Major Mineral Phases Research Articles

Exfoliation characteristics of Swat vermiculite clay and its application in the preparation of lightweight composite panels

Vermiculite is a natural clay that has significant exfoliation characteristics. The exfoliated vermiculite has much lighter density and water retaining properties that makes it suitable for lightweight construction, insulation, and horticulture applications. In the present study, vermiculite ore of Swat region, Pakistan was subjected to exfoliation in a rotary kiln. The exfoliated vermiculite was characterized in detail for physical, morphological, and mineralogical properties, before and after exfoliation. The optimum temperature where lowest density was observed for various size fractions of exfoliated vermiculite was 750 °C. Vermiculite, hydrobiotite and mica were found to be the major mineral phases in the raw and exfoliated vermiculite. The exfoliated vermiculite was then blended with unsaturated polyester resin in the resin: vermiculite ratios of 65:35, 60:40, 55:45, and 50:50, to produce lightweight exfoliated vermiculite composite samples. Analysis of physical and mechanical properties of the composite samples like density, water absorption, compressive strength, tensile strength, and thermal conductivity showed that a suitable resin: vermiculite ratio of lightweight exfoliated vermiculite composite panel may be selected for a particular application.

The Bazman and Taftan volcanoes of southern Iran: Implications for along-arc geochemical variation and magma storage conditions above the Makran low-angle subduction zone

Bazman and Taftan are two Late Miocene-Quaternary volcanoes of the Makran continental arc formed by the subduction of Arabian oceanic lithosphere beneath southern Eurasia. This study compares their bulk rock compositions as well as major and trace element contents of major mineral phases. Bazman is composed of a geochemically heterogeneous suite of low to medium-K basic to acidic compositions, while Taftan exposes more homogenous mainly andesitic rocks of medium to high-K affinity. Both volcanoes are characterized by the enrichment of LILE compared to HFSE and depletion of Nb, Ta, and Ti, reminiscent of subduction zone magmatism. At a given SiO2 content, the Taftan volcanics have higher concentrations of incompatible elements and, La/Yb, Th/Yb, and Sr/Y ratios (adakitic signature), here interpreted as being related to the more enriched mantle source, higher contribution of subducted sediments in magma genesis and thicker continental crust beneath Taftan. Thermobarometric calculations based on mineral chemistry (amphibole, orthopyroxene, clinopyroxene, and plagioclase) indicate pre-eruptive T = ∼1050–800 °C, P = 250–100 MPa and H2Omelt > 3.5 wt%. Bazman lavas record slightly lower P and T, and higher H2Omelt, suggesting a shallower magma reservoir and thus a more developed magma plumbing system. Trace element abundances in minerals show consistent distinctions between the two volcanoes, e.g., amphibole is REE-enriched in Taftan over Bazman samples. The features of trace element compositions and zoning patterns of minerals (amphibole, plagioclase and, pyroxene) along with available major element data are suggestive of both recharged magmatic systems and convective self-mixing magma chambers.

Modeling Thermal Emission under Lunar Surface Environmental Conditions

Thermal emission spectra can provide key insights into the composition and thermophysical properties of the regolith on the Moon and other airless bodies. However, under lunar surface environmental conditions, the uppermost millimeters of the regolith (from which thermal emission originates) cannot be characterized by a single temperature, leading to changes in spectral characteristics that should be accounted for in interpreting thermal emission measurements. Here, we develop and apply a Monte Carlo radiative transfer method to model thermal emission from particulate media with varying, nonisothermal subsurface temperature profiles. We model emission spectra for three major lunar mineral phases (pyroxene, olivine, and plagioclase), and investigate the effects of particle size and packing density. Modeled spectra are compared to lab measurements acquired under both ambient and simulated lunar conditions. We find that in some cases, the model provides useful constraints on the magnitude of the temperature profile established in a lab sample under lunar-like conditions, whereas in other cases, lab spectra are not well represented by the linear temperature profiles considered in this work. The model is generally successful at predicting changes in spectral contrast under lunar-like conditions, but less successful in accurately predicting shifts in the position of the Christiansen feature emissivity maximum; we illustrate and discuss the validity of the modeling approach for a range of different cases. Model results can also be used to quantify the depth within which observed thermal emission originates; this depth depends on composition and grain size, and ranges from ∼100 to 1000 μm for representative packing densities.

