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1.
湘西震旦—寒武纪交替时期古海洋环境的恢复 总被引：6，自引：0，他引：6
前寒武纪至寒武纪的交替时期是地质史和生命史的重要转折。中国南方地区广泛发育了上震旦统、下寒武统的黑色岩系。文中运用沉积学和沉积地球化学的理论和方法对湘西黑色岩系的岩石类型、矿物组成、元素地球化学特征、干酪根的结构以及碳同位素的组成等方面进行了研究 ,讨论了黑色岩系的形成条件 ,恢复了震旦纪 /寒武纪地史转折期的古环境。研究认为 ,湘西地区在晚震旦世和早寒武世地史转折期的生物爆发和高有机质的产率是形成缺氧环境的重要因素之一。 相似文献
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The Early Cambrian black shale sequence of the Niutitang Formation in South China hosts a synsedimentary, organic carbon-rich, polymetallic sulfide layer with extreme metal concentrations, locally mined as polymetallic Ni–Mo–PGE–Au ore. In combination with previously reported data, we present Mo isotope, platinum-group element (PGE), and trace and rare-earth element (REE) data for the polymetallic sulfide ores and host black shales from four mine sites (Dazhuliushui and Maluhe in Guizhou Province, and Sancha and Cili in Hunan Province, respectively), several hundred kilometers apart. The polymetallic sulfide ores have consistently heavy δ98/95Mo values of 0.94 to 1.38‰ (avg. 1.13 ± 0.14‰, 1σ, n = 11), and the host black shale and phosphorite have slightly more variable δ98/95Mo values of 0.81‰ to 1.70‰ (n = 14). This latter variation is due to variable paleoenvironmental conditions from suboxic to euxinic, and partly closed-system fractionation in isolated marine sedimentary basins. Both the polymetallic sulfides and host black shales show PGE distribution patterns similar to that of present-day seawater, but different from those of ancient submarine-hydrothermal deposits and modern submarine hydrothermal fluids. The polymetallic sulfide bed has a generally consistent metal enrichment by a factor of 107 compared to present-day seawater. PAAS-normalized REE + Y patterns of the polymetallic sulfide bed are characterized by a remarkably positive Y anomaly, consistent with an origin of the REE predominantly from seawater. Small positive Eu anomalies in some of the sulfide ores could reflect minor hydrothermal components involved. The Mo isotope, PGE, and trace and rare-earth element geochemical data suggest that metals in the polymetallic Ni–Mo–PGE–Au sulfide ore layer were scavenged mostly from Early Cambrian seawater, by both in-situ precipitation and local re-deposition of sulfide clasts. 相似文献
3.
Shao-Yong Jiang Yong-Quan Chen Hong-Fei Ling Jing-Hong Yang Hong-Zhen Feng Pei Ni 《Mineralium Deposita》2006,41(5):453-467
The Lower Cambrian black shale sequence of the Niutitang Formation in the Yangtze Platform, South China, hosts an extreme metal-enriched sulfide ore bed that shows >10,000 times enrichment in Mo, Ni, Se, Re, Os, As, Hg, and Sb and >1,000 times enrichment in Ag, Au, Pt, and Pd, when compared to average upper continental crust. We report in this paper trace- and rare-earth-element concentrations and Pb–Pb isotope dating for the Ni–Mo–PGE–Au sulfide ores and their host black shales. Both the sulfide ores and their host black shales show similar trace-element distribution