Major Clay Minerals Research Articles

An EXAFS study for characterizing the time-dependent adsorption of cesium on bentonite.

Bentonite is considered for use as a buffer material in the final disposal repositories of radioactive waste. Long-lived 135Cs with a half-life of 2.3 × 106 years is a key radionuclide in high-level waste, and lots of 137Cs with a half-life of 30.2 years exists in low-level waste. Therefore, the adsorption of Cs on bentonite is a critical issue in evaluating the long-term safety of radioactive waste disposal. In this study, EXAFS techniques were used to characterize the time-dependent process from the beginning of adsorption to equilibrium. From the results of this study, we found changes including to the Cs adsorption sites, the Cs-O distance between Cs and the oxygen atom, and that the adsorption of Cs ions occurred before the reaction reached equilibrium. The fraction of OS complexes when Cs was adsorbed on bentonite can refer to the CN (Cs-O1st)/CN (Cs-O2nd) ratio of coordination numbers, and this study found that the OS complex was the major adsorption species when Cs adsorbed onto bentonite. In addition to the ratio CN (Cs-O1st)/CN (Cs-O2nd) providing information on the adsorption site, we also discussed the change of Cs-O1st and Cs-O2nd bond distances to identify the adsorption sites at different times. Comparing the XRD patterns of montmorillonite and bentonite, we found that the interlayer collapsed after Cs was adsorbed onto montmorillonite, but it expanded after Cs was adsorbed onto bentonite. From the results of EXAFS fitting, we found that the movement of Cs ions was from regular interlayer sites to expanded interlayer sites, which caused the interatomic distance of Cs-O2nd to decrease with an increase in time. It was revealed that the adsorption of Cs on bentonite occurred in two steps. The first step includes the rapid uptake of Cs by attachment to the oxygen atoms of the H2O molecules at the regular interlayer sites, especially for the OS complexes. The second step includes a slower process where dehydrated Cs ions move from the regular interlayer sites to the expanded interlayer sites. In this study, Cs L3-edge EXAFS spectroscopy was conducted for the Cs adsorbed on bentonite to identify the Cs adsorption sites over time, as this is important in evaluating the mobility of Cs in the environment. These results are beneficial in finding the process of Cs adsorption on bentonite, which could be used for the design of the final disposal of spent nuclear fuel.

Zn sorption on Ca-illite and Ca-smectite: experiment and modelling

To predict Zn behaviour in soil, the retention properties of clay minerals plays a relevant role. In a continental environment, Ca is the main cation in solution. Soil reactivity may be reduced to sorption properties of Zn and Ca on illite and smectite, the major clay minerals in soil. With this assumption, a multi-site ion exchanger model has successfully been applied to the Zn sorption on Ca-illite and Ca-smectite. New batch experiments performed in this study enabled to collect sorption data for Zn on Ca-illite by concentration and pH isotherms. Zn sorption reversibility was then verified. These sorption data were modelled successfully with a multi-site ion exchanger (MSIE) formalism by using four sorption site types. Zn sorption isotherms on smectite were retrieved from literature and interpreted following the MSIE formalism. The obtained selectivity coefficients may be thereafter put into ion exchange models to describe the Zn sorption in natural environments.

Premature failure of a major highway in southwestern Nigeria: the case of Ipele\u2013Isua highway

Mineralogical, geochemical and geotechnical analyses were carried out to evaluate the contributions of geological and geotechnical properties of subgrade soils to the incidence of failure of the Ipele–Isua road, south-western Nigeria. Field observations showed that the road is in a very poor state of disrepair as major portions of the road alignment have failed. The road alignment is underlain in places by Quartz Schist, Banded Gneiss and Granite Gneiss. The results of the laboratory tests revealed that the natural moisture content ranges from 6.5 to 23.3%, liquid limit from 20.1 to 55.1%, plasticity index 5.2 to 22.2%. The grain size analysis showed that the amount of fines ranges from 13 to 60.8%. Others are linear shrinkage between 2.9 and 11%, free swell between − 16.67 and 41.94%, maximum dry density from 1520 to 1792.1 kg/m3 and CBR between 2 and 17%. The specific gravity ranges from 2.51 to 2.63. The major clay minerals present are kaolinite and dickite with dominance in 50% of the samples. Major oxides present are SiO2, Al2O3, Fe2O3, K2O. Na2O, MgO and CaO are generally less than 1%. Based on AASHTO classification, 19% of the samples are classified as A-2-4, 33% classified as A-2-6 while 44% classified as A-7. Dominance of low California bearing ratio, low maximum dry density, high linear shrinkage and A-7 soil group expectedly contributed to poor geotechnical properties of the subgrade. Absence of drainage is suspected to have worsened the failure as exhibited on the road.

