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Minerals, Volume 10, Issue 5 (May 2020) – 94 articles

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Open AccessFeature PaperReview
Sustainable Soil Bearing Capacity Improvement Using Natural Limited Life Geotextile Reinforcement—A Review
Minerals 2020, 10(5), 479; https://doi.org/10.3390/min10050479 (registering DOI) - 24 May 2020
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Abstract
Geotextiles are commercially made from synthetic fibres and have been used to enhance bearing capacity and to reduce the settlement of weak soil foundations. Several efforts have been made to investigate the possibility of using bio-based geotextiles for addressing environmental issues. This paper [...] Read more.
Geotextiles are commercially made from synthetic fibres and have been used to enhance bearing capacity and to reduce the settlement of weak soil foundations. Several efforts have been made to investigate the possibility of using bio-based geotextiles for addressing environmental issues. This paper attempts to review previous studies on the bearing capacity improvement of soils reinforced with bio-based geotextiles under a vertical static load. The bearing capacity of the unreinforced foundation was used as a reference to illustrate the role of bio-based geotextiles in bearing capacity improvement. The effects of first geotextile depth to footing width ratio (d/B), geotextile spacing to footing width ratio (S/B), geotextile length to footing width ratio (L/B) and the number of reinforcement layers (N) on the bearing capacity were reviewed and presented in this paper. The optimum d/B ratio, which resulted in the maximum ultimate bearing capacity, was found to be in the range of 0.25–0.4. The optimum S/B ratio was in the range of 0.12–0.5. The most suitable L/B ratio, which resulted in better soil performance against vertical pressure, was about 3. Besides, the optimum number of layers providing the maximum bearing capacity was about three This article is useful as a guideline for a practical design and future research on the application of the natural geotextiles to improve the short-term bearing capacity of weak soil foundations in various sustainable geotechnical applications. Full article
Open AccessArticle
Petrogenesis of the Snezhnoe Ruby Deposit, Central Pamir
Minerals 2020, 10(5), 478; https://doi.org/10.3390/min10050478 (registering DOI) - 24 May 2020
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Abstract
The Snezhnoe ruby deposit is located in the Muzkol–Rangkul anticlinorium within the Cimmerian zone of the Central Pamir. On the local scale, the deposit occurs on discrete relict bedding planes of calcitic marbles belonging to the Sarydzhilgin suite. Four ruby-bearing mineral assemblages are [...] Read more.
The Snezhnoe ruby deposit is located in the Muzkol–Rangkul anticlinorium within the Cimmerian zone of the Central Pamir. On the local scale, the deposit occurs on discrete relict bedding planes of calcitic marbles belonging to the Sarydzhilgin suite. Four ruby-bearing mineral assemblages are present within the main parts of the deposit: 1) scapolite + phlogopite + muscovite + margarite; 2) plagioclase + muscovite + margarite; 3) muscovite + phlogopite + margarite; 4) calcite. The ruby + calcite association is the most economically important, whereas the association of plagioclase + scapolite + phlogopite + muscovite is typical for the ruby-free parts of the deposit. Mica group minerals with a distinctive green color due to enhanced Cr and V concentrations are the main prospecting indicators for the ruby mineralization. The oxygen isotopic composition of the rubies is +15.3‰, a common value for crustal metamorphic and sedimentary rocks. The ratios of indicative trace elements in the rubies are Ga/Mg < 8.2, Fe/Mg < 51.2, Cr/Ga > 6.9 and Fe/Ti < 31.6. These values are characteristic for metamorphic corundum. The bulk ruby-bearing rocks have an initial 87Sr/86Sr ratio of ~0.70791 and εNd of ~−9.6, also pointing to the crustal origin of the deposit in agreement with the geological data. Ancient Al-enriched sediments are suggested to be a possible protolith for the ruby-bearing rocks. The temperature of the metamorphic processes was estimated at 760 ± 30 °C using Zr-in-rutile geothermometry. Raman mapping of rutile inclusions trapped within the ruby crystal indicates that the minimum pressure of mineralization was about one kilobar. The age determined by the Rb–Sr thermal ionization mass spectrometry of phlogopite, plagioclase and bulk rock is 23 ± 1.6 Ma, corresponding to the timing of relaxation after peak metamorphism during the Alpine–Himalayan Orogeny. Full article
(This article belongs to the Special Issue Mineralogy and Geochemistry of Ruby)
Open AccessArticle
Use of Seawater/Brine and Caliche’s Salts as Clean and Environmentally Friendly Sources of Chloride and Nitrate Ions for Chalcopyrite Concentrate Leaching
Minerals 2020, 10(5), 477; https://doi.org/10.3390/min10050477 (registering DOI) - 23 May 2020
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Abstract
A less harmful approach for the environment regarding chalcopyrite concentrate leaching, using seawater/brine and caliche’s salts as a source of chloride and nitrate ions, was investigated. Different variables were evaluated: sulfuric acid concentration, sodium nitrate concentration, chloride concentration, source of water (distilled water, [...] Read more.
A less harmful approach for the environment regarding chalcopyrite concentrate leaching, using seawater/brine and caliche’s salts as a source of chloride and nitrate ions, was investigated. Different variables were evaluated: sulfuric acid concentration, sodium nitrate concentration, chloride concentration, source of water (distilled water, seawater, and brine), temperature, concentrate sample type, nitrate source (analytical grade and industrial salt), and pre-treatment methods in order to obtain maximum copper extraction. All tests were performed at moderate temperatures (≤45 °C) and atmospheric pressure. The leaching system using distilled water, seawater, and brine base media resulted in copper extraction of 70.9%, 90.6%, and 86.6% respectively. The leaching media, with a concentration of 20 g/L Cl, obtained a maximum Cu extraction of 93.5%. An increase in the concentration of H2SO4 and NaNO3 from 0.5 to 0.7 M, led to an increase in the copper extraction. The use of an industrial salt compared to the analytical salt did not show great variations in the percentage of extraction achieved, which would be a good and cost effective alternative. The increase in temperature from 25 to 45 °C showed a great effect on the copper leaching (of 60% until 90.6%, respectively). The pre-treatment is suggested to increase copper extraction from 60.0% to 71.4%. Full article
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Open AccessArticle
Gold Exploration in Two and Three Dimensions: Improved and Correlative Insights from Microscopy and X-Ray Computed Tomography
Minerals 2020, 10(5), 476; https://doi.org/10.3390/min10050476 (registering DOI) - 23 May 2020
Viewed by 159
Abstract
In this contribution, we highlight a correlative approach in which three-dimensional structural/positional data are combined with two dimensional chemical and mineralogical data to understand a complex orogenic gold mineralization system; we use the Kirk Range (southern Malawi) as a case study. Three dimensional [...] Read more.