Lithium Potential of the Indian Granitic Pegmatites

Abstract There is a progressively increasing demand for lithium (Li) due to its growing applications in the Li-ion batteries for electric vehicles. Accordingly, to take stock of the situation with respect to lithium potentiality of the Indian granitic pegmatites, a critical synthesis is presented here. India’s exploration programme for lithium was not sustained due to fluctuating domestic demand and its availability in the world market. Data reveals that the Indian Li-pegmatites belong to the Lithium-Caesium-Tantalum (LCT) family, and occur manly in parts of Bihar-Jharkhand, Bastar-Odisha and Karnataka, with some in Rajasthan, Maharashtra, West Bengal and Assam. Major mineral phases of Li are lepidolite, amblygonite and spodumene, the last one being dominant in Karnataka. Bulk of the Li-pegmatites have been derived from the peraluminous, geochemically-evolved S-type granites. During fractionation, wherever saturation was attained, precipitation of independent minerals of Li took place. Lithium minerals are largely restricted to the replacement zones of pegmatites, and, at places, in the greisenised pockets within the pegmatites and parent granite margins. Pegmatites from Karnataka appear to have more potential relative to those from Bihar-Jharkhand and Rajasthan. Systematic exploration of Li-pegmatites may prove rewarding in establishing their Li-potential. Li-pegmatite fields may be mapped by applications of remote sensing, using various methods and sensors through spectral angle mapper (SAM) classification on ‘HyMap’ data. SAM classification may be used to assess the efficacy of advanced spaceborne thermal emission and reflection radiometer (ASTER), and Landsat-8 operational land imager (OLI) data, including new combinations of red, green and blue (RGB). By combined use of ASTER imagery and spectro-radiometric analysis, mapping of pegmatite veins may be carried out. As the LCT-type pegmatites are sourced mostly from previously un-melted, mica-enriched metamorphic rocks, muscovite and biotite groups of mica host bulk of the trace elements and thus fingerprint for the LCT-type pegmatites. Also, P- and Cs-enriched Li-pegmatites lend further support to the S-type sources for the LCT-type pegmatites. Accordingly, all the LCT-type pegmatites in India should form the first order target for Li-exploration. Characteristic replacement mineral assemblages like cleavelandite, topaz, greisen, schorl and lithian muscovite may also serve as guides for lithium exploration.

Quantitative phase analysis and rietveld texture determination of minerals in ash deposits in a 11.2 MW moving grate boiler

Some ash deposits were sampled from a 11.2 MW moving grate boiler to study the mineral transformation, ash deposition and mineral texture evolution behavior, which were determined by different analytical methods. Rietveld refinement was applied to determine the mineralogy, refine the crystallographic structures of minerals, and characterize texture heterogeneity of minerals in ash deposits. The results presented that the major mineral phases in ash deposits were identified as silicates, oxides, sulphates, sulfides and carbonates. The phase transformation between minerals during combustion was proposed. The variation of the diffraction peak intensities indicated the existence of the weak and strong textures. The texture indexes were larger than one mrd2 for most minerals, implying strong preferred orientation distributions, while the texture indexes of some other minerals were approaching one mrd2, indicating the existence of weak and random textures. Some pole figures showed strong texture features with a high degree of texture disorder in these minerals, while other minerals displayed weak textures with low volume diffractions of preferred orientations in these mineral phases. Owing to the diffraction peak overlapping of different minerals, different texture components with fibre-like or biaxial-like characteristics were found in ash deposits.

Valorization of copper smelter slag through the recovery of metal values by a synergistic bioprocess system of bio‐flotation and bio‐leaching

AbstractSlag sample generated as solid waste from a copper plant in Southern Africa contains strategically important base metals like copper, nickel and cobalt. X‐ray diffraction and X‐ray fluorescence analysis confirmed the presence of fayalite (Fe2SiO4), silica (SiO2) and alumina (Al2O3) as the major mineral phases in the slag sample. The presence of alumina and silicate minerals in copper slag are the major obstacles in the recovery of base metals in mineral processing industries. The copper slag may be hazardous if abandoned to the environment but it may be a valuable resource if the metal values can be recovered. Hence, the present study focused on the application of a bio‐surfactant extracted from Lactobacillus fermentum bacterium as a bio‐collector in the flotation of the slag sample to reduce its silica and alumina content. Subsequently, the slag sample was subjected to bio‐leaching by Acidithiobacillus ferrooxidans bacterium for recovery of the metal values. Flotation batch experiments were conducted in 1 L scale Denver flotation cell and during the process, about 37.90% of silica and 22.82% alumina were removed from the slag sample. The findings from this study further revealed the effectiveness of the bio‐surfactant‐assisted flotation process on the bio‐leaching of base metals from the slag sample. Flotation of silica and alumina from the slag improved bio‐leaching performance and recovered about 74.0% of copper, 60.0% of nickel and 33.4% cobalt in the bio‐leaching process conducted at laboratory scale.

