Unconformity-related uranium deposits, which represent a significant high-grade uranium resource, are systematically surrounded by a host-rock alteration halo enriched in clay minerals. Illite is often the major clay mineral component of the halo and it displays a variable crystal structure. New data are provided on the crystal structure and the chemistry of illite encountered within and outside of the alteration halo surrounding the Shea Creek deposit. Two illite populations were distinguished using textural and structural criteria: samples rich in the tv-1M polytype display thin (sub-micrometer) and ‘hairy’ shapes, while samples richer in the cv-1M polytype contain illites with rigid lath-like shapes several micrometers wide. In barren ‘regional’ sandstone, the trends with depth of the textural and microstructural properties of illite particles are: (1) an increase of particle size, (2) an evolution to a more isometric form, and (3) a dominance of the cv-1M polytype over the tv-1M polytype. These trends record diagenetic processes under conditions of deep burial and differ from those observed in altered sandstone around the uranium mineralization. The altered sandstone is characterized by enrichment in the tv-1M polytype near the unconformity and/or brittle structural features. This tv-1M illitization took place in response to structurally-controlled infiltration of basement rocks by diagenetic brines which were further recycled after interaction into the overlying basin. Variations of the illite structural and textural properties may result from nucleation/growth kinetics and may be indicative of a change in the flow regime, and/or a change of saturation state of the fluid vs. illite. The tv-1M illite may be favored in environments characterized by a high fluid/rock ratio and a high supersaturation state of the fluids in proximity to mineralization.

The spatial distribution of the dominant matrix minerals present in the middle-Proterozoic Athabasca Group sandstone (kaolin, illite, sudoite, dravite, hematite) was studied at a regional scale in the Shea Creek region (Saskatchewan, Canada), in which two epigenetic unconformity-type uranium deposits have been discovered. 3D models of matrix mineral distribution were derived from normative mineral calculations and 3D interpolation using whole-rock geochemical analyses of sandstone samples collected from both mineralized and barren areas. The calculations were constrained by information obtained from petrographic and crystal-chemical clay mineralogical studies on representative samples. The 3D mineral distribution models were compared to the lithostratigraphy and structural features of the Athabasca Group sandstone to ascertain the source and mobility of the main elements involved in the sandstone host-rock alteration processes related to the U mineralization. The distribution of Al is conformable with the lithostratigraphy throughout the studied area, regardless of proximity to basement-rooted structures and U ore bodies. The distribution of illite displays similar features, but the intensity of the illitization of kaolin decreases with increasing distance from the structures and U ore bodies. Hematite bleaching and neoformation of sudoite and dravite were restricted to the vicinity of the fault zones above the U ore bodies. The spatial configurations of the mineral anomalies show that syn-ore fluids flowed from the basement towards the sandstone cover via the fault zones, as described in current metallogenic models. Although Al remained immobile (mass transfer), the anomalous K, B and Mg present in the host-rock alteration haloes were probably imported from the basement rocks (mass transport). Unlike B and Mg, K migrated laterally at least several kilometers from the basement-rooted faults. The mineral distribution models were used to quantify the volume of altered sandstone (10−2−10−1 km3) and the amounts of K, Mg and B which were imported to the alteration haloes above the Shea Creek U ore bodies: 186,000 t of K, 66,000 t of Mg, and 11,000 t of B above the Anne ore body, and 24,000 t of K, 185,000 t of Mg, and a similar 11,000 t of B above the Colette ore body.

The clay fractions of Jurassic marls in the Great Estuarine Group in southern Isle of Skye are composed of mixed-layered illite-smectite (I-S) with large percentages (>85%) of illite layers, kaolinite, and generally smaller amounts of chlorite. These marls have not been buried to the depths normally required to convert smectite to illite-rich I-S, so it is possible that the conversion was in response to heat and hydrothermal fluids from nearby early Tertiary igneous activity ∼55 Ma ago. The large percentages of illite layers in I-S, the Środoń intensity ratios, and the Kübler index values appear to be consistent with the formation of diagenetic I-S as a result of relatively brief heating caused by igneous activity. The Jurassic rocks in southern Skye contain a secondary chemical remanent magnetization (CRM) that resides in magnetite and formed at approximately the same time as the Tertiary igneous rocks on Skye. K-Ar age values for I-S based on illite age analysis have been determined to test the hypothesis that the CRM was acquired coincidently with the smectite-to-illite conversion. However, linear extrapolation of K-Ar age vs. percentage of 2M1 polytype (detrital illite) from one marl (EL-6) yields an estimate for the age of diagenetic illite of 106 Ma, which is close to the measured age of the finest subfraction (108 Ma). These estimated and measured age values, however, could be substantially greater than the true age of the diagenetic illite in I-S because of the presence of detrital 1Md illite that was recycled from early Paleozoic shales and whose abundance relative to the diagenetic I-S may have been enhanced because the diagenetic fluid had a low K/Na ratio, limiting the amount of diagenetic illite formed. Nevertheless, most of the illite in the Elgol marls (80% or more in the finest fractions) must be diagenetic and probably formed in response to the early Tertiary magmatism.

