Fluid unmixing/immiscibility as an ore-forming process in the giant REE–Nb–Fe deposit, Inner Mongolian, China: Evidence from fluid inclusions

The giant Bayan Obo REE–Nb–Fe deposit consists of replacement bodies hosted in dolomite marble made up of magnetite, REE fluorocarbonates, fluorite, aegirine, amphibole, calcite and barite. Two or three phase CO₂-rich, three phase hypersaline liquid–vapor–solid, and two phase liquid-rich inclusions have been recognized in mineralized fluorite and quartz samples. Microthermometry measurements indicate that the carbonic phase in CO₂-rich inclusions is nearly pure CO₂. Fluids involving in REE–Nb–Fe mineralization at Bayan Obo might be mainly of H₂O–CO₂–NaCl–(F–REE) system. Coexistences of brine inclusions and CO₂-rich inclusions with similar homogenization temperatures give evidence that immiscibility happened during REE mineralization. An unmixing of an original H₂O–CO₂–NaCl fluid probably derived from carbonatitic magma. The presence of REE-carbonates as an abundant solid in fluid inclusions 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.     

Samarium–Neodymium and Rubidium–Strontium Isotopic Dating of Veined REE Mineralization for the Bayan Obo REE‐Nb‐Fe Deposit,Northern China

The Bayan Obo REE‐Nb‐Fe deposit in Inner Mongolia, China, consists of later REE‐mineralizing fluorocarbonate veins cutting the earlier banded and massive ores in the deposit. Samarium–neodymium dating using the minerals including huanghoite and rubidium–strontium dating using single‐grain biotites both from the later veins show concordant isochrons corresponding to 442 ± 42 Ma (2σ uncertainty) and 459 ± 41 Ma, respectively. The isochron ages suggest that the later REE vein mineralization took place during the middle Paleozoic at Bayan Obo, consistent with geological observations and age data previously reported.     

论内蒙古白云鄂博群和白云鄂博超大型稀土-铌-铁矿床成矿的年代

白云鄂博稀土铌铁矿床具十分独特的地质、地球化学特征.所以多时代成矿是难以置信的.白云鄂博矿床成矿时间势必晚于赋矿白云岩及其下伏地层.而较多的地层古生物证据表明白云鄂博群形成于震旦纪至奥陶纪之间.基于赋矿白云岩是热水沉积形成,碳酸盐脉是同源热液交代变质岩或砂岩等形成的认识,笔者等认为,碳酸盐脉中的锆石可能是变质岩或砂岩中的锆石,它们虽被热液改造,其U-Pb年龄仍可能老于成矿年龄.已报道的白云鄂博矿床Sm-Nd等时线年龄虽然主要集中在1.2～1.6 Ga.但也有多个分别为0.4～O.5 Ga、0.8～0.9 Ga和1.O～1.1 Ga的年龄值.笔者等收集了所有已发表的98件白云鄂博矿床矿石、矿物及碳酸岩墙和上覆板岩的Sm-Nd年龄分析数据,用Isoplot程序计算,发现这些数据,除两件异常外,可以拟合成一条直线,相关系数R=0.96325,求得等时线年龄t=1125.8±32.5 Ma,εNd=-3.02.这一结果表明在1125.8±32.5 Ma白云鄂博Sm-Nd同位素时钟启动,且未再受后来的地质作用扰动,指示成矿作用应晚于或等于1.1 Ga,但地质意义尚待研究.若假定Sm-Nd同位素时钟不易被一般地质作用重置,则可以采信白云鄂博矿床辉钼矿的R.e-Os模式年龄(439±8 Ma)或黄铁矿Re-Os等时线年龄(439±86Ma)为白云鄂博的成矿年龄.这与赋矿地层的古生物化石年代相符.     