In this contribution, we highlight a correlative approach in which three-dimensional structural/positional data are combined with two dimensional chemical and mineralogical data to understand a complex orogenic gold mineralization system; we use the Kirk Range (southern Malawi) as a case study. Three dimensional structures and semi-quantitative mineral distributions were evaluated using X-ray Computed Tomography (XCT) and this was augmented with textural, mineralogical and chemical imaging using Scanning Electron Microscopy (SEM) and optical microscopy as well as fire assay. Our results detail the utility of the correlative approach both for quantifying gold concentrations in core samples (which is often nuggety and may thus be misrepresented by quarter- or half-core assays), and for understanding the spatial distribution of gold and associated structures and microstructures in 3D space. This approach overlays complementary datasets from 2D and 3D analytical protocols, thereby allowing a better and more comprehensive understanding on the distribution and structures controlling gold mineralization. Combining 3D XCT analyses with conventional 2D microscopies derive the full value out of a given exploration drilling program and it provides an excellent tool for understanding gold mineralization. Understanding the spatial distribution of gold and associated structures and microstructures in 3D space holds vast potential for exploration practitioners, especially if the correlative approach can be automated and if the resultant spatially-constrained microstructural information can be fed directly into commercially available geological modelling software. The extra layers of information provided by using correlative 2D and 3D microscopies offer an exciting new tool to enhance and optimize mineral exploration workflows, given that modern exploration efforts are targeting increasingly complex and low-grade ore deposits. Full article
(This article belongs to the Special Issue Novel Methods and Applications for Mineral Exploration, Volume II)
Open AccessArticle
Application of GETFLOWS Coupled with Chemical Reactions to Arsenic Removal through Ferrihydrite Coprecipitation in an Artificial Wetland of a Japanese Closed Mine
Minerals 2020, 10(5), 475; https://doi.org/10.3390/min10050475 (registering DOI) - 23 May 2020
Viewed by 179
Abstract
Passive systems that utilize a natural power such as a pond, plant, or microorganisms, is expected to be a cost-effective method for acid mine drainage (AMD) treatment. The Ningyo-toge mine, a non-operational uranium mine located in Okayama Prefecture, Japan, generates AMD containing arsenic [...] Read more.
Passive systems that utilize a natural power such as a pond, plant, or microorganisms, is expected to be a cost-effective method for acid mine drainage (AMD) treatment. The Ningyo-toge mine, a non-operational uranium mine located in Okayama Prefecture, Japan, generates AMD containing arsenic and iron. To quantitatively study arsenic and iron ion removal in an artificial wetland and pond, chemical reactions were modeled and incorporated into the GETFLOWS (general-purpose terrestrial fluid-flow simulator) software. The chemical reaction models consisted of arsenite and ferrous oxidation equations and arsenic adsorption on ferrihydrite. The X-ray diffraction analysis of sediment samples showed ferrihydrite patterns. These results were consistent with the model for arsenite/ferrous oxidation and arsenic adsorption on ferrihydrite. Geofluid simulation was conducted to simulate mass transfer with the utilized topographic model, inlet flow rate, precipitation, and evaporation. The measured arsenic and iron ions concentrations in solution samples from the wetland and pond, fitted well with the model. This indicated that the main removal mechanism was the oxidation of arsenite/ferrous ions and that arsenic was removed by adsorption rather than dilution. Full article
(This article belongs to the Special Issue Pollutants in Acid Mine Drainage)
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Open AccessArticle
Mineralogical Prediction of Flotation Performance for a Sediment-Hosted Copper–Cobalt Sulphide Ore
Minerals 2020, 10(5), 474; https://doi.org/10.3390/min10050474 (registering DOI) - 23 May 2020
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Abstract
As part of a study investigating the influence of mineralogical variability in a sediment hosted copper–cobalt deposit in the Democratic Republic of Congo on flotation performance, the flotation of nine sulphide ore samples was investigated through laboratory batch kinetics tests and quantitative mineral [...] Read more.
As part of a study investigating the influence of mineralogical variability in a sediment hosted copper–cobalt deposit in the Democratic Republic of Congo on flotation performance, the flotation of nine sulphide ore samples was investigated through laboratory batch kinetics tests and quantitative mineral analyses. Using a range of ore samples from the same deposit the influence of mineralogy on flotation performance was studied. Characterisation of the samples through QEMSCAN showed that bornite, chalcopyrite, chalcocite and carrollite are the main copper-bearing sulphide minerals while carrollite is the only cobalt-bearing mineral. Mineralogical characteristics were averaged per sample to allow for a quantitative correlation with flotation performance parameters. Equilibrium recoveries, rate constants and final grades of the samples were correlated to the feed mineralogy through Multiple Linear Regression (MLR). Target sulphide minerals content and particle size, magnesiochlorite content, carrollite liberation and association of the copper and cobalt minerals with magnesiochlorite and dolomite were used to predict flotation performance. Leave One Out Cross Validation (LOOCV) revealed that the final copper and cobalt grades are predicted with an R2 of 0.80 and 0.93 and Root Mean Square Error of Cross Validation (RMSECV) of 4.41% and 1.34%. The recovery of cobalt and copper with time can be predicted with an R2 of 0.94 for both and an overall test error of 4.70% and 5.14%. Overall, it was shown that quantitative understanding of changes in mineralogy allows for prediction of changes in flotation performance. Full article
(This article belongs to the Section Mineral Processing and Metallurgy)
Open AccessArticle
Characterization of Mineralogy in the Highland Valley Porphyry Cu District Using Hyperspectral Imaging, and Potential Applications
Minerals 2020, 10(5), 473; https://doi.org/10.3390/min10050473 (registering DOI) - 23 May 2020
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Abstract
The Highland Valley Copper (HVC) district in British Columbia, Canada, is host to at least four major porphyry Cu systems: Bethlehem (~209 Ma), and Valley, Lornex, and Highmont (~208 to 207 Ma). High spatial resolution (0.2–1.0 mm/pixel) hyperspectral imagery in the shortwave infrared [...] Read more.
The Highland Valley Copper (HVC) district in British Columbia, Canada, is host to at least four major porphyry Cu systems: Bethlehem (~209 Ma), and Valley, Lornex, and Highmont (~208 to 207 Ma). High spatial resolution (0.2–1.0 mm/pixel) hyperspectral imagery in the shortwave infrared (SWIR) were acquired on 755 rock samples and 400 m of continuous drill core. Spectral metrics are used to measure the relative abundance of 12 minerals and an additional metric is derived to estimate white mica grain size. In the Valley and Lornex deposits, coarse-grained white mica is associated with mineralization and is detectable up to 4 km away from the deposits. Kaolinite is present within 2 km of the mineralized centers but does not necessarily occur within strongly mineralized intervals. Prehnite is ubiquitous from 4 to 8 km from the deposits. In the Bethlehem deposit, tourmaline and epidote are associated with mineralization. We propose a spectral alteration score based on these proximal hyperspectral SWIR mineralogical patterns to assist explorers in targeting porphyry Cu systems when using drill core, surface rock samples and potentially remote sensing imagery. In a production environment, this metric could serve to facilitate ore-sorting. Full article
(This article belongs to the Section Mineral Deposits)
Open AccessArticle
Coexisting Rubies and Blue Sapphires from Major World Deposits: A Brief Review of Their Mineralogical Properties
Minerals 2020, 10(5), 472; https://doi.org/10.3390/min10050472 - 22 May 2020
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Abstract
Gem corundum deposits are typically divided into blue sapphire and ruby deposits. However, this classification often overlooks the fact that the precious stones produced are the same mineral with only an overall slight difference in their trace element profiles. It can take only [...] Read more.