Adsorption of strontium and caesium onto an Na-illite and Na-illite/Na-smectite mixtures: Implementation and application of a multi-site ion-exchange model

The application of a multi-site ion-exchange (MSIE) model to the prediction of contaminant behaviour onto soils or sediments requires a coherent adsorption database. Following the same approach exposed in preceding works on smectite (Siroux et al., Appl. Geochem. 87, 167; Wissocq et al., Appl. Geochem., 93, 167), a database is here implemented to allow modelling the adsorption of radionuclides 90Sr and 137Cs onto Na-illite, one of the major clay mineral encountered in the terrestrial environment. This database allows describing the adsorption properties of Sr2+ and Cs+ competing with major cations H+ — considered as the reference cation — and Na+ onto an Na-illite. To obtain the adsorption site capacities and selectivity coefficients of illite sites for Na+ towards H+, a saturation curve of Na+ on Na-conditioned illite was acquired. Adsorption isotherms issued from literature have been reinterpreted using the MSIE model to obtain the adsorption properties of Sr2+ and Cs+ onto purified and Na-conditioned illite. Afterwards, the predictability and robustness of the database were verified simulating experimental adsorption of Sr2+ and Cs+ onto Na-illite/Na-smectite mixtures.

Sorption of Eu(III) on Fe–montmorillonite relevant to geological disposal of HLW

Abstract Montmorillonite (Mt) is the major clay mineral of bentonite, which is the candidate buffer material in the engineered barrier system for geological disposal of high level waste (HLW). The alteration of Mt due to its interaction with carbon steel (overpack) can produce Fe–Mt. In order to understand the basic properties of Fe–Mt, the sorption studies using Eu(III) are reported here. For this, Fe(III)–Mt was prepared by conventional cation exchange method using FeCl3 with Na–Mt. The obtained Fe(III)–Mt was then reduced to Fe(II)–Mt using ascorbic acid. Both the samples were characterized based on their X-ray diffraction, Fourier transform infrared spectra, cation exchange capacity and specific surface area. The batch sorption studies of Eu(III) were conducted for both Fe(III)–Mt and Fe(II)–Mt as a function of pH (3–10), ionic strength (0.001 M–1 M) and Eu(III) concentration (10−8–10−3 M). The distribution coefficient (Kd) was found to be higher for Fe(III)–Mt compared to Fe(II)–Mt and Na–Mt. The sudden increase in sorption in the pH range 4.5–6 and remaining constant beyond it indicates ion exchange mechanism at pH<4.5, with surface complexation mechanism dominating the sorption at pH>4.5. This is further corroborated by ionic strength dependent sorption data which shows decrease in sorption capacity of Fe–Mt with increasing ionic strength at low pH, but remaining more or less unchanged at higher pH. Eu(III) adsorption isotherm on Fe–Mt increased linearly with [Eu(III)] reaching saturation at 10−5 M and 10−4 M for Fe(III)–Mt and Fe(II)–Mt, respectively. The amount of iron released from Fe–Mt and Fe(II)/Fetotal during sorption were estimated to understand the effect on Eu(III) sorption behaviour by release of interlayer iron in Fe–Mt.

