Mixed-layer Minerals Research Articles

Mineralogical indicators of Holocene climate in sediments of the high-mountain Lake Sagan-Nur (East Sayan Mountains)

We present the first results of study of bottom sediments taken from the high-mountain freshwater Lake Sagan-Nur of glacial origin which is located on the Oka plateau (East Sayan Mountains). Comprehensive investigations of the mineral composition of Lake Sagan-Nur sediments accumulated during the last ~8600 cal. years were carried out. The research methods include X-ray diffractometry (XRD), infrared spectroscopy, laser grain size analysis, SiO2bio determination, AMS and 210Pb dating. The mineral composition of the bottom sediments is dominated by layered silicates, quartz and plagioclase; and also, the X-ray amorphous component consisting of biogenic silica and organic matter is constantly present. The method of mathematical modeling of XRD profiles was used for correct identification of the layered silicates. It was found that the clay mineral assemblage was stable comprising muscovite, chlorite, illite, mixed-layer illite-smectite and chlorite-smectite, kaolinite. At the same time, the quantitative ratios of these minerals and their structural characteristics were modified significantly in response to paleoenvironmental changes in the region. This feature reveals the potential of a number of phyllosilicates (illite, mixed-layer minerals) as indicators of paleoclimate in sedimentary sections of freshwater basins. The study of sediment composition and, especially, the precision mineralogical-crystallochemical analysis of layered silicates allowed us to reconstruct the paleolandscapes and climatic conditions of sediment accumulation for different Holocene sub-stages.

Mineral inclusions in the accretion ice above Lake Vostok

The paper is based on additional studies of mineral inclusions in the accretion ice sampled by deep drilling at Vostok Station in central Antarctica. The studies include X-ray microtomography of two mineral inclusions with identification of their mineral composition; analysis of clay minerals in the soft aggregate of the largest inclusion; and geochronological study of zircon grains. X-ray microtomography shows intact morphology of the inclusions in the ice core and their internal texture. The soft aggregate of the largest inclusion is characterized by the dominance of illite, intermediate concentrations of chlorite and small amounts of kaolinite. A notable feature is the absence of mixed-layer minerals typical of Antarctic coastal areas. The most valuable information is derived from new geochronological data and their integration with previous dating data. The detrital zircon U-Pb ages show strong probability peaks between 900 and 1100 Ma, while the detrital monazite ages are clustered between 1250 and 1450 Ma. Both of these age intervals correspond to the Rayner Orogeny.

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.

ИССЛЕДОВАНИЕ СВОЙСТВ ГЛИНИСТОГО СЫРЬЯ МЕТОДАМИ ФИЗИКО-ХИМИЧЕСКОГО АНАЛИЗАиза

The article presents the results of the study of the properties of clay raw materials using modern methods of physico-chemical analysis: X-ray fluorescence analysis (XRF), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and thermal analysis. Two types of clay raw materials based on the color of the ceramic shard were considered: light-burning and red-burning clays. The studied clay raw materials contain a small amount of clay minerals and a high content of dusty particles, belong to moderately plastic and medium plastic clays and loams. X-ray spectral analysis allowed to determine the chemical quantitative composition of the main oxides of clay raw materials. Thermal analysis of natural clay raw materials, which have a polymineral composition, reveals exothermic and endothermic effects characteristic of the studied minerals – montmorillonite and kaolinite. According to the mineral composition, the clay raw materials of Central Yakutia are polymineral, with the main clay minerals being montmorillonite and kaolinite, and quartz, calcite, chlorite, minerals from the mica and feldspar groups, and mixed-layer minerals found as impurities. The low quality of the clay raw material suggests that further research should be conducted to improve the technological and physical-mechanical properties of ceramic products made from local clay raw material. In the design of raw material mixtures, local natural and man-made mineral raw materials can be used.

