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1.
K. A. Novoselov E. V. Belogub V. A. Kotlyarov K. A. Filippova S. A. Sadykov 《Geology of Ore Deposits》2018,60(3):265-276
The paper discusses the mineralogical and geochemical features of oolitic ironstones from the Sinara–Techa deposit, Transural region, Kurgan district. The ore unit is localized in the lower part of a thick Mesozoic–Cenozoic sequence of sedimentary rocks that fill the West Siberian Basin beneath calcareous clay and overlying beds enriched in glauconite and clinoptilolite. The ironstone consists of goethite ooids in smectite–opal cement. Accessory minerals are pyrite, galena, sphalerite, and monazite. The texture and structure make it possible to suggest the formation of sediments enriched in iron as a result of colloid coagulation. The most probable source of iron is related to inland drift. Deposition of iron took place in the estuaries of subtropical rivers due to mixing of colloidal solution of river water with seawater electrolyte. The chemical features of rocks are controlled by the composition of the adsorbed iron oxi/hydroxide complex. 相似文献
2.
长江口地区绿色颗粒的矿物学研究 总被引：1，自引：0，他引：1
本文对长江下游河道、长江口现代沉积区、口外残留砂沉积区及大陆架现代沉积区表层沉积物中的绿色颗粒进行了系统的矿物学研究。特别运用透射间和能谱分析对其内部超微结构、单晶结构和单晶化学组成进行了研究。长江口地区的绿色颗粒从宏观形态上可分为三类：颗粒状、书页状和生物状，不同的形态者，其形成机制基本相同，只是微晶聚集的微空间环境不同。绿色颗粒的颜色和成熟度有较密切的关系，颜色愈深，K和Fe含量愈高。其成熟度也愈高，K2O含量为3－7％，仅少数可达8.5％。绿色颗粒主要矿物成分为海绿石、鲕绿泥石、磁绿泥石和蒙4皂石。其中以海绿石为主，因此是一种复合型绿色颗粒。不同形态及不同沉积亚环境中绿色颗粒的矿物成分并无太大差别。 相似文献
3.
Detailed mineralogical characteristics of various forms of glauconite occurrence in Lower Cretaceous marine terrigenous rocks
of the White Island (Binnel Bay, southern England) are discussed. It has been shown that glauconite was formedin situ due to the transformation of fine-dispersed and sandy-silty terrigenous materials. The influence of bacterial activity on
glauconite formation is supported by the study of dissolution zones on quartz and feldspar grains, which revealed biomorphic
structures akin to fossilized bacteria. 相似文献
4.
Keisuke Fukushi Tomonori Sugiura Tomoaki Morishita Yoshio Takahashi Noriko Hasebe Hiroshi Ito 《Applied Geochemistry》2010
Greenish veins occurring in brecciated bentonite were found in the Kawasaki bentonite deposit of the Zao region in Miyagi Prefecture, Japan. Their occurrence possibly indicates the interaction of bentonite with Fe-rich hydrothermal solutions. In order to prove the hypothesis and understand the long-term mineralogical and petrographic evolution of bentonite during such interactions, the greenish veins and the surrounding altered bentonite were analyzed using X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe micro-analysis (EPMA), scanning transmission electron microscopy with energy dispersed spectroscopy (STEM-EDS) and micro X-ray absorption near-edge structure (XANES). The greenish veins resulting from hydrothermal solution are composed of mixed-layer minerals consisting of smectite and glauconite (glaucony), pyrite and opal. The occurrences indicate that glaucony and pyrite formed almost simultaneously from hydrothermal solution prior to opal precipitation. The mineral assemblages of the greenish veins and their surroundings indicate that the hydrothermal activity had most likely taken place at a temperature of less than 100 °C and that the pH and Eh conditions of the reacted solution were neutral to alkaline pH and reducing. The unaltered bentonite is composed mainly of Al smectite and opal. These minerals coexist as a mixture within the resolution level of the microprobe analyses. On the other hand, the bentonite in contact with the greenish veins consists of discrete opal grains and dioctahedral Al smectite containing Fe and was altered mineralogically and petrographically by the hydrothermal activity. Both the clay minerals and the opal were formed by dissolution and subsequent precipitation from the interaction of the original bentonite with the hydrothermal solution. 相似文献
5.
