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1.
Four outcrops of Lower Cretaceous (Barremian) karst bauxites located in Teruel (NE Spain) were analysed to determine their mineral associations and genesis related to climatic palaeoweathering events and late superimposed kaolinization processes. The materials comprise metric‐sized pisolitic blocks embedded in a clay‐rich red groundmass. Fourteen samples were examined by X‐ray diffraction, optical microscopy, scanning and transmission electron microscopy and the major elements were analysed by inductively‐coupled plasma mass spectroscopy (ICPMS). The samples are composed of kaolinite, gibbsite, goethite, and hematite as the main phases, with diaspore, boehmite, anatase, and rutile as accessory minerals. The results show a complex sequence of mineralogical and geochemical processes that transformed the parent rock into the current bauxite materials. The clay‐rich groundmass constitutes the lateritic parent material of the pisolitic bauxites. In the parent material authigenic kaolinite (e.g. vermicular kaolinite and kaolinite between cleavage sheets of pre‐existing mica) has been observed; Fe oxides formed subsequent to kaolinite. In the pisolitic bauxites, mineralogical and textural evidence indicates that bauxitization took place at the expense of previous kaolinite, with gibbsite post‐dating the other Al hydroxides. The pisolitic bauxites also show a more homogeneous chemical composition and a relative Ti, Al and Zr enrichment. The data are consistent with an intense palaeoweathering event during the Lower Cretaceous (Barremian) under tropical climatic conditions (warm and humid). Several stages probably took place during the bauxitization process, suggesting variations in water saturation conditions. Subsequent karst reactivation stages and related collapses were responsible for the present lithostructure of the deposits and allowed late kaolinization not related to climate to take place. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
2.
Three vertical sections through the Zagrad deposit of Jurassic karst bauxite in central Montenegro have provided knowledge of the vertical distribution of major and some selected trace elements, including rare earth elements (REE). Variations in the mineralogy, particularly those hosting REE, have been studied. This has revealed the presence of authigenic mineral phases such as xenotime, mottramite and monazite (best proved using Raman microprobe analysis) as well as residual phases such as zircon, titanite and monazite. The mobility of the elements during bauxitization processes has been studied to show that the REE minerals ensure progressive concentration of these elements during removal of major elements through weathering. The similarity of normalized REE in the bauxite to the typical Post-Archean Australian Shales (PAAS) and Upper Continental Crust (UCC) profile, and the preserved Eu anomaly, are evidence that the bauxite was not derived from carbonates and represents alteration of shale, marly limestone and volcanogenic or proximal igneous sourced detritus that accumulated in the original karst landform. Mass change during bauxitization, using Ti as “index” element and compared to PAAS composition, revealed almost 100% depletion of Si and weak enrichment in Al. Deeper parts of the deposit with authigenic minerals exhibit very strong enrichment in all REE. The bauxite ores have high ΣREE contents (693.5–6953.4 ppm), especially ΣLREE contents (582.8–4882.9 ppm), while ΣHREE contents (106.6–2070.5 ppm) are much lower. 相似文献
3.
The Mandan and Deh-now bauxite deposits are located 40 km northeast of the Dehdasht city in the Zagros simply fold belt. These deposits occur in eroded major NW–SE trending anticlines and occupy karst cavities near or at the boundary between the Sarvak and Ilam Formations. Local uplifts at the end of the Cenomanian and the mid-Turonian caused erosion and karstification of the Sarvak Formation. These unconformities in the Upper Cretaceous favoured the formation and enrichment of bauxite deposits in the Zagros fold belt. The bauxite sequence in the Mandan deposit consists of white, gray, black, pisolitic, red, and yellow bauxites. This sequence was repeated in the Deh-Now area, but without gray and black bauxites. The present mineralogical studies of the Sarvak Formation and the Mandan and Deh-now bauxite deposits indicate oxidizing to reducing conditions during the Upper Cretaceous in the Zagros fold belt, which had a significant effect on the compositions of the bauxites. At least two phases of bauxitization can be distinguished in the study area: (i) an oxidizing phase represented by boehmite, diaspore, hematite and kaolinite; and (ii) a reducing phase represented by pyrite and chlorite. Geochemical data show that trace elements, like Zr, Hf, Nb, Ta, Th, and U, were enriched during bauxitization. The bauxite deposits and carbonate rocks show similar REE patterns, namely they are enriched in REEs although the LREEs are more enriched than the HREEs. Mass change calculations demonstrate that Mg, Mn, Ca, K, and P2O5 were leached out of the weathered system whereas Al, Fe, and Si become concentrated in the residual system. This study indicates that the Mandan and Deh-now deposits are karst-type bauxites formed by karstification and weathering of the Sarvak Formation. 相似文献
4.