Mineralogical differences between seam and prism material in loess‐derived fragipans in western Kentucky

AbstractFragipan horizons are common diagnostic subsurface features typically identified by their dense, brittle nature under field conditions. Fragipan horizons are often hypothesized to contain various silicate bonding agents, including phyllosilicates, amorphous aluminosilicates/silica, and silica sorbed to iron oxyhydroxides. However, the association of silica (Si) with other minerals in these horizons remains uncertain. To fill this knowledge gap, we sampled the prism and seam material of four loess‐derived fragipan horizons in western Kentucky. We characterized and compared the clay mineral composition of the prism and seam material using X‐ray diffraction (XRD), selective extractions, and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Fragipan prism and seam material exhibited a mixed clay mineralogy comprised of vermiculite, mixed layer minerals (hydroxyl‐interlayered vermiculite), illite, kaolinite, and quartz. We identified goethite in fragipan prisms in much greater quantities when compared to seam material, confirmed by both XRD and DRIFTS and corroborated by higher dithionite‐extractable iron in prisms. DRIFT spectra showed a peak near 3180 cm−1 assigned to OH‐stretching mode of goethite, which was prominent in prism materials. Goethite 110 XRD peak positions were negatively correlated to dithionite‐extractable aluminum (Al) and Si content of the prism material, which may suggest greater Si sorbed to the surfaces of Al‐substituted goethite. These results demonstrate the potential importance of Al‐substituted goethite in fragipan prisms and provide insight about possible associations with Si.

The evidence for survival of high-grade diagenesis by dioctahedral vermiculite, as exemplified by upper Triassic rocks of the Tomanová Formation, Tatra Mountains Poland

The aim of the present work was to study the clay mineralogy of the Tomanová Formation - a ∼ 65 m thick complex of inland freshwater mudstones and shales of the upper Triassic age occurring in the Tatra Mountains. The formation was chosen for the study because it was assumed that, even though it underwent high-grade diagenesis, it could contain dioctahedral vermiculite-bearing clays. The clays have unique properties concerning the selective adsorption and the fixation of Cs+. Samples used in the present study were collected from outcrops located within Czerwone Żlebki in the Tomanová Valley in the Polish part of the Tatra Mountains. Seven horizons rich in clays were selected for the detailed mineralogical study. Both bulk samples and the clay fractions were analyzed using X-ray diffractometry, Fourier-transform infrared spectroscopy, and optical microscopy. Layer charges of swelling clays separated from the samples were measured using the OD method.All studied samples contained dioctahedral R0 and R1 illite-vermiculite-smectite mixed layered minerals mixed layered minerals (hereafter I-V-S) rich in dioctahedral vermiculite interlayers, kaolinite, quartz, anatase, and rutile. Three of the studied samples contained also berthierine. The swelling clays' measured mean layer charge values were in the vermiculitic range (i.e. 0.64–0.68/O10(OH)2). The common presence of kaolinite having a “poor degree of ordering” in the studied rocks indicated that quite an intense chemical weathering likely occurred within the alimentation area. The vermiculite-bearing clays (i.e. I-V-S) identified in the studied rocks were most likely also the products of the paleo weathering. The I-V-S minerals survived the high-grade diagenesis most likely due to the potassium deficiency in the system preventing the clays from the illitization. Those findings may suggest that deposits of dioctahedral vermiculite-bearing clays can be found even within geological formations that underwent high-grade diagenesis, which is of exploration importance because dioctahedral vermiculite could be possibly used/utilized as a molecular sieve for 137-Cs immobilization in environmental applications.

Features of the mineralogical composition of solod and solod meadow-chestnut soil, the case of soils of the liman depression at Dzhanybek research station of the Institute of Forest Science RAS

