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Minerals, Volume 8, Issue 6 (June 2018)

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Cover Story (view full-size image) We deduced that the ophiolitic system was able to locally produce a high extent of Au-enrichment as [...] Read more.
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Open AccessArticle Trace Element Analysis of Pyrite from the Zhengchong Gold Deposit, Northeast Hunan Province, China: Implications for the Ore-Forming Process
Minerals 2018, 8(6), 262; https://doi.org/10.3390/min8060262
Received: 1 June 2018 / Revised: 14 June 2018 / Accepted: 15 June 2018 / Published: 20 June 2018
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Abstract
The Zhengchong gold deposit is located in the central segment of the Jiangnan Orogen in northeastern Hunan Province, South China. The host rocks of this deposit are the Neoproterozoic slates of the Lengjiaxi Group and granodiorite. The structures in the Zhengchong gold deposit
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The Zhengchong gold deposit is located in the central segment of the Jiangnan Orogen in northeastern Hunan Province, South China. The host rocks of this deposit are the Neoproterozoic slates of the Lengjiaxi Group and granodiorite. The structures in the Zhengchong gold deposit are dominated by NE-trending reverse faults, which control the gold-bearing veins. The orebody consists of NE-trending laminated quartz veins and NW-trending quartz veins. The alteration styles include silicification, carbonatization, sulfidation, sericitization and chloritization. The Zhengchong gold mineralization can be divided into four stages: Quartz-pyrite (stage I), quartz-pyrite-arsenopyrite (stage II), quartz-polysulfide (stage III) and quartz-carbonate (stage IV). Three generations of hydrothermal pyrite were identified: Disseminated euhedral to subhedral cubes in altered wall-rock (PyI), euhedral to subhedral cubes inter-grown with arsenopyrite and tetrahedrite in quartz veins and wall-rock (PyII), and euhedral cubes with microinclusions (native gold, galena, sphalerite, chalcopyrite, tetrahedrite, and pyrrhotite) or metasomatic textures in sulfide-rich veins or veinlets (PyIII). PyII and PyIII are arsenian pyrite and represent the main Au-bearing minerals. PyI records the lowest concentrations of Au; PyII and PyIII record similar amounts of Au, Cu, Pb, Zn, and Bi, but PyIII is more enriched in Co, Ni, Te, and Se. The substitution of As, Se and Te for S and that of Co and Ni for Fe occurs by direct-ion exchange. Invisible gold is uniformly distributed within the arsenian pyrite, and visible gold fills microfractures in PyII or occurs as inclusions in PyIII. Co, Ni, Cu exhibit positive correlations with Au and a negative correlation between Au + Cu + Co + Ni and Fe reflect that Fe vacancies may have been a major cause of the precipitation of invisible Au and other metal elements in pyrite structure. There are systematic trace element differences between the three generations of pyrite (PyI, PyII, PyIII). The more Co, Ni and Se, Te substitution that occurred for Fe and S, respectively, the greater the increase in the Co/Ni ratio (<1) and the decrease in the Se/Te ratio (<10) in stage III, indicating that a more reduced, lower-temperature metamorphic hydrothermal fluid was present in stage III. Full article
(This article belongs to the Section Mineral Deposits)
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Open AccessArticle (Bio)leaching Behavior of Chromite Tailings
Minerals 2018, 8(6), 261; https://doi.org/10.3390/min8060261
Received: 20 April 2018 / Revised: 2 June 2018 / Accepted: 14 June 2018 / Published: 20 June 2018
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Abstract
Chromite beneficiation operations in Sukinda valley (India) produce large amounts of tailings, which are stored in open air. In this study, bioleaching experiments were carried out in batch reactors with Acidithiobacillus thiooxidans or Pseudomonas putida in order to determine the potential leachability of