在内蒙古西乌珠穆沁旗晚石炭世—早二叠世阿木山组第三段泥晶灰岩中发现有海绿石。对海绿石的微观特征分析表明,阿木山组海绿石呈团粒状结构,同时呈胶体产出于方解石周边,显示了原生海绿石的基本特点。电子探针的组分分析表明,阿木山组中的海绿石为高成熟度的海绿石。通过对不同地区和不同环境下海绿石的组分特征分析,建立了一种海绿石沉积的理想模式,同时揭示了阿木山组第三段海绿石化作用是在含氧量不够充分的弱还原状态下的正常浅海中进行的。本区阿木山组的下碎屑岩段和上灰岩段是在海水两进两退环境下的沉积,阿木山组灰岩中发现的海绿石则有可能代表了一个海进的开始。本区海绿石的发现及研究,对于进一步研究该区层序地层特征、地层格架及区域地层对比具有重要意义。 相似文献
6.
S.G. McRae 《Earth》1972
The term glauconite has been employed in two senses. It has been used most commonly as a morphological term for sand-sized greenish grains found in sedimentary rocks, but also as a name for a specific mineral species, a hydrated iron-rich micaceous clay mineral. The two uses are not synonymous, since not all morphological glauconite consists exclusively of mineral glauconite, nor is the latter restricted in its occurrence to such pellets. Mineral glauconite in sensu lato is a random interstratification of nonexpanding 10A?layers and expanding montmorillonitic layers. The amount of expandable layers may be over 50 % but it is customary to restrict the name mineral glauconite in sensu stricto to varieties with less than 10 % expandable layers. The variation in amount of expandable layers explains many of the observed variations in the properties of glauconite including chemical composition (especially potassium content), thermal characteristics, cation exchange capacity, colour, refractive index and specific gravity. Mineral glauconite is believed to form by the progressive absorption of potassium and iron by a degraded layer silicate lattice of low lattice charge and elimination of other silicate-lattice types under suitable environmental conditions, of which the most critical seems to be the redox potential. The catalytic activity of marine organisms is no longer thought to be essential, although decaying organic matter and empty foraminiferal tests supply the ideal environment for glauconite genesis. The process of glauconitization is arrested by rapid sedimentation, so that there is a relationship between the variety of mineral glauconite formed and the nature of the host rock. Glauconite is found associated particularly with marine transgressions. Morphological glauconite grains are believed to form as casts, faecal pellets or by accretionary growth, but may have their morphology modified by subsequent re-working. A number of characteristic internal and external morphologies have been recognised. The wide range of environmental conditions suitable for its formation and its common detrital occurrence debars the use of glauconite in palaeo-environmental studies. Its major use in geology is for the absolute age dating of sedimentary rocks by the K-Ar method. Glauconitic deposits have no present day commercial value, but soils formed on glauconitic parent materials are notable for their fertility. Glauconite weathers by loss of potassium to produce a montmorillonitic or vermiculitic product with the release of, or oxidation of, structural iron, so that the grain has the appearance of having weathered to limonite. 相似文献
7.
Arsenic (As) concentrations as high as 179 μg/L have been observed in shallow groundwater in the Alberta’s Southern Oil Sand Regions. The geology of this area of Alberta includes a thick cover (up to 200 m) of unconsolidated glacial deposits, with a number of regional interglacial sand and gravel aquifers, underlain by marine shale. Arsenic concentrations observed in 216 unconsolidated sediment samples ranged from 1 and 17 ppm. A survey of over 800 water wells sampled for As in the area found that 50% of the wells contained As concentrations exceeding drinking water guidelines of 10 μg/L. Higher As concentrations in groundwater were associated with reducing conditions. Measurements of As speciation from 175 groundwater samples indicate that As(III) was the dominant species in 74% of the wells. Speciation model calculations showed that the majority of groundwater samples were undersaturated with respect to ferrihydrite, suggesting that reductive dissolution of Fe-oxyhydroxides may be the source of some As in groundwater. Detailed mineralogical characterization of sediment samples collected from two formations revealed the presence of fresh framboidal pyrite in the deeper unoxidized sediments. Electron microprobe analysis employing wavelength dispersive spectrometry indicated that the framboidal pyrite had variable As content with an average As concentration of 530 ppm, reaching up to 1840 ppm. In contrast, the oxidized sediments did not contain framboidal pyrite, but exhibited spheroidal Fe-oxyhydroxide grains with elevated As concentrations. The habit and composition suggest that these Fe-oxyhydroxide grains in the oxidized sediment were an alteration product of former framboidal pyrite grains. X-ray absorption near edge spectroscopy (XANES) indicated that the oxidized sediments are dominated by As(V) species having spectral features similar to those of goethite or ferrihydrite with adsorbed As, suggesting that Fe-oxyhydroxides are the dominant As carriers. XANES spectra collected on unoxidized sediment samples, in contrast, indicated the presence of a reduced As species (As(−I)) characteristic of arsenopyrite and arsenian pyrite. The results of the mineralogical analyses indicate that the oxidation of framboidal pyrite during weathering may be the source of As released to shallow aquifers in this region. 相似文献
8.