Gem corundum deposits are typically divided into blue sapphire and ruby deposits. However, this classification often overlooks the fact that the precious stones produced are the same mineral with only an overall slight difference in their trace element profiles. It can take only a couple thousand ppm chromium to create the rich, red color expected of a ruby. This contribution deals specifically with economically important gem corundum mining regions that produce both blue sapphires and rubies either in comparable quantities (Mogok, Myanmar, and the basalt-related gem fields on the border between Thailand and Cambodia at Chanthaburi, Thailand, and Pailin, Cambodia) or predominantly blue sapphires with rare rubies (secondary Montana sapphire deposits and Yogo Gulch in Montana as well as the gem fields of Sri Lanka). Comparison of the trace element profiles and inclusions in the blue sapphire/ruby assemblages in these deposits shows that there are both monogenetic and polygenetic assemblages in which the blue sapphires and rubies have the same geological origin (monogenetic) or distinct geological origins (polygenetic). In the monogenetic assemblages, the rubies and blue sapphires have essentially indistinguishable inclusions and trace element chemistry profiles (with the exception of Cr contents). On the other hand, polygenetic assemblages are composed of rubies and blue sapphires with distinct inclusions and trace element chemistry profiles. Notably, in the monogenetic assemblages, chromium seems to vary independently from other trace elements. In these assemblages, Cr can vary by nearly four orders of magnitude with essentially no consistent relationship to other trace elements. The observations described herein are an attempt to address the question of what the geochemical and geological constraints are that turn gem corundum into a spectacular ruby. Full article
(This article belongs to the Special Issue Mineralogy and Geochemistry of Ruby)
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Open AccessArticle
Three-Dimensional Regularized Focusing Migration: A Case Study from the Yucheng Mining Area, Shandong, China
Minerals 2020, 10(5), 471; https://doi.org/10.3390/min10050471 - 22 May 2020
Viewed by 155
Abstract
Gravity migration is a fast imaging technique based on the migration concept to obtain subsurface density distribution. For higher resolution of migration imaging results, we propose a 3D regularized focusing migration method that implements migration imaging of an entire gravity survey with a [...] Read more.
Gravity migration is a fast imaging technique based on the migration concept to obtain subsurface density distribution. For higher resolution of migration imaging results, we propose a 3D regularized focusing migration method that implements migration imaging of an entire gravity survey with a focusing stabilizer based on regularization theory. When determining the model parameters, the iterative direction is chosen as the conjugate migration direction, and the step size is selected on the basis of the Wolfe–Powell conditions. The model tests demonstrate that the proposed method can improve the resolution and precision of imaging results, especially for blocky structures. At the same time, the method has high computational efficiency, which allows rapid imaging for large-scale gravity data. It also has high stability in noisy conditions. The developed novel method is applied to interpret gravity data collected from the skarn-type iron deposits in Yucheng, Shandong province. Migration results show that the depth of the buried iron ore in this area is 750–1500 m, which is consistent with the drilling data. We also provide recommendations for further mineral exploration in the survey area. This method can be used to complete rapid global imaging of large mining areas and it provides important technical support for exploration of deep, concealed deposits. Full article
(This article belongs to the Special Issue Geophysics for Mineral Exploration)
Open AccessArticle
Greenockite Whiskers from the Bytom Burned Coal Dump, Upper Silesia, Poland
Minerals 2020, 10(5), 470; https://doi.org/10.3390/min10050470 - 22 May 2020
Viewed by 183
Abstract
Orange greenockite (CdS) aggregates were found in a small fumarole at a burned coal dump near Bytom, Upper Silesia, Poland and were studied using a variety of techniques in order to determine their chemistry, morphology, and most importantly, the mechanism of crystal growth. [...] Read more.
Orange greenockite (CdS) aggregates were found in a small fumarole at a burned coal dump near Bytom, Upper Silesia, Poland and were studied using a variety of techniques in order to determine their chemistry, morphology, and most importantly, the mechanism of crystal growth. Greenockite rods, wires, and whiskers with bismuth drops on crystal tops are predominant in these aggregates. Greenockite rods oriented sub-perpendicular to the substrate surface. The rod thickness reaches 5–6 μm and about 10 μm in length. The catalyst bismuth drop has a diameter comparable to the rod thickness. Fiber forms (wires and whiskers) are sub-parallel to the substrate surface. The thickness of these forms is usually less than 2 μm, and the length can be close to 1 mm. The bismuth drop diameter can show a large excess over the fiber thickness. Catalyst drops on the tops of whiskers began to change their form dynamically and exploded, spraying bismuth under the electron beam effect. Rods grow along the [01–10] direction, and whiskers and wires (axial forms) along the [0001] direction. Greenockite rod crystals, carrying on top a relatively homogenous bismuth catalyst drop, were formed on the heated substrate according to the VLS (vapor–liquid–solid) mechanism at temperatures not lower than 270 °C. Greenockite whiskers and wires grew just above of the substrate surface according to the VQS (vapor–quasiliquid–solid) mechanism at temperatures lower than 200 °C. These mechanisms of growth have very rarely been recorded to occur in nature and even less so in burning coal dumps. The cooperative growth effects of the fiber greenockite crystals were also described. Full article
(This article belongs to the collection Minerals in Coal and Coal Combustion Products)
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Open AccessArticle
Textural Identification of Polycrystalline Magmatic, Tectonically-Deformed, and Shock-Related Zircon Aggregates
Minerals 2020, 10(5), 469; https://doi.org/10.3390/min10050469 - 21 May 2020
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Abstract
Zircon with polycrystalline or polygranular appearance is either produced in the magmatic environment through crystallization, or due to deformation in metamorphic settings (including regional metamorphism and ductile shear zones), or as a result of shock-induced recrystallization. All three types can be easily confused [...] Read more.
Zircon with polycrystalline or polygranular appearance is either produced in the magmatic environment through crystallization, or due to deformation in metamorphic settings (including regional metamorphism and ductile shear zones), or as a result of shock-induced recrystallization. All three types can be easily confused and potentially lead to incorrect interpretations, especially if the crystallographic orientation analyses of zircon are not conducted. It is particularly important to establish the difference between tectonically-deformed polygranular zircon and shock-induced polygranular zircon because the latter serves as an indicator of shock event and is often used for dating asteroid impacts. In this paper, a series of polycrystalline zircon grains from ductile shear zones and metamorphic rocks are analyzed using a combination of techniques (BSE, CL, orientation contrast, EBSD, and microprobe mapping), and their properties are compared to reported polycrystalline zircons from magmatic and impact settings. This work shows how appearance, crystallographic orientation, and CL signature of “granules” differ between the different types of deformed zircon. Full article
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Open AccessArticle
Use of Temperature Controlled Stage Confocal Raman Microscopy to Study Phase Transition of Lead Dioxide (Plattnerite)
Minerals 2020, 10(5), 468; https://doi.org/10.3390/min10050468 - 21 May 2020
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Abstract
The present work concerns the study of the phase transition of plattnerite [β-PbO2 lead (IV) oxide]-based samples when they are analysed by Raman spectroscopy. The laser-induced degradation process was carried out either on historical painting samples, where plattnerite was present as a [...] Read more.