白云鄂博巨型REE-Nb-Fe矿区矽卡岩化时代：单颗粒金云母Rb-Sr法定年

内蒙古白云鄂博REE-Nb-Fe矿是目前世界上最大的稀土矿床.在白云鄂博东矿体的东南侧,分布有大面积的晚古生代花岗岩.花岗岩与赋矿白云岩（H8）呈直接的侵入接触关系,接触带发育强烈的矽卡岩化和小型铁矿化.我们在东矿采坑南侧22线1598m平台北倾探矿钻孔650～660m岩芯段,首次发现两段矽卡岩化蚀变带.对矽卡岩中的金云母进行超低本底Rb-Sr法定年,获得309±12Ma年龄.结合矽卡岩与矿体的侵入接触关系,可以认为,晚古生代花岗岩虽已深入到矿体下部,但其侵位时间应晚于矿区最后一期强烈的稀土矿化事件,它对白云鄂博矿床来说只是一次后期破矿的构造-岩浆活动.     

A Geochemical Study of an REE-rich Carbonatite Dyke at Bayan Obo, Inner Mongolia, Northern China

An REE-rich carbonatite dyke was found in Dulahala, close to the Bayan Obo superlarge REE-Nb-Fe mineral deposit in Inner Mongolia, northern China. The REE content in the dyke varies greatly, from 1% up to 20% (wt), which might constitute rich REE ores. Light REEs in the carbonatite are enriched and highly fractionated relative to heavy REEs and there is no Eu anomaly. The REE and trace element distribution patterns of the carbonatite are identical to those of fine-grained dolomite marble which is the host rock of the Bayan Obo REE-Nb-Fe superlarge mineral deposit. This indicates a petrogenetic linkage between the REE-rich carbonatite and the mineralizations in this region.     

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士36(2d),MSWD1.01.全岩Rb-Sr同位素分析结果分散,不构成等时线.87Rb/86Sr0～2.092×100-2,87Sr/86Sr0.70341～0.70541.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士210(2σ)Ma,1Nd=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REE—Fe—Nb矿床稀土氟碳酸盐矿物激光拉曼光谱特征及流体包裹体内稀土子矿物的鉴定

白云鄂博REE－Fe-Nb矿床典型稀土氟碳酸盐矿物都具有碳酸根离子最特征的拉曼振动频率，并普遍出现有氟化物的拉曼光谱振动峰。利用子矿物的激光拉曼峰特征，结合矿物晶形和扫描电镜能谱分析结果，可以确定这些矿物可能为氟碳铈矿和氟碳铈钡矿，说明初始成矿热液中极富含稀土元素，矿脉内多相包裹体中含稀土元素的子矿物是从被包裹体捕获的流体中结晶出来的，是真正的子矿物，激光拉曼光谱仪可以作为鉴定流体包裹体中未知子矿物的较为可靠手段之一。     

Fenitized Wall Rock Geochemistry of the First Carbonatite Dyke at Bayan Obo,Inner Mongolia,China

The first carbonatite dyke at Bayan Obo is well exposed on the surface for a length and width of approximately 60 m and 1.1–1.5 m, respectively. Along its strike, the fenitized H1(Qs) and H2(Cs) quartzite is replaced by Na-amphiboles, aegirines, and alkali-feldspars, intermittently stretching as far away as 800 m in length. Based on petrographical characteristics, the dyke's fenitized wall rocks are divisible into different zones:(1) outer,(2) middle, and(3) inner. The outer zone is 5–17 m from the NW margin of the dyke. The middle zone is located at 3.5–5 m from the NW margin of the dyke. The inner contact zone is located between direct contact with the dyke and 3.5 m from the dyke. In the outer zone, upon visual examination, no evidence of outcrop fenitization was found and the major elemental rock composition is nearly identical to the unaltered H1 and H2 lithologies. In the thin sections, however, small amounts of Na-amphibole and phlogopite are present. Despite relatively poor development throughout the 5 m of fenitization, the wall rocks have retained at least a small geochemical signature comparable to the original sedimentary protolith. The fenites occurring in the inner zone exhibit distinct variations, not only for the sharp contact at the outcrop scale, but also for variations in major, rare earth elements(REE), and trace elements and Sm-Nd isotope composition. The wall rocks within 3.5 m have undergone strong fenitization, inheriting the geochemical signature derived from the carbonatite dyke. Fenitization in the middle zone was not as strong, at least compared to the inner zone, but was stronger than the outer zone. Compared to some trace elements and REEs, the major elements are relatively immobile during fenitization. The Sm-Nd isotope data for the carbonatite dyke and the adjacent fenitized wall rocks, where the Sm and Nd originate solely from the dyke, plots as a six-point isochron with an age of 1308±56 Ma. This age is identical to that of ore-bearing dolomite carbonatite and the related ore-forming events, indicating that there may be a petrogenetic link between the two. Based on Sr and Nd isotope compositional data, the first carbonatite dyke may be derived from an enriched mantle.     