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Chromite beneficiation operations in Sukinda valley (India) produce large amounts of tailings, which are stored in open air. In this study, bioleaching experiments were carried out in batch reactors with Acidithiobacillus thiooxidans or Pseudomonas putida in order to determine the potential leachability of metals contained in these tailings due to biological activity. Acidic and alkaline pH resulted from the incubation of tailings with A. thiooxidans and P. putida, respectively. Tailings were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM), and chemical extraction of Cr(VI) with KH2PO4 was performed. Mineralogical investigations showed that tailings are mainly composed of chromite, hematite, lizardite, chlorite, and goethite, which are all known as Cr-bearing phases. During the leaching with A. thiooxidans and P. putida, total Cr was initially extracted as Cr(VI) due to the presence of phosphates in the medium, and subsequently decreased because of Cr(VI) adsorption and reduction to Cr(III). Reduction was associated with bacterial activity, but also with the presence of ferrous iron. Despite the occurrence of siderophores in the tailings after incubation with P. putida, under acidic conditions, Fe extracted remained higher. Extracted Ni, Mn, and Al concentrations also increased over time. Given the significant amount of chromite tailings produced every year, this study shows that tailings storage and leachability represent a potential source of chromium. However, our findings suggest that the presence of bacterial communities, as well as physicochemical processes, favor Cr(VI) reduction. Full article
(This article belongs to the collection Bioleaching)
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Open AccessArticle Three-D Mineralogical Mapping of the Kovdor Phoscorite–Carbonatite Complex, NW Russia: I. Forsterite
Minerals 2018, 8(6), 260; https://doi.org/10.3390/min8060260
Received: 30 May 2018 / Revised: 14 June 2018 / Accepted: 16 June 2018 / Published: 20 June 2018
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Abstract
The Kovdor alkaline-ultrabasic massif (NW Russia) is formed by three consequent intrusions: peridotite, foidolite–melilitolite and phoscorite–carbonatite. Forsterite is the earliest mineral of both peridotite and phoscorite–carbonatite, and its crystallization governed evolution of magmatic systems. Crystallization of forsterite from Ca-Fe-rich peridotite melt produced Si-Al-Na-K-rich
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The Kovdor alkaline-ultrabasic massif (NW Russia) is formed by three consequent intrusions: peridotite, foidolite–melilitolite and phoscorite–carbonatite. Forsterite is the earliest mineral of both peridotite and phoscorite–carbonatite, and its crystallization governed evolution of magmatic systems. Crystallization of forsterite from Ca-Fe-rich peridotite melt produced Si-Al-Na-K-rich residual melt-I corresponding to foidolite–melilitolite. In turn, consolidation of foidolite and melilitolite resulted in Fe-Ca-C-P-F-rich residual melt-II that emplaced in silicate rocks as a phoscorite–carbonatite pipe. Crystallization of phoscorite began from forsterite, which launched destruction of silicate-carbonate-ferri-phosphate subnetworks of melt-II, and further precipitation of apatite and magnetite from the pipe wall to its axis with formation of carbonatite melt-III in the pipe axial zone. This petrogenetic model is based on petrography, mineral chemistry, crystal size distribution and crystallochemistry of forsterite. Marginal forsterite-rich phoscorite consists of Fe2+-Mn-Ni-Ti-rich forsterite similar to olivine from peridotite, intermediate low-carbonate magnetite-rich phoscorite includes Mg-Fe3+-rich forsterite, and axial carbonate-rich phoscorite and carbonatites contain Fe2+-Mn-rich forsterite. Incorporation of trivalent iron in the octahedral M1 and M2 sites reduced volume of these polyhedra; while volume of tetrahedral set has not changed. Thus, trivalent iron incorporates into forsterite by schema (3Fe2+)oct → (2Fe3+ + □)oct that reflects redox conditions of the rock formation resulting in good agreement between compositions of apatite, magnetite, calcite and forsterite. Full article
(This article belongs to the Special Issue Arctic Mineral Resources: Science and Technology)
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Open AccessArticle Near-Infrared Spectroscopy of Hydrothermal versus Low-Grade Metamorphic Chlorites
Minerals 2018, 8(6), 259; https://doi.org/10.3390/min8060259
Received: 30 April 2018 / Revised: 14 June 2018 / Accepted: 16 June 2018 / Published: 19 June 2018
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Abstract
Although the composition of chlorite group minerals represents a known proxy for conditions in various geological environments, few comparative studies of chlorites from different geological environments have been carried out. In this study, we compare chlorites from a hydrothermal system with those formed
