Search Results (483)

Understanding mineral–fluid interactions in shale under supercritical CO₂ (scCO₂) conditions is relevant for assessing long-term geochemical containment. This study characterizes mineralogical transformations and elemental redistribution in five Caney Shale samples serving as proxies for reservoir (R1, R2, R3) and caprock (D1, D2) facies, subjected to 30-day static exposure to pure scCO₂ at 60 °C and 17.23 MPa (2500 psi), with no brine or impurities introduced. SEM-EDS analyses were conducted before and after exposure, with mineral phases classified into silicates, carbonates, sulfides, and organic matter. Initial compositions were dominated by quartz (38–47 wt.%), illite (16–23 wt.%), carbonates (12–18 wt.%), and organic matter (8–11 wt.%). Post-exposure, carbonate loss ranged from 15 to 40% in reservoir samples and up to 20% in caprock samples. Illite and K-feldspar showed depletion of Fe²⁺, Mg²⁺, and K⁺ at grain edges and cleavages, while pyrite underwent oxidation with Fe redistribution. Organic matter exhibited scCO₂-induced surface alteration and apparent sorption effects, most pronounced in R2 and R3. Elemental mapping revealed Ca²⁺, Mg²⁺, Fe²⁺, and Si⁴⁺ mobilization near reactive interfaces, though no secondary mineral precipitates formed. Reservoir samples developed localized porosity, whereas caprock samples retained more structural clay integrity. The results advance understanding of mineral reactivity and elemental fluxes in shale-based CO₂ sequestration. Full article

The Carboniferous–Permian tight sandstone gas reservoirs in the Shenfu area of the Ordos Basin in China are characterized by the widespread development of multiple formations. However, significant differences exist among the tight sandstones of different formations, and their formation mechanisms and key controlling factors remain unclear, hindering the effective selection and development of favorable tight gas intervals in the study area. Through comprehensive analysis of casting thin section (CTS), scanning electron microscopy (SEM), cathodoluminescence (CL), X-ray diffraction (XRD), particle size and sorting, porosity and permeability data from Upper Paleozoic tight sandstone samples, combined with insights into depositional environments, burial history, and chemical reaction processes, this study clarifies the characteristics of tight sandstone reservoirs, reveals the key controlling factors of reservoir quality, confirms the differential evolutionary mechanisms of tight sandstone of different formations, reconstructs the diagenetic sequence, and constructs an evolution model of reservoir minerals and porosity. The research results indicate depositional processes laid the foundation for the original reservoir properties. Sandstones deposited in tidal flat and deltaic environments exhibit superior initial reservoir qualities. Compaction is a critical factor leading to the decline in reservoir quality across all formations. However, rigid particles such as quartz can partially mitigate the pore reduction caused by compaction. Early diagenetic carbonate cementation reduces reservoir quality by occupying primary pores and hindering the generation of secondary porosity induced by acidic fluids, while later-formed carbonate further densifies the sandstone by filling secondary intragranular pores. Clay mineral cements diminish reservoir porosity and permeability by filling intergranular and intragranular pores. The Shanxi and Taiyuan Formations display relatively poorer reservoir quality due to intense illitization. Overall, the reservoir quality of Benxi Formation is the best, followed by Xiashihezi Formation, with the Taiyuan and Shanxi Formations exhibiting comparatively lower qualities. Full article

The cements industry is increasingly under pressure to reduce carbon emissions while maintaining performance standards. Limestone calcined clay cement (LC³) presents a promising low-carbon alternative; however, its performance depends significantly on the type and reactivity of clay used. This study investigates the effect of three common low-grade clay minerals—kaolinite, montmorillonite, and illite—on the behavior of LC³ blends. The clays were thermally activated and characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), X-ray fluorescence spectroscopy (XRF), and Blaine air permeability testing to evaluate their mineralogical composition, thermal behavior, chemical content, and fineness. Pozzolanic reactivity was assessed using the modified Chapelle test. Microstructural development was examined through scanning electron microscopy (SEM) of the hydrated specimens at 28 days. The results confirmed a strong correlation between clay reactivity and hydration performance. Kaolinite showed the highest reactivity and fineness, contributing to a dense microstructure with reduced portlandite and enhanced formation of calcium silicate hydrate. Montmorillonite demonstrated comparable strength and favorable hydration characteristics, while illite, though less reactive initially, showed acceptable long-term behavior. Although kaolinite delivered the best overall performance, its limited availability and higher cost suggest that montmorillonite and illite represent viable and cost-effective alternatives, particularly in regions where kaolinite is scarce. This study highlights the suitability of regionally available, low-grade clays for use in LC³ systems, supporting sustainable and economically viable cement production. Full article