CO<Subscript>2</Subscript>-rich fluid inclusions with chalcopyrite daughter mineral from the Fenghuangshan Cu–Fe–Au deposit,China: implications for metal transport in vapor

CO₂-rich fluid inclusions containing opaque mineral crystals were found in the Fenghuangshan skarn-porphyry Cu–Fe–Au deposit in Tongling, Anhui, China. These inclusions show variable CO₂ contents and are accompanied by aqueous inclusions, both occurring as secondary inclusions in quartz and being locally associated with chalcopyrite mineralization. Laser Raman microspectroscopic analyses confirm the predominance of CO₂ in the vapor and the presence of H₂S as high as 8 mol%, and identify the opaque mineral with yellow reflectance color in the inclusions as chalcopyrite. More than half of the CO₂-bearing inclusions contains chalcopyrite, whereas few of the associated aqueous inclusions do so. The chalcopyrite, occupying less than 1% (volume) of the inclusions, is interpreted to be a daughter mineral, and calculated Cu concentrations in the inclusions range from 0.1 to 3.4 wt%. Copper is inferred to have been transported in CO₂-dominated fluids as HS⁻ complexes. The occurrence of chalcopyrite daughter crystals in CO₂-rich fluid inclusions indicates that CO₂-rich vapor has the capacity of transporting large amounts of Cu, and possibly Au. This finding has significant implications for metal transport and mineralization in hydrothermal systems enriched in CO₂, such as orogenic-type and granitic intrusion-related gold deposits.     

Research on fluid inclusions of the Yinshan polymetallic deposit, Jiangxi Province, China

In this paper some new advances in the study of fluid inclusions of the Yinshan deposit in Jiangxi Province,China,are presented.The fluid inclusions of the deposit can be divided into four types:1) gas-rich inclusions;2)liquid-rich inclusions;3)salt-saturated H2O inclusions;and 4)single-phase or multiphase CO2-rich inclusions.Homogenization temperatures of the fluid inclusions range from 100 to 520℃,aminly in the range 120-400℃.The daughter crystal-bearing multiphase inclusions present in quartz porphyries(including Nos.13 and 4 dikes)have been observed.In ore veins,some daughter crystal-bearing multiphase inclusions have been observed.too.On the basis of the results of fluid inclusion research,the authors suggest that the ore-forming fluid must have a close genetic relation to magmatic hydrothermal solution.The ore-forming fluid was dominantly originated from the depth and the mixing of magmatic solution with meteoric water was enhanced during ascending of the fluid,accompanying immiscibility and boiling of fluid.Teher may be a conceales igneous body at the depth of the Yinshan deposity,which furnishes the scientific basis for metallogenic prognosis at th depth of the Yinshan deposit.     

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.     

