Small Amounts Of Illite Research Articles

Late Carboniferous marine-continental transitional sediments in the Datong Basin, North China: Mineralogical and geochemical characteristics and paleoenvironmental significance

To understand the sedimentary paleoenvironmental changes in the marine-terrestrial strata of the Upper Carboniferous Taiyuan Formation in the Datong Basin of North China, we generated mineralogical and geochemical data of the Tashan and Emaokou mines in the eastern Datong Basin. The study strata vertically comprise kaolinitic claystones in the upper and lower parts and calcareous mudstones in the middle. The kaolinitic claystones are primarily composed of kaolinite and quartz, with a small amount of illite, feldspar and siderite, whereas the calcareous mudstones comprise mixed-layer illite/smectite (I/S) clay and carbonate minerals, with a minor amount of quartz, kaolinite, feldspar, and siderite. The paleosalinity indicators (B/Ga, Sr/Ba, and paleontological detritus) indicate that kaolinitic claystones are formed in freshwater, whereas calcareous mudstones are formed in marine water. The redox-sensitive trace element ratios (U/Th and Ni/Co) and trace metal enrichment factors (MoEF and UEF) indicate that kaolinitic claystone and calcareous mudstone formed under oxic and anoxic–suboxic conditions, respectively. Clay assemblages, chemical alteration index (CIA), and the Sr/Cu ratios show that kaolinitic claystones and calcareous mudstones were deposited under hot, humid, intense weathering conditions and warm, humid, and moderately weathering conditions, respectively. Based on these data and combined with previous studies, we conclude that transgressive events caused the changes in sediments in the study area, and the occurrence of transgressive events is related to the global glacio-eustatic fluctuation and paleoclimate changes during the Late Paleozoic Ice Age (LPIA). Our results are essential for unraveling the relationship between the study area and global paleoenvironmental changes during the LPIA.

Geology and exploration indications of the lithocap in Qianpu area, Luzong Basin, Anhui

The lithocap is a large-scale alteration including silicification, advanced argillic and argillic that developed near the surface by hydrothermal activities. It is helpful for exploring high-sulfidation epithermal deposits and porphyry deposits in its root and deep parts, respectively, and is used as a new prospecting indicator. There are many minerals in the lithocap and it is difficult to identify them; alunite is the most representative mineral and one of the new minerals used to guide exploration; it plays an important role in assessing the metallogenic potential and guiding ore prospecting. The Luzong basin is dominated by iron oxide apatite deposits (IOAs). In recent years, many researchers have been searching for porphyry copper–gold deposits and epithermal deposits as studies on alunite and lithocaps in the basin have gradually been undertaken. In field explorations and investigations of the Luzong basin, the author found that in Qianpu area of the central basin, where kaolinite deposits were mainly explored in the past, Well-occurring alunite minerals and advanced argillic alterations have developed. A typical lithocap developed in Qianpu area after a series work of geology and mineralogy, such as alteration mineral species, alteration types, and alteration zoning, which were formed by the hydrothermal alteration of the volcanic rocks of the Zhuanqiao Formation. The minerals in this lithocap are mainly quartz, alunite (including aluminum-phosphate-sulfate, APS), pyrite, zunyite, dickite, pyrophyllite, kaolinite, and a small amount of illite, which are present sequentially from the center to the peripheral quartz-alunite-pyrite alteration, alunite-dickite alteration, dickite-pyrophyllite alteration, alunite-kaolinite-illite alteration, and alunite veins superimposed on quartz-alunite-pyrite alteration and alunite-dickite alteration. Three types of alunite were produced in large quantities and were formed in three kinds of environments. The I-type alunite, which was formed by hydrothermal metasomatism alteration in the early stage and is densely disseminated distribution, coexisting with quartz and pyrite, is a magmatic hydrothermal alunite. Relatively pure alunite veins (II-alunite) of varying thicknesses formed in the open space in the mid-hydrothermal period in a magmatic steam environment. The fine-grained III-alunite that coexists with kaolinite formed in the late hydrothermal period and in a steam-heated environment. The alunite produced by various origins represents multiphase hydrothermal activity in the Yanshanian period in the Qianpu area; the Na content decreased, the K and Pb content increased, and the K/Na molar ratios ranged from 2.82 to 6.58 (EPMA) and 1.59 to 3.93 (LA-ICP MS) from the early to middle and late hydrothermal stages, indicating that the formation temperatures were more than 200 °C and gradually decreased with hydrothermal evolution. There is a high-sulfidation epithermal system in Qianpu area. In combination with the specific environmental significance of zunyite indicating a high temperature and closeness to the fluid channel, as well as the characteristics and genesis of the Huangzhuyuan silver polymetallic deposit near Qianpu, it is inferred that the Qianpu-Huangzhuyuan area has prospecting potential for porphyry-epithermal deposits.

