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1.
白云鄂博地区碳酸岩脉侵位序列与稀土元素富集机制 总被引：5，自引：2，他引：3
白云鄂博地区发育大量的火成碳酸岩脉。按照矿物组成,碳酸岩脉可分为白云石型、白云石-方解石共存型和方解石型。野外穿插关系表明,白云石型碳酸岩脉形成得早,而方解石型碳酸岩脉形成得晚。白云鄂博地区的碳酸岩浆存在由白云石型到共存型再到方解石型的先后结晶顺序和演化趋势。碳酸岩脉的主量、稀土和微量元素组成特征表明,随着碳酸岩脉中方解石矿物组分的增加,轻稀土元素的含量呈明显富集趋势,而长期的结晶分异作用正是稀土元素,尤其是轻稀土元素在晚期岩浆中强烈富集的内在机制。 相似文献
2.
Geochemical constraints on the genesis of the Bayan Obo Fe-Nb-REE deposit in Inner Mongolia, China 总被引：2，自引：0，他引：2
Trace element and isotopic compositions of carbonate from ore bodies, country rock which hosts the ore bodies (H8 dolomite), a carbonatite dyke exposed in Dulahala near Bayan Obo, and rare earth element (REE)-rich dolomite in Bayan Obo have been determined to understand the genesis of the Bayan Obo Fe-Nb-REE ore deposit, the world’s largest resource of REE. The REE and trace element distribution patterns of samples from the REE-rich carbonatite dykes are identical to those of mineralized carbonate rocks, indicating a genetic linkage between the REE-rich carbonatite and mineralization in this region. By contrast, carbon and oxygen isotopes in the mineralized carbonate varied significantly, δ13C = −7.98‰ to −1.12‰, δ18O = 8.60-25.69‰, which are distinctively different from those in mantle-derived carbonatite. Abnormal isotopic fractionations between dolomite and calcite suggest that these two minerals are in disequilibrium in the carbonatite dyke, ore bodies, and H8 marble from Bayan Obo. This isotopic characteristic is also found in mineralized sedimentary marine micrite from Heinaobao, ∼25 km southeast of the Bayan Obo Fe-Nb-REE ore deposit. These facts imply that the carbonate minerals in the Bayan Obo deposit have resulted from sedimentary carbonate rocks being metasomatised by mantle-derived fluids, likely derived from a REE-enriched carbonatitic magma. The initial Nd isotope values of ore bodies and carbonatite dykes are identical, indicating that ore bodies, carbonatite dykes and veins may have a similar REE source. 相似文献
3.
Flat rare earth element patterns as an indicator of cumulate processes in the Lesser Qinling carbonatites, China 总被引：1，自引：0，他引：1
Cheng Xu Ian H. Campbell Charlotte M. Allen Zhilong Huang Liang Qi Huan Zhang Guishan Zhang 《Lithos》2007,95(3-4):267-278
The Lesser Qinling carbonatite dykes are mainly composed of calcites. They are characterized by unusually high heavy rare earth element concentrations (HREE; e.g. Yb > 30 ppm) and flat to weakly light rare earth element (LREE) enriched chondrite-normalized patterns (La/Ybn = 1.0–5.5), which is in marked contrast with all other published carbonatite data. The trace element contents of calcite crystals were measured in situ by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). Some crystals show reduced LREE from core to rim, whereas their HREE compositions are relatively constant. The total REE contents and chondrite-normalized REE patterns from the cores of carbonate crystals are similar to those of the whole rock. The carbon and oxygen isotopic compositions of calcites fall within the range of primary, mantle-derived carbonatites. The initial Sr isotopic compositions (0.70480–0.70557) of calcites are consistent with an EM1 source or mixing between HIMU and EM1 mantle sources. However these sources cannot produce carbonatite parental magmas with a flat or slightly LREE enrichment pattern by low degrees of partial melting. Analyses of carbonates from other carbonatites show that carbonates have nearly flat REE pattern if they crystallize from a LREE enriched carbonatite melt. This implies that when carbonates crystallize from a carbonatite melt the calcite/melt partition coefficients (D) for HREE are much greater than the D for the LREE. The nearly flat REE patterns of the Lesser Qinling carbonatites can be explained if they are carbonate cumulates that contain little trapped carbonatite melt. Strong enrichment of HREE in the carbonatites may require their derivation by small degrees of melting from a garnet-poor source. 相似文献
4.