Authigenic clays in close textural relation to carbonate fluorapatite within finely laminated phosphate stromatolites of Upper Jurassic age have been studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and analytical electron microscopy (AEM). Stromatolite laminae consist of hexagonal prisms of francolite (sizes ranging between 0·1 and 1 μm) that are surrounded by poorly crystalline smectite and amorphous Fe–Si–Al oxyhydroxides. Microanalyses show that smectite is Fe rich, with highly variable composition, particularly regarding Fe and Si contents. Smectite has significant beidellitic, montmorillonitic and non-tronitic substitutions. Although the lack of fringe contrast in some areas adjacent to the smectite packets with 1·0–1·3 nm spacing is due to differences in orientation of layers, textural and analytical data clearly indicate the presence of Fe–Si–Al amorphous phases intimately intergrown with smectite. The occurrence of poorly crystalline smectite and associated amorphous phases within microbially precipitated stromatolite laminae, both as envelopes around, and as pore-fillings between extremely small calcium phosphate crystals, demonstrates authigenic smectite growth from a precursor Fe–Si–Al amorphous material. This material is formed in close association with a phosphate-rich precursor. The textural and structural relations, the preservation of chemical precursors of glauconite such as nontronitic montmorillonite, and the presence of Fe–Si–Al amorphous mineral phases, imply crystallization of the observed crystalline phases from synsedimentary (bacterially precipitated) amorphous precursors during early diagenesis in postoxic environments. Carbonate fluorapatite was the first phase to crystallize from the primary gel; smectite and associated amorphous Fe–Si–Al oxyhydroxides were the residual material of the crystallization process. The slow rate of transformation (at low temperatures) from Fe–Si–Al-rich gels to smectite, explains the textural relations between the poorly crystalline phases and the phosphate crystals, as well as the preservation of amorphous substances in relation to clays. Authigenic smectite represents the first step in glauconitization. 相似文献
9.
Deep-sea sediments from a basin in the Southeast Pacific are described, in which strong carbonate dissolution and strong diagenetic migration of metals can be observed. Clay minerals of smectite type are formed in large quantities during the early diagenesis of this sediment, in a first stage as an X-ray amorphous phase, which later crystallizes to smectite. Rb, Sc, Na and K become enriched during the process of clay-mineral formation, probably due to uptake of these elements from sea-water to interlayer positions of smectite. The unsolved question is what sort of mechanism connects the calcite dissolution with the formation of smectite? The source of the Al, necessary for the formation of smectite is also unknown. 相似文献
10.
The field-name “glauconite” is applicable to a great variety of green grains, particularly mud clasts, which are found in the fraction >63μ in surface sediments from the Persian Gulf. These grains occur in areas of low sedimentation rates in all water depths to 110 m, the shelf break in the Gulf of Oman (Fig. 1). Glauconite grains coarser than 250,μ were magnetically separated from 15 samples and then handpicked. Their carbonate fractions (75->90%, predominantly aragonite) are basically different from those of the corresponding total samples (50–65%, predominantly calcite). The clay minerals in the glauconite grains fall into two groups. The samples away from the shore contain abundant montmorillonite, compared to the small amount in the 2μ (fractions of the total samples; the near shore samples are predominantly amorphous material and illite. Because of these and other differences from the remaining parts of the samples (Tab. 1) the glauconite grains are considered to be parautochthonous relicts from the underlying late Pleistocene. They were apparently formed under the special conditions of a transgressing shallow marine environment. 相似文献
11.
12.
