Interstratified Illite Smectite Research Articles

Hydrologic regulation of clay-mineral transformations in a redoximorphic soil of subtropical monsoonal China

Abstract Clay-mineral evolution in supergene environments is commonly a complex process subject to hydrologic influences on clay-mineral transformations, yet these influences remain insufficiently investigated to date. A quaternary red soil profile with evident redoximorphic features in subtropical monsoonal China was investigated with a focus on processes of secondary clay-mineral transformation. Evidence provided by soil physical and chemical descriptions, clay-mineral analysis, spectroscopic characterization, extractions of pedogenic Al and Fe species, and geochemical compositions reveals a complex relationship of clay minerals and iron phases to pedogenic weathering conditions as a function of depth in the studied soil profile. The soil profile can be divided into a homogenous horizon (HH; 0–2.0 m), a redoximorphic horizon (RH; 2.0–6.0 m), and a basal layer (BL; 6.0–7.2 m), and these three horizons are dominated by various intermediate clay phases. The HH is characterized by moderately acidic conditions (mean pH = 5.2) and low total organic content (TOC; TOC ≤2.1 g kg–1). More importantly, compared with the lower horizons, the HH contains significantly more active acid-forming cations, as reflected by a greater abundance of Al phases and higher aluminum saturation levels. We infer that the occurrence of hydroxy-interlayered vermiculite (HIV) in the HH is tightly coupled with the nature of the soil acidic pools, which include both H+ ions (i.e., pH) and active acid-forming cations (e.g., Al3+ and Fe3+). The reaction pathway from primary minerals to final weathering products appears to be highly sensitive to dynamic hydrological processes. HIV is favored in generally oxic, well-drained soil systems with adequate acidic cations to maintain acidic weathering. When soils are more waterlogged and the aqueous solution is dominated by base cations, primary minerals tend to transform to smectite group minerals. Therefore, discrete smectite, interstratified illite-smectite (I-S), and interstratified kaolinite-smectite (K-S) were observed only in the RH and BL. We present a novel framework that links clay-mineral transformation pathways to soil hydrological disturbances, providing new insights into understanding the kinetics of water-mineral interactions in natural soil systems.

Characterization and distribution of clay minerals in the soils of Fildes Peninsula and Ardley Island (King George Island, Maritime Antarctica)

AbstractThe environmental conditions in Maritime Antarctica are more favorable to soil development than in continental areas, which is reflected in the content and type of clay minerals present. In this context, soil clay minerals of Fildes Peninsula, South Shetland Islands were studied with the aim of relating them to periglacial and paraglacial processes as possible indicators of initial pedogenic processes. In this work, textural, mineralogical and crystallochemical characterization of clay minerals as well as chemical and physical soil analyses were carried out. The soil samples represented various surface cover types present on Fildes Peninsula. All samples were composed mainly of clay minerals, plagioclase, quartz and minor zeolites and pyroxene. The clay mineral content was very variable and reached up to 63% w/w. The clay minerals present are mainly smectite, vermiculite, chlorite and minor kaolinite, mica, corrensite and interstratified illite–smectite, with smectite and vermiculite dominating in almost all of the samples. The primary minerals display chemical alteration, and smectite formed by alteration of plagioclase. The clay mineral types were related to the parent material, which was affected by low-grade metamorphism and hydrothermal alteration that transformed biotite and chlorite into vermiculite via interstratified chlorite–vermiculite. Furthermore, this process and/or ongoing surface weathering transformed vermiculite into smectite. The genetic relationship observed between vermiculite and smectite suggests progressive alteration and transformation into a phase with intermediate composition between vermiculite and smectite. Therefore, vermiculite could be at least in part the smectite precursor. Samples closer to the current Collins Glacier front are composed mainly of vermiculite, with the greatest chemical variation occurring where the soils were developed from a mixture of initially glacially transported volcanic rocks through periglacial and fluvial processes. The clay minerals from the centre and south of Fildes Peninsula are mixtures of montmorillonite and vermiculite, as well as of chlorite and corrensite in various proportions. The clay minerals in soils developed on the west coast are a mixture of Fe-rich montmorillonite and vermiculite.