《地学前缘(英文版)》2016,7(3)
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. 相似文献
5.
白云鄂博碳酸岩墙的稀土和微量元素地球化学及对其成因的启示 总被引：11，自引：1，他引：11
根据矿物组成白云鄂博矿区的碳酸岩岩可墙可分为白云石型、白云石－方解石共存型和方解石型三种类型。REE和微量元素地球化学表明，这三类碳酸岩岩墙为碳酸岩浆演化不同阶段的产物，白云石型和白云石－方解石共存型对应于早期岩浆阶段，其（La/Nd)n、(La/Yb)n比值随稀土总量的增加而增大，方解石型则对应于碳酸岩浆演化的晚期热液阶段，其稀土总量明显富集，但其（La/Nd)n、(La/Y)n和（La/Yb)n比值随稀土总量的增加却有减小的趋势，热液阶段也是白云鄂博稀土矿化的主要阶段。 相似文献
6.
白云鄂博碳酸岩型REE-Nb-Fe矿床——一个罕见的中元古代破火山机构成岩成矿实例 总被引：16，自引：4，他引：16
白云鄂博碳酸岩型REE-Nb-Fe矿床是世界上最大的稀土矿床。稀土矿石产于整个白云石碳酸岩体和部分脉状碳酸岩中。对比世界上20余个火成碳酸岩地区的特征后发现,白云鄂博地区完全具备国外火成碳酸岩区的地质特征。在岩石、矿石组合上,本区也发育一套碳酸岩+超基性岩+碱性基性岩(含基性熔岩)+碱性岩+稀土矿石+铁矿石组合;在矿物组合上,以白云石为主,方解石次之,伴生一套碱性闪石、长石、霓石、磷灰石、萤石、磁铁矿、稀土矿物组合;在全岩化学成分、微量元素、稀土元素和Sr、Nd、Pb、C、O同位素上,这些岩石具有一定的亲缘关系,有着共同的来源;在岩体的形态与岩石组构上,它们以岩席、岩筒和脉岩的形式出现,并发育有强烈的熔离作用与流动构造;在区域构造上,发育隐伏穹窿构造、岩筒构造和巨型断裂汇聚构造。综合分析上述特征表明:白云鄂博地区具有中元古代破火山机构的痕迹,赋矿白云石碳酸岩体则是顺层侵入的火成碳酸岩体,东矿、主矿可能是一个火山颈构造控矿,而赋矿白云石碳酸岩体西南侧的苏木图矿床则是隐伏岩筒构造控矿。 相似文献
7.
白云鄂博矿区碱性基性岩—碳酸岩岩墙岩石学研究 总被引：8，自引：1，他引：8
白云鄂博地区广泛发育碳酸岩墙 -碱性基性岩墙,通过对其岩石学、矿物学、岩石化学、稀土元素、微量元素的系统研究表明,碳酸岩墙为火成碳酸岩,部分碳酸岩墙的REE含量高达14 6 75 %,与赋矿白云石碳酸岩体的REE含量(最高达 10 % )相近,两者均为富稀土矿石。矿区基性岩墙的K2 O +Na2 O含量( >5 % )高于普通基性岩石(4 % ),表明它们属于碱性岩类,是碱性基性岩墙。碳酸岩墙 -碱性基性岩墙的REE与微量元素的分配型式近似,Sr、Nd、Pb同位素特征亦相近,表明它们形成于一个比较特殊的、近似的源区,两者有一定的成因关系。 相似文献
8.
