm-Nd年龄和Th-Pb年龄的不一致。本区的碱性岩在基底杂岩中即有出露,随后在白云鄂博群中和1.3～1.4Ga白云鄂博碳酸岩形成时皆有产出。目前所获资料表明,至少1.3～1.4Ga的碱性杂岩在成因上与碳酸岩有密切的联系。本区基底杂岩显示了白云鄂博地区在2.0Ga左右曾经有一个弧地质体,该区在2.0～1.9Ga间经历了从被动大陆边缘到活动大陆边缘增生碰撞的一个完整的造山过程。

白云鄂博矿床成矿构造环境分析

白云鄂博矿床是世界著名的超大型铁铌稀土矿床,但因为其成因和形成时代的证据复杂多样,其成因、形成时代及其形成的大地构造环境均有多种不同认识。笔者等曾对赋矿白云岩成因、成矿时代及赋矿地层白云鄂博群的年代这两个关键问题进行了系统的地质、地球化学研究,获得了一系列关键证据,并对前人资料进行了系统地梳理,论证了白云鄂博矿床赋矿白云岩为一大型微晶丘,而微晶丘是热水沉积形成;确定其成矿时代及白云鄂博群的年代均为早古生代。本文进一步报道了在与白云鄂博群下部相当的腮林忽洞群中发现了宏体化石海绵和腹足类,在白云鄂博群中发现了与腮林忽洞群中相同的振动液化脉和振动液化角砾岩。从而笔者等认为,白云鄂博矿床成矿和白云鄂博群的沉积环境是早古生代被动大陆边缘。

内蒙白云鄂博矿区H_9中火山岩岩石特征及其意义

白云鄂博矿区Ｈ＿９地层岩石被中外学者长期看作是板岩或页岩，经近期研究发现岩性极为复杂。Ｈ＿９地层岩石是一套呈互层产出的粗面岩、流纹岩、流纹英安岩、变辉绿岩、白云岩、石英岩、黑云母岩、钠闪石－长石岩、钠辉石－长石岩、红柱石－黑云母角岩及碳质绢云板岩等。文中详细论述了这些火山岩石的结构构造、矿物成分和岩石化学成分，以及微量元素。对Ｈ＿９地层中火山岩，尤其是粗面质火山碎屑岩的确定，对了解白云鄂博矿床的成因和白云鄂博群形成的地质背景有重要意义。