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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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15 pages, 2863 KiB  
Article
Structural and Elastic Behaviour of Sodalite Na8(Al6Si6O24)Cl2 at High-Pressure by First-Principle Simulations
by Gianfranco Ulian and Giovanni Valdrè
Minerals 2022, 12(10), 1323; https://doi.org/10.3390/min12101323 - 20 Oct 2022
Cited by 5 | Viewed by 3310
Abstract
Sodalite Na8(Al6Si6O24)Cl2 (space group P4¯3n) is an important mineral belonging to the zeolite group, with several and manyfold fundamental and technological applications. Despite the interest in this mineral from [...] Read more.
Sodalite Na8(Al6Si6O24)Cl2 (space group P4¯3n) is an important mineral belonging to the zeolite group, with several and manyfold fundamental and technological applications. Despite the interest in this mineral from different disciplines, very little is known regarding its high-pressure elastic properties. The present study aims at filling this knowledge gap, reporting the equation of state and the elastic moduli of sodalite calculated in a wide pressure range, from −6 GPa to 22 GPa. The results were obtained from Density Functional Theory simulations carried out with Gaussian-type basis sets and the well-known hybrid functional B3LYP. The DFT-D3 a posteriori correction to include the van der Waals interactions in the physical treatment of the mineral was also applied. The calculated equation of state parameters at 0 GPa and absolute zero (0 K), i.e., K0 = 70.15(7) GPa, K’ = 4.46(2) and V0 = 676.85(3) Å3 are in line with the properties derived from the stiffness tensor, and in agreement with the few experimental data reported in the literature. Sodalite was found mechanically unstable when compressed above 15.6 GPa. Full article
(This article belongs to the Section Clays and Engineered Mineral Materials)
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15 pages, 2058 KiB  
Article
Chemical and Mineralogical Characterization of Montevive Celestine Mineral
by Noemi Ariza-Rodríguez, Alejandro B. Rodríguez-Navarro, Mónica Calero de Hoces, Jose Manuel Martin and Mario J. Muñoz-Batista
Minerals 2022, 12(10), 1261; https://doi.org/10.3390/min12101261 - 5 Oct 2022
Cited by 9 | Viewed by 4106
Abstract
The Montevive celestine mineral deposit, set in the Granada Basin in a marine evaporitic uppermost Tortonian–lowermost Messinian sequence, is the largest reserve in Europe of this economically important strontium ore. Currently, the mine has a large amount of tailings resulting from the rejection [...] Read more.
The Montevive celestine mineral deposit, set in the Granada Basin in a marine evaporitic uppermost Tortonian–lowermost Messinian sequence, is the largest reserve in Europe of this economically important strontium ore. Currently, the mine has a large amount of tailings resulting from the rejection of a manual dry screening of high-grade celestine mineral. This visual and density screening was carried out in the early days of mining (1954–1973). Concentrating the celestine mineral and increasing the ore recovery rate would reduce mine operation costs and the generation of new tailings, reducing the impact on the environment. In order to define more adequate concentration methods, we have used complementary analytical techniques such as optical (OM) and scanning and transmission electron microscopy (SEM and TEM), energy-dispersive X-rays (EDXs), X-ray fluorescence (XRF), and X-ray diffraction (XRD) to fully characterize the morphology, microstructure, chemistry, and mineralogy of the celestine mineral. The low-grade mineral is made of prismatic celestine crystals that are replacing a matrix of micro sparry calcite. Other minority minerals are strontianite, dolomite, quartz, and clays (kaolinite, paragonite, and illite). There is also a certain amount of iron oxides and hydroxides (mainly magnetite) associated with clays. We showed that the concentration of low-grade celestine mineral can be achieved through a low-cost and eco-friendly method based on grinding and size separation. The coarser fractions (>5 mm) have more celestine (up to 12 percent units higher than the starting unprocessed mineral) due to the selective loss of calcite and minority minerals (quartz, clays, and iron oxides) that are mainly found in the finer fraction (<1 mm). This process can make mine exploitation more sustainable, reducing the generation of residues that negatively impact the environment. Full article
(This article belongs to the Section Mineral Exploration Methods and Applications)
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34 pages, 31457 KiB  
Article
Coastal Environment Impact on the Construction Materials of Anfushi’s Necropolis (Pharos’s Island) in Alexandria, Egypt
by Abdelrhman Fahmy, Eduardo Molina-Piernas, Javier Martínez-López, Philip Machev and Salvador Domínguez-Bella
Minerals 2022, 12(10), 1235; https://doi.org/10.3390/min12101235 - 28 Sep 2022
Cited by 2 | Viewed by 4380
Abstract
The only example and reference of Ptolemaic Alexandrian tombs, with clear integrations of Egyptian-style scenes and decorations, is considered an endangered archaeological site due to different coastal environmental risks in Alexandria and the absence of maintenance. Anfushi’s Necropolis is located near the western [...] Read more.