Palygorskite fibers growing along fault planes in the outcrops of a large fault zone in SE Spain (Carboneras Fault Zone: CFZ; Serrata de Níjar) were studied by X-ray diffraction, scanning electron microscopy-energy dispersive X-ray analysis, and transmission electron microscopy-analytical electron microscopy. The structural formulae, calculated per half unit-cell, is: Si7.95Al0.05O20(Al1.93Fe0.08Mg1.92) (OH)2(OH2)4Na0.09K0.01Ca0.034(H2O). The samples have minor tetrahedral substitutions, with Mg/Al ratios close to one, and contain very small amounts of Fe3+. The number of octahedral cations per half unit-cell is 3.93. The fault-hosted palygorskite shows macroscopic ductile features including incipient foliation. Based on field and laboratory observations, as well as on regional geological evidence indicating the existence of widespread hydrothermal processes along the Serrata de Níjar and surrounding areas, we suggest that palygorskite may have formed during ongoing deformation in the CFZ, as a precipitate from Mg-rich hydrothermal fluids.

Talc deposits, located mainly in three areas of north-central Turkey, are present in the ophiolitic series of the Cretaceous and in siliciclastic rocks of the Paleocene. Talc deposits related to ophiolites are between tectonite and cumulate occurring as beds and/or lenses and 0.1–3 cm thick fracture fillings within a 5 m brecciated zone with a vein-type bedding. Sedimentary-hosted talc beds and semi-rounded to angular talc grains (0.1–2 cm) range in thickness from 0.1 to 30 cm within marls and conglomerates. Talc veins form lenses (a few meters long) and spheroidal and/or ellipsoidal nodules (1–10 cm). Calcite, dolomite, serpentine and/or mixed-layered illite-smectite (I-S) minerals are encountered in the talc samples. Serpentine with positive U and Hf anomalies, and talc with positive Nb and Zr anomalies, and negative Ta and Ce anomalies are typically depleted in P and Ti, based on chondrite-normalized trace element patterns. The light rare earth element content of sedimentary-hosted talc with a negative Gd anomaly is richer than those of ultramafic-hosted talc with a negative anomaly for Eu as well as serpentine. Significantly, talc with a uniquely sedimentary origin tends to be the principal source of Nb, Hf, Zr, La, Ce, Pr and Nd with respect to serpentine. δ18O and δD values for talc range from +13.8 to +17.5‰ and −60 to −36‰, and those of serpentine are +9.4 and −88‰, indicating supergene conditions for sedimentary-hosted talc and hypogene for ultramafic-hosted talc. When compared with seawater, δ18O data indicate temperatures of 68°C and 80–98°C for the sedimentary- and ultramafic-hosted talc formations, respectively, and 100°C for serpentine, suggesting that talcification and serpentinization of ultramafic rocks both occurred at nearly the same time with various stages. All data show that the talc occurrences are divided into two types based on their mode of formation. The first corresponds to a serpentinization stage within the ophiolites. The others are the neoformation products of sedimentary deposition, diagenetic and post-diagenetic processes, respectively. Sedimentary-hosted talc also seems to have inherited trace element and isotopic compositions from the parent ultramafic rocks.

The early stages of amphibole weathering result in the crystallization of several clay mineral species: tri- and dioctahedral smectites, interstratified dioctahedral kaolinite-smectite (K-S), and halloysite. Each clay mineral crystallizes into specific microsites which develop from etch pits along specific crystallographic directions in the host amphibole. Two types of microsites are recognized according to their location in the amphibole crystal and their clay mineral crystallizations. The first type is a plane surface related to the (110) amphibole cleavages where saponite particles crystallize in a characteristic honeycomb texture. The second type is a ‘sawtooth’ (001) fracture surface generated by etch-pit coalescence where (1) platy K-S particles crystallize directly in contact with the amphibole at the top of ‘teeth’, (2) halloysite particles with tubular habits crystallize directly in contact with the amphibole on the side of the ‘teeth’, and/or on the K-S particles, and (3) montmorillonite crystallizes in the central part of the (001) fracture as a layer with honeycomb texture in contact with the K-S platelets located at the top of ‘teeth’. The microtextural relationships between the clay minerals and their host mineral suggest the following crystallization sequence: (1) saponite and montmorillonite crystallize first on the (110) and (001) surfaces, respectively; (2) as amphibole dissolution proceeds perpendicular to the (001) fracture planes, montmorillonites continue to form in the middle part of the widening fracture whereas K-S crystallizes on the ‘sawtooth’ termination; (3) in the last stage of weathering, tubular halloysite crystallizes on the side of the ‘teeth’, and/or on the K-S.