Geochemical characteristics of different dolomites in the Bayan Obo giant REE–Nb–Fe deposit in Inner Mongolia have been studied. Intensively REE-mineralized dolomites (total REE over 800 ppm) show similar geochemical characteristics to associated carbonatite dykes, with Ba, Th, REE enrichments and Sr, Nb, Ti, Cu depletions, which is different from those of dolomites in the deposit with low REE contents (total REE less than 800 ppm). The low REE dolomites display some transitional characteristics between carbonatite dyke and sedimentary carbonate, with La depletion and Nb enrichment. This indicates that the genesis of the REE-mineralized dolomites might be related to both carbonatite magma and sedimentary carbonates. Sulfur isotope data indicates two sulfur sources, a mantle source (δ34S c.a. 0‰) and seawater (δ34S c.a. +25‰). It is proposed that mineralized dolomites in the Bayan Obo giant REE–Nb–Fe deposit are the product of sedimentary carbonate hydrothermally metasomatised by carbonatite magma and/or associated fluids. These dolomites formed the large-scale rare earth mineralization in the unique Bayan Obo REE–Nb–Fe deposit. 相似文献
9.
Bayan Obo Carbonatites: Texture Evidence from Polyphase Intrusive and Extrusive Carbonatites 总被引：5，自引：0，他引：5
<正>Most of the so-called Bayan Obo fine-grained dolomite marbles collected from the main and east orebodies show a microporphyritic texture,namely the microphenocrysts are set in a very finegrained matrix,although nearly all of them have undergone recrystallization caused either by deformation or alteration.The texture seems likely to have maintained the original features.It is known that one of the most characteristic textures of volcanic rocks is the porphyritic texture,and the microporphyritic texture is a variety in which both the phenocrysts and the matrix are only distinguishable with the microscope.Therefore,the dolomite marbles in the main and east orebodies may be related to the extrusive carbonatites.In addition,there also occur some carbonatite sills and dykes with different textures at Bayan Obo.Thus,the Bayan Obo carbonatites are polyphase intrusive and extrusive carbonatites. 相似文献
10.
《International Geology Review》2012,54(14):1720-1731
The origin of the Bayan Obo ore deposit, the largest REE deposit in the world, has long been debated and various hypotheses have been proposed. Among them is that the Bayan Obo ore deposit is correlated with and has the same origin as the Sailinhudong micrite mound in the southern limb of the Bayan Obo synclinorium. To test this model, the Bayan Obo ore deposit and the Sailinhudong micrite mound are systematically compared for their geological features, elemental geochemistry, and C, O, and Mg isotopic geochemistry. We show that the Bayan Obo ore deposit and the Sailinhudong micrite mound are both calcareous, lens-like in shape, lack bedding features, and are both hosted in a sedimentary formation that consists of clastic sediments and carbonates, unconformably overlying the Archaean–Palaeoproterozoic crystalline basement. However, their geochemical characteristics differ markedly. Compared with the Sailinhudong micrite carbonates, the Bayan Obo ore-hosting dolomite marbles are strongly enriched in LREEs, Ba, Th, Nb, Pb, and Sr, and have very different (PAAS)-normalized REE patterns. Sailinhudong micrite carbonates have higher δ13CPDB and δ18OSMOW values, falling into the typical sedimentary field, but the Bayan Obo ore-hosting dolomites are isotopically intermediate between primary igneous carbonatite and typical sedimentary limestone. The δ26 Mg values of the Sailinhudong micrite carbonates are lighter than those of normal Mesoproterozoic sedimentary dolostone, while those of the Bayan Obo ore-hosting dolomite marble are isotopically heavier, similar to δ26 Mg of mantle xenoliths and Bayan Obo intrusive carbonatite. We conclude that the Bayan Obo ore deposit is not correlated with the Sailinhudong micrite mound; it is neither a micrite mound nor an altered micrite mound. 相似文献
11.
12.
对白云鄂博矿床大地构造环境的几点认识 总被引：1，自引：0，他引：1
分布于华北地台北缘的白云鄂博群厚万米，EW向展布长500km，宽20-50km，以碎屑岩为主，碳酸盐岩约占1/10。1997年，我们首次确定厚千余米的含矿岩系为海相火山沉积稀有金属碳酸岩—粗面岩；1982的，李继亮确定厚320m的次闪绿帘石岩（H15）为裂陷槽中的细碧角斑岩系。从而奠定了白云鄂博群属象谷沉积的基础。世界上许多富含轻稀土和铌和碱性岩、碳酸岩多产于裂谷系中。白云鄂博矿床中的特殊元素组合和稳定同位素组成只有裂谷带下的异常地幔才能提供。大量Sm-Nd同位素年龄资料说明白云鄂博矿床稀土成矿时代主要是中元古代，更证明了矿床成矿作用与裂谷发展的同步性。 相似文献
13.
