Illite-smectite Mixed-layer Minerals Research Articles

Research status and prospects on overall mineral use of mixed-dimensional attapulgite clay

<p indent="0mm">In recent years, the high-efficiency and high-value development and use of mixed-dimensional clay minerals with large natural reserves have attracted great attention with the over-exploitation and rapid consumption of high-quality clay mineral resources. The reserves of mixed-dimensional attapulgite clay ore in China exceed 1 billion tons. Their main mineral component is attapulgite, but they also contain illite, chlorite, kaolinite, illite-smectite mixed-layer minerals, and other minerals. At the same time, the phenomenon of isomorphic substitution is common, and part of the octahedral sheet may be replaced by Al³⁺, Fe³⁺, and other metal ions; therefore, the mixed-dimensional attapulgite clays are mostly brick-red, gray, or khaki. The relative complexity of associated minerals and darker color restrict the large-scale development of the industry. Scientific and technological innovation to realize the “best use” of mixed-dimensional clay mineral resources to develop high-value-added products will be the most important development trend in the future. However, basic theoretical research on the high-value application of mixed-dimensional clay minerals is lacking, so new ideas, approaches, and methods are urgently needed to solve the difficulties and sore points of industrial development. On the basis of a deep understanding of the microstructure of clay minerals, progress has been made in using the total mineral resources of mixed-dimensional attapulgite clay, which has preliminarily formed a comprehensive utilization system of “simultaneous transformation of associated minerals—acid leaching for whitening—functional material construction—recovery of acid leaching metal ions—clay mineral biochar—create red pigments based on the red appearance—quartz sand utilization”. Specifically, using mixed-dimensional attapulgite clay to construct various porous silicate materials by structural reorganization; developing a series of methods, including wet, semi-dry, and microwave techniques, to achieve efficient whitening-variegated mixed-dimensional attapulgite clays without damaging the aspect ratio of attapulgite nanorods and the properties of other associated minerals; using the whitened mixed-dimensional attapulgite clays containing one-dimensional fibrous attapulgite and two-dimensional layered clay minerals to construct nanocomposites, such as films and plastics, showing the advantages of mixed-dimensional attapulgite clays in improving mechanical properties and realizing the high value of associated minerals; recovering iron, aluminum, magnesium, and other metal ions from the wastewater of acid leaching attapulgite clay to synthesize layered double hydroxide materials to adsorb dyes, antibiotics, and other organic matter, then producing mineral biochar materials by anaerobic calcination for heavy metal-contaminated soil remediation; using the iron-rich properties of mixed-dimensional attapulgite clays to construct nanohybrid iron-red mineral pigments, which significantly improve the weather resistance of iron-red pigments; and employing quartz sand obtained by dry separation from clay minerals to construct cobalt-blue hybrid pigments via mechanochemical method. The long-term practice has shown that whitening is the premise for the high-value use of mixed-dimensional attapulgite clays, and overall mineral use is the key to industrial development. Therefore, an effective way to simultaneously transform associated clay minerals into attapulgite or other single minerals should be further explored. The structural regulation and transformation mechanism of mixed-dimensional attapulgite clays should be clarified to open a new approach for the functional application of mixed-dimensional attapulgite clays. In addition, on the basis of the acid leaching for whitening, the differences and complementarities of one-dimensional rod crystals and two-dimensional layered structures in constructing functional composite materials must be systematically studied, and the foundation for mixed-dimensional nanorod crystal/layered structures in functional materials must be laid, finally providing a feasible and reliable approach for the comprehensive use of mixed-dimensional attapulgite clay resources.

A baseline study of mineralogical and morphological properties of different size fractions of illite du Puy

The objective of this study is to revisit the mineralogical and physico-chemical properties of illite du Puy material (Puy-en-Velay, France), which is envisaged as a model clay system in the European Joint Programme on Radioactive Waste Management (EURAD) project. This illite material is compared to the raw illite material commonly extracted from the Velay ore site. Both materials were collected and separated into different subfractions (i.e., <0.05, 0.05–0.1, 0.1–0.2, and 0.2–2 μm) to examine the mineralogical heterogeneity. The X-ray diffraction bulk analyses indicated that the observed variability in the literature, in terms of the nature of accessory minerals and the presence of kaolinite, was directly related to the locations of geological sampling. Moreover, the respective mass contributions of the different subfractions were similar for the two materials.Further analyses were performed on the subfractions of the illite used for the EURAD project by utilizing a suite of different techniques. The clay mineralogy was refined as an illite–smectite mixed-layer mineral with a small amount (<5%) of smectite layers. No significant changes in chemical properties or particle lamellarity were observed between the different subfractions. However, the different subfractions displayed a wide range of specific surface areas (i.e., N2 BET surface) and cation exchange capacity values, the latter of which increased by factors of ~3 and ~ 5 from the 0.2–2 μm to the <0.05 μm size fractions, respectively. The EURAD illite and associated subfractions can be considered appropriate material models to be used for the refinement of our understanding of the adsorption and diffusion processes of solutes in porous media made from charged clay particles.