Characterization of Some Red Clays from Morbi-Wankaner Region (Gujarat, India)

ABSTRACTIn this work, an attempt to correlate chemical, mineralogical, textural and physical properties of red clays of Morbi-Wankaner region, Gujarat (India) were made using various characterization techniques. General properties, such as specific gravity, slaking nature and grit content were noted. Bulk chemical composition of clays was determined by wet chemical method. Mineralogical characterization was carried out by XRD and FTIR. Crystallinity and distortion in structure of clay minerals were ascertained in terms of Hinckley index, and change in intensity and wave number of OH stretching bands in FTIR spectrum. Thermal characteristics were evaluated through TG-DTG-DTA. Textural analysis was carried out by SEM, PSA and BET surface area analyzer. As the presence of aggregates was large in red clays, the ground clay was used for determining plastic properties. XRD analysis confirmed presence of partially ordered kaolinite and hematite as the major minerals, with variation in amount of quartz in all the investigated clays. Chemical analysis, FTIR, TG-DTGA and DTA support the major clay minerals identified by XRD. Plastic property was found to be influenced by type and amount of various minerals present in each clay sample and their physical properties. Studies showed that these clays are suitable for ceramic production.

Study of clay minerals effect on curing characteristics of polymer blends and physical-mechanical properties of prepared vulcanizates

The given paper deals with the study of the properties of clay minerals, namely montmorillonite and moreover, it is focused on effect of these clay minerals on the curing characteristics of the polymer blends and the physical-mechanical properties of prepared vulcanizates. Montmorillonite is a major clay mineral which has a wide application in many industrial branches. It belongs to the group of dioctahedral smectite minerals with structural type in the ratio of 2:1. Characteristics of prepared modified and organomodified clay minerals are based on sulphur vulcanisation accelerators which are used for the preparation of real polymer blend where they represent a partial replacement of the common carbon black filler and then, the effect on the curing characteristics of polymer blends as well as physical-mechanical properties of the prepared vulcanizates are investigated. The results exhibit that the clay-based filler (modified and organomodified clay minerals) can be used as a partial replacement while the quality of the prepared blends is preserved.

Effects of fines content on hydraulic conductivity and morphology of laterite soil as hydraulic barrier

Laterite soil was investigated to find out the effects of fines content and to identify the micro-structural and molecular characteristics to evaluate its potentiality as a compacted soil landfill liner material. Tests were carried out on natural soil and reconstituted soil by dry weight of soil samples to determine the physical and engineering properties of the soil. All tests were carried out on the samples by adopting the British Standard 1377:1990. The possible mechanisms that contributed to the clay mineralogy were analyzed using spectroscopic and microscopic techniques such as field emission scanning electron microscopy (FESEM), energy-dispersive X-ray (EDX) and X-ray diffractometry (XRD). The laterite soil was found to contain kaolinite as the major clay minerals. A minimum of 50% fines content of laterite soil met the required result for hydraulic barriers in waste containment facilities.

Potential shale resource plays in southeastern Nigeria: Petroleum system modelling and microfabric perspectives

Nigeria is witnessing significant increase in energy demand as a result of rising population and economic growth; as more focus on clean energy take hold. These challenges have triggered the search for shale gas and shale oil in the inland basins of Nigeria. The aim of the study is to carry out an integrated study that incorporates petroleum systems modelling, field studies and advanced analytical programs in order to define the hydrocarbon prospectivity of Upper Cenomanian-Lower Turonian Eze-Aku Shale and Ekenkpon Shale as potential shale gas/oil plays in southeastern Nigeria. Available subsurface information which includes exploration wells and proprietary Oil Company archive data were used to calibrate and simulate 1-D basin models. Amount of silica content, major clay mineral group and microfabric of the potential shale resource plays were determined using Energy Dispersive X-ray Fluorescence analysis, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy respectively. The simulated models showed that deeply buried Eze-Aku Shale and Ekenkpon Shale have undergone episodic generation of hydrocarbon. Significant amount of silica content (>30%) in Eze-Aku and Ekenkpon Shale samples suggested a brittle nature of the samples and the possibilities of the samples to capture portion of expelled hydrocarbon. Identification of non-swelling clay mineral group in the analyzed shale samples indicated that the samples have the potential for shale gas/oil. The SEM images of analyzed samples showed differences in cementation. This study recommends that deeply buried Eze-Aku Shale and Ekenkpon Shale are potential exploration targets for shale gas/oil in Abakaliki Fold Belt and Calabar Flank of the southeastern Nigeria.

