Formation Of Kaolinite Research Articles

Clay mineralogy in mylonite weathering products from Njimom (west Cameroon): origin and terracotta suitability

This study investigated the mineralogical assemblage of weathering products developed on mylonite rocks in west Cameroon. Smectite and vermiculite occurrence was studied, particularly to emphasize its origin and the potential of the samples in terracotta production. Samples characteristics were determined through X-Ray Diffraction (XRD) and X-ray Fluorescence (XRF) methods. Weathering products were observed along road trenches of 450 m long and 50 m height on a syenitic basement rock intruded by magmatic rock veins. Clay minerals are mainly composed of kaolinite and illite. 2:1 swelling clay minerals (vermiculite, montmorillonite) occur in some samples mainly originated from the contact between weathering materials and quartzo feldspatic bands. The main oxides are SiO2 (46–72%), Al2O3 (16–31%), Fe2O3 (2–16%) and K2O (0.1–6%). Vermiculite may be formed by fluid-mineral interactions during alteration of the chlorite in the plasmic microsystems of the soil. Structural changes in the upper part of the saprolite leading to the transformation of vermiculite into smectite under supergene alteration control, which predominates in humid tropical zones. Heavy rainfall leads to the formation of kaolinite at the expense of 2:1 clay minerals. Empirical classification revealed that the studied weathering products can be used to produce common bricks.

Fatigue mechanical properties and Kaiser effect characteristics of the saturated weakly cemented sandstone under different loading rate conditions

Weakly cemented sandstone (WCS) is a unique rock type widely distributed on the surface. Environmental factors such as groundwater and stress variations easily influence its fatigue mechanical properties and fracture characteristics. To design and evaluate the long-term stability of surrounding rock support in tunnel excavation and underground resource mining projects, investigating the fatigue mechanical properties and acoustic emission (AE) response characteristics of saturated WCS under different loading rates is of great practical and theoretical significance. This study employed experimental techniques such as X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and natural water absorption tests to investigate the mineral composition, pore size, and connectivity characteristics of WCS. The multi-level cyclic loading-unloading tests (MCLU) combined with the AE system were conducted on dry and saturated WCS specimens at different loading rates. The results reveal that the deformation modulus of these specimens initially increases and then decreases under cyclic loading conditions. Water significantly influences the fatigue strength and deformation resistance of sandstone. As the loading rate increases, the range of RA values broadens, accompanied by a marked increase in the number of AE signals with high RA values. Saturated sandstone specimens are more prone to developing macroscopic shear fracture surfaces. Water has a more substantial effect on the stress distribution ranges corresponding to the response of the Kaiser effect in WCS than loading rates. The capacity of the Kaiser effect to indicate the extent of rock damage is intricately linked to the progression of internal micro-cracks. When internal damage surpasses the critical value of the Kaiser effect memory damage, the accelerated propagation of shear cracks becomes pivotal in the internal damage of the sandstone. It seems that the presence of water within the interior of the rock may facilitate the dissolution of K-feldspar in WCS, which could result in the formation of kaolinite, which will be further transformed into illite. The hydration expansion of illite may further exacerbate the deterioration effect of the mechanical properties of WCS.

Deep regolith weathering controls δ30Si composition of groundwater under contrasting landuse in tropical watersheds