Characterization of clays from the Fez area (northern Morocco) for potential uses in the ceramics industry

AbstractClays from the Saïss basin (northern Morocco) used traditionally in the ceramic industry in the Fez area were studied using mineralogical and physicochemical techniques to evaluate their potential suitability as raw materials for ceramics manufacture. X-ray diffraction was used to determine their mineralogical composition. The physical properties determined were particle-size distribution and consistency limits. The chemical composition was determined using X-ray fluorescence analysis and Fourier-transform infrared spectrometry. The structural changes of the mineral phases in the raw materials during firing were studied over a temperature range of 500–1000°C. In the pottery site from Fez, generally potters use a mixture of 25% fine clay (ARFS) from the upper part of the Miocene marls and 75% sandy clay (ARFR) from the lower part of the Miocene marls. The ARFS clay yielded very rigid specimens after firing that artisan potters would find difficult to handle so as to produce desired shapes and sizes. However, the specimens obtained from ARFR clay show signs of faltering. The mixture of these two clayey materials from this pottery site is therefore necessary to obtain the optimal paste for ceramics purposes. The chemical compositions indicated that SiO2, Al2O3, CaO and Fe2O3 are the major minerals, with trace amounts of K2O and MgO. Quartz, feldspars and clay minerals prevail in all samples. Kaolinite, illite and smectite are the dominant clay mineral phases, with traces of chlorite and interstratified illite–smectite. The classification of these samples using appropriate ternary diagrams showed that the proportions used in the mixture produce a new material with adequate characteristics for the production of traditional ceramics.

Structural Analysis of Interstratified Illite-Smectite by the Rietveld Method

Rietveld method is a powerful tool in obtaining structural information of clay minerals by using of X-ray diffraction (XRD) patterns. However, the interstratified illite-smectites (I-S) show various stacking defects preventing the direct application of this method. It was shown that the Rietveld method combined with a recursive structure-factor calculation can be used for describing the stacking disorder of I-S. In this study, a series of samples with different stacking sequences and different proportions of layer types were chosen to verify the applicability of Rietveld method in determination of structural parameters of I-S. The Rietveld refinements were carried out on powder samples and oriented specimens in air-dry (AD) and ethylene glycol (EG) state. The structural information obtained by X-ray fluorescence (XRF) and thermal analysis were used as an independent test of the reliability of the refinements. The refined and experimental results were compared systematically and the relationship between structural parameter was discussed. For powder and oriented specimens, the refined results of occupancies of potassium and iron and the proportion of illitic layers showed consistent results. The refined value of cis-vacant layers was in good agreement with the experimental data. The reliability of the refinements increased with increasing proportion of illitic layers.

Origin of dioctahedral smectites in Lower Eocene Lulehe Formation paleosols (Qaidam Basin, China)