patterns with pronounced depletion in Th, Nb, Hf, Zr, and Ti, and extreme enrichment in U, Ni, Mo, and V compared to average upper crust. The high-field-strength elements, such as Zr, Hf, Nb, Ta, Sc, Th, rare-earth elements, Rb, and Ga, show significant inter-element correlations and may have been derived mainly from terrigenous sources. The redox sensitive elements, such as V, Ni, Mo, U, and Mn; base metals, such as Cu, Zn, and Pb; and Sr and Ba may have been derived from mixing of seawater and venting hydrothermal sources. The chondrite-normalized REE patterns, positive Eu and Y anomalies, and high Y/Ho ratios for the Ni–Mo–PGE–Au sulfide ores are also suggestive for their submarine hydrothermal-exhalative origin. A stepwise acid-leaching Pb–Pb isotope analytical technique has been employed for the Niutitang black shales and the Ni–Mo–PGE–Au sulfide ores, and two Pb–Pb isochron ages have been obtained for the black shales (531±24 Ma) and for the Ni–Mo–PGE–Au sulfide ores (521±54 Ma), respectively, which are identical and overlap within uncertainty, and are in good agreement with previously obtained ages for presumed age-equivalent strata.Editorial handling: R. Coveney Jr. 相似文献
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Total organic carbon content (TOC), trace element and platinum-group element (PGE) concentrations were determined in the black shales of the Lower Cambrian Niutitang Formation in the Nayong area, Guizhou Province, South China, in order to study the polymetallic Ni–Mo–PGE mineralization. The results demonstrate that numerous elements are enriched in the polymetallic ores compared to those of the nearby black shale, particularly Ni, Mo, Zn, TOC and total PGE, which can reach up to 7.03 wt.%, 8.49 wt.%, 11.7 wt.%, 11.5 wt.% and 943 ppb, respectively. The elemental enrichment distribution patterns are similar to those in the Zunyi and Zhangjiajie areas except that the Nayong location is exceptionally enriched in Zn. Whereas positive correlations are observed between the ore elements of the polymetallic ores, no such correlations are observed in the black shale. These positively correlated metallic elements are classified into three groups: Co–Ni–Cu–PGE, Zn–Cd–Pb and Mo–Tl–TOC. The geological and geochemical features of these elements suggest that Proterozoic and Early Palaeozoic mafic and ultramafic rocks, dolomites and/or Pb–Zn deposits of the Neoproterozoic Dengying Formation and seawater could be the principal sources for Co–Ni–Cu–PGE, Zn–Cd–Pb, and Mo–Tl–TOC, respectively. Furthermore, the chondrite-normalized patterns of PGEs with Pd/Pt, Pd/Ir and Pt/Ir indicate that PGE enrichment of the polymetallic ores is most likely related to hydrothermal processes associated with the mafic rocks. In contrast, PGE enrichment in the black shale resembles that of the marine oil shale with terrigenous and seawater contributions. Our investigations of TOC, trace elements and PGE geochemistry suggest that multiple sources along with submarine hydrothermal and biological contributions might be responsible for the formation of the polymetallic Ni–Mo–PGE mineralization in the black shales of the Lower Cambrian Niutitang Formation across southern China. 相似文献