Land use changes are known to alter terrestrial silicon cycling and the export of dissolved silicon from soil to fluvial systems, but the impact of such changes on groundwater systems remain unclear. In order to identify the processes responsible for groundwater geochemistry and to assess the impact of agricultural processes, we examined multiple isotopic tracers (δ30Si, oxygen (δ18O) and hydrogen (δ2H) isotopes) in groundwater, soil porewater and surface water from two contrasted watersheds having the same gneissic lithology, one forested (Mule Hole) and one intensely cultivated (Berambadi) in the Kabini basin in South India. In the cultivated watershed, groundwater exhibits high Cl− and NO3− concentrations indicative of fertilizer inputs and solute enrichment from evapotranspiration due to multiple groundwater pumping/recharge cycles. The DSi concentration in groundwater is significantly higher in the cultivated watershed (980 ± 313 μM) than in the forested one (711 ± 154 μM), indicating more intense evapotranspiration due to irrigation cycles. The groundwater δ30Si values ranged from 0.6 ‰ to 3.4 ‰ and exhibit no significant differences between cultivated (1.2 ± 0.5 ‰) and forested (1.0 ± 0.2 ‰) watersheds, indicating limited impact of land use and land cover. Groundwater also shows no significant seasonal differences in DSi and δ30Si within watersheds, indicating a buffer to seasonal recharge during wet season. The δ30Si of a majority of groundwater samples fits a steady-state open flow through system, with an isotopic fractionation factor (30ε) between precipitating phase and groundwater ranging from −1.0 ‰ and − 2.0 ‰, consistent with precipitation of kaolinite-type clays, dominant in the study area. The steady-state flow through system in groundwater can be interpreted as a continuous DSi input from mineral weathering reactions with a dynamic equilibrium between Si supply and precipitation of secondary phases. We also observe, in both watersheds, similar DSi and δ30Si values in local surface water that includes small streams and a river (406 ± 194 μM, 1.6 ± 0.3 ‰) and in soil porewater (514 ± 119 μM, 1.6 ± 0.2 ‰). Compared to soil porewater, groundwater exhibits significantly lower δ30Si signatures and higher DSi, reflecting the contribution of an isotopically light silicon source, resulting from water-rock interaction during percolation through the unsaturated zone. We assign this steady input of DSi to the weathering of primary silicate minerals in the regolith, such as Na-plagioclase, biotite and chlorite, with formation of kaolinite and smectites type clays. A simple isotopic mass balance suggests that deep regolith weathering can contribute to almost half of the DSi in groundwater. We conclude that silicon cycling in soil porewaters, and surface waters are directly impacted by land use, while the isotopic composition of groundwater remains unaffected. Our results indicate that Si isotopic signatures of weathering, adsorption, and plant uptake occurring in the shallow soil and saprolite horizons are partly overprinted and homogenized by the regolith weathering in the deep critical zone, irrespective of land use and seasonality.

Diagenesis and reservoir quality evolution of estuarine sandstones: Insights from the Cenomanian-Turonian Yolde Formation, northern Benue Trough, NE Nigeria

Estuarine sandstones often exhibit complex diagenetic pathways due to the interaction of fluvial and shallow marine processes, resulting in significant reservoir heterogeneities. The Yolde Formation is an important petroleum reservoir in the Northern Benue Trough, NE Nigeria. However, diagenetic and reservoir quality evolution of the formation are still poorly understood. This study utilizes thin-section petrography, XRD, SEM, and fluid inclusion microthermometry to analyse the composition, diagenesis, and reservoir quality of the sandstones. Results show that the sandstones are mainly arkose and subarkose in composition; they are generally well-sorted and vary in grain size from very fine-to coarse-grained. Three diagenetic stages are identified: early, middle, and late. The early stage includes feldspar dissolution, formation of kaolinite, development of clay coating, and mechanical compaction. The middle stage comprises the formation of authigenic chlorite and Fe-oxide cements. The late-stage diagenesis involves illitization of kaolinite, formation of dickite, albitization of K-feldspar, and precipitation of quartz overgrowths. The diagenetic evolution of the sandstones was strongly controlled by their compositional makeup. The feldspathic nature of the sandstones resulted in the formation of kaolinite, illite, and quartz overgrowths, through feldspar dissolution and silica supply. The inner and middle estuarine facies have inhibited the development of quartz overgrowths due to well-developed clay coatings, whereas the outer estuarine facies were well-cemented by quartz overgrowths due to lack of clay coatings. Illitic clay coatings were found to be effective in preventing quartz cementation. Fluid inclusion analysis reveals that the formation temperatures of the quartz overgrowths range from 98 °C to 135.5 °C, corresponding to burial depths ranging between 2.3 and 3.5 km. These findings would provide useful insights that would reduce the risks of exploration of the sandstones and also supplies potential input data for forward diagenetic modelling of their subsurface equivalents in similar depositional settings elsewhere.

Mineralogical Characterization and Geochemical Signatures of Supergene Kaolinitic Clay Deposits: Insight of Ropp Complex Kaolins, Northcentral Nigeria

This study presents the chemical and mineralogical composition of clay deposits and associated rock types within the Ropp Complex in order to assess the influence of parent lithology on the kaolinization, genesis, and utility of the deposit. Representative kaolin samples from E horizons of the weathering profiles and their bedrocks were collected from six sites in the Ropp Complex. Clay mineralogy was determined via the XRD technique, while a geochemical analysis was conducted using XRF, SEM coupled with EDS, and ICP-MS. The results showed that all kaolins dominantly contain kaolinite with a content of 77%–98% except for the AS1 kaolin with only minor kaolinite (20%) but mainly illite (65%). The notably lower crystallinity of kaolinite (HI value of 0.53–1.1) as well as its markedly small grain size is consistent with the formation of kaolinite from intensive chemical weathering of igneous rocks. The AS1 kaolin was probably formed from hydrothermal alteration in the burial stage due to the heating of groundwater by the late volcanism. Mobile trace elements (Sr, Ba, and Eu) exhibited a depletion trend, while immobile elements (Hf, Ta, Th) showed enrichment. The relatively more zirconium in kaolins implies the formation of low-temperature kaolinization. The notably high kaolinite content, accompanied by reasonable levels of Fe2O3 and TiO2, signifies a medium-grade quality. Furthermore, chondrite-normalized rare earth element (REE) patterns exhibit congruent trends in rocks and kaolin samples, indicating a relative enrichment in light rare earth elements (LREEs) alongside a discernible negative Eu anomaly. The abundant kaolinite and silicon–aluminum composition make the kaolins suitable for refractories, pharmaceutics, cosmetics, and supplementary cementitious material (SCM).

