Search Results (391)

Multiple ironstone beds formed during the Callovian-Oxfordian times as a consequence of intense continental weathering, upwelling, and hydrothermal activity. This study examines the compositional differences between core and rim, and the origin of iron ooids along the northwestern margin of the Neo-Tethys Ocean to highlight sea-level fluctuations, redox conditions, and elemental influx. An integrated sedimentological study, including petrography, mineralogy, micro-texture, and mineral chemistry, was carried out to explain the origin and implications of ironstones. The ~14 m thick Callovian-Oxfordian, marginal marine deposits in the Kutch Basin, in western India, exhibit iron ooids, predominantly formed in oolitic shoals during transgression, associated with lagoonal siliciclastics. Callovian shoals interbedded with lagoonal facies record minor sea-level fluctuations, whereas the Oxfordian deposit records a major transgression and condensation, resulting in extensive ironstone deposits. The ooid cortices and nuclei exhibit distinctive mineralogy and micro-textures: glauconitic smectite exhibits poorly-developed rosettes, chamosite displays flower-like, and goethite shows rod-like features. Three types of ooids are formed: (i) monomineralic ooids are entirely of chamosite or goethite, (ii) quartz-nucleated ooids, and (iii) composite ooids with either chamosite core and goethite rim, or chamosite core and glauconitic smectite rim. The assemblages within iron ooids reflect variation in depositional redox conditions: glauconitic smectite develops under suboxic lagoonal flank, chamosite forms in anoxic central lagoon, and goethite precipitates on oxic shoals. Full article

The transformation of smectite to illite documents multi-scale water–rock–hydrocarbon interaction dynamics. Current studies predominantly emphasize the influence of inorganic systems on this process, while overlooking the dynamic regulation by organic matter and the synergistic effects of multiple controlling factors under actual geological conditions. In this study, we conducted integrated semi-open pyrolysis experiments on natural samples from the Chang-7 Member and hydrothermal experiments using synthetic analogs. The illitization process of smectite was characterized through XRD analysis and SEM observations, while organic geochemical testing was employed to track the corresponding thermal evolution of organic matter. The semi-open pyrolysis results reveal that significant changes in illite–smectite (I/S) mixed layer minerals and illite content/morphology occur above 320 °C, which coincides with the critical threshold for extensive organic matter evolution. Thermal degradation of organic matter generates pore space, thereby enhancing water–rock interactions involving clay minerals. This demonstrates the co-evolution of organic matter and smectite, and indicates that temperature indirectly influences illitization by regulating organic matter thermal evolution. The hydrothermal simulation experiments demonstrate the early-stage characteristics of illitization. Unlike long-term geological evolution, K⁺ under experimental conditions primarily originates from the aqueous medium due to kinetic constraints on feldspar dissolution. Notably, organic matter regulates K⁺ partitioning dynamics—increased organic matter content hinders K⁺ incorporation into smectite interlayers, thereby suppressing the illitization process. Cross-system experimental analysis reveals that organic matter exhibits temporally dependent dual functionality, serving both mediating and modulating roles within inorganic diagenetic systems. This study delineates diagnostic-stage-dependent mechanisms governing smectite illitization through multifactorial synergistic interplay, establishing a predictive framework applicable to organic-rich systems exemplified by the Chang-7 Shale. Full article