The structure of the soil cover at the territory of the clayey semidesert of the Northern Caspian Sea is represented by triparted soil complex and peculiar soils like solod. Solods are formed in relief elements that are constant for this territory – mesodepressions, which are referred to limans. Two soil profiles were studied in the bottom of the liman – solod, and on its peripheral part – solodized meadow-chestnut soil. The formation of the solod profile occurs because of periodic moistening with fresh water and systematic flooding during the snowmelt period. The second soil is in the zone of transit of surface water to the liman. The soil profiles have the same type of eluvialilluvial distribution of the clay fraction, while differentiation is more distinct in solod. Mineralogical analysis established the same type of qualitative composition of clay and clastogenic minerals in both soils. Clay minerals are represented by illite, smectite, mixed-layer illite-smectite, accompanied by kaolinite and chlorite. Clastogenic minerals are represented by quartz, mica, K-feldspar, plagioclase, and chlorite. Quartz and feldspars are accumulated in the solodized horizons of the soil profiles; the content of quartz and feldspars decreases in the textural horizons, while the content of mica and chlorite increases. The distribution of the smectite phase in the solod profile reveals a difference in the ratio of illite-smectite packets, structures with a low content of smectite packets predominate in the solod part of the profile, and the proportion with a swelling packet in mixed-layer minerals increases in textural horizons. The solodized meadow-chestnut soil is distinguished by a smaller thickness of the solodized horizon, a higher content of the smectite component, and a calm character of the profile differentiation of clay and clastogenic minerals. In both soils, labile minerals with signs of superdispersion are recorded in the solodized and textural horizons. The superdispersion of labile minerals has different causes. In solod, it is associated with the action of low-mineralized water and the hydrolysis of soil minerals during the wet seasons of the year, as well as with the intense regime of intrasoil weathering in situ, and in the solodized meadow-chestnut soil, with the passage of the stage of solonetz soils. Differences in the smectite component were also revealed: in the solodized horizons of solod, it is represented by individual smectite and the mixed-layer phase of illitesmectite; and in the meadow-chestnut soil – by mixed-layer illite-smectite.

Quantitative phase analysis method of palygorskite based on XRD orientational sample analysis and Rietveld full spectrum fitting

Palygorskite is a kind of water-rich magnesium aluminosilicate mineral with a chain-layered structure. Due to the difference in forming environment, the phase composition of palygorskite clay is various, and chemical compositions of palygorskite of different origins are also significantly different, which leads to a great difference in its application performance. Due to the coexistence of various types of layered and chain-layered minerals, conducting quantitative phase analysis of palygorskite raw ore becomes highly challenging. This significantly restricts the development and utilization of palygorskite. Herein, a new scheme is proposed to solve this problem by combining Rietveld full spectrum fitting based on the XRD patterns from internal standard method and orientational sample analysis. The new scheme was applied to the quantitative phase analysis of palygorskite raw ores from Mingguang, Xuyi, and Linze, three of the most representative places of origin in China. Not only the exact content of palygorskite and other crystalline phases in the raw ore, but also the content of mixed-layer minerals, and amorphous phase in the raw ore were obtained. The contents of palygorskite, quartz, illite-smectite mixed-layer minerals, and amorphous in the raw ore of Mingguang were 70.81%, 6.43%, 18.81%, and 3.98%, respectively; the contents of palygorskite, quartz, calcite, illite-smectite mixed-layer minerals in the raw ore of Xuyi were 36.08%, 16.18%, 27.06%, 18.04%, and 2.64%, respectively; the contents of palygorskite, quartz, illite-smectite mixed-layer minerals, calcite, illite, gypsum, feldspar, dolomite, microcline and amorphous in the raw ore of Linze were 10.11%, 34.82%, 5.77%, 1.07%, 5.57%, 8.06%, 12.38%, 17.05%, 2.21%, and 2.96%, respectively.

Late Oligocene monsoonal climate in the Lunpola Basin, central Tibetan Plateau: evidence from palaeosol records