Base metal mobility linked to brine and hydrocarbon migration at the Huincul High in the Neuquén Basin, Argentina: Implications for the formation of sediment-hosted base metal deposits

This contribution discusses the discovery of PbZn mineralization in hydrocarbon exploration drill holes hosted in siliciclastic Jurassic rocks below the Cretaceous sediment hosted Cu mineralization located north of the Huincul High. In the Early Cretaceous, hydrocarbon and basinal water expulsion took place from the oil source rocks (Los Molles Formation) into the reservoir rocks Lajas Formation (Middle Jurassic), after the formation of diagenetic quartz overgrowths. Marcasite, pyrite and illite + illite-smectite mixed layer minerals then formed together with hydrocarbons. Marcasite (δ34S −3.5 and −2.2‰) and pyrite (δ34S −11.6 to 18.1‰) precipitated via bacterial sulfate reduction from fluids showing temperatures <80 °C and fluctuating pH conditions. During the Paleogene, Andean tectonism triggered migration of oxidized basinal brine containing dissolved leached Zn and Pb from the Los Molles Formation source rocks and S from the evaporites of the basin. This brine entered in the hydrocarbon reservoir of the Lajas Formation, resulting in the precipitation of sphalerite (δ34S +10.4 to +10.8‰) and galena (δ34S +5.2‰) by TSR at temperatures of 119–123 °C together with siderite. The Andean orogeny may also have triggered the migration of hydrocarbons + brines from the shallowest source rocks (Vaca Muerta Formation) and reservoir rocks (Mulichinco, Lajas and Lotena formations) into the red beds of the upper Cretaceous Neuquén Group, which became bleached as a result. Marcasite (δ34S −36.4 to 18.2‰) and pyrite (δ34S −60.2 to −24‰) precipitated by BSR, while calcite (δ13C −12.3 to −5.6‰) formed due to redox reactions accompanying formation of quartz overgrowths, clay mineral coatings (δD −92.4‰ to −82.8‰ and δ18O 16.2‰ to 18.40‰), and barite (δ34S −5.9‰). Quartz overgrowths and barite precipitated from brines (1.5–10 wt% NaCl equiv.) at temperatures of 91–120 °C, with barite precipitating close to the feeder zones. Calcite cements are more widespread and generated from several pulses of brine and hydrocarbons up flow, evidenced by the wide range of homogenization temperatures (100–185 °C) and diversity of UV fluorescence colors of hydrocarbon-rich fluid inclusions. In subsequent Miocene tectonic events, basinal brines were able to leach Cu from the underlying thick red beds of the basin, entering the Neuquén Group oil reservoir traps or carrier beds where they became reduced. Chalcopyrite and bornite precipitated at temperatures >100 °C close to the feeder zones at the expense of barite as a local sulfur source. Chalcocite group minerals (δ34S −21.3‰ to −7.3‰) precipitated outwards in pore spaces of the sandstones at lower temperatures (<100 °C) through BSR of sulfate in the mineralizing brines. Final exhumation of the Neuquén Group (Upper Miocene-Pliocene) promoted the infiltration of the meteoric water, the oxidation of the sulfides and formation of supergene FeCu, V and U minerals. Isotope geochemistry and fluid inclusion results combined with alteration and ore mineralogy document the processes controlling the distribution of base metals in the Huincul High region that can be applied to evaluate the metal potential in other areas of the Neuquén Basin and further extrapolated to similar geological systems elsewhere.