Smectites affecting water and soil exchangeable cations, especially potassium and ammonium related to plants, are common swelling clay minerals in sediments and paleosols that can record paleoenvironmental and paleoclimatic information. Paleoenvironmental and paleoclimatic interpretations are potentially ambiguous, because smectite minerals may have either detrital or pedogenic origins. This study analyzes smectites in Lower Eocene paleosols of the Qaidam Basin, China, with the goal of determining their origin and paleoclimatic significance. Twelve smectite-rich vertisol samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma-mass spectrometry (ICP-MS), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) in the Dahonggou (DHG) section of the Lulehe Formation. The samples from DHG section contained predominant dioctahedral smectites (60–65%) in the <2 μm clay fractions. Minor dioctahedral illites, dioctahedral interstratified illite-smectite (I-Sm), kaolinite, and traces of dioctahedral chlorites and palygorskites were present. The chemical data and FTIR spectra revealed both tetrahedral substitutions (i.e., Al for Si) and octahedral substitutions (i.e., Mg and minor Fe for Al) in the dioctahedral smectites. Montmorillonite comprised the dominance of the fine-clay fractions (< 0.2 μm) with minor contributions of beidellite, as determined by the Greene-Kelly test (GK-test), geochemical and FTIR analyses. SEM observations revealed two morphological types of dioctahedral smectites, the less abundant one with typical ‘honeycomb’ structure, interpreted as neoformed, and the other occurring as thin, well-defined plates and irregular masses considered to be detrital. DSC revealed two dehydroxylation temperatures (500–550 °C and 600–700 °C), indicating the presence of trans-vacant (tv) and cis-vacant (cv) layers, respectively. The cv layers were attributed to montmorillonite originating as catchment-delivered detritus, as the study Lulehe Formation exhibited no evidence of volcanic ash layers or diagenesis that would have promoted formation of montmorillonite with high dehydroxylation temperatures. The tv layers represented pedogenic beidellite formed via solution crystallization in a floodplain pedogenic environment. The accumulation of abundant inherited montmorillonite and neoformed beidellite in paleosols of the Lulehe Formation was probably promoted by a relatively warm climate with alternating wet-dry seasons during the Early Eocene. Admixture of detrital montmorillonite makes paleoclimatic reconstructions based on bulk-smectites concentrations and isotopic compositions unreliable, showing that integrated clay mineralogical analyses of the type undertaken in this study are necessary to identify the provenance and paleoclimatic significance of smectites in sediments.

Mechanisms of lateral and linear extension of gullies (dongas) in a subhumid grassland of South Africa

AbstractThe formation of deep gullies (called ‘dongas’ locally) in rangeland in KwaZulu‐Natal Province in South Africa is a natural phenomenon. These U‐shaped, very wide gullies have considerable lateral expansion due to the episodic collapse of sidewalls.The dongas have developed in duplex soils such as Luvisols and Lixisols formed on Permian sedimentary rocks or unconsolidated Quaternary colluvium. This study combined morphological, mineralogical and chemical characterization with measurements of grain‐size content, structural stability and the complete shrinkage curve to detect changes in soil properties of the different horizons located in the gully banks.The different soil horizons present clear and sharp differences in physical and mineralogical properties. The topsoil with complete grass cover is very resistant to soil detachment. However, the leached E horizon and the BC horizon have low structural stability. The soil profile down to and including the Bt horizon contains exclusively illite in the clay fraction, while the BC colluvial layer and the C horizon (mudstone) contain expandable interstratified illite–smectite. The Bt horizon has a high water content at saturation and high shrinkage, while the BC and C horizons have a high residual shrinkage and a very low water content at saturation.Because this type of gully expansion is not significantly linked to slope value or the stream power index (SPI) at the gully head, to land‐use change, high rainfall intensities or the threshold of concentrated runoff being exceeded at the gully head, other causes were investigated. It was concluded that the heterogeneity between horizons with different mineralogical properties and structural stabilities, soil types and parent material, anisotropic water‐saturation and shrink‐swell properties are of major importance. This heterogeneity between different soil horizon morphologies and their physical properties can explain why the relationship between the critical slope and the drainage area for gully initiation showed a threshold for gullying much lower than that found elsewhere. © 2020 John Wiley &amp; Sons, Ltd.

Rock fabric and origin of the expandable phyllosilicates in the sands of the Ashdown Formation, East Sussex, UK