Genesis and possible applications of Lwamondo and Zebediela Kaolins, Limpopo Province, South Africa

ABSTRACT The genesis and potential industrial applications of Lwamondo and Zebediela Kaolins in South Africa were determined. Selected physico-chemical characteristics were determined. Mineralogical characteristics were determined using XRD and SEM; and geochemical characteristics were determined using XRF and LA-ICP-MS. Kaolin colours were generally light (Lwamondo) and brown (Zebediela). Both kaolins had low pH (<6.5) and EC (<50 µS/cm). The texture of Lwamondo Kaolin was generally loam and clay loam, whereas that of Zebediela was clayey, silty and loamy. Major mineral phases were kaolinite, smectite and plagioclase in Lwamondo Kaolin, and kaolinite in Zebediela Kaolin. The morphology of the kaolins consisted mainly of stacks of kaolinite flakes. The most dominant major oxides were SiO2, Al2O3 and Fe2O3, and the kaolins were slightly depleted in light rare earth elements. The studied characteristics indicated that the kaolins (i) formed in a supergene environment and (ii) are suitable for hollow bricks.

Magnetic Fabrics and Petrography of Rocksalts Reveal Preferred Orientation of Anhydrites within a Halite Matrix

We investigate the magnetic fabrics and microstructures of diamagnetic rocksalt samples from the Sedom salt wall (diapir), Dead Sea Basin, as possible strain markers. A comprehensive study of anisotropy of magnetic susceptibility (AMS), combined with magnetic, microtextural, geochemical and mineralogical analyses allows us to depict the deformation mechanisms and to reveal the mineral sources of the AMS. The rocksalts are composed of halite as the major mineral phase (&gt;80%) and anhydrite as a minor phase (5–20%), and have an average magnetic susceptibility value of −13.4 ± 0.7 × 10−6 SI. Ferromagnetic and paramagnetic minerals make a negligible contribution to the bulk magnetic properties of the samples. The AMS indicates and reveals significant anisotropy with the maximum susceptibility axis (K1) subparallel to the bedding strike, although the cubic halite crystals are isotropic. Polarizing microscope and SEM images show preferred alignment of needle-like anhydrite crystals parallel to the direction of the K1 axis. Petrographic investigation of gamma irradiated thin sections reveals the deformation recorded in the microstructures of the rocksalts and points to a dominant contribution by dislocation creep, although both dislocation creep and pressure solution were active deformation mechanisms. We infer that during dislocation creep, the thin bands of anhydrite crystals deform along with the surrounding halite grains. We suggest that although the shape preferred orientation of halite grains is not indicative of finite strain because of resetting by grain boundary migration, the preferred orientation of the anhydrite crystals may be. These results suggest that the AMS of the rocksalts provides a textural proxy that reflects deformation processes of the rocksalts, despite their very low magnetic susceptibility.

Multisensor hyperspectral imaging approach for the microchemical analysis of ultramarine blue pigments

This work presents a multisensor hyperspectral approach for the characterization of ultramarine blue, a valuable historical pigment, at the microscopic scale combining the information of four analytical techniques at the elemental and molecular levels. The hyperspectral images collected were combined in a single hypercube, where the pixels of the various spectral components are aligned on top of each other. Selected spectral descriptors have been defined to reduce data dimensionality before applying unsupervised chemometric data analysis approaches. Lazurite, responsible for the blue color of the pigment, was detected as the major mineral phase present in synthetic and good quality pigments. Impurities like pyrite were detected in lower quality samples, although the clear identification of other mineral phases with silicate basis was more difficult. There is no correlation between the spatial distribution of the bands arising in the Raman spectra of natural samples in the region 1200–1850 cm−1 and any of the transition metals or rare earth elements (REE). With this information, the previous hypothesis (based on bulk analysis) attributing these bands to luminescence emissions due to impurities of these elements must be revised. We propose the consideration of CO2 molecules trapped in the cages of the aluminosilicate structure of sodalite-type. Additionally, correlation between certain Raman features and the combined presence of Ca, P, and REE, in particular Nd, was detected for the lowest quality pigment. Our results highlight the usefulness of fusing chemical images obtained via different imaging techniques to obtain relevant information on chemical structure and properties.