Ran Liu Amy L. Wolfe David A. Dzombak Colin P. Horwitz Brian W. Stewart Rosemary C. Capo 《Applied Geochemistry》2008
The dissolution of pyrite is of interest in the formation of acid mine drainage and is a complex electrochemical process. Being able to measure the rate of dissolution of particular pyrite samples under particular conditions is important for describing and predicting rates of AMD generation. Electrochemical techniques offer the promise of performing such measurements rapidly and with small samples. The oxidation of pyrite and the reduction of Fe3+ ions and/or O2 half reactions involved in the pyrite dissolution process were investigated by cyclic voltammetry and steady-state voltammetry using three pyrite materials formed in both sedimentary and hydrothermal environments. For each sample, two kinds of pyrite working electrodes (conventional constructed compact solid electrode, and carbon paste electrode constructed from fine-grained pyrite particles) were employed. Results indicated that for both the hydrothermal and sedimentary pyrite samples the oxidation and reduction half reactions involved in dissolution were governed by charge transfer processes, suggesting that hydrothermal and sedimentary pyrites obey the same dissolution mechanism despite their different formation mechanisms. In addition, the results showed that it is feasible to use a C paste electrode constructed from fine-grained or powdered pyrite to study the pyrite dissolution process electrochemically and to derive approximate rate expressions from the electrochemical data. 相似文献
13.
V. A. Drits T. A. Ivanovskaya B. A. Sakharov B. B. Zvyagina A. Derkowski N. V. Gor’kova E. V. Pokrovskaya A. T. Savichev T. S. Zaitseva 《Lithology and Mineral Resources》2010,45(6):555-576
The detailed mineralogical and structural-crystal-chemical characteristics are reported for the first time for glauconite grains extracted from the fine-platy silty-sandy dolomites at the roof of the lower subformation of the Yusmastakh Formation (Riphean, Anabar Uplift, North Siberia). Based on the complex study (X-ray diffraction, classical chemical analysis, microprobe analysis, IR-spectroscopy, thermogravimetric analysis, scanning electron microscopy with microprobe analysis, and Mössbauer spectroscopy), it was demonstrated that the studied glauconite sample is characterized by unique chemical and structural heterogeneity.The mineral structure consists of micaceous (90%), smectite (6%), and di-trioctahedral chlorite (4%) layers. Mica is classed with Al-glauconite (Al > Fe3+) with elevated Mg content. The elevated Mg mole fraction of the mineral is caused by the presence of Mg-bearing brucite-type interlayers of di-trioctahedral chlorite and the high Mg content in the octahedral sheets of 2: 1 layers. It was first discovered that glauconites are characterized by the heterogeneous distribution of cations over the available trans- and cis-octahedra due to the coexistence of trans- and cis-vacant octahedra and small trioctahedral clusters in octahedral sheets. The distribution of isomorphic cations over the accessible octahedral sites is also heterogeneous due to the tendency of Fe, Mg and Al, Mg cations to segregation and formation of corresponding domains.It was found that structure of the studied glauconite has a specific stacking defect: in addition to the predominant subsequent layers of similar azimuthal orientation according to 1M type (～77%), some layer fragments are rotated at 180° (～15%) and ±120° (8%). The structural-crystal-chemical heterogeneity of the mineral is explained by the fact that its microcrystals grew in the dolomitic sediment under nonequilibrium conditions of the reduction zone of a shallow-water basin with a sufficiently high content of Mg cations, which significantly contributed to the glauconite formation. 相似文献
14.
