Illite Phases Research Articles

A strontium isotope and trace element geochemical study of dolomite-bearing bentonite deposits in Bavaria (Germany)

AbstractThe Landshut bentonites that formed from Ca- and Mg-poor rhyolitic tuffs in a fluviatile-lacustrine depositional environment of the Miocene Upper Freshwater Molasse, southern Germany, contain abundant palustrine, pedogenic and groundwater carbonates. Geochemical analyses of dolomites, calcites and smectites from bentonites of various environments by X-ray diffraction, thermal ionization mass spectrometry, inductively coupled plasma-mass spectrometry, and handheld X-ray fluorescence yield new insights into the compositions of fluids and sources of imported components involved in carbonate formation and bentonitization, as well as the timing of bentonite formation. Evaporated, Sr-rich brackish surface water with a molar Mg/Ca ratio of 2–5, derived mostly from the weathering of detrital carbonates, was involved in dolomite and bentonite formation in palustrine and some pedogenic environments. However, Sr-poor groundwater with a molar Mg/Ca ratio of ∼ 1 and a stronger silicate weathering component caused bentonite and calcite formation in strictly pedogenic and groundwater settings. The 87Sr/86Sr and molar Mg/Ca in the smectite interlayers indicate later cation exchange with water having more radiogenic Sr sources and smaller molar Mg/Ca ratios. The Rb-Sr data indicate the common presence of detrital illitic phases in the <0.2 μm fractions of the bentonites. Cogenetic palustrine dolomite and a single smectite residue sample which lacks this detrital illitic phase provide an age constraint for bentonitization at 14.7 ± 4.1 Ma identical to primary ash deposition. Thus a rapid onset of bentonitization of accumulated ash and dolomite formation in evaporation-driven wetland environments is indicated for the genesis of the Landshut bentonites.

The importance of illitic minerals in shale instability and in unconventional hydrocarbon reservoirs

Abstract It is generally accepted that the clay mineralogy of the shale formation is a primary causative factor of shale instability. This review considers a scenario of shale instability relating to illitic minerals. From the literature the thickness of the double electric layer (DEL) of the aqueous solutions associated with the charged external surfaces of clay minerals is of the same order or even thicker than the sizes of a significant proportion of the pores found in shales. In these circumstances, overlap of the DELs associated with the exposed outer surfaces of clay minerals on opposing sides of slit-like micropores (<2 nm in diameter) and mesopores (2–50 nm in diameter) in a lithostatically compressed shale would bring about electrostatic repulsion and lead to increased pore/hydration pressure in illitic shales. In shales and sandstones, illitic material is usually described in terms of two different phases, namely illite per se and mixed-layer illite–smectite (I/S). Evidence is presented to show that it is often the case that only one illite phase exists and that in reality the mixed-layer I/S is simply very thin illite (<5 nm in thickness) in the early stages of its growth. Such material is of common occurrence in the unconventional hydrocarbon reservoirs of the USA.

The role of pedogenic overprinting in the obliteration of parent material in some polygenetic landscapes of Sicily (Italy)

Many soils older than the Holocene have experienced several changes, and possess properties that may be due to the complex effect of several stages of soil development; these soils are called polygenetic. It is still rather unclear, however, if, as time elapses, pedogenic processes tend to diverge generating different soils, or converge towards increasingly similar soils. We studied five pedons (37°60′N, 13°90′E) exposed to present weathering simultaneously since the Holocene but located on Upper Miocene or Holocene parent material. Their XRD and FTIR clay mineralogy reveal an overall homogeneity; smectites, calcite and gypsum reach the thermodynamic equilibrium, a slight undersaturation of the illitic phase occurs in all soil profiles. Also soil micromorphology confirms a general similarity: vertic features detected as anisotropic lines and aureoles occur in all soils. Net mass chemical fluxes, based on mean translocation values per profile, excluded vertical (depth to the soil profile) and horizontal (topographical positions of profiles) pedogenic domains. Here, we show that the elapsed time of weathering has obliterated the effects of past sea transgression, revealing the vertic character independently on the age of its parent material in the case of soils that develop from Holocene, Messinian and Tortonian deposits, with a rate of pedogenesis plausibly in the order of 1/10mm per year. The soils of today reveal a strong homogeneity, in particular, in the mineralogical composition of the very fine earth; twenty-five per cent kaolinite and 75% interstratified illite/smectite are independently inherited from the parent material and are thermodynamically very stable. Vertic properties here could be considered to be in a steady-state condition nevertheless they experienced significant environmental disturbance.

