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1.
Trace elements in supergene phosphorites   总被引：1，自引：0，他引：1  
Supergene phosphorites were analyzed for Sr, Ba, Zn, Cd, Sc, Cr, Ag, and V, i.e., elements incorporated in carbonate-apatite by isomorphic substitution. The phosphorites were subdivided into four groups: (1) phosphorites related to the weathering of sedimentary rocks, (2) phosphorites related to the weathering of endogenous rocks, (3) lacustrine coprolite phosphorites, and (4) phosphorites of ocean islands. In all the phosphorites groups, Sr, Zn, and Ba were the most abundant of the trace elements, whereas Cd, Ag, and Sc showed the lowest concentrations. Variations in trace element contents between supergene phosphorites of different genetic groups or within a single group can be explained by the different compositions of weathered rocks and geochemical environments of supergene phosphorite formation. At the same time, the contents of some trace elements are correlated with the structural type of phosphorite. In particular, phosphorite crusts or only their outer parts show elevated contents of chalcophile elements (Cd, Zn, and Ag), whereas massive phosphorites and inner parts of crusts are often enriched in such lithophile elements as Sc, V, and Cr. It was found that Cd, Zn, Ag, Sr, and Ba are positively correlated with CO2 but show negligible correlations with other constituents of carbonate-apatite.  相似文献   

2.
Major and trace element composition of the Ordovician Obolus phosphorites and associated Dictyonema shales were determined by ICP-MS and chemical and microchemical elemental analyses. Relative to the phosphorites, the Dictyonema shales are substantially enriched in a variety of trace elements, except for As, Be, Co, Y, REE, Sr, and Pb. The Obolus phosphorites show enrichment of As, Bi, Hg, Mo, La, Y, Pb, and Sr and depletion of Ag, Ba, Be, Cd, Cr, Cu, Hf, Ni, Sc, Sn, U, V, Zn, and Zr relative to the world average phosphorite composition. The average trace element composition of the Dictyonema shales is close to the mean shale composition, except for higher contents of Mo, Hg, Pb, Se, Ta, Te, Th, V, and U and lower contents of Ba, Bi, Cd, Co, Re, Sr, and Zn. The results suggest that the change from phosphate sedimentation in aerated environments to anoxic carbonaceous sedimentation was accompanied by changes in the composition and concentration of trace elements in the sediment. Both facies show similar trends of trace element distribution indicative of the stability of the composition of seawater and terrigenous sediment input.  相似文献   

3.
《Chemical Geology》2002,182(2-4):483-502
Detailed petrological, mineralogical, geochemical and radiogenic (U, Sr, Nd) and stable isotope (C, O, S) studies have been carried out on the Quaternary phosphorites of the continental margin off Chennai, southeast coast of India. These phosphorites are formed as a result of trapping and binding of sediments by microbial mats and are similar to phosphate stratiform stromatolites. Detrital and biogenic constituents enclosed in the phosphorites controlled the major and minor element composition. Except for Sr and U, the concentrations of most of the trace metals are lower than those in average shale and phosphorite. Middle rare earth element (MREE)-enriched patterns are the characteristic feature. The U–Th dating method indicates that the ages of the phosphorites are beyond 300,000 years. 87Sr/86Sr ratios of the phosphorites are higher than that of present-day seawater and εNd values are more negative than those of seawater of the Atlantic Ocean. Carbon isotope ratios are within the range expected for the oxic/suboxic zone but sulfur isotope ratios indicate suboxic conditions during phosphorite formation. These results imply that the benthic microbial mats thrived on the shallow shelf during the Quaternary low sea level conditions. Periodic or episodic sedimentation onto the mats led to their death. The bacteria associated with decaying microbial mats utilised phosphorus supplied by continental sources and rapidly precipitated phosphate. The availability of a high percentage of phosphorus in seawater seems to be an important controlling factor for the formation of phosphate stromatolites. The composition of these phosphorites differs from the modern phosphorites in upwelling regions, but are similar to Cambrian apatite stromatolites. These phosphorites provide evidence that the replicates of ancient phosphate stromatolites do exist in the Quaternary.  相似文献   