The only example and reference of Ptolemaic Alexandrian tombs, with clear integrations of Egyptian-style scenes and decorations, is considered an endangered archaeological site due to different coastal environmental risks in Alexandria and the absence of maintenance. Anfushi’s Necropolis is located near the western harbour (Island of Pharos) and dates back to the 2nd century BC. Sea level rises, earthquakes, flooding, storminess, variations in temperature, rainfall, and wind are the factors that have the largest effect on the destruction and decay of Anfushi’s Necropolis building materials. This paper’s main objectives were to characterize this necropolis’s building materials and assess its durability problems and risks regarding the coastal environment. Additionally, the vector mapping of its architectural and structural elements was applied for documentation and recording purposes for the necropolis. To achieve these aims, field (recording and photographs), desk (engineering drawing and mapping), and laboratory works (X-ray diffraction, X-ray fluorescence, binocular microscopy, polarizing microscopy, and scanning electron microscopy) were carried out. The results confirmed the probabilistic risk of sea level rises and its impact on the submergence of Anfushi’s Necropolis. The structural deficiencies of the tombs were caused by the effect of earthquake tremors along with anthropogenic factors. In addition, chemical and microscopic investigations showed that salt weathering (halite and gypsum) induced the decay of the building materials. Full article
(This article belongs to the Special Issue Natural and Artificial Building Stones: Insights from Petrophysical Properties and Consolidation Procedures)
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23 pages, 6309 KiB  
Article
Paleoenvironmental Conditions and Factors Controlling Organic Carbon Accumulation during the Jurassic–Early Cretaceous, Egypt: Organic and Inorganic Geochemical Approach
by Ahmed Mansour, Thomas Gentzis, Ibrahim M. Ied, Mohamed S. Ahmed and Michael Wagreich
Minerals 2022, 12(10), 1213; https://doi.org/10.3390/min12101213 - 26 Sep 2022
Cited by 7 | Viewed by 2598
Abstract
The Jurassic–Early Cretaceous was a time of variable organic carbon burial associated with fluctuations of marine primary productivity, weathering intensity, and redox conditions in the pore and bottom water at paleo-shelf areas in north Egypt. This time interval characterized the deposition of, from [...] Read more.
The Jurassic–Early Cretaceous was a time of variable organic carbon burial associated with fluctuations of marine primary productivity, weathering intensity, and redox conditions in the pore and bottom water at paleo-shelf areas in north Egypt. This time interval characterized the deposition of, from old to young, the Bahrein, Khatatba, Masajid, and Alam El Bueib Formations in the north Western Desert. Although several studies have been devoted to the excellent source rock units, such as the Khatatba and Alam El Bueib Formations, studies on paleoenvironmental changes in redox conditions, paleoproductivity, and continental weathering and their impact on organic carbon exports and their preservation for this interval are lacking. This study presents organic and inorganic geochemical data for the Jurassic–Lower Cretaceous sediments from the Almaz-1 well in the Shushan Basin, north Western Desert. A total of 32 cuttings samples were analyzed for their major and trace elements, carbonates, and total organic carbon (TOC) contents. Data allowed the reconstruction of paleoenvironmental conditions in the southern Tethys Ocean and assessment of the changes in paleo-redox, paleo-weathering, and marine primary productivity, and the role of sediment supply. Additionally, factors that governed the accumulation of organic matter in the sediment were interpreted. Results showed that the Khatatba Formation was deposited during a phase of enhanced marine primary productivity under prevalent anoxia, which triggered enhanced organic matter production and preservation. During the deposition of the Khatatba Formation, significant terrigenous sediment supply and continental weathering were followed by a limited contribution of coarse clastic sediment fluxes due to weak continental weathering and enhanced carbonate production. The Bahrein, Masajid, and Alam El Bueib Formations were deposited during low marine primary productivity and prevalent oxygenation conditions that led to poor organic matter production and preservation, respectively. A strong terrigenous sediment supply and continental weathering predominated during the deposition of the Bahrein Formation and the lower part of the Alam El Bueib Formation compared to the limited coarse clastic supply and continental weathering during the deposition of the carbonate Masajid Formation and the upper part of the Alam El Bueib Formation. Such conditions resulted in the enhanced dilution and decomposition of labile organic matter, and, thus, organic carbon-lean accumulation in these sediments. Full article
(This article belongs to the Special Issue “Palaeolimnological Archives”: Unpacking Secrets of Ancient Lakes through the Lens of Geochemistry, Mineralogy and Petrology)
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15 pages, 7043 KiB  
Review
On the Origin of New and Rare Minerals Discovered in the Othrys and Vermion Ophiolites, Greece: An Overview
by Maria Economou-Eliopoulos and Federica Zaccarini
Minerals 2022, 12(10), 1214; https://doi.org/10.3390/min12101214 - 26 Sep 2022
Viewed by 2078
Abstract
In this contribution we review the mineralogical characteristics of five new and rare minerals discovered in the Othrys and Vermion ophiolites located in Greece, with the aim to better understand their origin. Three new minerals, namely tsikourasite Mo3Ni2P(1+x) [...] Read more.
In this contribution we review the mineralogical characteristics of five new and rare minerals discovered in the Othrys and Vermion ophiolites located in Greece, with the aim to better understand their origin. Three new minerals, namely tsikourasite Mo3Ni2P(1+x) (x < 0.25), grammatikopoulosite NiVP and eliopoulosite V7S8, were found in the chromitite from the Agios Stefanos deposit, whereas arsenotučekite Ni18Sb3AsS16 was discovered in the Eretria (Tsangli) chromium mine, located in the Othrys ophiolite complex. The formation of the new phosphides tsikourasite and grammatikopoulosite and the sulfide eliopoulosite from Agios Stefanos took place after the precipitation of the host chromitite. Very likely, they formed at lower pressure in an extremely low fO2 and reducing environment during the serpentinization that affected the host ophiolite. The origin of arsenotučekite in chromitites coexisting with Fe–Ni–Cu-sulfide mineralization and magnetite at the Eretria (Tsangli) mine, is believed to be related to a circulating hydrothermal system. The most salient feature of theophrastite Ni(OH)2 and associated unnamed (Ni,Co,Mn)(OH)2 with a varying compositional range and a concentrating development, as successive thin layers, composed by fine fibrous crystals. The extremely tiny crystals of these hydroxides and the spatial association of mixed layers of Ni-silicides with theophrastite may reflect the significant role of the interaction process between adjacent layers on the observed structural features. The scarcity in nature of the new minerals reviewed in this paper is probably due to the required extreme physical-chemical conditions, which are rarely precipitated. Full article
(This article belongs to the Special Issue Recent Contributions of Female Scientists to the Advancement of Mineral Science)
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12 pages, 2454 KiB  
Article
Prediction of the Adsorption Behaviors of Radionuclides onto Bentonites Using a Machine Learning Method
by Do-Hyeon Kim and Jun-Yeop Lee
Minerals 2022, 12(10), 1207; https://doi.org/10.3390/min12101207 - 25 Sep 2022
Cited by 5 | Viewed by 2599
Abstract
This study builds a model to predict distribution coefficients (Kd) using the random forest (RF) method and a machine learning model based on the Japan Atomic Energy Agency Sorption Database (JAEA-SDB). A database of ten input variables, including the distribution coefficient, [...] Read more.