Molecular Models of Cesium and Rubidium Adsorption on Weathered Micaceous Minerals

Understanding the adsorption mechanisms of metal cations onto soils and sediments is of critical importance in the protection of the environment, especially for the case of radioactive materials including the fission product (137)Cs. Mechanism-based adsorption models for the long-term interaction of chemical and radionuclide species with clay minerals are needed to improve the accuracy of groundwater reaction and flow models, as well as related simulations for performance assessment of waste sites and repositories. Toward this goal, molecular simulation using geometry optimization and molecular dynamics methods have been used to investigate the adsorption behavior of Cs(+) and Rb(+) cations at frayed edge wedges (a proxy for frayed edge sites, FES) and in the interlayer region formed as a result of the transformation of muscovite to Al-hydroxy interlayered vermiculite (HIV) during weathering and pedogenesis. Frayed edge wedges, formed both on individual smectite and illite phases and on the mica-HIV intergrade, have previously been recognized as significant sinks for the strong adsorption of Cs(+) and Rb(+). Atomic density profiles, interlayer adsorption site maps, radial distribution functions, and adsorption enthalpies derived from the equilibrated structural models are used to evaluate the optimal adsorption configurations and thermodynamics for Cs- and Rb-endmembers, a 50:50 Cs-Rb composition for the aqueous interlayer of vermiculite, and for the interlayer wedge zone as mica is transformed to HIV (i.e., HIV-mica wedge). Adsorption enthalpies for both cations are significantly larger for the frayed edge wedges (as represented by the HIV-mica wedge model) compared to values for the vermiculite and mica interlayers. Cesium cation binds more strongly than Rb(+) in the vermiculite interlayer, while Rb(+) binds more strongly than Cs(+) in the HIV-mica wedge. In all cases, the derived adsorption enthalpies for both cations indicate a preference for the wedge environment where electrostatic interaction is enhanced due to the presence of layer charge and the increased size of interlayer at the wedge accommodating cations larger than K(+).

Mineralogical and chemical variability of mountain red/brown Mediterranean soils

The purpose of the current study was to quantitatively explore the dynamics of clay pedogenesis in red-brown soils of the terra-rossa type and associated soils (mainly Rhodoxeralfs) of the Mediterranean region with respect to bedrock and dust composition, and the impact of the vegetation-translocated elements silicon and potassium. Fifteen non-cultivated, shallow and leached mountain pedons were sampled in Israel along three transects that represent various rainfall ranges and bedrock lithologies. Bulk and clay fraction chemical and mineralogical compositions, as well as grain size, were determined. Quantitative relative analysis of clay minerals displayed a large variability that was largely affected by leaching. Leaching was dependent on rainfall amount and bedrock/soil permeability. In general, if the better soils were drained and leached the higher were the amounts of both kaolinite and illitic phases. Soil clay assemblages lay between two mineralogical end members: one with dominance of smectite and the second with high values of kaolinite and illitization parameters. Potassium and silicon were mobile in soils relative to aluminum, but under high rainfall or certain vegetation, translocation by vegetation reached a degree that promoted illite or smectite formation. Local combinations of rainfall, bedrock/soil permeability, and vegetation translocation of potassium and silicon dictated a large variability in clays, including illite formation, within a restricted group of red-brown Mediterranean soils.

Evolution of clay mineral assemblages in the Tinguiririca geothermal field, Andean Cordillera of central Chile: an XRD and HRTEM-AEM study