The Aptian–Albian interval represents a significant cooling phase within the Cretaceous “hothouse” climate, marked by dynamic climatic fluctuations. High-resolution continental records are essential for reconstructing terrestrial climate and ecosystem evolution during this period. This study examines a lacustrine-dominated succession of the Shahezi Formation (Lishu Rift Depression, Songliao Basin, NE Asia) to access paleo-weathering intensity and paleoclimate variability between the Middle Aptian and Early Albian (c. 118.2–112.3 Ma). Multiple geochemical proxies, including the Chemical Index of Alteration (CIA), were applied within a sequence stratigraphic framework covering four stages of lake evolution. Our results indicate that a hot and humid subtropical climate predominated in the Lishu paleo-lake, punctuated by transient cooling and drying events. Periods of lake expansion corresponded to episodes of intense chemical weathering, while two distinct intervals of aridity and cooling coincided with phases of a reduced lake level and fan delta progradation. To address the impact of potassium enrichment on CIA values, we introduced a rectangular coordinate system on A(Al₂O₃)-CN(CaO* + Na₂O)-K(K₂O) ternary diagrams, enabling more accurate weathering trends and CIA corrections (CIA_corr). Uncertainties in CIA correction were evaluated by integrating geochemical and petrographic evidence from deposits affected by hydrothermal fluids and external potassium addition. Importantly, our results show that metasomatic potassium addition cannot be reliably inferred solely from deviations in A-CN-K diagrams or the presence of authigenic illite and altered plagioclase. Calculations of “excess K₂O” and CIA_corr values should only be made when supported by robust geochemical and petrographic evidence for external potassium enrichment. This work advances lacustrine paleoclimate reconstruction methodology and highlights the need for careful interpretation of weathering proxies in complex sedimentary 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

The rheological behavior of clay in a water–salt environment determines the long-term deformation and structural stability of building materials and geotechnical engineering. In this study, the effects of salinity on the rheological behavior and microstructure stability of the clay mineral illite were investigated through steady-state and dynamic rheological tests. The results reveal that specimens with different salinities exhibit shear thinning behavior during the steady-state rheological test. When the shear rate is higher than 0.5 s⁻¹, the flow curves are described well by the Herschel–Bulkley model. As the salinity increases from 0 to 1.8 mol/L, the yield stress varies from 1500 to 3500 Pa. With the increase in salinity, the consistency factor of the specimens increases, while the flow coefficient decreases. Under dynamic loading, high-salinity specimens exhibit higher modulus and yield stresses, thereby enhancing the stability of the microstructure. The viscoelastic–plastic constitutive model under dynamic loading has been established, which can effectively describe and calculate the long-term deformation of clay minerals. These research results provide reference and guidance for understanding the rheological behavior of clay. Full article