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黔北下寒武统黑色岩系的沉积环境与地球化学响应 总被引：2，自引：0，他引：2
下寒武统黑色岩系在我国华北、华南及塔里木盆地等广泛发育,但富有机质泥页岩的分布特征及其控制因素未有定论。本文对黔北地区下寒武统牛蹄塘组(及同时期地层)不同沉积相带典型剖面中的富有机质泥页岩及其上下层位进行了地球化学分析,识别出寒武纪早期不同沉积相带氧化还原环境的明显差异。台内凹陷相主要岩性为黑色页岩,底部为不等厚的薄层磷块岩和硅质岩或硅磷质结核,沉积的黑色页岩厚度大,有机质丰度高,V、Ni、Mo、U等微量元素显著富集,反映了贫氧-缺氧环境,以及短暂动态的硫化环境,Mo/TOC反映了其为局限盆地特征;上斜坡相为贫氧到氧化的沉积环境,但更多地是表现为氧化的沉积环境,其中牛蹄塘期存在局部的硫化环境,沉积的黑色页岩厚度小,但有机质丰度最高,V、Ni、Mo、U等微量元素的富集程度较低;盆地相为黑色硅质岩与富有机质的黑色硅质页岩间互沉积,同期沉积厚度较小,有机质丰度相对较低,V和U的富集程度大于台内凹陷相,而Ni和Mo的富集程度则低于台内凹陷相,指示了缺氧环境,期间伴随有贫氧和短暂的氧化环境存在,且可能存在局部的硫化环境,Mo/TOC反映了中等的局限程度。总的来说,黔北下寒武统黑色岩系的有机质丰度、厚度以及微量元素富集程度等特征主要受控于不同的氧化还原环境。 相似文献
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Abstract: The black shales of the Lower Cambrian Niutitang Formation in Weng’an, on the Yangtze platform of south China, contain voluminous polymetallic sulfide deposits. A comprehensive geochemical investigation of trace, rare earth, and platinum group elements (PGE) has been undertaken in order to discuss its ore genesis and correlation with the tectono-depositional setting. The ore-bearing layers enrich molybdenum (Mo), nickel (Ni), vanadium (V), lead (Pb), strontium (Sr), barium (Ba) , uranium (U) , arsenic (As), and rare earth elements (REE) in abundance. High uranium/thorium (U/Th) ratios (U/Th>1) indicated that mineralization was mainly influenced by the hydrothermal process. The dU value was above 1.9, showing a reducing sedimentary condition. The REE patterns showed high enrichment in light rare earth elements (LREE) (heavy rare earth elements (HREE) (LREE/HREE=5–17), slightly negative europium (Eu) and cerium (Ce) anomalies (dEu=0.81–0.93), and positive Ce anomalies (dCe=0.76–1.12). PGE abundance was characterized by the PGE-type distribution patterns, enriching platinum (Pt), palladium (Pd), ruthenium (Ru) and osmium (Os). The Pt/Pd ratio was 0.8, which is close to the ratios of seawater and ultramafic rocks. All of these geochemical features suggest that the mineralization was triggered by hydrothermal activity in an extensional setting in the context of break-up of the Rodinian supercontinent. 相似文献
7.
贵州遵义寒武系底部黑色页岩中含Mo、Ni、U等重金属的富集层，它们一直被认为与热水沉积作用有关。本文通过对贵州遵义松林小竹一带的寒武系底部地层的系统的岩石、矿物、地球化学研究，认为遵义松林小竹一带寒武系底部黑色页岩中富含Mo、Ni、U等重金属层属于热液（水）喷流沉积，主要依据有：①含大量的黄铁矿、针镍矿、硫钼矿及较多的锑硫镍矿、黄铜矿、闪锌矿、重晶石、石英、石膏等矿物；②具有大量的同生砾屑，砾屑成分为黑色碳质体和碎屑状黄铁矿、针镍矿、硫钼矿等矿石，它们堆积成层状结构，碎屑呈被撕裂状、棱角状、熔蚀港湾状等结构，球状、脸盆状、枕头状等构造，它们类似海底喷流沉积；③硅同位素、锶同位素、Re／Os值、Th／Sc值、Th／U值都表明有深部物质加入；④黑色岩系中夹碳酸盐岩透镜体，碳同位素具有强烈负异常特征，表明有热液作用；⑤超强富集元素Mo、As、Se、Re和T1都属于典型的气相迁移元素，而钼是典型的高温气相迁移元素，暗示了可能存在火山射气作用；而强富集的Ni、U、Au、Ag、PGE元素组合是超基性岩浆活动的产物，表明有热液活动。研究发现在热液（水）喷流沉积形成的富集Mo、Ni、U等重金属硫化物层之上，产出丰度大、分异度低、含大型海绵类、双壳类、菌藻类和少量大型蠕虫化石的生物群，它的特征与现代太平洋海底热喷口附近的生物群类似，因此认为遵义小竹一带寒武系底部生物群属于与海底热喷口相关生物群，这一新发现对研究寒武纪生态和生物爆发具有重要意义。 相似文献
8.
