Types Of Phyllosilicates Research Articles

Hydrogen generation during hydrothermal alteration of peralkaline granite

It is well known that oxidation of ferrous to ferric iron by water can generate molecular hydrogen (H2), with the most widely recognized natural manifestation being serpentinization of olivine and pyroxene in ultramafic rocks. A less known yet extremely important source of natural H2 are peralkaline igneous intrusions, where spectacular enrichments of H2 are documented from fluid inclusions and as free gas migrating through fractured rocks and soils. Of these occurrences, the best studied are those at Strange Lake in Canada, Lovozero and Khibiny in Russia, and Ilímaussaq in Greenland. Based on petrographic observations and fluid inclusions analysis, it has been proposed that the hydrothermal alteration of arfvedsonite, an FeII-bearing amphibole, is the source of H2 in this context, although it is yet to be unequivocally demonstrated. To investigate the generation of H2 during alteration of peralkaline granites, we performed hydrothermal experiments on pure arfvedsonite grains and arfvedsonite-bearing granite (10 wt% arfvedsonite) from the Strange Lake pluton (Canada). These materials, in the presence of aqueous solutions, were sealed inside gold capsules or placed within titanium autoclaves, which allowed monitoring H2 generation in function of temperature (280–400 °C), chlorinity (0 and 3 m NaCl), pH, and starting mineral assemblage. Blank experiments were conducted to quantify the background amounts of H2 generated from Au/Ti oxidation, diffusing through the reaction cells, release from fluid inclusions or otherwise occluded in minerals. Solids were characterized by XRD, SEM, TEM on FIB foils, and STXM-XANES. Outcomes of this study demonstrate the production of H2 in agpaitic peralkaline rocks by the hydrothermal alteration of arfvedsonite. The rate of H2 production, normalized to the specific surface area of arfvedsonite, increases with temperature from 1100 to 2200 pmol cm−2 day−1 between 280 and 400 °C, respectively. Chlorinity tends to have a negative impact on the reaction rate, while circumneutral to alkaline conditions clearly promote H2 generation. Altering whole granite samples instead of arfvedsonite grains only also enhances H2 production rate. The presence of aluminum, released from microcline and albite dissolution, may increase both the solubility and the dissolution rate of arfvedsonite by promoting precipitation of phyllosilicates. At least two different types of phyllosilicates were observed, chlorite and smectite. Magnetite and secondary zircon were also identified at the surface of reacted arfvedsonite (Zr content = 1200 ppm). The H2 production rates reported here at 280–400 °C are comparable, and even faster than those documented for serpentinization of olivine and harzburgite. A major feature of arfvedsonite alteration in peralkaline plutons is the formation of aegirine as a replacing mineral. However, aegirine was never observed in the reacted solids from our experiments, under the condition tested (up to 400 °C and 400 bar). This may be an effect of pressure, oxygen fugacity, or reaction progress, parameters that remain to be investigated to better constrain the reaction mechanism of arfvedsonite alteration. Agpaitic peralkaline igneous intrusions thus represent a fertile geological setting for deep microbial subsurface ecosystems, abiotic synthesis of organic molecules, and natural H2 exploration for an alternative source of energy.

Incorporation of Rheological Characterization in Grinding and Tailings Slurries to Optimize the CMP Magnetic Separation Plant

Compañía Minera del Pacífico (CMP) is the main iron producer on the Pacific coast of the American continent. The Cerro Negro Norte (CNN) operation of CMP is facing important challenges, such as the processing of low-grade ores containing complex gangue minerals which negatively affect the performance of the magnetic separation, grinding and solid–liquid separation stages. CMP is working on a program, aimed at optimizing the efficiency of the CNN plant, which considers a rheological characterization of the slurries produced by the different ores treated, information which will be useful to optimize the performance of the physical separation processes. The objective of this work was to characterize the slurries obtained from the secondary grinding and tailings thickener stages through rheological measurements. The rheological data were correlated with the physical, chemical and mineralogical characteristics of the different geological units (GU) tested. The results show that the rheological flow curves of the slurries taken from the secondary grinding product display a pseudoplastic behavior which follows a Casson model pattern. An exponential model was used to correlate the Casson yield stresses with the solids content of the slurries taken from the secondary grinding product. The results of this fitting process indicate that the yield stresses increase with the % −325# Tyler mesh and with the percentage of minerals with a tendency to generate fines (MTF = smectite + illite/mica + talc + chlorite + kaolinite), and in contrast the yield stresses decrease with the ore iron grade (Fe). For the tailings characterization, the results of settling rates and turbidity values of the supernatant obtained from tests with different GU samples show no significant differences. A linear regression model was used to correlate the results of yield stresses of compacted tailings with the chemical and mineralogical characteristics of the GU. The results of the fitting process indicate that the MTF content in the head ore samples influence the rheological properties of the tailings, which correlates with the behavior of the secondary grinding product. The increase in the GU iron grades also reduced the Casson yield stress. The experimental results were explained in terms of the microrheological effects and the physicochemical properties of the different types of phyllosilicates existing in the ore samples tested in this work.