TEKSTUR DAN BAHAN ORGANIK TANAH SERTA HUBUNGANNYA DENGAN BATAS ATTERBERG DAN AKTIVITAS LIAT

Clay minerals are an important indicator of soil plasticity, influencing clay activity. This study aimed to elucidate the effect of clay minerals, organic C and primary minerals on the Atterberg limit and clay activity. The study was conducted in the Kemuning sub-watershed, Jember, East Java. The study began by preparing a thematic map to determine sample points with stratified random sampling. They were taken as many as 35 disturbed soil sample points at 0-20 cm from the surface. Soil texture was determined using the pipette method, and organic C was determined by the spectrophotometer method. The liquid limit and plastic limit were used to determine the plasticity index. A microscopic analysis of sand mineralogy was carried out to compare activity values with a magnification of 20-40 times to assess the primary soil minerals. The results showed that clay and C-organic affect fluidity, plastic limit, and plasticity index. The presence of andesine, albite, olivine, and orthoclase in the sand fraction and the low clay activity indicated that kaolinite dominated the study area, with smaller amounts of illite and halloysite.

Engineering and environmental evaluation of red mud amended volcanic ash as a sustainable subgrade material

With the increasing stockpiles of red mud (RM) and the pollution caused to the environment, there is an urgent requirement to utilize the RM. This research carried out laboratory tests to explore engineering properties and environmental impact of RM-reinforced volcanic ash (VA) as subgrade material. VA is mixed with RM in six proportions (Percentage of RM is 5%, 10%, 15%, 20%, 25%, and 30% by VA weight). According to scanning electron microscope (SEM) images, the RM particles will not only fill the voids among the VA particles, but also fill the pores formed by the broken bubbles in VA particles, which increases the compactness of the specimens. The mixtures contain a small amount of illite, which exhibit the characteristics of non-cohesive soil. The water stability of the specimens is poor, and the strength of specimens diminishes with the increasing water content. When RM content (RMc) does not exceed 15%, the pH values and heavy metal contents of the specimens do not exceed the safety limit values required by the standards. And when RMc is 15%, the specimens obtain the maximum compactness and mechanical strength. Therefore, the optimal amount of RM is about 15%. This study provides a new material selection strategy for road construction in volcanic areas and is the first time to propose the use of RM as an reinforced material for VA. This also enriches the application of RM and solves the problems of resource shortage in volcanic areas, overproduction of RM and environmental pollution caused by storage of RM, which is of great significance for sustainable development and environmental protection.

Provenance and ore-forming process of Permian lithium-rich bauxite in central Yunnan, SW China