The present work concerns the study of the phase transition of plattnerite [β-PbO2 lead (IV) oxide]-based samples when they are analysed by Raman spectroscopy. The laser-induced degradation process was carried out either on historical painting samples, where plattnerite was present as a degradation product of lead-based pigments, or commercial plattnerite samples as powder and pellets. The Raman spectra of plattnerite taken at low excitation power, to avoid phase transformations, are reported up to low wavenumbers, and they were characterized by the features at 159, 380, 515 and 653 cm−1 and a shoulder at 540 cm−1. The degradation of plattnerite was induced by increasing the laser power on the sample, and the formation of its secondary products red lead (Pb3O4), litharge (α-PbO) and massicot (β-PbO), when varying the laser power, is discussed. The analyses were performed in a controlled condition by coupling the Raman spectrometer to a temperature-controlled stage (Linkam THMS600- Renishaw), which allows for varying the sample temperature (from room temperature up to 600 °C) and keeping it constant inside the stage during the analysis. In this way, commercial plattnerite samples were heated by increasing the cell temperature to verify the temperature range at which the phase transitions of lead dioxide occur. In addition, thanks to the construction of temperature ramps, all the degradation pathways were shown, and other lead compounds were identified, generated by the laser power contribution. A different behaviour was found between pigments from historical painting samples and commercial samples under the effect of the laser. This information could be useful in order to recognize their nature when they are found in cultural heritage materials. Full article
(This article belongs to the Special Issue Historical Mineral Pigments)
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Open AccessArticle
Richardsite, Zn2CuGaS4, A New Gallium-Essential Member of the Stannite Group from the Gem Mines near Merelani, Tanzania
Minerals 2020, 10(5), 467; https://doi.org/10.3390/min10050467 - 20 May 2020
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Abstract
The new mineral richardsite occurs as overgrowths of small (50–400 μm) dark gray, disphenoidal crystals with no evident twinning, but epitaxically oriented on wurtzite–sphalerite crystals from the gem mines near Merelani, Lelatema Mountains, Simanjiro District, Manyara Region, Tanzania. Associated minerals also include graphite, [...] Read more.
The new mineral richardsite occurs as overgrowths of small (50–400 μm) dark gray, disphenoidal crystals with no evident twinning, but epitaxically oriented on wurtzite–sphalerite crystals from the gem mines near Merelani, Lelatema Mountains, Simanjiro District, Manyara Region, Tanzania. Associated minerals also include graphite, diopside, and Ge,Ga-rich wurtzite. It is brittle, dark gray in color, and has a metallic luster. It appears dark bluish gray in reflected plane-polarized light, and is moderately bireflectant. It is distinctly anisotropic with violet to light-blue rotation tints with crossed polarizers. Reflectance percentages for Rmin and Rmax in air at the respective wavelengths are 23.5, 25.0 (471.1 nm); 27.4, 28.9 (548.3 nm); 28.1, 29.4 (586.6 nm); 27.7, 28.9 (652.3 nm). Richardsite does not show pleochroism, internal reflections, or optical indications of growth zonation. Electron microprobe analyses determine an empirical formula, based on 8 apfu, as (Zn1.975Cu0.995Ga0.995Fe0.025Mn0.010Ge0.005Sn0.005)Σ4.010S3.990, while its simplified formula is (Zn,Cu)2(Cu,Fe,Mn)(Ga,Ge,Sn)S4, and the ideal formula is Zn2CuGaS4. The crystal structure of richardsite was investigated using single-crystal and powder X-ray diffraction. It is tetragonal, with a = 5.3626(2) Å, c = 10.5873(5) Å, V = 304.46(2) Å3, Z = 2, and a calculated density of 4.278 g·cm−3. The four most intense X-ray powder diffraction lines [d in Å (I/I0)] are 3.084 (100); 1.882 (40); 1.989 (20); 1.614 (20). The refined crystal structure (R1 = 0.0284 for 655 reflections) and obtained chemical formula indicate that richardsite is a new member of the stannite group with space group . Its structure consists of a ccp array of sulfur atoms tetrahedrally bonded with metal atoms occupying one-half of the ccp tetrahedral voids. The ordering of the metal atoms leads to a sphalerite(sph)-derivative tetragonal unit-cell, with a » asph and c » 2asph. The packing of S atoms slightly deviates from the ideal, mainly due to the presence of Ga. Using 632.8-nm wavelength laser excitation, the most intense Raman response is a narrow peak at 309 cm−1, with other relatively strong bands at 276, 350, and 366 cm−1, and broader and weaker bands at 172, 676, and 722 cm−1. Richardsite is named in honor of Dr. R. Peter Richards in recognition of his extensive research and writing on topics related to understanding the genesis of the morphology of minerals. Its status as a new mineral and its name have been approved by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association (No. 2019-136). Full article
Open AccessArticle
Adsorption and Separation of Crystal Violet, Cerium(III) and Lead(II) by Means of a Multi-Step Strategy Based on K10-Montmorillonite
Minerals 2020, 10(5), 466; https://doi.org/10.3390/min10050466 - 20 May 2020
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Abstract
A multi-step procedure, based on the employment of K10-Montmorillonite, is proposed for the selective removal of metal ions and dyes from a multicomponent solution. The objective is twofold: decontaminate the effluents and separate and recover the valuable byproducts present in wastewaters. Three common [...] Read more.
A multi-step procedure, based on the employment of K10-Montmorillonite, is proposed for the selective removal of metal ions and dyes from a multicomponent solution. The objective is twofold: decontaminate the effluents and separate and recover the valuable byproducts present in wastewaters. Three common contaminants, i.e., crystal violet dye (CV), Ce(III) and Pb(II) were chosen as “model” pollutants. The main factors affecting the pollutants’ sorption were investigated. The experimental data were correlated with adsorption isotherms and kinetic models to obtain a deeper insight into the adsorption processes. The affinity of the clay toward the pollutants is favored by an increasing pH and follows the order CV > Pb(II) > Ce(III). Whereas Ce(III) metal ions do not adsorb onto clay under strongly acidic conditions, both Pb(II) and CV can adsorb under all the investigated pH conditions. The analysis of isotherms and kinetic profiles revealed that CV adsorbs onto clay through a mechanism consisting of two parallel processes, namely cation exchange on the external mineral surface and in the interlayer and surface complexation at the edge sites, while metal ion uptake is due solely to cation exchange processes involving mineral surfaces. The time required for the complete removal of pollutants follows the order CV > Ce(III) >> Pb(II). The possibility to modulate the adsorption features by changing experimental conditions was successfully employed to propose the best strategy for the progressive removal of different components from aqueous solutions. Full article
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Open AccessArticle
Lithogeochemistry of the Mid-Ocean Ridge Basalts near the Fossil Ridge of the Southwest Sub-Basin, South China Sea
Minerals 2020, 10(5), 465; https://doi.org/10.3390/min10050465 - 20 May 2020
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Abstract
Mid-ocean ridge basalts (MORB) in the South China Sea (SCS) record deep crust-mantle processes during seafloor spreading. We conducted a petrological and geochemical study on the MORBs obtained from the southwest sub-basin of the SCS at site U1433 and U1434 of the International [...] Read more.