白云鄂博含矿碱性火山岩建造及其地球化学 总被引：3，自引：1，他引：2
白云鄂博矿床历经几十年的研究,主要集中在矿区H8岩性段矿化白云岩成因的认识,许多研究显示含矿白云岩是岩浆碳酸岩,本文主要从岩石学和地球化学方面进一步分析其属于火山喷发环境形成的火山碳酸熔岩。H8含矿白云岩段和H9板岩段作为一套含矿岩系主要由含矿白云岩、霓闪钠长岩、钾长板岩3类岩石组成,白云岩和霓闪钠长岩都具有的碎屑结构及角砾状构造、条带构造,显示为火山熔岩和火山碎屑岩特征,而钾长板岩则主要显示致密微晶火山熔岩特征。工业矿物主要是磁铁矿、赤铁矿、稀土矿物和铌铁矿物,其重要特征是出现大量原生赤铁矿,反映岩石氧化系数高,与火山喷发环境一致。霓闪钠长岩、钾长板岩岩石化学显示碱性特征,稀土元素与CaO、F相关系数在0.7以上,并与Fe2O3高氧化物相关,而与硅酸盐矿物组分反相关,表示碳酸岩与稀土成矿密切相关,并显示为表生氧化环境形成。稀土地球化学特征显示白云岩∑REE最高,钾长板岩∑REE最低,相应的岩脉∑REE低于喷发岩。各种岩石均表现为明显的轻重稀土分异,但是以白云岩LREE/HREE比值最大,霓闪钠长岩LREE/HREE比值最小,而纯钠长石岩脉和含稀土磁铁矿LREE/HREE明显高于其他岩石。白云岩和霓闪钠长岩均表现出不同的铕、铈负异常,但是碳酸岩脉和钾长板岩则显示弱正铈异常,霓闪钠长岩和钾长板岩铕异常不明显。矿化白云岩和碳酸岩脉的δ18O、δ13C值介于沉积灰岩与已知碳酸岩的δ18O、δ13C值之间,碳酸岩中白云石的δ18O低于方解石的δ18O,而δ13C高于方解石的δ13C,稀土矿物的δ13C、δ18O与碳酸岩脉δ13C、δ18O接近。归纳这些特征,含矿白云岩与霓闪钠长岩、钾长板岩是碱性火山岩组合,与一系列同期的碳酸岩、霓闪钠长岩碱性岩脉一起,构成一套完整碱性火山岩系。 相似文献
14.
白云鄂博碳酸盐矿物的矿物化学成分标型特征 总被引：5，自引：1，他引：4
对白云鄂博地区不同产状的碳酸盐矿物进行了系统的电子探针分析,其结果表明白云鄂博ＲＥＥ－Ｎｂ－Ｆｅ矿床的赋矿白云岩中,无论是粗粒结构的,还是细粒结构的白云岩,其主要造岩矿物白云石或者铁白云石均具高锰（ＭｎＯ〉０．５ｗｔ％）和高锶（ＳｒＯ〉１．５ｗｔ％）的特征,与矿床北东方向０￣３．５ｋｍ范围内切割五台群花岗片麻岩－混合岩及白云鄂博群碎屑岩的火成碳酸岩岩墙中的碳酸盐矿物非常相似。它们完全不同于宽沟段裂以北典型沉积石灰岩厦白云质石灰岩中的方解石和白云(MnO<0.1wt％ ,SrO<0.1wt％ )。赋矿白云岩中自云石的锶和锰含量系统变他反映碳酸岩浆发生了分离结晶作用,其结果可以导致其余岩浆中REE高度富集．本文认为碳酸盐矿物的锶和锰含量可以作为识别其成囡的重要标型特征,其氧化物MnO>0.15wt％ 和Sr>0.15wt％为火成碳酸岩的标志。 相似文献
15.