Identifying the phyllosilicate minerals of hypogene ore deposits in lateritic saprolites using the near-IR spectroscopy second derivative methodology

Infrared field-based reflectance spectroscopy in the Visible - Near-Infrared - Short-wave Infrared (VIS-NIR-SWIR) domain is a useful tool in mining geology particularly efficient for investigating the clay mineralogy of alteration haloes around ore deposits. It is used as a routine technique for the basic identification, mapping and semi-quantification of clay mineral species. However, the use of this technique for prospecting in hypogene deposits at depth in intertropical areas is strongly limited because of the presence of a thick, kaolinite-rich lateritic cover. Due to the strong IR absorption of kaolinite and the overlapping of its IR bands with those of most of the phyllosilicates in the SWIR domain, the use of field based near-infrared spectroscopy does not permit efficient identification and mapping of the phyllosilicates inherited from hypogene alteration that persist in the saprolite of lateritic profiles.In this paper, we propose a methodology to enhance the detection and semi-quantification of hypogene phyllosilicate minerals in kaolinite-rich lateritic saprolites using calibration curves. Those curves are built from the NIR spectra of binary admixtures of kaolinite or smectite with muscovite, Fe-Mg chlorite, clinochlore or talc in different known proportions.For each admixture series, calibration curves were established, based on investigation of two regions of interest within the NIR domain (1350–1470nm and 2080–2500nm) using a field-based spectrometer. For each binary mixture series of phyllosilicates, the second derivative of the NIR spectra was used to enhance the detection of the diagnostic absorption bands of each type of phyllosilicate, and hence to optimize the calculation of the intensity ratios between the diagnostic bands of the phyllosilicate components as a function of their percentage in the mixture. In presence of large amounts of lateritic kaolinite, the detection limit of the major types of hypogene phyllosilicates has been found at ranges from 5 to 10wt% of the total clay content using the second derivative of the NIR spectra acquired with a field-based spectrometer. Above these aforementioned limits of detection, the semi-quantitative data obtained by comparing the NIR reflectance spectra of natural samples with those of the calibration curves could permit to map hypogene alteration haloes directly from the lateritic saprolite.Finally the described approach has been successfully tested on natural samples from the skarn deposits of the Ity gold mine (Ivory Coast).

A preliminary rheological classification of phyllosilicate group minerals

With the increased exposure to progressively complex ores, there is growing concern over the effects of phyllosilicate gangue minerals. These minerals present challenges during ore beneficiation, with issues such as reduced flotation performance and complex tailings treatment arising. Often broadly classified as ‘clays’, the understanding of the distinct behaviour of phyllosilicates remains poor. This work focusses on talc, illite and kaolinite, and forms part of an ongoing study which aims at investigating the entire phyllosilicate group, categorised as serpentine, micas; talc/pyrophillite, kaolinites, illites, smectites and vermiculite. Using pure minerals belonging to each phyllosilicate type, a comprehensive surface charge and rheological analysis was conducted, incorporating their charge anisotropy and non-spherical morphology. The mineralogy was discussed, based on pre-existing knowledge of the minerals. Talc, kaolinite and illite suspensions are characterised by high yield stresses and low viscosities, with differences in their behaviour attributed to variations in charge anisotropy, aspect ratio and surface morphology. A comparison with other phyllosilicates showed that muscovite (mica) results in the least rheologically complex suspensions, while the fibrous nature of chrysotile (serpentine) leads to suspensions with the highest yield stresses and viscosities. The other minerals demonstrate intermediate rheological behaviour. Such a classification may be foundational to geometallurgical advances which can enable process performance predictions based on mineralogy.