Mineralogical and Geochemical Appraisal of Clay Deposits in Papalanto and Its Environs, Southwestern, Nigeria

Three residual clay occurrences in Papalanto, Ifo, and Imoto areas which belong to the sedimentary basin of southwestern Nigeria were investigated to determine their industrial applications.The samples were pulverized, sieved, digested with mineral acids and characterized. Clay mineralogy was determined using X-ray Diffraction (XRD). Elemental compositions of the clay samples were determined using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS). Grain size distribution data were obtained by conducting grain size analysis in two parts; sieve analysis and sedimentation. Thermal properties, plasticity tests, density measurement, linear shrinkage and water absorption capacity were determined to evaluate their industrial potentials. Chemical Index of Alteration (CIA) was calculated to determine the degree of weathering in the area.The X-ray diffraction results showed that kaolinite is the dominant mineral, while quartz, anatase and hematite are the major non clay minerals. Chemical data showed that the average values of SiO2, Al2O3, and Fe2O3were 59.46%, 22.16%, and 3.06% respectively constituting 98.3% of the bulk compositions. Papalanto possessed high plasticity and mouldability.Evaluation of the clay thermal characteristics, firing colour, water absorption capacities and shrinkage values showed that the whitish Ifo clay and Papalanto kaolinitic clays could serve as raw materials for ceramics, building bricks, and other structural wares. Kaolin which is the dominant mineral in all the clays can be used for cosmetics, tooth paste, pharmaceutical purposes

Pore Structure Characteristics of Marine–Continental Transitional Shale: A Case Study in the Qinshui Basin, China

Organic shales deposited in a marine–continental transitional environment are well developed in the Qinshui Basin, northern China. However, previous research concerning shales has predominantly focused on marine shales and barely on marine–continental transitional shales. In this study, geochemical and mineralogical analyses were performed on 23 marine–continental transitional shale samples obtained from four wells in a currently active shale gas play, Yushe-Wuxiang area in the Qinshui Basin. Furthermore, the complex pore structure of the transitional shales was well characterized by scanning electron microscopy (SEM), mercury intrusion, and low pressure gas physisorption. The results showed the abundance of organic matter (OM) with an average of 2.03% in the target shales. The dominant minerals in the shale were found to be clay and quartz, and the major clay minerals type is kaolinite and Illite/smectite. SEM images clearly exhibited that the pores in the shale matrix are mainly associated with clay min...

Diagenesis and Reservoir Properties of the Permian Ecca Group Sandstones and Mudrocks in the Eastern Cape Province, South Africa

Diagenesis is one of the most important factors that affects reservoir rock property. Despite the fact that published data gives a vast amount of information on the geology, sedimentology, and lithostratigraphy of the Ecca Group in the Karoo Basin of South Africa, little is known about the diagenesis of the potentially feasible or economically viable sandstones and mudrocks of the Ecca Group. This study aims to provide an account of the diagenesis of sandstones and mudstones from the Ecca Group. Twenty-five diagenetic textures and structures were identified and grouped into three stages that include early diagenesis, burial diagenesis and uplift-related diagenesis. Clay minerals are the most common cementing materials in the sandstones. Smectite, kaolinite, and illite are the major clay minerals that act as pore lining rims and pore-filling materials. A part of the clay minerals and detrital grains was strongly replaced by calcite. Calcite precipitates locally in the pore spaces and partially or completely replaced clay matrix, feldspar, and quartz grains at or around their margins. Precipitation of cements and formation of pyrite and authigenic minerals occurred during the early diagenetic stage. This process was followed by lithification and compaction which brought about an increase in tightness of grain packing, loss of pore spaces, and thinning of bedding thickness due to overloading of sediments and selective dissolution of the framework grains. Mineral overgrowths, mineral replacement, clay-mineral transformation, dissolution, deformation, and pressure solution occurred during burial diagenetic stage. After rocks were uplifted, weathered and unroofed by erosion, this resulted in decementation and oxidation of iron-rich minerals. The rocks of the Ecca Group were subjected to moderate-intense mechanical and chemical compaction during their progressive burial. Intergranular pores, secondary dissolution, and fractured pores are well developed in the sediments of the Ecca Group. The presence of fractured and dissolution pores tend to enhance reservoir quality. However, the isolated nature of the pore linkage makes them unfavorable producers of hydrocarbons, which at best would require stimulation. The understanding of the space and time distribution of diagenetic processes in these rocks will allow the development of predictive models of their reservoir quality, which may contribute to the reduction of risks involved in hydrocarbon (oil and gas) exploration.