The pores evolution of lacustrine shale induced by smectite-to-illite conversion and hydrocarbon generation: upper Triassic Yanchang Formation, Ordos Basin, China

The lacustrine shales (e.g. shales deposited in the lake) are important commercial production targets for the oil and gas industrial. The pore network of shales has a significant effect on the occurrence state of natural gas&oil and reserve calculation. The exploration practice has indicated that the pore network of lacustrine shale is very different from that of marine shale. Although many researches have proposed that the pore network of lacustrine shales is influenced by clay minerals, however, the origin, evolution and preservation of pores in the lacustrine shales are still obscure. This study aims to reveal the effect of synchronous hydrocarbon generation and smectite-illite conversion on the formation and evolution of pores in lacustrine shales from the Chang #7 (C7) Member of the Upper Triassic Yanchang Formation in Ordos Basin, China. The middle and lower part of C7 Member is known as the “Zhangjiatan” shale, which is focused by oil shale exploration recently in China. The combination of analytical techniques was used to investigate the pore evolution related to clay minerals. The clay minerals within shales from the C7 Member consist of illite-smectite mixed layer minerals, illite, kaolinite and chlorite, accounting for 25.9–59.1% of the whole rock. There is a positive relationship between density functional theory (DFT) pore volumes and the content of clay minerals. DFT method is appropriate for all types of the pore, especially micropores. The mesopores (2–50 nm) dominated in the shale samples, while the organic matter only hosted a small amount of micropores (<2 nm). In the study, it's shown that the development of mesopores is controlled by the smectite-illite conversion. The mesopores volume and surface areas will decrease with the smectite layers converting into illite. However, the marcopores (>50 nm) can increase with the formation of illite layers, caused by the minerals volume shrinks and overpressure. The smectite-to-illite conversion is favorable for the pore network under the moderate thermal maturity. The synchronous smectite-to-illite conversion and hydrocarbon generation is a critical mechanism for the formation and preservation of pores in the lacustrine shale.

Glucose-stimulation of natural microbial activity changes composition, structure and engineering properties of sandy and loamy soils

High inputs of easily available organic matter to the subsurface may quickly activate the native microbial communities, thereby changing soil engineering properties. We studied the effect of glucose addition, an easily available carbon source, on stress-strain properties, mineralogy, and microstructure of several loamy and sandy soils over 30 days in laboratory experiments. During the period of high microbial activity, direct shear tests revealed a reduction of the friction angle of 15–30 % and a raise of cohesion in sands. Unconfined compression tests showed a 20–30 % decrease in the compressive strength of loamy soils. With the decline of microbial activity, the stress-strain properties recovered partially. The alterations of the stress-strain properties with increasing microbial activity were linked to changes in mineralogy and composition. X-ray diffraction showed that the proportion of smectite layers in illite-smectite mixed layer minerals increased, as well as the overall imperfection of clay minerals. Glucose addition resulted in a temporary increase in the content of microaggregates (0.1-0.05 mm). Newly formed linkages of organic matter between solid particles, biofilm formation and direct interaction of cells with mineral surfaces were observed by scanning electron microscopy. Our data show that microbial-mediated processes may adversely influence stress-strain properties of soils and endanger the safety of buildings.

Pore connectivity and water accessibility in Upper Permian transitional shales, southern China

Abstract Pore connectivity of shale controls shale gas migration and production behavior. The pore connectivity and water accessibility in clay-rich Upper Permian transitional shales remain unclear. Contrast matching small-angle neutron scattering (CM-SANS) tests were used to determine the accessibility of water to pores in the transitional shales. Complementary analyses with SANS, gas (CO2 and N2) physisorption isotherm, mercury intrusion capillary pressure (MICP), helium ion microscopy (HIM), as well as field emission-scanning electron microscopy (FE-SEM) were conducted to study the pore connectivity and distribution characteristics of closed pores. The results show that closed pores (inaccessible to nitrogen molecules and mercury) are mainly distributed in pore diameters ＜10 nm and associated with organic pores and interlayer spaces of illite-smectite mixed-layer mineral. The pore volume values obtained from MICP and N2 adsorption underestimate the large pores (pore diameters ＞100 nm) in shales. Based on deuterated water CM-SANS tests, 87–98% of the pores (2–200 nm diameters) are water-connected in transitional samples. The low accessibility to water is at pore-sizes of 5–10 nm and 20–30 nm. Results from in-situ gas contents show that closed pores have a certain gas bearing capacity, but micropores (pore diameters ＜2 nm) control the gas occurrence in transitional samples. The connectivity of the organic pore network and between organic pores and surrounding interparticle pores is directly supported by FE-SEM and HIM imaging. Overall, improving pore-fracture connectivity through effective fracturing techniques is a means of mitigating the rapid decline in shale gas production.