The Asian monsoon affects the natural patterns of climate in China and its origin and evolution have been a matter of much debate in palaeoclimatology. Results from recent studies indicate that the Asian monsoon had reached the subtropical zone by at least c. 41 Ma and expanded to the central Tibetan Plateau during the Late Oligocene, although more geological evidence is required to confirm its spatial and temporal evolution. The well-developed Late Oligocene palaeosol in the Lunpola Basin, central Tibetan Plateau is an ideal material for addressing the issue. Observations of various climatic indicators suggest that these palaeosols were forest cinnamon soils, as shown by the compound Bt and Bk horizons, abundant clay coatings and carbonate nodules, and the diagnostic chemical composition of clays in the Bt horizon. A high chemical weather index, the Rb/Sr ratios and high contents of illite/smectite mixed-layer minerals show that these palaeosols experienced intense weathering and leaching during pedogenesis. The mean annual temperature and mean annual precipitation during the developmental period of the palaeosols were 10.4–14.8°C and 615–1128 mm, respectively, as estimated by empirical formulas, which are comparable with those of cinnamon soils in current monsoon climates. This study provides important independent evidence from palaeosols for studies of the evolution of the Asian monsoon. Supplementary material: The data about the clay chemical composition and climatic indicators of palaeosol and modern soils are available at https://doi.org/10.6084/m9.figshare.c.6850703 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Geology, geochronology, geochemistry and Hf-Sr-Nd isotopes of the ‘green-bean rocks’ (felsic tuffs) in the western Yangtze Block, China: Implications for genesis and enrichment mechanism of Li

The widespread ‘green-bean rocks’ (GBRs) in the western Yangtze Block (YZB) are traditionally considered to be originally felsic volcanic tuff. These greenish or yellowish green GBRs are characterized by the presence of bean-like grains. Although the GBRs are enriched in Li in addition to K, the enrichment mechanism of Li during the formation process of GBRs remains controversial. Detailed petrography, scanning electron microscopy, X-ray diffraction, whole-rock geochemistry, U-Pb dating and Hf-Sr-Nd isotopes have been conducted on the GBRs from the Longmendong section in the western YZB to shed light on the genesis of GBRs, Li enrichment mechanism, and further exploration.The zircon and apatite from Longmendong GBRs yielded U-Pb ages of 247.2 ± 0.6 Ma and 247.0 ± 11.0 Ma, respectively. Longmendong GBRs show bull-rock (87Sr/86Sr)i ratios ranging from 0.72602 to 0.72948 and εNd(t) values between −9.8 and −10.4. Zircons have low εHf(t) values and old two-stage Hf model ages (TDM2) ranging from −16.1 to −7.4 and 1741 to 2285 Ma, respectively. Apatite grains display high (87Sr/86Sr)i ratios and low εNd(t) values in the range of 0.72225–0.72461 and −9.93–−11.18, respectively. The combined evidence from textures, mineral compositions, whole-rock geochemistry and Sr-Nd-Hf isotopic compositions indicates that the GBRs originated from felsic volcanic ashes that erupted along the Sanjiang Orogen. The magma of volcanic ashes was sourced from the remelting of ancient crust in response to the initial collision of Indochina-Yangtze Blocks during the closure of the eastern Paleo-Tethys Ocean. The apatite grains separated from GBRs show significantly low Sr and Eu contents (136–223 ppm and 4.23–6.53 ppm, respectively) and low (La/Sm)N (0.97–1.11) and (Sm/Yb)N (3.49–4.56) ratios, indicating that apatite crystallized earlier than the plagioclase and the original magma are highly evolved. The magma of GBRs originated from ancient crust with significant differentiation, facilitating the initial enrichment of Li during the magma evolution. On the other hand, the GBRs have elevated levels of K2O, MgO and clay minerals (e.g., illite and illite/smectite mixed layer minerals), which are proportional to the Li concentrations. This suggests that Li in the GBRs is adsorbed by clay minerals in ionic form and experience additional enrichment during the transformation from volcanic ashes into clay minerals. Furthermore, the GBRs in the northeastern Sichuan basin under a limited sedimentary environment have relatively higher Li concentrations, suggesting that continuous evaporation also positively contributed to Li enrichment in GBRs. Geographically, GBRs in the Sichuan basin are closely related to underground Li-rich brines hosted within the adjacent strata. Therefore, the widespread Li-rich GBRs in the western YZB not only hold promise as a potential Li resource, but also serve as a marker layer for the prospecting Li brines in the Sichuan basin.