The Olmedo bauxite deposit occurs in the Nurra district of northwest Sardinia. It forms a stratiform horizon in Cretaceous
limestone and marl. Uplift in mid-Cretaceous had exposed recently deposited limestone to karst weathering, and a layer of
argillaceous debris accumulated on its surface and was partly converted to bauxite. Intermediate products were desiccated
marl, bauxitic argillite and argillaceous bauxite. Subsidence followed, and the bauxite was preserved by the deposition of
late Cretaceous limestone and other sediments. Uplift in Oligocene-Miocene time, with ensuing erosion, exposed the bauxite
horizon to its present configuration. Concentrations of normative minerals illustrate chemical processes and the build-up
of Al in the bauxite horizon. Plots of chemical data and correlation coefficients show that Al, Ti, Zr, Nb, Th, Cr and V were
immobile during the bauxitization process. Mass changes point to large net removal of Si, Mg and K from the system, although
some of this material and slightly mobile Al were reprecipitated in the underlying argillite and altered marl. Immobile element
ratios trace the source of the bauxite to the underlying argillaceous limestone. Al in the bauxite was accumulated from the
degradation of 25 to 50 m of the argillaceous limestone.
Received: 10 June 1996 / Accepted: 15 April 1997 相似文献
5.
N. Özlü 《Mineralium Deposita》1983,18(3):469-476
This work deals with a concise but comprehensive study of trace-element distribution in the bauxite deposits of Mediterranean belt. Although the alloctonous and mainly detritic characters of several “karst bauxite” deposits are well established, their parent rock has remained largely enigmatic. Evidence is available that some chemical elements, notably Zr, Cr and Ga are largely immobile during the weathering and diagenesis and study of such trace-elements in “karst bauxites” permits to make an approach to the lithological nature of their parent rocks. It is shown, by reference to analyses of bauxites from Mediterranean areas, that all the deposits studied are aligned from a Cr rich pole related to ultramafics to another pole rich in Ga and Zr contents and in genetical relation with acidic parent rocks. The results obtained by this way have been controlled by application of “trace-element accumulation coefficient” which permits to distinguish four principal zones of bauxite derived from the parent rock of different lithological characters (Fig. 3). 相似文献
6.
In a lateritic bauxite formed by weathering of nepheline syenite at Passa Quatro, Minas Gerais State, Brazil, bauxites on the hill-tops directly develop from the syenite bed-rock, while downslope, a kaolinitic layer occurs between bauxite and synetie. A petrological investigation was performed on undisturbed weathered rock samples collected from a representative upslope pit. The undisturbed weathered rocks were chemically analysed for major trace elements including REE and Zr. Mass balance calculations were applied, and the behaviour of the REE in the Passa Quatro weathering system was established compared to REE reference chondrite and to REE reference parent rock. In the lateritic bauxite, the results suggest that the first stages of weathering induce a volumetric change of 50%, i.e. collapse, with respect to the parent rock, and remove REE with a slightly larger loss of the LREE, except Ce, compared to the HREE. In the upper layers, where bauxite is more mature, a net mass gain in REE is observed relative to the underlying layers. This gain takes place during the reduction of the upper layer during the downward progression of the weathering front. Very significant REE losses occurs during the bauxitization processes throughout the upslope profile. In addition, the downslope kaolinitic system is demonstrated to be depleted in REE in the same proportions as the upslope bauxite. We proposed that the REE exported in solution from the whole weathering mantle have enriched neighbouring watershed sediments. 相似文献
7.
