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Minerals, Volume 9, Issue 7 (July 2019)

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Cover Story (view full-size image) Eudialyte deposits could provide a low-cost, low-impact source of rare earth elements (REE) and [...] Read more.
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Open AccessArticle
Selenium Minerals: Structural and Chemical Diversity and Complexity
Minerals 2019, 9(7), 455; https://doi.org/10.3390/min9070455
Received: 27 June 2019 / Revised: 19 July 2019 / Accepted: 21 July 2019 / Published: 23 July 2019
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Abstract
Chemical diversity of minerals containing selenium as an essential element has been analyzed in terms of the concept of mineral systems and the information-based structural and chemical complexity parameters. The study employs data for 123 Se mineral species approved by the International Mineralogical [...] Read more.
Chemical diversity of minerals containing selenium as an essential element has been analyzed in terms of the concept of mineral systems and the information-based structural and chemical complexity parameters. The study employs data for 123 Se mineral species approved by the International Mineralogical Association as of 25 May 2019. All known selenium minerals belong to seven mineral systems with the number of essential components ranging from one to seven. According to their chemical features, the minerals are subdivided into five groups: Native selenium, oxides, selenides, selenites, and selenates. Statistical analysis shows that there are strong and positive correlations between the chemical and structural complexities (measured as amounts of Shannon information per atom and per formula or unit cell) and the number of different chemical elements in a mineral. Analysis of relations between chemical and structural complexities provides strong evidence that there is an overall trend of increasing structural complexity with the increasing chemical complexity. The average structural complexity for Se minerals is equal to 2.4(1) bits per atom and 101(17) bits per unit cell. The chemical and structural complexities of O-free and O-bearing Se minerals are drastically different with the first group being simpler and the second group more complex. The O-free Se minerals (selenides and native Se) are primary minerals; their formation requires reducing conditions and is due to hydrothermal activity. The O-bearing Se minerals (oxides and oxysalts) form in near-surface environment, including oxidation zones of mineral deposits, evaporites and volcanic fumaroles. From the structural viewpoint, the five most complex Se minerals are marthozite, Cu(UO2)3(SeO3)2O2·8H2O (744.5 bits/cell); mandarinoite, Fe2(SeO3)3·6H2O (640.000 bits/cell); carlosruizite, K6Na4Na6Mg10(SeO4)12(IO3)12·12H2O (629.273 bits/cell); prewittite, KPb1.5ZnCu6O2(SeO3)2Cl10 (498.1 bits/cell); and nicksobolevite, Cu7(SeO3)2O2Cl6 (420.168 bits/cell). The mechanisms responsible for the high structural complexity of these minerals are high hydration states (marthozite and mandarinoite), high topological complexity (marthozite, mandarinoite, carlosruizite, nicksobolevite), high chemical complexity (prewittite and carlosruizite), and the presence of relatively large clusters of atoms (carlosruizite and nicksobolevite). In most cases, selenium itself does not play the crucial role in determining structural complexity (there are structural analogues or close species of marthozite, mandarinoite, and carlosruizite that do not contain Se), except for selenite chlorides, where stability of crystal structures is adjusted by the existence of attractive Se–Cl closed-shell interactions impossible for sulfates or phosphates. Most structurally complex Se minerals originate either from relatively low-temperature hydrothermal environments (as marthozite, mandarinoite, and carlosruizite) or from mild (500–700 °C) anhydrous gaseous environments of volcanic fumaroles (prewittite, nicksobolevite). Full article
(This article belongs to the Special Issue Selenide Mineralization)
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Open AccessArticle
The Chemical Composition and Surface Texture of Transparent Heavy Minerals from Core LQ24 in the Changjiang Delta
Minerals 2019, 9(7), 454; https://doi.org/10.3390/min9070454
Received: 12 May 2019 / Revised: 18 July 2019 / Accepted: 19 July 2019 / Published: 22 July 2019
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Abstract
The assessment of textural and compositional modifications of detrital sediments is required to reconstruct past source to sink dynamics. The Changjiang Delta is an ideal location to study the sedimentary environment from the Pliocene to Quaternary transition. In the present study, we aim [...] Read more.
The assessment of textural and compositional modifications of detrital sediments is required to reconstruct past source to sink dynamics. The Changjiang Delta is an ideal location to study the sedimentary environment from the Pliocene to Quaternary transition. In the present study, we aim to decipher the response of heavy minerals to mechanical wear and chemical weathering since the Pliocene. With the application of a scanning electron microscope and an electron probe, the geochemistry and surface texture of different heavy minerals (amphibole, epidote, and tourmaline groups) with grain-size fractions of 32–63 µm and 63–125 µm were studied. The result shows that the surface texture of unstable minerals (amphibole, epidote) changed under strong chemical weathering in the Pliocene sediments. By contrast, unstable minerals of the Pleistocene sediments are relatively fresh and similar to those of the modern Changjiang sediment. The stable mineral tourmaline does not exhibit morphology changes in different chemical weathering conditions. No effect of grain size on geochemical composition is noticed. The single minerals of very fine sand and coarse silt show similar geochemical and morphological features. The integration of mineralogy, geochemical data, and grain size parameters yield a more precise understanding of the physical and chemical response of heavy minerals to different weathering conditions. The outcome of the study is also helpful in deciphering sediment provenance changes and environmental changes in the Changjiang basin. Full article
(This article belongs to the Special Issue Heavy Minerals)
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Open AccessArticle
Evaluation of the Sorption Potential of Mineral Materials Using Tetracycline as a Model Pollutant
Minerals 2019, 9(7), 453; https://doi.org/10.3390/min9070453
Received: 18 June 2019 / Revised: 15 July 2019 / Accepted: 18 July 2019 / Published: 21 July 2019
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Abstract
Tetracycline (TC) is among the most used antibiotics in animal feedstock in the EU. Antibiotics’ persistence as emerging pollutants in the environment is evidenced by their long half-life in residual organic-mineral sediments and waters. The risk associated with this persistence favours antibiotic-resistant microbiota, [...] Read more.
Tetracycline (TC) is among the most used antibiotics in animal feedstock in the EU. Antibiotics’ persistence as emerging pollutants in the environment is evidenced by their long half-life in residual organic-mineral sediments and waters. The risk associated with this persistence favours antibiotic-resistant microbiota, affecting human health and ecosystems. The purpose of the present work is to assess the adsorption of TC into natural clay minerals, synthetic iron hydroxides and calcined sewage sludge. TC adsorption isotherms were performed in three replicated batch tests at three different pH values (4, 6, 8) and TC concentrations (33–1176 mg·L−1). X-Ray diffraction (XRD) mineralogy, cation exchange capacity (CEC), Brunauer, Emmett and Teller specific surface area (BET-SSA) and point of zero charge salt effect (PZSE) were determined for the characterization of materials. Sorption was analysed by means of fitting Langmuir and Freundlich adsorption models, which showed good fitting parameters for the studied materials. Low-charge montmorillonite (LC Mnt) is displays the best sorption capacity for TC at maximum TC concentration (350–300 mgTC·g−1) in the whole range of pH (4–8). Sepiolite and smectites adsorbed 200–250 mgTC·g−1, while illite, calcined sludge or iron hydroxides present the lowest adsorption capacity (<100 mgTC·g−1). Nevertheless, illite, sepiolite and ferrihydrite display high adsorption intensities at low to medium TC concentrations (<300 mg·L−1), even at pH 8, as is expected in wastewater environmental conditions. Full article
(This article belongs to the Special Issue Special Clays and Their Applications)
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Open AccessArticle
Effect of Comminution Methods on Low-Rank Coal Bubble–Particle Attachment/Detachment: Implications for Flotation
Minerals 2019, 9(7), 452; https://doi.org/10.3390/min9070452
Received: 1 July 2019 / Revised: 16 July 2019 / Accepted: 18 July 2019 / Published: 21 July 2019
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Abstract
The floatability of fine low-rank coal particles can be greatly influenced by their morphological characteristics, such as shape and surface roughness. In this study, the attachment efficiency and detachment amplitude of fine low-rank coal particles produced by various comminution methods onto/from the bubble [...] Read more.