内蒙古白云鄂博矿床碳酸岩侵位方式与三维形态及稀土潜在资源

稀土元素是关键金属的重要成员, 我国稀土资源禀赋优越, 并主要来自白云鄂博矿床, 但其巨量金属富集机理、矿体空间形态以及潜在资源等, 一直存在不同认识, 制约了稀土资源评价以及有效利用。在地质、地球化学和地球物理多学科联合攻关基础上, 本文对白云鄂博碳酸岩就位机制、演化过程和三维形态, 以及稀土超常富集机理与潜在资源等进行了探讨。白云鄂博早-中元古代沉积岩经历了区域性的挤压构造变形, 原水平地层褶皱后又被置换成陡立、近E-W走向的构造片理, 这为碳酸岩浆的上涌提供了有利通道。白云鄂博H8白云岩为火成碳酸岩, 它侵位于~13亿年, 经历了铁质-镁质-钙质的演化, 碳酸岩既为稀土成矿母岩, 也是稀土矿体; 古生代两次改造作用导致了稀土活化及新生矿物生成, 但没有外来稀土的明显加入。高磁与低阻地球物理异常体揭示出了碳酸岩体的三维形态, 碳酸岩的侵位中心位于主、东矿之间, 侵位后沿构造置换陡立面理, 往东西两侧推进。利用获得的碳酸岩体积、(最小)密度以及稀土含量, 推算出白云鄂博矿区500~1000m以浅稀土潜在资源为3.33亿t, 这远超目前公认的矿山及全球稀土资源量。建议开展新一轮以稀土为主的勘探与验证工作, 以获取白云鄂博战略矿产资源的准确家底。

     

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(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。     

Scandium-Bearing Minerals in the Bayan Obo Nb-REE-Fe Deposit, Inner Mongolia, China

Aegirine, “perrierite‐(Ce)”, and ferrocolumbite, occurring in the Bayan Obo Nb‐REE‐Fe deposit in Inner Mongolia, China, contain appreciable amounts of scandium. The Sc₂O₃ content in aegirine (sample TS‐15) was 0.34–1.81 wt% (with one exceptionally high value of 3.45%) with an average value of 1.19%. The Sc₂O₃ content of “perrierite‐(Ce)” (TS‐20) was 2.82–3.64% with an average value of 3.26%. In the ferrocolumbite samples (TS‐16, TS‐23), the Sc₂O₃ content was 0.20–0.25% with an average value of 0.22% in sample TS‐16, and 0.56–1.04% with an average value of 0.67% in sample TS‐23. These data provide the basic information for future possible recovery of scandium as a by‐product from the deposit.     

安徽庐枞矿集区东顾山钨矿床成矿流体来源与演化:来自H、O、S同位素和流体包裹体的证据

长江中下游成矿带是我国重要的铁铜金等金属成矿带,庐枞矿集区中新勘探发现的东顾山矿床与成矿带内燕山期铁、铜大规模成矿作用不同,矿化以钨为主,且已达大型规模。前人已对该矿床开展了基础地质特征和成岩成矿年代学工作,但该矿床的成矿流体和来源特征仍不清楚,矿床成因的确定需要开展相关研究。本文在详细的野外调查基础上,对各成矿阶段流体包裹体及H、O、S同位素进行了系统测定及分析,并结合地质事实,确定了成矿流体特征和来源,为成矿带内钨矿床的成因认识和下一步找矿提供理论依据。流体包裹体研究表明,东顾山矿床流体包裹体类型以纯液相包裹体（L）和气液两相包裹体（V+L）为主,矽卡岩阶段（Ⅰ）的包裹体均一温度集中变化于351~397℃,盐度变化于10.87%~13.60% NaCleqv;氧化物阶段（Ⅱ）的包裹体均一温度集中变化于283~367℃,盐度变化于7.73%~10.62% NaCleqv;第三阶段石英-硫化物阶段（Ⅲ）的包裹体均一温度变化于180~284℃,盐度变化于4.08%~7.57% NaCleqv。从Ⅰ阶段到Ⅲ阶段,均一温度和盐度均有降低的趋势,显示流体混合的特征,可能是其矿质沉淀的重要机制。H-O同位素分析结果（δ¹⁸O_H2O值为-0.37‰~2.79‰,δD值为-60.56‰~-46.16‰）显示成矿流体主要为岩浆流体,并有约40%大气降水的加入。硫化物S同位素研究显示,黄铁矿δ³⁴S值范围为4.39‰~6.00‰,高于幔源硫,略低于赋矿地层硫值（7.60‰~8.13‰）,指示东顾山钨矿床硫源为地层硫和岩浆硫混合,地层硫的贡献不容忽视。综合矿床地质、流体包裹体及H、O、S同位素特征可知,东顾山矿床热液成矿过程中发生了显著的流体混合作用,破坏了钨络合物的稳定性,使得大量钨等金属离子从络合物载体中脱离出来并与Ca²⁺相结合,最终钨酸钙沉淀成矿。通过与成矿带铜铁矿床的成矿流体对比可知,长江中下游成矿带内钨矿床与铜（金）、铁矿床的成矿流体温度和盐度特征相似（中高温、中高盐度向中低温、中低盐度演化）,但是由于围岩性质不同导致硫来源不同,且沉淀机制各不相同,根本原因是不同矿种的成矿岩体性质和搬运金属元素的方式存在差异。     