Studies of early syn-rift successions in the Duwi Basin have revealed repetitive lacustrine carbonate deposits exhibiting regressive sequences and early diagenetic processes. Two main informal stratigraphic units (Units 1 and 2), spanning the Late Oligocene to Early Miocene, have been identified in the area. Unit 1 primarily consists of lacustrine limestone and calcrete deposits that formed in a palustrine environment, whereas Unit 2 is composed of dolomites and cherts, which developed during times of lake evaporation and desiccation under arid climatic conditions. A wide variety of pedogenic features, including brecciation, nodulization, rhizocretions, fissuring, microkarsts, and circumgranular cracks, dominate the carbonate sequence, indicating deposition in a marginal lacustrine setting. Integrated petrographic, mineralogical, geochemical, and isotopic studies of carbonate facies reveal two distinct evolutionary stages in the Duwi Basin, with dolomitization and silicification characterizing the late stage. Their isotopic compositions show a wide range of δ¹³C and δ¹⁸O values, ranging from −9.00‰ to −7.98‰ and from −10.03‰ to −0.68‰, respectively. Dolomite beds exhibit more negative δ¹³C and δ¹⁸O values, whereas palustrine limestones display higher (less negative) values. The upward trend of δ¹⁸O enrichment in carbonates suggests that the lake became hydrologically closed. Trace element concentrations serve as potential markers for distinguishing carbonate facies, aiding with paleoenvironmental and diagenetic interpretations. Our findings indicate that the studied dolomites and cherts formed under both biogenic and abiogenic conditions in an evaporative, alkaline-saline lake system. Biogenic dolomite and silica likely resulted from microbial activity, whereas abiogenic formation was driven by physicochemical conditions, including decreasing pH values and the presence of smectite clays. Tectonics, local climate, and provenance played crucial roles in controlling the overall diagenetic patterns and evolutionary history of the lake basin system during the Late Oligocene to Early Miocene. Full article

The stability of a formulation of 1% N-chlorotaurine (NCT) in a smectite clay as a gel was characterized using a range of physicochemical parameters, and its antimicrobial efficacy was determined against Staphylococcus aureus and Pseudomonas aeruginosa. The stability of the NCT gel was determined by UV–visible spectroscopy. The efficacy against S. aureus and P. aeruginosa was tested in single- and dual-species biofilms using a dynamic in vitro chronic wound infection model and only showed efficacy against S. aureus. The gel proved stable over time at room temperature and at 4 °C with half-life values of ~161 days and 4 years, respectively. The compatibility of NCT with the preferred pH of the clay gel makes this formulation a candidate for durable topical application to chronic wounds. Full article

As critical components in continental shale systems, the composition and evolution of clay minerals are fundamental to their diagenetic processes and petrophysical properties. The Chang-7 shales in the Ordos Basin exhibit abundant clay mineral content, offering a valuable case study for clay mineral research under moderate diagenetic conditions. This study employed XRD analysis to determine the whole-rock mineralogy, clay mineral composition, and the evolution characteristics of illite-smectite mixed-layer minerals (I/S). Comprehensive clay mineral datasets compiled from 13 newly analyzed wells and existing literature revealed distinct lateral distribution patterns. Total Organic Carbon (TOC) analysis and vitrinite reflectance (R_o) measurements provided systematic quantification of organic matter abundance and thermal maturation parameters in the studied samples. The results reveal that the Chang-7 shale exhibits a characteristic clay mineral assemblage, with I/S (average 44.2%) predominating over illite (34.7%), followed by chlorite (15.6%) and limited kaolinite (5.4%). Frequent volcanic activities provided substantial precursor materials for smectite formation, which actively participated in subsequent illitization processes, while chlorite and kaolinite distributions were predominantly controlled by provenance inputs and sedimentary facies, respectively. Inconsistencies exist between diagenetic stages inferred from I/S mixed-layer ratios and R_o values, particularly in low-maturity samples exhibiting accelerated illitization. The observed negative correlation between TOC content and mixed-layer ratios in Well YY1 and YSC Section samples demonstrates the catalytic role of organic matter in facilitating smectite-to-illite transformation. These results systematically clarify the coupled effects of sedimentary-diagenetic processes, offering new insights into the mutual interactions between inorganic and organic phases during illitization under natural geological conditions. The findings advance the understanding of Chang-7 shale oil and gas systems and offer practical guidance for future exploration. Full article