Mineralogical Characterization and Acid Pretreatment of a Gold Calcine Leach Residue

Miners around Zimbabwe used to supply gold concentrates from sulphide flotation to the Kwekwe Roasting Plant (Zimbabwe) for toll treatment. The concentrates were roasted in Edward’s roasters and the calcine product was leached by cyanidation. Due to inefficient roasting, overall gold recoveries of 75–80% left behind a rich calcine leach residue at the Kwekwe Roasting Plant. The characterization performed to establish a potential process route involved several techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM), fire assaying and inductively coupled plasma (ICP). Assays conducted on samples from the 350,000 tons tailings dam residue, created over the operational years, gave an average Au grade of 8.58 g/t and 12.54 g/t for Ag. The base metals assayed—0.11% Cu, 0.10% Pb, 0.17% Zn and 26.05% Fe. SiO2 (36.1%), Fe2O3 (36.9%), Mg3Si4O10 (OH)2 (8.9%), NaAlSi3O8 (6.9%), and Fe3O4 (6.4%)—were the major mineral phases in the cyanide leach residue. SEM gold scans on 24 polished sections showed only 2 discrete gold particles of less than 5 µm, with one partially liberated and associated with quartz, while the other was fully liberated. Therefore, the particulate gold in the calcine leach residue was negligible. It was deduced from the analysis after ultrafine milling (P80 &lt; 5 µm) followed by cyanidation that 68.53% of the gold was sub-microscopic. Direct cyanidation using bottle roll resulted in only 2.33% of the total gold being leachable, indicating that the calcine leach residue was highly refractory. Diagnostic leaching by sequential use of acids in order of their strength resulted in HCl leachable phases (CaCO3, CaMg(CO3)2, PbS, Fe1-XS, and Fe2O3) freeing 4.2% of the total Au during subsequent cyanidation leach. H2SO4 leachable phases (Cu–Zn sulphides, labile FeS2) released an additional 26.57% during cyanidation, whereas HNO3 leachable phases (FeS2, FeAsS) released a further 20.98% of Au. After acid treatment and subsequent cyanidation, hot caustic leach of the residue followed by carbon in pulp resulted 4.43% of the total gold being eluted. Therefore, 4.43% of the total gold was surface bound. From the analysis after diagnostic acid leaching, it was deduced that a total of 54.08% of the gold was in the acid-leachable phase. Due to cost and environmental considerations, H2SO4 was selected for the evaluation of acid digestion as a pretreatment stage followed by cyanidation. Increasing the H2SO4 strength for the pretreatment of the calcine leach residue increased gold recoveries during cyanidation.

The Effect of Red Mud on Sintering Processes and Minerals of Portland Cement for Roads

As a solid waste generated in the alumina industry, red mud poses a significant environmental hazard and a storage problem. In this study, red mud was added to road cement clinker in order to utilize it. The sintering red mud was first de-alkalized, and then mixed with fly ash, clay, limestone, and sandstone, among other materials, to make Portland cement for road clinker. The effect of the addition of red mud on the thermal decomposition characteristics of Portland cement for roads was studied. The existent states of alkali and radioactive elements in Portland cement for road clinker were investigated by XRD and SEM analysis. The research results showed that the addition of red mud in Portland cement for road raw material significantly promoted the decomposition of carbonates in raw material. The major mineral phases of Portland cement for road clinker were C3S with a polyhedral morphology, quasi-spherical C2S, and tubular C4AF. A small part of the alkali combined with the silicate phase to form a solid solution, and most of the alkali combined with S to form vermiform sulfate in the intermediate phase. The radionuclide 226Ra was mainly distributed in the silicate phase. 232Th was mainly distributed in interstitial phases and then silicate phases, while 40K was mainly distributed in the interstitial phases.

