Illite Smectite Research Articles

Differential mineral diagenetic evolution of lacustrine shale: Implications for CO2 storage

Understanding the differential diagenetic evolution of different lithofacies is essential for assessing the spatial development of shale reservoirs. These insights are crucial in predicting sealing integrity and storage capacity for sequestered CO2. In this study, we examined seven wells from the Cretaceous Qingshankou Formation in the Songliao Basin, China, with vitrinite reflectance (Ro) values ranging from 0.60 % to 1.62 %. Thin section-based petrographic observations, coupled with QEMSCAN analysis, were used to classify the different lithofacies. X-ray diffraction (XRD) analysis of clay minerals, field emission scanning electron microscope (FE-SEM), and energy-dispersive spectrum (EDS) analyses were employed to analyze the mineral textures, pore types, and diagenetic pathways. The results showed that early diagenetic mineral phases include calcite cement (1st phase), framboidal and microcrystalline pyrite, ferroan and non-ferroan dolomite. Intermediate diagenetic mineral phases were marked by illitization of smectite, chlorite formed by chloritization of smectite and alteration of K-feldspar, and the formation of authigenic albite and quartz, calcite cement (2nd phase) and ankerite. Given the higher potential reaction rate of CO2-fluid‑carbonate systems, we propose that the lithofacies dominated by carbonate minerals are not effective for CO2 storage, even in short-term. In contrast, lithofacies rich in feldspar and clay minerals are likely to be more effective for long-term CO2 storage.

Illitization of smectite influenced by chemical weathering and its potential control of anatase formation in altered volcanic ashes

Abstract Illitization of smectite in sedimentary systems, a process akin to “reverse weathering,” is a diagenetic process that has significant implications for sediment paragenesis and hydrocarbon exploration. However, the potential influence of chemical weathering on the illitization of smectite and its possible control of the neogenesis of titanium (Ti)-oxides remain unclear. Altered volcanic tephra layers (i.e., K-bentonites) characterized by an interstratified illite-smectite (I-S) clay mineralogy serve as an excellent medium to investigate the illitization of smectite. In this study, we first investigated the fine structure of clay minerals and in situ nano-mineralogy of Ti-bearing minerals from altered volcanic ashes and then undertook a meta-analysis of geochemical compositional data for bentonites spanning a wide range of ages and depositional environments globally. We found that Ti mainly occurs as discrete micrometer-scale magmatic srilankite and nanoscale authigenic anatase crystals. During the weathering process, the magmatic srilankite partly dissolved under acidic conditions, resulting in a local buildup of Ti in porewaters. The I-S displays a platy habit and curved edges and is found closely associated with anatase crystals under TEM. Our compilation results combined with microscopic evidence suggest that chemical weathering may potentially promote the illitization reaction by changing the chemical composition of the fluids through increased terrestrial inputs and by creating larger pore spaces through the decomposition of weatherable components. Positive correlations between K and Ti are especially common in (K-)bentonites that are dominated by I-S, suggesting that I-S can adsorb Ti during the weathering process and provide a suitable site for the nucleation of anatase. Our study highlights the role of chemical weathering in the illitization of smectite and their combined effect on the formation of Ti-oxides.

Hydrothermal overprinting of the Li-rich strata deposited in the Mesoproterozoic Wumishan Formation, Hebei Province, North China

Lithium (Li), as a strategic critical metal, plays a pivotal role in the emerging energy landscape, particularly in the context of Li-ion batteries driving the new energy economy. Recently, Li-rich strata (with Li2O > 0.3 wt%) have been discovered in the Mesoproterozoic Wumishan Formation in Hebei Province, North China, suggesting a prospective Li reservoir. This study investigates these Li-rich strata using geochemical and in-situ micro-analytical techniques to explore the occurrence of Li and the formation mechanism of Li-host minerals, aiming for a comprehensive understanding of the supernormal enrichment of Li. The Li-rich samples are predominantly composed of dolomite and quartz, followed by clay minerals such as illite, interstratified illite–smectite (I/S), and chlorite, with minor amounts of K-feldspar, albite, biotite, calcite, baryte, fluorite and fluorapatite. In-situ analysis and 7Li NMR spectroscopy reveal that Li predominantly occupies the octahedral sites within the structures of authigenic illite and I/S, while its absence in clastic illite, clastic chlorite, unaltered K-feldspar, and dolomite. The presence of veined minerals (e.g., fluorite, baryte, and calcite) and a strong positive correlation between Li and F imply that post-depositional hydrothermal fluids have significantly contributed to the formation of Li-host minerals. The paragenesis of these minerals suggests that Li-bearing illite has formed through the hydrothermal alteration of K-feldspar. These Li-bearing illites subsequently transformed into Li-bearing I/S, consisting of illite-rich I/S and smectite-rich I/S, under continuous hydrothermal alteration. Lithium could have been leached from the surrounding carbonate rock and tuff through water–rock interaction and subsequently enriched by post-depositional hydrothermal fluids in specific regions, leading to mineralization. These findings provide valuable insights for targeting exploration of this promising Li resource.