This study aimed to investigate vertical variations in dissolved organic matter (DOM) properties, humus (HS) composition, humic acid (HA) characteristics, and clay mineral dynamics, with a particular focus on the vertical distribution of HS components and mineral composition across Dark-brown, Meadow, and Paddy soil profiles. Results indicated that: (1) DOM in all three soil types was predominantly endogenous, primarily derived from microbial metabolism with minimal contributions from plant residues. (2) Vertical trends in DOM carbon content (C_DOM) were specific to soil type: in Dark-brown soil, C_DOM slightly increased from the Ap to Bt layer, followed by a sharp increase in the C layer; Meadow soil exhibited a significant decrease in C_DOM in the AB layer but remained relatively stable in other layers; Paddy soil showed a consistent decline in C_DOM with increasing depth. (3) HS and its fractions exhibited vertical variability: Paddy soil showed higher HS content in surface layers; carbon contents of water-soluble substances, HA, and humic-extracted acid (C_WSS, C_HA, and C_HE) decreased with depth in Dark-brown and Paddy soils, whereas they remained relatively stable in deeper layers of Meadow soil. (4) HA characteristics, including C/N ratio, functional groups, and aromaticity, were influenced by both depth and soil type: the Ap2 layer of Paddy soil effectively restricted the downward movement of organic matter; Fe³⁺ complexation played a key role in HA stabilization in Dark-brown soil; Meadow soil exhibited transitional HS properties. (5) Clay mineral assemblages were dominated by 2:1 type minerals (illite, smectite, illite–smectite interstratifications), showing distinct vertical weathering patterns: illite content decreased with depth due to hydrolysis, while proton-driven dissolution promoted kaolinite formation in surface layers, particularly in Dark-brown soil 2:1 minerals enhancing organic–mineral complexation in Meadow soil. The findings of this study provided a scientific basis for optimizing soil carbon pool management and offer insights into organic–mineral interactions that can enhance organic matter sequestration in agricultural soils. Full article

The technological potential and sustainability of red clays from the Taveiro region (Coimbra, Portugal) for structural ceramic applications have been investigated. Thirteen representative samples granulometric, mineralogical, chemical analysis, and technological characterization were conducted to determine the suitability for extrusion-based ceramics, aligned with circular economy and climate goals (e.g., PNEC2030, RNC2050). The samples exhibited a high fine fraction content (<0.002 mm up to 76%) and plasticity index (PI; up to 41%), associated with significant smectite, illite, and kaolinite content. Bulk mineralogy was dominated by Σ phyllosilicates (up to 77%) and quartz (12%–29%), while chemical analyses showed high SiO₂ and Al₂O₃ content, moderate Fe₂O₃, and low CaO/MgO, typical of aluminosilicate clays for red ceramics. High cation exchange capacity (CEC; up to 49 meq/100 g) and specific surface area (SSA; up to 83 m²/g) reflected smectite-rich samples. Firing tests at 900 and 1000 °C demonstrated decreasing water absorption and shrinkage with increased temperature, with some samples yielding lower porosity and higher strength (~12 MPa), confirming suitability for bricks and tiles. Two samples showed higher plasticity but greater shrinkage and porosity, suggesting applicability in porous ceramics or blends. This work highlights the role of mineralogical and technological indicators in guiding the eco-efficient use of georesources for ceramic manufacturing. Full article

In the exploration of unconventional petroleum resources in the Nanpu Sag of China, several tight oil sandstone reservoirs have been identified; however, their physical properties display pronounced heterogeneity. Using methods such as scanning electron microscopy (SEM), thin-section petrography, X-ray Diffraction (XRD), and high-pressure mercury intrusion, this study analyzed the mineralogical, petrological, and reservoir characteristics of the tight oil sandstone reservoirs in the second member of the Dongying Formation in the Nanpu Sag. This study also examined the relationship between the heterogeneity of the pore networks in the tight oil sandstone reservoirs and their fractal dimensions. The results indicate that as the fractal dimension (Df) of the tight oil sandstone reservoirs increases, their permeability decreases exponentially. The Df is strongly linked to pore morphology: larger Df values correspond to smaller pore sizes, more complex pore shapes, and greater pore heterogeneity. Additionally, variations in Df are closely linked to mineralogy: lower quartz content and higher clay content, particularly abundant illite–smectite mixed layers and illite along with reduced kaolinite, are associated with higher Df values. These findings highlight the complex, irregular nature of pore structures in tight sandstones and demonstrate that integrating high-pressure mercury intrusion analysis with fractal theory provides an effective approach for quantitatively characterizing their heterogeneity. Full article