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Although the composition of chlorite group minerals represents a known proxy for conditions in various geological environments, few comparative studies of chlorites from different geological environments have been carried out. In this study, we compare chlorites from a hydrothermal system with those formed under low-grade metamorphic conditions. Both sets of samples were collected from the Pilbara Craton, Western Australia. Near-infrared (NIR) spectroscopy was used to determine if spectral differences record compositional differences between chlorites from the two geological environments. The spectra showed a significant difference in the Mg-OH absorption wavelength, near 2350 nm, with the hydrothermal group showing longer absorption wavelengths than the metamorphic one. A comparison of the spectral data with geochemical analyses showed a relation between the absorption wavelength and the magnesium-to-iron ratio (magnesium number) of chlorite, as well as the bulk rock composition. Metamorphic rocks have a higher magnesium-to-iron ratio than the hydrothermal ones, predominantly explained by differences in the degree of metasomatism. In the hydrothermal system, mass transfer changes the bulk rock composition while for the metamorphic samples the original bulk chemistry determines the current composition of the rock. Full article
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Open AccessArticle Pinnoite Deposit in DaQaidam Saline Lake, Qaidam Basin, China: Hydroclimatic, Sedimentologic, and Geochemical Constraints
Minerals 2018, 8(6), 258; https://doi.org/10.3390/min8060258
Received: 24 May 2018 / Revised: 12 June 2018 / Accepted: 15 June 2018 / Published: 19 June 2018
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Abstract
Mg-borates were traditionally thought to be diagenetic products of other primary borate minerals. Here we report results from the study of pinnoite deposit from DaQaidam saline lake, indicating that pinnoite minerals are primary in origin. Within the detecting limit of X-ray powder diffraction
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Mg-borates were traditionally thought to be diagenetic products of other primary borate minerals. Here we report results from the study of pinnoite deposit from DaQaidam saline lake, indicating that pinnoite minerals are primary in origin. Within the detecting limit of X-ray powder diffraction analysis (XRD) analysis, no other borate minerals than pinnoite are detected from the Mg-borate deposit. The cemented pinnoite orebody shows the sedimentary structure of light-dark lamination couplets, which signal marked seasonal variations in brine chemistry. The scanning electronic microscopy coupled with an energy dispersive X-ray spectrometer (SEM-EDX) examination reveals that all pinnoite minerals displayed euhedral, giving no indication of diagenetic origin. A marked shift in lithology from clastic sediment to evaporitic deposit reflects a critical change in sedimentation regime associated with abrupt changes in hydroclimatic conditions. The deposition of the pinnoite ore-layer containing abundant hydromagnesite marked the beginning of the evaporite formation and the end of the clastic deposition. This suggests that aridification occurred abruptly and the saline lake was much more alkaline than today in the early-stage of the evaporite deposition. The intensified summer evaporation and seasonal variations in water chemistry brought about a shallow to nearly desiccated paleo-lake with pH exceeding 9.3, Mg/Ca ratio >39, and boron concentration >600 mg/L, which favored pinnoite precipitation and the formation of pinnoite deposit in the central DaQaidam saline lake. Full article
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Open AccessArticle Potential of Soil, Sludge and Sediment for Mineral Carbonation Process in Selinsing Gold Mine, Malaysia
Minerals 2018, 8(6), 257; https://doi.org/10.3390/min8060257
Received: 25 March 2018 / Revised: 21 April 2018 / Accepted: 3 May 2018 / Published: 17 June 2018
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Abstract
Soil, sludge and sediment that are rich in alkaline earth silicates play significant roles as passive agents for removing carbon dioxide through mineral carbonation process. This study was conducted to characterize the mineralogical component and chemical composition of gold mining wastes and to