The floatability of fine low-rank coal particles can be greatly influenced by their morphological characteristics, such as shape and surface roughness. In this study, the attachment efficiency and detachment amplitude of fine low-rank coal particles produced by various comminution methods onto/from the bubble surface were investigated using homemade bubble–particle wrap angle and bubble–particle attachment/detachment testing systems. Results showed that the length–diameter ratio of rod-milled products was smaller than that of crushed products. The wrap angle of particles obtained by the crushed method was larger than that obtained by the rod-milled method, i.e., particles with greater length–diameter ratio showed higher attachment efficiency onto the bubble surface. Meanwhile, particles with greater length–diameter ratio exhibited a larger detachment amplitude, which suggests that it is more difficult to be detached from the bubble surface. However, rod-milled products showed lower attachment onto the bubble surface. The flotation test confirmed that the floatability ratio of crushed products was higher than that of rod-milled products, consistent with evidence from experimental analyses. This study provides a fundamental understanding of particle shapes for low-rank coal flotation by a novel research method combining the attachment efficiency and detachment amplitude of bubble–particle combinations. Full article
(This article belongs to the Special Issue Mineral Liberation)
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Open AccessArticle
Modeling of REE and Fe Extraction from a Concentrate from Araxá (Brazil)
Minerals 2019, 9(7), 451; https://doi.org/10.3390/min9070451
Received: 7 June 2019 / Revised: 2 July 2019 / Accepted: 11 July 2019 / Published: 21 July 2019
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Abstract
The study aimed to employ a comprehensive methodology for the acid processing of a rare earth element (REE) concentrate obtained from the ore from Araxá (MG-Brazil). The most important process variables have been identified and their levels determined to maximize REE extraction (%RE) [...] Read more.
The study aimed to employ a comprehensive methodology for the acid processing of a rare earth element (REE) concentrate obtained from the ore from Araxá (MG-Brazil). The most important process variables have been identified and their levels determined to maximize REE extraction (%RE) and minimize Fe extraction (%Fe). The thermodynamic analysis showed that the roasting temperature (TF) is crucial for the control of Fe solubilization in the aqueous leaching step of the acid processing. A statistic design of laboratory experiments and a process optimization method were applied to address the interaction among the process variables. Experimental results showed that a TF of about 700 °C can significantly reduce the Fe concentration in the aqueous leaching liquor. Mathematical models were proposed to predict the effect of process variable on REE and Fe extraction of the concentrate. A multi-objective technique was employed for optimization of chemical processing and the best conditions were reached for roasting temperature (TF) = 700 °C, acid to sample mass ratio (ACs) = 0.8 and leaching time (tL) = 20 min, which led to %RE = 96.91% and %Fe = 21.69%. Full article
(This article belongs to the Section Mineral Processing and Metallurgy)
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Open AccessArticle
Novel Insights into the Hydroxylation Behaviors of α-Quartz (101) Surface and its Effects on the Adsorption of Sodium Oleate
Minerals 2019, 9(7), 450; https://doi.org/10.3390/min9070450
Received: 9 May 2019 / Revised: 11 July 2019 / Accepted: 18 July 2019 / Published: 19 July 2019
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Abstract
A scientific and rigorous study on the adsorption behavior and molecular mechanism of collector sodium oleate (NaOL) on a Ca2+-activated hydroxylated α-quartz surface was performed through experiments and density functional theory (DFT) simulations. The rarely reported hydroxylation behaviors of water molecules [...] Read more.
A scientific and rigorous study on the adsorption behavior and molecular mechanism of collector sodium oleate (NaOL) on a Ca2+-activated hydroxylated α-quartz surface was performed through experiments and density functional theory (DFT) simulations. The rarely reported hydroxylation behaviors of water molecules on the α-quartz (101) surface were first innovatively and systematically studied by DFT calculations. Both experimental and computational results consistently demonstrated that the adsorbed calcium species onto the hydroxylated structure can significantly enhance the adsorption of oleate ions, resulting in a higher quartz recovery. The calculated adsorption energies confirmed that the adsorbed hydrated Ca2+ in the form of Ca(H2O)3(OH)+ can greatly promote the adsorption of OL on hydroxylated quartz (101). In addition, Mulliken population analysis together with electron density difference analysis intuitively illustrated the process of electron transfer and the Ca-bridge phenomenon between the hydroxylated surface and OL ions. This work may offer new insights into the interaction mechanisms existing among oxidized minerals, aqueous medium, and flotation reagents. Full article
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Open AccessArticle
Microstructure and Minerals Evolution of Iron Ore Sinter: Influence of SiO2 and Al2O3
Minerals 2019, 9(7), 449; https://doi.org/10.3390/min9070449
Received: 17 June 2019 / Revised: 16 July 2019 / Accepted: 17 July 2019 / Published: 19 July 2019
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Abstract
SiO2 and Al2O3 are two important minerals that can affect the mechanical and metallurgical properties of sinter. This investigation systematically studied the influences of these minerals and revealed their functional mechanisms on sinter quality. Results showed that with an [...] Read more.
SiO2 and Al2O3 are two important minerals that can affect the mechanical and metallurgical properties of sinter. This investigation systematically studied the influences of these minerals and revealed their functional mechanisms on sinter quality. Results showed that with an increasing Al2O3 content in sinter, the sintering indexes presented an improvement before the content exceeded 1.80%, while the quality decreased obviously after the content exceeded 1.80%. With an increasing SiO2 content, the sinter quality presented a decreasing tendency, especially when the content exceeded 4.80%. Consequently, the optimal content of Al2O3 was ≤1.80% and that of SiO2 was ≤4.80%. The evolution of the microstructure and minerals in sinter showed that enhancing the Al2O3 content increased the proportion of SFCA generated, which improved the sinter’s mechanical strength, while excessive Al2O3 led to the formation of sheet-like SFCA with weak mechanical strength. Increasing the content of SiO2 strained the formation of SFCA and promoted the formation of calcium silicate, the mechanical strength of which is lower than that of SFCA. The research findings will be useful in guiding practical sintering processes. Full article
(This article belongs to the Special Issue Mineralogy of Iron Ore Sinters)
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Open AccessFeature PaperArticle
Application of Falcon Centrifuge as a Cleaner Alternative for Complex Tungsten Ore Processing
Minerals 2019, 9(7), 448; https://doi.org/10.3390/min9070448
Received: 15 June 2019 / Revised: 11 July 2019 / Accepted: 17 July 2019 / Published: 19 July 2019
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Abstract
Scheelite (CaWO4) is one of the main raw material for the production of tungsten. It is usually encountered in skarn deposits where it is commonly associated with other calcium minerals as fluorite, apatite, and calcium silicates. Worldwide, scheelite is upgraded to [...] Read more.
Scheelite (CaWO4) is one of the main raw material for the production of tungsten. It is usually encountered in skarn deposits where it is commonly associated with other calcium minerals as fluorite, apatite, and calcium silicates. Worldwide, scheelite is upgraded to the chemical grades by direct flotation, but the separation efficiency remains limited due to similar flotation behaviors of scheelite and gangue minerals with fatty acid. The only solutions used to overcome this issue involve high energy consumption or ecotoxic reagents. In the present study, a novel method based on the use of a centrifugal Falcon concentrator was investigated to perform an efficient elimination of gangue minerals and fine particles as well as an acceptable scheelite recovery enabling a decrease of the flotation reagents consumption. The performances of the two types of laboratory Falcon bowls, Falcon UltraFine (UF) and Falcon Semi-Batch (SB), were modeled using the design of experiments (DoE) methodology, which allowed to determine the best operating parameters for each bowl. The separation performances were mainly affected by the rotary speed and the pulp density for the Falcon UF and by the rotary speed and the fluidization pressure for the Falcon SB. Due to the fluidization pressure, the Falcon SB exhibited higher gangue minerals rejection with slightly lower recoveries than the Falcon UF. Overall, the optimized Falcon SB test allowed to reach 71.6%, 22.6%, 17.2%, and 12.6% for scheelite, calcium salts, dense calcium silicates, and light non-calcic silicates respectively while the desliming efficiency reached 98.8%. For comparison purposes, a classical hydrocyclone allowed to attain 89.1%, 89.3%, 79.5%, and 76.5% for scheelite, calcium salts, dense calcium silicates, and light non-calcic silicates respectively while the desliming efficiency reached 52.0%. Theses results can be used reliably to assess the separation performances of an industrial Falcon C which can be regarded, along with Falcon SB, as a sustainable and efficient gangue rejection method for complex W skarn ore, which allows the use of environmentally friendly reagents during downstream flotation stages. Full article
(This article belongs to the Section Mineral Processing and Metallurgy)
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Open AccessArticle
Invisible Gold in Pyrite from Epithermal, Banded-Iron-Formation-Hosted, and Sedimentary Gold Deposits: Evidence of Hydrothermal Influence
Minerals 2019, 9(7), 447; https://doi.org/10.3390/min9070447
Received: 6 June 2019 / Revised: 10 July 2019 / Accepted: 12 July 2019 / Published: 19 July 2019
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Abstract
“Invisible gold” in pyrite is defined as an Au solid solution of the pyrite lattice, sub-microscopic Au nanoparticles (NPs) in the pyrite, or other chemisorption complexes of Au. Because the relationship between the Au and As concentrations in pyrite could indicate the genesis [...] Read more.