Dissolution Kinetics of Iron Carbonate, Illite and Labradorite – CO2-Saline Fluid-mineral Experiments within the GaMin’11 Inter-laboratory Comparison Exercise

Abstract Experiments to investigate individual CO2-brine-mineral interactions were designed to provide dissolution kinetics for rock-forming minerals. Separates of an iron carbonate, a clay mineral and a feldspar mineral were stored in flexible Titanium Grade-2 cells together with 2 M NaCl brine and pure CO 2 at 80 °C and 20 (30) MPa for one (iron carbonate), two (clay) and three (feldspar) weeks, respectively. The carbonate separate consists of 96.3±3.2 wt% iron carbonate and 3.7±0.8 wt% quartz with the iron carbonate phase being composed of 72.3±1.4 wt% siderite and 27.7±1.2 wt% ankerite. During the experiments, siderite abundance increased to 83.3±1.5 wt%, while that of ankerite decreased to 16.7±1.4 wt%. The average empirical formula of untreated and treated siderite is Fe0.8Mg0.1Mn0.1CO3, that of untreated ankerite changed slightly from (Ca1.0Mg0.2Mn0.1Fe0.7)(CO3)2 to (Ca0.9Mg0.3Mn0.1Fe0.7)(CO3)2 during CO 2 exposure. Fluid data obtained during these experiments show similar behavior for Ca2+ and Mg2+, as well as Fe2+ and Mn2+, respectively. The clay separate initially consists of 84.2±6.9 wt% illite, 11.9±0.4 wt% orthoclase and 3.9±0.2 wt% quartz with untreated illite actually being an illite-smectite mixed-layer mineral composed of 87.2±1.5 wt% illite and 12.8±1.5 wt% Ca-smectite. During the experiments using the clay separate it was found that the composition changed to 88.3±7.8 wt% illite, 9.2±0.5 wt% orthoclase, and 2.5±0.2 wt% quartz, with CO2-treated illite now consisting of 89.0±1.7 wt% illite and 10.5±1.6 wt% Ca-smectite. Fluid data show, besides others, increase Ca2+ concentrations over time. Analyses of the feldspar separate reveal pure labradorite with a stoichiometric composition of Na0.5-0.6Ca0.4-0.5Al1.3-1.6Si2.4-2.6O8. During labradorite exposure experiments cation brine concentrations (e.g. Ca2+, Ba2+ and Al3+) increased. Based on the acquired geochemical data sets, the experiments using individual mineral separates indicate (i) dissolution of ankerite and stable siderite, (ii) preferred dissolution of the Ca-smectite component out of the illite-smectite mixed-layer mineral, and (iii) dissolution of labradorite.

Mineral Solubilities in CO2-Saturated NaCl Brine Systems

Experiments on CO2-brine-mineral interactions were designed to provide kinetic data for individual rock-forming minerals. Samples of an illite-smectite mixed layer mineral and a labradorite separate were stored in flexible Ti-cells together with 2M NaCl brine and pure CO2 at 80°C and 20MPa for two and three weeks, respectively. The empirical formulae K0.5-0.7(Mg0.1-0.2Al1.8-1.9)(Al0.4-0.6Si3.4-3.6)O10(OH)2 and Na0.5-0.6Ca0.4-0.5Al1.3-1.6Si2.4-2.6O8 were calculated for illite and labradorite. X-ray diffraction data with Rietveld refinements reveal a pure labradorite separate. The illite separate is composed of 73.5±1.3 wt% illite, 10.8±1.3 wt% Ca-smectite, 11.9±0.4 wt% orthoclase, and 3.9±0.2 wt% quartz. Based on the acquired geochemical data, the experiments on monomineralic separates indicate (i) preferred dissolution of the Ca-smectite component out of the illite-smectite mixed layer mineral, and (ii) dissolution of labradorite.