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Soil, sludge and sediment that are rich in alkaline earth silicates play significant roles as passive agents for removing carbon dioxide through mineral carbonation process. This study was conducted to characterize the mineralogical component and chemical composition of gold mining wastes and to identify the availability of natural silicate minerals as a feedstock for the mineral carbonation process. Particle-size distribution analysis was performed, and pH of the soil, sludge, and sediment were determined, whereas the mineralogical component and chemical composition of the samples were also analyzed. Results demonstrated that the presence of sepiolite and chlorite-serpentine in the stockpile and mine tailings can sequester carbon dioxide into magnesium carbonates, while the presence of stilpnomelane in the stockpile can be sequestered into iron carbonate. The presence of large amounts of small-size particles (silt fraction) in sludge (78.23%) at the mine tailings was identified to have higher surface area to absorb carbon dioxide. pH conditions of sludge (pH 7.9) and sediment (pH 8.3) from the mine tailings were favorable to enhance carbonate precipitation. Therefore, gold mine wastes have shown the potential for passive sequestration of carbon dioxide, thus, providing more insights into the enhancement of mineral carbonation process and the potential of natural silicate minerals. Full article
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Open AccessArticle Temporal Evolution of Calcite Surface Dissolution Kinetics
Minerals 2018, 8(6), 256; https://doi.org/10.3390/min8060256
Received: 13 April 2018 / Revised: 10 June 2018 / Accepted: 12 June 2018 / Published: 16 June 2018
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Abstract
This brief paper presents a rare dataset: a set of quantitative, topographic measurements of a dissolving calcite crystal over a relatively large and fixed field of view (~400 μm2) and long total reaction time (>6 h). Using
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This brief paper presents a rare dataset: a set of quantitative, topographic measurements of a dissolving calcite crystal over a relatively large and fixed field of view (~400 μm2) and long total reaction time (>6 h). Using a vertical scanning interferometer and patented fluid flow cell, surface height maps of a dissolving calcite crystal were produced by periodically and repetitively removing reactant fluid, rapidly acquiring a height dataset, and returning the sample to a wetted, reacting state. These reaction-measurement cycles were accomplished without changing the crystal surface position relative to the instrument’s optic axis, with an approximate frequency of one data acquisition per six minutes’ reaction (~10/h). In the standard fashion, computed differences in surface height over time yield a detailed velocity map of the retreating surface as a function of time. This dataset thus constitutes a near-continuous record of reaction, and can be used to both understand the relationship between changes in the overall dissolution rate of the surface and the morphology of the surface itself, particularly the relationship of (a) large, persistent features (e.g., etch pits related to screw dislocations; (b) small, short-lived features (e.g., so-called pancake pits probably related to point defects); (c) complex features that reflect organization on a large scale over a long period of time (i.e., coalescent “super” steps), to surface normal retreat and step wave formation. Although roughly similar in frequency of observation to an in situ atomic force microscopy (AFM) fluid cell, this vertical scanning interferometry (VSI) method reveals details of the interaction of surface features over a significantly larger scale, yielding insight into the role of various components in terms of their contribution to the cumulative dissolution rate as a function of space and time. Full article
(This article belongs to the Special Issue Mineral Surface Reactions at the Nanoscale)
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Open AccessArticle A Mosaic of Colors: Investigating Production Technologies of Roman Glass Tesserae from Northeastern Italy
Minerals 2018, 8(6), 255; https://doi.org/10.3390/min8060255
Received: 25 May 2018 / Revised: 8 June 2018 / Accepted: 12 June 2018 / Published: 16 June 2018