《Applied Geochemistry》2005,20(1):1-21
In the northern part of the Indian sub-continent, the Ganga alluvial plain (GAP) feeds its weathering products to the Ganga–Brahmaputra River system, one of the world’s largest fluvial systems. The authors present a geochemical study of the GAP weathering products transported by the Gomati River (the Ganga River tributary) to understand weathering processes of an alluvial plain in a humid sub-tropical climate. A total of 28 sediment samples were collected during the monsoon season and were analysed by X-ray fluorescence spectrometry for 25 major and trace elements. Bulk chemistry of the channel, flood and suspended sediments mostly consists (>90%, >80% and >75%, respectively) of three elements; Al, Si and Fe. Major element concentrations normalised with respect to upper continental crust (UCC) show strong depletion of highly mobile elements (Na, Ca) and enrichment of immobile elements (Ti, Si). Silica enrichment in the sand fraction is probably caused by chemical weathering of feldspar. Mineral sorting during fluvial transportation acts as the single important factor that controls the geochemistry of these weathering products and also strongly influences major and trace element distribution in the individual sediment samples. Trace element (Ba, Cr, Cu, Nb, Ni, Pb, V and Zn) concentrations were strongly correlated with major element (Si, Al, Fe, Mn and K) concentrations indicating that the abundance of trace elements is controlled by the same processes that control the major element distribution in these sediments.The GAP weathering products were geochemically distinguished as arkose to litharenite in rock classification. Chemical mobility, normalised with respect to TiO2 in UCC, indicates that Si, Na, Zr, Ba and Sr, mainly derived from feldspar, muscovite and biotite, are lost during weathering. Iron and Zn remained immobile during weathering and were strongly adsorbed by phyllosilicates and concentrated in fine-grained sediment fractions. The chemical index of alteration indicates that the GAP has experienced chemical weathering of incipient to moderate intensity. The GAP weathering products also demonstrated a progressive incomplete alteration in the alluvial sequence made-up of the Himalayan-derived sediments. A model has been proposed to better understand weathering processes and products of the GAP in temporary storage of ∼50 ka in a humid sub-tropical climate. 相似文献
8.
Lateritic bauxites in the coastal lowlands of Suriname form part of a belt along the northern margin of the Guiana Shield that has long been one of the world's major bauxite producing regions. The Surinamese deposits, many of which with an extensive mining history, originated on Tertiary siliciclastic sediments and were mostly buried under a layer of young sediments. The bauxite-bearing sequences are generally topped with an iron-rich layer largely made up of hematite and goethite. It covers a gibbsite-rich bauxite horizon that passes downward into a kaolinitic bottom section containing anatase and zircon as main accessory minerals. Weathering profiles across formerly mined deposits were analyzed for geochemical and mineralogical properties aimed at exploring compositional diversity, underlying controls of bauxite-formation and the nature of precursor sediments.Studied profiles in different parts of the coastal plain reveal overall similarities between individual deposits in showing significant depletion of Si, K, Na, Mg and Ca and strong, primarily residual, relative enrichment of Al, Ti, Zr, Nb, Hf, Ta and Th. In detail, however, there are distinct differences in major and trace-element signatures, accessory mineral assemblages, facies distribution and provenance of the terrigenous precursor sediments. Enrichments in high field-strength elements and heavy rare earth elements are largely attributable to accumulation of heavy minerals like zircon in the precursor. Petrological and trace-element evidence does not support a direct genetic relationship between bauxite and the underlying saprolitic clays. The complex petrologic characteristics and compositional heterogeneity of the coastal-plain deposits can essentially be explained by element fractionation, primarily through selective leaching, in combination with relative and absolute enrichment processes, erosion and reworking during two-stage, polycyclic bauxitization of a heterogeneous precursor. 相似文献
9.
Paola Mameli Giovanni Mongelli Giacomo Oggiano Enrico Dinelli 《International Journal of Earth Sciences》2007,96(5):887-902
Bauxite deposits are widespread in NW Sardinia. They formed during the middle Cretaceous, in consequence of a period of emergence of the Mesozoic carbonate shelf. In the Nurra area the geometries derived by the Middle Cretaceous tectonic phases controlled the ore typologies. Two bauxite profiles, laying on different bedrocks, were sampled. The bauxitization proceeded from the surface downward, with the accumulation of Al2O3 and residual ‘immobile’ elements (Al, Ti, HFSE), and corresponding mobility and loss of SiO2 and Fe2O3. Epigenetic kaolinite formed close to faults and joints, probably as a result of silicification, introduced by low temperature hydrothermal solutions. Rare earth elements, especially LREE, are concentrated in Fe-rich bauxite horizons, probably due to scavenging by goethite. REE-enrichment is not observed in the boehmite-rich horizons. Very high REE contents are observed in a Fe-depleted horizon due to the occurrence of REE accessory minerals, probably of the bastnäsite group. Conservative indices, including TiO2/Al2O3 and Ti/Cr ratios, and Eu anomalies (Eu/Eu*), suggest that the deposits formed by weathering of sediments derived from mafic rocks of the Hercynian basement. This, in turn, implies that the basement was exposed during middle Cretaceous. 相似文献
10.