“Invisible gold” in pyrite is defined as an Au solid solution of the pyrite lattice, sub-microscopic Au nanoparticles (NPs) in the pyrite, or other chemisorption complexes of Au. Because the relationship between the Au and As concentrations in pyrite could indicate the genesis of the deposit, the purpose of this study is to assess the micro-analytical characteristics of the Au–As relationship in pyrite from epithermal and hydrothermally affected sedimentary Au deposits by secondary ion mass spectrometry. The Au and As concentrations in pyrite vary from 0.04 to 30 ppm and from 1 to 1000 ppm, respectively, in the high-sulfidation Nansatsu-type epithermal deposits; these concentrations are both lower than those of the low-sulfidation epithermal Hishikari deposit. The Au concentrations in pyrrhotite and pyrite reach 6 and 0.3 ppm, respectively, in the Kalahari Goldridge banded-iron-formation-hosted gold deposit, and Au in pyrrhotite may sometimes exist as NPs, whereas As concentrations in pyrrhotite and pyrite are both low and lie in a narrow range from 6 to 22 ppm. Whether Au is present as NPs is important in ore dressing. The Au and As concentrations in pyrite from the Witwatersrand gold field range from 0.02 to 1.1 ppm and from 8 to 4000 ppm, respectively. The shape of the pyrite grains might prove to be an indicator of the hydrothermal influence on deposits of sedimentary origin, which implies the genesis of the deposits. Full article
(This article belongs to the Special Issue Minerals Down to the Nanoscale: A Glimpse at Ore-Forming Processes)
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Open AccessArticle
In Situ LA-ICP-MS Analysis of Minerals Hosted by Late Cenozoic Basaltic Rocks from Thailand
Minerals 2019, 9(7), 446; https://doi.org/10.3390/min9070446
Received: 19 June 2019 / Revised: 16 July 2019 / Accepted: 17 July 2019 / Published: 19 July 2019
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Abstract
Shortly after the cessation of seafloor spreading, intraplate magmatism affected large areas in the South China Sea (SCS) region. The origin and geodynamic setting of the post-spreading volcanism is still in debate, for many previous studies have focused on petrogenesis and mantle source [...] Read more.
Shortly after the cessation of seafloor spreading, intraplate magmatism affected large areas in the South China Sea (SCS) region. The origin and geodynamic setting of the post-spreading volcanism is still in debate, for many previous studies have focused on petrogenesis and mantle source of the late Cenozoic basalts from the SCS region. In this study, we obtained in situ major element compositions (by using Electron microprobe analysis—EMPA) and trace element compositions (by using laser ablation inductively coupled plasma mass spectrometry— LA-ICP-MS) for minerals (clinopyroxenes (Cpx), plagioclases (Pl), and olivines (Ol)) hosted by late Cenozoic basaltic rocks from Thailand. The results showed that the olivines had forsterite contents between 60.12% and 84.74%. Clinopyroxene were diopside and augite, and they were enriched in light rare earth elements (LREEs) (LaN/YbN = 1.93–4.27) and depleted in large-ion lithophile elements (LILEs). Mineral compositions (mainly based on clinopyroxene) confirmed that these late Cenozoic basaltic rocks were of an intraplate affinity and were similar to contemporaneous basaltic fields in the SCS region (Southern Vietnam, Northern Hainan, and SCS seamounts). Plagioclases were predominantly labradorite, with a few andesine and bytownite, and they were enriched in LREEs and Ba, Sr, and Pb, and most of them exhibited strong positive Eu anomalies. The source lithology of Thailand basaltic rocks could be garnet pyroxenite. The mantle potential temperature beneath Thailand is in the range of 1448–1467 °C, which can be comparable to those beneath Southern Vietnam and Northern Hainan, indicating the Thailand basaltic rocks could be produced by the Hainan mantle plume. In addition, the crystallization temperature of clinopyroxenes (1145–1214 °C) and plagioclase (1067–1133 °C) and their composition characteristics indicate that the magmatic processes have a conspicuous characteristic of fast rate of magma upwelling. Thus, we proposed that the deep geodynamic setting of Thailand late Cenozoic basaltic rocks is similar to those of the whole SCS region, and Hainan mantle plume plays a significant role in the petrogenesis of these basaltic rocks. Full article
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Open AccessCase Report
Environmental and Business Challenges Presented by Mining and Mineral Processing Waste in the Russian Federation
Minerals 2019, 9(7), 445; https://doi.org/10.3390/min9070445
Received: 4 June 2019 / Revised: 16 July 2019 / Accepted: 17 July 2019 / Published: 19 July 2019
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Abstract
Using Murmansk Region, one of Russia’s largest mining regions, as a case study, this paper examines the environmental safety challenges arising in the storage of mining and mineral processing waste (MMPW). It was found that MMPW causes environmental damage even after the deposit’s [...] Read more.
Using Murmansk Region, one of Russia’s largest mining regions, as a case study, this paper examines the environmental safety challenges arising in the storage of mining and mineral processing waste (MMPW). It was found that MMPW causes environmental damage even after the deposit’s exhaustion. While being stored, the MMPW composition experiences a major change in the process properties of the recoverable minerals. As a consequence, the potential value of the MMPW as a mineral resource falls. Imperfections of the regulatory framework, leading to a higher unit cost of recovery and a reduced profitability of MMPW processing, are demonstrated. Potential amendments to the Russian laws are proposed in order to make MMPW processing commercially more viable. Full article
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Open AccessArticle
Low Temperature Synthesis of Aegirine NaFeSi2O6: Spectroscopy (57Fe Mössbauer, Raman) and Size/Strain Analysis from X-ray Powder Diffraction
Minerals 2019, 9(7), 444; https://doi.org/10.3390/min9070444
Received: 2 July 2019 / Revised: 13 July 2019 / Accepted: 16 July 2019 / Published: 18 July 2019
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Abstract
Using a low temperature synthesis protocol, it was possible to obtain phase-pure synthetic aegirine (NaFeSi2O6) at temperatures as low as 130 °C, albeit only with rather long synthesis times of ~200 h; at 155 °C, a nano-crystallite shaped phase-pure [...] Read more.