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Abstract
In the current study, a set of 60 glass tesserae from two disrupted Roman mosaics located in Pordenone and Trento (northeastern Italy) are analyzed, with the aim of investigating the coloring and opacification techniques, with a focus on the causes of specific textural
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In the current study, a set of 60 glass tesserae from two disrupted Roman mosaics located in Pordenone and Trento (northeastern Italy) are analyzed, with the aim of investigating the coloring and opacification techniques, with a focus on the causes of specific textural features. All the available colors and textures were selected for archaeometric analyses, in order to guarantee the full characterization of both assemblages and comparisons between the two sites. The applied analytical protocol comprises micro-textural and preliminary chemical characterizations of the tesserae by means of OM and SEM-EDS, mineralogical analysis of the opacifiers by XRD and chemical analysis of the glassy matrices by EPMA; in addition, on specific tesserae, micro-Raman spectroscopy, FORS, and EPR were also performed to clarify the type of opacifer, coloring ion and oxidation state, respectively. Results show that both the base-glass and the coloring/opacification techniques identified are consistent with the presumed Roman dating of the mosaics. All the tesserae are natron-based and chemically comparable with major Roman compositional groups, except for red samples. Antimony-based opacifiers are identified in most of the blue, turquoise, white, yellow and green tesserae, and copper-based opacifiers in the red ones; cobalt and copper are the most frequent ionic colorants used to obtain various shades of blue, turquoise and green colors. Despite the general comparability of both assemblages with the published data on glass tesserae coeval in age, the present study shows differences in the technological solutions used for obtaining the same color, and less common coloring and opacification techniques in three samples from Pordenone. The banded textures of some tesserae were also carefully investigated, and multiple factors influencing the changes in color (different distribution or relative abundance of opacifiers, crystal size, micro-texture, chemical composition of glassy matrix) are identified. Full article
(This article belongs to the Special Issue Mineralogical Applications for Cultural Heritage)
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Open AccessArticle Structural Controls on Copper Mineralization in the Tongling Ore District, Eastern China: Evidence from Spatial Analysis
Minerals 2018, 8(6), 254; https://doi.org/10.3390/min8060254
Received: 4 May 2018 / Revised: 11 June 2018 / Accepted: 14 June 2018 / Published: 15 June 2018
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Abstract
Structures exert significant controls on hydrothermal mineralization, although such controls commonly have cryptic expression in geological datasets dominated by 2D maps. Analysis of spatial patterns of mineral deposits and quantification of their correlation with detailed structural features are beneficial to understand the plausible
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Structures exert significant controls on hydrothermal mineralization, although such controls commonly have cryptic expression in geological datasets dominated by 2D maps. Analysis of spatial patterns of mineral deposits and quantification of their correlation with detailed structural features are beneficial to understand the plausible structural controls on mineralization. In this paper, a series of GIS-based spatial methods, including fractal, Fry, distance distribution and weights-of-evidence analyses, were employed to reveal structural controls on copper mineralization in the Tongling ore district, eastern China. The results indicate that Yanshanian intrusions exert the most significant control on copper mineralization, followed by EW-trending faults, intersections of basement faults and folds. The scale-variable distribution patterns of copper occurrences are attributed to the different structural controls operating in the basement and sedimentary cover. In the basement, EW-trending faults serve as pathways for channeling Yanshanian magma from a deep magma chamber to structurally controlled trap zones in the caprocks, imposing an important regional control on the spatial distribution of Cretaceous magmatic-hydrothermal system genetically related to copper mineralization. In the sedimentary cover, bedding-parallel shear zones, formed during the progressive folding and shearing in Indosinian and overprinted by tensional deformation in Yanshanian, act as favorable sites for hosting, focusing and depositing the ore-bearing fluids, playing a vital role in the localization of stratabound deposits at fine scale. Full article