内蒙古白云鄂博矿床巨量稀土的堆积及再活化历史: 来自矿物微区Sm-Nd同位素的制约

内蒙古白云鄂博矿是世界著名的超大型稀土-铌-铁矿床, 但该矿床的同位素定年结果复杂, 成矿时代备受争议。为限定白云鄂博矿床的形成-演化历史, 本文对矿床中的富稀土矿物——独居石、氟碳铈矿及磷灰石开展了微区Sm-Nd同位素研究。结果显示, 独居石、氟碳铈矿及变形磷灰石的Sm-Nd同位素组成沿着13亿年的等时线分布, 其ε_Nd(t=1300Ma)值和矿床中火成碳酸岩脉的ε_Nd(t=1300Ma)值十分接近。因此, 白云鄂博矿床的稀土矿物主要形成于中元古代, 成矿和幔源碳酸岩浆活动具有密切的成因关系。矿床中还发育未变形的磷灰石。多数未变形磷灰石的Sm-Nd同位素组成沿着4.5亿年的等时线分布, 说明其形成于早古生代。值得注意的是, 早古生代磷灰石的ε_Nd(t=450Ma)值和矿石中独居石及氟碳铈矿演化至4.5亿年的ε_Nd值高度一致, 说明磷灰石生长所需要的稀土主要来自中元古代矿石中的物质再活化。此外, 少量未变形的磷灰石形成于晚古生代(2.7亿年), 其ε_Nd(t=270Ma)值和矿石中独居石及氟碳铈矿演化至2.7亿年的ε_Nd值非常接近, 同样说明新生磷灰石中的稀土来自此前矿石中的物质再活化。总之, 该研究表明白云鄂博矿床的巨量金属堆积主要发生在13亿年左右; 矿床形成后分别在早古生代和晚古生代经历了两次改造作用, 矿床改造过程没有明显提升资源量, 但导致成矿元素的活化及部分矿物的新生, 可能改变了矿石的品位及工艺性质。

     

白云鄂博矿区北部韧性剪切带特征及其构造意义

在白云鄂博主矿北西约6.5km处的查干楚鲁一带,有一条近东西向延伸的断层带,前人在该带中部识别出了蛇绿岩混杂堆积。本文作者在蛇绿岩东部的大理岩质糜棱岩中发现鞘褶皱、拉伸线理及旋转碎斑系等变形构造,在大理岩周围发现石英岩型宏观压力影构造,在变质石英砂岩中识别出褶劈理以及方解石脉等相关构造,在这条东西向断裂带北边发现典型的黄铁矿型压力影。根据上述特征判断,查干楚鲁一带为一条近东西向延伸的韧性剪切带,同时具有NEE—SWW向逆左旋走滑的特征。该带揭示出蒙古洋板块与华北板块在晚古生代汇聚拼合的基本格局。     