Integration of fine grinding and H2SO4 leach for the liberation, dissolution and redistribution of long-life radionuclides in copper flotation concentrate

The economically significant deposits – iron oxide-copper-gold (IOCG) usually contains elevated amount of naturally occurring radioactive material (NORM), which hinders the utilization of IOCG deposits and leads to the waste of resources on site due to the presence of these radionuclides. Herein, a new fine grinding – H2SO4 leach method was used to efficiently dissolve and liberate long-life radionuclides (238U, 230Th, 226Ra, 210Pb, 210Po) from uranium-bearing NORM that are finely disseminated in the major economical minerals. The fine grinding treatment reduced the average particle sizes, interrupted the mineral textures and partially dissolved uranium minerals, thereby liberating them onto the newly formed secondary copper phases. The following H2SO4 leach changed the chemical and phase compositions by dissolving non-copper elements where the locked 238U and 230Th were largely removed close to the safe activity (1 Bq/g) and 226Ra, 210Pb, 210Po were mobilized onto the copper mineral surfaces. For the first time, the quantitative correlations between radionuclide species and major mineral phases were built by QXRD and radionuclide analysis. Such quantification methodology of radionuclide deportment can be applied in the processing a broad range of NORM-bearing resources, providing a crucial guidance in radionuclide management for environmental and process engineers.

Sedimentary diagenesis and pore characteristics for the reservoir evaluation of Domanik formations (Semiluksk and Mendymsk) in the central part of Volga-Ural petroleum province

The Upper Devonian Semiluksk (Domanik) and Mendymsk carbonate successions have been identified as the most promising unconventional oil and gas deposits in Russia's Volga-Ural petroleum province. Three lithofacies were identified: limestones, organic matter-rich siliceous carbonate, and dolomitic limestones/dolomite. Their sediments are thought to have accumulated in the relatively deep-sea shelf depositional environment. According to X-ray analysis, calcite is the most common mineral phase in the limestones. The siliceous carbonate rocks' major mineral phases were identified to be quartz, followed by calcite. The rocks have relatively poor reservoir qualities, with porosity ranging from 0.1 to 5% and permeability ranging from 0.01 to 10 mD. Petrographic examination of thin sections reveals four major types of pores: 1. interparticle pores, which are abundant in all of the examined lithofacies; 2. intercrystalline pores formed between dolomite crystals and the very fine components of the siliceous carbonate rocks. 3. vugs as a result of leaching, and 4. fracture as a result of tectonic and/or diagenetic events. Plotting the obtained data from the petrographically examined thin sections on the ternary pore plot diagram resulted in the identification of six pore facies and their related diagenetic patterns. Pore facies 1 depicts the pores that formed during the depositional process. Pore facies 4 displays moldic pores. The vugs are represented by pore facies 6. Pore facies 2 is a mixture between pore facies 1 and pore facies 4. Pore facies 3 is a mixture between pore facies 1 and pore facies 6. Pore facies 5 is a mixture between pore facies 4 and pore facies 6. Comparing the petrographic results and the identified pore facies show that pore facies 6 have touching pores and they played the most important role in improving the reservoir quality. The pore facies 4 which have separate pores have the most influence in the reduction of the reservoir quality. The diagenetic origin secondary pores are the most pores identified in the studied carbonate section. This reflects the strong modification of the pores by the diagenetic overprinting. The massive dissolution that forms the touching vugs, and the dolomitization process are the most diagenetic processes that affect the pore system within the studied rocks.

Binding mechanism and binding free energy of amino acids and citrate to hydroxyapatite surfaces as a function of crystallographic facet, pH, and electrolytes