(This article belongs to the Special Issue Structural Control of Mineral Deposits: Theory and Reality)
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Open AccessArticle Bio-Minerals Combined with Bacillus cereus for Enhancing the Nitrogen Removal Efficiency under Aerobic Conditions
Minerals 2018, 8(6), 253; https://doi.org/10.3390/min8060253
Received: 29 May 2018 / Revised: 11 June 2018 / Accepted: 12 June 2018 / Published: 15 June 2018
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Abstract
Nitrogen compounds such as nitrate, nitrite, and ammonium are among the prolonged contaminants in surface water and groundwater worldwide. In this study, we evaluated nitrogen removal efficiency using the combination of biologically synthesized Pd-FeS and Bacillus cereus in comparison between two batch reactors,
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Nitrogen compounds such as nitrate, nitrite, and ammonium are among the prolonged contaminants in surface water and groundwater worldwide. In this study, we evaluated nitrogen removal efficiency using the combination of biologically synthesized Pd-FeS and Bacillus cereus in comparison between two batch reactors, one with a single nitrate (NO3–N) and the other with a mixed nitrogen (NO3–N + NO2–N + NH4+–N) under aerobic conditions. The removal efficiency of NO3–N by bio-Pd-FeS + Bacillus cereus in a single nitrate reactor showed 100% with a low production (ca. 10%) of NO2–N and NH4+–N for 5 days and this combination was three-fold more effective than a single application of bio-Pd-FeS and Bacillus cereus respectively. Also, bio-Pd-FeS + Bacillus cereus in the mixed nitrogen (NO3–N + NO2–N + NH4+–N) removed 95% NO3–N, 20% NO2–N, and 35% NH4+–N, respectively. Since iron and sulfur-based bio-minerals could be reusable in a reducing condition of in-situ and in an oxygen-limited closed condition of ex-situ applications, the results suggested that the combination should get more attention for an efficient eco-friendly sustainable bioremediation technology. Full article
(This article belongs to the Section Environmental Mineralogy and Biogeochemistry)
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Open AccessArticle Contribution of Benthic Processes to the Growth of Ooids on a Low-Energy Shore in Cat Island, The Bahamas
Minerals 2018, 8(6), 252; https://doi.org/10.3390/min8060252
Received: 1 May 2018 / Revised: 7 June 2018 / Accepted: 11 June 2018 / Published: 14 June 2018
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Abstract
Ooids are typically found in frequently reworked coastal sediments, and are thought to accrete by inorganic chemical precipitation around moving grains. The high organic content and the presence of biosignatures, however, suggest that ooids interact with benthic microbial communities. Here, we investigate the
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Ooids are typically found in frequently reworked coastal sediments, and are thought to accrete by inorganic chemical precipitation around moving grains. The high organic content and the presence of biosignatures, however, suggest that ooids interact with benthic microbial communities. Here, we investigate the role of benthic processes on ooid growth on a leeward shore of Cat Island, The Bahamas. Polished ooids are present in the surf zone, whereas dull ooids and grapestones are present in microbially colonized sediments seaward of the surf zone. Wave hydrodynamics and sediment transport modeling suggest that microbially colonized sediments are mobilized at monthly time scales. We propose a new conceptual model for both ooids and grapestone. Ooids rest and accrete in the area covered by microbial mats, but are periodically transported to the surf zone where wave abrasion polishes them within days. Ooids are then transported back to microbially colonized areas where the accretion cycle resumes. Ooids too large to be transported become trapped outside the surf zone, exit the “conveyor belt” and become grapestones. The benthic growth mechanism predicts petrographic characteristics that match observations: successive ooid laminae do not thin outward, laminae exhibit irregularities, and some ooids include multiple nuclei. Full article