Subaerial leaching process of sedimentary bauxite and the discussion on classifications of bauxite deposits 
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下载免费PDF全文 Bauxite is the ultimate fine-grained products of chemical weathering,and thus it is closely linked with the intense chemical weathering. Based on variations of parent rock and weathering processes,the weathering products can be subdivided into laterite and terra rossa,of which the former is formed by weathering of aluminosilicates and the latter is produced by the weathering of carbonates. During the intense chemical weathering,minerals in original subaerial sediments(parent rocks)would suffer a series of processes(dissolution,hydrolyzation,hydration,carbonation,and oxidation)and be destroyed or transformed,leading to formation of new minerals. In the favorable environment,continuously intense chemical weathering would cause the loss of most mobile elements(e.g., K,Na,Ca,Mg,Si)and the enrichment of Al,resulting in the formation of bauxite. Although sedimentary bauxites are closely linked with the weathering curst,they show obvious differences in formation processes. Sedimentary bauxites are composed of intense chemical weathering products that are transported from outside of the basin and re-deposited in the basin,while most weathering crusts are transformed from saprolite and/or deluvium in-situ,and they can only form low-grade bauxites. Sedimentary environments also differ in bauxite ore layers and bauxitic claystone layers. Bauxite ore layers are formed in the subaerial environment and controlled by the leaching process of groundwater in the vadose zone. Based on the analysis of bauxitization,this study proposes to use multiple parameters,such as provenance,sedimentation and mineralization,to build the new classification of Chinese bauxite deposits. In this classification,lateritic and karstic types of bauxite deposits are autochthonous or parautochthonous saprolite and/or deluvium,while sedimentary type is dominated by heterochthonous provenance. 相似文献
11.
铝土矿是化学风化作用的细粒终极产物,与强烈的化学风化作用密切相关。根据母岩的类别及作用过程,风化作用进一步分为铝硅酸盐岩强化学风化形成的红土化作用和碳酸盐岩强化学风化形成的钙红土化作用。在强烈的化学风化过程中,地表的原始沉积物(母岩)的原生矿物发生溶蚀、水解、水化、碳酸化、氧化,破坏原始的矿物结构,形成新的细粒矿物(主要是黏土质矿物)。在适合的地质条件下,持续的强烈化学风化作用会造成大部分活动的元素(如K、Na、Ca、Mg、Si)的流失与Al的残留富集从而形成铝土矿。现在观察到的沉积型铝土矿,虽然与古风化壳具有密切联系,但沉积型铝土矿多数是由沉积过程搬运到沉积盆地中所形成的强化学风化产物的沉积层,与古风化壳的残坡积层具有显著差别,只有少数工业价值不大(品位低、品质差)的残坡积相铝土矿。铝土矿含矿岩系的沉积环境与铝土矿(尤其是高品位、高品质的铝土矿)的成矿环境不尽相同。铝土矿主要形成于暴露于大气中的陆表环境(而非水下环境),由地下水淋滤作用形成(在渗流带由活动元素流失、Al等稳定元素残留富集而成)。本研究在铝土矿成矿作用分析等基础上,提出了以铝土矿沉积物等物源和沉积、成矿作用为依据的中国铝土矿床分类方案,包括原地或准原地残坡积物成因的红土型和喀斯特型,和异地物源沉积成因的沉积型。 相似文献
12.