A MAS-NMR analysis of 29Si, 27Al and 1H on the temperature's impact on geopolymer grouts derived from argillite and metakaolin

This study investigates how the curing temperature can enhance the reactivity of poorly reactive aluminosilicate source for geopolymer synthesis using a structural approach. The studied geopolymers are based on different aluminosilicate sources, a metakaolin and argillite, under varying curing temperatures (20 and 80°C). The impact of curing temperature on the reactivity of the two aluminosilicate sources and on the resulting consolidated materials was highlighted using pH value measurements, X-ray diffraction (XRD), and MAS-NMR for silicon (29Si), aluminum (27Al), and hydrogen (1H) nucleus. Metakaolin-based samples exhibited stable pH values, unvaried amorphous content, and structural consistency whatever the curing temperature. In contrast, argillite-based samples showed a significant drop in pH values (from 13 to 12) and a rise of amorphous content when cured at 80°C, indicating a reactivity change with temperatures. This was corroborated with MAS-NMR analysis, that highlighted a dissolution of the associated minerals such as illite and smectite. It was evidenced the presence of the geopolymer phase Q4(2Al) and Q4(3Al), in addition to two other networks based on silicon (Q4(1Al) and Q4(0Al)), and on aluminum Q4(4Al). The 1H MAS-NMR corroborated this finding by an increase of the bounded water (the band at 4.8 ppm) in the geopolymer network. All these data underline how temperature influences the reactivity of geopolymer materials, especially argillite-based samples by enhancing the dissolution of associated minerals (illite muscovite and smectite).

Heterogeneity of Organoclay Complexes in Shale Regulates the Generation of Shale Oil.

Organic matter (OM) and clay minerals are important components in shale, which are intimately associated with each other in the form of organoclay complexes. The diverse mineral-OM associations result in varying OM occurrences, which possess distinct hydrocarbon generation potential and ultimately affect the accumulation of shale oil. Therefore, the investigation of the heterogeneity of organoclay complexes is crucial to gaining a comprehensive understanding of the varying exploration potential of shale oil resources. In the present study, shale samples from three intervals in Dongying Depression were collected to investigate the mineralogical and organic characteristics of the organoclay complexes, aiming to explore their impact on the yield and composition of shale oil. Results showed that the smectite gradually converted into illite, which was accompanied by the release of OM from clay mineral interlayers and the desorption of chemically adsorbed OM. The yield and composition of shale oil cannot solely be explained by the OM content and types in the shale. Instead, they are intricately linked to the evolution of minerals and OM occurrence. From the perspective of the heterogeneity of organoclay complexes, despite the abundant OM content in shallower intervals (Es3x), the shale oil formation remains limited due to the low degree of mineral evolution and the stabilization of the adsorbed OM by clay minerals. Consequently, this leads to a higher proportion of resin, which is not conducive to the mobility of shale oil. In contrast, despite the OM content varying slightly in the deeper interval (Es4s), the elevated smectite illitization degree promotes the desorption of OM and its conversion into hydrocarbons. This results in a substantial increase in shale oil formation and a higher proportion of saturates, greatly enhancing the mobility of shale oil. These findings are profoundly significant for understanding shale oil generation and accumulation.