Mid-ocean ridge basalts (MORB) in the South China Sea (SCS) record deep crust-mantle processes during seafloor spreading. We conducted a petrological and geochemical study on the MORBs obtained from the southwest sub-basin of the SCS at site U1433 and U1434 of the International Ocean Discovery Program (IODP) Expedition 349. Results show that MORBs at IODP site U1433 and U1434 are unaffected by seawater alteration, and all U1433 and the bulk of U1434 rocks belong to the sub-alkaline low-potassium tholeiitic basalt series. Samples collected from site U1433 and U1434 are enriched mid-ocean ridge basalts (E-MORBs), and the U1434 basalts are more enriched in incompatible elements than the U1433 samples. The SCS MORBs have mainly undergone the fractional crystallization of olivine, accompanied by the relatively weak fractional crystallization of plagioclase and clinopyroxene during magma evolution. The magma of both sites might be mainly produced by the high-degree partial melting of spinel peridotite at low pressures. The degree of partial melting at site U1434 was lower than at U1433, ascribed to the relatively lower spreading rate. The magmatic source of the southwest sub-basin basalts may be contaminated by lower continental crust and contributed by recycled oceanic crust component during the opening of the SCS. Full article
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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Open AccessArticle
Covalent Protein Immobilization onto Muscovite Mica Surface with a Photocrosslinker
Minerals 2020, 10(5), 464; https://doi.org/10.3390/min10050464 - 20 May 2020
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Abstract
Muscovite mica with an amino silane-modified surface is commonly used as a substrate in atomic force microscopy (AFM) studies of biological macromolecules. Herein, the efficiency of two different protein immobilization strategies employing either (N-hydroxysuccinimide ester)-based crosslinker (DSP) or benzophenone-based photoactivatable crosslinker (SuccBB) has [...] Read more.
Muscovite mica with an amino silane-modified surface is commonly used as a substrate in atomic force microscopy (AFM) studies of biological macromolecules. Herein, the efficiency of two different protein immobilization strategies employing either (N-hydroxysuccinimide ester)-based crosslinker (DSP) or benzophenone-based photoactivatable crosslinker (SuccBB) has been compared using AFM and mass spectrometry analysis. Two proteins with different physicochemical properties—human serum albumin (HSA) and horseradish peroxidase enzyme protein (HRP)—have been used as model objects in the study. In the case of HRP, both crosslinkers exhibited high immobilization efficiency—as opposed to the case with HSA, when sufficient capturing efficiency has only been observed with SuccBB photocrosslinker. The results obtained herein can find their application in commonly employed bioanalytical systems and in the development of novel highly sensitive chip-based diagnostic platforms employing immobilized proteins. The obtained data can also be of interest for other research areas in medicine and biotechnology employing immobilized biomolecules. Full article
Open AccessArticle
An X-ray Absorption Near-Edge Structure (XANES) Study on the Oxidation State of Chromophores in Natural Kunzite Samples from Nuristan, Afghanistan
Minerals 2020, 10(5), 463; https://doi.org/10.3390/min10050463 - 20 May 2020
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Abstract
Kunzite, the pink variety of spodumene is famous and desirable among gemstone lovers. Due to its tenebrescent properties, kunzite always remains a hot research candidate among physicists and mineralogists. The present work is continuing the effort towards value addition to kunzite by enhancing [...] Read more.
Kunzite, the pink variety of spodumene is famous and desirable among gemstone lovers. Due to its tenebrescent properties, kunzite always remains a hot research candidate among physicists and mineralogists. The present work is continuing the effort towards value addition to kunzite by enhancing its color using different treatments. Before color enhancement, it is essential to identify the chromophores and their oxidation states. In this paper, the authors investigated the main impurities in natural kunzite from the Nuristan area in Afghanistan and their valence states. Some impurities in the LiAlSi2O6 spodumene structure were identified and quantified by using sensitive techniques, including Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS), UV−VIS and X-ray absorption near-edge structure (XANES). LA-ICP-MS indicated many trace elements as impurities in kunzite, among which Fe and Mn are the main elements responsible for coloration. The oxidation states of these two transition elements were determined by the XANES technique. The study reveals that Mn is present in both Mn2+ and Mn3+ oxidation states, while Fe is present only in Fe3+ oxidation state. Full article
(This article belongs to the Special Issue X-ray Absorption Spectroscopy of Synthetic and Natural Minerals)
Open AccessArticle
Layered Double Hydroxides with Intercalated Permanganate and Peroxydisulphate Anions for Oxidative Removal of Chlorinated Organic Solvents Contaminated Water
Minerals 2020, 10(5), 462; https://doi.org/10.3390/min10050462 - 20 May 2020
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Abstract
The contamination by chlorinated organic solvents is a worldwide problem as they can deeply penetrate aquifers, accumulating in the sub-surface as lenses of highly hazardous pollutants. In recent years, so called in situ oxidation processes have been developed to remediate chlorinated organic solvents [...] Read more.
The contamination by chlorinated organic solvents is a worldwide problem as they can deeply penetrate aquifers, accumulating in the sub-surface as lenses of highly hazardous pollutants. In recent years, so called in situ oxidation processes have been developed to remediate chlorinated organic solvents from groundwater and soil by injecting solutions of oxidising agents such as permanganate or peroxydisulphate. We here present modified layered double hydroxides (LDHs) with intercalated oxidising agents that might serve as new reactants for these remediation strategies. LDHs might serve as support and stabiliser materials for selected oxidising agents during injection, as the uncontrolled reaction and consumption might be inhibited, and guarantee that the selected oxidants persist in the subsurface after injection. In this study, LDHs with hydrotalcite- and hydrocalumite-like structures intercalated with permanganate and peroxydisulphate anions were synthesised and their efficiency was tested in batch experiments using trichloroethene or 1,1,2-trichloroethane as the target contaminants. All samples were characterised using powder X-ray diffraction, thermal analysis coupled with mass spectrometry to directly analyse evolving gases, and Fourier-transform infrared spectroscopy. Additionally, particle size distribution measurements were carried out on the synthesised materials. Results of the batch experiments confirmed the hypothesis that oxidising agents keep their properties after intercalation. Permanganate intercalated LDHs proved to be most efficient at degrading trichloroethene while peroxydisulphate intercalated Ca,Al-LDHs were the most promising studied reactants degrading 1,1,2-trichloroethane. The detection of dichloroethene as well as the transformation of the studied reactants into new LDH phases confirmed the successful degradation of the target contaminant by oxidation processes generated from the intercalated oxidising agent. Full article
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Open AccessArticle
Successful Ecological Regeneration of Opencast Coal Mine Spoils through Forestation: From Cradle to Grove
Minerals 2020, 10(5), 461; https://doi.org/10.3390/min10050461 - 20 May 2020
Viewed by 214
Abstract
The reclamation of surface (opencast) coal mines is not always successful; there remains a legacy of degraded land that burdens local communities. This article evaluates a community-oriented, low-cost means of geoecological regeneration, the “Cradle for Nature” strategy, which uses mosaic tree planting to [...] Read more.