Vanadium mineralization at Los Chihuidos sediment-hosted Cu–V deposit, Neuquén Basin, Argentina: An approach to vanadium ore forming processes

Vanadium mineralization at Los Chihuidos deposit of the Neuquén Basin is linked to the development of a redox front system related to the inflow of hydrocarbons into the red sandstone of the Huincul Formation. Interaction of hydrocarbons with oxidized red beds and connate water generated redox reactions where hematite was dissolved due to iron reduction resulting in the discoloration of the red strata. At the contact between oxidized red sandstone and reduced white sandstone, precipitation of specific mineral phases resulted in the V ore with minor amounts of Cu. With the implementation of the redox interface, abundant V-montmorillonite and V-hematite precipitated at the more oxidizing conditions and Cu-V-corrensite-type at the more reducing conditions of the redox front. As the redox front advanced with fluids constantly migrating into the reservoir, more reducing conditions were stablished, promoting chloritization and minor illitization with V-Cu incorporation and continuous upgrading of the ore. Main ore mineralogy consists of clay minerals including V-bearing montmorillonite, Cu-V-corrensite-type, V-di-trioctahedral chlorite and Cu-tri-trioctahedral chlorite with minor V-illite–smectite mixed-layer minerals and associated secondary V-hematite. Chloritization over illitization was favored due to high amounts of Fe and Mg in detrital clasts and in connate fluids and by low K availability related to low amounts of detrital K-feldspar. The spatial transition of V and /or Cu bearing clay minerals observed through the mineralized redox front at Los Chihuidos deposit (kaolinite → smectite → illite/smectite → corrensite-type → di- trioctahedral -chlorite → tri- trioctahedral -chlorite) and the related variation of V–Cu concentrations in bulk rock are indicative of increasing pH and decreasing Eh of resident solutions from red to white sandstones during the hypogene mineralization process. Late influx of Cu-rich oxidized basinal brines precipitated main copper ore with Cu-sulfides in the white sandstone up to the contact with the redox front in contact with hydrocarbons. During uplift and exhumation, percolation of meteoric water promoted remobilization of V and Cu and the precipitation of oxidized V–Cu ore.

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 <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.

Taphonomy of early life (2.1 Ga) in the francevillian basin (Gabon): Role of organic mineral interactions

The taphonomy of early soft-bodied organisms in Palaeoproterozoic sediments is not yet clearly understood, even though some locations where these fossils are found present all the conditions for exceptional fossil preservation. Indeed, the degree of fossil preservation has received attention, but better knowledge of the environmental conditions and associated taphonomic processes is also essential. In the Gabonese Francevillian Basin, the discovery of macrofossils (2.1 Ga) of multicellular organisms in black shales is an outstanding example of this degree of preservation. Indeed, the biological diversity, as a wide variety of fossil morphologies are observed, is associated with two major taphonomic processes – moulding (lenticular-shaped forms) or early pyritization, while the fossil host rocks were not deeply buried and were affected only by weak to moderate diagenesis. However, usually, the mechanisms of this preservation remain difficult to assess, as the original taphonomic processes are impacted by diagenesis and still misunderstood. In this way, by closely observing fossil mineralization in four morphotypes of macrofossils and associated host rocks from mineralogical and textural points of view, this work aims to provide some keys to a taphonomic comprehension of soft-bodied organism preservation. After the deposition of dead organisms on the clayey sediment, an illitization process, which depends on the availability of dissolved K driven by bacterial activity, started from the first stages of preservation by moulding the lenticular-shaped forms and proceeded in the pores of the other macrofossils after their pyritization. At the fossil level, the intensity of illitization is controlled by the mode of preservation and the evolution of the associated permeability. In the nonpyritized lenticular-shaped specimens, illitization was not achieved, preserving I-S mixed-layer minerals, while in the pyritized forms, the illitization degree was more extensive. In comparison, I-S mixed-layer minerals are almost absent in pyritized abiotic concretions. A second process, which occurred later, consists of general chloritization from fluid circulation. Our detailed results show that each specimen behaved like a microsystem with its own physico-chemical and mineralogical evolution during preservation/diagenesis. This finding allows us to propose a conceptual model of the taphonomic history, describing the fossilization stages for each type of specimen.