The molybdenum-nickel deposits in Shuidong District of Nayong County (Guizhou Province, Southwest China) are found mainly in black shale series of Lower Cambrian Niutitang Formation, which is another Mo-Ni-rich region besides Zunyi District (Guizhou province). Our systematic study on the Mo-Ni deposits in Tangjiaba of Nayong reveals that layered coarse-grained limestones, spherical beaded limestones concretions are hosted at the lower seam of the Mo-Ni deposits. Its strong negative carbon isotope anomaly (the carbon isotope value of the coarse-grained limestones varies from ?2.148‰ to 8.223‰) is similar to that in the modern submarine black smoker chimney. The carbon in the coarse-grained limestones from black rock series of Nayong County might be deep source inorganic carbon. The seams, coarse-grained limestones, ore-bearing coarse-grained limestones and the roof and floor of the deposits are characterized by co-variation on the trace element spider diagram, showing good homology. The extraordinary enrichment of Ag, As and Sb resembles hydrothermal sedimentation. Pro-Earth's core elements Se is strongly enriched in Ni-Mo ore-bearing coarse-grained limestones. The ore-bearing rock series has an extremely low Th/U value (0.012–0.19); in the logU-logTh Cartesian Coordinates, the samples of the roof and floor of the deposits and ore-bearing coarse-grained limestones are found in the East Pacific tise; and the samples of coarse-grained limestones are found between the paleo-hydrothermal dedimentary area and the East Pacific tise. The chondrite-normalized rare earth element patterns of the Ni-Mo deposits show LREE enrichment, Ce negative anomaly, and Eu negative anomaly (which is supposed to be influenced by the deep magmatic processes in an extensional environment) resembles the rare earth element distribution patterns of the fluid and its sediments in modern submarine hydrothermal system. It proves that coarse-grained limestones is characterized by typical hydrothermal limestones, being closely related with the genesis of Mo-Ni deposits in Nayong County, which provides new evidence for hydrothermal sedimentary genesis of Mo-Ni deposit and negative carbon anomaly in the basal Cambrian on a global scale. 相似文献
9.
The black shale in the Lower Cambrian Niutitang Formation on the southeastern margin of the Yangtze Platform hosts a layer of polymetallic sulfide ores containing extremely high concentrations of Ni (up to 3.8 wt.%) and Mo (up to 7.5 wt.%). Abundant micrometer-sized microfossils were observed in the Ni–Mo sulfide enriched layer under scanning electron microscopy. The microfossils include vesicles with clear organic wall structures and permineralized internal contents. These structures resemble unicellular green algae. Both biomass-adsorbed transition metals and biological structural protein metals could be accumulated and mineralized from the blooming algae, followed by anoxic microbial reduction and immobilization. The biotic impact may be a substantial mechanism for the massive Ni- and Mo-sulfide deposition in a typical restricted ocean basin environment. 相似文献
10.
通过对鄂西震旦系陡山沱组和寒武系牛蹄塘组页岩气勘查大量实际资料总结研究,创新性地提出了针对鄂西地区震旦系和寒武系"岩相控炭、成岩控烃、构造控藏"的页岩气成藏理论认识。震旦系陡山沱组和寒武系牛蹄塘组富有机质页岩沉积受控于鄂西裂陷海槽,富有机质页岩甜点层段主要形成于海侵体系域和早期高水位体系域。黄陵古隆起周缘震旦纪—三叠纪长期浅埋,为生油提供了充足时间,三叠纪短暂快速深埋,为页岩气生成的主峰期。古隆起刚性基底、区域性泥页岩盖层以及后期逆冲推覆构造,为页岩气保存提供了良好的条件。从而建立了鄂西震旦—寒武系"深水海槽控炭、古隆起浅埋控烃、古隆起+逆冲断裂控藏"的页岩气成藏模式。 相似文献
11.