HRTEM textural evidence shows that clay minerals in the Tinguiririca geothermal field (Andean Cordillera, central Chile) are the result of direct alteration of former volcanic glass and minerals by hydrothermal fluids at similar temperatures to the present day. They show the classical pattern of diagenetic transformation from smectite at the top to illite at the bottom, with the progressive formation of corrensite and chlorite. The high fluid/rock ratio, disposability of necessary cations and absence of previous detrital phyllosilicates allow the consideration of this area as a natural laboratory to establish the extreme ideal conditions for very low-T reactions. Transformations from smectite to R1 illite–smectite (I–S) and from these to R3 mixed-layers occur respectively at 80–120°C and 125–180°C. In spite of ideal genetic conditions, the new-formed minerals show all the defective character and lack of textural and chemical equilibrium previously described in the literature for diagenetic and hydrothermal low-temperature assemblages. Chemistry of smectite–illite phases evolves basically through a diminution of the pyrophyllitic component toward a theoretical muscovite (Si4+ + □ -> Al3++ K+). However, a second chemical vector (Si4++Mg2+ → Al3++Al3+), that is, decreasing of the tschermack component, also contributes to the evolution toward the less Si-more Al rich muscovite in relation to the original smectite. Residual Mg (and Fe) from the latter reaction is consumed in the genesis of chloritic phases. Nevertheless, as a consequence of the lack of chemical equilibrium (probably because of the short time-scale of the geothermal alteration processes), the composition of clay minerals is highly heterogeneous at the level of a single sample. Consequently, the respective fields of smectite, R1 I–S and R3 I–S overlap each other, making the distinction among these three phases impossible based exclusively on chemical data.

Mineralogy of Egyptian Bentonitic Clays II: Geologic Origin

AbstractReconstructing the origin of bentonitic clays is often a challenging and rather complicated undertaking, but the analysis of certain predictor clay minerals is proving to be an excellent method to simplify this process. The goal of the present investigation was to use abundance changes of five X-ray diffraction (XRD) predictor minerals to determine the relative contributions of weathering and parent-rock changes to the origin of clay minerals in Egyptian bentonitic clays as the test case. The XRD predictor minerals, selected in an earlier discriminant function analysis of quantitative abundances of 14 minerals, provided a simpler approach to the interpretation of clay-mineral origins because they are the minerals that were most responsible for statistically significant differences among the samples. Changes in mineral composition were basically a function of parent-rock lithology, drainage, and climate interactions. A Paleo-Climate Index (CI; the ratio of coarsely crystalline kaolinite to Fe-rich smectite), and a Parent-Rock Index (PI; the ratio of the illitic phases and quartz abundances to pure smectite) were established to track the paleo-climate and parent-rock changes, respectively. Low CI values indicated that a long, seasonally dry climate prevailed during the Middle Eocene, uppermost Eocene, Lower Miocene, and Upper Pliocene bentonitic clay deposition. Lowermost Upper Eocene and the Middle Miocene bentonitic clays were produced when a wet climate prevailed throughout the year. Moderate to high PI values suggested derivation of the clays from the acidic basement crystalline rocks at Uweinat-Bir Safsaf uplift and Lower Paleogene shales during the Middle Eocene and lowermost Upper Eocene. The youngest Upper Eocene and Lower Miocene materials contained abundant Fe-smectite and low PIs indicating derivation from tholeiitic basalts. Diagenetic and sedimentary segregation modifications were not apparent. Direct evidence for in situ derivation from volcanic precursor materials was lacking in general, but volcanic eruptions were common in the region. The minerals in the Egyptian bentonitic clays formed as weathering products on land and have been transported by north-flowing streams and rivers to the sites of accumulation.

Surface binding site analysis of Ca2+-homoionized clay–humic acid complexes

Clay-humic substance complexes play a major role in controlling the mobility of toxic metals in contaminated soils. However, our understanding of the underlying mechanisms is limited. Binding site analysis of clay and clay-mineral-humic composites, in this study, revealed an enhanced surface reactivity for the clay surface by the sorbed humic substances. Kaolinite and illite had three binding sites with pK(a) values ranging from ∼4.5 to 9.6 at Ca(2+) concentrations of 0.01 and 0.1 M respectively. In the presence of peat humic acid (PHA), four or five binding sites were observed for humics sorbed kaolinite surface at Ca(2+) concentrations of 0.01 and 0.1 M respectively. pK(a) values ranged from ∼4.4 to 9.6 for humic acid concentration of 0.01 and 0.1 mg/mL. For illite, four or five binding sites were found with pK(a)s ranging from ∼4.1 to 9.4. From zeta potential measurements of PHA-kaolinite or PHA-illite suspensions, the already negative potential decreased by 30 mV from pH 4 to 7, and by 10 mV for pH values greater than 7. For illite the initial negative surface potential decreased by 15 mV up to a pH of 9. Above this pH, the potential decrease diminished to 2 or 5 mV. These changes in surface potential confirm the adsorption of PHA to the clay mineral surface. FTIR measurements of clay samples were able to identify the kaolinite and illite phases. In addition, FTIR absorption bands found in the range of 1950-1800 cm(-1), suggest the interaction of PHA with kaolinite and illite surfaces. The results of this study indicate that the sorption of humic substances increases the availability of clay surface functional groups for deprotonation and potential sorption of toxic metal cations.