Mineralogical and Geochemical Composition of Late Permian Coals from Dengfeng Coalfield, North China: Conversion of Clay Minerals in Coal during Coalification

Dengfeng Coalfield represents a significant coalfield in Henan Province, North China. It is therefore essential to gain an understanding of the mineralogy and geochemistry of the Dengfeng coal, both from a geochemical perspective and in terms of the wider environmental context. In this study, a total of 27 coal bench samples were collected from the No. II1 coal of the Dengfeng Coalfield. The mineral species and major elements were quantitatively analysed using the X-ray diffraction and X-ray fluorescence methods, respectively. The minerals in the Dengfeng coal are dominated by ammonian illite and kaolinite with average contents of 3.73% and 7.47%, respectively. These are followed by calcite (2.74% on average) and ankerite (0.49%). The mean value of the kaolinite Hinkley index, which is a quantitative measure of kaolinite crystallinity, is 1.26. This suggests that kaolinite formation is primarily driven by diagenetic recrystallisation. The ammonian illite exhibits an average d001 of 10.2995 Å, indicative of a prevalence of NH4+ interlayer cations, with K+ also present in notable quantities. The ratio of NH4⁺ to (NH4⁺ + K⁺) has an average value of 0.90, which is indicative of the predominance of NH4⁺. The mean value of the illite Kübler index, which is a quantitative measure of illite crystallinity, is 0.264. This suggests that the diagenetic conditions correspond to the rank of the Dengfeng coal. The kaolinite present in the Dengfeng coal is suggested to have been derived from terrigenous detritus and subsequently subjected to diagenetic recrystallisation, resulting in a relatively high Hinkley index. The ammonian illite in the Dengfeng coal was predominantly formed through the conversion of the precursor kaolinite, with the influence of seawater during peat accumulation favouring the conversion of kaolinite to ammonian illite.

Soil development trajectories, chemical weathering and pedogenic mineral (trans)formation on glauconitic calcarenites in a Mediterranean area

Glauconite forms in shallow marine basins under oxic to suboxic conditions. It is an Fe-rich sheet silicate often found in calcareous sandstones. How soils evolve on glauconitic sandstones (calcarenite) is poorly addressed: therefore, we investigated the evolutional trajectories. These soils should be enriched in Fe, depleted in K and contain kaolinite and smectite resulting from weathering. We investigated 11 soil profiles on glauconitic calcarenite in a Mediterranean area. The elemental contents, fractions of Fe and Al, soil mineralogy, magnetic susceptibility and stable isotopic composition (C, O) of the bulk soil and carbonates were analysed to explore pedogenesis.The carbonates reflect a former marine basin having onshore organic matter resulting from freshwater input. With soil formation, the primary carbonates were replaced by pedogenic carbonates having a lower δ13C and δ18O signal. Several sites were influenced by human activity since ancient times, reflected by the magnetic susceptibility. The shallow soils had a low weathering degree (CIA of 55 to 70). The better developed Vertisols exhibited a CIA value of up to 85. All soils contained smectite and quartz and, depending on the weathering degree, calcite. Kaolinite formation was connected to high Ca, K, Mg and Na losses. The high oxalate- and dithionite-extractable Fe contents are explained by glauconite weathering. Kaolinite is inherited from the parent material but also actively forms in the soils probably through precipitation from soil water. Due to the presence of smectite and oxyhydroxides the soils sequester a high amount of soil organic carbon (up to 30 kg/m2). Topography exerts a distinct influence on weathering and soil formation. Deepest soils and an advanced weathering stage were measured on footslope sites and shallow soils having a low weathering degree on crest/shoulder sites. Soils on glauconitic calcarenite represent a unique weathering environment that should be investigated even more at the micro-scale.