Compacted Na-bentonite clay barriers, widely used in the isolation of solid-waste landfills and other contaminated sites, have been proposed for a similar use in the disposal of high-level radioactive waste. Molecular diffusion through the pore space in these barriers plays a key role in their performance, thus motivating recent measurements of the apparent diffusion coefficient tensor of water tracers in compacted, water-saturated Na-bentonites. In the present study, we introduce a conceptual model in which the pore space of water-saturated bentonite is divided into ‘macropore’ and ‘interlayer nanopore’ compartments. With this model we determine quantitatively the relative contributions of pore-network geometry (expressed as a geometric factor) and of the diffusive behavior of water molecules near montmorillonite basal surfaces (expressed as a constrictivity factor) to the apparent diffusion coefficient tensor. Our model predicts, in agreement with experiment, that the mean principal value of the apparent diffusion coefficient tensor follows a single relationship when plotted against the partial montmorillonite dry density (mass of montmorillonite per combined volume of montmorillonite and pore space). Using a single fitted parameter, the mean principal geometric factor, our model successfully describes this relationship for a broad range of bentonite-water systems, from dilute gel to highly-compacted bentonite with 80% of its pore water in interlayer nanopores.

The Hançılı bentonite from Turkey shows significant changes in surface area, micro- and mesoporosity, surface acidity and acid strength with heating from 100 to 900°C for 2 h. The specific surface area (S) and specific micro-mesopore volume (V) of the original and heated samples were evaluated from N2 adsorption and desorption data, respectively, by standard methods. The adsorption of n-butylamine from the solution in cyclohexane on the samples was used to determine the total surface acidity (nm) and the adsorption equilibrium constant (K) was taken as a measure of the acid strength. S, V and nm having initial values of 98 m2g−1, 0.080 cm3g−1 and 4.8 × 10−4 mol g−1, respectively, stayed approximately constant as the temperature increased to 450°C and then decreased almost in parallel with each other, reaching their minimum or zero at 900°C. The total surface acidity, in general, declines with increasing temperature. The most acidic sites, however, increase with heating, and especially at dehydration and dehydroxylation. Acid strength reaches its maximum during the dehydroxylation phase at ∼600°C. It was concluded that the total surface acidity does not necessarily parallel the strength of the most acid sites.

Cobalt (II) and Al (III) layered double hydroxides were precipitated from homogeneous solutions using urea hydrolysis under hydrothermal conditions. The particle sizes were controlled successfully by changing the reaction temperature and period. It was found that larger particles formed by reactions at lower temperatures over longer reaction periods because the slow urea hydrolysis at lower temperatures suppresses the formation of nuclei in the solution. When the reaction was conducted at 60°C for 100 days, particles >40 µm wide were obtained.

A reference sample of sepiolite and products of its comminution by vibrating dry-milling have been studied using X-ray diffraction (XRD) line-broadening analysis, complementary field emission scanning electron microscopy (FESEM) images and surface area measurements. The apparent crystallite sizes determined via XRD are in agreement with observations on FESEM images. The sepiolite aggregates consist of lath-shaped agglutinations of prisms and pinacoids elongated along [001], each lath including several crystallites in that direction. The surface area magnitudes are in the range of previous experimental measurements of other sepiolites. The results obtained show the effectiveness of vibro-milling as the procedure to use for the comminution of sepiolite.

Adsorption isotherms and differential heats of adsorption of water vapor by muscovite were measured at 303 K. The heats of adsorption are stepwise and each step corresponds to the stoichiometric formation of adsorption complexes of H2O molecules with K+ ions, (H2O)n/K+, (n = 1–6), which are located on the basal and lateral (edge) faces. At saturation, the ditrigonal cavities of the basal faces are fully occupied by hexameric clusters. It is suggested that half of the K+ ions on the basal faces come from neighboring layers by migration under the influence of the adsorbed H2O at the initial stage of adsorption. Similar migration of K+ to the edges was also hypothesized, suggesting that only every second site can be occupied by a cluster. At the final stage of adsorption, H2O molecules are believed to form H-bonded bridges between the hexameric water/cation clusters on the basal faces, whereas on the edge faces no such effect is believed to occur. The mean molar integral adsorption entropy of water is ∼−7 J/mol K less than the molar entropy of the bulk liquid. The mobility of H2O on muscovite is slightly less than in bulk water. Migration of K+ cations under the influence of adsorbed H2O both on the basal and lateral faces of muscovite is reversible.