This study builds a model to predict distribution coefficients (Kd) using the random forest (RF) method and a machine learning model based on the Japan Atomic Energy Agency Sorption Database (JAEA-SDB). A database of ten input variables, including the distribution coefficient, pH, initial radionuclide concentrations, solid–liquid ratio, ionic strength, oxidation number, cation exchange capacity, surface area, electronegativity, and ionic radius, was constructed and used for the RF model calculation. The calculation parameters employed in this work included two different hyperparameters, the number of decision trees and the maximum number of variables to divide each node, together with the random seeds inside the RF model. The coefficients of determination were derived with various combinations of hyperparameters and random seeds, and were employed to assess the RF model calculation result. Based on the results of the RF model, the distribution coefficients of 22 target nuclides (Am, Ac, Co, Cm, Cd, Cs, Cu, Na, Np, Ni, Nb, U, Sr, Sn, Pb, Pa, Pu, Po, I, Tc, Th, and Zr) were predicted successfully. Among the various input variables, pH was found to make the highest contribution to determining the distribution coefficient. The novelty of this study lies in the first application of the machine learning method for predicting the Kd value of bentonites, using JAEA-SDB. This study has established a model for reliably predicting the distribution coefficient for various radionuclides that is intended for use in evaluating the Kd value in arbitrary aqueous conditions. Full article
(This article belongs to the Special Issue The Role of Clays in Geological Disposal of Radioactive Waste)
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17 pages, 3760 KiB  
Article
Geochemical and Sr-Isotopic Study of Clinopyroxenes from Somma-Vesuvius Lavas: Inferences for Magmatic Processes and Eruptive Behavior
by Valeria Di Renzo, Carlo Pelullo, Ilenia Arienzo, Lucia Civetta, Paola Petrosino and Massimo D’Antonio
Minerals 2022, 12(9), 1114; https://doi.org/10.3390/min12091114 - 31 Aug 2022
Cited by 4 | Viewed by 2890
Abstract
Somma-Vesuvius is one of the most dangerous active Italian volcanoes, due to the explosive character of its activity and because it is surrounded by an intensely urbanized area. For mitigating the volcanic risks, it is important to define how the Somma-Vesuvius magmatic system [...] Read more.
Somma-Vesuvius is one of the most dangerous active Italian volcanoes, due to the explosive character of its activity and because it is surrounded by an intensely urbanized area. For mitigating the volcanic risks, it is important to define how the Somma-Vesuvius magmatic system worked during the past activity and what processes took place. A continuous coring borehole drilled at Camaldoli della Torre, along the southern slopes of Somma-Vesuvius, allowed reconstructing its volcanic and magmatic history in a previous study. In this work, the wide range of chemical (Mg# = 92–69) and isotopic (87Sr/86Sr = 0.70781–0.70681) compositions, collected on single clinopyroxene crystals separated from selected lava flow units of the Camaldoli della Torre sequence, have been integrated with the already available bulk geochemical and Sr-isotopic data. The detected chemical and isotopic signatures and their variation through time allow us to better constrain the behavior of the volcano magmatic feeding system, highlighting that mixing and/or assimilation processes occurred before a significant change in the eruptive dynamics at Somma-Vesuvius during a period of polycyclic caldera formation, starting with the Pomici di Base Plinian eruption (ca. 22 ka). Full article
(This article belongs to the Special Issue Minerals of Alkaline Igneous Rocks: Chemical and Isotopic Features as Tracers of Magmatic Processes)
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22 pages, 10057 KiB  
Article
Geochemical Indication of Functional Zones at the Archaeological Sites of Eastern Europe
by Marianna Kulkova
Minerals 2022, 12(9), 1075; https://doi.org/10.3390/min12091075 - 25 Aug 2022
Cited by 5 | Viewed by 2212
Abstract
The article considers a new approach for determining the functional zones of the prehistoric archaeological sites in Eastern Europe by the method of geochemical indication: the use of mathematical statistics for processing the geochemical data of cultural deposits at archaeological sites, and the [...] Read more.
The article considers a new approach for determining the functional zones of the prehistoric archaeological sites in Eastern Europe by the method of geochemical indication: the use of mathematical statistics for processing the geochemical data of cultural deposits at archaeological sites, and the identification of groups of interrelated chemical elements and compounds that reflects the processes of natural sedimentation and anthropogenic activity. It makes it possible to separate the lithological and anthropogenic components. This approach is important for the identification of geochemical element groups associated with different functional zones. The reconstructions were conducted at the Neolithic, Early Metal Age, and the Bronze-Early Iron Age sites in Eastern Europe. Abnormal concentrations of the association (P2O5antr, CaOantr and Srantr) in sediments are attributed to zones of accumulation of bone remains. Anomalous concentrations of a group of elements (K2Oantr, Rbantr) in deposits are associated with wood ash and fireplaces, ash residues from ritual activities, and fires. The group of elements (Ba, MnO, Corg) reflects the accumulation of humus and organic remains, and can characterize areas with food residues, skins, and rotten wood. With the help of the distribution of the main lithological elements (SiO2, Al2O3) in sediments, it is possible to reconstruct the paleorelief at the sites. Full article
(This article belongs to the Special Issue Environment and Geochemistry of Sediments)
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14 pages, 1481 KiB  
Article
Coal Feed-Dependent Variation in Fly Ash Chemistry in a Single Pulverized-Combustion Unit
by James C. Hower, John G. Groppo, Shelley D. Hopps, Tonya D. Morgan, Heileen Hsu-Kim and Ross K. Taggart
Minerals 2022, 12(9), 1071; https://doi.org/10.3390/min12091071 - 24 Aug 2022
Cited by 4 | Viewed by 2102
Abstract
Four suites of fly ash, all generated at the same power plant, were selected for the study of the distribution of rare earth elements (REE). The fly ashes represented two runs of single-seam/single-mine coals and two runs of run-of-mine coals representing several coal [...] Read more.