The reclamation of surface (opencast) coal mines is not always successful; there remains a legacy of degraded land that burdens local communities. This article evaluates a community-oriented, low-cost means of geoecological regeneration, the “Cradle for Nature” strategy, which uses mosaic tree planting to foster positive natural ecological processes. Results show that, while the autocompaction of minestones quickly raises soil densities to levels hostile to plant growth, forestation helps moderate soil densities. Weathering concentrates metals in minestones, but 14 years of forestation reduced the loadings of five metals by 35–52%. Twenty years of forestation doubled soil organic carbon to >7%; increased bacilli from 7% to 46%; actinomycetes from 10% to 26%; and soil microbe counts 12–15 times, especially in tree plantings treated with fertiliser. Soils under trees also supported a significantly greater earthworm biomass than under grass but, while open-canopy plantings had increased ground flora biodiversity, closed-canopy plantings had lower diversity and biomass. Following closure to grazing, ground biomass increased sevenfold. Young trees act as bird perches and significantly increase seed fall. Small mammal biomass and biodiversity increases after tree planting and higher predators appear. Varteg’s constructed forest provides an effective “cradle” for an emergent geoecological system and its habitat mosaic maximises biodiversity. Full article
(This article belongs to the Special Issue Sustainable Use of Abandoned Mines)
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Open AccessArticle
Cleaner Production of Chromium Oxide from Low Fe(II)-Chromite
Minerals 2020, 10(5), 460; https://doi.org/10.3390/min10050460 - 19 May 2020
Viewed by 243
Abstract
Sulfuric acid-based leaching is a promising cleaner method to produce chromium salts, but its feasibility for treating low Fe(II)-chromite still remains to be proven. A Box–Behnken design (BBD)-based set of experiments for sulfuric acid leaching of low Fe(II)-chromite was utilized in this work [...] Read more.
Sulfuric acid-based leaching is a promising cleaner method to produce chromium salts, but its feasibility for treating low Fe(II)-chromite still remains to be proven. A Box–Behnken design (BBD)-based set of experiments for sulfuric acid leaching of low Fe(II)-chromite was utilized in this work for generating an experimental dataset for revealing the functional relationships between the processing parameters and the extraction yields of Cr and Fe. The dependent variables were found to exhibit strong intercorrelations and the models developed on the basis of statistical criteria showed excellent prediction accuracy. The optimum process conditions of leaching treatment were found to be a temperature of 176 °C, a dichromic acid/chromite mass ratio of 0.12, and a sulfuric acid concentration of 81%. Furthermore, the dissolution behavior of chromite in the leaching process and the effect of dichromic acid were experimentally investigated. It was found that the decomposition efficiency was highly dependent on the Fe(II) content of chromite, and that the dichromic acid acted both as an oxidant and a catalyst in the leaching process. On the basis of the results of this study, a novel process for treating low-Fe(II) chromite was proposed. Full article
(This article belongs to the Special Issue Cleaner Production in Mineral Processing)
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Open AccessArticle
A Morphological and Size-Based Study of the Changes of Iron Sulfides in the Caples and Torlesse Terranes (Otago Schist, New Zealand) during Prograde Metamorphic Evolution
Minerals 2020, 10(5), 459; https://doi.org/10.3390/min10050459 - 19 May 2020
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Abstract
It is widely accepted that metamorphism induces a remobilization of iron sulfides, sweeping away original ones while creating new ones. This paper analyzes size distributions of iron sulfides in several samples from the Caples and Torlesse terranes from the Otago Schist (New Zealand) [...] Read more.
It is widely accepted that metamorphism induces a remobilization of iron sulfides, sweeping away original ones while creating new ones. This paper analyzes size distributions of iron sulfides in several samples from the Caples and Torlesse terranes from the Otago Schist (New Zealand) using high-resolution X-ray computed tomography, which allows all iron sulfides larger than the resolution at which X-ray scans were performed to be characterized. Framboids and clusters of framboids are common in unmetamorphosed samples, but disappear in greenschist/amphibolite facies samples, where iron sulfides have anhedral habits. By contrast, the size and standard deviation of the new iron sulfides both remain within the same range. The results illuminate the evolution of iron sulfides throughout metamorphism, proposing boundaries for the metamorphic processes based on the shape of these iron sulfides. Full article
(This article belongs to the Section Mineral Deposits)
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Open AccessArticle
Model Test and Numerical Study on Surrounding Rock Deformation and Overburden Strata Movement Law of Gob-Side Entry Retaining via Roof Cutting
Minerals 2020, 10(5), 458; https://doi.org/10.3390/min10050458 - 19 May 2020
Viewed by 199
Abstract
The effects of roof cutting techniques on the movement law of the overlying strata and deformation features of the surrounding rock in gob-side entry retaining mines were studied using 200 working faces of the Dianping coal mine in Shanxi Province. Using a mechanical [...] Read more.
The effects of roof cutting techniques on the movement law of the overlying strata and deformation features of the surrounding rock in gob-side entry retaining mines were studied using 200 working faces of the Dianping coal mine in Shanxi Province. Using a mechanical analysis, a cantilever beam model formed by roof cutting was used to derive a deformation equation. The physical model test based on the field prototype revealed an asymmetrically distributed displacement curve and reduced collapse displacement when the rock stratum was far from the cutting seam. Outside of the roof cutting height, the collapse of the overlying strata gradually reached a symmetric distribution with increasing height. The deformation of the retained roadway was mainly concentrated on the roof, and the maximum deformation was 14 mm near the roof cutting side. A numerical simulation of the original size of the model test proved that the laws of strata movement and surrounding rock deformation were consistent with the physical test results. Finally, field measurements were performed, which verified the rationality of this study. Full article
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Open AccessArticle
Exploration of Seafloor Massive Sulfide Deposits with Fixed-Offset Marine Controlled Source Electromagnetic Method: Numerical Simulations and the Effects of Electrical Anisotropy
Minerals 2020, 10(5), 457; https://doi.org/10.3390/min10050457 - 19 May 2020
Viewed by 190
Abstract
Seafloor massive sulfide (SMS) deposits have attracted growing interest and become the focus of current seafloor mineral exploration. One key challenge is to delineate potential SMS accumulations and estimate their quantity and quality for prospective resource mining. Recently, geophysical electromagnetic methods which are [...] Read more.