Permian lithium-rich karstic bauxites are newly discovered in central Yunnan province, western margin of the South China Block, with a reserve of 16 million tonnes, which has a great potential for aluminum and lithium exploitation. Provenance and ore-forming processes are still debatable. Mineralogical, geochemical, and geochronological analyses were conducted on two typical bauxite profiles to explore the genetic process of the Permian bauxites in central Yunnan province. Profile A contains three layers from bottom to top: clayey bauxite, claystone, pisolitic bauxite. Profile B contains five layers from bottom to top: claystone, pisolitic bauxite, claystone, pisolitic bauxite, and mottled claystone. Pisolitic bauxite mainly consists of diaspore and chamosite, with small amounts of goethite, anatase, and boehmite. Clayey bauxite dominantly consists of boehmite and kaolinite, with small amounts of diaspore and anatase. Claystone predominantly consists of kaolinite or illite. Three stages of bauxite formation are identified: (1) during weathering of regional sedimentary strata, boehmite, kaolinite, and illite were formed; (2) during bauxite deposition, diaspore, chamosite, anatase, pyrite, with small amounts of illite, kaolinite, and barite were formed; (3) during second exposure caused by paleo-uplift, goethite was formed. Correlation analyses demonstrate that kaolinite is the most likely host mineral of Li in the studied bauxites and the leaching process after bauxite deposition can significantly reduce the lithium contents. Two profiles’ differences in sequence can be attributed to their different locations in the paleokarst terrain. Topography of karst terrain controls the ore-forming conditions, thus affecting the sequence and mineralogy of bauxite profiles. In our case, during the bauxite deposition, the uplifted area was not submerged at first, then as the groundwater rose, the uplifted area was immersed. Therefore, the ore-forming conditions in uplifted areas changed from oxidizing to reducing and became more alkaline. In contrast, the karstic depression was submerged throughout the bauxite deposition. All layers in the karstic depression were formed under reducing and alkaline conditions. Data from U-Pb isotope measurements of detrital zircons from bauxites in central Yunnan province provides 3 main ages, which are 500–650 Ma, 800 Ma, and 980 Ma. There are several minor peak ages in the age spectrum, which are 288–310 Ma, 1500 Ma, 1800 Ma, 2000 Ma, and 2500 Ma. Age distribution pattern of bauxites is more similar to that of the Ordovician sedimentary units than other regional rocks in central Yunnan province, which indicates the major contribution of the eroded Ordovician sedimentary rocks to bauxites.

Geochemistry of Carboniferous coals from the Laoyaogou mine, Ningwu coalfield, Shanxi Province, northern China: Emphasis on the enrichment of valuable elements

This paper provides new geochemical data focussing on valuable elements and their origins in the coals from the Laoyaogou mine, Ningwu coalfield, Shanxi Province, northern China. Kaolinite, pyrite, calcite, and boehmite are the main minerals, along with a small amount of illite and anatase, present in the coals studied.The studied coals are enriched with Li, Ga, Zr, Zn, Hf, Sr, Nb, Sn, Th, and REY, especially the case of high average concentration of Li (163.42 μg/g) which is more than ten-times higher than that in world hard coals. Zirconium and Hf, the average concentrations of which are more than five-times higher than those in world hard coals. Lithium, Ga, Zr, Hf, and Th have strong inorganic affinities, whereas Sr and REY have organic affinities. The main carrier of Li in the No. 5 Coal is kaolinite, illite, and boehmite. Gallium, Zr, Hf, and Th probably have the same origin and are largely associated with kaolinite and Ti/Ca-bearing minerals which originate from the source region. In Shanxi Province, the main coalfields are enriched in several valuable elements (e.g. Li, Ga, Zr, Hf, and Th), especially the high average content of Li in the Ningwu coalfield (116 μg/g) and the Qinshui Basin (110 μg/g). The Laoyaogou coals and the coals from the main coalfields in Shanxi Province have economic significance as hidden treasures of the coals themselves and in their by-products.