Role of depositional environment on clay coat distribution in deeply buried turbidite sandstones: Insights from the Agat field, Norwegian North Sea

The preservation of reservoir quality in deeply buried sandstones largely depends on the presence of grain-coating clays that can inhibit quartz overgrowth and cementation. These grain-coating clays are the focus of today's hydrocarbon exploration as they enable new oil and gas discoveries in sedimentary basins. However, the origin and distribution of these clays in turbidites are poorly documented in scientific literature. Our study addresses this knowledge gap by investigating the mechanisms and parameters governing the clay coat development in turbidite sandstones, with a focus on the Agat Formation (Fm) in the Norwegian North Sea. Petrographic observations, scanning electron microscopy, and X-ray diffraction analyses were used to identify the origin of clay minerals and their distribution, as well as to understand the diagenetic evolution of the sandstone and its impact on reservoir quality. Based on the sedimentary facies description, the Agat Fm comprises four principal members deposited in various depositional environments, ranging from distal lobe fringe to amalgamated proximal lobes and weakly confined channels. Chlorite and kaolinite are the main authigenic clay minerals in these sandstones, associated with a variable amount of inherited detrital clays consisting in Fe-bearing kaolinite and mixed-layer minerals composed of illite and hydroxyl-interlayered clay minerals formed in acidic soil environments. Well-developed chlorite coats are associated with the highest reservoir quality (φ > 10%), while discontinuous chlorite coats are linked to extensive quartz cementation and poor reservoir quality (φ < 5%). Samples with abundant pore-filling chlorite also exhibit poor reservoir quality (φ < 7%). Proximal lobe deposits and weakly confined channels show well-developed chlorite coats, whereas discontinuous chlorite coats are mainly found in proximal lobe deposits associated with high velocity escaping fluids during dewatering. Pore-filling chlorites are typically present in distal lobe fringes and levee deposits. Chlorite in the Agat Fm is mainly derived from the replacement of inherited detrital clays via an intermediate berthierine precursor forming during early diagenesis. The dissolution of Fe-rich grains such as biotite and ferric detrital clays under reducing conditions governed the kinetics of berthierine/chlorite growth. The late diagenesis is characterized by extensive feldspar dissolution in a closed diagenetic system, leading to the precipitation of kaolinite and quartz cement. The presence of chlorite coatings around detrital grains preserved the porosity from extensive quartz cementation during deep burial, highlighting the role of chlorite in maintaining the quality of deeply buried turbidite reservoirs.

Hydrothermal Alteration in the Nevados de Chillán Geothermal System, Southern Andes: Multidisciplinary Analysis of a Fractured Reservoir

The interplay between a heat source, primary plus secondary permeability, and hydrothermal fluids makes geothermal systems a highly dynamic environment where evolving physico-chemical conditions are recorded in alteration mineralogy. A comprehensive characterization of hydrothermal alteration is therefore essential to decipher the major processes associated with geothermal system development. In this study, we defined the hydrothermal mineralogical evolution of the Nevados de Chillán Geothermal System (NChGS), located in the Southern Volcanic Zone (SVZ) of the central Andes, where the regional framework of the system is formed by a direct association with a currently active volcanic complex, a favorable structural control, and vertically inhibited fluid circulation. To characterize the secondary mineralogy present in the NChGS, we integrated optical petrography, Scanning Electron Microscopy (SEM) observations, X-ray Diffraction (XRD) analysis, and microthermometric measurements along a drill core with a depth of 1000 m at the Nieblas-1 well. These mineralogical approaches were combined with a structural field analysis to highlight the relevance of multidisciplinary study in understanding active geothermal systems. The results indicated that the evolution of the system involved four paragenetic stages, with the main processes in each phase being the heating, boiling, and mixing of fluids and re-equilibration to new physico-chemical conditions. Additionally, three hydrothermal zones were recognized: an upper argillic section, an intermediate sub-propylitic zone, and a deep propylitic domain. Sampled thermal springs are characterized by pH values of 2.4–5.9 and high SO4= concentrations (&gt;290 ppm). These acid-sulfate steam-heated waters suggest the contribution of primary magmatic volatiles to the hydrothermal system. Alunite recorded in the alteration halos of veinlets presents at depths of 170–230 m denote the circulation of acidic fluids at these levels which were favored by reverse faults. These findings indicate that, at this depth range, the condensation of magmatic volatiles into shallow aquifers controls the recharge area of the superficial thermal manifestations. Conversely, deep-seated hydrothermal fluids correspond to near-neutral chloride fluids, with salinities ranging from 0.1 to 6.9 wt.% NaCl eq. The distribution of illite/smectite and chlorite/smectite mixed-layered minerals outline the presence of a significant clay cap, which, in this system, separates the steam-heated domain from the deep hydrothermal realm and restricts fluid circulation to existing permeable channels. Our mineralogical and structural study provides critical data for the interpretation of heat–fluid–rock interaction processes in the NChGS. The interplay between hydrothermal fluids and active faults is also discussed in the context of the complex of geological processes in active geothermal systems along the Chilean Southern Volcanic Zone.