Four suites of fly ash, all generated at the same power plant, were selected for the study of the distribution of rare earth elements (REE). The fly ashes represented two runs of single-seam/single-mine coals and two runs of run-of-mine coals representing several coal seams from several mines. Plots of the upper continental crust-normalized REE, other parameters derived from the normalization, and the principal components analysis of the derived REE parameters (including the sum of the lanthanides plus yttrium and the ratio of the light to heavy REE) all demonstrated that the relatively rare earth-rich Fire Clay coal-derived fly ashes have a different REE distribution, with a greater concentration of REE with a relative dominance of the heavy REE, than the other fly ashes. Particularly with the Fire Clay coal-derived fly ashes, there is a systematic partitioning of the overall amount and distribution of the REE in the passage from the mechanical fly ash collection through to the last row of the electrostatic precipitator hoppers. Full article
(This article belongs to the Special Issue Characterization of Rare Earth Elements and Critical Minerals in Geologic and Engineered Materials)
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22 pages, 7810 KiB  
Article
Deep Learning Optimized Dictionary Learning and Its Application in Eliminating Strong Magnetotelluric Noise
by Guang Li, Xianjie Gu, Zhengyong Ren, Qihong Wu, Xiaoqiong Liu, Liang Zhang, Donghan Xiao and Cong Zhou
Minerals 2022, 12(8), 1012; https://doi.org/10.3390/min12081012 - 12 Aug 2022
Cited by 13 | Viewed by 3895
Abstract
The noise suppression method based on dictionary learning has shown great potential in magnetotelluric (MT) data processing. However, the constraints used in the existing algorithm’s method need to set manually, which significantly limits its application. To solve this problem, we propose a deep [...] Read more.
The noise suppression method based on dictionary learning has shown great potential in magnetotelluric (MT) data processing. However, the constraints used in the existing algorithm’s method need to set manually, which significantly limits its application. To solve this problem, we propose a deep learning optimized dictionary learning denoising method. We use a deep convolutional network to learn the characteristic parameters of high-quality MT data independently and then use them as the constraints for dictionary learning so as to achieve fully adaptive sparse decomposition. The method uses unified parameters for all data and completely eliminates subjective bias, which makes it possible to batch-process MT data using sparse decomposition. The processing results of simulated and field data examples show that the new method has good adaptability and can achieve recognition with high accuracy. After processing with our method, the apparent resistivity and phase curves became smoother and more continuous, and the results were validated by the remote reference method. Our method can be an effective alternative method when no remote reference station is set up or the remote reference processing is not effective. Full article
(This article belongs to the Special Issue Electromagnetic Exploration: Theory, Methods and Applications)
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18 pages, 2080 KiB  
Review
Data Quality in Geochemical Elemental and Isotopic Analysis
by V. Balaram and M. Satyanarayanan
Minerals 2022, 12(8), 999; https://doi.org/10.3390/min12080999 - 8 Aug 2022
Cited by 14 | Viewed by 4316
Abstract
Appropriate sampling, sample preparation, choosing the right analytical instrument, analytical methodology, and adopting proper data generation protocols are essential for generating data of the required quality for both basic and applied geochemical research studies. During the last decade, instrumental advancements, in particular further [...] Read more.
Appropriate sampling, sample preparation, choosing the right analytical instrument, analytical methodology, and adopting proper data generation protocols are essential for generating data of the required quality for both basic and applied geochemical research studies. During the last decade, instrumental advancements, in particular further developments in ICP-MS, such as the use of tandem ICP-MS, high-resolution mass spectrometry to resolve several interferences, and the use of the second path with a collision/reaction cell in multi-collector ICP-MS (MC-ICP-MS) to effectively resolve interferences, have brought in remarkable improvements in accuracy and precision in both elemental and isotopic analyses. The availability of a number of well-characterized geological certified reference samples having both elemental and isotopic data-enabled matrix-matching calibrations and contributed to the quality and traceability of the geochemical data in several cases. There have been some developments in the sample dissolution methods also. A range of quality issues related to sampling, packaging and transport, powdering, dissolution, the application of suitable instrumental analytical techniques, calibration methods, accuracy, and precision are addressed which are helpful in geochemical studies. Full article
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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25 pages, 5971 KiB  
Article
Origin of Historical Ba-Rich Slags Related to Pb-Ag Production from Jihlava Ore District (Czech Republic)
by Jaroslav Kapusta, Zdeněk Dolníček, Ondra Sracek and Karel Malý
Minerals 2022, 12(8), 985; https://doi.org/10.3390/min12080985 - 2 Aug 2022
Cited by 4 | Viewed by 2877
Abstract
The aim of this study was to characterize historical slags which originated during silver production from the Jihlava ore district, Czech Republic. The area was among the head producers of silver within the Lands of the Czech Crown in 13th–14th centuries. The mined [...] Read more.