Consolidation deformation of Baghmisheh marls of Tabriz, Iran

Vast parts of the east of Tabriz city have been covered by Baghmisheh formation marls. These marls can be classified into three types based on their color as identified in yellow, green, and gray marls. Many high-rise buildings and other projects were founded and now is constructing on these marls. Baghmisheh formation marls are classified as stiff soil to very weak rock, therefore they undergo considerable consolidation settlement under foundation loads. This study presents the physical properties and consolidation behavior of these marls. According to the XRD tests, major clay minerals of marls are Illite, Kaolinite, Montmorillonite and Chloride. Uniaxial compressive strength are 100-250, 300-480 and 500-560 kPa for yellow, green and gray marls, respectively. Consolidation and creep behavior of Baghmisheh marls investigated by using of one dimensional consolidation apparatus under stress level up to 5 MPa. The results indicate that yellow marls have high compressibility, settlement and deformation modules. Green marls have an intermediate compressibility and settlement and while gray marls have low compressibility and settlement and from the foundation point of view have high stability. According to the creep test results, all types of marls have not been entered to progressive creep phase up to pressure 5 MPa.

Geotechnical Assessment of Crushed Shales from Selected Locations in Nigeria as Materials for Landfill Liners

Crushed shales obtained from two locations (Ahoko, Bida basin and Ifon, Dahomey basin) in Nigeria were evaluated to determine their suitability as compacted landfill liners. The shale samples were subjected to X-ray diffraction, hydraulic conductivity, classification, compaction, consolidation and cation exchange capacity tests. The result of the XRD revealed kaolinite and illite as the major clay minerals while quartz was the dominant non-clay minerals. The average CEC of Ifon and Ahoko shales was 5.37 and 8.34 mEq/100 g, respectively. The liquid limit, plastic limit and plasticity index of crushed Ifon shales ranged from (33.9 to 37.4%), (25.2 to 27.2%) and (8.6 to 10.2%) while the Ahoko shales ranged from (44 to 46.4%), (26.3 to 27.4%) and (16.6 to 19.6%), respectively. In addition, the estimated activity of the clay fractions of the two shales ranged from 0.41 to 0.51, suggesting inactive clays. The compacted shales have low compressibility and when compacted at modified Proctor level of compaction. At molding water content between optimum moisture content (OMC) ±2%, the hydraulic conductivities of the compacted shale were in the order of 10−6–10−7 cm/s when compacted at modified Proctor level. At OMC, hydraulic conductivities of the compacted shales were in the order of 10−7 cm/s when exposed to different concentration of calcium chloride solutions. Overall, the crushed shale samples from Ahoko and Ifon generally fulfilled the basic geotechnical properties for compacted clay liners.

Simulation of Sr Transport in Soil Column

In order to predict the dissemination of radioelement in soil, a reactive transport model must be able to simulate contaminant behavior in a complex physico-chemical context. In this study, a multi-site ion exchanger model combined with the classical advection-dispersion equation is successfully applied to predict Sr transport in a soil column. Reactivity is attributed to sorption properties of illite and smectite, major clay minerals present in the studied soil, towards Sr and Ca. Simulations are compared to two experiments performed on a saturated soil column. A good agreement is obtained meaning the dispersivity value adjustment to compensate a delay between simulation and data. This may result from illite and smectite cations exchange constant uncertainties or kinetic process.

A Thermodynamic Analysis on the Effect of Salinity on Interlayer Space of Na-Montmorillonite