Study on the sensitivities and damage mechanisms of ultra-low permeability sandstone reservoirs: taking Chang 6 reservoir in Jingbian oilfield as an example

This paper takes the ultra-low permeability sandstone reservoir of Jingbian oilfield in Ordos Basin as the research object, analyzes the petrological characteristics, diagenesis, physical characteristics and pore structure characteristics of the reservoir, and carries out reservoir sensitivity evaluation by using rock casting thin sections, X-ray diffraction, and sensitive flow experiments. The research results show that the ultra-low permeability Chang 6 sandstone reservoir has weak velocity sensitivity, medium-weak water sensitivity, weak salt sensitivity, weak alkali sensitivity and strong acid sensitivity; the damage mechanism of reservoir sensitivity mainly depends on the composition of clay minerals and pore structure after diagenesis. The clay mineral content from high to low is chlorite, illite, a small amount of illite / smectite layer, and kaolinite, of which the chlorite content is as high as 75 %; the reservoir has poor physical properties, the types of small hole-thin throat and small hole-fine throat. The reservoir is prone to blockage such as bridge plugging. Therefore, ultra-low permeability sandstone reservoirs are prone to different degrees of sensitivity. The reservoir characteristics are consistent with the reservoir sensitivity evaluation results.

Geology, Mineralogy, Geochemistry, and Genesis of Bentonite Deposits in Miocene Volcano–Sedimentary Units of the Balikesir Region, Western Anatolia, Turkey

AbstractThe widespread Balıkesir bentonite deposits within the Miocene volcano-sedimentary units in western Anatolia have economic potential; they are important raw materials for the paper and bleaching industries in Turkey. No detailed geological, mineralogical, geochemical, or genesis characterizations of these bentonite deposits have been carried out to date. The present study was undertaken to close this gap. The mineralogical characteristics of the bentonites and their parent rocks were examined using polarized-light microscopy, X-ray powder diffractometry (XRD), scanning- and transmission-electron microscopies (SEM–EDX and TEM), and chemical (ICP–AES and –MS) methods. In the bentonite deposits, smectite is associated with smaller amounts of illite, chlorite, quartz, feldspar, dolomite, calcite, opal-CT, and amphibole. The smectite was identified by sharp basal reflections at 14.42–14.93 Å. Plagioclase and sanidine crystals in volcanic units are altered and sericitized. Biotite and hornblende are partly to completely Fe-(oxyhydr)oxidized and chloritized. Smectite flakes occur on altered feldspar and mica grains and devitrified volcanic glass fragments in association with or without calcite ± dolomite crystals. Increasing Al+Fe+Mg/Si ratios with increasing degree of alteration reveal that hydration of volcanogenic grains (feldspar, mica, hornblende, glass shard) favored precipitation of smectite with montmorillonite composition, with an average structural formula: (Ca0.31Na0.05K0.08)(Al2.72Fe0.17Mg1.27Ti0.011Mn0.01)(Si7.94Al0.06)O20(OH)4. The concentration of Al2O3 and MgO and increase of LREE/HREE ratio, and a distinct, negative Eu anomaly show that smectite was probably formed as a result of the decomposition of volcanic feldspar, mica, amphibole, and volcanic glass. Association of carbonate rocks within the smectite-rich material and the absence of chlorite and detrital materials such as rock fragments in the bentonites suggest that the bentonite deposits formed authigenetically as ‘primary bentonites’ from volcanoclastic materials deposited in a calm lacustrine–palustrine environment during an early diagenetic process.

Clay mineral assemblages in the Zhaotong Basin of southwestern China: Implications for the late Miocene and Pliocene evolution of the South Asian monsoon

The characteristics of the evolution of the South Asian monsoon during the late Miocene through the Pliocene are highly debated. To obtain a better understanding, we studied the clay mineral assemblages and the clay fraction content of a high-quality sedimentary sequence (borehole core ZK1) spanning the interval of 8.8–2.62 Ma in the Zhaotong Basin, southwestern Yunnan Province, on the southeastern margin of the Tibetan Plateau. Smectite, kaolinite, illite and vermiculite were the four main clay minerals identified, and changes in their relative abundance reveal a distinct pattern of climate change during the study interval. Until the very late Miocene kaolinite and smectite, with a small amount of illite, were dominant, suggesting a relatively warm and humid climate; from ~6.2 to ~2.8 Ma smectite was dominant, with a minor amount of kaolinite and illite, indicating a relatively cool and humid climate; and from ~2.8 to 2.62 Ma vermiculite (HIV) and illite were dominant, with a minor amount of kaolinite, indicating a relatively cold and humid climate. The variation in clay mineral assemblages indicate substantial changes in the South Asian monsoon in the Zhaotong Basin that promoted a change from a warm and humid climate in the late Micoene to cool and humid climate in the very late Miocene through Pliocene, followed by a gradual trend towards a cold and humid climate in the very late Pliocene. Comparison with records from elsewhere indicates that the observed variations in the South Asian monsoon were mainly controlled by global cooling rather than by Tibetan Plateau uplift.