Smectite Illitization Geothermometry of the Upper Indus Basin Hydrocarbon Source Rocks (Pakistan)

Abstract —Smectite illitization geothermometry has been used to assess the thermal maturity and hydrocarbon generation potential of the late Paleocene to early Eocene Patala Formation in the Upper Indus Basin. X-ray diffraction (XRD) detected illite, muscovite, quartz, kaolinite, chlorite, and calcite. Comparison between air-dried (AD) and ethylene glycol (EG)-solvated XRD patterns reveals the absence of discrete smectite and interstratified illite-smectite (I-Sm). Additionally, authigenic illite-2M1 indicates that the Patala Formation has entered the late-stage diagenetic zone or the low anchizone, which lies in the R3 illitization zone. Abundant SiO2 and Al2O3 in the Patala clay fraction indicate the substitution of tetrahedral Si4+ by Al3+ within the smectite interlayers. Likewise, the relative abundance of K2O to CaO and MgO indicates the exchange of K+ with Ca2+ and Mg2+ during smectite illitization. Scanning electron microscopy (SEM) reveals in situ growth of platy illite crystals that form within the R3 zone. Furthermore, the total organic carbon (TOC) of the Patala shale exposed in Tirah suggests a poor to good source rock. The absence of discrete smectite and I-Sm, combined with the detection of discrete illite in the Patala shale, suggests that hydrocarbon might have potentially migrated from the source to the reservoir rock during smectite illitization.

Grain size control on organo-clay complexation and REE fractionation in the Paleozoic strata of the Permian Basin (West Texas, U.S.A.)

As a major component of mudstone, clay minerals are known to conserve organic matter (OM) as well as a range of trace elements through the mechanisms of adsorption, encapsulation, and/or intercalation. The associations of the clay minerals on one hand and trace elements and OM on the other hand impact the diagenetic evolution of such rocks and is of substantial importance for their characterization and assessment. Subsurface core samples collected from Late Paleozoic mudstone within the Permian Basin of Texas were separated into four grain size fractions (>2 µm, 2 to 1 µm, 1 to 0.6 µm, and <0.6 µm) to determine the clay mineralogy, OM abundances, and rock geochemistry using a suite of diffraction, spectroscopic, and chemical analysis. All separates were largely consisted of illite-smectite (I-S), illite-tobelite-smectite (I-T-S), mica/illite and chlorite coupled with some minor quartz and feldspar. The smectite component of I-S was shown to increase with decreasing grain size fractions. Additionally, t he rise in the content of smectite interlayers correlated with an increase in the total organic carbon (TOC) content towards the finest grain size separates in all samples. This suggested that a significant portion of the TOC content resided in the fraction below 2 µm and that smectite interlayers promoted the preservation of OM. Rare earth elements (REE) concentrations were found to be the highest in the finest grain size separates and align with an increased content of smectite interlayers, denoting a plausible interaction between the two. Further on, REE and TOC concentrations display a significant positive correlation in all size fractions and increase with respect to smectite interlayer content. This three-component relation suggests the REE adsorption to illite-smectite was likely promoted by OM. Understanding the close relation between the clay minerals, OM, and trace element content is indicative of polyvalent cationic bridging, ligand exchange, and organo-metallic complexation, which eventually l eads to the enrichment of OM and fractionation of REE in mudstone.

NH3-probe X-ray photoelectron spectroscopy method to characterize solid acidity of clay minerals

Accurate determination of solid acidity is essential for evaluating the catalytic activity of clay minerals. However, the conventional Fourier-transform infrared (FTIR) method using NH3 as the probe encounters challenges in measuring the solid acidity owing to the presence of water on the surface or within interlayer spaces of clay minerals as well as the influence of environmental water during the detection process. To mitigate water interference, a NH3-probe X-ray photoelectron spectroscopy (XPS) approach was adopted as an alternative to the FTIR method for the identification and semi-quantification of solid acidity of clay minerals. Following NH3 adsorption, the types of solid acid sites in clay minerals were identified through the chemical shift in N1s XPS spectra. The ratio of Brønsted and Lewis acid sites in a given sample and the relative concentration of acid sites across different samples were determined by examining the specific N1s peak area ratio. According to the XPS data, the ratios of Brønsted and Lewis acid sites in Ca-montmorillonite (SAz-2) and Na-montmorillonite (SWy-2) were nearly 1:1, whereas that for the illite–smectite mixed-layer mineral (ISCz-1) was 4. The acid site contents in SAz-2 were more than twice those of SWy-2. This work highlights the promising application prospects of the NH3-probe XPS method in solid acidity investigations of clay minerals.