Seafloor massive sulfide (SMS) deposits have attracted growing interest and become the focus of current seafloor mineral exploration. One key challenge is to delineate potential SMS accumulations and estimate their quantity and quality for prospective resource mining. Recently, geophysical electromagnetic methods which are routinely used for land-based mineral exploration are being adapted to detect and assess SMS occurrences by imaging their conductivity distributions. However, the rough seafloor topography and electrical anisotropy of the seafloor formations encountered in practical surveys pose challenges for reliable data interpretation, and recent studies have revealed that the rough bathymetry could cause measurable distortions. Here, we consider a fixed-offset marine controlled-source electromagnetic method (CSEM) for SMS exploration, and investigate the effects of electrical anisotropy of sedimentary formations through numerical simulations for marine CSEM surveys aiming at conductive targets in the shallow regions of the seafloor. Numerical results demonstrate that the presence of electrical anisotropy could impose significant influence on fixed-offset marine CSEM data and suggest that the distortions should be sufficiently accounted for reliable data interpretation, thus lending confidence to subsequent quantification of available SMS minerals. Full article
(This article belongs to the Special Issue Marine Geology and Minerals)
Open AccessArticle
Composition of Garnet from the Xianghualing Skarn Sn Deposit, South China: Its Petrogenetic Significance and Exploration Potential
Minerals 2020, 10(5), 456; https://doi.org/10.3390/min10050456 - 18 May 2020
Viewed by 221
Abstract
The Xianghualing skarn Sn deposit in the southwestern part of the southern Hunan Metallogenic Belt is a large Sn deposit in the Nanling area. In this paper, the garnet has been analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to obtain the concentrations [...] Read more.
The Xianghualing skarn Sn deposit in the southwestern part of the southern Hunan Metallogenic Belt is a large Sn deposit in the Nanling area. In this paper, the garnet has been analyzed by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to obtain the concentrations of the major and trace elements. The results reveal that the garnets from the Xianghualing deposit mainly belong to andradite-grossular (grandite) solid solution and are typically richer in Al than in Fe. They show enrichment in heavy rare earth elements (HREEs) and notably lower light rare earth elements (LREEs), and commonly negative Eu anomalies, indicative of a relatively reduced formation environment. The garnets have high Sn concentrations between 2313 ppm and 5766 ppm. It is also evident that there is a positive correlation between Sn and Fe, suggesting that Sn4+ substitutes into the garnets through substituting for Fe3+ in the octahedral position. Combined with previous studies, it can be recognized that the Sn concentrations of garnet in skarn Sn deposits are generally high, whereas the W concentrations are relatively low. This is just the opposite in garnets from skarn W deposits that typically have high W, but low Sn concentrations. In polymetallic skarn deposits with both economic Sn and W, the concentrations of both metals in garnets are relatively high, although varying greatly. Therefore, the Sn and W concentrations in garnets can be used to evaluate a skarn deposit’s potential to produce Sn and (or) W mineralization, which is helpful in exploration. Full article
(This article belongs to the Special Issue Magmatic–Hydrothermal Alteration and Mineralizing Processes)
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Open AccessArticle
The Isotopic (δ18O, δ 2H, δ13C, δ15N, δ34S, 87Sr/86Sr, δ11B) Composition of Adige River Water Records Natural and Anthropogenic Processes
Minerals 2020, 10(5), 455; https://doi.org/10.3390/min10050455 - 18 May 2020
Viewed by 223
Abstract
The water composition of the river Adige displays a Ca–HCO3 hydrochemical facies, mainly due to rock weathering. Nitrate is the only component that has increased in relation to growing anthropogenic inputs. The aim of this paper was to identify the origin of [...] Read more.
The water composition of the river Adige displays a Ca–HCO3 hydrochemical facies, mainly due to rock weathering. Nitrate is the only component that has increased in relation to growing anthropogenic inputs. The aim of this paper was to identify the origin of the dissolved components in this river and to establish the relationship between these components and critical zone processes within an evolving framework where climatic and human impacts are influencing the riverine system. In particular, emphasis is given to a wide spectrum of isotope data (δ18O, δ2H, δ13C, δ15N, δ34S, 87Sr/86Sr, δ11B), which is considered useful for determining water origin as well as natural and anthropogenic impacts on riverine geochemistry. Together with oxygen and hydrogen isotopes, which are strictly related to the climatic conditions (precipitation, temperature, humidity), the carbon, sulphur, strontium and boron signatures can describe the magnitude of rock weathering, which is in turn linked to the climatic parameters. δ13CDIC varies regularly along the riverine profile between −4.5‰ and −9.5‰, and δ34SSO4 varies regularly between +4.4‰ and +11.4‰. On the other hand, δ15NNO3 shows a more scattered distribution between +3.9‰ and +10.5‰, with sharp variations along the riverine profile. 87Sr/86Sr varies between 0.72797 in the upper part of the catchment and 0.71068 in the lower part. δ11B also shows a rough trend, with values approaching 7.6‰ in the upper part and 8.5‰ in the lower part. In our view, the comparatively low δ34S, δ11B, and high 87Sr/86Sr values, could be a proxy for increasing silicate weathering, which is a process that is sensitive to increases in temperature. Full article
(This article belongs to the Special Issue Elemental and Isotope Geochemistry of the Earth’s Critical Zone)
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Open AccessArticle
Mineralogical and Geochemical Constraints On the Origin of Mafic–Ultramafic-Hosted Sulphides: The Pindos Ophiolite Complex
Minerals 2020, 10(5), 454; https://doi.org/10.3390/min10050454 - 18 May 2020
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Abstract
Sulphide ores hosted in deeper parts of ophiolite complexes may be related to either primary magmatic processes or links to hydrothermal alteration and metal remobilization into hydrothermal systems. The Pindos ophiolite complex was selected for the present study because it hosts both Cyprus-type [...] Read more.
Sulphide ores hosted in deeper parts of ophiolite complexes may be related to either primary magmatic processes or links to hydrothermal alteration and metal remobilization into hydrothermal systems. The Pindos ophiolite complex was selected for the present study because it hosts both Cyprus-type sulphides (Kondro Hill) and Fe–Cu–Co–Zn sulphides associated with magnetite (Perivoli-Tsoumes) within gabbro, close to its tectonic contact with serpentinized harzburgite, and thus offers the opportunity to delineate constraints controlling their origin. Massive Cyprus-type sulphides characterized by relatively high Zn, Se, Au, Mo, Hg, and Sb content are composed of pyrite, chalcopyrite, bornite, and in lesser amounts covellite, siegenite, sphalerite, selenide-clausthalite, telluride-melonite, and occasionally tennantite–tetrahedrite. Massive Fe–Cu–Co–Zn-type sulphides associated with magnetite occur in a matrix of calcite and an unknown (Fe,Mg) silicate, resembling Mg–hisingerite within a deformed/metamorphosed ophiolite zone. The texture and mineralogical characteristics of this sulphide-magnetite ore suggest formation during a multistage evolution of the ophiolite complex. Sulphides (pyrrhotite, chalcopyrite, bornite, and sphalerite) associated with magnetite, at deeper parts of the Pindos (Tsoumes), exhibit relatively high Cu/(Cu + Ni) and Pt/(Pt + Pd), and low Ni/Co ratios, suggesting either no magmatic origin or a complete transformation of a preexisting magmatic assemblages. Differences recorded in the geochemical characteristics, such as higher Zn, Se, Mo, Au, Ag, Hg, and Sb and lower Ni contents in the Pindos compared to the Othrys sulphides, may reflect inheritance of a primary magmatic signature. Full article
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Open AccessArticle
Origin of Fluoride and Arsenic in the Main Ethiopian Rift Waters
Minerals 2020, 10(5), 453; https://doi.org/10.3390/min10050453 - 18 May 2020
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Abstract
In the Main Ethiopian Rift (MER) area, rural populations often use water that exceeds the World Health Organization thresholds for fluoride (F) and arsenic (As), two elements that are hazardous for human health. In this study, twenty-nine water samples were collected [...] Read more.