The aim of this study was to characterize historical slags which originated during silver production from the Jihlava ore district, Czech Republic. The area was among the head producers of silver within the Lands of the Czech Crown in 13th–14th centuries. The mined ores had complex composition, being formed mostly by pyrite, sphalerite, galena, chalcopyrite, and accessory silver-rich minerals such as silver-bearing tetrahedrite (freibergite) or pyrargyrite, with gangue represented by quartz and Mn-rich carbonates or baryte. Large volumes of slags with contrasting composition were generated during the Pb-Ag production. Altogether, two main types of slags were identified in the district. The first type is characterized by high BaO contents (up to 34.5 wt.%) and dominancy of glass, minor quartz, and accessory amounts of Ba-rich feldspar (up to 93 mol.% of Cls), metal-rich inclusions, Ba-Pb sulphates and only rare pyroxene, wollastonite and melilite. The composition of the second group belongs to fayalitic slags containing glass, Fe-rich olivine, accessory pyroxene, feldspar, quartz, and inclusions of various metallic phases. Fluxes were derived from gangue (quartz, carbonates, baryte) or local host rocks for both types of slag. The calculated viscosity indexes reflect (with minor exceptions) medium-to-high effectivity of metal separation. Smelting temperatures were estimated from a series of ternary plots; however, more reliable estimates for both types of slags were obtained only from experimental determination of melting temperature and calculations using bulk/glass compositions (~1100–1200 °C). Full article
(This article belongs to the Special Issue Applications of Geochemistry in Archaeology)
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23 pages, 2489 KiB  
Review
Application of Raman Spectroscopy for Studying Shocked Zircon from Terrestrial and Lunar Impactites: A Systematic Review
by Dmitry A. Zamyatin
Minerals 2022, 12(8), 969; https://doi.org/10.3390/min12080969 - 29 Jul 2022
Cited by 6 | Viewed by 3398
Abstract
A highly resistant mineral, zircon is capable of preserving information about impact processes. The present review paper is aimed at determining the extent to which Raman spectroscopy can be applied to studying shocked zircons from impactites to identify issues and gaps in the [...] Read more.
A highly resistant mineral, zircon is capable of preserving information about impact processes. The present review paper is aimed at determining the extent to which Raman spectroscopy can be applied to studying shocked zircons from impactites to identify issues and gaps in the usage of Raman spectroscopy, both in order to highlight recent achievements, and to identify the most effective applications. Method: Following PRISMA guidelines, the review is based on peer-reviewed papers indexed in Google Scholar, Scopus and Web of Science databases up to 5 April 2022. Inclusion criteria: application of Raman spectroscopy to the study of shocked zircon from terrestrial and lunar impactites. Results: A total of 25 research papers were selected. Of these, 18 publications studied terrestrial impact craters, while 7 publications focused on lunar breccia samples. Nineteen of the studies were focused on the acquisition of new data on geological structures, while six examined zircon microstructures, their textural and spectroscopic features. Conclusions: The application of Raman spectroscopy to impactite zircons is linked with its application to zircon grains of various terrestrial rocks and the progress of the electron backscatter diffraction (EBSD) technique in the early 2000s. Raman spectroscopy was concluded to be most effective when applied to examining the degree of damage, as well as identifying phases and misorientation in zircon. Full article
(This article belongs to the Special Issue Geochronology, Crystallography and Phase Transition in Shocked Minerals)
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20 pages, 5195 KiB  
Article
Recovery of Rare Earth Elements from Mining Tailings: A Case Study for Generating Wealth from Waste
by Luver Echeverry-Vargas and Luz Marina Ocampo-Carmona
Minerals 2022, 12(8), 948; https://doi.org/10.3390/min12080948 - 28 Jul 2022
Cited by 33 | Viewed by 8385
Abstract
The growing demand for rare earth elements (REE) driven by their applications in modern technologies has caused the need to search for alternative sources of these elements as their extraction from traditional deposits is limited. A potential source of light rare earth elements [...] Read more.
The growing demand for rare earth elements (REE) driven by their applications in modern technologies has caused the need to search for alternative sources of these elements as their extraction from traditional deposits is limited. A potential source of light rare earth elements (LREE) may be the monazite present in the mining waste generated in the Bagre-Nechí mining district in Colombia due to the processing of sands containing alluvial gold. Consequently, in this research, a systematic evaluation has been carried out for the extraction of Ce, La, and Nd from a leach liquor obtained from monazite present in alluvial gold mining tailings. The leaching process carried out with HCl indicated the recovery of approximately 90% of La and Nd and ∼60% of Ce; the solvent extraction tests of these elements showed that increasing the contact time and pH of the leaching liquor positively affects the extraction of lanthanum, cerium, and neodymium, achieving extractions close to 100% with D2EHPA and to a lesser extent with Cyanex572. McCabe–Thiele diagrams for extraction with D2EHPA indicated the requirement of three stages for the extraction of Ce, La and Nd. Full article
(This article belongs to the Special Issue Leaching and Solution Treatments of Rare Earth Elements from Various Sources, Volume II)
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13 pages, 3764 KiB  
Article
The Heavy Mineral Map of Australia: Vision and Pilot Project
by Patrice de Caritat, Brent I. A. McInnes, Alexander T. Walker, Evgeniy Bastrakov, Stephen M. Rowins and Alexander M. Prent
Minerals 2022, 12(8), 961; https://doi.org/10.3390/min12080961 - 28 Jul 2022
Cited by 5 | Viewed by 5652
Abstract
We describe a vision for a national-scale heavy mineral (HM) map generated through automated mineralogical identification and quantification of HMs contained in floodplain sediments from large catchments covering most of Australia. The composition of the sediments reflects the dominant rock types in each [...] Read more.