Using a low temperature synthesis protocol, it was possible to obtain phase-pure synthetic aegirine (NaFeSi2O6) at temperatures as low as 130 °C, albeit only with rather long synthesis times of ~200 h; at 155 °C, a nano-crystallite shaped phase-pure material is formed after 24 h. These are, to the best of our knowledge, the lowest temperatures reported so far for phase-pure aegirine synthesis. Powder X-ray diffraction (PXRD) was used to characterize phase purity, structural state and microstructural properties (size and strain) of the as-synthesized (130–230 °C) and heat treated (300–900 °C) samples, via Rietveld analysis of powder patterns. Melting was observed at 999 °C. With increasing synthesis temperature, crystallite size linearly increased from 10 nm to 30 nm at 230 °C, while unit cell parameters decreased. The microstrain was very small. Additional heat treatment of as synthesized samples showed that the crystallite size remained rather unaffected up to 700 °C. The lattice parameters, however, already changed at low temperatures and successively became smaller, indicating increasing ordering towards more regular arrangements of building units. This was confirmed by 57Fe Mössbauer spectroscopy, where a distinct decrease of the quadrupole splitting with increasing synthesis temperature was found. Finally, Raman spectroscopy showed that some weakly-developed pre-ordering effects were present in the samples, which appeared to be amorphous in PXRD, while well-resolved spectra appeared as soon as the long-range ordered crystalline state could be found with X-ray diffraction. Full article
(This article belongs to the Section Crystallography and Physical Chemistry of Minerals)
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Open AccessArticle
Copper Sulfide Remobilization and Mineralization during Paleoproterozoic Retrograde Metamorphism in the Tongkuangyu Copper Deposit, North China Craton
Minerals 2019, 9(7), 443; https://doi.org/10.3390/min9070443
Received: 6 May 2019 / Revised: 6 July 2019 / Accepted: 16 July 2019 / Published: 18 July 2019
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Abstract
The Tongkuangyu copper deposit, North China Craton, is hosted in a volcano-sedimentary sequence (ca. 2.2 Ga) that metamorphosed to the lower amphibolite facies at ca. 1.9 Ga. Petrographic observations revealed various metamorphic fabrics (mineral alignment and foliations) and several generations of biotite, chlorite, [...] Read more.
The Tongkuangyu copper deposit, North China Craton, is hosted in a volcano-sedimentary sequence (ca. 2.2 Ga) that metamorphosed to the lower amphibolite facies at ca. 1.9 Ga. Petrographic observations revealed various metamorphic fabrics (mineral alignment and foliations) and several generations of biotite, chlorite, and pyrite. Sulfide Pb-Pb dating indicates that copper mineralization occurred at 1960+46/−58 Ma, younger than the zircon U-Pb age of the host metatuff (2180 Ma to 2190 Ma), but close to the timing of regional metamorphism (ca. 1.9 Ga). Electron probe analyses show that the biotites belong to the magnesium-rich variety, and were formed at 470 to 500 ° C based on Ti-in-biotite thermometry. Chlorites belong to ripidolite and pycnochlorite, and were formed at ca. 350 ° C based on the Al geothermometer. Pyrites in porphyry, metatuffs, and quartz veins have contrasting Ni and Co concentrations, pointing to a local remobilization. Hydrogen and oxygen isotopic analyses suggest that biotite and chlorite were formed by metamorphic waters whereas quartz records much lower δ D f l u i d values, reflecting the influence of meteoric water. Fluid inclusions in pyrite and chalcopyrite in metatuff and quartz vein contain extremely radiogenic 4 He and 40 Ar, indicating a crustal origin for the fluids. Sulfides show a magmatic sulfur isotopic signature, likely indicating the presence of preexisting volcanism-related sulfides. We proposed that the early layered copper sulfides formed during metamorphic retrogression at ca. 1.9 Ga and the late vein-type sulfides were derived from the remobilization of the earlier sulfides by infiltration of external fluids such as residual seawater and metamorphic fluids at shallow level. Full article
(This article belongs to the Section Mineral Deposits)
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Open AccessArticle
Magmatic-Hydrothermal Processes Associated with Rare Earth Element Enrichment in the Kangankunde Carbonatite Complex, Malawi
Minerals 2019, 9(7), 442; https://doi.org/10.3390/min9070442
Received: 14 March 2019 / Revised: 5 July 2019 / Accepted: 14 July 2019 / Published: 18 July 2019
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Abstract
Carbonatites undergo various magmatic-hydrothermal processes during their evolution that are important for the enrichment of rare earth elements (REE). This geochemical, petrographic, and multi-isotope study on the Kangankunde carbonatite, the largest light REE resource in the Chilwa Alkaline Province in Malawi, clarifies the [...] Read more.
Carbonatites undergo various magmatic-hydrothermal processes during their evolution that are important for the enrichment of rare earth elements (REE). This geochemical, petrographic, and multi-isotope study on the Kangankunde carbonatite, the largest light REE resource in the Chilwa Alkaline Province in Malawi, clarifies the critical stages of REE mineralization in this deposit. The δ56Fe values of most of the carbonatite lies within the magmatic field despite variations in the proportions of monazite, ankerite, and ferroan dolomite. Exsolution of a hydrothermal fluid from the carbonatite melts is evident based on the higher δ56Fe of the fenites, as well as the textural and compositional zoning in monazite. Field and petrographic observations, combined with geochemical data (REE patterns, and Fe, C, and O isotopes), suggest that the key stage of REE mineralization in the Kangankunde carbonatite was the late magmatic stage with an influence of carbothermal fluids i.e. magmatic–hydrothermal stage, when large (~200 µm), well-developed monazite crystals grew. The C and O isotope compositions of the carbonatite suggest a post-magmatic alteration by hydrothermal fluids, probably after the main REE mineralization stage, as the alteration occurs throughout the carbonatite but particularly in the dark carbonatites. Full article
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Open AccessArticle
Structural Phase Transition and Metallization of Nanocrystalline Rutile Investigated by High-Pressure Raman Spectroscopy and Electrical Conductivity
Minerals 2019, 9(7), 441; https://doi.org/10.3390/min9070441
Received: 19 May 2019 / Revised: 1 July 2019 / Accepted: 1 July 2019 / Published: 18 July 2019
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Abstract
We investigate the structural, vibrational, and electrical transport properties of nanocrystalline rutile and its high-pressure polymorphs by Raman spectroscopy, and AC complex impedance spectroscopy in conjunction with the high-resolution transmission electron microscopy (HRTEM) up to ~25.0 GPa using the diamond anvil cell (DAC). [...] Read more.
We investigate the structural, vibrational, and electrical transport properties of nanocrystalline rutile and its high-pressure polymorphs by Raman spectroscopy, and AC complex impedance spectroscopy in conjunction with the high-resolution transmission electron microscopy (HRTEM) up to ~25.0 GPa using the diamond anvil cell (DAC). Experimental results indicate that the structural phase transition and metallization for nanocrystalline rutile occurred with increasing pressure up to ~12.3 and ~14.5 GPa, respectively. The structural phase transition of sample at ~12.3 GPa is confirmed as a baddeleyite phase, which is verified by six new Raman characteristic peaks. The metallization of the baddeleyite phase is manifested by the temperature-dependent electrical conductivity measurements at ~14.5 GPa. However, upon decompression, the structural phase transition from the metallic baddeleyite to columbite phases at ~7.2 GPa is characterized by the inflexion point of the pressure coefficient and the pressure-dependent electrical conductivity. The recovered columbite phase is always retained to the atmospheric condition, which belongs to an irreversible phase transformation. Full article
(This article belongs to the Special Issue Nanomineralogy)
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Open AccessArticle
Automated Quantitative Mineralogy Optimized for Simultaneous Detection of (Precious/Critical) Rare Metals and Base Metals in A Production-Focused Environment
Minerals 2019, 9(7), 440; https://doi.org/10.3390/min9070440
Received: 17 June 2019 / Revised: 12 July 2019 / Accepted: 15 July 2019 / Published: 18 July 2019
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Abstract
Automated Scanning Electron Microscopy (ASEM) systems are applied in the mining industry to quantify the mineralogy of the ore feed and products. With society pushing towards sustainable mining, this quantification should be comprehensive and include trace minerals since they are often either deleterious [...] Read more.
Automated Scanning Electron Microscopy (ASEM) systems are applied in the mining industry to quantify the mineralogy of the ore feed and products. With society pushing towards sustainable mining, this quantification should be comprehensive and include trace minerals since they are often either deleterious or potential by-products. Systems like QEMSCAN® offer a mode for trace mineral analysis (TMS mode); However, it is unsuitable when all phases require analysis. Here, we investigate the potential of detecting micron-sized trace minerals in fieldscan mode using the QEMSCAN® system with analytical settings in line with the mining industry. For quality comparison, analysis was performed at a mining company and a research institution. This novel approach was done in full collaboration with both parties. Results show that the resolution of trace minerals at or below the scan resolution is difficult and not always reliable due to mixed X-ray signals. However, by modification of the species identification protocol (SIP), quantification is achievable, although verification by SEM-EDS is recommended. As an add-on to routine quantitative analysis focused on major ore minerals, this method can produce quantitative data and information on mineral association for trace minerals of precious and critical metals which may be potential by-products in a mining operation. Full article
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Open AccessArticle
Hydrogenetic, Diagenetic and Hydrothermal Processes Forming Ferromanganese Crusts in the Canary Island Seamounts and Their Influence in the Metal Recovery Rate with Hydrometallurgical Methods
Minerals 2019, 9(7), 439; https://doi.org/10.3390/min9070439
Received: 10 May 2019 / Revised: 12 July 2019 / Accepted: 13 July 2019 / Published: 17 July 2019
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Abstract
Four pure hydrogenetic, mixed hydrogenetic-diagenetic and hydrogenetic-hydrothermal Fe-Mn Crusts from the Canary Islands Seamount Province have been studied by Micro X-Ray Diffraction, Raman and Fourier-transform infrared spectroscopy together with high resolution Electron Probe Micro Analyzer and Laser Ablation Inductively Coupled Plasma Mass Spectrometry [...] Read more.