Abstract Phyllosilicate minerals have the potential to be used as indicators of past environmental conditions and climate. However, the appropriate use of this tool requires that the origin of the phyllosilicates be ascertained to correspond to the age under investigation, as mineralogical changes postdating it would lead to wrong conclusions. The soft sandstone of the Ashdown Formation (south-central and southeaster UK) contains fine-grained Al-phyllosilicates of limited interlayer expandability that have been described by other authors as vermiculite, smectite, interstratified illite-vermiculite and interstratified illite-smectite. The origin of these mineral phases is not yet agreed, with some authors reporting them as detrital and some as authigenic, generated by the weathering of detrital mica in the sandstone. In order to investigate whether or not these fine-grained minerals are detrital, four samples of the sandstone of variable softness were studied because they most likely had different clay content and because the different clay content could be possibly due to differential weathering. Investigation of mineralogy (X-ray diffraction), chemistry (bulk and SEM-EDS microanalysis) and rock fabric (image analysis of SEM micrographs) indicated that the sandstone consists of quartz, microcline, albite, anorthite, muscovite/illite, kaolinite, interstratified illite-smectite and smectite, where smectite layers expand only partially. Kaolinite is mainly detrital. Rock hardness was controlled by quartz abundance in the original sediment, not by later weathering. Alteration of the investigated sandstone samples after deposition was limited but reaction models are compatible with partial (

Quantitative Mineralogy of Clay-Rich Siliciclastic Landslide Terrain of the Sorrento Peninsula, Italy, Using a Combined XRPD And XRF Approach

AbstractQuantitative mineralogical analysis of clay-bearing rocks is often a non-trivial problem because clay minerals are characterized by complex structures and are often affected by structural disorder, layer-stacking disorder, and interstratification. In the present study, internal-standard Rietveld X-ray powder diffraction (XRPD) analyses were combined with X-ray fluorescence (XRF) chemical analyses for the mineralogical characterization and quantitative analysis of heterogeneous clay-rich sedimentary rocks that are involved in a slow-moving landslide in the Termini-Nerano area, Sorrento Peninsula (Italy), in order to investigate the relationship between the mineralogy of these rocks and landslides. Slow-moving landslides are usually considered to be associated with the more weathered and surficial parts of structurally complex slopes, and mineralogical analysis can help to clarify the degree of weathering of siliciclastic rocks. XRPD quantitative analyses were conducted by combining the Rietveld and internal standard methods in order to calculate the amounts of poorly ordered phyllosilicate clays (considered amorphous phases in Rietveld refinements) by difference from 100%. The vbAffina program was used to refine the amounts of mineral phases determined with XRPD using the element compositions determined by XRF analysis. XRPD analyses indicated that the samples mainly contain several different clay minerals, quartz, mica, and feldspars. Analysis of the clay fraction identified kaolinite, chlorite, and interstratified illite-smectite (I-S) and chlorite-smectite (C-S). The mineralogy of the materials involved in the landslide in comparison with the mineralogy of the “undisturbed” rocks showed that the landslide is located in the weathered realm that overlies an arkosic bedrock. The interstratified I-S and C-S occurred at landslide activity locations and confirmed that areas more susceptible to sliding contained the most weathered parts of the rocks and perhaps represent areas of past and currently active fluid flow.

Characterization of Tunisian clay suitable for pharmaceutical and cosmetic applications

The aim of this study is to assess the suitability of purified Tunisian clay for its possible pharmaceutical and cosmetic uses. Mineralogical, chemical and physicochemical characterization was performed with the aid of tools like X-ray diffraction (XRD), Chemical composition, DTA/TGA analysis, Cation exchange capacity (CEC), particle size distribution by laser dispersion (PSD), surface area (BET method), Point of zero charge (PZC) and surface charge density σH. Pharmacopoeia tests were also carried: Swelling capacity, sedimentation volume and pH measurement. For microbiological tests, the absence of Salmonella species, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa was tested.The X-ray diffraction data revealed that the Tunisian sample is an interstratified illite-smectite. The percentage of smectitic fraction is estimated to be 78%. The chemical, textural and porosimetric results show important values suggesting that this mineral clay can function in creams, powders and emulsions.In view of the fundamentals of major pharmacopoeias for use of bentonite in pharmacy and considering the swelling capacity and sedimentation volume values, and microbiological results we could designate a pharmaceutical acceptable denomination for Tunisian purified clay.