The Elfeija Dune Field (EDF) is a continental aeolian system in an arid region of southeastern Morocco. Studying this system is critical for understanding the effects of mounting climatic and anthropogenic pressures. This study provides a comprehensive characterization of the EDF’s morphology, sedimentology, aeolian dynamics, genesis, and recent evolution. A multi-scale, multidisciplinary approach was adopted, integrating field observations, sedimentological analyses, MERRA-2 reanalysis wind data, cartographic analysis, digital terrain modeling, and morphometric measurements. The results reveal an active 30 km² dune field, elongated WSW-ENE, which is divisible into three morphodynamic zones with a high dune density (80–90 dunes/km²). The wind regime is predominantly from the W to WSW, driving a net ENE sand transport and creating conditions conducive to barchan formation (RDP/DP > 0.78). Sediments are quartz dominated, with significant calcite and various clay minerals (illite, kaolinite, and smectite). Dune sands are primarily fine- to medium-grained and well sorted, in contrast to the more poorly sorted interdune deposits. The landscape is dominated by barchans (mean height H = 2.5 m; mean length L = 50 m) and their coalescent forms, indicating sustained aeolian activity. The potential sand flux was estimated at 1.7 kg/m/s, with a dune collision probability of 32%. The field’s genesis is hypothesized to be controlled by a topographically induced Venturi effect, with an initiation approximately 1000 years ago, potentially linked to the Medieval Climatic Optimum. Significant anthropogenic impacts from expanding irrigated agriculture are observed at the dune field margins. By providing a detailed characterization of the EDF and its sensitivity to natural and anthropogenic forcings, this study establishes a critical baseline for the sustainable management of arid environments. Full article

This study investigates the potential of residual clays from a traditional ceramic-producing region in southern Portugal as raw materials for red ceramic applications. This work aims to support more sustainable ceramic practices through the local valorization of naturally available, underutilized clay resources. A multidisciplinary approach was employed to characterize clays, integrating mineralogical (XRD), chemical (XRF), granulometric, and thermal analyses (TGA/DTA/TD), as well as technological tests on plasticity, extrusion moisture, shrinkage, and flexural strength. These assessments were designed to capture both the intrinsic properties of the clays and their behavior across key ceramic processing stages, such as shaping, drying, and firing. The results revealed a broad diversity in mineral composition, particularly in the proportions of kaolinite, smectite, and illite, which strongly influenced plasticity, water demand, and thermal stability. Clays with higher fine fractions and smectitic content exhibited excellent plasticity and workability, though with increased sensitivity to drying and firing conditions. Others, with coarser textures and illitic or feldspathic composition, demonstrated improved dimensional stability and lower shrinkage. Thermal analyses confirmed expected dehydroxylation and sintering behavior, with the formation of mullite and spinel-type phases contributing to densification and strength in fired bodies. This study highlights that residual clays from varied geological settings can offer distinct advantages when matched appropriately to ceramic product requirements. Some materials showed strong potential for direct application in structural ceramics, while others may serve as additives or tempering agents in formulations. These findings reinforce the value of integrated characterization for optimizing raw material use and support a more circular, resource-conscious approach to ceramic production. Full article