Hydroxyapatite (HAP) is the major mineral phase in bone and teeth. The interaction of individual amino acids and citrate ions with different crystallographic HAP surfaces has remained uncertain for decades, creating a knowledge gap to rationally design interactions with peptides, proteins, and drugs. In this contribution, we quantify the binding mechanisms and binding free energies of the 20 end-capped natural amino acids and citrate ions on the basal (001) and prismatic (010)/(020) planes of hydroxyapatite at pH values of 7 and 5 for the first time at the molecular scale. We utilized over 1500 steered molecular dynamics simulations with highly accurate potentials that reproduce surface and hydration energies of (hkl) hydroxyapatite surfaces at different pH values. Charged residues demonstrate a much higher affinity to HAP than charge-neutral species due to the formation of superficial ion pairs and ease of penetration into layers of water molecules on the mineral surface. Binding free energies range from 0 to −60 kJ/mol and were determined with ∼ 10% uncertainty. The highest affinity was found for citrate, followed by Asp(-) and Glu(-), and followed after a gap by Arg(+), Lys(+), as well as by His(+) at pH 5. The (hkl)-specific area density of calcium ions, the protonation state of phosphate ions, and subsurface directional order of the ions in HAP lead to surface-specific binding patterns. Amino acids without ionic side groups exhibit weak binding, between −3 and 0 kJ/mol, due to difficulties to penetrate the first layer of water molecules on the apatite surfaces. We explain recognition processes that remained elusive in experiments, in prior simulations, discuss agreement with available data, and reconcile conflicting interpretations. The findings can serve as useful input for the design of peptides, proteins, and drug molecules for the modification of bone and teeth-related materials, as well as control of apatite mineralization.

Paleoproterozoic emplacement and Cambrian ultrahigh-temperature metamorphism of a layered magmatic intrusion from the Central Madurai Block, southern India: From Columbia to Gondwana

The Madurai Block in the Southern Granulite Terrane (SGT) of Peninsular India is one of the largest crustal blocks within the Neoproterozoic Gondwana assembly. This block is composed of three sub-blocks: the Neoarchean Northern Madurai block, Paleoproterozoic Central Madurai block and the dominantly Neoproterozoic Southern Madurai Block. The margins of these blocks are well-known for the occurrence of ultrahigh-temperature (UHT) granulite facies rocks mostly represented by Mg-Al metasediments. Here we report a dismembered layered mafic–ultramafic intrusion occurring in association with Mg-Al granulites from the classic locality of Ganguvarpatti in the Central Madurai Block. The major rock types of the layered intrusion include spinel orthopyroxenite, garnet-bearing gabbro, gabbro and gabbroic anorthosite showing rhythmic stratification and cumulate texture. The orthopyroxene-cordierite granulite from the associated Mg-Al layer is composed of spinel, cordierite and orthopyroxene. The pyroxene in both rock units is high-Al orthopyroxene formed under UHT metamorphic conditions. Conventional thermobarometry yields near-peak metamorphic conditions of 9.5–10 kbar pressure and a minimum temperature of 980 °C. We computed P–T pseudosections and contoured for the compositional as well as modal isopleths of the major mineral phases, which yield temperature above 1000 °C. FMAS petrogenetic grid, Al-in-orthopyroxene isopleth, conventional thermobarometry and calculated pseudosection reveal a clockwise pressure–temperature (P–T) path and near isothermal decompression. The U–Pb data on zircon grains from the layered magmatic suite indicate emplacement of the protolith at ca. 2.0 Ga and the metamorphic overgrowths yield weighted 206Pb/238U mean ages ca. 520 Ma. Monazite from the garnet-bearing gabbro and Opx-Crd granulite yielded 206Pb/238U weighted mean ages of ca. 532 Ma and 523 Ma marking the timing of metamorphism. We correlate the layered intrusion to a Paleoproterozoic suprasubduction zone setting, defining the Ganguvarpatti area as part of a collisional suture assembling the Northern and Central Madurai Blocks. The Paleoproterozoic magmatism and late Neoproterozoic-Cambrian UHT metamorphism can be linked to the tectonics of the Columbia and Gondwana supercontinents.

Geochemical Fractions of Heavy Metals in Bottom Sediments of the Pobeda Hydrothermal Cluster in the Mid-Atlantic Ridge (17°07′–17°08′ N)