Characterization and use of acid‐activated montmorillonite‐illite type of clay for lead(II) removal

AbstractThe natural local deposits of montmorillonite‐illite type of clay (MIC) were susceptible for acid activation. Raw clay was taken for experimentation, disintegrated on acid activation with sulfuric acid, which showed a particle size distribution. The montmorillonite and illite phases in the raw clay disappeared on acid activation and the activated clay, MIC(AA), showed with sodium‐aluminum‐silicate and beidellite phases apart from quartz (low) phase. The raw and acid‐activated clays were characterized using X‐ray powder diffractometry, X‐ray fluorescence, Fourier transform infrared spectrometry, and energy dispersive X‐ray, and their adsorption capacities were compared. When tested for adsorption of Pb(II) in aqueous solutions, the acid‐activated clay showed about 50% increased adsorption than raw clay. Sips adsorption isotherm and pseudo‐second‐order kinetic models were found to be best for the batch adsorption data. Kinetic studies showed the existence of film diffusion and intraparticle diffusion. A two‐stage batch adsorber was designed for the removal of Pb(II) from aqueous solutions. © 2010 American Institute of Chemical Engineers AIChE J, 2010

Responses of soil clay mineralogy in the Rothamsted Classical Experiments in relation to management practice and changing land use

Changes in the clay mineralogy of soil samples collected from the Rothamsted Classical Experiments over the past ~ 150 years were examined. Comparisons were undertaken to assess the impact of (i) different fertiliser practices on the top soil and sub soil of the Park Grass Experiment and (ii) the effects of changing land use from agriculture to woodland where soil pH either remained close to pH 7 or became acidic. Analyses were undertaken on the < 0.2 µm clay fraction and measurements included cation exchange capacity (CEC), surface area and X-ray diffraction (XRD). The fine clay fraction of all the samples is composed of illite/smectite (I/S), illite and kaolinite minerals. Decomposition modelling of XRD spectra identified three I/S phases including (i) a high smectite I/S phase ( d(001) ~ 15 Å), (ii) a low smectite I/S phase ( d(001) ~ 12.5 Å) and (iii) an illite phase ( d(001) ~ 11.2 Å). The I/S phase is typically made up of ~ 60% of high smectite I/S, ~ 20% low smectite I/S and ~ 20% illite. Attempts to account for changes in clay CEC and surface area with time proved to be inconclusive, possibly because of the differing proportions of the three I/S phases in each sample. Some temporal changes in the d(001) spacing of I/S mineral phases from the decomposed XRD spectra (> 0.4 Å) are reported in both top soil (0–23 cm) and sub soil (46–69 cm) and are likely related to (i) changes in soil K + or NH 4 + status and/or (ii) increasing soil acidity. The greatest change was found in the Park Grass Experiment (NH 4) 2SO 4 plot where soil pH fell below 3.7. It is believed that solubilisation of hydroxyl-Al in smectite interlayers enabled renewed access to K + or NH 4 + ions, leading to increased collapse in d(001) spacing. However, the results show that over a diverse range of soil conditions, I/S minerals of the Batcombe series soils showed considerable resilience to major change. This is considered to be a result of competition for sorption sites by (i) the presence of competing ions added as fertiliser or liming materials, (ii) an increase in H + ions as soil acidity increases, (iii) the possible role of organic carbon in protecting I/S minerals and (iv) the role of the I/S minerals as K + reservoirs. However, the impact of decreasing soil pH should be considered when land is re-forested as this may lead to decreases in the d(001) spacing of I/S minerals, thus compromising useful clay properties such as CEC.

Influence of mineralogy of Tunisian clays on pozzolanic activity—assessment by different methods

Five local clays were characterised by several physicochemical methods to predict their pozzolanic reactivity. The studied samples were treated thermally at 600, 700 and 800°C. The heat-treated samples were characterised by X-ray diffraction. The pozzolanic activity was assessed by chemical (Chappelle test), mechanical (compressive strength at 28 days) and physical (differential thermal analysis/thermogravimetry) methods. It was found that under the chosen conditions, the kaolinitic clay fraction was transformed to an amorphous phase that was reactive with lime, whereas the illitic phase remained in a crystalline form and was consequently unable to produce pozzolans. The montmorillonitic fraction started to gain pozzolanic activity above a calcination temperature of 700°C. It was also demonstrated that the pozzolanic activity of the clays calcined at 700°C was directly related to the percentage of kaolinite in the crude samples. The hydration products were C–S–H and C4AH13, and C3AH6 and C2ASH8 were also detected in samples that were rich in alumina.