4.
The paper presents the uranium (U) concentration and distribution pattern in the Paleoproterozoic phosphorites of Lalitpur district of Uttar Pradesh. The study of thin sections, SEM and XRD reveal that apatite is the essential phosphate mineral while quartz and feldspars are the dominant gangue in the phosphorites of the investigated area. The collophane is observed to be mostly oolitic in form and microspherulitic in texture. The major element geochemistry indicated that the phosphorite samples are rich in P2O5, CaO, SiO2 and Fe2O3 whereas depletion of MgO, MnO, K2O and Al2O3 was observed. The CaO/P2O5 ratio ranges from 1.13 to 1.46 which is slightly lower than that of cations and anions substituted francolite (1.621) and close to that of carbonate-fluorapatite (1.318). The trace element geochemistry indicates that the phosphorites of Lalitpur have the significant range of U concentration (1.67 to 129.67 μg/g) which is more than that of Th (0.69 to 0.09 μg/g) among the analysed trace elements in the phosphorite samples of the area. The positive correlation of U with P2O5, CaO and U/P2O5 indicates a close association of U with phosphate minerals like collophane (apatite), whereas negative correlation of U with SiO2 and Fe2O3 may be due to mutual replacement. The antipathetic relationship of U with Ni may be an indication of high oxidizing conditions, whereas sympathetic relationship of U with K2O points towards higher alkaline conditions of the basin of deposition during phosphatization. The variable concentration of U and its relationship with significant major and trace elements in most of the phosphorite samples lead one to believe that the deposition of these phosphorites might have taken place in highly alkaline medium during fairly oxidizing to weakly reducing environmental conditions of geosynclinal basin.  相似文献   

5.
High levels of Cd and Zn in Jamaican soils observed in geochemical surveys are related to the presence of phosphorites of possible Late-Miocene or Pliocene age. The trace element and REE geochemistry of the phosphorites, together with SEM studies, indicate a guano origin for the phosphorites. No specific host minerals for Cd could be identified in the fossiliferous phosphorite which is characterized by uniquely high levels of Cd, Zn, Ag, Be, U and Y. However, in the soil Cd is present in lithiophorite and a complex history of pedological development is preserved in the aluminous–goethite present in the soil. The unique guano signature is preserved in the soil despite the fact that guanos themselves have either not been observed or have been destroyed by continuing karst and soil development. The phosphorite geochemical signature can be traced in the data of a 1988 island-wide soil geochemical survey, identifying areas where the Palaeo-environment that supported bird ‘rookeries’ existed in the Late-Miocene or Pliocene.  相似文献   

6.
贵州织金新华含稀土磷矿床扫描电镜研究   总被引：27，自引：1，他引：26  
张杰  陈代良 《矿物岩石》2000,20(3):59-64
用扫描电子显微镜和Ｘ射线能谱仪等方法研究织金新华含稀土磷矿床矿物组成,结构特征及微量元素含量变化特征。通过ＥＤＡＸ能谱仪进行矿物成分分析,得出Ｙ２Ｏ３质量分烽与胶磷矿物密切相关的结论。对伴生矿物作了相关研究,初步探讨了稀土元素赋存状态及富集规律。  相似文献   

7.
The Precambrian phosphorites of Bijawar Group of rocks show characteristics of a epicontinental sea with restricted and very shallow marine environment of formation along some shoals, which existed during the iron-rich Precambrian times. These phosphorite deposits located in the Hirapur-Bassia areas show extensive leaching of carbonate and phosphate minerals during episodes of weathering. X-ray diffraction studies indicated that carbonate-flourapatite is the major apatitic phase in these phosphorites while crandallite developed on the surface outcrops. There is a general tendency for the depletion of CO2 in these apatites leading to formation of flourapatite. This CO2 is an indicator of hidden weathering in the rocks. Major and trace element determinations of phosphorite have been used to indicate various correlation factors responsible for the concentration of elements in these Precambrian leached phosphorites.The paper is a contribution to the aims and objectives of IGCP Project 156The paper is dedicated to Prof. Dr. R. C. Misra, who as a teacher and guide had been a source of inspiration to the senior author for the last two decades  相似文献   