Four pure hydrogenetic, mixed hydrogenetic-diagenetic and hydrogenetic-hydrothermal Fe-Mn Crusts from the Canary Islands Seamount Province have been studied by Micro X-Ray Diffraction, Raman and Fourier-transform infrared spectroscopy together with high resolution Electron Probe Micro Analyzer and Laser Ablation Inductively Coupled Plasma Mass Spectrometry in order to find the correlation of mineralogy and geochemistry with the three genetic processes and their influence in the metal recovery rate using an hydrometallurgical method. The main mineralogy and geochemistry affect the contents of the different critical metals, diagenetic influenced crusts show high Ni and Cu (up to 6 and 2 wt. %, respectively) (and less Co and REY) enriched in very bright laminae. Hydrogenetic crusts on the contrary show High Co and REY (up to 1 and 0.5 wt. %) with also high contents of Ni, Mo and V (average 2500, 600 and 1300 μg/g). Finally, the hydrothermal microlayers from crust 107-11H show their enrichment in Fe (up to 50 wt. %) and depletion in almost all the critical elements. One hydrometallurgical method has been used in Canary Islands Seamount Province crusts in order to quantify the recovery rate of valuable elements in all the studied crusts except the 107-11H, whose hydrothermal critical metals’ poor lamina were too thin to separate from the whole crust. Digestion treatment with hydrochloric acid and ethanol show a high recovery rate for Mn (between 75% and 81%) with respect to Fe (49% to 58%). The total recovery rate on valuable elements (Co, Ni, Cu, V, Mo and rare earth elements plus yttrium (REY)) for the studied crusts range between 67 and 92% with the best results for Co, Ni and V (up to 80%). The genetic process and the associated mineralogy seem to influence the recovery rate. Mixed diagenetic/hydrogenetic crust show the lower recovery rate for Mn (75%) and Ni (52.5%) both enriched in diagenetic minerals (respectively up to 40 wt. % and up to 6 wt. %). On the other hand, the presence of high contents of undigested Fe minerals (i.e., Mn-feroxyhyte) in hydrogenetic crusts give back low recovery rate for Co (63%) and Mo (42%). Finally, REY as by-product elements, are enriched in the hydrometallurgical solution with a recovery rate of 70–90% for all the studied crusts. Full article
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Open AccessArticle
Morphology of Detrital Zircon as a Fingerprint to Trace Sediment Provenance: Case Study of the Yangtze Delta
Minerals 2019, 9(7), 438; https://doi.org/10.3390/min9070438
Received: 21 June 2019 / Revised: 13 July 2019 / Accepted: 15 July 2019 / Published: 17 July 2019
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Abstract
Deltaic areas and marginal seas are important archives that document information on regional tectonic movement, sea level rise, river evolution, and climate change. Here, sediment samples from boreholes of the Yangtze Delta and the modern Yangtze drainage were collected. A quantitative analysis of [...] Read more.
Deltaic areas and marginal seas are important archives that document information on regional tectonic movement, sea level rise, river evolution, and climate change. Here, sediment samples from boreholes of the Yangtze Delta and the modern Yangtze drainage were collected. A quantitative analysis of detrital zircon morphology was used to discuss the provenance evolution of the Yangtze Delta. This research demonstrated that a dramatic change in sediment provenance occurred in the transition from the Pliocene to Quaternary. Zircon grains in the Pliocene sediments featured euhedral crystals with large elongation (>3 accounted for 13.2%) and were closely matched to tributary samples in the Lower Yangtze (>3 accounted for 11.3%), suggesting sediment provenance from the proximal river basin. However, most detrital zircon grains of the Quaternary samples exhibited lower values of elongation and increased roundness (rounded grains were 9.4%), which was similar to those found in the modern Yangtze mainstream (rounded grains were 12.5%) and the middle tributaries (rounded grains were 7.0%). The decrease in zircon elongation and improvement of its roundness in the Quaternary strata implied that the Yangtze Delta received sediments of different provenance that originated from the Middle-Upper Yangtze basin due to the uplift of the Tibetan Plateau. Statistical analysis of detrital zircon morphology has proven useful for studying the source-to-sink of sediments. Full article
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Open AccessArticle
Electrochemical, Spectroscopic, and Computational Investigations on Redox Reactions of Selenium Species on Galena Surfaces
Minerals 2019, 9(7), 437; https://doi.org/10.3390/min9070437
Received: 15 June 2019 / Revised: 11 July 2019 / Accepted: 13 July 2019 / Published: 15 July 2019
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Abstract
Despite previous studies investigating selenium (Se) redox reactions in the presence of semiconducting minerals, Se redox reactions mediated by galena (PbS) are poorly understood. In this study, the redox chemistry of Se on galena is investigated over a range of environmentally relevant Eh [...] Read more.
Despite previous studies investigating selenium (Se) redox reactions in the presence of semiconducting minerals, Se redox reactions mediated by galena (PbS) are poorly understood. In this study, the redox chemistry of Se on galena is investigated over a range of environmentally relevant Eh and pH conditions (+0.3 to −0.6 V vs. standard hydrogen electrode, SHE; pH 4.6) using a combination of electrochemical, spectroscopic, and computational approaches. Cyclic voltammetry (CV) measurements reveal one anodic/cathodic peak pair at a midpoint potential of +30 mV (vs. SHE) that represents reduction and oxidation between HSeO3 and H2Se/HSe. Two peak pairs with midpoint potentials of −400 and −520 mV represent the redox transformation from Se(0) to HSe and H2Se species, respectively. The changes in Gibbs free energies of adsorption of Se species on galena surfaces as a function of Se oxidation state were modeled using quantum-mechanical calculations and the resulting electrochemical peak shifts are (−0.17 eV for HSeO3−/H2Se, −0.07 eV for HSeO3−/HSe, 0.15 eV for Se(0)/HSe, and −0.15 eV for Se(0)/H2Se). These shifts explain deviation between Nernstian equilibrium redox potentials and observed midpoint potentials. X-ray photoelectron spectroscopy (XPS) analysis reveals the formation of Se(0) potentials below −100 mV and Se(0) and Se(−II) species at potentials below −400 mV. Full article
(This article belongs to the Special Issue Selenide Mineralization)
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Open AccessArticle
Origin and Sources of Minerals and Their Impact on the Hydrocarbon Reservoir Quality of the PaleogeneLulehe Formation in the Eboliang Area, Northern Qaidam Basin, China
Minerals 2019, 9(7), 436; https://doi.org/10.3390/min9070436
Received: 13 May 2019 / Revised: 8 July 2019 / Accepted: 12 July 2019 / Published: 15 July 2019
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Abstract
The Lulehe sandstone in the Eboliang area is a major target for hydrocarbon exploration in the northern Qaidam Basin. Based on an integrated analysis including thin section analysis, scanning electron microscopy, X-ray diffraction, cathodoluminescence investigation, backscattered electron images, carbon and oxygen stable isotope [...] Read more.