Short-Wavelength Infrared Characteristics and Indications of Exploration of the Jiawula Silver–Lead–Zinc Deposit in Inner Mongolia

For the Jiawula lead–zinc deposit, as easily accessible resources become depleted, mines are becoming deeper to replenish ore reserves. Identifying large, continuous, and high-grade ore bodies in deep areas has become a daunting problem. Moreover, separating lead–zinc-bearing complex ore bodies from waste material and extracting them from associated minerals are also difficult. Thus, pioneering exploratory strategies and technological methodologies are required to make breakthroughs in mineral discovery. Based on extensive-scale structural lithofacies mapping, this paper uses short-wave infrared (SWIR) spectroscopy technology to investigate hydrothermal alteration minerals in the mining area. It has identified a total of 16 hydroxyl-bearing alteration minerals, including chlorite, muscovite, illite, calcite, ankerite, kaolinite, and smectite. These minerals establish zoning characteristics around the ore bodies and on their flanks. They comprise a segmented assemblage that follows the pattern of comb-textured quartz–illite–chlorite–carbonate → muscovite–illite–chlorite–ankerite → illite–smectite–chlorite → chlorite–kaolinite–calcite. Deep-zone illitization with a lower Al–OH absorbance peak wavelength (<2206 nm) and higher crystallinity indices (>1.1) and chloritization with higher Fe–OH absorbance peak wavelengths (>2254) and higher crystallinity indices (>3.0) are indicators of potential hydrothermal centers in the deeper regions. By finding hydrothermal centers and connecting their spatial distribution with existing ore bodies, a pertinent relationship between diabase + andesite, Fe-chlorite + illite, and high-grade mineralization has been established. They correspond well with the lithology-alteration mineralization. This research provides a basis for predicting the positioning of concealed ore bodies deep inside a mine or at the periphery.

Evolution of weathering intensity in the Qaidam Basin, northeastern Tibetan Plateau, since the middle Miocene: Insights from clay mineral records

Terrestrial silicate weathering records from the tectonically active Tibetan Plateau are crucial to explore the interactions among climate change, tectonic uplift and chemical weathering during the Cenozoic. However, the complex sedimentary facies changes and frequent occurrence of coarse lithologies related to intense tectonic uplift of the Tibetan Plateau have largely limited the reliability of bulk chemical weathering indexes to reveal the silicate weathering history. Here, we present detailed records of clay minerals and geochemical compositions from clay-sized (< 2 μm) sediments collected from the well-dated Huaitoutala section (ca. 15.3–1.8 Ma) in the NE Qaidam Basin to reconstruct the chemical weathering history of the NE Tibetan Plateau during the late Cenozoic. The relatively high (illite–smectite mixed layers + smectite)/(chlorite + illite) ratio indicates a strong silicate weathering intensity from 15.3 to 12.6. Ma, while a continuous decrease in this ratio since 12.6 Ma reflects a long-term decreasing intensity of silicate weathering. By comparing the clay mineral records with the climatic reconstruction and the tectonic events in the NE Tibetan Plateau, the results reveal that middle Miocene global cooling-related drying exerted a significant influence on the decreasing weathering intensity since ca. 12.6 Ma. Furthermore, the late Cenozoic episodic and persistent uplift of the NE Tibetan Plateau may have exerted an additional influence on the long-term decrease in weathering intensity. Specifically, the dramatic fluctuation in the silicate weathering intensity during ∼11–9.6 Ma is mainly due to uplift-induced provenance changes. Moreover, the fluctuating increase in the silicate weathering intensity during ∼8–5 Ma may have been caused by intensified East Asian summer monsoon precipitation. Our study suggests that both climate change and tectonic deformation controlled the chemical weathering intensity in the NE Tibetan Plateau during the late Cenozoic.

The Effect of Diagenetic Minerals on the Petrophysical Properties of Sandstone Reservoir: A Case Study of the Upper Shallow Marine Sandstones in the Central Bredasdorp Basin, Offshore South Africa