8.
海州—大悟地区变质磷矿含磷岩系(锦屏岩群、宿松岩群、红安岩群)岩层组合,标志岩层,微量、稀土元素特征和沉积环境皆可与鄂西陡山沱期磷矿类比,时代归属为新元古代,其中磷矿层属震旦系。江苏沭阳滥洪—华冲、湖北广济牛头山—黄梅塔儿畈和应山—广水一带为磷矿找矿有利地区。  相似文献   

9.
The Cambrian Gezhongwu Formation in Southwest China is the lowest Cambrian phosphorite unit. The Formation belongs to the Meishucun stage with small shelly fossils. Rare-earth element (REE)data from the Gezhongwu phosphorites of Zhijin documented the depositional conditions. The total REE concentrations are high in the Gezhongwu phosphorites, which are especially rich in yttrium. The PAASnormalized REE patterns of the Gezhongwu phosphorites are characterized by negative Ce anomalies and slight enrichment of MREE, as being hat-shaped. The hat-shaped patterns suggest that the REE originated from depositional environments rather than from subsequent diagenesis. The negative Ce anomalies indicate that the depositional environments are oxic. The positive Eu anomaly, the high total REE and the hatshaped REE pattern revealed contributions from the normal marine environment mixed with hydrothermal water to the REE budget of the Gezhongwu phosphorites.  相似文献   

10.
In the past, there has been little interest in the trace element characteristics of quartz, and in consequence little activity in the trace element characteristics of reference materials with high silicon content. The main purpose of this paper is to contribute to the characterisation of two international certified reference materials, BCS 313/1 from the Bureau of Analysed Samples, (BAS), UK and SRM 1830 from the National Institute of Standards and Technology (NIST), USA. BCS 313/1 was analysed by laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS), solution ICP-MS and instrumental neutron activation analysis (INAA). NIST SRM 1830 was analysed by LA-ICP-MS and INAA. Analytical results are reported for more than forty elements, most of them for the first time. For most elements, the results obtained by the different methods agree within 15 % relative. The recent, heightened interest in quartz and in particular the precise determination of trace0element contents in natural quartz samples requires the use of well characterised reference materials such as BCS 313/1 and SRM 1830, to which this study is designed to contribute.  相似文献   

11.
The content, distribution patterns, and occurrence forms of Cl in phosphorites and bone phosphate from the ocean bottom, as well as in a set of samples from the land, are studied. The total Cl content ranges from 0.05 to 4.25% in phosphorites and from 2.48 to 2.75% in recent phosphate-bearing sediments. Recent phosphorites are enriched in Cl relative to ancient ones. The bound Cl content (not extractable by washing), which increases with lithification, ranges from 0.17 to 0.60% in oceanic and land phosphorites and from 0.02% to 1.30% in the bone phosphate. The Na content in most samples is higher relative to NaCl due to its incorporation into the crystal lattice of apatite. However, the opposite relationship is observed in some samples, indicating a partial Cl incorporation into the anion complex of phosphate. The behavior of Cl in phosphorites from the present-day ocean bottom is controlled by early diagenetic processes, whereas the role of weathering, catagenesis, and hydrogeological factors may be crucial for phosphorites on continents.Translated from Litologiya i Poleznye Iskopaemye, No. 1, 2005, pp. 65–77.Original Russian Text Copyright © 2005 by Baturin.  相似文献   