We describe a vision for a national-scale heavy mineral (HM) map generated through automated mineralogical identification and quantification of HMs contained in floodplain sediments from large catchments covering most of Australia. The composition of the sediments reflects the dominant rock types in each catchment, with the generally resistant HMs largely preserving the mineralogical fingerprint of their host protoliths through the weathering-transport-deposition cycle. Heavy mineral presence/absence, absolute and relative abundance, and co-occurrence are metrics useful to map, discover and interpret catchment lithotype(s), geodynamic setting, magmatism, metamorphic grade, alteration and/or mineralization. Underpinning this vision is a pilot project, focusing on a subset from the national sediment sample archive, which is used to demonstrate the feasibility of the larger, national-scale project. We preview a bespoke, cloud-based mineral network analysis (MNA) tool to visualize, explore and discover relationships between HMs as well as between them and geological settings or mineral deposits. We envisage that the Heavy Mineral Map of Australia and MNA tool will contribute significantly to mineral prospectivity analysis and modeling, particularly for technology critical elements and their host minerals, which are central to the global economy transitioning to a more sustainable, lower carbon energy model. Full article
(This article belongs to the Special Issue Feature Papers in Mineral Exploration Methods and Applications 2022)
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15 pages, 5399 KiB  
Article
An Assessment of the Role of Combined Bulk Micro- and Nano-Bubbles in Quartz Flotation
by Shaoqi Zhou, Yang Li, Sabereh Nazari, Xiangning Bu, Ahmad Hassanzadeh, Chao Ni, Yaqun He and Guangyuan Xie
Minerals 2022, 12(8), 944; https://doi.org/10.3390/min12080944 - 27 Jul 2022
Cited by 22 | Viewed by 3273
Abstract
Bulk micro-nano-bubbles (BMNBs) have been proven to be effective at improving the flotation recovery and kinetics of fine-grained minerals. However, there is currently no research reported on the correlation between the properties of BMNBs and flotation performance. For this purpose, aqueous dispersions with [...] Read more.
Bulk micro-nano-bubbles (BMNBs) have been proven to be effective at improving the flotation recovery and kinetics of fine-grained minerals. However, there is currently no research reported on the correlation between the properties of BMNBs and flotation performance. For this purpose, aqueous dispersions with diverse properties were created by altering preparation time (0, 1, 2, 3, 5, and 7 min), aeration rate (0, 0.5, 1, 1.5, and 2 L/min) and aging time (0, 0.5, 1, and >3 min). Micro- and nano-bubbles were characterized using focused beam reflection measurements (FBRM) and nanoparticle tracking analysis (NTA), respectively. The micro-flotation of quartz particles was performed using an XFG-cell in the presence and absence of BMNBs with Cetyltrimethylammonium bromide (CTAB) as a collector. The characterization of bubble sizes showed that the bulk micro-bubble (BMB) and bulk nanobubble (BNB) diameters ranged from 1–10 μm and 50–400 nm, respectively. It was found that the preparation parameters and aging time considerably affected the number of generated bubbles. When BNBs and BMBs coexisted, the recovery of fine quartz particles significantly improved (about 7%), while in the presence of only BNBs the promotion of flotation recovery was not significant (2%). This was mainly related to the aggregate via bridging, which was an advantage for quartz flotation. In comparison, no aggregates were detected when only nano-bubbles were present in the bulk solution. Full article
(This article belongs to the Special Issue Hydrodynamics and Gas Dispersion in Flotation)
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21 pages, 6107 KiB  
Article
Charge Distribution and Bond Valence Sum Analysis of Sulfosalts—The ECoN21 Computer Program
by Gheorghe Ilinca
Minerals 2022, 12(8), 924; https://doi.org/10.3390/min12080924 - 22 Jul 2022
Cited by 11 | Viewed by 2510
Abstract
The charge distribution (CD) and the bond valence sum (BVS) methods are used to calculate the charges assignable to atomic positions in crystal structures, based on the distribution of bond lengths. Discrepancies between calculated and formal charges may point to errors in the [...] Read more.
The charge distribution (CD) and the bond valence sum (BVS) methods are used to calculate the charges assignable to atomic positions in crystal structures, based on the distribution of bond lengths. Discrepancies between calculated and formal charges may point to errors in the determination of atomic coordinates, in the initial allocation of oxidation numbers, occupancies, or site populations. Unlike the BVS method, which has been frequently used for the validation and interpretation of sulfosalt crystal structures, the CD method has been scarcely and limitedly employed for this group of minerals. In this paper, the applicability of the CD method to sulfosalts is practically tested for the first time. The calculation is made using ECoN21—a novel software tool designed for CD, BVS, and general coordination geometry analysis of crystal structures. The program addresses normal valence compounds with distorted homoligand or heteroligand polyhedra in both cation- and anion-centered descriptions. The program is also able to calculate a comprehensive set of parameters describing the internal and external distortion of coordination polyhedra. The paper presents the background of the CD, BVS, and coordination geometry calculations, as well as several case studies focusing on various applications of these methods to sulfosalts. Full article
(This article belongs to the Section Crystallography and Physical Chemistry of Minerals & Nanominerals)
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19 pages, 11716 KiB  
Article
Ion and Particle Size Effects on the Surface Reactivity of Anatase Nanoparticle–Aqueous Electrolyte Interfaces: Experimental, Density Functional Theory, and Surface Complexation Modeling Studies
by Moira K. Ridley, Michael L. Machesky and James D. Kubicki
Minerals 2022, 12(7), 907; https://doi.org/10.3390/min12070907 - 20 Jul 2022
Cited by 1 | Viewed by 2268
Abstract
At the nanoscale, particle size affects the surface reactivity of anatase–water interfaces. Here, we investigate the effect of electrolyte media and particle size on the primary charging behavior of anatase nanoparticles. Macroscopic experiments, potentiometric titrations, were used to quantitatively evaluate surface charge of [...] Read more.