The upper shallow marine sandstone reservoirs of the Barremian-to-Valanginian formation are the most porous and permeable sandstone reservoirs in the Bredasdorp Basin and an important target for oil and gas exploration. There is a paucity of information on the reservoir characterization and effect of diagenetic mineral studies focusing on the upper shallow marine sandstone reservoirs in the central Bredasdorp Basin; thus, there is a need to investigate the effect of diagenetic minerals and to characterize these reservoirs due to their high porosity and permeability. Datasets, including a suite of geophysical wireline logs, routine core analysis, geological well completion reports, description reports, and core samples, were utilized. A total of 642 core porosity measures, core water saturation, and core permeability data were used for calibration with the log-derived parameters, ranging in depth from 3615 m to 4259 m. Rock samples were prepared for diagenetic mineral analyses, such as thin sections and Scanning electron microscopy, for each well to investigate the presence of diagenetic minerals in the selected reservoir units. The petrophysical analyses showed the results of porosity, volume of clay, water saturation, and permeability, ranging from 9% to 27%, 8.6% to 19.8%, 18.9% to 30.4%, and 0.096 mD to 151.8 mD, respectively, indicating a poor-to-good reservoir quality. Mineralogical analyses revealed that micrite calcite, quartz cement, quartz overgrowth, and authigenic pore-filling and grain-coating clay minerals (illite–smectite and illite) negatively affected intergranular porosity. Porosity-versus-permeability cross plot showed good correlation of 0.86 for ZN1 and 0.83 for ZN3 reservoirs, suggesting that although porosity is the main drive of permeability, there were other geological factors at play, such as diagenetic minerals and compaction.

Geochemistry of hydrothermal illitizations in Eocene Kösedağ magmatic rocks, Zara-Suşehri area, NE Sivas, East-Central Anatolia: Origin and age of alteration

The study area located at the periphery of the collision zone between the Eurasian plate (i.e. Pontides) and Tauride-Anatolide platform, NE of Sivas in the east-central Turkey, which is part of the Tethyan Metallogenic Belt. Mixed-layer illite-smectite (IS) and illite minerals are derived within the hydrothermal alteration zones with a few km2 surface areas (up to 30 km2) in Eocene volcanic and plutonic rocks. The representative IS and illite samples taken from plutonic- and volcanic-hosted alteration zones are investigated by optical and scanning electron microscopy (SEM), X-ray diffraction (XRD), major and trace elements and OH isotope geochemistry and KAr dating methods. Different types of hydrothermal alterations, such as propylitic and phyllic alteration in the plutonic rocks and argillic alteration in the volcanic rocks were developed as a result of intrusion of Kösedağ Pluton (syenite) into Karataş Volcanics (basaltic trachy-andesite and trachyte) with relations of hot-hot contact. The main phyllosilicate/clay minerals are characterized by kaolinite and IS in volcanic-hosted argillic alteration zones, whereas IS and illite in plutonic-hosted phyllic zones. The ordering types (Reichweite) of IS and illites are represented by R1 IS (I = 65–80 % in IS) + R3 IS (I = 90 % in IS) in the volcanic-hosted rocks, and R3 IS (I = 90 % in IS) and illite (S = 3–5 %). Dioctahedral (d060 ≤ 1.500 Å) R3 IS and illites have 1 Md + 1 M and 1 Md + 1 M + 2 M1 polytypes, respectively. The major and trace elements such as TiO2, Fe2O3, MgO, Na2O, P2O5, Sc, V, Cu, Ge, Sr, Hf, Zr and Y increase in the volcanic-hosted IS, whereas SiO2, Al2O3, K2O, Pb, W, Mo, As, Sb, Rb and U in the plutonic-hosted IS and illites. The chondrite-normalized distributions of IS and illites present a great similarity to those of host rocks. The chondrite-normalized rare earth element (REE) concentrations are more enriched in the volcanic-hosted IS in comparison with the plutonic-hosted IS and illites having distinctive Eu negative anomaly, which indicate deriving from volcanic matrix and K-feldspar, respectively. Oxygen and hydrogen isotope data of illitic clays indicate that the hydrothermal fluids are originated from magmatic water. According to stable isotopes and fluid inclusion data, IS and illites were formed at the temperature conditions ~150 °C in volcanic-hosted argillic zone, whereas ~250 °C in plutonic-hosted phyllic zones. KAr dating of alunite, IS and illite minerals indicate that the hydrothermal alteration was started at 40.45 ± 1.28 Ma, almost 2 Ma after the Q-syenite intrusion, within the plutonic body as phyllic alteration stage, and continued up to 35.27 ± 2.81 Ma, with a duration of ~5 Ma, and finalized before the exhumation of the Kösedağ Pluton (28–30 Ma). The geochemical characteristics of IS and illites were controlled by host-rock, condition, origin, and ages of alterations and they can be used as an important tool for magmatic-hydrothermal systems.