Physicochemical and ceramic properties of clays from jebel kebar (Central Tunisia)

The mineralogical and chemical compositions and the physical properties are determined for three representative clay samples from the Sidi Bouzid area in Tunisia in order to evaluate their industrial aptitude for ceramic applications. The semi-quantitative mineralogical analysis shows that illite and kaolinite are the major clay phases associated with crystalline phases as quartz, K-feldspar and calcite. In addition, some quantities of smectite, interstratified illite–smectite, dolomite and gypsum are also detected. The chemical analysis reveals that the silica phase is relatively high. The CaO rate is approved by the mineralogical analysis. The classification of the selected clays by the Holtz and Kovacs diagram suggests their possible use in the manufacturing of the red bricks in ceramic industry. For the Geotechnical test, ceramic products were prepared by mixing the three clays with different weight proportions (40, 40, and 20% respectively for green clay, red clay and red silty clay samples).

The effect of preparation method on textural and structural properties of alumina-pillared interstratified illite-smectite

In order to study the effect of the preparation method on structural and textural properties of pillared clays, alumina-pillared bentonite clay (Al-PILC) was prepared using two different methods: the conventional and ultrasonic one, during the aging process for the pillaring solution and during the aging in the intercalation stage. Compared with the conventional treatment, the use of an ultrasonication method considerably reduces the modification time (from 24 h to 20 min) for the synthesis of the pillared clay. The characterization of solids by the elemental chemical analysis, X-ray diffraction (XRD), cation exchange capacity (CEC), N2 adsorption/desorption isotherms, scanning electron microscopy (SEM) and temperature-programmed reduction (H2-TPR) techniques showed that the use of ultrasound brings not only very similar results to those obtained with the classical method, but also present a better structural and textural properties than the clay pillared with the conventional treatment.

Comparing clay mineral diagenesis in interbedded sandstones and mudstones, Vienna Basin, Austria

AbstractThere is no consensus about the rate and style of clay mineral diagenesis in progressively buried sandstones v. interbedded mudstones. The diagenetic evolution of interbedded Miocene sandstones and mudstones from the Vienna Basin (Austria) has therefore been compared using core-based studies, petrography, X-ray diffraction and X-ray fluorescence. There was a common provenance for the coarse- and fine-grained sediments, and the primary depositional environment of the host sediment had no direct effect on illitization. The sandstones are mostly lithic arkoses dominated by framework grains of quartz, altered feldspars and carbonate rock fragments. Sandstone porosity has been reduced by quartz overgrowths and calcite cement; their pore-filling authigenic clay minerals consist of mixed-layer illite–smectite, illite, kaolinite and chlorite. In sandstones, smectite illitization progresses with depth; at 2150 m there is a transition from randomly interstratified to regular interstratified illite–smectite. The overall mineralogy of mudstones is surprisingly similar to the sandstones. However, for a given depth, feldspars are more altered to kaolinite, and smectite illitization is more advanced in sandstones than in mudstones. The higher permeability of sandstones allowed faster movement of material and pore fluid necessary for illitization and feldspar alteration than in mudstones. The significance of this work is that it has shown that open-system diagenesis is important for some clay mineral diagenetic reactions in sandstones, while closed-system diagenesis seems to operate for clay mineral diagenesis in mudstones.

Influence of organic matter on the reactivity of clay minerals in highly alkaline environments

Soil organic matter has important implications in dissolution reactions of clay minerals and their transformation. Under acidic conditions increased dissolution rates are generally reported. However, in high pH environments, organic matter (OM) might have a passivation effect on the mineral surface, thereby hindering dissolution and transformation substantially. The reduced reactivity of clay minerals is an important consideration when clays are used as backfill materials in nuclear waste disposals or when lime is used for soil stabilization. Here the outcome of a comparative study is presented using soil, containing common clay minerals such as smectite, interstratified illite–smectite, illite and kaolinite, that was treated with highly concentrated alkaline solutions in the presence and absence of naturally occurring organic matter. The results clearly show that clay mineral dissolution and the formation of new zeolitic phases at room T are delayed in the presence of OM. The soils' OM content is, thus, an important parameter to be considered in systems where clay minerals are exposed to highly alkaline environments.