The Sanandaj–Sirjan Zone and Zagros Fold–Thrust Belt in Iran host numerous Mediterranean-type karst bauxite deposits; however, their formation mechanisms and critical raw material potential remain ambiguous. This study combines mineralogical and geochemical analyses to explore (1) the formation of authigenic minerals, (2) the role of microbial organic processes in Fe cycling, and (3) the assessment of their critical raw materials potential. Mineralogical analyses of the Late Cretaceous Daresard and Middle–Late Permian Yakshawa bauxites reveal distinct horizons reflecting their genetic conditions: Yakshawa exhibits a vertical weathering sequence (clay-rich base → ferruginous oolites → nodular massive bauxite → bleached cap), while Daresard shows karst-controlled profiles (breccia → oolitic-pisolitic ore → deferrified boehmite). Authigenic illite forms via isochemical reactions involving kaolinite and K-feldspar dissolution. Scanning electron microscopy evidence demonstrates illite replacing kaolinite with burial depth enhancing crystallinity. Diaspore forms through both gibbsite transformation and direct precipitation from aluminum-rich solutions under surface conditions in reducing microbial karst environments, typically associated with pyrite, anatase, and fluorocarbonates under neutral–weakly alkaline conditions. Redox-controlled Fe-Al fractionation governs bauxite horizon development: (1) microbial sulfate reduction facilitates Fe³⁺ → Fe²⁺ reduction under anoxic conditions, forming Fe-rich horizons, while (2) oxidative weathering (↑Eh, ↓moisture) promotes Al-hydroxide/clay enrichment in upper profiles, evidenced by progressive total organic carbon depletion (0.57 → 0.08%). This biotic–abiotic coupling ultimately generates stratified, high-grade bauxite. Finally, both the Yakshawa and Daresard karst bauxite ores are enriched in critical raw materials. It is worth noting that the overall enrichment appears to be mostly driven by the processes that led to the formation of the ores and not by the chemical features of the parent rocks. Divergent bauxitization pathways and early diagenetic processes—controlled by paleoclimatic fluctuations, redox shifts, and organic matter decay—govern critical raw material distributions, unlike typical Mediterranean-type deposits where parent rock composition dominates critical raw material partitioning. Full article

This study investigated the effects of natural polysaccharides—guar gum (GG) and xanthan gum (XG)—on the properties and structure of illitic clay. Clay samples were prepared using five different GG and XG solutions, with polysaccharide concentrations of 0.5%, 1.0%, 1.5%, 2.0%, and 2.5%. The physical, mechanical, and hygroscopic properties of the samples were evaluated, along with water erosion resistance and structural characteristics, using SEM analysis. The addition of GG or XG significantly increased compressive strength and water erosion resistance, reduced shrinkage, and slightly improved the bulk density compared to the control clay sample. The results showed that compressive strength increased by 28–63% and 46–84% with the incorporation of GG and XG solutions, respectively. These findings suggest that environmentally friendly clay-based building materials can be effectively produced even using small amounts of natural polysaccharides. Full article

The Roman site at Makariopolsko village in Northeastern Bulgaria has been identified as a ceramic production center, featuring single- and double-chamber kilns, abundant ceramic material, and a nearby water source. Geological assessments also reveal local clay deposits. Previous archaeological studies have noted similar Roman production sites in the region, primarily focusing on the study of the kilns and the macroscopic description and classification of the ceramics. However, there has been a lack of research into the pottery’s composition and the sourcing of raw materials, which is essential for understanding the area’s cultural and economic context. This study aims to determine the raw material and firing temperature of the ceramic from the site at Makariopolsko village. Clay samples (both raw and fired at 1100 °C) and ceramic were subjected to chemical, statistical, phase X-ray structural, and thermal analyses. The findings indicate the use of calcareous illite–kaolinitic clay, sourced locally, with an added sandy component. The ceramics were fired at temperatures of 570–760 °C and 920–945 °C. These results, which support the site’s identification as a pottery production center, highlight advanced pottery skills and the dual functional capabilities of the kilns. Additionally, they pave the way for further research into regional production center relationships. Full article

Clays are fundamental raw materials in the ceramics industry due to their plasticity, mineralogical composition, and thermal behavior. This study characterizes four clay samples from Bustos (Portugal), aiming to assess their suitability for ceramic applications through granulometric, geochemical, mineralogical, and technological assays, looking at aspects such as their plasticity and sintering behavior. A textural analysis of the samples revealed distinct granulometric profiles, being dominated by silty–clayey fractions and low amounts of coarse particles, indicating high plasticity potential. Three samples showed an alkaline pH (8.17–8.63), and one an acidic pH (5.11), which can significantly influence the rheology and firing behavior of the ceramic body. Samples had a predominance of phyllosilicate minerals, followed by quartz and magnetite–maghemite, and trace amounts of feldspars, anatase, bassanite, and siderite. In the clay fraction, smectite, illite, and kaolinite were identified. By combining classical analysis techniques with ceramic technology principles, this study contributes to the sustainable development of local ceramic industries, emphasizing the importance of characterizing natural raw materials for industrial applications. The plasticity tests showed strong workability in two samples, which exhibited high values of plasticity and moldability, making them suitable for shaping processes in ceramic production. Also, sintering behavior tests revealed that the same clays exhibited good densification during firing, with relatively low shrinkage. Full article