국내 석유자원탐사 퇴적분자의 광물온도

우리나라 육상의 제3기 포항분지와 백악기 경상분지, 그리고 동해와 서해의 대륙붕 퇴적분지에 대하여 일라이트-스멕타이트 점토광물 변화에 의하여 퇴적층 온도를 인지하고, 이를 근거로 하여 석유생성과의 관련성을 연구하였다. 포항분지는 불규칙배열의 일라이트-스멕타이트만 산출되며, 이것은 석유가 생성되기 어려운 <TEX>$100^{\circ}C$</TEX> 이하의 매우 낮은 온도를 지시한다. 이에 반해, 경상분지는 일라이트만 산출되면, 일라이트 결정도 값에 의하면 이 지역은 <TEX>$200^{\circ}C$</TEX> 이상의 높은 온도를 지시한다. 따라서 경상분지는 석유생성 단계를 이미 지난 상태인 것으로 생각된다. 동해의 대륙붕 지역은 상위 지층에서 불규칙배열의 일라이트-스멕타이트가 산출되지만, 약 2,500 m 이상의 매몰심도에서는 석유생성을 기대할 수 있는 온도를 지시하는 R=1 규칙배열의 일라이트-스멕타이트가 신출된다. 서해 대륙붕 지역은 상위 구간에서는 불규칙 배열의 일라이트-스멕타아트(R=0 I-S)가 나타나며, 중간의 구간에서는 R=1 규칙배열의 일라이트-스멕타이트(R=1 I-S)가 나타나고, 하위의 심부 구간에서는 R=3 규칙배열의 일라이트-스멕타이트(R=3 I-S)가 나타난다. 이 지역은 석유생성단계에서 가스생성 단계에 이르는 양호한 탄화수소 생성의 온도 조건을 보여주고 있다. 일라이트-스멕타이트 점토광물로 측정된 온도는 우리나라 육상분지에서는 석유가 존재하기 어렵다는 것을 보여준다. 그러나 대륙붕 지역은 석유와 가스를 생성하기 좋은 온도조건이므로 석유가스의 발견이 기대된다. The potential of petroleum generation was investigated by clay mineralogical changes of illite-smectite on the sedimentary basins: Tertiary Pohang basin and Cretaceouls Gyeongsang basin on land, and offshore basins east and west of Korea. Only disordered illite-smectite mixed layer minerals occur in the Pohang sediment, where petroleum generation cannot be expected due to low temperatures below <TEX>$100^{\circ}C$</TEX>. By contrast, the Gyeongsang basin is characterized by the occurrence of illite and high temperatures above <TEX>$200^{\circ}C$</TEX> which are obtained by illite crystallinity. The high temperatures indicate that the Gyeongsang sediment ha, already passed through the oil generation stage. The change of disordered illite-smectite to R-l ordered illite-smectite is shown in the sediment of the East Sea continental shelf area at a depth of 2,500 m. Therefore, the oil generation can be expected in the sediments below the depth of 2,500 m. The sequential change of disordered illite-smectie to R=3 ordered illite-smectite through R=l ordered illite-smectite occurs in the sediments of West Sea continental shelf area with burial depth which shows the favorable condition for oil and gas generation. The temperatures of sediments measured by illite-smectite indicate that hydrocarbon potential is very low in the onland basins but high in the continental shelf areas.

Formation of Illite-Smectite Mixed-Layer Minerals in Hydrothermally Altered Volcanic Rocks: Integration of Geological, Fluid Chemical, Isotopic, XRD, and TEM Evidence at Kakkonda Geothermal System

Formation of Illite-Smectite Mixed-Layer Minerals in Hydrothermally Altered Volcanic Rocks: Integration of Geological, Fluid Chemical, Isotopic, XRD, and TEM Evidence at Kakkonda Geothermal System

Depositional and geotechnical properties of marine clays in Lianyungang, China

The mineralogy, geochemistry and geotechnical properties of clay samples in Lianyungang, China are presented. The correlations of depositional history, depositional environmental and geotechnical properties are discussed. A series of X-ray diffraction tests show that the principal clay minerals of the soil are illite–smectite mixed-layer mineral and illite. The geochemistry investigation results indicate that the pore water of the Lianyungang marine clay is dominant by sodium. The pH of the soils varies in the range of 7.8 to 8.9. The depositional environment is oxidation condition. The correlations of the geochemistry with the geotechnical properties are examined by the statistic analysis.

Cation exchanged Fe(II) and Sr compared to other divalent cations (Ca,Mg) in the bure Callovian–Oxfordian formation: Implications for porewater composition modelling