The influence and mechanism exploration of hydration environment on the stability of natural clay crude oil emulsion

The study investigated the effects and mechanisms of clay content, emulsion water content, pH, and metal cations on clay-crude oil emulsions. The results indicate the following: 1) At a water content of 50 V/V%, montmorillonite can form emulsions with crude oil at different concentrations, with the highest stability observed at 5 wt% content. In contrast, chlorite, illite, and kaolinite cannot form emulsions at low concentrations. 2) Under acidic conditions, montmorillonite, illite, and chlorite cannot form emulsions with crude oil, or the emulsions are highly unstable. However, kaolinite forms more stable emulsions under acidic conditions. In alkaline environments, emulsions formed by all clay minerals exhibit increased stability. 3) The order of the effectiveness of different metal cations in reducing the stability of montmorillonite-crude oil emulsions is K+ > Na+ > Mg2+ > Ca2+, while for chlorite, illite, and kaolinite, it is Mg2+ > Ca2+ > K+ > Na+. 4) The factors that influence the stability of clay-crude oil emulsions are the arrangement of clay particles in water and the dispersion capability of clay particles in water. The most significant influencing factor is the arrangement of clay particles in water.

Diagenetic controls on the quality of shallow marine sandstones: An example from the Cambro-Ordovician Saq Formation, central Saudi Arabia

The Saq Formation is the most important Paleozoic aquifer in central and northern Saudi Arabia. However, owing to the continued depletion of the aquifers and the great depths to which the aquifers are buried in undrilled/underexplored regions, the aquifers porosity and permeability are increasingly becoming an issue of concern. Here, we employed thin-section petrography, petrophysical measurements, X-ray diffraction and scanning electron microscopic analyses, and fluid inclusion microthermometry to investigate the composition and diagenetic evolution of the Saq sandstones. The results of this study indicate that the sandstones are mainly quartz arenite in composition, mostly well sorted, and ranged in grain size from silt to coarse-grained sandstones. We observed three diagenetic stages (early, middle, and late) that impacted the porosity evolution of the Saq sandstones. Mechanical compaction, formation of authigenic kaolinite, and infiltration of smectitic clays occurred during early shallow burial diagenesis. The middle (deep-burial) diagenesis was dominated by mechanical and chemical compaction, formation of authigenic quartz overgrowths, transformation of kaolinite and smectite into illite, and precipitation of late calcite. The late (uplift-related) diagenesis resulted in the formation of authigenic kaolinite, dissolution of the late calcite, and the formation of predominantly pore-filling Fe-oxide (goethite) cement. Fluid inclusion results of this study show that quartz cement mostly formed at temperatures ranging between 151 °C and 175 °C and reached up to 272 °C, with, at least, two phases of overgrowth development. The overall high amounts of rigid grain contents (>65 %), low detrital matrix (<10 %), and coarser grain size have maintained the Saq sandstone quality (average permeability = 2100 mD) despite having been buried to great depths. The findings of this study provide useful insights into the diagenetic evolution of the Saq Formation, which has provided important input data for forward diagenetic modelling of their subsurface equivalent in Saudi Arabia and sandstones of similar depositional settings elsewhere.

Diagenetic Genesis and Evolution of Coal-Bearing Tight Sandstone Reservoir in the Yangxia Formation, Northern Kuqa Depression, Tarim Basin.

Coal seams of the Yangxia Formation are widespread in the northern part of the Kuqa Depression in the Tarim Basin. During the thermal evolution of the coal seams, the generated fluids of different periods and natures have a significant impact on tight sandstone reservoirs. To further investigate the diagenetic characteristics and reservoir genesis of the tight sandstones due to the influence of coal seams, an in-depth exploration of the causes of dissolution and cementation in the reservoirs was conducted through thin-section casting, cathode luminescence, scanning electron microscopy, carbon-oxygen isotopic analyses, and X-ray diffraction of whole rock and authigenic clay minerals, along with burial evolution history and fluid evolution history. It is suggested that two phases of acidic fluids are mainly produced during the thermal evolution process of coal seams, including an early humic acid and a late organic carboxylic acid. The early phase humic acid plays a purifying role in reservoirs with coarse particles, rigidity-rich particles, and good permeability conditions. It selectively dissolves sedimentary calcareous mud and calcite, and the dissolution products are completely migrated. At the same time, it inhibits early carbonate cementation. The late organic carboxylic acid will dissolve potassium feldspar and some volcanic rock debris, and the dissolution products are difficult to migrate under the sealing conditions caused by lithological differences, which often take the cementation form of siliceous overgrowth and kaolinite or illite. In addition to the cementation resulting from the dissolution products of acidic fluids produced by the coal seams, the CO2-rich fluids generated by the coal seam thermal evolution will combine with ions such as Ca2+ from different sources, resulting in two phases of carbonate cementation. Based on the above research, this study summarizes a set of diagenetic evolution models for coal-bearing reservoirs.