De glauconiarum origine 总被引：4，自引：0，他引：4
The glauconitic facies is widespread on present-day continental shelves from 50° S to 65° N and at water depths between 50 and 500 m, and is in particularly great abundance on the upper slope and outer shelf between 200 and 300 m. It is also common in many ancient rocks of post-late Precambrian age. It occurs as sand- to pebble-sized, essentially green particles (granular facies) but also as a surface coating on particles and hardgrounds and as a diffuse impregnation (film and diffuse facies). We suggest the replacement of the term ‘glauconite’, which has been interchangeably used to designate a morphological form and a specific mineral, by glaucony (facies) and glauconitic smectite and glauconitic mica as end members of the glauconitic mineral family. The widely accepted model of Burst and Hower for glauconitization requires a degraded, micaceous (2: 1 layer lattice structure) parent clay mineral. However, detailed analysis of numerous samples of Recent glaucony reveals that such a parent substrate is exceptional. The model therefore requires modification. Generally the parent material is carbonate particles, argillaceous (kaolinitic) faecal pellets, infillings of foraminiferal tests, various mineral grains and rock fragments, that pass gradually into the commonly occurring green grains. We show that the process of glauconitization is achieved by de novo authigenic growth of automorphous crystallites in the pores of the substrate, accompanied by progressive alteration and replacement of the substrate. It is this two-fold evolution that causes the ‘verdissement’of granular substrates, macrofossils and hardgrounds. The authigenic mineral is an iron-rich and potassium-poor glauconitic smectite. While new smectites are growing into the remaining pore space the earlier smectites are modified by incorporation of potassium, producing decreasingly expandable minerals with a non-expandable glauconitic mica as the end member. This mineralogical diversity of the glauconitic mineral family explains the highly variable physical and chemical properties of glaucony. Four categories, nascent, little-evolved, evolved and highly-evolved glaucony are distinguished. Glauconitization appears to be controlled by a delicate balance between degree of physical confinement of a particle and the amount of ionic exchange between the micro-environment and ambient open marine sea water. The optimum conditions for glauconitization are those of semi-confinement. As a result the interior of a grain is more glauconitized than its less confined periphery. Similarly, for identical substrate types, large grains (500μm) provide more favourable substrates for glauconitization than lesser confined small grains. On a larger scale the formation of glaucony is governed by the availability of iron and potassium and the balance between detrital influx and winnowing. Low accumulation rates expose grains to the open marine environment for sufficiently long times (105-106 years for highly-evolved glaucony). 相似文献
15.
Ezz El Din Abdel Hakim Khalaf 《Arabian Journal of Geosciences》2014,7(7):2603-2624
Wadi Queih basin hosts a ～2,500-m thick Neoproterozoic volcanoclastic successions that unconformably lie over the oldest Precambrian basement. These successions were deposited in alluvial fan, fluviatile, lacustrine, and aeolian depositional environments. Diagenetic minerals from these volcaniclastic successions were studied by X-ray diffractometry, scanning electron microscopy, and analytical electron microscopy. The diagenetic processes recognized include mechanical compaction, cementation, and dissolution. Based on the framework grain–cement relationships, precipitation of the early calcite cement was either accompanied or followed by the development of part of the pore-lining and pore-filling clay cements. Secondary porosity development occurred due to partial to complete dissolution of early calcite cement and feldspar grains. In addition to calcite, several different clay minerals including kaolinite, illite, and chlorite with minor smectite occur as pore-filling and pore-lining cements. Chlorite coating grains helps to retain primary porosity by retarding the envelopment of quartz overgrowths. Clay minerals and their diagenetic assemblages has been distinguished between primary volcaniclastics directly produced by pyroclastic eruptions and epiclastic volcaniclastics derived from erosion of the pre-existing volcanic rocks. Phyllosilicates of the epiclastic rocks display wider compositional variations owing to wide variations in the mineralogical and chemical compositions of the parent material. Most of the phyllosilicates (kaolinite, illite, chlorite, mica, and smectite) are inherited minerals derived from the erosion of the volcanic basement complex, which had undergone hydrothermal alteration. Smectites of the epiclastic rocks are beidellite–montmorillonite derived from the altered volcanic materials of the sedimentary environment. Conversely, phyllosilicate minerals of the pyroclastic rocks are dominated by kaolinite, illite, and mica, which were formed by pedogenetic processes through the hydrothermal influence. 相似文献
16.
Glauconitic peloids from a Hauterivian condensed level in a hemipelagic unit of the Internal Prebetic (Los Villares Formation, eastern Betic Cordillera) have been studied by X‐ray diffraction (XRD), optical microscopy, scanning electron microscopy (SEM) and high‐resolution transmission electron microscopy (HRTEM) and analytical electron microscopy (AEM). The sediments forming the condensed level are characterized by abundant spherical to ovoid green glauconite peloids with radial cracks. Quartz, feldspar and muscovite are also abundant, whereas calcium phosphate is rarely detected. XRD analysis of the peloids reveals glauconite and small amounts of berthierine. SEM and HRTEM data show feldspar dissolution features, a Si–Al‐rich gel‐like substance filling K‐feldspar micropores and interlayering of well‐crystallized glauconite and berthierine packets. The last stage of the glauconitization process resulted in conversion of the smectitic precursor. Sedimentary and mineralogical features indicate an autochthonous origin for the glauconite. The depositional environment was a distal, hemipelagic ramp on the Southern Iberian Continental Palaeomargin. Low sedimentation rates lead to sediment condensation in a general transgressive context. The margin was affected by extensional tectonics, creating tilted blocks, resulting in lateral facies changes. The dissolution of K‐feldspars probably occurred after their deposition in the marine environment but predating the glauconitization. An influx of meteoric water is therefore required, probably related to subsurface fluxes from adjacent emergent areas (the higher parts of tilted blocks). Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
17.