Thair Al-Ani 《Arabian Journal of Geosciences》2017,10(3):72
Nuwaifa Formation is a part of sequence stratigraphy that belongs to the Jurassic system exposed in the western desert of Iraq. The Jurassic system consists of Ubaid, Hussainiyat, Amij, Muhaiwir, and Najmah formations. Each formation is composed of basal clastic unit overlain by upper carbonate unit. Nuwaifa karst bauxite was developed in fossil karsts within the Ubaid Formation in areas where maximum intersection of fractures and faults exist. This bauxitization process affected the upper surface of the Ubaid limestone formation, which directly underlies the Nuwaifa bauxite Formation. Nuwaifa Formation represents karst-filling deposit that consists of a mixture of allochthonous (sandstone, claystone, and mudstone) and autochthonous lithofacies (bauxite kaolinite, kaolinitic bauxite, iron-rich bauxite, and flint clay). Most bauxite bodies occur within the autochthonous lithofacies and are lenticular in shape with maximum thickness ranges from few meters to 35 m and in some place up to 100 m. Petrographically, the bauxite deposit exhibits collomorphic-fluidal, pisolitic, oolitic, nodular, brecciated, and skeletal textures indicative of authigenic origin. Mineralogy boehmite and gibbsite are the only bauxite minerals; the former is dominant in the upper parts of the bauxite profiles, whereas the latter is dominant throughout the lower and middle part of the bauxite. Kaolinite, hematite, goethite, calcite, and anatase occur to a lesser extent. The study bauxites are mainly composed of Al2O3 (33–69.6 wt.%), SiO2 (8.4–42 wt.%), Fe2O3 (0.5–15.9 wt.%), and TiO2 (0.7–6.1 wt.%) with LOI ranging from 13.5 to 19.1 wt.%. Geochemical investigations indicate that the immobile elements like Al2O3, TiO2, Cr, Zr, and Ni were obviously enriched, while SiO2, Fe2O3, CaO, MgO, Zn, Co, Ba, Mn, Cu, and Sr were depleted during bauxitization process. The results of this study strongly suggest that the bauxite deposits of the Nuwaifa Formation are derived from the kaolinite of the Lower Hussainiyat Formation. 相似文献
13.
Bauxite is a residual rock, consisting mainly of a mixture of aluminium hydroxides, whose industrial significance is primarily due to its profitably exploitable alumina contents. In the last decades, bauxite, mainly karst bauxite, has been also considered as possible resource of a great number of economically interesting elements including some critical metals such as rare earth elements, Sc, Co, Ni, and Nb. In this study, we present results of univariate and multivariate (R-mode factor analysis) statistics performed on a large data set including chemical composition of the principal Cretaceous karst bauxites from central and southern Italy with the twofold aim to evaluate the inter-elemental relationship among major oxides and critical metals, and describe factors affecting their distribution. Univariate statistics reveal that some critical metals Co, Ni, and LREE, have a significant number of outliers. The Co-Ni relationship associated to the outliers dataset suggests that Co is likely hosted in Ni-rich phases whereas Ce accumulation in authigenic minerals, carbonate-fluoride and phosphate, is at the origin of LREE outliers. Multivariate R-mode statistics, applied to the outliers-devoid database, instead demonstrate that in absence of specific mineralization events, the distribution of most critical metals is controlled by Al-, Fe-, and Ti-oxi-hydroxides and, to a lesser extent, by detrital phases. Among the critical metals, Cr and Y are the exceptions. Their geochemical behaviour seems to be influenced primarily by their own chemical features that are responsible for the mobility of Cr during bauxitization and for the decoupling of Y from the REEs. 相似文献
14.
桂西二叠纪喀斯特型铝土矿是第四纪萨伦托型铝土矿的矿源层,但是其具体成矿地质过程并不清楚.在矿带东部平果矿田1∶5万区域地质调查基础上,针对性地对二叠纪铝土矿床进行了合山组含铝岩系基本层序、铝土矿成矿物质来源、古喀斯特地貌对铝土矿的控制作用及含铝矿物生成顺序的研究,并阐述了该类型铝土矿从源岩风化到搬运沉积的具体成矿过程.综合前人研究成果,提出桂西二叠纪喀斯特型铝土矿的四阶段成矿模式,分别为孤立台地隆升接受火山喷发沉积物阶段、原地深度风化阶段、积水潜育化阶段和埋藏成矿阶段. 相似文献
15.
黔北白云岩红色风化壳元素地球化学特征 总被引：5，自引：3，他引：2
选取贵州高原喀斯特地区典型白云岩风化剖面作为研究对象,探讨了红土剖面元素迁移特征及其影响因素,为进一步认识红色风化壳元素地球化学特征提供依据。结果表明:（1）红土剖面中土壤样品（XPS-4~XPS-25）Fe、K、Mn常量元素及Co、Pb、Zn微量元素的分布曲线相对于其他元素靠近 UCC,元素Mg、Ca、Na、Ti和 Li、Cr、Ba、V 的数据点则显著偏离了上部陆壳的平均组成。（2）元素对协变分析得出Ti与Fe、Ba和V的积累特征一致,呈增加趋势;Ti与Mg呈反向变化特征。（3）以Ti为参比元素的剖面迁移特征表明,绝大部分元素的地球化学行为表现为迁移淋失,仅 Fe 、Cr和V 富集。K、Ba总体上呈迁出趋势,个别层段有轻微富集;Na和Co在风化原岩处有一个富集端点。元素在风化过程中的迁移聚集与土壤剖面的pH值和剖面结构变化、粘土矿物和有机质等的吸附有关。 相似文献
16.