Multiscale modeling of smectite illitization in bentonite buffer of engineered barrier system

With the increasing usage of nuclear energy, how to properly dispose nuclear waste becomes a critical issue. In this study, a multiscale modeling approach combining the experimental findings is presented to address the illitization process, its impact on transport properties, and system behavior of bentonite buffer in engineered barrier systems (EBS). Through the pore-scale modeling, reactive transport properties such as illite generation rate and effective diffusion coefficient of potassium ion as a function of porosity and temperature are quantified by employing the findings of hydrothermal reaction experiments of Bentonil-WRK. The capability of pore-scale modeling has been developed based on the Darcy-Brinkmann-Stokes equation, involving the processes of smectite illitization and clay swelling. Obtained reactive transport properties are utilized as input parameters for the macroscale modeling to predict the long-term behavior of bentonite buffer in EBS. As such, this study involves the whole workflow of quantifying the reaction parameters of smectite illitization through the hydrothermal reaction experiments, and numerically modeling the reactive transport process of smectite illitization in bentonite buffer of EBS from pore-scale to macroscale. The presented multiscale modeling findings are expected to provide reliable solution for safe nuclear waste disposal with EBS.

Mineral transformation, element transport and hydrological impact in weathering at the Bingling Temple Grottoes: Implications for weathering in alkaline environments in NW China

Alkaline environments are common in arid and semi-arid regions in northwestern China and have preserved quantities of rock heritages along the Silk Road. In contrast to the frequently reported weathering mechanism of stone heritages in acidic conditions, mineral weathering mechanism (especially the transformation mechanism of smectite) in natural alkaline environments still remains to be evaluated. To deepen the understanding of weathering in such an environment, research idea from critical zone science was applied to investigate the element transport and mineral transformation from protolith (interbedded sandstone and conglomerate) to regolith in a world cultural heritage, Bingling Temple Grottoes (BTG), in northwestern China. From geochemical and mineralogical characterizations on boreholes, excavated profiles, fractures and cliff surface, we found that dissolution of calcite, plagioclase (anorthite, albite) and K-feldspar (orthoclase) caused major elemental loss of Na, K and Ca (to aqueous solution) in the BTG, and elements of Mg and Fe mostly retained in solid materials. Characterizations on the cliff surface demonstrated higher extents of element depletion and mineral weathering and lower ultrasonic P-wave velocities in sandstone than in conglomerate, and in the bottom sandstone layers (located in the capillary zone and exposure to rain scouring) than in upper sandstone layers (located in the cave and free of precipitation). The transformation of smectite from protolith to regolith follows the sequential reactions: dehydrated smectie → bihydrated smectite → randomly interstratified illite/smectite → illite. Such transformation pathway is favored by alkaline pH and wetting–drying cycles frequently occurred at the BTG. Typical weathering patterns such as clay swelling damage, efflorescence, salt precipitation, etc., are highly-linked to seasonal changes in the hydrological process influenced by both reservoir construction and groundwater system. Our study provides more evidence for the illitization of smectite in natural alkaline environments and highlights the hydrological impacts on weathering patterns of rock grottoes.

Physico-chemical properties of illite in the organic matter (OM)-rich claystone of Nankai Trough contrast with coeval OM-poor claystone: IODP Expedition 348

Naturally occurring microbially induced smectite-to-illite (Sm-I) reaction is of great interest to understand the control for the conventional Sm-I transformation, the source of bioavailable iron (Fe) in sediments, and the evolution of the microbial community in the deep biosphere. Direct comparisons of physico-chemical properties of illite-like phases including collapsed high-charge smectite and transient phase, and mature illite were performed for the organic matter (OM)-rich claystone in contrast with those of coeval OM-poor claystone (2163 m–2217 m below sea floor) buried at Nankai Trough (Integrated Ocean Discovery Program Site C0002). These clay layers are interbedded with 70°–90° dipping angle, such that they have nearly identical burial conditions of temperature, time, and fluid geochemistry except for OM content, one of the significant controls that can fuel heterotrophic microbial Fe (III) reduction. Unlike the abiotic Sm-I reaction, the local variations in the crystal structure, elemental composition, and oxidation states of Fe for the illite and illite-like phases in the OM-rich claystone suggest that illitization is promoted through the reduction of structural Fe (III) in smectite by microbial activity, however the effects of OM cannot be ruled out.