Erzsébet Tóth Tamás G. Weiszburg Teresa Jeffries C. Terry Williams András Bartha Éva Bertalan Ildikó Cora 《Chemical Geology》2010,269(3-4):312-328
Samples of glauconite, representing different stages of glauconitisation, as well as different formation environments, were analysed for rare earth elements (REE) and other trace elements using a combination of bulk sample and spatially-resolved in situ techniques. The results indicate that the high-sensitivity, spatially-resolved technique of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) produces values up to two orders of magnitude lower than the bulk sample analyses. This suggests that submicroscopic rare earth element-bearing phases are distributed within the glauconite aggregates comprising the bulk samples. Analytical scanning electron microscopy (ASEM) revealed the presence of micrometre-sized grains of apatite and pore filling precipitates of an unidentified (REE, Ca)-phosphate (approximate composition Ca0.3–0.4(Ce0.4La0.1–0.2Nd0.1)PO4) in some glauconite grains.The inherent REE concentrations of the glauconite aggregates (i.e., glauconite crystallites without accidental mechanical inclusions or authigenic, not layer silicate mineral precipitates) was found to be relatively low (e.g., typically less than 100 ppm), and this value decreased with increasing glauconitisation (smectite–mica transformation through a series of recrystallisation processes). These results suggest that the REEs substitute for Ca in the interlayer space of the layer silicate structure and, therefore, the REE content decreases as Ca is progressively removed from the interlayer (smectite–mica transition).LA-ICP-MS, when combined with electron probe microanalysis (EPMA) or ASEM, offers an opportunity to exclude submicroscopic accessory minerals from glauconite trace element analyses, and so produces reliable trace element data for the respective minerals which host those elements.These results illustrate that accessory minerals are difficult to eliminate from clay samples, and that care needs to be taken in the interpretation of clay mineral REE distributions, irrespective of the aggregation state of the studied clay (i.e., whether finely dispersed within the sedimentary rock, or forming millimetre-sized aggregates). Model calculations showed that authigenic apatite associated with the studied green marine clays tends to have higher REE content than “bioapatites”, the total REE content being above 10 000 ppm. 相似文献
18.
Evaluation of redox-active iron sites in smectites using middle and near infrared spectroscopy 总被引：1，自引：0，他引：1
Redox processes of structural Fe in clay minerals play an important role in biogeochemical cycles and for the dynamics of contaminant transformation in soils and aquifers. Reactions of Fe(II)/Fe(III) in clay minerals depend on a variety of mineralogical and environmental factors, which make the assessment of Fe redox reactivity challenging. Here, we use middle and near infrared (IR) spectroscopy to identify reactive structural Fe(II) arrangements in four smectites that differ in total Fe content, octahedral cationic composition, location of the negative excess charge, and configuration of octahedral hydroxyl groups. Additionally, we investigated the mineral properties responsible for the reversibility of structural alterations during Fe reduction and re-oxidation. For Wyoming montmorillonite (SWy-2), a smectite of low structural Fe content (2.8 wt%), we identified octahedral AlFe(II)-OH as the only reactive Fe(II) species, while high structural Fe content (>12 wt%) was prerequisite for the formation of multiple Fe(II)-entities (dioctahedral AlFe(II)-OH, MgFe(II)-OH, Fe(II)Fe(II)-OH, and trioctahedral Fe(II)Fe(II)Fe(II)-OH) in iron-rich smectites Ölberg montmorillonite, and ferruginous smectite (SWa-1), as well as in synthetic nontronite. Depending on the overall cationic composition and the location of excess charge, different reactive Fe(II) species formed during Fe reduction in iron-rich smectites, including tetrahedral Fe(II) groups in synthetic nontronite. Trioctahedral Fe(II) domains were found in tetrahedrally charged ferruginous smectite and synthetic nontronite in their reduced state while these Fe(II) entities were absent in Ölberg montmorillonite, which exhibits an octahedral layer charge. Fe(III) reduction in iron-rich smectites was accompanied by intense dehydroxylation and structural rearrangements, which were only partially reversible through re-oxidation. Re-oxidation of Wyoming montmorillonite, in contrast, restored the original mineral structure. Fe(II) oxidation experiments with nitroaromatic compounds as reactive probes were used to link our spectroscopic evidence to the apparent reactivity of structural Fe(II) in a generalized kinetic model, which takes into account the presence of Fe(II) entities of distinctly different reactivity as well as the dynamics of Fe(II) rearrangements. 相似文献
19.