ABSTRACTBentonite is used as one of the materials for engineered barrier systems in a radioactive waste repository. Since the major clay mineral constituent of bentonite is montmorillonite, its physico-chemical properties are important. Basal spacing of water-saturated Na-montmorillonite is reported to decrease with increasing Na-montmorillonite density. This paper presents a thermodynamic model to calculate change in the interlayer space of Na-montmorillonite based on the relative partial molar Gibbs free energy (dG) of interlayer water as contacted with a solution of an arbitrary salinity (NaCl concentration). Directly change in montmorillonite density (ρdm) against salinity was calculated by the thermodynamic model. The dG of interlayer water as contacted with a solution of an arbitrary salinity can be calculated by dG = dGH2O+ dGS (dGH2O: relative partial molar Gibbs free energy of interlayer water, dGS: that of water in a solution of an arbitrary salinity). The author previously reported an empirical correlation of dGH2O vs. water content for Na-montmorillonite. The dependence of ρdm on salinity was calculated by replacing dGH2O in the empirical correlation with dG. ρdm increased with salinity. Concretely, initially the ρdm-values of 0.5 and 1.0 Mg/m3 increased to 1.05 and 1.16 Mg/m3 under 0.5 m-NaCl, respectively. Interlayer space vs. salinity was estimated based on the measured results of basal spacing vs. ρdm by XRD and the average density of montmorillonite vs. salinity calculated by this model.

Potassium reserves in soils with arid and semi-arid climate in southern Iran: a perspective based on potassium fixation

ABSTRACT- The present research was conducted to study K forms and fixation in soils of southern Iran (Hormozgan Province) with aridic and aridic-ustic regimes and to address the relations between soil mineralogy and potassium forms. Thirteen surface soil samples (0-25 cm) were collected from different regions and analyzed in laboratory. Illite and feldspar and mica are the major clay and soil minerals for K reservoir, respectively. Mean of non-exchangeable, exchangeable and total content of K were equal to 31.3, 283.9 and 1080.6 mg kg-1 soils, respectively. These forms of K were abundant in plateau and piedmont plain physiographical unites while the greatest amount of soluble potassium was observed in flood and alluvial plain units. Despite the aridity of the region with low clay fraction and unlike the previous studies in calcareous arid soils of Iran, the amount of potassium fixation in soils was high, probably due to the predominance of micaceous minerals. In an adsorption experiment, the average K adsorption in soils was 71 percent after adding 1000 mg K kg-1. In general, the most active component in the K fixation was the silt fraction, dominated mica and illite. Potassium fixation boosted after increasing the wetting and drying cycles in relation to the samples that did not suffer these cycles.

Illitization of Late Devonian-Early Carboniferous K-bentonites from Western Pontides, NW Turkey: Implications for their origin and age

K-bentonite (tephra) layers are exposed as thin beds within Late Devonian-Early Carboniferous carbonates of the Yilanlı formation at four different locations in northwestern, Turkey. Clays separated from K-bentonites in the Gavurpınarı, Yılanlı Burnu (Bartın) and Çimşir Çukurları (Şapça) quarries and the Güdüllü-Gökgöl highway tunnel section near Zonguldak were analyzed by X-ray diffraction, optical, scanning and high-resolution transmission electron microscopy and inductively coupled plasma-mass spectrometry. The clay mineralogy is dominated by illite and mixed-layer illite-smectite (I-Sm) along with subordinate amounts of kaolinite, dolomite, calcite, quartz, feldspar, and gypsum. Morphologically, platy shaped illite is the major clay mineral in the Gavurpınarı and Yılanlı Burnu sites, while sponge-like to platy shaped mixed-layer illite-smectites occur in the Şapca Çimşir Çukurları and Gökgöl sites. Illite Kübler index (KI, Δ°2θ) and polytype data indicate high-grade diagenesis for illite-bearing site, and low-grade diagenesis for I-Sm-bearing sites. Lattice d060 values (Ǻ) of illite and I-Sm reflect a dioctahedral composition, with relatively larger d060 values in the Yılanlı Burnu site, which is related to Mg incorporation into the octahedral layer from dolomitic limestone host-rocksIllites have relatively lower tetrahedral Al substitution and higher octahedral Fe and Mg substitutions compared to those of I-Sm. Illites with phengitic composition occur in the Gavurpınarı and Yılanlı Burnu sites, whereas muscovitic composition at Şapca Çimşir Çukurları site. Chondrite-normalized rare earth element patterns for the Gavurpınarı and Yılanlı Burnu sites exhibit similar trends, with relatively higher values when compared to trends for the Şapça Çimşir Çukurları sites. Oxygen (δ18O) isotope values of illites and I-Sm range from 17.7 to 21.9‰ (V-SMOW), whereas hydrogen (δD) isotope values range widely from −10.1 to −69.9‰ (V-SMOW). The depleted values of δ18O for the Gavurpınarı site imply geologically sudden crystallization under higher temperature conditions. K/Ar ages of different size illite fractions indicate the presence of older detrital illites (2μm) together with younger diagenetic fractions (0.5μm) that correspond with an increase of 2M1 polytype in the coarser fraction. Illitization ages of K-bentonites in the Bartın area indicate an Early Permian event corresponding to the Variscan orogeny, whereas the illitization of K-bentonites in the Zonguldak area is Early Jurassic in age, related to the Cimmerian deformation in the region.