At the nanoscale, particle size affects the surface reactivity of anatase–water interfaces. Here, we investigate the effect of electrolyte media and particle size on the primary charging behavior of anatase nanoparticles. Macroscopic experiments, potentiometric titrations, were used to quantitatively evaluate surface charge of a suite of monodisperse nanometer sized (4, 20, and 40 nm) anatase samples in five aqueous electrolyte solutions. The electrolyte media included alkaline chloride solutions (LiCl, NaCl, KCl, and RCl) and Na-Trifluoromethanesulfonate (NaTr). Titrations were completed at 25 °C, as a function of pH (3–11) and ionic strength (from 0.005 to 0.3 m). At the molecular scale, density functional theory (DFT) simulations were used to evaluate the most stable cation surface species on the predominant (101) anatase surface. In all electrolyte media, primary charging increased with increasing particle size. At high ionic strength, the development of negative surface charge followed reverse lyotropic behavior: charge density increased in the order RbCl < KCl < NaCl < LiCl. Positive surface charge was greater in NaCl than in NaTr media. From the DFT simulations, all cations formed inner-sphere surface species, but the most stable coordination geometry varied. The specific inner-sphere adsorption geometries are dependent on the ionic radius. The experimental data were described using surface complexation modeling (SCM), constrained by the DFT results. The SCM used the charge distribution (CD) and multisite (MUSIC) models, with a two-layer (inner- and outer-Helmholtz planes) description of the electric double layer. Subtle charging differences between the smallest and larger anatase particles were the same in each electrolyte media. These results further our understanding of solid–aqueous solution interface reactivity of nanoparticles. Full article
(This article belongs to the Special Issue Mineral-Water Interfaces and Interfacial Reactions with (Radioactive) Contaminants)
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27 pages, 4870 KiB  
Article
Quaternary Glauconitization on Gulf of Guinea, Glauconite Factory: Overview of and New Data on Tropical Atlantic Continental Shelves and Deep Slopes
by Pierre Giresse
Minerals 2022, 12(7), 908; https://doi.org/10.3390/min12070908 - 20 Jul 2022
Cited by 13 | Viewed by 3661
Abstract
For a long time, particular attention was paid to glauconitization in the surficial sediments lying on the outer continental shelves of present oceans. Subsequently, the processes observed and analyzed may have served as models for studies of glauconite in Cenozoic or even Mesozoic [...] Read more.
For a long time, particular attention was paid to glauconitization in the surficial sediments lying on the outer continental shelves of present oceans. Subsequently, the processes observed and analyzed may have served as models for studies of glauconite in Cenozoic or even Mesozoic shelf deposits. Access to the sedimentary domains of deep oceans, particularly those of contouritic accumulation fields, has made it possible to discover unexpected processes of glauconitization. Thus, the long-term prevalence of control using fairly high-temperature water has become obsolete, and the prerequisite influence of continental flows has come to be considered on a new scale. Frequently, sediments from contouritic accumulation provide a condensed and undisturbed sedimentary record without periods of sediment erosion. Glauconitic grains could possibly integrate the signatures of bottom-water masses over prolonged periods of time, which, while preventing their use in high-resolution studies, would provide an effective means of yielding reliable average estimates on past εNd signatures of bottom-water masses. In this regard, glauconitic grains are probably better-suited to paleoceanographic reconstructions than foraminifera and leached Fe-oxyhydroxide fractions, which appear to be influenced by sediment redistribution and the presence of terrestrial continental Fe-oxides, respectively. Direct methodological access to the compositions of the semi-confined microenvironments of neoformation has largely renewed the information, chemical or crystallographic, that was previously, and for a long time, restricted to macromeasurements. The various granular supports (mudclasts, fecal pellets, and foraminifera infillings) include inherited 1:1 clays (or Te-Oc; i.e., clay minerals consisting of one tetrahedral sheet and one octahedral sheet, such as kaolinite) that are gradually replaced by 2:1 clays (Te-Oc-Te) dominated first by smectite, and then by glauconite. In small pores, the water’s activity is diminished; as a consequence, the precipitation of a great number of mineral species is thereby made easier, and their stability domains are changed. A specific methodological approach allows the study of the mineralogy and chemistry of the fine-scale mineral phases and to avoid the global aspect of the analytical methods previously used in the initial studies. Wide-field micrographs taken at a mean direct magnification of 100.000 show the intimate and characteristic organization of the main phases that occur in a single grain. One or several “fine” (about 10 nanometers in scale) microchemical analyses can be recorded, and directly coupled with each interesting and well-identified structure image observed in HRTEM. Full article
(This article belongs to the Special Issue Formation and Evolution of Glauconite. New Scale Approach)
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20 pages, 5942 KiB  
Article
Evolution of the Reaction and Alteration of Granite with Ordinary Portland Cement Leachates: Sequential Flow Experiments and Reactive Transport Modelling
by Keith Bateman, Shota Murayama, Yuji Hanamachi, James Wilson, Takamasa Seta, Yuki Amano, Mitsuru Kubota, Yuji Ohuchi and Yukio Tachi
Minerals 2022, 12(7), 883; https://doi.org/10.3390/min12070883 - 13 Jul 2022
Cited by 4 | Viewed by 2063
Abstract
The construction of a repository for the geological disposal of radioactive waste will include the use of cement-based materials. Following closure, groundwater will saturate the repository, and the extensive use of cement will result in the development of a highly alkaline porewater, pH [...] Read more.