Thermal stability of artificial radiation-induced defects in kaolinite: Enhancing EPR dating protocol

Kaolinite naturally contains radiation-induced electron defects in its structure induced by ionizing radiations and can be analyzed with electron paramagnetic resonance spectroscopy (EPR). They include the so-called A-center, which is crucial for geochronological applications due to its stability at the scale of geological periods. Indeed, previous studies have substantiated the thermal stability of naturally occurring A-centers in kaolinite through annealing experiments. However, the stability of artificially created A-centers, which are used to determine paleodose through calibration via irradiation experiments and subsequent dating of kaolinite formation, still needs to be more adequately specified to confirm their relevance. Therefore, this research probed the thermal stability of A-centers produced by ionizing 1.5 MeV He+ beams in two samples, i.e., the reference KGa-2 and a very disordered lateritic soil kaolinite. Heating experiments showed that the annealing of irradiated samples at 250 °C was relevant to determining A-center concentration. Second, the annealing of artificial A-centers at higher temperatures was found to be a second-order process, as for natural A-centers. Annealing parameters such as activation energy (2–2.6 eV) were determined with estimates of half-life at 300 K, which was found to be >1012 years for natural and artificial A-centers. Thus, the parameters for artificial A-centers are consistent with the thermal annealing behavior of their natural counterparts. These new findings affirm that artificially generated A-centers mimic natural ones in terms of EPR spectra and thermal stability, enhancing the reliability and precision of the EPR dating methodology used in kaolinite dating.

Variation in the structural order of kaolinite in regolith as an effective indicator of REE mineralization

Abstract Regolith-hosted rare earth element (REE) deposits hosted by the granitic regolith in South China provide &gt;90% of the world’s heavy REEs. Kaolinite is one of the major carriers of REE ions in regolith. The formation and transformation of kaolinite can be affected by chemical weathering and hydrodynamic conditions, but the contribution of each factor has not been evaluated. This study systematically investigated the variation in abundance of phyllosilicate minerals and structural order of kaolinite in the Renju regolith-hosted REE deposit. The total abundance of 1:1 phyllosilicate minerals increased upwards along the profile from Section I to Section III. However, semi-quantitative analyses indicated that Section III-1 (depth at 10–16 m) featured an evident decrease in both abundance and structural order of kaolinite upward along the profile. The morphological feature and abundance of kaolinite revealed intensive kaolinite-to-halloysite transformation and kaolinite dissolution in Section III-1. This suggests that the alternating wetting and drying zone in Section III-1 provided a favorable kinetic environment for the entry of water molecules into the kaolinite interlayer and the kaolinite-to-halloysite transformation, resulting in both lower structural order and abundance of kaolinite in Section III-1. Moreover, REE ions started to be enriched from the alternating wetting and drying zone and formed high-grade ores at the lower part of the water table, due to a significant increase in pore water and decrease in the seepage velocity. Therefore, the abundance and structural order of secondary kaolinite can serve as important indicators of hydrodynamic changes in regolith, as well as the mineralization of regolith-hosted REEs.

Sedimentary Environments and Paleoclimate Control of the Middle Miocene Balikpapan Group, Lower Kutai Basin (Indonesia): Implications for Evaluation of the Hydrocarbon Potential

Sedimentary organic matter concentrated in source rocks forms the main source for the formation of hydrocarbons. Its deposition and preservation are strongly controlled by the depositional environment and paleoclimate. This study evaluates the paleoenvironment and the paleoclimatic controls of sediments in the Middle Miocene Balikpapan Group, Mahakam Delta of the Lower Kutai Basin, Indonesia. The sedimentary succession of the Mentawir Formation, encountered in three wells (MHK 1, MHK 3, and MHK 4), contains interbedded sandstones, siltstones, shales, and coal. Gamma ray log analysis has revealed four facies associations: (a) funnel-, (b) bell-, (c) cylindrical-, and (d) bow-shaped patterns, which, together with sedimentological and mineralogical analysis, suggest a fluvio-deltaic depositional environment during the Middle Miocene in the study area. Sedimentary successions from wells MHK 1 and MHK 3 comprise interbedded sandstone and siltstones and are interpreted to represent repeatedly occurring delta plain, delta front, and prodelta deposits. The succession encountered in well MHK 4 mostly consists of amalgamated sandstones and indicates a predominantly fluvial to upper delta plain environment with distributary channels and crevasse splays interbedded with only thin delta front deposits. X-ray diffraction–clay fraction analysis shows that the &lt;2 μm clay-sized fraction consists of kaolinite (38%–67%), illite (14%–29%), chlorite (2%–17%), and mixed-layer illite/smectite (I/S) (14%–30%). Kaolinite formation and abundance indicates a hinterland climate classified as type Af (tropical rainforest) and intensive chemical weathering conditions in the source areas related to tropical to sub-tropical climates with high precipitation. Under such climatic conditions, kaolinite and I/S mixed-layer minerals are preferentially formed because the characteristic ions, K+, Na+, Ca2+, and Fe2+, are leached away. Thus, the production, transport, distribution, and preservation of sedimentary organic matter in the onshore Mentawir Formation of the Balikpapan Group are predominantly controlled by the humid tropical climate and fluvio-deltaic processes.