(This article belongs to the Special Issue Microbialites: Preservation of Extant and Extinct Systems)
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Open AccessEditorial Editorial for Special Issue “Geochemistry and Mineralogy of Hydrothermal Metallic Mineral Deposits”
Minerals 2018, 8(6), 251; https://doi.org/10.3390/min8060251
Received: 12 June 2018 / Accepted: 13 June 2018 / Published: 14 June 2018
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Abstract
The Special Issue of Minerals on Geochemistry and Mineralogy of Hydrothermal Metallic Mineral Deposits presents the results of diverse geochemical and mineralogical research from across the globe[…] Full article
(This article belongs to the Special Issue Geochemistry and Mineralogy of Hydrothermal Metallic Mineral Deposits)
Open AccessArticle Effect of Ammonium Chloride on the Efficiency with Which Copper Sulfate Activates Marmatite: Change in Solution Composition and Regulation of Surface Composition
Minerals 2018, 8(6), 250; https://doi.org/10.3390/min8060250
Received: 14 May 2018 / Revised: 7 June 2018 / Accepted: 11 June 2018 / Published: 13 June 2018
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Abstract
Zinc sulfide minerals are the primary choice for zinc extraction and marmatite is one of the two most common zinc sulphide minerals (sphalerite and marmatite), therefore it is of great significance to study and optimize the flotation of marmatite. To improve the activation
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Zinc sulfide minerals are the primary choice for zinc extraction and marmatite is one of the two most common zinc sulphide minerals (sphalerite and marmatite), therefore it is of great significance to study and optimize the flotation of marmatite. To improve the activation of copper sulfate on marmatite, a method involving the addition of ammonium chloride is devised. The method has been proven to be an effective way of improving the activation efficiency of copper sulfate towards marmatite under alkaline conditions. The strengthening mechanism was studied using micro-flotation, adsorption test, X-ray photoelectron spectroscopy, and by analyzing changes in solution composition. Flotation test results show that the activation effect of the copper sulfate towards marmatite is enhanced with the addition of ammonium chloride. According to the results of the adsorption measurements and X-ray photoelectron spectroscopy analysis, when the marmatite surface is activated using copper sulfate with added ammonia chloride, it adsorbs more copper sulfide and less copper hydroxide and zinc hydroxide. These changes in surface composition are believed to occur via the following process: NH3(aq) promotes the dissolution of zinc hydroxide and then facilitates the conversion of surface copper hydroxide to copper sulfide. In addition, the occurrence of Cu(NH3)n2+ can promote the adsorption of copper ions (Cu2+ can be stored as Cu(NH3)n2+ via complexation, and then, when the concentration of copper ions decreases, Cu2+ can be released through the decompositionof Cu(NH3)n2+. Hence, the copper ion concentration can be maintained and this can facilitate the adsorption of Cu2+ on marmatite). Based on a comprehensive analysis of all our results, we propose that adding ammonium chloride to the copper sulfate changes the solution components (i.e., the presence of NH3(aq) and Cu(NH3)n2+) and then regulates the surface composition of marmatite. The change in surface composition improves the hydrophobicity of mineral surface and this leads to an improvement in activation of marmatite. Full article
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Open AccessArticle Raman Micro-Spectroscopy Identifies Carbonaceous Particles Lying on the Surface of Crocidolite, Amosite, and Chrysotile Fibers
Minerals 2018, 8(6), 249; https://doi.org/10.3390/min8060249
Received: 4 May 2018 / Revised: 4 June 2018 / Accepted: 12 June 2018 / Published: 13 June 2018
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Abstract
Micro-Raman spectroscopy has been applied on UICC (Union for International Cancer Control’s) crocidolite and amosite from South Africa and on UICC chrysotile from Canada. Under Optical Microscope (OM), the surface of the fibers was often characterized by areas, micrometric in size, appearing dark.