Magnetic characterization of Fe nanoparticles dispersed in phyllosilicate type silicon oxide

We present the magnetic properties of silica-supported metal (Fe,catalyst) nanoparticles synthesized by precipitation of metal nitrate in ammonia-based medium. Our goal is the study of possible metal-support interactions in the nanoporous catalyst. The temperature dependence of the magnetization for all samples display spin-glass like behavior below c.a. 11-12 K, with clear Curie-Weiss dependence in the high-temperature regime. Spin-glass-like behavior was inferred from dynamic AC susceptibility data after analyzing the frequency-dependence of the in-phase component χ′(f) by the expression W = ΔTf/[Tf Δlog(f)] = 3.0 × 10−3. We found that the magnetic behavior of the catalyst is drastically affected by the existence of interactions between the metal and the support.

A new method to investigate hyperspectral image cubes: An application of the wavelet transform

Data analysis of the Observatoire pour la Minéralogie, l'Eau, les Glaces, et l'Activité (OMEGA), the imaging spectrometer aboard Mars Express, necessitates the use of techniques able to extract the relevant information of large data sets. Numerous efficient algorithms have already been developed for similar purposes for terrestrial imaging spectrometers such as the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). We propose here a complementary method based on the wavelet transform. Our algorithm allows the detection of the absorption bands in each spectrum and returns their position, width, and depth. We use it either to study separately the properties of each absorption band or as a classification method, grouping together the pixels whose spectra contain the same absorption bands. We test our algorithm on an AVIRIS observation of Mauna Kea, Hawaii. The method identifies the dominant mineralogy of this area: variability in the ferric and ferrous mineralogy and several types of phyllosilicates. We also study six Martian observation sessions acquired by the Infrared Spectrometer for Mars onboard Phobos 2. We identify ferric and ferrous absorption bands in the data set and variations in the ferrous mineralogy corresponding to different proportions of high and low calcium pyroxene. Finally, we apply our technique to the first 6 months of Mars surface observation by OMEGA/Mars Express, resampled on a 1° × 1° grid. We thus retrieve the global large‐scale variability of the OMEGA data set and identify a global spectral discrepancy inside Martian dark regions which corresponds to the spectral difference between type I and type II terrains previously identified by the Thermal Emission Spectrometer.

Changes in Zinc Speciation in Field Soil after Contamination with Zinc Oxide

Recent studies on the speciation of Zn in contaminated soils confirmed the formation of Zn-layered double hydroxide (LDH) and Zn-phyllosilicate phases. However, no information on the kinetics of the formation of those phases under field conditions is currently available. In the present study, the transformation of Zn in a field soil artificially contaminated with ZnO containing filter dust from a brass foundry was monitored during 4 years using extended X-ray absorption fine structure (EXAFS) spectroscopy. Soil sections were studied by micro-X-ray fluorescence (micro-XRF) and micro-EXAFS spectroscopy. EXAFS spectra were analyzed by principal component analysis (PCA) and linear combination fitting (LCF). The results show that ZnO dissolved within 9 months and that half of the total Zn reprecipitated. The precipitate was mainly of the Zn-LDH type (>75%). Only a minor fraction (<25%) may be of Zn-phyllosilicate type. The remaining Zn was adsorbed to soil organic and inorganic particles. No significant changes in Zn speciation occurred from 9 to 47 months after the contamination. Thermodynamic calculations show that both Zn-LDH and Zn-phyllosilicate may form in the presence of ZnO but that the formation of Zn-phyllosilicate would be thermodynamically favored. Thus, the dominance of Zn-LDH found by spectroscopy suggests that the formation of the Zn precipitates was not solely controlled bythermodynamics but also contained a kinetic component. The rate-limiting step could be the supply of Al and Si from soil minerals to the Zn-rich solutions around dissolving ZnO grains.