Comparison of Change in Nanopore Structure of Oil Shale after Anhydrous and Sub/Supercritical Water Pyrolysis

Oil shale is an important part of unconventional resources, which is considered as an important replacement for traditional oil resources. At present, the underground in-situ conversion method of oil shale is mainly aimed at shallow reservoirs, and it is difficult to apply to in-situ exploitation of oil shale with a depth of more than 1000m. In view of the portability, fracturing and extraction characteristics of high-pressure sub/supercritical water, it has become the research direction of in-situ mining of deep oil shale. The evolution of pore structure of oil shale is the basis for exploring the production mechanism of sub/supercritical water pyrolysis of oil and gas, which has important theoretical and scientific significance for improving the development and utilization of in-situ injection of sub/supercritical water in deep oil shale. Therefore, in this paper, the oil shale of Jijuntun Formation of Paleogene in Fushun Basin is taken as the research object. The pyrolysis experiments of oil shale in three ways, namely, water-free (electric heating), subcritical water and supercritical water, are carried out by means of high temperature and high-pressure source rock pyrolysis simulation device. The evolution characteristics of nano-pore structure under different pyrolysis methods are studied by XRD and low temperature nitrogen adsorption technology. The results show that, compared with anhydrous pyrolysis at the same temperature, the pore size of 3-30 nm of oil shale increases significantly after sub/supercritical water pyrolysis. The phenomenon of kaolinite illite fossilization increases, and the overall weak acidic environment is more conducive to the transformation of illite into Illite and montmorillonite mixed layer minerals, easier to increase the pore space in oil shale, and conducive to the migration and accumulation of produced oil and gas.

Pore structure characteristics of shale in coal-bearing strata: In the case of the Shanxi formation of lower Permian in Huainan coalfield in China

Reservoir pore characteristics are an important part of shale gas reservoir capacity evaluation. Compared with Marine shale, the study of coal measure shale is relatively backward in China. In order to deeply analyze the reservoir properties of coal measure shale gas and give priority to favorable reservoirs, the pore structure characteristics of shale in coal measures from the Shanxi Formation of Lower Permian in Huainan Coalfield of China were investigated in this study. The pore size distribution, specific surface area (SSA), and pore volume (PV) were obtained. The BET surface area and PVs are inconsistent with the variability in total organic content (TOC) and composition of the samples. There are unobvious negative correlations between PV, SSA, and TOC for the samples in this study. However, the contribution of clay minerals to PV and SSA seems to be positive, especially for the mixed-layer minerals of illite and smectite.