This work aims to perform a detailed mineralogical, crystal-chemical, and geochemical characterization of bentonites from the Benavila outcrop, the largest known deposit of bentonites in continental Portugal. Bulk samples and different size fractions were characterized through X-Ray Diffraction (XRD). Structural formulae of the smectites were fitted from point analyses acquired by analytical electron microscopy (AEM) with transmission electron microscopy (TEM). Smectites are the major component with variable amounts of calcite and minor amounts of quartz, feldspar, illite, and chlorite. Occasionally, amphiboles and dolomite have also been identified. The high content of carbonates in different parts of the sampling area is related to the circulation of carbonate-rich fluids. The smectites present high-layer charge, are intermediate terms of the montmorillonite–beidellite series, and also show an intermediate cisvacant–transvacant configuration. Major and trace elements concentrations were determined by ICP-MS. The geochemical analysis of the samples indicates an enrichment in SiO₂ and Al₂O₃ and a depletion of the more clayey materials in REE, HFSE, and Y, among others. The calculation of the PIA and CIA alteration indices, along with other parameters observed, shows the possible alteration pathways of the Benavila deposit. Research to evaluate the ability of these bentonites to be used as engineering barrier systems (EBS) and sealing materials for radioactive waste repositories is ongoing. Full article

Petrological knowledge on weathering processes controlling the mobility of chemical elements is still limited in the dry tropical zone of Cameroon. This study aims to investigate the mobility of major and trace elements during rhyolite weathering and soil formation in Mobono by understanding the mineralogical and elemental vertical variation. The studied soil was classified as Cambisols containing mainly quartz, K-feldspar, plagioclase, smectite, kaolinite, illite, calcite, lepidocrocite, goethite, sepiolite, and interstratified clay minerals. pH values ranging between 6.11 and 8.77 indicated that hydrolysis, superimposed on oxidation and carbonation, is the main process responsible for the formation of secondary minerals, leading to the formation of iron oxides and calcite. The bedrock was mainly constituted of SiO₂, Al₂O₃, Na₂O, Fe₂O₃, Ba, Zr, Sr, Y, Ga, and Rb. Ce and Eu anomalies, and chondrite-normalized La/Yb ratios were 0.98, 0.67, and 2.86, respectively. SiO₂, Al₂O₃, Fe₂O₃, Na₂O, and K₂O were major elements in soil horizons. Trace elements revealed high levels of Ba (385 to 1320 mg kg⁻¹), Zr (158 to 429 mg kg⁻¹), Zn (61 to 151 mg kg⁻¹), Sr (62 to 243 mg kg⁻¹), Y (55 to 81 mg kg⁻¹), Rb (1102 to 58 mg kg⁻¹), and Ga (17.70 to 35 mg kg⁻¹). LREEs were more abundant than HREEs, with LREE/HREE ratio ranging between 2.60 and 6.24. Ce and Eu anomalies ranged from 1.08 to 1.21 and 0.58 to 1.24 respectively. The rhyolite-normalized La/Yb ratios varied between 0.56 and 0.96. Mass balance revealed the depletion of Si, Ca, Na, Mn, Sr, Ta, W, U, La, Ce, Pr, Nd, Sm, Gd and Lu, and the accumulation of Al, Fe, K, Mg, P, Sc, V, Co, Ni, Cu, Zn, Ga, Ge, Rb, Y, Zr, Nb, Cs, Ba, Hf, Pb, Th, Eu, Tb, Dy, Ho, Er, Tm and Yb during weathering along the soil profile. Full article