12.
Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) is a high spatial resolution analytical method which has been applied to the analysis of silicic tephras. With current instrumentation, around 30 trace elements can be determined from single glass shards as small as ～ 40 µm, separated from tephra deposits. As a result of element fractionation during the ablation process using a 266 nm laser, a relatively complex calibration strategy is required. Nonetheless, such a strategy gives analyses which are accurate (typically within ±5%) and have an analytical precision which varies from ～ ±2% at 100 ppm, to ～ ±15% at 1 ppm. Detection limits for elements used in correlation and discrimination studies are well below 1 ppm. Examples of the application of trace element analysis by LA‐ICP‐MS in tephra studies are presented from the USA, New Zealand and the Mediterranean. Improvements in instrumental sensitivity in recent years have the potential to lower detection limits and improve analytical precision, thus allowing the analysis of smaller glass shards from more distal tephras. Laser systems operating at shorter wavelengths (e.g. 193 nm) are now more widely available, and produce a much more controllable ablation in glasses than 266 nm lasers. Crater sizes of <10 µm are easily achieved, and at 193 nm many of the elemental fractionation issues which mar longer wavelengths are overcome. By coupling a short wavelength laser to a modern ICP‐MS it should be possible to determine the trace element composition of glass shards as small as 20 µm and, providing sample preparation issues can be overcome, the determination of the more abundant trace elements in glass shards as small as 10 µm is within instrumental capabilities. This will make it possible to chemically fingerprint tephra deposits which are far from their sources, and will greatly extend the range over which geochemical correlation of tephras can be undertaken. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

13.
磷块岩的胶结作用   总被引：1，自引：0，他引：1       下载免费PDF全文
磷块岩胶结物有泥质、硅质、磷质和碳酸盐质4种,共形成19种胶结结构,其中尤以磷泥晶环边结构、等厚纤状环边结构、似重力式结构、磷质纤状环边叠加云质亮晶充填结构特征突出,具有指示沉积成岩环境的意义。4种类型的胶结物在剖面和平面上的演变与水体深度和沉积成岩环境有关,而胶结作用的地球化学特征,既是磷块岩的环境指示,又反映微生物的影响状况。  相似文献   

14.
磷块岩矿床的形成总是同特定的沉积相和沉积环境相联系的。从古地理分布看,它们多半产在该成矿时期的海侵前缘带、陆表海和深水盆地的过度部位或水下高地的周围地带。磷矿层多出现于海侵序列的底部或下部,但是含磷岩系本身则既可以是退积式的,也可以是进积式的。  相似文献   

15.
The Khubsugul phosphate-bearing basin divided into the western and eastern zones. Phosphorites composed of alternating structureless phosphate layers (1–3 cm) and thinner lenticular dolomite laminae prevail in the western zone corresponding to the distal part of the sedimentation profile. Contents of all trace elements are approximately equal and correspond to the clarke level in both phosphate and dolomite layers. The laminae are also identical in terms of the low (–7 PDB) 13 values. Phosphorites of the western zone were rapidly buried and the presence of dolomite intercalations is explained by postsedimentary segregation. The eastern proximal zone is dominated by the so-called dolomitic phosphorites with variable-size irregular fragments of phosphate matter enclosed in the later dolomitic matrix. Relative to structureless varieties, granular (pelletal) phosphorites of the basin are subordinate and enriched in trace elements (particularly, rare earth elements). Phosphate facies are replaced by black shales on the western side of the basin.  相似文献   