华南扬子地块是我国古热水沉积成矿作用最为发育的地区之一,其热水沉积特性最早引起我国学者的关注。华南下寒武统黑色岩系中赋存多个与热水沉积成矿作用相关的大型、超大型重晶石矿床与N i-Mo-U-V多金属富集层。进一步研究分布在华南扬子地块黑色岩系中的金属、非金属矿床成因及其地球化学特征,对认识华南乃至全球晚震旦—早寒武世生物与环境演化有着十分重要的意义。本文对华南下寒武统镍-钼富集层矿石进行电子探针研究,识别出黄铜矿、黝铜矿等铜的独立矿物;闪锌矿等锌的独立矿物;方铅矿、白铅矿等铅的独立矿物。研究表明,在镍-钼矿石中这些矿物的发现为镍-钼矿层是热水沉积作用产物提供了直接的矿物学证据。 相似文献
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塔里木盆地北部下寒武统底部黑色页岩形成的次氧化条件 总被引：3，自引：0，他引：3
富有机质黑色页岩的形成长期以来被认为是缺氧沉积环境的证据,并被作为全球缺氧事件的标志。塔里木盆地下寒武统底部黑色页岩的岩石学特征说明其沉积在受陆源有一定影响的陆棚环境中。矿物学研究表明,硫均以硫酸盐状态存在,没有见到黄铁矿,说明其形成在硫酸盐还原带以上。黑色页岩中结核状氟磷灰石的存在以及剖面底部结核状磷块岩的出现,表明了一种与现代热带太平洋东海岸和阿拉伯海相类似的广泛发育上升洋流的大陆边缘沉积环境。黑色页岩的地球化学特征中,Re和Mo的高度富集、高的Re/Mo比以及含有一定量的Mn,Cd和U的相对富集以及低的Cd/U比等,这些特点均支持了黑色页岩沉积于次氧化条件的认识。 相似文献
15.
Ni-Mo-PGE-Au-rich ores in Chinese black shales and speculations on possible analogues in the United States 总被引：22，自引：0，他引：22
Molybdenum-rich black shales from the Cambrian of south China contain sulfide beds with >2 wt.% Mo, >2 wt.% Ni and 200–700 mg/T each for Au, Pt and Pd. Similar deposits occur in Canada. In the U.S. Midwest, Paleozoic black shales contain an extensive Mo anomaly and sporadic enrichments for Pt group elements, suggesting the presence of Ni-Mo-PGE-Au sulfide deposits like those being mined in China. 相似文献
16.
贵州省福泉桅杆坪地区寒武系底部牛蹄塘组黑色页岩中以炭质印模的形式保存有大量宏观后生动物化石.化石微细特征保存较差,多属于疑难化石.该化石组合以化石个体较大的蠕虫状化石和疑似杆壁虫类化石为优势分子,还常见管状类化石、遗迹化石,以及少量的软舌螺、海绵骨针等化石碎片.该化石组合紧位于镍钼多金属层之上,与遵义等地区的松林生物群(牛蹄塘组下生物群)的层位相当,化石组成基本一致,但优势生物存在明显差异.福泉地区牛蹄塘组蠕虫状化石组合的发现,丰富了寒武系牛蹄塘组的生物群面貌,为研究早期后生动物演化提供了新资料和新信息.对该化石组合的进一步研究,也必将为这种特殊生物群的古环境恢复和埋藏学研究提供有利的古生物学证据. 相似文献
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下寒武统牛蹄塘组与下志留统龙马溪组页岩是扬子地区发育的两套富有机质黑色页岩,由于其分布面积广、厚度大、有机质丰度高而成为页岩气勘探的重点层位.然而牛蹄塘组孔隙度表现出了与龙马溪组截然不同的规律,两套页岩的孔隙结构、有机碳含量、密度也存在显著差异.结合测井、埋深（上覆压力）、孔隙度、有机碳及成熟度测试数据进行了对比分析.结果显示,牛蹄塘组过高的有机碳含量和热演化程度严重影响了页岩的孔隙结构,使有机质碳化,有机质孔发生坍塌和充填;牛蹄塘组埋深大、上覆压力也大,导致无机孔被压实,因此其总孔隙度明显小于龙马溪组. 相似文献
18.