Geological features and geochemical characteristics of Late Devonian–Early Carboniferous K-bentonites from northwestern Turkey

AbstractNewly discovered K-bentonite beds, interstratified with limestones/dolomitic limestones of the Upper Devonian–Lower Carboniferous Yılanlı Formation, are exposed in the northwestern Black Sea region of Turkey, around Zonguldak and Bartın. K-bentonite samples collected from four different locations: the Gavurpınarı and Yılanlı Burnu quarries from the Bartın area, the Çimşir Çukurları quarry from the Şapça area, and the Güdüllü and Gökgöl highway tunnel section near Zonguldak city were investigated using optical microscopy, X-ray diffraction and inductively coupled plasma mass spectrometry in order to reveal their mineralogical and geochemical characteristics and understand their origin and evolution. The K-bentonites occur at different levels in the Yılanlı Formation as 2–40 cm-thick, greenish to yellowish beds cropping out several hundred metres along strike. Preliminary biostratigraphic data suggest that the protoliths of the Bartın (Gavurpınarı and Yılanlı Burnu) and Güdüllü K-bentonites were deposited at around the boundary between the Frasnian and Famennian, whereas those in the Şapça and Gökgöl sections are slightly younger (Devonian–Carboniferous boundary interval). The lithofacies types of the host carbonate rocks suggest an ‘epeiric’ shallow carbonate platform environment. Illite and mixed-layer illite-smectite were the major clay minerals in the K-bentonites. The K-bentonites from the Bartın area display a high degree of illitization and consist mainly of illite indicating high-grade diagenesis, whereas illite-smectite-rich samples from the Şapca and Gökgöl tunnel locations reflect relatively lower diagenetic conditions. According to their geochemical compositions, two groups of K-bentonites were distinguished, one with alkali basalt (Bartın area and Güdüllü locations) and one with trachyte affinities (Gökgöl tunnel and Şapça locations). Geochemical fingerprinting of K-bentonites by trace and rare earth element (REE) data suggest that tephras with alkali basalt composition have been derived by a source formed in a ‘continental back-arc’ setting, whereas the source of K-bentonites with trachytic precursors is related to ‘continental within-plate rifting’. An evaluation of the global Late Devonian and Devonian–Carboniferous volcanism suggests that the bentonite precursors may be related to late-Variscan magmatism in Laurussia.

The Ndop plain clayey materials (Bamenda area – NW Cameroon): Mineralogical, geochemical, physical characteristics and properties of their fired products

The physicochemical, mineralogical and technological properties of clayey materials from the Ndop plain (NW Cameroon) have been investigated, for their ceramic applications. The clayey materials have mixed facies with colour ranging from brown, grey, mottled and yellowish brown. The thickness of the exploitable clay layer is more than 5 m. Their mineralogical constituents are quartz, kaolinite, illite and feldspars, with kaolinite as major clay mineral. Based on the geochemistry, their source rocks might be felsic, with a mafic rock inference. These materials display high percentage in fine particles and high Atterberg limits. For all the firing temperatures, flexural strength (1.2–11 MPa), water absorption (8.03–24.27%), linear shrinkage (2.10%), weight loss (4.88–16.54%) and bulk density (1.57–2.03 g/cm3) indicate good ceramic properties for firing samples between 900 and 1100 °C. Most of the fired test bricks show a brick red colour with good to very good cohesion. The studied clays were thus, suitable as raw materials for roof tiles, light weight blocks and hollow bricks; however, mixing of high clayey and highly silty materials could improve the quality of the products.