Abstract Iron and Sr bearing phases were thoroughly investigated by means of spectrometric and microscopic techniques in Callovian–Oxfordian (COX) samples originating from the ANDRA Underground Research Laboratory (URL) in Bure (France). Strontium was found to be essentially associated with celestite, whereas Fe was found to be distributed over a wide range of mineral phases. Iron was mainly present as Fe(II) in the studied samples (∼93% from Mossbauer results). Most of the Fe(II) was found to be in pyrite, sideroplesite/ankerite and clay minerals. Iron(III), if present, was associated with clay minerals (probably illite, illite-smectite mixed layer minerals and chlorite). No Fe(III) oxy(hydro)xide could be detected in the samples. Strontianite was not observed either. Based on these observations, it is likely that the COX porewater is in equilibrium with the following carbonate minerals, calcite, dolomite and ankerite/sideroplesite, but not with strontianite. It is shown that this equilibrium information can be combined with clay cation exchange composition information in order to give direct estimates or constraints on the solubility products of the carbonate minerals dolomite, siderite and strontianite. As a consequence, an experimental method was developed to retrieve the cation exchanged Fe(II) in very well preserved COX samples. The very homogeneous cation exchange composition of the formation is completely in agreement with a homogeneous presence of calcite and dolomite minerals whose equilibrium reactions control part of the porewater composition. Amongst the broad range of values available for dolomite solubility products in thermodynamic databases, the value of log Kdolomite = −3.57 is the most appropriate for the one present in the COX formation. With regard to strontianite, it appears that the equilibrium constant tabulated in the Llnl database is not valid for natural clay systems. The value given by Busenberg et al. used by most of the other available thermodynamic databases seems to be far more appropriate. Concerning Fe(II) and siderite/ankerite equilibrium, the measured Fe/Ca ratio on the clay exchanger (∼0.01) could only be considered as a maximum value due to possible experimental bias, leading to the following constraint for the solubility of the sideroplesite phase present in the COX: Fe0.7Mg0.2Ca0.1CO3 + H+ ⇔ 0.7 Fe2+ + 0.2 Mg2+ + 0.1 Ca2+ + HCO 3 - logKsid_COX This constraint is in agreement with the estimated solubility of this phase based on a solid solution model: log Ksid_COX = 0.23.

Anthropic acceleration of a natural clay mineral reaction in marshland soils (Atlantic Coast, France)

AbstractSoil clay minerals in recent natural polders react on a human timescale in response to local environmental conditions. With increasing age, the mineral reaction leads to the dissolution of the chlorite component and a composition change of the different illite-smectite mixed-layer minerals (I-S MLMs): i.e. smectite layer content decreases and illite content increases. The process of oxidation, which is proven by magnetic susceptibility to trigger clay mineral reaction, changes the mineralogical composition of the sediment above the redox front. The mineral changes appear to be a non-linear function of time. In natural conditions the process lasts &gt;1000 y. However, anthropoic forcing such as artificial drainage accelerates the oxidation reaction to complete the whole process in a few tens of years.

Illite-Smectite Mixed-Layer Minerals in the Hydrothermal Alteration of Volcanic Rocks: II. One-Dimensional HRTEM Structure Images and Formation Mechanisms

AbstractSmectite illitization was investigated in felsic volcaniclastic rocks from a drill core near the Kakkonda active geothermal system, Japan, using high-resolution transmission electron microscopy (HRTEM) that provided one-dimensional structure images of mixed-layer illite-smectite (I-S) minerals normal to [M0]. Simulated images of a rectorite-like structure revealed that smectite can be distinguished from illite in mixed-layer I-S by HRTEM if the basal spacing of smectite is larger than that of illite. The larger basal spacing of smectite, 1.3 nm under HRTEM, was obtained by intercalation of dodecylammonium ions into smectitic interlayers. In simulated and observed images normal to [hk0], tetrahedral (T) and octahedral (O) cation planes are imaged as dark lines, an illitic interlayer as a bright line, and a smectitic interlayer as a dark line sandwiched between two bright lines.The samples are from depths of 435 m (5% I; R0), 635 m (35% I; R0), 656 m (62% I; R1), and 756 m (85% I; R3) where % I is the percentage of illite layers in a sample and R is the Reichweite parameter. Sample 435 consisted mostly of smectite, and illite layers occurred, though small in amount, as M1 units (module of type 1, defined as consisting of two polar T-O-T silicate layers with one central illitic interlayer and two, half smectitic interlayers at the outermost surface; the number corresponds to that of central illitic interlayers). The M1 units were dominant and isolated and consecutive smectite layers (&gt;2) were present in sample 635. Sample 656 consisted mostly of packets of M1 units of 1 to 5 layers containing M2 to M5 units occasionally. Isolated or consecutive smectite layers (&gt;2) were not present in 656. Illite layers occurred almost entirely as M1 units in samples 435, 635 and 656, and the number of M1 units increased with increase in % I. Sample 756 was characterized by the presence of M2 to M10 units accompanied by smectitic interlayers at the external surface and the absence of M1 units and isolated smectite layers. The HRTEM data strongly suggest that illitization in a hydrothermal system occurs by precipitation of M1 units for mixed-layer I-S minerals up to 60% I. This does not require the presence of precursor smectite. Illitization of I-S minerals with &gt;60% I proceeds by precipitation of various types of Mn (n ⩾ 2) units. Illite occurs only as Mn (n ⩾ 1) units throughout illitization.