Coupled transport-reaction modeling of the long-term interaction between iron, bentonite and Callovo-Oxfordian claystone in radioactive waste confinement systems

Appropriate geological disposals are required to manage the high level and intermediate level long lived radioactive waste. Several concepts have been developed in a number of nations. In France, different concepts have been investigated successively with time by Andra: either the steel waste package for vitrified waste was separated from the host rock (Callovo-Oxfordian (COx) claystone) by a bentonite engineered barrier or in the actual design, is in direct contact with the COx claystone. The long term interactions of the geological groundwater and steel overpack with the bentonite and/or claystone barriers were carried out by using the Kirmat 1D reactive transport code. Three different modeling approaches with the (T, t) conditions expected in the repository were implemented to (i) investigate the influence of the surface area of the primary minerals and the diffusion coefficient on the evolution of the iron–bentonite system and to (ii) compare the reactivity of the iron–bentonite and iron–COx claystone systems.For the iron–bentonite interactions, the simulated results showed significant differences depending on the different hypotheses used to calculate surface areas for minerals. When different sizes of mineral particles are assumed to estimate the surface areas of primary minerals, the system explored a larger change in porosity and more intense mineralogical modifications in the zone close to the bentonite/steel overpack interface. This result is likely related to the lower diffusion of aqueous corrosion products through the bentonite barrier. The comparison between iron–bentonite and iron–COx claystone interactions confirmed a clear different behavior of reactivity. For the iron–bentonite the alteration concerns two zones in direct contact with the geological groundwater and steel overpack but for the iron–COx claystone the mineralogical modifications are predicted to occur in the whole medium. The mineralogical evolution of the COx claystone barrier is mainly impacted by the dissolution of primary minerals, especially for total transformation of interstratified illite/smectite (I-Sm) and formation of secondary minerals such as illite and berthierine-FeII. The modeling results obtained from the sensitivity test showed a significant impact of the diffusion parameter on the evolution of the COx barrier, especially the changes in pH, porosity and the mineralogical modification of the zone in contact with the steel container.

Cu–Mn–Fe alloys and Mn-rich amphiboles in ancient copper slags from the Jabal Samran area, Saudi Arabia: With synopsis on chemistry of Fe–Mn(III) oxyhydroxides in alteration zones

In the Jabal Samran area (western Saudi Arabia), secondary copper mineralization in a NE-trending shear zone in which the arc metavolcanic host rocks (dacite–rhyodacite) show conjugate fractures and extensive hydrothermal alteration and bleaching. The zones contain frequent Fe–Mn(III) oxyhydroxides (FeOH–MnOH) that resulted from oxidation of pyrite and Mn-bearing silicates. In the bleached part, the groundmass is represented by Fe-bearing interstratified illite–smectite with up to 4.02wt% FeOt. FeOH–MnOH are pre-weathering phases formed by hydrothermal alteration in a submarine environment prior to uplifting. Five varieties of FeOH are distinguished, four of them are exclusively hydrothermal with ∼20wt% H2O whereas the fifth contains ∼31–33wt% H2O and might represent reworking of earlier hydrothermal FeOH phases by weathering. FeOH fills thin fractures in the form of veinlets and crenulated laminae or as a pseudomorph for pyrite, goethite and finally ferrihydrite, and this oxyhydroxide is characterized by positive correlation of Fe2O3 with SiO2 and Al2O3. On the other hand, MOH shows positive correlation between MnO2 and Al2O3 whereas it is negative between Fe2O3 and SiO2. Paratacamite is the most common secondary copper mineral that fills fractures and post-dates FeOH and MnOH. It is believed that Cl− in the structure of paratacamite represents inherited marine storage rather than from surfacial evaporates or meteoric water.The mineralogy of slags suggests a complicated mineral assemblage that includes native Cu prills, synthetic spinifixed Mn-rich amphiboles with 16.73wt% MnO, brown glass and Ca–Mn–Fe phase close to the olivine structure. EMPA indicate that the some Cu prills have either grey discontinuous boarder zone of S-rich Mn–Cu alloy (with up to 21.95wt% S and 19.45wt% Mn) or grey Cu–Mn–Fe alloy (with up to 15.9wt% Cu, 39. 12wt% Mn and 61.64wt% Fe). Mn in the Cu prills is expelled inward as Cu–Mn–Fe alloy inclusions whereas S is expelled outward as S-rich Mn–Cu alloy crust. Remains in the Samran smelter sites suggest the use of charcoal as a source of energy, quartzite as a flux and an air-cooling technique was used.