16.
为重建黔中地区震旦纪陡山沱期古海洋环境,选取小河磷矿(XH)、息烽磷矿(XF)含磷岩系剖面,通过系统采样及岩矿鉴定、扫描电镜、微量元素和稀土元素分析,揭示古海洋环境对磷块岩沉积的影响作用。结果表明,磷矿成矿受黔中古陆长期剥蚀夷平形成的无障壁海岸海滩环境控制。陡山沱期洋水组磷块岩Sr/Ba值一般大于1,均值分别为1.90(XH)和0.95(XF),而澄江组沉积物Sr/Ba值均小于1,均值分别为0.11(XH)和0.18(XF),说明沉积环境由澄江期的湖泊相转变为陡山沱期的海相。小河剖面V/Cr和Ni/Co均值分别为1.77和2.17,息烽剖面V/Cr和Ni/Co均值分别为1.26和2.83,均位于弱氧化—氧化区间。息烽磷矿磷块岩δCe为0.75~0.95,均值0.85,小河磷矿磷块岩δCe为0.74~1.09,均值0.88,Ce负异常由底部至顶部逐渐增大,显示沉积环境由次氧化—氧化的转变。这种氧化转变不仅造成了浅水富磷海岸大洋生产力的提升,进一步促使与生物作用相关的磷块岩沉积,同时造成的生命演化也改变了大洋含氧结构,因此成磷环境的氧化转变是对新元古代氧化事件与生命演化的响应。  相似文献   

17.
Trace element profiles for common divalent cations (Sr, Zn, Ba), rare-earth elements (REE), Y, U, and Th were measured in fossil bones and teeth from the c. 25 ka Merrell locality, Montana, USA, by using laser-ablation ICP-MS. Multiple traverses in teeth were transformed into 2-D trace element maps for visualizing structural influences on trace element uptake. Trace element compositions of different soils from the fossil site were also analyzed by solution ICP-MS, employing progressive leaches that included distilled H2O, 0.1 M acetic acid, and microwave digestion in concentrated HCl-HNO3. In teeth, trace element uptake in enamel is 2-4 orders of magnitude slower than in dentine, forming an effective trace element barrier. Uptake in dentine parallel to the dentine-enamel interface is enhanced by at least 2 orders of magnitude compared to transverse, causing trace element “plumes” down the tooth core. In bone, U, Ba and Sr are nearly homogeneous, implying diffusivities ∼5 orders of magnitude faster than in enamel and virtually complete equilibration with host soils. In contrast all REE show strong depletions inward, with stepwise linear segments in log-normal or inverse complementary error function plots; these data require a multi-medium diffusion model, with about 2 orders of magnitude difference in slowest vs. fastest diffusivities. Differences in REE diffusivities in bone (slow) vs. dentine (fast) reflect different partition coefficients (Kd’s). Although acid leaches and bulk digestion of soils yield comparable fossil-soil Kd’s among different elements, natural solutions are expected to be neutral to slightly basic. Distilled H2O leachates instead reveal radically different Kd’s in bone for REE than for U-Sr-Ba, suggest orders of magnitude lower effective diffusivities for REE, and readily explain steep vs. flat profiles for REE vs. U-Sr-Ba, respectively. Differences among REE Kd’s and diffusivities may explain inward changes in Ce anomalies. Acid washes and bulk soil compositions yield misleading Kd’s for many trace elements, especially the REE, and H2O-leaches are preferred. Patterns of trace element distributions indicate diagenetic alteration at all scales, including enamel, and challenge the use of trace elements in paleodietary studies.  相似文献   