阿尔泰塔拉特铅锌矿床的变质叠加改造——地质和流体包裹体证据

塔拉特(阿巴宫)铅锌矿位于阿尔泰克兰火山-沉积盆地南东段,矿床受区域性NW向断裂——克因宫断裂和阿巴宫断裂的控制,Pb-Zn矿体赋存于下泥盆统康布铁堡组下亚组第二岩性段上部(D1k12)的变质岩系中,具明显的层控特征,后期脉状硫化物-石英脉叠加作用明显。根据矿体产出特征可识别出2个明显的成矿期:海相火山沉积喷流成矿期和变质热液叠加成矿期。变质热液期可包括2个阶段,早阶段透镜状石英脉沿含矿层位中绿泥石片岩、浅粒岩等顺层分布,并有浸染状黄铁矿产出;晚阶段含黄铁矿-黄铜矿石英脉穿切绿泥石片岩、浅粒岩或块状铅锌矿石,硫化物稀疏浸染状分布。海相火山沉积喷流成矿期的闪锌矿存在残留的L-V盐水包裹体及后期沿次生裂隙分布的L-V和H2O-CO2包裹体,原生L-V包裹体的均一温度Th,tot=267~334℃,次生H2O-CO2包裹体Tm,CO=-61.2~-60.2℃,T2h,CO=6.5~11.0℃。2变质热液期早阶段石英脉(QI)赋存有大量的H2O-CO2包裹体和较多的碳质流体包裹体(CO2±CH4体系),H2O-CO2包裹体Th,tot=294~368℃,盐度为5.5%~7.4%NaC leqv。碳质流体包裹体的Tm,CO=-60.1~-58.5℃,T.2~20.6℃。2h,CO=-42晚阶段切层含黄铁矿-黄铜矿石英脉中也有大量H2O-CO2包裹体和较多的碳质流体包裹体,H2O-CO2包裹体Th.tot=142~360℃,盐度为2.4%~16.5%NaC leqv。碳质流体包裹体的Tm,CO=-61.5~-57.3℃,T2h,CO0.6℃2有-27.0~-2和27.1~28.7℃两组。次生L-V包裹体的Tm,ice=-9.8~-1.3℃,Th,tot=205~412℃。克兰盆地造山运动过程中形成的区域性富CO2流体,其运移对促进岩(矿)石变形变质以及金属富集产生重要影响。塔拉特铅锌矿床的矿石变形、交代结构及石英脉中富CO2流体的大量出现,说明变质流体参与了叠加改造作用,且具有多阶段的特点。富CO2包裹体形成环境与造山带区域变质晚期或峰期后的P-T演化一致。     

Detrital Zircon U–Pb Geochronology and Provenance of Bayan Obo Group, Northern Margin of North China Craton: New Implications for the Position of NCC in Rodinia

The paleoposition of North China Craton in Rodinia has long been in controversial. This paper mainly focuses on the U–Pb geochronological studies of detrital zircons obtained from Bayan Obo Group exposed in the Shangdu area, Inner Mongolia, aiming to provide more information for interprating this problem. Based on the acquired data, this paper comes to the following conclusions. Firstly, the depositional age of Bayan Obo Group might be from Meso– to Neoproterozoic according to the zircons U–Pb dating results. The lower succession of this group, namely Dulahala and Jianshan formations deposited between 1800 and 1650 Ma. The Halahuogete and Bilute formations deposited between 1500 and 1350 Ma. For Baiyinbaolage and Hujiertu formations, their depositional age was 1250–900 Ma. Secondly, for the provenance of Bayan Obo Group, this paper believes detrital zircons with age of 2.51–2.71 Ga and 2.00–2.48 Ga were from Guyang, Xi Ulanbulang and Zhuozi area; the Khondalite Belt provided detrital zircons with age of 1.95–1.80 Ga; zircons with age of 1.60–1.75 Ga might come from granitic rocks in Miyun Area. The magmatism after 1.60 Ga was rarely recorded in the NCC, therefore those zircons with ages younger than 1.60 Ga might come from outside of NCC. The magmatism with the same age existed in Baltic, Amazonia and Laurentia. Based on previous paleomagnetic researches, this paper proposes that NCC might receive detritus from Baltic during 1560–1350 Ma and had affinity with Laurentia and Amazonia at ～0.9 Ga in Rodinia. Baltic, Amazonia and Laurentia might be potential provenances for non–NCC detritus in Bayan Obo Group.