Vermiculite-like minerals in low-grade metasediments from the Coastal Range of central Chile

AbstractMixed-layer minerals with optical properties similar to metamorphic vermiculite were identified in rocks belonging to a Palaeozoic and a Triassic formation separated by an angular unconformity and exposed in the Coastal Range of central Chile. Both formations are affected by low-grade metamorphism. The mixed-layer minerals were studied by optical microscopy, X-ray diffraction (XRD), electron microprobe (EMPA), and transmission/ analytical electron microscopy (TEM/AEM). Two types of phyllosilicates were identified: chlorite-vermiculite and mica-chlorite, which are present in the Palaeozoic and Triassic rocks respectively. Chlorite-vermiculite mixed layers form packets with well-defined boundaries and mainly show 1:1 ordered sequences. On the contrary, mica-chlorite mixed layers show, in most cases, random sequences evolving laterally toward chlorite. The AEM data indicate compositions close to that of chlorite in the ternary Si-Al- (Fe+Mg+Mn) diagrams for both types of mixed-layer phyllosilicates. Relative to the coexisting chlorite, they have lower (Fe+Mg) contents, and a higher Si/Al ratio. They are interpreted as products of the transformation of chlorite, developed during prograde metamorphism, and probably represent intermediate, metastable phases, in the chlorite to biotite transformation.

Heavily‐hydrated lithic clasts in CH chondrites and the related, metal‐rich chondrites Queen Alexandra Range 94411 and Hammadah al Hamra 237

Abstract—Fine‐grained, heavily‐hydrated lithic clasts in the metal‐rich (CB) chondrites Queen Alexandra Range (QUE) 94411 and Hammadah al Hamra 237 and CH chondrites, such as Patuxent Range (PAT) 91546 and Allan Hills (ALH) 85085, are mineralogically similar suggesting genetic relationship between these meteorites. These clasts contain no anhydrous silicates and consist of framboidal and platelet magnetite, prismatic sulfides (pentlandite and pyrrhotite), and Fe‐Mn‐Mg‐bearing Ca‐carbonates set in a phyllosilicate‐rich matrix. Two types of phyllosilicates were identified: serpentine, with basal spacing of ˜0.73 nm, and saponite, with basal spacings of about 1.1–1.2 nm. Chondrules and FeNi‐metal grains in CB and CH chondrites are believed to have formed at high temperature (&gt;1300 K) by condensation in a solar nebula region that experienced complete vaporization. The absence of aqueous alteration of chondrules and metal grains in CB and CH chondrites indicates that the clasts experienced hydration in an asteroidal setting prior to incorporation into the CH and CB parent bodies. The hydrated clasts were either incorporated during regolith gardening or accreted together with chondrules and FeNi‐metal grains after these high‐temperature components had been transported from their hot formation region to a much colder region of the solar nebula.

Selected enzyme activities as affected by free iron oxides and clay particle size1

The effect of soil clay size phyllosilicates, particle size, and iron oxides on the activities of α‐ and β‐glucosidases, phosphomonoesterases, and urease were examined. The two clay fractions (0.2–2 and <0.2 μm) of selected soils had similar mineralogy and were illitic, kaolinitic, and smectitic in composition. In general, enzyme activities were reduced in the presence of clay size phyllosilicates. The montmorillonitic samples were the most effective inhibitors. Activities were generally lower in the presence of the finer clay fractions. The effect of iron oxides on enzyme activities varied. Acid phosphatase activity was significantly influenced by phyllosilicate type, iron oxides, and particle size. The inhibitory effect of phyllosilicates on acid phosphatase activity increased when iron oxides were removed from the clay fraction. Removal of iron oxides, on the other hand, enhanced the activity of alkaline phosphatase. Unlike β‐glucosidase, α‐glucosidase was deactivated in the presence of montmorillonitic and illitic samples regardless of clay particle size. The activity of urease was significantly reduced in the presence of iron oxides.

Aluminium speciation in surface waters and soil solutions in areas of sulphide mineralization in Galicia (N.W. Spain)

The composition of soil solutions and surface waters in a mining region rich in metallic sulphides in Galicia (N.W. Spain) has been analyzed. Heavily contaminated waters showed high acidity (pH < 3.5) and levels of soluble Al greater than 2000 μmol l−1. Most of the Al is in the labile form, as AlSO4 and Al3+ species, in contrast with areas not affected by acidification, in which the Al in solution is partitioned, between labile and non-labile forms, the latter is predominantly bound to fluorine. The activity of Al3+ in contaminated zones appears to be controlled by minerals of the jurbanite or alunite type, there being instability for gibbsite and kaolinite. In uncotaminated waters, control of Al3+ activity is by minerals of the gibbsite and/or 1:1 phyllosilicate type.