In this study, to better understand the influence of hydrothermal processes on ore metal accumulation in bottom sediments, we examined distribution of Fe, Mn, Cu, Zn, As, and Pb in core of metalliferous sediments from the Pobeda hydrothermal cluster, and in core of non-mineralized (background) carbonate sediments (located 69 km northwards). Mechanisms of Fe, Mn, Cu, and Zn accumulation in sediments (12 samples) were evaluated based on sequential extraction of geochemical fractions, including a conditional mobile (F-1, exchangeable complex; F-2, authigenic Fe-Mn oxyhydroxides and associated metals; F-3, metals bound to organic matter/sulfides), and residual (F-4), fixed in crystalline lattices ones. The element contents were determined by the XRF and AAS methods, total carbon (TC) and total organic carbon (TOC) were determined using a Shimadzu TOC-L-CPN. Mineral composition and maps of element distribution in sediment components were obtained using the XRD and SEM-micro-X-ray spectrometry methods, respectively. In metalliferous sediments, according to our data, the major Fe mineral phase was goethite FeOOH (37–44% on a carbonate-free basis, cfb). In the metalliferous core, average contents (cfb), of Fe and Mn were 32.1% and 0.29%, whereas those of Cu, Zn, Pb, and As, were 0.74%, 0.27%, 0.03%, and 0.02%, respectively. Metalliferous sediments are enriched in Fe, Cu, Zn, Pb, and As, relatively to background ones. The exception was Mn, for which no increased accumulation in metalliferous core was recorded. Essential mass of Fe (up to 70% of total content) was represented by the residual fraction composed of crystallized goethite, aluminosilicates, the minerals derived from bedrock destruction processes mineral debris. Among geochemically mobile fractions, to 80% Fe of the (F-1 + F-2 + F-3) sum was determined in the form of F-2, authigenic oxyhydroxides. The same fraction was a predominant host for Mn in both metalliferous and background sediments (to 85%). With these Fe and Mn fractions, a major portion of Cu, Zn, and Pb was associated, while a less their amount was found in sulfide/organic fraction. In the metalliferous sediment core, maximal concentrations of metals and their geochemically mobile fractions were recorded in the deeper core sediment layers, an observation that might be attributed to influence of hydrothermal diffused fluids. Our data suggested that ore metals are mostly accumulated in sediment cores in their contact zone with the underlying serpentinized peridotites.

Zircon and Melt Extraction From a Long‐Lived and Vertically Extensive Magma System Underneath Ilopango Caldera (El Salvador)

AbstractThe Tierra Blanca (TB) eruptive suite comprises the last four major eruptions of Ilopango caldera in El Salvador (≤45 ka), including the youngest Tierra Blanca Joven eruption (TBJ; ∼106 km3): the most voluminous event during the Holocene in Central America. Despite the protracted and productive history of explosive silicic eruptions at Ilopango caldera, many aspects regarding the longevity and the prevailing physicochemical conditions of the underlying magmatic system remain unknown. Zircon 238U‐230Th geochronology of the TB suite (TBJ, TB2, TB3, and TB4) reveals a continuous and overlapping crystallization history among individual eruptions, suggesting persistent melt presence in thermally and compositionally distinct magma reservoirs over the last ca. 80 kyr. The longevity of zircon is in contrast to previously determined crystallization timescales of &lt;10 kyr for major mineral phases in TBJ. This dichotomy is explained by a process of rhyolitic melt segregation from a crystal‐rich refractory residue that incorporates zircon, whereas a new generation of major mineral phases crystallized shortly before eruption. Ti‐in‐zircon temperatures and amphibole geothermobarometry suggest that rhyolitic melt was extracted from different storage zones of the magma reservoir as indicated by distinct but synchronous thermochemical zircon histories among the TB suite eruptions. Zircon from TBJ and TB2 suggests magma differentiation within deeper and hotter parts of the reservoir, whereas zircon from TB3 and TB4 instead hints at crystallization in comparatively shallower and cooler domains. The assembly of the voluminous TBJ magma reservoir was also likely enhanced by cannibalization of hydrothermally altered components as suggested by low‐δ18O values in zircon (+4.5 ± 0.3‰).

Behavioral differences between weathering and pedogenesis in a subtropical humid granitic terrain: Implications for chemical weathering intensity evaluation