Episodic mineralization of hydrothermal illite in the Soultz-sous-Forêts granite (Upper Rhine Graben, France)

Episodic and localized illite mineralization is documented in the hydrothermally altered Soultz-sous-Forets granite (Upper Rhine Graben, France). Separated grain-size fractions of altered granite and argillite vein samples contain mixtures of 2M1 and 1M trans-vacant illite varieties. The platy pseudohexagonal 2M1 illite phases dominate the vein fillings, whereas the 1M illite occurs largely as a fibrous pore-filling variety, which is particularly abundant in the granite matrix. Multiple phases of fluid injections into the granite body have resulted in different illite assemblages, each sample containing a mixture of polytype generations formed during different crystal growth events. On the basis of mineralogical and K–Ar isotopic constraints, the ages of these vein-mineralizing events are determined by plotting the K–Ar values of the various grain-size fractions against polytype abundance and the fitted volume-weighted crystallite thickness distributions. The results suggest a Permian age for the formation of the studied argillite veins, characterized by successive injections of hydrothermal fluids. Secondary episodes of illite crystallization occurred during Jurassic and Cretaceous (or even younger times) in both the veins and the granite matrix. There are indications that the polytype structure and composition of illite were strongly influenced by variations in fluid chemistry and the degree of fluid–rock interaction as the granite was progressively sealed during post-Variscan, episodic hydrothermal activity.

Chemical and structural variability of illitic phases formed from kaolinite in hydrothermal conditions

The transformations of kaolinite in the system Na 2O–K 2O–MgO–Al 2O 3–SiO 2–H 2O–HCl at 200 °C, with different MgCl 2 contents, have been investigated by X-ray diffraction and transmission/analytical electron microscopy. Two contrasting mechanisms of illite formation were identified: 1) direct precipitation of illite from dissolution of zeolites, which occurs at high pH and low Mg contents; and 2) formation of illitic phases from recrystallized kaolinite, either through dissolution–precipitation processes or by topotactic replacement. The second mechanism occurs at higher Mg contents and almost neutral conditions. Under these later conditions, kaolinite dissolution–precipitation processes occur at the earliest stages of reaction, which lead to the formation of Mg-rich kaolinite. The illitic phases formed through both mechanisms have different structural and chemical characteristics. Direct precipitation from solution produces well-ordered illites with scarce phengitic substitution and high Na contents. Illitic phases formed from kaolinite show an evolution from illite/smectite mixed-layers to illite, at increasing run times. These phases are characterized by high octahedral Mg content (in the order of 0.8 apfu, for O 10(OH) 2), and lack of Na. The activity diagrams constructed from the data of solutions confirm the data obtained from the study of the solid products.

Removal of gases by thermal-acid leached kaolinitic clays: Influence of mineralogical composition

Natural and modified kaolinitic clays were used as retention for gas adsorptions. The kaolinitic clays containing different mineralogical compositions were used. The modifications were carried out by heating the clays at 600 °C and then by acid treatment with 2.5 mol/L sulphuric acid solution at boiling temperature for 180 min. Equilibrium adsorption was measured using a volumetric apparatus, at 25 °C and 0.1 MPa. The gases tested were N 2, O 2, CO, CO 2, CH 4, C 2H 2 and SO 2. The samples were characterised by chemical analysis, BET surface area, X-ray diffraction and infrared spectroscopy. The thermal-acid modifications on kaolins improved the capacity of the clays for gas adsorptions. Retention of SO 2 (0.914–1.242 mmol/g), C 2H 2 (0.450–0.721 mmol/g) and CO 2 (0.437–0.602 mmol/g) by modified clays were higher than the other gases previously mentioned. The external surface area and amorphous silica developed by modified clays, due mainly to presence of kaolinite in raw clays, improved the capacity for gas retention. Whereas the main cause for gas retention by raw kaolinitic materials was the presence of the illite phase in raw kaolin clays. The thermal-acid kaolins could be potential solids for separations of gases mixtures.