The Kaolin and Bentonite Deposit of Tamame De Sayago (Zamora, Spain): Mineralogy, Geochemistry, and Genesis

A geological, mineralogical, and geochemical characterization of the Tamame de Sayago (Zamora, Spain) deposit was carried out with the aim of knowing the conditions that facilitated the genesis in the same deposit of kaolinite and smectites. The alteration processes affecting a Variscan granite were deduced throughout the study of a very wide group of representative samples by X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical analyses of major, minor, and trace elements, as well as δ18O, δ34S stable isotope and K/Ar dating analyses. In addition, 2D and 2.5D graphs of the kaolinite and smectite isoconcentrations were obtained from core data. According to the color and texture, two different clayey rock types were identified and named as homogeneous alteration zones (ZAHO) and heterogeneous alteration zones (ZAHE). The ZAHO are regoliths in which the granite texture is preserved, and the feldspars are almost completely kaolinized. In the ZAHE, the original texture of the granitic rock is lost, and the main clay mineral is smectite. The mineralogical composition is similar, with kaolinite, smectite, mica, quartz, scarce feldspar, and occasionally natroalunite and APS (aluminum-phosphate-sulphate); however, the mineral concentration varies considerably because ZAHO are rich in kaolin areas whereas ZAHE are bentonitic areas. Both rock types contain numerous veins and nodules. The weathering of the Paleozoic granite alongside the absence of sedimentation during the Mesozoic led to the formation of kaolinite that is preserved in ZAHO materials. Nonetheless, during the Cretaceous–Tertiary transit, the conditions of tectonic stability varied. Late Variscan faults reactivated which allowed the percolation of Mg- and Ca-rich hydrothermal fluids through the already kaolinized granite, increasing the alteration of the primary silicates and leading to the formation of smectites in ZAHE materials. The amount of smectites is greater closer to the faults. The stable isotopes indicate the meteoric nature of the low-temperature hydrothermal fluids. The K/Ar data obtained from the natroalunite of veins indicate that those hydrothermal fluids circulated in different pulses from 66.4 ± 1.7 to 58.8 ± 1.5 Ma, as a minimum. Those ages are coincident with the first formation stages of the Duero Basin.

Stable neodymium isotopic fractionation during chemical weathering

Stable Nd isotope ratio is a potentially useful tool to provide new constraints on the geological reservoir formation processes, complementing information from the radiogenic Nd isotope system. Here for the first time, we present the behavior of stable Nd isotopes during low-temperature weathering via a well-studied basaltic soil profile on Hainan Island, South China. The results showed that δ146/144Nd values spanned a range of approximately 0.21‰, from +0.058‰ in the lower profile to −0.152‰ in the upper soil profiles, while the τTh,Nd (%) values decreased from +387.7% to −68.2%, indicating that significant fractionation of stable Nd isotopes and migration of Nd elements occur during chemical weathering. Sequential extraction experiments suggest that the majority of Nd in this profile was hosted in the exchangeable and residual phases. The exchangeable phase was enriched with the heavy Nd isotope (146Nd) due to the adsorption of Nd onto gibbsite and the adsorption/precipitation of Fe-oxides from a heavier dissolved Nd pool in soils. The evidence for adsorption of Nd onto gibbsite is the positive correlation between the abundance of gibbsite and the proportion of Nd in the exchangeable phase, as well as the δ146/144Nd values. The evidence for the adsorption/precipitation of Nd on Fe-oxides comes from the positive correlations between Fe and Nd concentrations and δ146/144Nd values in the exchangeable fractions. The residual phases acquire depleted 146Nd signatures in the upper soil horizon, which could be caused by preferential desorption of heavy Nd isotopes from clay minerals or preferential incorporation of light Nd isotopes during kaolinite formation. These findings elucidate the mechanisms affecting stable Nd isotopic fractionation in low-temperature geochemistry and indicate that the stable Nd isotope ratio is a highly useful indicator for chemical weathering. This, combined with the radiogenic 143Nd/144Nd ratio, will be a powerful geochemical tracer for understanding global Nd cycles.