Mineral carbonation of ceramic brick at low pressure and room temperature. A simulation study for a superficial CO2 store using a common clay as sealing material

Abstract This research explores the possibilities of CO2 sequestration on ceramic bricks in a short time and at surface conditions. The experiment was carried out in a specially designed reaction chamber, filled with brick wastes and sealed with common clays. The brick used were composed of quartz, wollastonite, diopside, orthoclase and anhydrite, and the common clay was a marl composed of calcite, quartz, illite, smectite and kaolinite. Experimental condition in the reaction chamber were: reaction time 5 months, pressure of CO2 0.5 bar, 4:1 solid/water ratio. The experiment was followed by XRD, XRF, BET, physical sorption by N2 and CO2, Hg porosity, TG-DTA, SEM and ICP-EOS. After the CO2 treatment, wollastonite and anhydrite were practically destroyed and some diopside and orthoclase. Calcite precipitated as new phase (up to 48 wt%), and small amount of illite was the result of orthoclase alteration. Concerning the sealing clay, the CO2 produced an increment of calcite content (from 32 to 41 wt%) and a partial destruction of smectite, particularly close to the upper part of the brick layer. These results are hopeful in relation with the possible mineral carbonation of building ceramic waste in a short time at surface conditions, and open the opportunity to use those wastes for CO2 trapping in an appropriate system, as a quarry reclamation.

CHEMICAL AND MINERALOGICAL PROPERTIES OF ULTISOLS OF SASAMBA AREA, EAST KALIMANTAN

Ultisols are a major group of marginal soils extensively found in the upland area of Indonesia. To better understand the potential of the Ultisols developed from claystone and sandstone in the Sasamba Integrated Economical Development Area in East Kalimantan, chemical and mineralogical characteristics of 27 Ultisols pedons consisting of 76 topsoil and 118 subsoil samples were investigated. Besides analysis and interpretation of data, relationships of several soil characteristics were constructed using simple regression. The results indicated that Ultisols showed acid to very acid reaction, had low content of organic matter and low base saturation. Soils generally exhibited net negative charge, and the point of zero charge was reached at pH 3.6. Both potential and available phosphates were low, and there was a trend that amorphous aluminum was responsible for phosphate fixation. The low content of exchangeable potassium in topsoil and subsoil indicated a positive correlation with potential potassium. Clay mineral was composed chiefly of kaolinite, with small amounts of illite, vermiculite, and quartz. The domination of kaolinite and low organic matter content causes the soils to have low cation exchange capacity. Soil management in this area should be focused on building up and maintaining soil fertility, and applying appropriate soil conservation techniques to minimize erosion. To obtain sustained productivity, various soil amendments including the use of farm and/or green manure, liming with agricultural lime, and application of rock phosphate and K fertilizers were highly recommended.