A new simple approach to evaluate pedogenic clay transformation in a Vertic Calcisol

The aim of this study is to characterize the pedogenic clay minerals by using simple approach: mixing mineralogical and geochemical findings. The fine clay fractions (< 0.1 μm) of a Vertic Cambisol profile were studied by means of X-ray diffraction (XRD), infrared spectroscopy (FTIR) and cation exchange capacity (CEC). Qualitative and quantitative mineralogical compositions of the clay mixture were determined. Moreover, chemical equilibria and thermodynamic stabilities of minerals (calcite, gypsum, kaolinite, smectites and illites) were studied using results of ionic activities obtained from total concentration of various aqueous species in water extracts from soil-saturated pastes. XRD analysis shows a good homogeneity in the mineralogical composition of the soil material, with depth of soil profiles. The identified clay minerals are mainly illite–smectite mixed layers (I/S) and kaolinite. The chemical analysis of saturated paste extracts with clay minerals shows a slight undersaturation of the illitic phase while smectites and also calcite and gypsum reach the thermodynamic equilibrium along the soil profile.

Clay-mineral signatures of fossil and active hydrothermal circulations in the geothermal system of the Lamentin Plain, Martinique

Whereas the study of clay minerals (using parameters such as structure modifications, crystal chemistry) has proved to be an effective approach in order to mark the circulation zones and fluid temperatures in high-temperature systems, there is an important lack of data dealing with such problems in moderate- to low-temperature systems. This paper proposes to fill this lack by studying the site of the Lamentin Plain (Martinique), characterized by a low-temperature geothermal activity (50°C< T<90°C). Preliminary data acquired on the three studied exploration wells (LA01, LA02 and LA03) show that the current low-temperature geothermal activity is particularly well expressed through the LA03 well. This low-temperature activity is superimposed on evidence of a high-temperature fossil activity, particularly well expressed in the non-productive levels of the LA01 and LA02 wells. After a petrographic characterization, this work focuses on the textural and microstructural properties of the low-temperature hydrothermal clay phases utilizing X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry and scanning electron microscope (SEM). The petrographic observations have permitted successive hydrothermal events to be recognized, which express the thermal collapse of the system, as shown by the superposition of ancient episodes, characterized by vein and pervasive alterations of high to moderate temperatures, and recent episodes, characterized by alterations associated with present-day circulations of low-temperature fluids. The fossil activity results from several hydrothermal episodes, with fluid temperatures ranging from 100 to over 200°C. Illitic phases (i.e. I/S ( R=1) to illite) appear as the main markers of the fossil solution paths, due to their abundant development close to major veins and fractures, while chloritic phases (chlorite, corrensite) seem to mark a pervasive alteration, better preserved further from the fossil solution channels. On the other hand, the recent hydrothermal alteration is characterized by the massive presence of kaolinite, dioctahedral smectite and siderite. Whereas smectites are only observed abundantly farther from the current solution channels, kaolinite appears to be the dominant clay mineral in these channels, or in the surroundings of sealed fractures which do not currently drain any more hydrothermal fluids. The crystallinity estimations on XRD and FTIR patterns from the <2 μm fraction, along with SEM morphological observations, clearly show that the microstructural and textural properties of the kaolinites can be related to fluid temperatures. Indeed, kaolinites with the best crystallinity, or the best-ordered, are located in the fractures carrying the hottest fluid temperature (90°C). The comparison with the other flow paths, with fluids of lower temperature (50 and 70°C), shows that the kaolinite crystallinity decreases with temperature. As a consequence, while kaolinite appears to be the signatory clay mineral of the present-day fluid circulation in the Lamentin Plain, its crystallinity can be interpreted as a tracer of the fluid temperature.

Characterization and Transport of Contaminated Sediments in the Southern Central Lake Superior

Three major source sediments were characterized and classified in terms of mineralogical and chemical composition in the west coastal area of the Keweenaw Peninsula. Bulk chemical analysis reveals that concentrations of Cu, Ag, Co, and As were enriched in metal rich mine tailings. SEM-EDS analysis indicates that the Ontonagon River sediments have high P and S concentrations . X-ray diffraction analysis of clay fraction shows that the mine tailings (chlorite rich) could be distinguished from the other two sources, Ontonagon River sediments (low chlorite and high illite) and Wisconsin red clay (low illite and high expandable phase). Local environmental conditions, including currents, bathymetry, weather conditions, and sediments texture, are important factors for cross-margin and longshore transport of contaminated sediments. The Keweenaw Current is responsible for the longshore transport of fine fraction of tailings , whereas wave action causes the lateral transport of the coarse deposits along the shore.