Rock–water interaction, chemical weathering and solute transport of two rivers draining contrasting climate gradients in Western Ghats, India

AbstractRock–water interactions and chemical weathering are critical factors that determine the quality and quantity of solute transport in river catchments. However, most studies in this field have been limited to temperate regions and data from the tropics and subtropics are scarce, particularly for small rivers that are more responsive to environmental and climate changes. In this study, we investigated chemical weathering, its causal mechanisms and controlling factors that determine changes in the quality and quantity of solutes in two small, tropical mountainous rivers‐the west‐flowing Thuthapuzha river and the east‐flowing Bhavani river‐that drain through contrasting climate and geologic gradients across the southern part of the Western Ghats, in India. This region is an elevated passive continental margin and an ecologically sensitive area. Hydrochemical analysis of river water revealed that the cationic and anionic concentrations in the samples are in descending order of importance Ca2+ &gt; Na+ &gt; Mg2+ &gt; K+ and HCO3− &gt; Cl− &gt; SO42−. Principal component analysis (PCA) indicated that geogenic factors (geology, chemical weathering and leaching/erosion) have a significant role in determining the hydrochemical characteristics of the rivers. To discriminate the relative contributions of silicate weathering in the river basins, we performed a detailed analysis of the major ion ratios along with forward and inverse modelling. The weathering index computed from the molecular ratio of cations and silica concentrations suggested that silicate weathering leads to kaolinite formation in the soil profile. The carbon dioxide consumption rate (CCR) estimated for the Thuthapuzha river, which is draining the humid western flank of the Western Ghats, was 2.18 × 105 mol·km−2 year−1, whereas the Upper Bhavani river, which is draining the semi‐arid area of the Western Ghats was 1.39 × 105 mol·km−2 year−1. Our study highlights the interplay of climatic factors and the geologic characteristics of the terrain that significantly influence the nature and characteristics of solute transport through the rivers in the study area.

Impact of magmatic intrusion on diagenesis of shallow marine sandstones: An example from Qasim Formation, Northwest Saudi Arabia

Igneous intrusions are common in sedimentary basins, and their occurrence can significantly affect the diagenesis and reservoir quality evolution of sandstones, thereby strongly impacting their hydrocarbons-, geothermal-, and CO2-storage potentials. The Qasim sandstones in the Tabuk region (NW Saudi Arabia) experienced shallow burial diagenesis (&amp;lt;2 km) when the Tertiary magma intruded to form basaltic sills (0.4–4 m thick). The sedimentology, tectono-stratigraphic framework, provenance, and chemostratigraphy of the Qasim Formation have been extensively covered in the literature. However, the impact of the magmatic intrusion on diagenesis and reservoir quality evolution of the sandstones remains enigmatic. This study employed thin-section petrography, QEMSCAN, XRD, SEM, and energy-dispersive spectrometer analyses to investigate the role of magmatic intrusion on diagenesis and reservoir quality of the Qasim sandstones. The results of the study indicate that reservoir porosity is principally influenced by primary depositional characteristics (grain size and sorting), diagenetic alterations, and magmatic intrusions. Sandstones with coarser grain size and better sorting have the best intergranular porosity and vice versa. The “normal” diagenetic processes that have significantly affected the reservoir porosity of the sandstones occurred during both shallow burial (eodiagenesis) and uplift (telodiagenesis). The eogenetic alterations include mechanical compaction, early diagenetic cementation by calcite, pyrite, and kaolinite, whereas the telogenetic alterations include the formation of kaolinite, goethite, hematite. Overall, mechanical compaction is the main driver for porosity loss in the sandstones. The intrusion-related diagenetic processes include the dissolution of quartz grains, rounded quartz overgrowths, and calcite cement, and the transformation of kaolinite into dickite and chlorite. Detrital quartz and rounded quartz overgrowths have undergone dissolution due to acidic pore fluids from magma and high temperature. The transformation of kaolinite into dickite occurred in a dissolution-recrystallization fashion, and the amounts of kaolinite and dickite increase in fine-grained sediments away from sill contact due to hydrodynamic processes that deposited muscovite (which form kaolinite) in low energy environments. The chloritization of kaolinite was localized, and the magma-induced dissolution of goethite likely supplied the requisite high Fe content. Additionally, the intrusion has resulted in the dissolution of the early calcite and increase in porosity towards the sill contact. However, values for compactional porosity loss have relatively remained similar both at and away from the sill contact, as the sill is too thin to exert significant vertical loading. This study has relevance to understanding hydrocarbon exploration and exploitation in sediment-lava sequences, and to understanding the development of sediment-lava systems.