The aim of this study was to improve the efficiency of in situ uranium leaching by developing a specialized methodology for selecting rational parameters for the chemical treatment of production wells. This approach was designed to enhance the filtration properties of ores and extend the uninterrupted operation period of wells, considering the clay content of the productive horizon, the geological characteristics of the ore-bearing layer, and the composition of precipitation-forming materials. The mineralogical characteristics of ore and precipitate samples formed during the in situ leaching of uranium under various mining and geological conditions at a uranium deposit in the Syrdarya depression were identified using an X-ray diffraction analysis. It was established that ores of the Santonian stage are relatively homogeneous and consist mainly of quartz. During well operation, the precipitates formed are predominantly gypsum, which has little impact on the filtration properties of the ore. Ores of the Maastrichtian stage are less homogeneous and mainly composed of quartz and smectite, with minor amounts of potassium feldspar and kaolinite. The leaching of these ores results in the formation of gypsum with quartz impurities, which gradually reduces the filtration properties of the ore. Ores of the Campanian stage are heterogeneous, consisting mainly of quartz with varying proportions of clay minerals and gypsum. The leaching of these ores generates a variety of precipitates that significantly reduce the filtration properties of the productive horizon. Effective compositions and concentrations of decolmatant (clog removal) solutions were selected under laboratory conditions using a specially developed methodology and a TESCAN MIRA scanning electron microscope. Based on a scanning electron microscope analysis of the samples, the effectiveness of a decolmatizing solution based on hydrochloric and hydrofluoric acids (taking into account the concentration of the acids in the solution) was established for the destruction of precipitate formation during the in situ leaching of uranium. Geological blocks were ranked by their clay content to select rational parameters of decolmatant solutions for the efficient enhancement of ore filtration properties and the prevention of precipitation formation. Pilot-scale testing of the selected decolmatant parameters under various mining and geological conditions allowed the optimal chemical treatment parameters to be determined based on the clay content and the composition of precipitates in the productive horizon. An analysis of pilot well trials using the new approach showed an increase in the uninterrupted operational period of wells by 30%–40% under average mineral acid concentrations and by 25%–45% under maximum concentrations with surfactant additives in complex geological settings. As a result, an effective methodology for ranking geological blocks based on their ore clay content and precipitate composition was developed to determine the rational parameters of decolmatant solutions, enabling a maximized filtration performance and an extended well service life. This makes it possible to reduce the operating costs of extraction, control the geotechnological parameters of uranium well mining, and improve the efficiency of the in situ leaching of uranium under complex mining and geological conditions. Additionally, the approach increases the environmental and operational safety during uranium ore leaching intensification. Full article

Smectite clay minerals are known to readily form thixotropic physical gels in aqueous media, even at low volume fractions. Although the rheological properties of these gels are closely related to the microstructure of the network, the influence of the clay’s physicochemical characteristics remains insufficiently understood. In this study, we systematically investigated the relationships between particle size, cation exchange capacity, and zeta potential, and the rheological behavior of aqueous dispersions of four synthetic smectites. After thorough deionization, dispersions were prepared at controlled NaCl concentrations. We found that the zeta potential strongly correlates with the fineness of the network structure and governs macroscopic rheological responses such as viscosity, yield stress, and gelation behavior. Even under identical conditions, gel transparency and structural coarseness varied significantly among clay types. Furthermore, the storage modulus was influenced not only by network density but also by the intrinsic stiffness of the clay branches. These findings demonstrate that zeta potential serves as a unified indicator of structure and function in smectite dispersions and offer useful insights for gel design in colloidal and soft matter systems. Full article

Illitic clays are one of the most important materials used in the ceramic industry. Carbonates support the densification and the sintering of ceramics. Five mixtures of illitic clay with calcite were prepared aiming for the crystallization of anorthite ceramics. The stoichiometric ratio of anorthite crystallization was determined at 21.6 wt.% of calcite content. To reveal the effect of calcite on the crystallization processes, two more mixtures were prepared below the stoichiometric composition (17.6 wt.% and 19.6 wt.%) and two more mixtures above the ideal composition (23.6 wt.% and 25.6 wt.%). X-ray diffraction revealed that gehlenite and Ca-feldspar were formed, which are the intermediate phases in anorthite crystallization. However, due to the low purity of illitic clay and the low firing temperature, no anorthite formation was observed. The influence of calcite content on Young’s modulus was negligible. However, a clear effect on the open porosity was revealed. Full article