The Lulehe sandstone in the Eboliang area is a major target for hydrocarbon exploration in the northern Qaidam Basin. Based on an integrated analysis including thin section analysis, scanning electron microscopy, X-ray diffraction, cathodoluminescence investigation, backscattered electron images, carbon and oxygen stable isotope analysis and fluid inclusion analysis, the diagenetic processes mainly include compaction, cementation by carbonate and quartz, formation of authigenic clay minerals (i.e., chlorite, kaolinite, illite-smectite and illite) and dissolution of unstable materials. Compaction is the main factor for the deterioration of reservoir quality; in addition, calcite cement and clay minerals are present, including kaolinite, pore-filling chlorite, illite-smectite and illite, which also account for reservoir quality reduction. Integration of petrographic studies and isotope geochemistry reveals the carbonate cements might have originated from mixed sources of bioclast- and organic-derived CO2 during burial. The quartz cement probably formed by feldspar dissolution, illitization of smectite and kaolinite, as well as pressure solution of quartz grains. Smectite, commonly derived from alteration of volcanic rock fragments, may have been the primary clay mineral precursor of chlorite. In addition, authigenic kaolinite is closely associated with feldspar dissolution, suggesting that alteration of detrital feldspar grains was the most probable source for authigenic kaolinite. With the increase in temperature and consumption of organic acids, the ratio of K+/H+ increases and the stability field of kaolinite is greatly reduced, thereby transforming kaolinite into mixed layer illite/smectite and illite. Within the study area, porosity increases with chlorite content up to approximately 3% volume and then decreases slightly, indicating that chlorite coatings are beneficial at an optimum volume of 3%. A benefit of the dissolution of unstable minerals and feldspar grains is the occurrence of secondary porosity, which may enhance porosity to some extent. However, the solutes cannot be transported over a large scale in the deep burial environment, and simultaneous precipitation of byproducts of feldspar dissolution such as authigenic kaolinite and quartz cement will occur in situ or in adjacent pores, resulting in heterogeneity of the reservoirs. Full article
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Open AccessEditorial
Editorial for Special Issue “Polymetallic Metallogenic System”
Minerals 2019, 9(7), 435; https://doi.org/10.3390/min9070435
Received: 5 July 2019 / Accepted: 10 July 2019 / Published: 15 July 2019
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Abstract
In the last century, following the development of Earth System Science, the metallogenic system has become an important topic in the study of mineral deposits [...] Full article
(This article belongs to the Special Issue Polymetallic Metallogenic System)
Open AccessArticle
Electron Donor Utilization and Secondary Mineral Formation during the Bioreduction of Lepidocrocite by Shewanella putrefaciens CN32
Minerals 2019, 9(7), 434; https://doi.org/10.3390/min9070434
Received: 30 April 2019 / Revised: 12 June 2019 / Accepted: 4 July 2019 / Published: 14 July 2019
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Abstract
The bioreduction of Fe(III) oxides by dissimilatory iron reducing bacteria (DIRB) may result in the production of a suite of Fe(II)-bearing secondary minerals, including magnetite, siderite, vivianite, green rusts, and chukanovite; the formation of specific phases controlled by the interaction of various physiological [...] Read more.
The bioreduction of Fe(III) oxides by dissimilatory iron reducing bacteria (DIRB) may result in the production of a suite of Fe(II)-bearing secondary minerals, including magnetite, siderite, vivianite, green rusts, and chukanovite; the formation of specific phases controlled by the interaction of various physiological and geochemical factors. In an effort to better understand the effects of individual electron donors on the formation of specific Fe(II)-bearing secondary minerals, we examined the effects of a series of potential electron donors on the bioreduction of lepidocrocite (γ-FeOOH) by Shewanella putrefaciens CN32. Biomineralization products were identified by X-ray diffraction, Mössbauer spectroscopy, and scanning electron microscopy. Acetate, citrate, ethanol, glucose, glutamate, glycerol, malate, and succinate were not effectively utilized for the bioreduction of lepidocrocite by S. putrefaciens CN32; however, substantial Fe(II) production was observed when formate, lactate, H2, pyruvate, serine, or N acetylglucosamine (NAG) was provided as an electron donor. Carbonate or sulfate green rust was the dominant Fe(II)-bearing secondary mineral when formate, H2, lactate, or NAG was provided, however, siderite formed with pyruvate or serine. Geochemical modeling indicated that pH and carbonate concentration are the key factors determining the prevalence of carbonate green rust verses siderite. Full article
(This article belongs to the Special Issue Bio-Transformation and Mineralization Induced by Microorganisms)
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Open AccessArticle
Flocs Properties and Flotation Performance of Fine Diaspore with Energy Input Pretreatment Induced Using Sodium Oleate
Minerals 2019, 9(7), 433; https://doi.org/10.3390/min9070433
Received: 18 June 2019 / Revised: 6 July 2019 / Accepted: 12 July 2019 / Published: 14 July 2019
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Abstract
Energy input, an important factor affecting flocs properties and flotation performance, has rarely been studied in the field of diaspore flotation, which has severely limited our understanding of the flocculation flotation of fine diaspore. Therefore, in this study, the flocs properties and flotation [...] Read more.
Energy input, an important factor affecting flocs properties and flotation performance, has rarely been studied in the field of diaspore flotation, which has severely limited our understanding of the flocculation flotation of fine diaspore. Therefore, in this study, the flocs properties and flotation performance of fine diaspore with energy input pretreatment were studied through flotation kinetics, flocs size measurements, and fractal dimension analysis. The results showed that the flocs size increased and the flocs structure became looser with the increasing energy input, while the flocs size decreased and the structure became compact when the energy input exceeded 10.93 kJ/m3. Meanwhile, there were significant differences in the flotation performance under different energy input pretreatment conditions, suggesting that the flotation performance of the fine diaspore was closely related with the flocs properties generated during the agitation process. In particular, the flotation performance was positively correlated with the flocculation degree of flocs, to a certain extent. The flocculation flotation of the fine diaspore benefited from a suitable energy input, and an excessive energy input was not conducive to flotation performance. Full article
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Open AccessArticle
Insights into B-Mg-Metasomatism at the Ranger U Deposit (NT, Australia) and Comparison with Canadian Unconformity-Related U Deposits
Minerals 2019, 9(7), 432; https://doi.org/10.3390/min9070432
Received: 13 June 2019 / Revised: 10 July 2019 / Accepted: 11 July 2019 / Published: 14 July 2019
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Abstract
The Ranger deposit (Northern Territory, Australia) is one of the largest uranium deposits in the world. Uranium mineralisation occurs in crystalline basement rocks and is thought to belong to the unconformity-related category. In order to address the sources of magnesium and boron, and [...] Read more.
The Ranger deposit (Northern Territory, Australia) is one of the largest uranium deposits in the world. Uranium mineralisation occurs in crystalline basement rocks and is thought to belong to the unconformity-related category. In order to address the sources of magnesium and boron, and the temperature of the fluids related to boron and magnesium metasomatism that occurred shortly before and during the main uranium stage, in situ analyses of chlorite and tourmaline were carried out. The chemical composition of tourmaline shows an elevated X-site vacancy and a low Fetot/(Fetot + Mg) ratio typical of Mg-foitite. Uranium-related chlorite has relatively low Fe content (0.28–0.83 apfu) and high Mg content (3.08–3.84 apfu), with Si/Al = 1.08−1.22 and Mg/(Mg + Fetot) = 0.80−0.93 indicating a composition lying between the clinochlore and Mg-amesite fields. Chlorite composition indicates crystallisation temperature of 101–163 °C. The boron isotopic composition of tourmaline shows a range of δ11B values of ~1–9‰. A model is proposed involving two boron sources that contribute to a mixed isotopic signature: (i) evaporated seawater, which is typically enriched in magnesium and boron (δ11B ~ 40‰), and (ii) boron from the crystalline basement (δ11B ~ −30 to +10‰), which appears to be the dominant source. Collectively, the data indicate similar tourmaline chemistry but significant differences of tourmaline boron isotopic composition and chlorite chemistry between the Ranger deposit and some of the Canadian unconformity-related uranium deposits. However, lithogeochemical exploration approaches based on identification of boron- and magnesium-enriched zones may be usefully applied to uranium exploration in the Northern Territory. Full article
(This article belongs to the Special Issue Geology and Mineralogy of Uranium Deposits)
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Open AccessArticle
Constraints from Geochemistry and Field Relationships for the Origin of Kornerupine-Bearing Gneiss from the Grenvillian New Jersey Highlands and Implications for the Source of Boron
Minerals 2019, 9(7), 431; https://doi.org/10.3390/min9070431
Received: 11 June 2019 / Revised: 9 July 2019 / Accepted: 12 July 2019 / Published: 14 July 2019
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Abstract
Kornerupine ± prismatine is present in granulite-facies paragneiss at two locations in the Grenvillian New Jersey Highlands, occurring in an assemblage composed of quartz + biotite + K-feldspar + plagioclase + garnet + Fe-Ti oxides ± sillimanite ± rutile ± graphite. Estimates of [...] Read more.