The Lower Jurassic section at Makhtesh Ramon, in the northeastern Negev of Israel, comprises a sequence of fluviatile sediments of laterite composition. Post-depositional chemical weathering has resulted in marked facies changes whereby the clastic sequence passes laterally into high-alumina flint clays and bauxites (Goldbery, 1979). A geochemical and mineralogical investigation was initiated on 216 samples from several key sections of the facies change to obtain a more refined definition of the diagenetic overprint, to reconstruct the history of chemical weathering and finally to recognize the parent material of the unaltered laterite sediments.Results are presented herein on major and trace-element composition, normative mineralogical composition, kaolinite crystallinity and porosity and density measurements. Kaolinite crystallinity values proved to be a good indicator of intensity of leaching, showing a marked decline in ordering with increase of diagenetic reorganization. On the basis of mineralogical parameters it was possible to subdivide the section of flint clays and bauxites, generated under karstic conditions, into four units. Bivariate plots of Al2O3 vs. several elements within the section, plotted into four distinctive fields coinciding with the subdivision. Enrichment/depletion ratios, calculated from the element concentrations within these flint clays against element concentrations of the clastic parent material of the karstic infill, led to the reconstruction of a multi-cyclic leaching event, whose “signature” is left in each of the four units. At least 3 individual episodes of leaching, related to a rising water table and punctuated by “still-stands” could be recognized.Zr/TiO2: Nb/Y plots of stable elements, using the diagram of Floyd and Winchester (1978) for determination of source rocks, indicated a rhyolite or alkaline rhyolite provenance for the clastic laterite detritus. 相似文献
17.
The present study focuses on the Late Cretaceous Bidgol bauxite deposit in the Zagros Simply Fold Belt, SW Iran. The orebody is located in the eroded major NW–SE trending Koh-e-Hosseyn anticline and hosted as discontinuous stratified layers and lenses within the upper member of the Cenomanian–Turonian Sarvak Formation. Detailed mineralogical analysis reveals that diaspore, hematite, goethite, anatase, clinochlore, chamosite, and calcite are the major mineral components accompanied by minor amounts of detrital and REE-bearing minerals such as rutile, zircon and parisite. The ore texture suggest that the bauxite material has an authigenic origin but in some parts it has been transported short distances from a primary in situ environment and redeposited in karstic depressions. The spheroidal pisolites of the Bidgol bauxite formed under conditions of low water activity, favouring the formation of large diaspore cores and a single dry-to-wet climatic fluctuation. The mass change calculations relative to the immobile element Ti show that elements such as Si, Fe, Mg, K, Na and Sr are leached out of the weathered system; Al, Ni, Zr, Ga, Cr and Ba are concentrated in the residual system; and Hf, Ta, Co, Rb, Cs, Be, and U are relatively immobile during the bauxitisation processes. The Nb, Th, Y, V, Sc, Sn and ΣREE are relatively immobile in the initial stage of bauxitisation processes in the bauxite ores, but were slightly mobile at the later stage of bauxitisation. Geochemical data reveal progressive enrichment of the REE and intense LREE/HREE fractionation toward the lower parts of the bauxite profile. Cerium behaves differently from the other REEs (especially LREE) and show positive anomalies in the upper horizons that gradually become negative in the deeper parts of the profile. The distribution and fractionation of trace elements and REEs during the bauxitisation process in the Bidgol deposit are mainly controlled by the presence of REE-bearing minerals, fluctuations in soil solution pH, REE ionization potential and the presence of bicarbonates or organic matter. Geochemical analyses confirm a protolith contribution from the bedrock argillaceous limestone and suggest that the source material for the Bidgol bauxite was provided from a siliciclastic material derived from a continental margin. The mid-Turonian uplift led to the formation of karstic topography, rubbly breccia and a layer of ferruginous–argillaceous debris that was affected by lateritic weathering under humid tropical climate. Subsequently, mobile elements are removed from the profiles, while Al, Fe and Ti are enriched, resulting in the formation of the pristine bauxite materials. When the platform subsided into the water again, the pristine bauxitic materials were partly converted to bauxite. During the exposure of bauxite orebodies on the limbs and crests of anticlines and subsequent eroding and accumulation in the karstic depressions during folding and faulting in Oligocene–Miocene, important factors such as intensity of the weathering, drainage and floating flow may have improved the qualities of the bauxite ores. 相似文献
18.