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Micro-Raman spectroscopy has been applied on UICC (Union for International Cancer Control’s) crocidolite and amosite from South Africa and on UICC chrysotile from Canada. Under Optical Microscope (OM), the surface of the fibers was often characterized by areas, micrometric in size, appearing dark. The laser beam was successively focused on areas of the same sample showing different optical contrasts. On the bright zones, Raman spectra peculiar for crocidolite, amosite or chrysotile were recorded. When dark areas were optically identified, the laser beam was addressed onto these regions and, in the Raman patterns, in addition to the bands produced by the mineral fiber, bands ascribing to substituted carbonaceous phases were observed. These bands were lying in the 4000–1100 cm−1 spectral range. On the basis of the shape of the bands and their relative intensities, suggestions about the order-disorder of the carbonaceous particles could be proposed, and they appeared more ordered on amosite than on crocidolite and chrysotile. From the exposed data, crocidolite and amosite fibers from South Africa, and chrysotile fibers from Canada, largely used in industry in the past, are characterized by many carbonaceous micrometric particles, lying on the fiber surfaces. Based on the noxiousness of the carbon particles on human health, their presence on asbestos fibers may play a role in increasing the carcinogenic effects of the analyzed fibrous minerals. Full article
(This article belongs to the Special Issue Occurrence, Crystal-Chemistry and Properties of Fibrous Minerals)
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Open AccessArticle Fiemmeite Cu2(C2O4)(OH)2∙2H2O, a New Mineral from Val di Fiemme, Trentino, Italy
Minerals 2018, 8(6), 248; https://doi.org/10.3390/min8060248
Received: 28 May 2018 / Revised: 7 June 2018 / Accepted: 11 June 2018 / Published: 12 June 2018
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Abstract
The new mineral species fiemmeite, Cu2(C2O4)(OH)22H2O, was found NE of the Passo di San Lugano, Val di Fiemme, Carano, Trento, Italy (latitude 46.312° N, longitude 11.406° E). It occurs in coalified woods
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The new mineral species fiemmeite, Cu2(C2O4)(OH)22H2O, was found NE of the Passo di San Lugano, Val di Fiemme, Carano, Trento, Italy (latitude 46.312° N, longitude 11.406° E). It occurs in coalified woods at the base of the Val Gardena Sandstone (upper Permian) which were permeated by mineralizing solutions containing Cu, U, As, Pb and Zn. The oxalate anions have originated from diagenesis of the plant remains included in sandstones. The mineral forms aggregate up to 1 mm across of sky blue platelets with single crystals reaching maximum dimensions of about 50 μm. Associated minerals are: baryte, olivenite, middlebackite, moolooite, brochantite, cuprite, devilline, malachite, azurite, zeunerite/metazeunerite, tennantite, chalcocite, galena. Fiemmeite is monoclinic, space group: P21/c with a = 3.4245(6), b = 10.141(2), c = 19.397(3) Å, β = 90.71(1)°, V = 673.6(2) Å3, Z = 4. The calculated density is 2.802 g/cm3 while the observed density is 2.78(1) g/cm3. The six strongest reflections in the X-ray powder diffraction pattern are: [dobs in Å (I)(hkl)] 5.079(100)(020), 3.072(58)(112), 9.71(55)(002), 4.501(50)(022), 7.02(28)(012), 2.686(25)(114). The crystal structure was refined from single-crystal data to a final R1 = 0.0386 for 1942 observed reflections [I > 2σ(I)] with all the hydrogen atoms located from a Difference–Fourier map. The asymmetric unit contains two independent Cu2+ cations that display a distorted square-bipyramidal (4+2) coordination, one oxalate anion, two hydroxyl anions and two water molecules. The coordination polyhedra of the two copper atoms share common edges to form polymeric rows running along [100] with composition [Cu2(C2O4)(OH)22H2O]n. These rows are held together by a well-established pattern of hydrogen bonds between the oxalate oxygens not involved in the coordination to copper, the hydrogen atoms of the water molecules and the hydroxyl anions. Full article
(This article belongs to the Special Issue New Mineral Species and Their Crystal Structures)
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