Kornerupine ± prismatine is present in granulite-facies paragneiss at two locations in the Grenvillian New Jersey Highlands, occurring in an assemblage composed of quartz + biotite + K-feldspar + plagioclase + garnet + Fe-Ti oxides ± sillimanite ± rutile ± graphite. Estimates of the metamorphic conditions of the host gneiss are ≥600 MPa and ~740 °C during the Ottawan phase of the Grenvillian Orogeny. Geochemical compositions of kornerupine-bearing gneiss are consistent with protoliths that were graywacke sandstone and pelite. Metagraywacke is characterized by (in wt. %) 62–76% SiO2, 0.3–0.8% TiO2, 13–16% Al2O3, 0.6–4.3% CaO, 2.2–6.4% Na2O, 1.7–7.4% K2O, and 90–260 ppm Zr; metapelite has lower SiO2 (53–66%) and CaO (0.5–2.0%), higher TiO2 (0.9–1.8%), Al2O3, (15–26%), and Zr (210–490 ppm), and comparable Na2O (2.5–4.9%) and K2O (2.5–7.4%). Indices of weathering and alteration yield low to intermediate values implying a relatively unweathered sediment source. Provenance discriminants suggest the protoliths formed from immature, first-cycle sediments derived mainly from a felsic arc-related source. The geological relationships of kornerupine-bearing gneiss are most compatible with boron sourced from B-rich sediments deposited in the protoliths between ca. 1299 and 1238 Ma. The breakdown of these sediments due to dehydration reactions during Ottawan prograde metamorphism led to mobilization of a B-rich fluid that migrated short distances to favorable structural sites in the host gneiss, resulting in precipitation of the borosilicates. Full article
(This article belongs to the Special Issue Minerals of the Southern Grenville Province)
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Open AccessArticle
Ag-Pb-Sb Sulfosalts and Se-rich Mineralization of Anthony of Padua Mine near Poličany—Model Example of the Mineralization of Silver Lodes in the Historic Kutná Hora Ag-Pb Ore District, Czech Republic
Minerals 2019, 9(7), 430; https://doi.org/10.3390/min9070430
Received: 3 May 2019 / Revised: 26 June 2019 / Accepted: 6 July 2019 / Published: 12 July 2019
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Abstract
Significant selenium enrichment associated with selenides and previously unknown Ag-Pb-Sb, Ag-Sb and Pb-Sb sulfosalts has been discovered in hydrothermal ore veins in the Anthony of Padua mine near Poličany, Kutná Hora ore district, central Bohemia, Czech Republic. The ore mineralogy and crystal chemistry [...] Read more.
Significant selenium enrichment associated with selenides and previously unknown Ag-Pb-Sb, Ag-Sb and Pb-Sb sulfosalts has been discovered in hydrothermal ore veins in the Anthony of Padua mine near Poličany, Kutná Hora ore district, central Bohemia, Czech Republic. The ore mineralogy and crystal chemistry of more than twenty silver minerals are studied here. Selenium mineralization is evidenced by a) the occurrence of selenium minerals, and b) significantly increased selenium contents in sulfosalts. Identified selenium minerals include aguilarite and selenides naumannite and clausthalite. The previously unknown sulfosalts from Kutná Hora are identified: Ag-excess fizélyite, fizélyite, andorite IV, andorite VI, unnamed Ag-poor Ag-Pb-Sb sulfosalts, semseyite, stephanite, polybasite, unnamed Ag-Cu-S mineral phases and uytenbogaardtite. Among the newly identified sulfides is argyrodite; germanium is a new chemical element in geochemistry of Kutná Hora. Three types of ore were recognized in the vein assemblage: the Pb-rich black ore (i) in quartz; the Ag-rich red ore (ii) in kutnohorite-quartz gangue; and the Ag-rich ore (iii) in milky quartz without sulfides. The general succession scheme runs for the Pb-rich black ore (i) as follows: galena – boulangerite (– jamesonite) – owyheeite – fizélyite – Ag-exces fizélyite – andorite IV – andorite VI – freieslebenite – diaphorite – miargyrite – freibergite. For the Ag-rich red ore (ii) and ore (iii) the most prominent pattern is: galena – diaphorite – freibergite – miargyrite – pyragyrite – stephanite – polybasite – acanthite. The parallel succession scheme progresses from Se-poor to Se-rich phases, i.e., galena – members of galena – clausthalite solid solution – clausthalite; miargyrite – Se-rich miargyrite; acanthite – aguilarite – naumannite. A likely source of selenium is in the serpentinized ultrabasic bodies, known in the area of “silver” lodes in the South of the ore district, which may enable to pre-concentrate selenium, released into hydrothermal fluids during tectonic events. The origin of the studied ore mineralization is primarily bound to the youngest stage of mineralization of the whole ore district, corresponding to the Ag-Sb sequence of the ‘eb’ ore type of the Freiberg ore district in Saxony (Germany) and shows mineralogical and geochemical similarities to low-sulfidation epithermal-style Ag-Au mineralization. Full article
(This article belongs to the Special Issue Selenide Mineralization)
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Open AccessArticle
Factors Controlling Hydrothermal Nickel and Cobalt Mineralization—Some Suggestions from Historical Ore Deposits in Italy
Minerals 2019, 9(7), 429; https://doi.org/10.3390/min9070429
Received: 9 June 2019 / Revised: 9 July 2019 / Accepted: 10 July 2019 / Published: 12 July 2019
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Abstract
We compare three poorly known, historical Ni–Co-bearing hydrothermal deposits in different geological settings in Italy: The Ni–Co–As–Sb–Au-bearing Arburese vein system (SW Sardinia), the Co–Ni–As-rich Usseglio vein system (Piedmont), and the small Cu–Ag–Co–Ni–Pb–Te–Se stockwork at Piazza (Liguria). These deposits share various (mineralogical, chemical, thermal, [...] Read more.
We compare three poorly known, historical Ni–Co-bearing hydrothermal deposits in different geological settings in Italy: The Ni–Co–As–Sb–Au-bearing Arburese vein system (SW Sardinia), the Co–Ni–As-rich Usseglio vein system (Piedmont), and the small Cu–Ag–Co–Ni–Pb–Te–Se stockwork at Piazza (Liguria). These deposits share various (mineralogical, chemical, thermal, and stable isotopic) similarities to the Five Element Vein-type ores but only the first two were economic for Co–Ni. The Sardinian Ni-rich veins occur in Paleozoic basement near two Variscan plutons. Like the Co-rich Usseglio vein system, the uneconomic Piazza deposit is hosted in an ophiolite setting anomalous for Co. The Sardinian and Usseglio deposits share a polyphasic assemblage with Ni–Co–As–Sb–Bi followed by Ag-base metal sulfides, in siderite-rich gangue, whereas Piazza shows As-free, Ag–Pb–Te–Se-bearing Co–Ni–Cu sulfides, in prehnite–chlorite gangue. Fluid inclusions indicated Co–Ni arsenide precipitation at ≈170 °C for Usseglio, whereas for the Sardinian system late sulfide deposition occurred within the 52–126 °C range. Ore fluids in both systems are NaCl-CaCl2-bearing basinal brines. The chlorite geothermometer at Piazza provides the range of 200–280 °C for ore deposition from CO2-poor fluids. Enrichments in Se and negative δ13C in carbonates suggest interaction with carbonaceous shales. These deposits involve issues about source rocks, controls on Co/Ni and possible role of arsenic and carbonate components towards economic mineralization. Full article
(This article belongs to the Special Issue High-Tech Critical Metals: Evaluation and Deposit Models)
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Open AccessArticle
Pyrite Morphology as an Indicator of Paleoredox Conditions and Shale Gas Content of the Longmaxi and Wufeng Shales in the Middle Yangtze Area, South China
Minerals 2019, 9(7), 428; https://doi.org/10.3390/min9070428
Received: 26 April 2019 / Revised: 29 June 2019 / Accepted: 10 July 2019 / Published: 12 July 2019
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Abstract
Pyrite is the most common authigenic mineral preserved in many ancient sedimentary rocks. Pyrite also widely exists in the Longmaxi and Wufeng marine shales in the middle Yangtze area in South China. The Longmaxi and Wufeng shales were mainly discovered with 3 types [...] Read more.