Crystal chemistry of globular layered silicates of the Troitsko-Bainovskoye fre-clay deposit (Middle Urals)

Research subject. The composition and crystal chemistry of glauconite from the open deposits (K2cn-cp) of the Poldnevskaya area of the Troitsko-Bainovskoye deposit of fire clays.Materials and methods. An analysis of the mineralogical and crystallochemical properties of glauconite was carried out using a set of modern analytical methods (“Geonauka” Centre for Collective Use, IG FRC Komi SC UB RAS): X-ray diffractometry, IR-spectroscopy, scanning electron microscopy, modeling of diffraction profiles.Results and conclusions. The crystal-chemical features of glauconite were determined. Two main glauconite varieties (green and light green) in the rocks of the Zaikovskaya suite were distinguished and their differences and degree of maturity have been established. It was found that dark green globules are close to glauconite and represent a more “mature” variety, while the light green ones are a disordered mixed-layer mineral of the mica (glauconite) – smectite series and are a product of incomplete replacement of the original smectite by glauconite. Phase heterogeneity of glauconite globules was revealed. It has been established that the rocks of the Troitsko-Bainovskoe deposit are exposed to intensive transformation under the influence of acidic surface and technogenic waters, which result in the destruction of the initial minerals and the appearance of secondary mineralization. Clay minerals of the glauconite-bearing rocks are represented by disordered mixed-layer phases of predominantly illite/smectite type.

Complexity of clay minerals and its effects on silicon dynamics in hypersaline coastal wetland soils, Brazil

Context Tidal dynamics and high evaporative rates in hypersaline tidal flat (HTF) soils favour a range of clay reactions and the formation of complex clay assemblages. HTFs have a geochemical environment conducive to mineral reactions, and therefore, clay mineral alteration controls essential nutrients in coastal wetlands. Aims The crystallochemical characteristics of clay minerals from two HTFs were studied to provide insights into the complexity of fine clay assemblages in HTF soils and their effects on Si biogeochemistry. Methods The fine clay fraction (&lt;0.2 μm) from these HTFs were investigated using X-ray diffraction (XRD) modelling, XRF, FTIR, TEM–EDS, and silicon sequential extractions. Key results The results have indicated the presence of endmembers and R0 mixed-layered minerals such as kaolinite, smectite, illite, kaolinite–smectite (K–S), kaolinite–illite (K–I), illite–smectite (I–S), and illite–vermiculite (I–V). In general, K–S was the dominant mineral in the samples, occurring in a range of kaolinite layers. Alteration of detrital kaolinite to other mixed-layered minerals occurs in soils, leading to silicon removal from the soil solution because of mineral genesis. There is Mg enrichment at the expense of Al in the samples, and bio-opal appears to be the source of Si for the kaolinite alteration process. Conclusions Our findings indicate that clay authigenesis is an important factor controlling Si dynamics in HTF soils, acting as a sink of Si during the formation of new clay phases. Implications Chemical reactions involving clay minerals are critical for deepening our understanding of the biogeochemistry of wetland soils.

New laboratory procedure for distinguishing smectites with varying permanent layer charge based on the combination of Cu-trien and ethylene glycol solvation methods and X-ray diffraction

Permanent layer charge of smectites (or smectite layers in mixed-layer minerals) is important for their properties and materials' applicationss. However, distinguishing low- and high-charge smectites by traditional laboratory methods is time-consuming and instrumentally demanding and it can also produce equivocal results. In addition, the use of structural formulae based on chemical analyses combined with knowledge on crystallochemistry is challenging in arbitrary mineral mixtures. The aim of this work was to test a novel laboratory procedure for distinguishing actual multi-mineral specimens of smectites according to their permanent layer charge. This is conducted on interlayer cation exchange by the Cu-trien complex and subsequent solvation with ethylene glycol. This procedure returned more straightforward results than the traditional routine of ethylene glycol-saturated K+-exchanged specimens by producing better-resolved X-ray diffraction (XRD) patterns. The practical application was demonstrated by analysing sauconite samples from Skorpion in Namibia, which was shown to contain more sauconite phases of distinct crystallographic properties present in variable proportions. XRD of the oriented ethylene glycol-saturated specimens was insufficient for this purpose. The procedure was tested by reference clay minerals of the smectite group with varying structural parameters. It was distinguished more smectite phases with distinct layer charges and estimated the layer charge by combining interlayer cation exchange with the Cu-trien complex and ethylene glycol solvation. This was followed by XRD analyses and full-profile diffraction pattern modeling. Further investigation is required for comparison with other methods. Possible reasons for the formation of two populations of sauconites were discussed.