Chemical Speciation and Leaching of Trace Metals in Groundwater from the Depleted Landfills, India

Abstract The poor groundwater quality through the leaching of contaminants from depleted landfill is a concern to the scientific community. Therefore, the role of landfills on groundwater quality cannot be neglected in an urban area. The factors influencing the leaching of trace metals in groundwater are soil profile, geochemical and environmental condition of disposed of refuse materials, groundwater-table depth, and climatic factors. This research work delineates landfill role in contaminating groundwater through the chemical speciation of trace metals. Analyzed groundwater quality data indicate most of the samples were classified under Ca2+-Na+ type cation and Cl- type of anion hydrogeochemical facies. The investigations of the mineral equilibrium indicate equilibrium with silicate minerals, which favors kaolinite formation. Saturation index indicates that hematite, goethite, chrysotile, dolomite, ferric-hydroxide, hydro-xyapatite, jarosite-K, cerussite, vivianite, and willemite are reactive minerals in the aquifer water and control their hydrogeochemistry. The study of chemical speciation of trace metals indicates the high possibility of oxidation-reduction, ion-exchange, and chemical-weathering reaction mechanism, which causes the release of trace metal ions and further contaminated aquifer water through leaching. It also justifies through study of contaminant movement in vertical profile of the soil. The chemical speciation of trace metals indicates a reducing atmosphere in the aquifer due to the dominance of Fe2+, Mn2+, Zn2+, Pb2+, and Cu2+ ions in aquifer water. Mn2+ and Zn2+ concentration decreases with depth, while Fe2+ and Pb2+ ion concentration low in the middle layer of the aquifer indicate the contribution through anthropogenic input since it is not available in geology of study area.

Synergistic influence of diatomite and MoS2 nanosheets on the self-alkali-activated cementation of the municipal solid waste incineration fly ash and mechanisms

The solidification/stabilization technique recommended for the disposal of municipal solid waste incineration (MSWI) fly ashes in developed countries was inappropriate for the treatment in most developing counterparts. In this study, the diatomite and MoS2 nanosheets were synergistically employed to activate the self-alkali-activated cementation of the MSWI fly ashes to achieve efficient solidification, the immobilization of heavy metals (HMs), and the inhibition of chloride release. The compressive strength of 28.61 MPa and the leaching toxicities (mg/L) of Zn, Pb, Cu, Cd, and Cr of 2.26, 0.87, 0.5, 0.06, and 0.22 were obtained from the hardened mortars. Diatomite significantly influenced the self-alkali-activated cementation of the MSWI fly ashes while MoS2 nanosheets played both roles in intensifying the stabilization of HMs and strengthening the binding process by inducing the formation of sodalite and kaolinite, enhancing the growth rates of nucleation, and transforming the layered cementation to the partial and full three-dimensional cementation in the hardened matrix. This study not only verified the feasibility of diatomite and MoS2 in activating the self-alkali-activated cementation of the MSWI fly ashes but also supplied a reliable technique for the harmless disposal and efficient utilization of MSWI fly ashes in developing countries.

Microbially induced clay weathering: Smectite-to-kaolinite transformation

Abstract Microbially induced formation and transformation of clay minerals are known to be ubiquitous in nature. This work investigated the smectite-to-kaolinite transformation by Bacillus mucilaginosus, a kind of silicate-weathering bacterium. Results showed that the microbe-smectite system doubled protein production compared with the abiotic controls and enhanced dissolved 1.6% of total Si and 0.9% of total Al from smectite after the 25 days experiment. The formation of kaolinite was verified through its distinguished d(001)-spacing of 0.710 nm revealed by synchrotron radiation X-ray diffraction (SR-XRD) and high-resolution transmission electron microscope (HR-TEM). HR-TEM analysis indicated some mixed layers of smectite and kaolinite appeared in the form of a super-lattice structure. Moreover, the compositional and morphological changes of the solids suggested the emergence of kaolinite was associated with the formation of amorphous SiO2 and fragmented clay particles with lower Si/Al ratio and exposed crystal edge. Based on the detection of –C=O species on the smectite surface and the decrease of pH from 8.5 to 6.5, we inferred the organic ligands secreted by Bacillus mucilaginosus complexed with cations, especially for Si, which stripped the tetrahedral sheets and promoted the kaolinization of smectite. To our knowledge, this is the first report of microbially induced smectite-to-kaolinite transformation under ambient conditions in a highly-efficient way. This work could shed light on a novel pathway of microbe-promoted weathering of smectite to kaolinite at the Earth surface conditions. Such a robust and efficient transformation from expansive smectite to non-expansive clays as kaolinite may be of great potential in enhancing oil recovery in reservoirs.