Pyrite is the most common authigenic mineral preserved in many ancient sedimentary rocks. Pyrite also widely exists in the Longmaxi and Wufeng marine shales in the middle Yangtze area in South China. The Longmaxi and Wufeng shales were mainly discovered with 3 types of pyrites: pyrite framboids, euhedral pyrites and infilled framboids. Euhedral pyrites (Py4) and infilled framboids (Py5) belong to the diagenetic pyrites. Based on the formation mechanism of pyrites, the pyrites could be divided into syngenetic pyrites, early diagenetic pyrites, and late diagenetic pyrites. Under a scanning electron microscope (SEM), the syngenetic pyrites are mostly small framboids composed of small microcrystals, but the diagenetic pyrites are variable in shapes and the diagenetic framboids are variable in sizes with large microcrystals. Due to the deep burial stage, the pore space in the sediment was sharply reduced and the diameter of the late diagenetic framboids that formed in the pore space is similar to the diameter of the syngenetic framboids. However, the diameter of the syngenetic framboid microcrystals is suggested to range mainly from 0.3 µm to 0.4 µm, and that of the diagenetic framboid microcrystals is larger than 0.4 µm in the study area. According to the diameter of the pyrite framboids (D) and the diameter of the framboid microcrystals (d), the pyrite framboids could be divided into 3 sizes: syngenetic framboids (Py1, D < 5 µm, d ≤ 0.4 µm), early diagenetic framboids (Py2, D > 5 µm, d > 0.4 µm) and late diagenetic framboids (Py3, D < 5 µm, d > 0.4 µm). Additionally, the mean size and standard deviation/skewness values of the populations of pyrite framboids were used to distinguish the paleoredox conditions during the sedimentary stage. In the study area, most of the pyrite framboids are smaller than 5 µm, indicating the sedimentary water body was a euxinic environment. However, pyrite framboids larger than 5 µm in the shales indicated that the sedimentary water body transformed to an oxic-dysoxic environment with relatively low total organic carbon (TOC: 0.4–0.99%). Furthermore, the size of the framboid microcrystals could be used to estimate the gas content due to thermochemical sulfate reduction (TSR). The process of TSR occurs with oxidation of organic matter (OM) and depletes the H bond of the OM, which will influence the amount of alkane gas produced from the organic matter during the thermal evolution. Thus, syngenetic pyrites (d ranges from 0.35 µm to 0.37 µm) occupy the main proportion of pyrites in the Wufeng shales with high gas content (1.30–2.30 m3/t), but the Longmaxi shales (d ranges from 0.35 µm to 0.72 µm) with a relatively low gas content (0.07–0.93 m3/t) contain diagenetic pyrites. Because of TSR, the increasing size of the microcrystals may result in an increase in the value of δ13C1 and a decrease in the value of δ13C113C2. Consequently, the size of pyrite framboids and microcrystals could be widely used for rapid evaluation of the paleoredox conditions and the gas content in shales. Full article
(This article belongs to the Special Issue Nanomineralogy)
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Open AccessArticle
Experimental Study of Pyrite Oxidation at 100 °C: Implications for Deep Geological Radwaste Repository in Claystone
Minerals 2019, 9(7), 427; https://doi.org/10.3390/min9070427
Received: 3 June 2019 / Revised: 4 July 2019 / Accepted: 11 July 2019 / Published: 12 July 2019
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Abstract
The oxidation of pyrite is one of the near field processes of the chemical evolution of clay rock planned to host a deep geological radioactive waste repository during operation. Indeed, this process can lead to transitory acidic conditions in the medium (i.e., production [...] Read more.
The oxidation of pyrite is one of the near field processes of the chemical evolution of clay rock planned to host a deep geological radioactive waste repository during operation. Indeed, this process can lead to transitory acidic conditions in the medium (i.e., production of sulphuric acid, carbonic acid) which may influence the corrosion kinetics of the carbon steel components of some disposal cells. In order to improve the geochemical modelling of the long-term disposal, the oxidation of pyrite in contact with clays and carbonates at 100 °C must be evaluated. In this study, special attention was paid to the pyrite oxidation rate thanks to an original experimental set-up, involving several pyrite/mineral mixtures and a reactor coupled to a micro gas chromatograph (PO2 and PCO2 monitoring). Although thermodynamic modelling expects that hematite is the most stable phase in a pure pyrite heated system (low pH), experiments show the formation of native sulfur as an intermediate product of the reaction. In the presence of calcite, the pH is neutralized and drives the lower reactivity of pyrite in the absence of native sulfur. The addition of clay phases or other detrital silicates from the claystone had no impact on pyrite oxidation rate. The discrepancies between experiments and thermodynamic modelling are explained by kinetic effects. Two laws were deduced at 100 °C. The first concerns a pure pyrite system, with the following law: r P y =   10 4.8 · P O 2 0.5 · t 0.5 . The second concerns a pyrite/carbonates system: r P y + C a =   10 5.1 · P O 2 0.5 · t 0.5 where PO2 corresponds to the partial pressure of O2 (in bar) and t is time in seconds. Different mechanisms are proposed to explain the evolution with time of the O2 consumption during pyrite oxidation: (i) decrease of the specific or reactive surface area after oxidation of fine grains of pyrite, (ii) decrease of O2 pressure, (iii) growing up of secondary minerals (Fe-oxides or anhydrite in the presence of calcium in the system) on the surface of pyrite limiting the access of O2 to the fresh surface of pyrite, and (iv) change in the pH of the solution. Full article
(This article belongs to the Section Environmental Mineralogy and Biogeochemistry)
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Open AccessArticle
Using Rare Earth Elements (REE) to Decipher the Origin of Ore Fluids Associated with Granite Intrusions
Minerals 2019, 9(7), 426; https://doi.org/10.3390/min9070426
Received: 31 May 2019 / Revised: 8 July 2019 / Accepted: 9 July 2019 / Published: 11 July 2019
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Abstract
A practical method is presented to estimate rare earth element (REE) concentrations in a magmatic fluid phase in equilibrium with water-saturated granitic melts based on empirical fluid–melt partition coefficients of REE (kPREE). The values of kP [...] Read more.
A practical method is presented to estimate rare earth element (REE) concentrations in a magmatic fluid phase in equilibrium with water-saturated granitic melts based on empirical fluid–melt partition coefficients of REE ( k P R E E ). The values of k P R E E can be calculated from a set of new polynomial equations linking to the Cl molality ( m C l v ) of the magmatic fluid phase associated with granitic melts, which are established via a statistical analysis of the existing experimental dataset. These equations may be applied to the entire pressure range (0.1 to 10.0 kb) within the continental crust. Also, the results indicate that light REEs (LREE) behave differently in magmatic fluids, i.e., either being fluid compatible with higher m C l v or fluid incompatible with lower m C l v values. In contrast, heavy REEs (HREE) are exclusively fluid incompatible, and partition favorably into granitic melts. Consequently, magmatic fluids tend to be rich in LREE relative to HREE, leading to REE fractionation during the evolution of magmatic hydrothermal systems. The maximum k P R E E value for each element is predicted and presented in a REE distribution diagram constrained by the threshold value of m C l v . The REE contents of the granitic melt are approximated by whole-rock analysis, so that REE concentrations in the associated magmatic fluid phase would be estimated from the value of k P R E E given chemical equilibrium. Two examples are provided, which show the use of this method as a REE tracer to fingerprint the source of ore fluids responsible for the Lake George intrusion-related Au–Sb deposit in New Brunswick (Canada), and the Bakircay Cu–Au (–Mo) porphyry systems in northern Turkey. Full article
(This article belongs to the Special Issue REE Transport in High-Grade Crustal Fluids)
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