Illite-Smectite Mixed-Layer Minerals in the Hydrothermal Alteration of Volcanic Rocks: I. One-Dimensional XRD Structure Analysis and Characterization of Component Layers

AbstractFor a series of mixed-layer illite-smectite (I-S) minerals from a drillhole near the Kakkonda geothermal field, one-dimensional structure analysis by X-ray diffraction (XRD) was performed using Casaturated specimens in both air-dried and ethylene glycol-solvated states. The expandability characteristics of component layers were also examined by means of alkylammonium exchange and Li saturation. The K content in the illite layers was 1.5–1.7/O20(OH)4 in the I-S series from 3 to 85% of I-layer content (% I). The layer charge of the smectite layer varied slightly within the range of 0.3–0.5/O10(OH)2 by alkylammonium exchange experiments and the expandability was independent of the beidellite content within a range of 0–0.5 by the Li-saturation test. The degree of long-range ordering represented by Reichweite (R) parameters varied from R0 to R3 via R1 and R2 with increase in % I. The I-S samples contained &lt;10% vermiculite as the third component and the vermiculite content tended to decrease with progressive illitization.In contrast to the smectitic R0 samples (&lt;10% I), more illitic R0 (e.g. 35% I) and &gt;R1 I-S samples showed complicated expandability with alkylammonium exchange. The XRD patterns of dodecylammonium-exchanged I-S samples can be interpreted by random interstratification of several types of sub-units such as layer-doublets, layer-triplets and layer-quartets present in the crystallites. This interpretation is consistent with the variation in the occurrence probabilities of layer-multiplets calculated from the junction probabilities and the proportions of layers. Because the interpretation indicates that I-S is a stack of various types of the sub-units, the smectite illitization can be described by a systematic change in the type and proportion of the sub-units constituting crystallites.

Rosia Poieni copper deposit, Apuseni Mountains, Romania: advanced argillic overprint of a porphyry system

The Rosia Poieni deposit is the largest porphyry copper deposit in the Apuseni Mountains, Romania. Hydrothermal alteration and mineralization are related to the Middle Miocene emplacement of a subvolcanic body, the Fundoaia microdiorite. Zonation of the alteration associated with the porphyry copper deposit is recognized from the deep and central part of the porphyritic intrusion towards shallower and outer portions. Four alteration types have been distinguished: potassic, phyllic, advanced argillic, and propylitic. Potassic alteration affects mainly the Fundoaia subvolcanic body. The andesitic host rocks are altered only in the immediate contact zone with the Fundoaia intrusion. Mg-biotite and K-feldspar are the main alteration minerals of the potassic assemblage, accompanied by ubiquitous quartz; chlorite, and anhydrite are also present. Magnetite, pyrite, chalcopyrite and minor bornite, are associated with this alteration. Phyllic alteration has overprinted the margin of the potassic zone, and formed peripheral to it. It is characterized by the replacement of almost all early minerals by abundant quartz, phengite, illite, variable amounts of illite-smectite mixed-layer minerals, minor smectite, and kaolinite. Pyrite is abundant and represents the main sulfide in this alteration zone. Advanced argillic alteration affects the upper part of the volcanic structure. The mineral assemblage comprises alunite, kaolinite, dickite, pyrophyllite, diaspore, aluminium-phosphate-sulphate minerals (woodhouseite-svanbergite series), zunyite, minamyite, pyrite, and enargite (luzonite). Alunite forms well-developed crystals. Veins with enargite (luzonite) and pyrite in a gangue of quartz, pyrophyllite and diaspore, are present within and around the subvolcanic intrusion. This alteration type is partially controlled by fractures. A zonal distribution of alteration minerals is observed from the centre of fractures outwards with: (1) vuggy quartz; (2) quartz + alunite; (3) quartz + kaolinite ± alunite and, in the deeper part of the argillic zone, quartz + pyrophyllite + diaspore; (4) illite + illite-smectite mixed-layer minerals ± kaolinite ± alunite, and e) chlorite + albite + epidote. Propylitic alteration is present distal to all other alteration types and consists of chlorite, epidote, albite, and carbonates. Mineral parageneses, mineral stability fields, and alteration mineral geothermometers indicate that the different alteration assemblages are the result of changes in both fluid composition and temperature of the system. The alteration minerals reflect cooling of the hydrothermal system from >400 °C (biotite), to 300–200 °C (chlorite and illite in veinlets) and to lower temperatures of kaolinite, illite-smectite mixed layers, and smectite crystallization. Hydrothermal alteration started with an extensive potassic zone in the central part of the system that passed laterally to the propylitic zone. It was followed by phyllic overprint of the early-altered rocks. Nearly barren advanced argillic alteration subsequently superimposed the upper levels of the porphyry copper alteration zones. The close spatial association between porphyry mineralization and advanced argillic alteration suggests that they are genetically part of the same magmatic-hydrothermal system that includes a porphyry intrusion at depth and an epithermal environment of the advanced argillic type near the surface.