In the Main Ethiopian Rift (MER) area, rural populations often use water that exceeds the World Health Organization thresholds for fluoride (F) and arsenic (As), two elements that are hazardous for human health. In this study, twenty-nine water samples were collected from lakes and hot and cold springs in southern MER to investigate source(s) and health-risk of the F and As contamination. According to major ion and trace element analyses, only cold spring water is safe for consumption, whereas hot spring water is the most contaminated. Leaching tests performed with the MER rhyolitic volcanic rocks and their weathered products (fluvio-lacustrine sediments) demonstrate that the main cause of the F and As release is geogenic, i.e., not related to anthropogenic activities. The weathering of volcanic glass and minerals (apatites, clays, hydro-oxides) by CO2-bearing alkaline water induces the mobilisation of F and As from solid to liquid phase. This process is particularly fast, when fluvio-lacustrine sediments are involved, and can be further enhanced by hot groundwater leaching. This study, investigating the distribution, sources, and mechanisms of F and As release in MER water, could be of interest also for other sectors of the East African Rift and other similar volcano-tectonic settings. Full article
(This article belongs to the Special Issue Elemental and Isotope Geochemistry of the Earth’s Critical Zone)
Open AccessArticle
Carrier Flotation of Low-Rank Coal with Polystyrene
Minerals 2020, 10(5), 452; https://doi.org/10.3390/min10050452 - 18 May 2020
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Abstract
The problem of low-rank coal flotation continues to be a challenge due to the poor hydrophobicity and abundant oxygenated functional groups on particle surfaces. In this study, carrier flotation was used to improve the flotation performance of low-rank coal with polystyrene as a [...] Read more.
The problem of low-rank coal flotation continues to be a challenge due to the poor hydrophobicity and abundant oxygenated functional groups on particle surfaces. In this study, carrier flotation was used to improve the flotation performance of low-rank coal with polystyrene as a carrier material. Kerosene was used as a collector and played a role in the adhesion of fine low-rank coal to polystyrene due to its hydrophobic properties. The carrier feature of polystyrene was demonstrated by Turbiscan Lab Expert stability analysis and scanning electron microscopy analysis. The flotation experiments revealed that the optimum conditions were: collector dosage 5000 g/t, pulp concentration 40 g/L, and the ratio of low-rank coal to polystyrene 100:10. Under these conditions, the combustible recovery by carrier flotation was obtained as 70.59% when the ash content was 12.32%, which increased by 25.68 points compared with the combustible recovery of conventional flotation under almost the same ash content. The fine coal particles coated the coarse polystyrene particles through hydrophobic interactions between the polystyrene and hydrocarbon chains of the kerosene adsorbed on coal particles. The results suggested that the flotation performance of low-rank coal was significantly improved by carrier flotation with polystyrene, especially for fine particles. Full article
(This article belongs to the Special Issue Fine Particle Flotation: Experimental Study and Modelling)
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Open AccessReview
A Comprehensive Review of Rare Earth Elements Recovery from Coal-Related Materials
Minerals 2020, 10(5), 451; https://doi.org/10.3390/min10050451 - 17 May 2020
Viewed by 305
Abstract
Many studies have been published in recent years focusing on the recovery of rare earth elements (REEs) from coal-related materials, including coal, coal refuse, coal mine drainage, and coal combustion byproducts particularly fly ash. The scientific basis and technology development have been supported [...] Read more.
Many studies have been published in recent years focusing on the recovery of rare earth elements (REEs) from coal-related materials, including coal, coal refuse, coal mine drainage, and coal combustion byproducts particularly fly ash. The scientific basis and technology development have been supported by coal geologists and extractive metallurgists, and through these efforts, the concept has progressed from feasibility assessment to pilot-scale production over the last five years. Physical beneficiation, acid leaching, ion-exchange leaching, bio-leaching, thermal treatment, alkali treatment, solvent extraction, and other recovery technologies have been evaluated with varying degrees of success depending on the feedstock properties. In general, physical beneficiation can be a suitable low-cost option for preliminary upgrading; however, most studies showed exceedingly low recovery values unless ultrafine grinding was first performed. This finding is largely attributed to the combination of small RE-bearing mineral particle size and complex REE mineralogy in coal-based resources. Alternatively, direct chemical extraction by acid was able to produce moderate recovery values, and the inclusion of leaching additives, alkaline pretreatment, and/or thermal pretreatment considerably improved the process performance. The studies reviewed in this article revealed two major pilot plants where these processes have been successfully deployed along with suitable solution purification technologies to continuously produce high-grade mixed rare earth products (as high as +95%) from coal-based resources. This article presents a systematic review of the recovery methods, testing outcomes, and separation mechanisms that are involved in REE extraction from coal-related materials. The most recent findings regarding the modes of occurrence of REEs in coal-related materials are also included. Full article
(This article belongs to the Special Issue Leaching of Rare Earth Elements from Various Sources)
Open AccessArticle
Hydrothermal Alteration of Etna Ash and Implications for Mars
Minerals 2020, 10(5), 450; https://doi.org/10.3390/min10050450 - 17 May 2020
Viewed by 324
Abstract
Volcanic activity represents one of the main factors controlling the geological evolution of Mars, whose morphology has remarkable counterparts on Earth. Studies on the Martian surface revealed the widespread occurrences of newly formed minerals originated by the hydrothermal alteration of volcanic rocks. In [...] Read more.
Volcanic activity represents one of the main factors controlling the geological evolution of Mars, whose morphology has remarkable counterparts on Earth. Studies on the Martian surface revealed the widespread occurrences of newly formed minerals originated by the hydrothermal alteration of volcanic rocks. In this work, we carried out a series of experiments to test the reactions occurring during the hydrothermal alteration of basaltic ash from Etna (Italy) as a possible similar reaction fully grown on the Martian rock. The volcanic ash used for the hydrothermal alteration experiments was collected during the eruption of Etna in 2001, and its composition shares similarities with Martian bedrocks. Ash was altered under hydrothermal conditions at initial pH 5 at two temperatures (150 and 200 °C) and reaction times of 5, 10, and 31 days. After a number of runs, we attained analcime NaAlSi2O6·H2O. Our findings are in line with the hypothesis that zeolite on Mars probably originated from a low-temperature hydrothermal environment. The conclusions accord with the assumption that the analcime crystals recognized on Mars formed under the same conditions as those of our experimental setups. Full article
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