Atomistic Computer Simulations of Uranyl Adsorption on Hydrated Illite and Smectite Surfaces

A quantitative understanding of the molecular-scale mechanisms of radionuclide sorption on different clay minerals is crucial for the development and safe implementation of geological nuclear waste disposal technologies. We apply classical molecular dynamics (MD) computer simulations to study the adsorption of uranyl on the external basal surfaces of two typical clay models. In the illite model, negative charge is primarily localized in the tetrahedral sheets, while in the lower-charge smectite model, the isomorphic substitutions are introduced in the octahedral sheet. The comparison of atomic density distributions at the clay surfaces and adsorption-free energies profiles as a function of distance from these surfaces demonstrates that overall U behavior at the basal clay surface is quite similar for illite and smectite. Uranyl is sorbed as a mixture of outer-sphere aqua complexes [UO2(H2O)5]2+ and hydrolyzed aqua complexes [UO2(H2O)4–5OH]+ on both surfaces. The structural and compositional differences between the models do not greatly affect the uranyl’s nearest coordination environment and are mainly reflected in the specific localization and orientation of the uranyl ions at both surfaces and in the magnitude of the adsorption-free energies. The observed quantitative characteristics of uranyl interactions with illite and smectite surfaces will help to better understand U behavior during the sorption process on clay minerals for the entire range of mixed-layer illite–smectite structures. A comparison of two versions of the ClayFF force field in the simulations made it possible to more accurately and quantitatively evaluate some subtle features of the uranyl–clay interactions and to obtain a more precise composition of uranyl complex with the modified ClayFF force field (ClayFF-MOH).

Occurrence State and Enrichment Mechanism of Rhenium in the Qianjiadian Uranium Deposit in the Southwestern Songliao Basin, Northeast China

Rhenium is an extremely rare critical metal element in Earth’s continental crust. Owing to its extremely high melting point and heat-stable crystalline structure, rhenium is an essential component of alloy materials used in high-performance aircraft engines. Demand for rhenium resources is therefore growing. Currently, most rhenium is produced as a byproduct of molybdenum mining in porphyry copper–molybdenum deposits. Research has therefore focused on the enrichment characteristics of rhenium in this type of deposit, with little attention paid to rhenium in other types of deposits. This study reports the occurrence state and enrichment mechanism of rhenium in the Qianjiadian sandstone-type uranium deposit in the Songliao Basin, Northeast China. Sequential extraction revealed that the average proportions of different forms of rhenium are as follows: water-soluble (57.86%) &gt; organic-sulfide-bound (13.11%) &gt; residual (12.26%) &gt; Fe/Mn oxide-bound (10.67%) &gt; carbonate-bound (6.10%). Combining mineralogical analysis techniques such as SEM-EDS, EMPA, and XRD, it has been established that rhenium does not occur as a substitute in sulfides (e.g., molybdenite) or uranium minerals in various types of deposits. Instead, it is mainly adsorbed onto clay minerals and Fe-Ti oxides, and in a small number of other minerals (pyrite, organic matter, and pitchblende). Rhenium is similar to redox-sensitive elements such as uranium and vanadium, and it is transported in a water-soluble form by oxidizing groundwater to the redox transition zone for enrichment. However, unlike uranium, which generally forms as uranium minerals, rhenium is mainly adsorbed and enriched onto clay minerals (kaolinite and interlayered illite–smectite). Most of the rhenium in sandstone-type uranium deposits occurs in an ion-adsorption state, and is easily leached and extracted during in-situ leaching mining of uranium ores. This type of deposit demonstrates excellent production potential and will become a crucial recoverable resource for future rhenium supply.

Controls on organic matter enrichment of the early-middle Miocene lacustrine oil shale, central Tibet (SW China): New insights from clay minerals and geochemistry