Continental weathering plays a crucial role in the evolution of the Earth’s surface by linking Earth's spheres, shaping landscapes and regulating chemical cycles and global climate. Regolith weathering studies in some cases ideally assume successive and progressive bottom-up physicochemical variation trends. To validate this assumption, we target a granitic regolith profile in a subtropical monsoon climate-dominated region (southeast China). We present mineralogical, petrographic and geochemical data from soil, saprolite and bedrock samples to characterize physical and chemical alterations. The petrographic and mineralogical results indicate that both plagioclase and K-feldspar are depleted and kaolinite is the major neoformed mineral phase in top-soil samples, revealing intensive chemical weathering on the regolith. However, these top-soil samples have much lower chemical index of alteration (CIA, ca. 64–67) values than the underlying oxidized-soil samples (CIA values ranging 65–80). Some chemically immobile elements, such as Al, Ti, Zr and Hf, are depleted in top-soil samples but are comparatively enriched in oxidized-soil samples. This is attributed to vertical leaching and translocation of fine-grained minerals (e.g., kaolinite, illite and zircon) through the soils. Furthermore, the analyzed top-soil samples are comparatively rich in elements K and P, which are most likely due to the evident biological fixation process. These physical and biological processes in the unconsolidated, porous and biotic top-soil layer can be responsible for the unexpected low CIA values. Our findings demonstrate the complex physical, chemical and biological alterations on soils and the differential behaviors between weathering and pedogenic processes, especially for those tropical–subtropical high rainfall regions. This case study also highlights the importance of petrographic and mineralogical proxies to chemical weathering intensity evaluation for regolith profiles and siliciclastic sediments.

Geochemical fractionation and spectroscopic fingerprinting for evaluation of the environmental transformation of potentially toxic metal(oid)s in surface-subsurface soils.

The contamination of soil by toxic metal(oid)s has emerged as a major concern worldwide, particularly in developing countries. A metals behavior in the soil environment is influenced by organic matter, mineral phases, and oxidation states in which a particular metal exists. However, the spectroscopic evidence of metal(oid)s interactions in soil with organic matter and mineral phases can induce an extensive understanding. The surface and sub-surface soils (0-50cm) from four sites of upper Indus basin, Pakistan, were collected and analyzed by using FTIR (Fourier-transform infrared spectroscopy), XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy) in addition to ICP-MS (inductively coupled plasma mass spectrometry) and geochemical fractionation. Geochemical fractionation of metal(oid)s indicated that As, Cu, Ni, Pb, and Zn were mostly found in the potentially bioavailable fractions. However, an increase in the residual fraction was observed from top to bottom. The absorption bands of FTIR spectra were divided into three spectral regions 700-400, 1700-800, and 3700-2800cm-1. The soil was found rich in organic matter and capable of retaining metals as abundant peaks were observed in the mid-infrared region. The mineralogical analysis of soil samples testified silicon oxides and zeolite as major mineral phases. The XPS spectra showed broad peaks of As(III), As2O3, As4S4, PbO2, and PbCo3. The study concludes that the source identification of metal(oid)s in the upper Indus is crucial to find out the particular source of contamination in the soil.

Hydrothermal-processed volcanic ash-based geopolymers for immobilization of sodium salt wastes containing Cs

Volcanic ash-based sodium salts-containing geopolymer with target composition close to that of Pollucite Cs(AlSi2O6) was formulated at 200 °C by mild hydrothermal method to immobilize Cs as waste material. The impact of three salts, namely, Na2SO4, NaCl, and NaNO2 on mineral phases of geopolymer waste forms and immobilization of Cs+ was investigated, specifically, regarding salts/NaOH molar ratio. Results indicate that when salts/NaOH molar ratio was 1:9, major mineral phase of geopolymer waste was analcime, whereas major mineral phase of matrix samples with salts/NaOH molar ratio as 1:1 was sodalite, which is beneficial to accommodate amounts of anions. Pollucite was formed in all samples with the introduction of CsOH·H2O to matrix samples. Product Consistency Test (PCT) leaching results indicate that NaOH plays key role in immobilization of Cs+. Moreover, C–S–H gel exhibits functional adsorption on Cs+; therefore, it has positive effect on the immobilization of Cs+. In Cs-containing samples with high salts/NaOH molar ratio, PCT leaching results show that high salts/NaOH molar ratio leads to low leaching concentrations of salts. However, only partial amounts of NO2− can be immobilized by sodalite due to oxidation of NO2− to NO3−. Furthermore, the attachment of SO42− to the surface of C–S–H gel can prevent the destruction of structure of C–S–H gel by ion exchange of Al3+ and Si4+. As a result, SO42−-containing samples have the lowest Cs+ leaching concentration among all Cs-containing samples with high salts/NaOH molar ratios. The immobilization of Cs+ can be further improved by the adsorption of C–S–H gel on Cs+. Results suggest that besides the formation of Pollucite, the immobilization of Cs+ also depends on various salts in sodium salts wastes containing Cs.