东山峰背斜是湘鄂西褶皱冲断带的一部分,剖面构造为基底和盖层组成的双层结构。由于江南-雪峰基底拆离推覆隆起带向NW方向的推挤,导致湘鄂西区沉积盖层沿南华系和震旦系陡山沱组下段、寒武系牛蹄塘组、志留系龙马溪组等三个主滑面发生了三个层次的滑脱和褶皱,形成自底部滑脱层向上传播的以前展式的正向(倾向SE)冲断系。铅锌矿的产出层位与矿源层的分布层位有一定的依存关系,寒武系下统牛蹄塘组是区内主要的铅锌矿源层,矿源层与构造形迹共同控制了东山峰背斜范围内的铅锌矿分布。背斜两翼构造形迹的不同,造成了两翼铅锌矿化特征的差异,背斜西部轴部转折区带是最具找矿潜力的部位。 相似文献
19.
贵州开阳磷矿地区下寒武统牛蹄塘组地层层序及其As、Sb、Au、Ag丰度异常与赋存状态研究 总被引：3，自引：2，他引：1
贵州开阳磷矿地区出露较为完整的下寒武统黑色岩系层序,这套黑色岩系中富含多种金属元素,但目前对岩系中主要低温成矿元素As、Sb、Au、Ag的地球化学背景异常与分布规律了解极少,对其形成背景与赋存状态无法进行深入讨论。本文以开阳磷矿地区下寒武统牛蹄塘组黑色岩系剖面作为研究对象,通过详细的野外地质调查、系统采样并进行地球化学分析、全岩硫同位素分析及黄铁矿电子探针分析,划分了详细的牛蹄塘组地层层序,对主要低温成矿元素(As、Sb、Au、Ag)的丰度异常、富集特征及赋存状态进行了研究,结果表明,黑色岩系中普遍富集As、Sb、Ag三种主要低温成矿元素,Au也在大部分层位富集。四种元素具有层控性的特点,在牛蹄塘组下部有机质含量较高的黑色白云质粉砂质页岩和黑色页岩层位中具有较高的元素丰度异常,在泥岩和粉砂岩混合层位元素丰度异常较低,钙质成分含量较高的层位元素含量较低。黄铁矿是黑色页岩中金的主要赋存矿物,也是Sb的重要赋存矿物,同时是Ag和As的次要赋存矿物;不同类型的黄铁矿,元素富集规律也不相同:As、Ag更容易富集在不规则集合体和草莓状黄铁矿中,Sb和Au则在散布的单颗粒黄铁矿中富集系数最高。 相似文献
20.
D. E. Ayres 《Australian Journal of Earth Sciences》2013,60(3-4):155-168
The main Woodlawn ore lens is a polymetallic, massive sulphide deposit’ with pyrite the major constituent, variable sphalerite, galena and chalcopyrite, and minor arsenopyrite, tetrahedrite‐tennantite, pyrrhotite and electrum. The silicate gangue minerals are chlorite, quartz, talc and sericitic mica. Other mineralization in the vicinity consists of footwall copper ore in chlorite schist and several smaller massive sulphide lenses. The predominant country rocks are felsic volcanics and shales, with abundant quartz, chlorite and mica, and talc in mineralized zones. An important textural feature of the massive ore is the fine compositional banding. Bands, which vary in thickness from a few tens of micrometres to several millimetres, are produced by variations in the sulphide content. Post‐depositional metomorphism and minor fracturing have only slightly modified this banding. Apart from the major element constituents—Pb, Zn, Fe, Cu and S—the ore is characterized by significant (100–1000 ppm) values for Ag, As, Cd, Mn, Sb and Sn, and lower (1–100 ppm) values of Au, Bi, Co, Ga, Hg, Mo, Ni, Tl. In and Ge. Variations in the base‐metal sulphide content, the gangue mineralogy, and trace elements, are used to separate the orebody into hanging‐wall and footwall zones. The hanging‐wall zone shows a more variable trace element content, with higher Tl, Sn, Ni, Mn, Ge and Sb, but lower Ag, Cd, and Mo, than the footwall zone. In general style of mineralization, mineralogy, and chemistry, the Woodlawn deposit resembles other volcanogenic massive sulphide deposits in eastern Australia, in New Brunswick in Canada, and the Kuroko deposits of Japan. 相似文献