The Lunpola oil shale is the largest lacustrine oil shale deposit in Tibet (SW China), which deposited in a Cenozoic lacustrine rift basin and contains abundant organic matter (OM), whereas the crucial factors that controlled the OM enrichment remain elusive. Here, we present new datasets of total organic carbon (TOC) contents, clay minerals and whole-rock geochemistry of the early-middle Miocene Middle Dingqinghu Formation oil shale from the Lunpola basin, central Tibet, in order to elucidate the paleoclimate, paleo-environment condition and the controlling factors on the OM enrichment of the lacustrine oil shale.Oil shales from the Lunpola East section have high TOC contents (avg. 9.60%), while the contiguous mudstones contain low TOC contents (avg. 0.44%). During the oil shale deposition, high smectite and kaolinite contents, low illite contents and low Sr/Cu ratios suggest strong chemical weathering and hence warm and humid climate, which may probably have close relationship with the mid-Miocene climatic optimum (MMCO). However, during the mudstone deposition, the relatively high illite and low smectite contents and higher Sr/Cu ratios suggest weak chemical weathering, indicating relatively arid climatic condition. The paleo-environment indexes (Corg/P, MoEF and UEF) and MoEF-UEF covariation reflect an anoxic bottom water condition during the oil shale deposition, while the mudstone formed in oxic-dysoxic water environment. The weak and moderate positive relationship between bio-productivity proxies (P/Ti and Cu/Ti ratios) and TOC contents reveal that the bio-productivity condition is not the crucial factor for the OM enrichment. Moreover, the water column environment was brackish and stratified during the oil shale deposition, and the sedimentation rate was moderate, which were also conducive to the OM preservation. The positive correlations between the TOC and the paleoclimate and paleoenvironment proxies demonstrate that warm and humid climate during the MMCO and anoxic water conditions play predominant roles in OM enrichment of the Lunpola lacustrine oil shale. Besides, modest sedimentation rate can prevent the dilution of OM, which can also promote the OM enrichment. This study can not only deepen the understanding of OM enrichment mechanism in lacustrine rift basin but also provide important information for predicting the distribution of the oil shale in the Lunpola Basin.

Depositional and diagenetic controls on hydrocarbon generation of mudstones through clay–organic matter interactions: A comparative study of the Dongpu Depression, Bohai Bay Basin, China

Although the hydrocarbon generation of mudstones is greatly affected by depositional and diagenetic environments, how they affect the integrated theoretical framework of organic matter (OM) preservation, mudstone formation, and OM diagenetic conversion remains unresolved. Therefore, we addressed this issue from the perspective of clay–OM interactions during mudstone formation and diagenetic evolution. The northern and southern Dongpu Depressions represent two endmembers of depositional (weak vs. strong hydrodynamics and abundant vs. limited terrigenous input) and diagenetic (saline vs. freshwater pore fluid) environments. Results highlighted that the protection of clay minerals on OM preservation was more affected by the depositional fabric than mineral content. For the northern Depression mudstones, the predominance of laminated mudstones and remarkable enrichment of high-hydrogen index OM in the clay-sized fractions indicated the intimate clay-OM associations during mudstone formation, which led to better OM preservation and a higher hydrocarbon generation potential. For the southern Depression mudstones, the scattered distribution of OM particles and inconspicuous OM enrichment in the clay-sized fractions coincided with lower hydrocarbon generation potential. Additionally, the faster smectite illitization accelerated by the saline environment of the northern Depression led to OM desorption. Thus, OM lost the protection of clay minerals and the mineral reactive sites were liberated, both of which were beneficial to hydrocarbon generation. Generally, deposition controlled the material premise and diagenesis determined the hydrocarbon generation impetus. These findings provide a theoretical reference for shale oil accumulation in saline lacustrine systems and can potentially serve as a guide for future oil–gas exploration and development.

The Effect of K-Fertilization and Irrigation on the Composition of Cultivated Soils: Examples from Israel

Evaluation of soil sustainability should take into account chemical and mineralogical changes due to cultivation. Potassium (K) application is a key farming practice that may potentially affect phyllosilicate composition and soil properties. Irrigation is another agent that affects soil composition. This study aims to evaluate the imprints of cultivation on the chemical and mineralogical compositions of lowland soils under semi-arid and Mediterranean climate regimes and to assess them with the natural pedogenesis. The sites examined include two permanent plot experiments with crop rotation, and three single-plant plots. Cultivated, control, and fallow soils were analyzed for their chemical and mineralogical composition. The X-ray diffraction patterns of the clay fraction were decomposed to achieve quantitative detection of changes among the illite–smectite (IS) phases and in kaolinite amounts. In loamy and clayey soils dominated by IS phases, cultivation caused minor changes and diverse behavior of the IS phases. Yet, the K balance was negative under high fertilization levels and higher plant mass production. Fertilization enhanced the natural process of transforming IS into kaolinite and illite in the sandy soil, leading to a positive K balance. This study emphasizes the importance of IS minerals as a dynamic K pool that responds to plant needs.