Authigenic minerals in shale are products of the co-evolution of organic and inorganic components, affecting the heterogeneity of shale reservoirs. However, due to their fine granularity and complex rock composition, studies on these minerals in shale are still insufficient. This research focuses on the lacustrine shales from the upper sub-member of the fourth member in the Eocene Shahejie Formation, Dongying Sag, East China. Utilizing core samples, thin sections, scanning electron microscope, X-ray diffraction, elemental geochemistry, and organic geochemistry, we systematically characterized the features and origins of authigenic minerals. The results identified several typical authigenic minerals, including authigenic quartz, framboidal and euhedral pyrite, ferroan dolomite, kaolinite, chlorite, and albite. Authigenic quartz is predominantly diagenetic silica formed through smectite illitization, acidic dissolution of K-feldspar, and alkaline dissolution of detrital quartz. Pyrite is a product of microbial sulfate reduction, with framboidal pyrite forming during an early diagenetic stage under conditions with sufficient solute supply and euhedral pyrite forming during a later stage under conditions with insufficient solute supply. Ferroan dolomite originates from the precipitation of Fe and Mg during smectite illitization, with slight contributions from the acidic dissolution of chlorite and calcite. Kaolinite stems from the acidic dissolution of K-feldspar, while chlorite results from the transformation of kaolinite. Albite primarily arises from the alkaline alteration of anorthite and K-feldspar. Most non-clay authigenic minerals likely enhance reservoir quality by slightly reducing the effects of compaction, whereas authigenic clay minerals typically exert detrimental effects on reservoir properties. This study constrains the genesis of authigenic minerals to assess their influence on reservoir quality in lacustrine shale. Full article

Sedimentary rocks of the Gosau Group in the Grünbach–Neue Welt area (Eastern Alps, Austria) were analyzed to determine their mineralogical and geochemical compositions. This study includes the following: (1) the identification of major minerals using X-ray diffraction (XRD), (2) the analysis of major, minor, and trace elements via X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma mass spectrometry (ICP-MS), and (3) the quantification of total organic carbon (TOC), total nitrogen (TN), and total sulfur (TS) using an Elementar Unicube analyzer. Samples were collected from four artificial trenches and one outcrop in Maiersdorf, spanning the Grünbach and Piesting formations deposited during a terrestrial-to-marine transition in the upper Santonian to Campanian (Late Cretaceous). The dominant minerals—quartz, muscovite, illite, and calcite—exhibit relative abundances corresponding with variations in major oxide concentrations. Minor elements show variability but generally follow consistent trends. Trace and rare earth elements display greater variability but similar patterns, with a broader distribution in the Grünbach Formation. Elevated TOC, TN, and TS values are observed near the formation boundary and in the Piesting formation. These results offer the mineralogical and geochemical characterization of the strata, and lay a foundation for further investigations into the paleoenvironmental and basin evolution of the Gosau Group in the region, providing a comparative framework for Gosau basins across the Eastern Alps. Full article