桂西地区铝土矿为典型喀斯特型,包括二叠系沉积型和第四系堆积型两亚类。堆积型铝土矿是沉积型铝土矿经抬升、破碎、风化,最后堆积于喀斯特洼地中形成。以平果教美铝土矿为研究对象,探索堆积型铝土矿形成过程中矿物的变化与元素迁移。沉积型矿石的矿物组成包括硬水铝石、鲕绿泥石、锐钛矿及少量针铁矿、金红石和高岭石;堆积型矿石的矿物组成主要为硬水铝石、锐钛矿、高岭石及少量三水铝石和鲕绿泥石。转化过程中堆积型矿石中的硬水铝石含量明显增加,鲕绿泥石含量明显减少。沉积型铝土矿的主要化学组成为Al2O3、SiO2、FeO和TiO2;堆积型为Al2O3、SiO2、TiO2和Fe2O3。两类矿石中元素Zr 、Ba、Nb、V含量均较高,稀土总量变化大,富集轻稀土。质量平衡计算表明堆积型铝土矿形成过程中Al、Ba、Sr、Y等元素增加,而Si、Fe、Ti、Nb、V、Ce等元素减少,其余元素变化不明显。 相似文献
19.
[摘 要] 滇东南地区上二叠统吴家坪阶下部铝土矿不整合于峨眉山玄武岩或灰岩之上,查明其物质来源对铝土矿勘探具有重要意义。对铝土矿及峨眉山大火成岩省玄武岩、花岗岩及下伏灰岩的地球化学指标进行研究,结果表明:滇东南铝土矿常量元素主要由SiO2、Fe2O3、Al2O3、TiO2 和FeO 组成;铝土矿中富集Zr、Hf、Nb、Ta 元素,表明Zr、Hf、Nb、Ta 等高场强元素在滇东南地区铝土矿矿化过程中较为稳定,且Zr、Hf、Nb、Ta 表现出良好的相关性;铝土矿球粒陨石标准化曲线与峨眉山玄武岩配分曲线趋势一致,均富集轻稀土元素,而与下伏灰岩差异较大,且Zr-Hf、Nb-Ta 图解与峨眉山玄武岩呈线性关系,而与矮郎河过铝质花岗岩的相关性不强。据此推断滇东南地区上二叠统吴家坪阶下部铝土矿主要物质来源为峨眉山玄武岩。 相似文献
20.
碳酸盐岩风化形成的红土保存着喀斯特发展演化历史证据,同时也是喀斯特地区土壤研究的重要对象。文章选取云
南石林地区的两处典型碳酸盐岩剖面为研究对象,对主量元素,微量元素及稀土元素在风化层的迁移特征及分布规律进行
研究,为探究风化层的成因提供依据。结果显示：（1） 以Ti为参比元素的剖面迁移特征表明,两剖面的主量元素在成土过
程中有相似的迁移规律,多数表现为淋失;微量元素略有差异,富集淋失程度不一。（2） UCC 标准化蜘蛛图显示,相对于
基岩,风化层中的Ca和Sr均出现亏损;与UCC相比,Fe、Ti等元素轻微富集,Mg、Ca、Na、K、P等元素显示了强烈的亏
损特征。（3） 基岩与风化层的REE分布模式相似,但风化层的稀土相对富集,轻稀土元素间的分异较大而重稀土元素间的
分异较小,且SJC剖面的轻、重稀土元素比值大于QST剖面;稀土元素球粒陨石标准化后,SJC剖面的Eu为负异常,剖面
上部和下部出现Ce负异常;QST剖面Ce负异常,Eu明显负异常。（4） 元素含量变化和元素对Al-Ti、Al-Fe及Zr-Hf相关性
说明剖面上覆红土是下伏基岩风化的结果。研究结果显示,两个剖面的元素地球化学特征与基岩存在很好的继承性,风化
层是基岩原位风化的产物。 相似文献