Acid–base properties of pillared interlayered clays with single and mixed Zr–Al oxide pillars prepared from Tunisian-interstratified illite–smectite

Interstratified illite–smectite clay samples from Tunisia have been used in order to prepare Al, Zr and Zr–Al-pillared clays. Several Al/metal, OH/metal ratios were used in order to investigate the effect on the chemical and physical properties, specifically the point of zero charge (PZC) of the synthesized pillared clays. The structure of the pillared materials is studied by XRD and cationic exchange capacity. The textural property is investigated by the nitrogen adsorption/desorption method. The acid–base chemistry “surface acidity” of these products was analysed by using mass and potentiometric titration in order to determine the PZC and the equilibrium constants (pKa) of each sample. The resulting materials exhibited basal spacings in the range of 17.4–20.5Å, with high surface areas (134–199m2g−1). Titration curves obtained by acid–base potentiometric titration for the starting material showed an indistinct cross-over point at about pH=7.3, whereas in the case of pillared samples, points were observed at the acidic region between 4 and 6. In addition, the calculated pKas values of pillared clays show a shifting to the acidic values compared to the untreated sample.

Combining ammonium mapping and short-wave infrared (SWIR) reflectance spectroscopy to constrain a model of hydrothermal alteration for the Acoculco geothermal zone, Eastern Mexico

The Acoculco geothermal system is hosted by a caldera complex located at the eastern portion of the Trans-Mexican Volcanic Belt. Surface manifestations are scarce and consist of low temperature, bubbling, acid–sulfate springs that are concentrated in two zones separated from each other by ∼1750m. In the northernmost one, there are conspicuous features suggesting recent, explosive, hydrothermal activity. Most of the rocks that crop out are tuffs and breccias that show pervasive hydrothermal alteration. Six SWIR-active minerals have been revealed by reflectance spectroscopy in the surface altered rocks: Opal, kaolinite, alunite, ammoniojarosite, buddingtonite and interstratified illite–smectite; they are indicative of alteration assemblages comparable to those reported in other geothermal systems and in epithermal deposits. Opal is the most widespread alteration mineral and occurs in association with tridimite and anatase. Kaolinite is also widely distributed but has a greater presence in the area with active surface manifestations, which, moreover, is the only area with alunite and ammoniojarosite occurrences. Buddingtonite occurs in the same zones as sulfates. As a complement to the alteration maps, we are proposing a simple method for mapping ammonium anomalies, based on total N analyses in altered rocks. Total N data show a discontinuous distribution within a wide range of variation (0.01–3.28wt.%). All medium and high N values (>0.26wt.%) plot in three clusters, two of which coincide with zones of gas emission.A deep circulating, active hydrothermal system cannot be ruled out in Acoculco although it may be confined to the deep caldera structure by an impermeable cap-rock of silicic and argillic alteration. In this scenario, hydrothermal fluids would reach the surface periodically, when explosive hydrothermal fracturing allowed it. The occurrence of hydrothermal explosion features and of acid–sulfate alteration supports this scenario. Therefore, further exploration by drilling would be advisable in Acoculco.