Transmission Electron Microscopy Study of Smectite Illitization During Hydrothermal Alteration of a Rhyolitic Hyaloclastite From Ponza, Italy

AbstractDioctahedral phyllosilicates from an altered rhyolitic hyaloclastite located at Ponza Island, Italy, were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The samples are from a sequence previously characterized by X-ray diffraction (XRD) methods, indicating that a complete range of illitization accompanies alteration. Backscattered electron (BSE) images, obtained from ion-milled samples, show that samples partly retain the original textures since clay minerals pseudomorph lapilli fragments and preserve vesicular texture. The lowest-grade sample studied contains obsidian clasts partially replaced by smectite. As the alteration grade increases, illitization proceeds with formation of interstratified illite-smectite (I-S), zeolites, illitic phases, feldspars and quartz. The most altered sample contains illite, mica and quartz. Lattice-fringe images show that following the formation of smectite, illitization takes place through the formation of (R=1) I-S, highly illitic I-S and illite with mica; (R=1) I-S is the only ordered interstratified I-S. The BSE and TEM images of Ponza samples show irregular cavities filled with euhedral dioctahedral clay minerals and the zeolite mordenite, providing direct evidence for neocrystallization from a fluid. Chemical compositions by analytical electron microscopy (AEM) support the sequence described. Selected area electron diffraction (SAED) patterns indicate the predominance of 1 Md polytypism both in I-S and illitic phases, and the coexistence in the more altered samples of 1Md illite and a 2-layer mica polytype (probably 2M1), without the intermediate 1M polytype generally assumed to exist in prograde sequences. Previous XRD studies indicated progressive change from cis-vacant, turbostratically stacked smectite, to interstratified cis- and trans-vacant, 1Md I-S, to trans-vacant, 1M illite, and then to 2M1 illite in Ponza Island samples. We observed a clear correlation between the chemical compositions as determined by AEM and the proportion of cis-vacant determined by XRD, suggesting that the octahedral cation distributions change in the studied samples with increasing degree of illitization.

Late-Stage Diagenesis of Illitic Clay Minerals as Seen by Decomposition of X-Ray Diffraction Patterns: Contrasted Behaviors of Sedimentary Basins with Different Burial Histories

AbstractThe smectite-to-illite diagenetic transformation has been documented in 5 different sedimentary basins using X-ray diffraction (XRD). Intermediate reaction products coexisting because of the effect of kinetics on this reaction have been characterized using decomposition of XRD patterns and comparison with calculated patterns. The nature and relative abundances of the various subpopulations of particles are shown to vary as a function of the geothermal gradient and of the age of the sediment. In all sedimentary basins that experienced a low steady geothermal gradient the physico-chemical characteristics (coherent scattering domain size [CSDS], junction probabilities) of intermediate mixed-layered illite-smectites (I-S) are similar. However, both the relative abundance and the crystallinity of the end-member illite increase as a function of the age of the sediment.In basins that have experienced a higher geothermal gradient, the CSDS of the I-S subpopulation is higher for a given illite content, indicating a slightly different reaction pathway. This difference in the characteristics (peak position and width) of elementary peaks may be used to infer the presence of such a high geothermal gradient when no other data are conclusive. In this case the growth of the illite end-member is favored over the growth of intermediate I-S phases even in young basins. Illitic phases formed from the alteration of kaolin minerals exhibit characteristics similar to the reaction products of the smectite-to-illite diagenetic transformation in the case of a high geothermal gradient. In contrast with what is observed in shale diagenesis, the characteristics of the illitic subpopulations describe a continuum with absolutely no gap in between subpopulations. In sandstone reservoirs, the various subpopulations crystallize simultaneously from a kaolin precursor. As a consequence, no kinship is expected between the various subpopulations.

Mössbauer study of slovak brown coal

In the present contribution, the results of Mossbauer analyses of three types of Slovak brown coal are presented. Electron microscopy and X-ray photoelectron spectroscopy were used as supplementary techniques. The dominant Fe bearing mineral was pyrite which contains from 78% up to 95% of the total amount of iron. The rest of iron is present in ferrous carbonate (siderite) and silicate (illite) phases. In one of the three samples a magnetically ordered component was identified.