CHEMICAL AND MINERALOGICAL PROPERTIES OF ULTISOLS OF SASAMBA AREA, EAST KALIMANTAN

Ultisols are a major group of marginal soils extensively found in the upland area of Indonesia. To better understand the potential of the Ultisols developed from claystone and sandstone in the Sasamba Integrated Economical Development Area in East Kalimantan, chemical and mineralogical characteristics of 27 Ultisols pedons consisting of 76 topsoil and 118 subsoil samples were investigated. Besides analysis and interpretation of data, relationships of several soil characteristics were constructed using simple regression. The results indicated that Ultisols showed acid to very acid reaction, had low content of organic matter and low base saturation. Soils generally exhibited net negative charge, and the point of zero charge was reached at pH 3.6. Both potential and available phosphates were low, and there was a trend that amorphous aluminum was responsible for phosphate fixation. The low content of exchangeable potassium in topsoil and subsoil indicated a positive correlation with potential potassium. Clay mineral was composed chiefly of kaolinite, with small amounts of illite, vermiculite, and quartz. The domination of kaolinite and low organic matter content causes the soils to have low cation exchange capacity. Soil management in this area should be focused on building up and maintaining soil fertility, and applying appropriate soil conservation techniques to minimize erosion. To obtain sustained productivity, various soil amendments including the use of farm and/or green manure, liming with agricultural lime, and application of rock phosphate and K fertilizers were highly recommended.

The forms and availability to plants of soil potassium as related to mineralogy for upland Oxisols and Ultisols from Thailand

Potassium (K) deficiency is widespread in crops on highly weathered upland soils under a tropical monsoonal climate. Critical assessment of the forms of K in soils and of the ability of soils to release K for plant uptake is important for the proper management of K in crop production. The relationships between different pools of K were investigated as a function of silt and clay mineralogy for 14 upland Oxisols and 26 upland Ultisols soils from Thailand. Most soils contained no K-minerals in the silt fraction. XRD showed that kaolinite is the dominant clay mineral with variously minor or moderate amounts of illite, hydroxy-Al interlayered vermiculite and smectite present in some soils. For some soils, both conventional and synchrotron XRD were unable to detect illite. Analytical TEM including EFTEM of individual clay crystals showed that clay in the apparently illite-free samples contained very small amounts of illite. Many kaolinite particles appear to contain K which may be present in illite interleaved with kaolinite crystals. A glasshouse K-depletion experiment was conducted to assess the K supply capacity and changes in chemical forms of K and K-minerals using exhaustive K depletion by Guinea grass (Panicum maximum). Potassium deficiency symptoms and mortality of plants occurred on light textured soils, whereas plants survived for six harvests for Oxisols with clay texture, relatively high CEC and higher NH4OAc-K (exchangeable K plus water-soluble K). There is a strong linear relationship of unit slope between NH4OAc-K and cumulative K uptake by plants indicating that NH4OAc-K is a major form of K available to plants. Thus K-bearing minerals contributed little K to plants over the time scale of the experiment and XRD patterns of whole soil samples, silt and clay from soils after cropping mostly showed no change from those for the initial soil. An exception was for a single surface soil clay where a minor amount of smectite was formed from illite by K release to plants.

The kinetics of potassium release to sodium tetraphenylboron solution from the clay fraction of highly weathered soils

Thirty six soil clay samples from surface and subsurface horizons of 18 Thai upland Oxisols and Ultisols under a tropical monsoonal environment were characterized for chemical composition, mineralogy and K release to 0.3 M sodium tetraphenylboron (NaTPB) solution for periods up to 168 h. The clay fraction was dominated by kaolinite with various amounts of accessory minerals and analytical TEM showed that most clays contained small amounts of illite. The amounts of K released to the NaTPB solution from illite-containing clays were higher than from clays containing kaolinite and inhibited vermiculite with no detectable illite. Potassium release kinetics for all samples are adequately described by the parabolic diffusion (r = 0.91–0.99), power function (r = 0.87–0.99) and Elovich equations (r = 0.86–0.99). The intercept constants of the equations are strongly positively related to the ratio of illite to kaolinite and total K and Mg contents of the clays. These relationships indicate that minor amounts of illite in these clays strongly affect the kinetics of K release. The slope constants of the parabolic and Elovich equations are also positively related to these clay properties. Some kaolinite particles contained K which may be present in residual micaceous layers interleaved in kaolinite crystals. XRD patterns from samples extracted with NaTPB show a decrease in illite peak intensity with a concomitant increase in vermiculite peak intensity due to K removal from illite by NaTPB.