全球范围内出露的碳酸岩大多为钙质、镁质、铁质碳酸岩,少量为钠质和硅质碳酸岩,极少有富Sr碳酸岩的报道,其岩石成因、资源意义及对碳酸岩岩浆演化的指示意义尚不清楚。本次在四川省牦牛坪稀土矿区南部包子山稀土矿床的露天采坑中发现了超级富Sr的碳酸岩,其呈不规则的脉状侵入到构造角砾岩中。岩石呈紫色-淡紫色,微晶-斑状结构,斑晶主要为萤石,基质主要为菱锶矿、方解石、氟碳铈矿、氟碳钙铈矿、金云母、重晶石并含少量的金属硫化物和氧化物。全岩的微量元素分析表明,其稀土元素总量(∑REE)达3.5%～6.1%,Sr含量达19.0%～27.7%,已超过稀土矿床和锶矿床的工业品位要求。岩石中的中、重稀土元素含量占稀土元素总量的1.14%～1.77%,一些高价值稀土元素含量较高,如Pr(939×10~(-6)～1399×10~(-6))、Nd(2783×10~(-6)～3937×10~(-6))、Gd(237×10~(-6)～320×10~(-6)),因此除轻稀土元素外,中、重稀土和锶元素也具有重要的资源意义。岩石强烈富集REE、Sr、Ba,而明显亏损P、Nb、Ta、Zr、Hf元素,可能与岩浆演化过程中锆石和其它基性矿物的结晶分离有关。全岩的Sr-Nd同位素组成与牦牛坪、里庄稀土矿床的碳酸岩相似,表明它们为同源岩浆产物。笔者认为,富Sr的碳酸岩代表了碳酸岩岩浆演化晚期的产物,REE、Sr、Ba、F和S元素均在岩浆演化晚期的碳酸岩中高度富集。碳酸岩岩浆超浅成侵位至构造角砾岩中,并与下渗的大气水相遇导致岩浆的淬冷和微晶-斑状结构的形成。早期基性矿物(如霓辉石、黑云母)及碳酸盐矿物(如方解石、白云石等)的结晶分离是造成晚期碳酸岩中稀土元素富集的重要原因。富Sr碳酸岩中石英斑晶的发现和其较低的SiO_2含量表明碳酸岩岩浆演化晚期可能是硅饱和的,且这种岩浆具有很低的SiO_2溶解能力。以菱锶矿(体积分数 50%)为主要碳酸盐矿物的稀土碳酸岩可能代表了一种新的碳酸岩类型,明显不同于已知的钙质、镁质、铁质和钠质碳酸岩。 相似文献
16.
白云鄂博矿床碳酸岩墙/脉和赋矿白云岩中流体包裹体研究 总被引：2，自引：0，他引：2
Fluid inclusion study has been carried out for the carbonatite dykes/veins and the ore-hosted dolostone of the Bayan Obo superlarge REE-Fe-Nb deposit in order to provide the evidence and constraint for their origin.Based on the detailed geological observation and mineralogical investigation,the heating and cooling stage and laser Raman spectroscopy were mainly used for the laboratory work of this study.Following results have been obtained:(1)The discovery of melt and melt-fluid inclusions from carbonatite dykes/veins in the Dulahara and Jianshan Mountains,combined with the fine-grained(aplitic)texture of rocks,as well as the types and features of fluid inclusions such as CO_2 enrichment,higher homogenization temperature,provides a direct evidence for the magmatic origin of these dykes/veins.(2)The carbonatite dykes/veins distributed in two regions,nearby the axis of the Kuangou anticline and in the east to Bayan Obo town,mainly show coarse-grained texture.No melt inclusion was found,and the fluid inclusions possess features of less CO_2,lower homogenization temperature and higher salinity.They are tentatively identified as veins formed by some carbonate-rich hydrothermal solution.(3)Bedding carbonate layers/lens within the hanging wall and foot wall of ore-hosted dolostone,previously recognized as of magmatic origin,mainly composed by dolomite.The existence of single phase pure aqueous inclusions with very low homogenization temperature indicates their sedimentary origin.(4)The ore-hosted dolostone possesses apparent bedding and laminated structures.No melt inclusion was found,but,both single phase pure aqueous inclusions and CO_2 bearing multi-phase fluid inclusions coexisted in dolostones.In the direction towards ore-bodies,the homogenization temperature and CO_2 contents of fluid inclusion show an increasing tendency.It indicates the sedimentary origin of dolostone superimposed by late fluid metasomatism. 相似文献
17.