Surface Properties of Petrologic End-Members from Alberta Oil Sands and Their Relationship with Mineralogical and Chemical Composition

Clays cause problems in all crucial stages of bitumen extraction, and they affect bitumen recovery and waste management. It is thus of great importance to understand the mineralogy, chemistry, and surface properties of clays to improve both bitumen recovery and tailings treatment. Four petrologically different types of Alberta oil sands ores—called “end-members”—were examined in this study by cation exchange capacity (CEC), specific surface area (SSA), total specific surface area (TSSA), and negative layer charge density (LCD) measurements in order to better understand the effects of clay surface properties on bitumen nonaqueous extraction and solvent recovery from the extraction tailings. The surface properties are primarily controlled by the mineralogy of the petrologic end-members, mainly by the type and quantity of clay minerals. CEC, SSA, TSSA, and LCD increased as the amount of 2:1 clays (illite and illite–smectite), in particular expandable interstratified illite–smectite, increased. CEC values increased with increasing SSA and TSSA. The number of H-aggregates increased and the number of monomers decreased in the second derivative spectra of Rhodamine 6G and Methylene Blue as the 2:1 clays content in the petrologic end-members increased. This indicated a greater negative layer charge density with an increasing amount of 2:1 clays. The molecular aggregation of the organic dyes (Rhodamine 6G and Methylene Blue) was observed in the second derivative spectra for petrologic end-members bearing >25 wt % of 2:1 clays. Overall, the results indicate that interstratified illite–smectite may be largely responsible for high CEC, SSA, TSSA, and LCD in the fine size fractions of petrologic end-members from Alberta oil sands.

Characterisation of petrologic end members of oil sands from the athabasca region, Alberta, Canada

AbstractThe aim of this study was to perform mineral and chemical characterisation of the four petrologic end members of Alberta oil sands in order to better understand the mineralogical and geochemical factors affecting bitumen extraction. X‐ray diffraction (XRD) results revealed that the petrologic end members contain a variable amount of quartz, clay minerals, carbonates, K‐feldspar, TiO2 minerals and pyrite and the Fe‐containing phases were also observed in Mössbauer spectra. Scanning electron microscopy‐energy dispersive X‐ray (SEM‐EDX) analysis also showed the presence of Fe–Ti oxide minerals. Mössbauer results also indicated the presence of lepidocrocite in the fine fractions in amounts below the detection limit of XRD. Interstratified illite–smectite was found only in clay‐rich petrologic end members. Calcite and dolomite were primarily concentrated in the fine fractions of marine petrologic end members. Conversely, siderite was found mainly in the coarse fraction of estuarine petrologic end members.The relative amount of toluene insoluble organics was higher in the fine fractions of marine petrologic end members.

Toposequence of sandy soils in the northern coastal plain of Israel: Polygenesis and complexity of pedogeomorphic development

Catenary relationships of surface soils in the vicinity of kibbutz Shomrat in the Galilee coastal plain of Israel were studied including optically stimulated luminescence (OSL). The research provides new insights into the local pedogeomorphic history and confirms that the study area is of different age than the central coastal plain of Israel. The soil toposequence is composed of polygenic red Hamra (Rhodoxeralf) on the hilltop, a calcareous Rhodoxeralf (Husmas) on the middle slope, both older than 250ka, and a complex pedosedimentary sequence in a lower position spanning Middle Pleistocene–Holocene OSL ages. The hilltop red Hamra is strongly reworked by soil burrowing animals, magnetically enhanced, and contains aged clay coatings and a few petrocalcic nodules. Micromorphology revealed a relict nature of cemented carbonate nodules and allowed us to establish a sequence of pedogenic episodes, e.g. rubification and clay illuviation that intermittently affected nodule growth and re-crystallization. All soils are dominated by interstratified illite–smectite, whose amount and expandability increase downhill. In the lowest topographic positions, soil development was compounded by additional fine-grained accumulation via eolian and slope processes which may have intensified during periods of geomorphic instability. Our data and interpretations suggest that to the north of Haifa Bay, coastal geomorphic surfaces are formed by late Mid-Pleistocene exhumed paleosol toposequences, which are sporadically overprinted by younger paleosols, and continue to function as presently active soils.