Sodic metasomatism in a dacite weathering profile in Pinxiang, Guangxi, China

The Pinxiang weathering profile is well developed on Early Triassic dacite lavas of the Baisi Formation. At the top of the profile is developed a red clay zone which is characterized mineralogically by kaolinite, iron oxide minerals, quartz, and a small amount of illite, montmorillonite and vermiculite. In going downwards the red clay zone gives way to a saprolite zone in which plagioclase pseudomorphs have been well preserved although replaced by kaolinite. Beneath the saprolite zone is the saprock zone characterized by less weathering for dacite. At the bottom of the weathering profile is the parent material, dacite, which is composed mainly of plagioclase, quartz, K-feldspar and biotite which have been largely altered into chlorite owing to submarine extrusion of dacite lavas. Some layers in the weathering profile show obvious sodium enrichment and potassium depletion relative to others. In the Al2O3-(CaO*+Na2O)-K2O triangular diagram, the weathering trends of these layers in the middle stage are remarkably deviated from normal ones. Both mineralogy and micro-morphology of these layers indicate such deviation resulted from sodic metasomatism of orthoclase.

Alteration of Volcanic Rocks and Genesis of Kaolin Deposits in the Şile Region, Northern Istanbul, Turkey. I: Clay mineralogy

AbstractThe Şile Region contains discontinuous, cyclic, thin coal beds and industrial clay deposits that were accumulated in lacustrine basins which received extensive volcanoclastic sediments due to transport of highly weathered calc-alkaline volcanic rocks. The Sülüklü area has the largest kaolin deposit in this region. Cyclic kaolinization depended on the degree of leaching of Si and alkalis in cyclic swamp environments and, therefore, kaolinite contents vary in each discontinuous lens-shaped clay bed and underclay within the basin. The kaolins comprise disordered kaolinite, illite, smectite, gibbsite, quartz, pyrite, anatase, K-feldspar and goethite. Depth-related changes in the distribution of clay minerals, associated with coal beds, are indicative of organic acid-mineral reactions. Kaolinite crystallization initiated at the edges of sericitic mica sheets in the form of composite kaolinite stacks. The small size (<1 µm), morphology and poor crystallinity of kaolinite crystals suggest that kaolinization post dated transportation. Primary or secondary origins of particles can be determined from the stacking sequences of kaolinite particles using high-resolution transmission electron microscopy images. Kaolinite stacks always contain a small amount of illite, but smectite is only present in the middle and upper levels. Gibbsite is a main constituent of refractory bauxitic clays locally found as discontinuous lenses and exploited from the lower level of the basin.Genesis of kaolin deposits took place in two stages: first, there was in situ weathering of the oldest andesitic agglomerates, tuffs and ashes at the base of the lacustrine basin coupled with discharge of shallow thermal waters which were initiated by local hydrothermal alteration; second, surface weathering enhanced transportation of altered rocks from the surrounding hills into the lacustrine basin. Kaolinization took place in cyclic swamp environments, as indicated by the presence of cyclic thin- to thick-bedded coals that provided necessary humic and fulvic acids for the post-depositional alteration of altered volcanic rocks to kaolin in dysaerobic, relatively low-pH conditions in saturated groundwater zones.

The Kinetics of the Smectite to Illite Transformation in Cretaceous Bentonites, Cerro Negro, New Mexico