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 总被引：1，自引：0，他引：1
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(MgOFeO+MnO)和铁质碳酸岩(MgOFeO+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。 相似文献
18.
A rare earth element-rich carbonatite dyke at Bayan Obo, Inner Mongolia, North China 总被引：8，自引：0，他引：8
Summary ?A carbonatite dyke, extremely enriched in rare earth elements (REE), is reported from Bayan Obo, Inner Mongolia, North China.
The REE content in the dyke varies from 1 wt% to up to 20 wt%. The light REEs are enriched and highly fractionated relative
to the heavy REEs, and there is no Eu anomaly. Although carbon isotope δ13C (PDB) values of the carbonatites (−7.3 to −4.7‰) are within the range of normal mantle (−5±2‰), oxygen isotope δ18O (SMOW) (11.9 to 17.7‰) ratios apparently are higher than those of the mantle (5.7±1.0‰), indicating varying degrees of exchange
with hydrothermal fluids during or after magmatic crystallization. The carbonatite is the result of partial melting followed
by fractional crystallization. Primary carbonatite melt was formed by less than 1% partial melting of enriched mantle, leaving
a garnet-bearing residue. The melt then rose to a crustal magma chamber and underwent fractional crystallization, producing
further REE enrichment. The REE and trace element distribution patterns of the carbonatites are similar to those of fine-grained
dolomite marble, the ore-host rock of the Bayan Obo REE–Nb–Fe giant mineral deposit. This fact may indicate a petrogenetic
link between the dykes described here and the Bayan Obo mineral deposit.
Received November 1, 2001; revised version accepted June 16, 2002 相似文献
19.
白云鄂博矿区发育的脉状稀土碳酸岩，由于其结晶迅速，矿物颗粒细微，其中的微小矿物的鉴定一直是一个难题。应用显微共聚焦激光拉曼光谱仪则能较好地解决这一问题。研究表明，白云鄂博地区存在富稀土白云质岩浆碳酸岩脉，早期阶段形成碱性长石和铁白云石，无稀土矿化；铁白云石常常出溶铁质而自身则形成方解石。霓石和方解石形成略晚，常常与氟碳铈矿等稀土矿物共生，出现强烈的稀土矿化；而无解理的方解石则形成于更晚的岩浆期后热液阶段，发育大量的流体包裹体，并出现强烈的铌、稀土矿化。铌铁矿分布在氟碳铈矿中和赤铁矿边缘，为热液交代作用的产物。早期结晶的矿物如碱性长石、铁白云石稀土矿化弱，岩浆晚期分异出大量的流体相，稀土元素和Sr等进入岩浆热液中，并在热液结晶矿物中富集，甚至在非平衡结晶的石英中产生强烈的稀土矿化。结合岩相学显微观察，显微拉曼探针很好的揭示了这一地质过程。同时为白云鄂博矿床铌、稀土矿化的热液交代成因提供了依据。 相似文献
20.
本文对白云鄂博地区广泛分布的磷灰石进行了系统的电子探针分析。结果表明,赋矿粗粒白云石大理岩中磷灰石的矿物化学特征与碳酸岩岩墙中的非常相似,它们均属于富含锶和稀土元素的氟磷灰石,具有典型的火成碳酸岩特征。然而,它们在稀土元素分布模式以及轻稀土元素之间的分馏作用方面却存在着差异。造成这些差异的原因是,磷灰石的寄主岩石受富含氟和稀土元素的流体影响的程度不同：粗粒白云石大理岩受流体的影响比碳酸岩岩墙要大。 相似文献