Comparison of dissolution under oxic acid drainage conditions for eight sedimentary and hydrothermal pyrite samples 总被引：1，自引：0，他引：1
Ran Liu Amy L. Wolfe David A. Dzombak Brian W. Stewart Rosemary C. Capo 《Environmental Geology》2008,56(1):171-182
The abiotic oxidative dissolution behaviors of eight natural pyrite samples, five sedimentary and three hydrothermal, from
various geological environments were compared under oxic conditions at pH 3 and 6 in a highly controlled batch reactor dissolution
system. The three sedimentary pyrite samples associated with coal had greater specific surface areas and also exhibited greater
apparent dissolution rates and extent than the other two sedimentary and three hydrothermal samples under both pH conditions.
However, after normalizing for surface area, the dissolution rate constants for the different pyrite samples were similar;
the greatest difference was between the two non-coal sedimentary pyrite samples. Pyrite morphology and the presence of trace
metals could contribute to the differences in dissolution behavior as reflected in the normalized dissolution rates. The sulfur:iron
ratio observed in the aqueous solution at pH 3 increased with time, but was always less than 2.0 (predicted from the stoichiometry
of dissolution) for all the pyrite samples during the 24-h experimental duration. This can be explained by the disproportionation
dissociation of thiosulfate, an initial product of pyrite dissolution, to elemental sulfur and sulfate which does not occur
in a 1:1 ratio. The results of this work indicate the importance of extracting and using the specific pyrite(s) relevant to
particular mining areas in order to understand pyrite dissolution rates and the influence of environmental conditions on those
rates. 相似文献
20.
C. Lerouge S. Grangeon C. Tournassat C. Guerrot C. Fléhoc C. Ramboz S. Buschaert 《Geochimica et cosmochimica acta》2011,75(10):2633-2663
The Callovian-Oxfordian (COx) clayey unit is being studied in the Eastern part of the Paris Basin at depths between 400 and 500 m depth to assess of its suitability for nuclear waste disposal. The present study combines new mineralogical and isotopic data to describe the sedimentary history of the COx unit. Petrologic study provided evidence of the following diagenetic mineral sequence: (1) framboidal pyrite and micritic calcite, (2) iron-rich euhedral carbonates (ankerite, sideroplesite) and glauconite (3) limpid calcite and dolomite and celestite infilling residual porosity in bioclasts and cracks, (4) chalcedony, (5) quartz/calcite. Pyrite in bioturbations shows a wide range of δ34S (−38‰ to +34.5‰), providing evidence of bacterial sulphate reduction processes in changing sedimentation conditions. The most negative values (−38‰ to −22‰), measured in the lower part of the COx unit indicate precipitation of pyrite in a marine environment with a continuous sulphate supply. The most positive pyrite δ34S values (−14‰ up to +34.5‰) in the upper part of the COx unit indicate pyrite precipitation in a closed system. Celestite δ34S values reflect the last evolutionary stage of the system when bacterial activity ended; however its deposition cannot be possible without sulphate supply due to carbonate bioclast dissolution. The 87Sr/86Sr ratio of celestite (0.706872-0.707040) is consistent with deposition from Jurassic marine-derived waters. Carbon and oxygen isotopic compositions of bulk calcite and dolomite are consistent with marine carbonates. Siderite, only present in the maximum clay zone, has chemical composition and δ18O consistent with a marine environment. Its δ13C is however lower than those of marine carbonates, suggesting a contribution of 13C-depleted carbon from degradation of organic matter. δ18O values of diagenetic chalcedony range between +27‰ and +31‰, suggesting precipitation from marine-derived pore waters. Late calcite crosscutting a vein filled with chalcedony and celestite, and late euhedral quartz in a limestone from the top of the formation have lower δ18O values (∼+19‰), suggesting that they precipitated from meteoric fluids, isotopically close to present-day pore waters of the formation. Finally, the study illustrates the transition from very active, biotic diagenesis to abiotic diagenesis. This transition appears to be driven by compaction of the sediment, which inhibited movement of bacterial cells by reduction of porosity and pore sizes, rather than a lack of inorganic carbon or sulphates. 相似文献