Soil Mineralogy Evolution in the INRA 42 Plots Experiment (Versailles, France)

AbstractNatural soils change by long-term pedogenetic mechanisms, but tillage effects can also strongly affect the evolution of soils, mainly their physicochemical properties. The present paper describes the impact of fertilizers and amendments on soil mineralogy in experimental plots, without plant interaction.The soils of the 42 plots experiment at the INRA experimental station in Versailles (France) have been managed with fertilizers without plant growth since 1929. Strong changes in pH were observed and cation exchange capacities doubled between low and high pH (from 3.6 to 8.2). Strong acidification caused more evolution in the clay particle distribution without selective action on the clay composition.While the clay content varied only slightly, the organic matter content changed considerably, decreasing with non-organic treatment and increasing in the plot with manure treatment. The major clay minerals in the experimental plots are two disordered illite-smectite mixed-layer minerals, with minor amounts of illite/mica and kaolinite. Most treatments effected only minor changes in clay mineralogy. However the illite (non-expandable mineral) content increased in plots with K addition either as KCl treatment or in manure amendments by increasing the illite content and the illite (non-expandable layer) content of the I-S minerals. Manure changed the I-S mineral to a greater extent.

Isotope geochemistry and origin of illite-smectite and kaolinite from the Seilitz and Kemmlitz kaolin deposits, Saxony, Germany

AbstractResidual clays that developed on Permian and Carboniferous glass-rich silicic volcanic rocks (pitchstones, ignimbrites) at the Seilitz and Kemmlitz kaolin deposits, Saxony, Eastern Germany, contain locally abundant lath-shaped illite-rich illite-smectite mixed-layer minerals (I-S). Analyses by XRD and TEM-AES reveal a large illite percentage (&gt;∼90%) and R3 ordering in I-S from Seilitz (&gt;∼90%) and smaller illite percentage (∼70%) and R1 ordering in I-S from Kemmlitz. The clays never suffered a deep burial and there is no geological, petrographic or fluid inclusion evidence for aeolian input or hydrothermal origin of I-S at either deposit. The I-S formed exclusively at the expense of volcanic glass and not from K-feldspar. Residual quartz phenocrysts in the clays still preserve primary glassy silicate melt inclusions and lack secondary aqueous fluid inclusion trails. The dD and δ18O values of kaolinite and I-S are suggestive of low formation temperatures (&lt;40ºC). Rb-Sr and K-Ar dating of I-S-bearing clay separates yield Lower Cretaceous ages at Seilitz and indicates the presence of excess or inherited 40Ar in illite-rich I-S. In contrast, Triassic to Jurassic Rb-Sr ages are obtained for I-S from the Kemmlitz kaolin deposit.

Experimental constraints on illite crystal morphology

AbstractObservations of natural minerals and experimental run products show that I-S (illitesmectite mixed-layer minerals) with a high illite content as well as pure mica-illite crystallites can have a lath shape (aspect ratio &gt;3). This shape is common to the I-S minerals under a variety of conditions of formation. The experiments presented indicate that the occurrence of lath-shaped micaillite is due to a slow growth rate from supersaturated solutions. This lath-shaped crystallite is metastable as the ultimate stable shape is hexagonal. A longer period of crystal growth will replace the mica-illite laths with crystallites of a hexagonal form. Thus the presence of lath-shaped micaillite indicates the existence of a metastable crystal form for this mineral.

An empirical Scherrer equation for weakly swelling mixed-layer minerals, especially illite-smectite

AbstractThe Scherrer equation links the measured width of an X-ray diffraction peak (Scherrer width, SW) to the number of stacked cells (N) in the direction normal to the diffracting planes. The formula is only valid for one d-value occurring in the coherently diffracting domain. This equation can be modified for weakly swelling mixed-layer minerals. This assumes that the peak broadening caused by the mixed-layering is proportional to the amount of swelling component (S) and that the effects of size and mixed-layering are additive.If two SW can be measured on XRD patterns from samples treated in two different ways (such as air dried or glycolated), N and S can be determined. This equation is applicable to illite-smectite mixed-layer minerals with high illitic content. The results are most accurate for N&gt;30. The use of Scherrer's equation is discussed.