18.
Black shales and thin-bedded cherts in the basal Cambrian are widespread worldwide and they carry important information on the formation of sedimentary basins and on the tectonic history. We studied the geochemical signatures of the early Cambrian black shales and bedded cherts from the Northern Tarim Basin, China, with the objectives of understanding the depositional setting of these rocks and inferring the tectonic history in the region. Twenty two black shales, ten cherts, and two nodular phosphorites were collected from two outcrops at Xiaoerbulake and Sugaitebulake in the Northern Tarim Basin, spanning vertical sections of 8.8 and 7.5 m, respectively. A suite of techniques, including field investigations, X-ray diffraction, electron microscopy, trace element, rare earth element (REE), and isotope geochemistry, were employed to characterize the geochemical signatures of these rocks. Field evidence indicates that the black shales and bedded cherts are over- and underlain by dolomites, suggesting a shallow marine depositional environment. Mineralogical and trace element data suggest that the Tarim black shales and cherts were deposited in a suboxic continental shelf environment, and hydrothermal activity may have extracted certain trace elements from mafic continental crust and concentrated them in the sedimentary basin. REE characteristics for the cherts are very similar to those that are known to be deposited in pelagic ocean floor settings, suggesting that the hydrothermal fluids may be derived from the infant southern Tianshan Ocean in the north of the Tarim Basin. Os isotope signatures at the time of deposition (187Os/188Osi = 1.1–2.7) are typical of crustal signatures, and the radiogenic Os isotope signatures rule out the mantle as a possible source of Os and other metals. A positive correlation between 187Os/188Os and εNd is consistent with upper crust-derived basin sediments that contain a variable contribution of hydrothermal fluids possibly derived from ancient mafic continental crust. These trace element, REE, and isotope systematics collectively suggest that incorporation of hydrothermal fluids derived from ancient, mafic continental crust combined with deposition in relatively reducing conditions may have controlled the chemical and isotopic compositions of these rocks. We infer that the hydrothermal fluid was carried to the continental shelf by upwelling during the initial stages of formation of the southern Tianshan Ocean, where the fluid interacted with thinned, mafic crustal basement lithologies and was subsequently incorporated into the black shales and bedded cherts in the Northern Tarim Basin. This study provides important geochemical evidence for the creation of the Tianshan Ocean, which is a result of break-up of the Rodinia Supercontinent during the early Cambrian.  相似文献   

19.
Upper Cretaceous Phosphorites from different localities in Egypt were analyzed for their rare earth elements (REEs) contents and sulfur and strontium isotopes to examine the effect of depositional conditions versus diagenesis on these parameters.The negative Ce and Eu anomalies of the study phosphorites suggest its formation under reducing conditions. However, chondrite-normalized REEs patterns show relative enrichments of LREEs over the HREEs, which is obviously different from the seawater REEs pattern suggesting post-depositional modifications on the REEs distributions during diagenesis. The difference in the REEs concentrations and Ce anomalies among the study localities as well as the similarity between the REEs patterns of these phosphorites and associated black shales might support this interpretation.The concentration of structural SO42− (0.6-3.7%) and their δ34S values (+0.5 to -20‰) in the upper Cretaceous phosphorites in Egypt suggest the formation of these phosphorites in the zone of sulfate reduction. On the other hand, the sulfur isotopes in the pyrite from the study phosphorites (δ34S = +4.6‰ − 23‰ with an average of −7.7‰) are attributed to the influence of seawater from which pyrite was formed during diagenesis. The difference between the δ34S values in the phosphorites (all are positive values) and those in the associated pyrite (mostly negative values) reflect an asymmetric sulfate and sulfide sulfur isotopic composition due to the formation of francolite (source of sulfate) and pyrite (source of sulfide) in different conditions and/or process.The 87Sr/86Sr values of the upper Cretaceous phosphorites in Egypt are very close to the marine values during the Campanian-Maastrichtian time and their average (0.707622) is more or less comparable to the average 87Sr/86Sr values of the Cretaceous-Eocene Tethyan phosphorites. This suggests no post-depositional alteration (i.e. diagenetic effect) on the Sr isotopic composition of these phosphorites.  相似文献   

20.
This paper describes an extended application of the Rayleigh distillation law to trace element behavior in a fractional crystallization sequence. Using a trace element with a very low bulk partition coefficient as a reference (as suggested by Anderson and Greenland, 1969, and extended by Treuil and Varet, 1973), we can derive bulk partition coefficients for other elements and, in turn, the mineralogical composition of the cumulates. Trace elements with large D, such as Ni and Cr, further constrain the system, and we can deduce the initial composition of the magma. An example of this technique is shown for Terceira Island in the Azores.Contribution IPGNS no 229Now at Dept. of Geological Sciences, California Institute of Technology, Pasadena, California, USA  相似文献   

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