In recent years, the exploration of the Baibei Sag, located in the west of the Erlian Basin, has remained relatively underdeveloped. The Lower Cretaceous of the Baibei Sag hosts multiple tight sandstone reservoirs; however, research on the macro- and micro-characteristics, as well as the controlling factors of these reservoirs, is relatively limited. This study selected 105 Lower Cretaceous sandstone samples from the Baibei Sag for core observation, casting thin sections, scanning electron microscopy, X-ray diffraction, and high-pressure mercury intrusion analysis. The reservoir’s physical properties, pore throat structure, and diagenesis process were studied. The results indicate that the reservoir lithology is mainly composed of feldspar lithic sandstone, with an average composition of 44.3% lithic, 34.6% quartz, and 21.2% feldspar. The clay minerals in the interstitial material are primarily illite (69.3%) and illite–smectite mixed layers (12.7%), with smaller amounts of chlorite (10.9%) and kaolinite (7.2%), while smectite content is very low. The physical property analysis results indicate that the average effective porosity of the Tengger Formation sandstone is 3.3%. The average permeability is 0.01 × 10⁻³ μm². The average effective porosity of the Aershan Formation sandstone is 0.86%, and the average permeability is 0.05 × 10⁻³ μm². The Tengger Formation and Aershan Formation are both tight sandstone reservoirs. The analysis of pore throat structure shows that the reservoir space is mainly composed of dissolution pores. Three types of pore throat structures were identified, and corresponding pore models were established. Based on burial history and organic matter evolution characteristics, this study establishes a diagenetic evolution sequence of the Lower Cretaceous sandstone reservoir. Analysis suggests that the pore throat structure of different reservoir types is mainly controlled by material composition. In the process of diagenetic evolution, the Tengger Formation and Aershan Formation are in the Middle diagenetic stage A. Compaction and cementation are the main reasons for low porosity, while the dissolution improves reservoir performance. The intergranular and intragranular dissolution pores formed by dissolution are the main storage spaces of the reservoir. The early tectonic fractures are filled with calcite, and the residual small-scale fractures play a role in improving permeability. Full article

Carbonate-hosted clay-type lithium deposits have emerged as strategic resources critical to the global energy transition, yet their exploration faces the dual challenges of technical complexity and environmental sustainability. Traditional methods often entail extensive land disruption, particularly in ecologically sensitive ecosystems where vegetation coverage and weathered layers hinder mineral detection. This study presents a case study of the San Dan lithium deposit in central Yunnan, where we propose a hierarchical anomaly extraction and multidimensional weighted comprehensive analysis. This comprehensive method integrates multi-source data from GF-3 QPSI SAR, GF-5B hyperspectral, and Landsat-8 OLI datasets and is structured around two core parts, as follows: (1) Hierarchical Anomaly Extraction: Utilizing principal component analysis, this part extracts hydroxyl and iron-stained alteration anomalies. It further employs the spectral hourglass technique for the precise identification of lithium-rich minerals, such as montmorillonite and illite. Additionally, concealed structures are extracted using azimuth filtering and structural detection in radar remote sensing. (2) Multidimensional Weighted Comprehensive Analysis: This module applies reclassification, kernel density analysis, and normalization preprocessing to five informational layers—hydroxyl, iron staining, minerals, lithology, and structure. Dynamic weighting, informed by expert experience and experimental adjustments using the weighted weight-of-evidence method, delineates graded target areas. Three priority target areas were identified, with field validation conducted in the most promising area revealing Li₂O contents ranging from 0.10% to 0.22%. This technical system, through the collaborative interpretation of multi-source data and quantitative decision-making processes, provides robust support for exploring carbonate-clay-type lithium deposits in central Yunnan. By promoting efficient, data-driven exploration and minimizing environmental disruption, it ensures that lithium extraction meets the growing demand while preserving ecological integrity, setting a benchmark for the sustainable exploration of clay-type lithium deposits worldwide. Full article

This paper assesses the thermodynamic stability of clay minerals in the upper organo-mineral horizon of podzolic soil, as well as in the rhizosphere of Norway spruce (Picea abies (L.) H. Karst.) and Norway maple (Acer platanoides L.). Moreover, it determines the impact of soil organic matter on the thermodynamic stability of clay minerals. Calculations of ΔG_f and the saturation index (SI) for clay minerals in laboratory experiments simulating soil conditions without soil moisture outflow allowed us to find out that the thermodynamic stability of clay minerals decreased in the series kaolinite > illite > vermiculite > chlorite. In the rhizosphere of spruce, kaolinite, vermiculite and illite have the lowest, and in the soil under maple-the highest thermodynamic stability, which is associated with differences in the properties of soil organic matter of rhizospheres of different tree species. Laboratory experiments on the sorption of soil humic acid (HA) on clay minerals demonstrated that sorbed HA decreased the thermodynamic stability of biotite and increased the thermodynamic stability of kaolinite and muscovite. Thermodynamic stability of clay minerals decreased with increased proportion of sorbed thermolabile organic matter. Full article