AbstractThe thermal effects, as well as the survivability and origins of microorganisms in Cretaceous rocks, are evaluated from the timing and extent of the smectite to illite transformation in Cretaceous bentonites collected from cores outside the thermal aureole of the Pliocene Cerro Negro volcanic neck. Overall, randomly ordered mixed-layered illite-smectite (I-S) is the predominant clay mineral in these bentonites, and the K-Ar ages of I-S range from 36 to 48 Ma (21 analyses, two additional analyses were outside this range). Increased temperature from burial is thought to be the primary factor forming I-S in these bentonites. Kinetic model calculations of the smectite to illite transformation are also consistent with I-S formed by burial without any appreciable thermal effects due to the emplacement of Cerro Negro. In a core angled toward Cerro Negro, the percentages of illite layers in I-S from the bentonite closest to Cerro Negro are slightly higher (32-37%) than in most other bentonites in this study. The K-Ar ages of the closest I-S are slightly younger as a group (38-43 Ma; Average = 41 Ma; N = 4) than those of I-S further from Cerro Negro in the same core (41-48 Ma; Average = 44 Ma; N = 6). A small amount of illite in this I-S may have formed by heat from the emplacement of Cerro Negro, but most illite formed from burial. Vitrinite reflectance, however, appears to record the effects of heating from Cerro Negro better than I-S. Tentatively, the temperature of this heat pulse, based on vitrinite data alone, ranged from 100 to 125°C and this is most evident in the CNAR core. The upper temperature, 125°C, approximates the sterilization temperatures for most microorganisms, and these temperatures probably reduced a significant portion of the microbial population. Thermophiles may have survived the increased temperatures from the combined effects of burial and the intrusion of Cerro Negro.

Cs adsorption on the clay-sized fraction of various soils: effect of organic matter destruction and charge compensating cation

The association of organic matter with clay minerals may decrease their affinity for Cs and thus enhance its bioavailability. We have investigated this hypothesis by comparing Cs adsorption on several soils, both topsoils and the corresponding subsoils, before and after organic matter destruction with H 2O 2. The clay-sized fractions were homoionic in either K, Na or Ca, to avoid artefacts due to variable composition of the exchange complex. All experiments were carried out in dilute suspension under controlled conditions. The affinity of the clay-sized fractions for Cs and the value of the Freundlich b parameter are typical of illites. This supports the hypothesis that the adsorption properties of soils are dominated by small amounts of illite. However, if this is the case, the affinity of soil illites is higher than that of reference illites. The destruction of organic matter has a variable effect. In some cases, a marked enhancement is observed, in others there is no significant effect, or a small decrease. There is no clear pattern relating the effect of organic matter destruction and either dominant clay mineralogy or organic matter content.

Electron microscopic study of the illite–smectite transformation in the bentonites from Cerro del Aguila (Toledo, Spain)

AbstractA mineralogical and microstructural study of bentonites from 'Cerro del Aguila' located in the Tagus Basin (Toledo, Spain) was carried out using XRD, SEM and TEM observations and chemical data obtained by TEM-EDX. The bentonites are mainly composed of trioctahedral smectite with a unit-cell formula (Si3.76Al0.24)(Al0.44Fe3+0.26Mg1.81)Ca0.05K0.19O10(OH)2 and small amounts of illite. The relationships between illite and smectite particles observed by SEM and TEM allowed the study of the weathering process of illite to form smectite through possible intermediate stages. The transformation begins as an exfoliation normal to the stacking direction and develops by opening of the interlayer spacing, the replacement of K+ by hydrated interlayer cations and slight reorganization of the 2:1 layer structure. The so-called solid-state transformation process then proceeds by further dissolution and the formation of a colloidal phase acting as raw material in the growth of new phyllosilicates such as smectite.

Electron Microscopic Study of the Illite-Smectite Transformation in the Bentonites from Cerro Del Aguila (Toledo, Spain)

A mineralogical and microstructural study of bentonites from ‘Cerro del Aguila’ located in the Tagus Basin (Toledo, Spain) was carried out using XRD, SEM and TEM observations and chemical data obtained by TEM-EDX. The bentonites are mainly composed of trioctahedral smectite with a unit-cell formula (Si3.76Al0.24)(Al0.44Fe3+ 0.26Mg1.81)Ca0.05K0.19O10(OH)2 and small amounts of illite. The relationships between illite and smectite particles observed by SEM and TEM allowed the study of the weathering process of illite to form smectite through possible intermediate stages. The transformation begins as an exfoliation normal to the stacking direction and develops by opening of the interlayer spacing, the replacement of K+ by hydrated interlayer cations and slight reorganization of the 2:1 layer structure. The so-called solid-state transformation process then proceeds by further dissolution and the formation of a colloidal phase acting as raw material in the growth of new phyllosilicates such as smectite.