The construction of a repository for the geological disposal of radioactive waste will include the use of cement-based materials. Following closure, groundwater will saturate the repository, and the extensive use of cement will result in the development of a highly alkaline porewater, pH > 12.5; this fluid will migrate into and react with the host rock. The chemistry of the fluid will evolve over time, initially with high Na and K concentrations, evolving to a Ca-rich fluid, and finally returning to the natural background groundwater composition. This evolving chemistry will affect the long-term performance of the repository, altering the physical and chemical properties, including radionuclide behaviour. Understanding these changes forms the basis for predicting the long-term evolution of the repository. This study focused on the determination of the nature and extent of the chemical reaction, as well as the formation and persistence of secondary mineral phases within a granite, comparing data from sequential flow experiments with the results of reactive transport modelling. The reaction of the granite with the cement leachates resulted in small changes in pH and the precipitation of calcium aluminium silicate hydrate (C-(A-)S-H) phases of varying compositions, of greatest abundance with the Ca-rich fluid. As the system evolved, secondary C-(A-)S-H phases redissolved, partly replaced by zeolites. This general sequence was successfully simulated using reactive transport modelling. Full article
(This article belongs to the Special Issue Near-Field Processes and Evolution toward to Assessment of Radionuclide Migration in Geological Disposal of High-Level Radioactive Waste)
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23 pages, 11379 KiB  
Article
Assessment of the Effect of Organic Matter on Rare Earth Elements and Yttrium Using the Zhijin Early Cambrian Phosphorite as an Example
by Shengwei Wu, Haiying Yang, Haifeng Fan, Yong Xia, Qingtian Meng, Shan He and Xingxiang Gong
Minerals 2022, 12(7), 876; https://doi.org/10.3390/min12070876 - 12 Jul 2022
Cited by 11 | Viewed by 2555
Abstract
The geochemistry of rare earth elements and yttrium (REY) in phosphorite has been widely studied. However, the effect of organic matter on REY enrichment has not been well determined. We utilized paired inorganic (δ13Ccarb) and organic (δ13C [...] Read more.
The geochemistry of rare earth elements and yttrium (REY) in phosphorite has been widely studied. However, the effect of organic matter on REY enrichment has not been well determined. We utilized paired inorganic (δ13Ccarb) and organic (δ13Ccarb) carbon isotopes, total organic carbon (TOC), and REY content (∑REY) of the Zhijin Motianchong (MTC) phosphorite and compared them with those of Meishucun (MSC) phosphorite to reveal the effect of organic matter on REY. The δ13Ccarb of the MTC area (≈0‰) is heavier than that of the MSC area (−5.23‰ to −1.13‰), whereas δ13Corg is lighter (−33.85‰ to −26.34‰) in MTC than in MSC (−32.95‰ to −25.50‰). Decoupled δ13Ccarb and δ13Corg in MTC indicate the contribution of chemoautotrophic organisms or methanotrophic bacteria. Compared to the MSC phosphorite, the MTC phosphorite has higher ∑REY and TOC, and these parameters have a positive relationship. MTC phosphorite has REY patterns resembling those of contemporary organic matter. Furthermore, dolomite cement has a higher ∑REY than dolomite in the phosphorus-bearing dolostone. Additionally, pyrites are located on the surface of fluorapatite in the Zhijin phosphorites. It is reasonable to suggest that the REY was released into the pore water owing to the anaerobic oxidation of organic matter at the interface between seawater and sediment, resulting in the REY enrichment of Zhijin phosphorites. Full article
(This article belongs to the Section Mineral Geochemistry and Geochronology)
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14 pages, 3730 KiB  
Article
Fe(III)–Chitosan Microbeads for Adsorptive Removal of Cr(VI) and Phosphate Ions
by Swati A. Tandekar, Manoj A. Pande, Anita Shekhawat, Elvis Fosso-Kankeu, Sadanand Pandey and Ravin M. Jugade
Minerals 2022, 12(7), 874; https://doi.org/10.3390/min12070874 - 11 Jul 2022
Cited by 19 | Viewed by 2521
Abstract
Fe(III)–chitosan microbeads (Fe–CTB) were prepared using a chemical coprecipitation method. SEM–EDX, FTIR, XRD, TGA, BET, and pH pzc were performed for the characterization of the adsorbent. Various parameters were optimized as pH, adsorption time, adsorbent dose, initial Cr(VI), and PO43− ion [...] Read more.
Fe(III)–chitosan microbeads (Fe–CTB) were prepared using a chemical coprecipitation method. SEM–EDX, FTIR, XRD, TGA, BET, and pH pzc were performed for the characterization of the adsorbent. Various parameters were optimized as pH, adsorption time, adsorbent dose, initial Cr(VI), and PO43− ion concentration and the effect of assorted ions for adsorption studies. Fe–CTB microbeads revealed more than 80% detoxification for a 100 mg L−1 initial concentration at pH 3 with 60 min stirring of Cr(VI) and PO43− ion having adsorption capacities of 34.15 and 32.27 mg g−1, respectively. The adsorption process for Cr(VI) and PO43− ion followed the monolayer adsorption as they favored the Langmuir isotherm model. Kinetic and thermodynamic studies’ emphasis on the adsorption process was spontaneous and exothermic with pseudo-second-order kinetics for both adsorbates. The microbeads were found to be reusable in multiple cycles. Full article
(This article belongs to the Special Issue Innovations in Nanotechnology for Wastewater and Acid Mine Drainage Treatment, Volume II)
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15 pages, 2214 KiB  
Article
Adsorption of Cs(I) and Sr(II) on Bentonites with Different Compositions at Different pH
by Yulia Izosimova, Irina Gurova, Inna Tolpeshta, Michail Karpukhin, Sergey Zakusin, Olga Zakusina, Alexey Samburskiy and Victoria Krupskaya
Minerals 2022, 12(7), 862; https://doi.org/10.3390/min12070862 - 7 Jul 2022
Cited by 12 | Viewed by 3245
Abstract
This paper deals with adsorption regularities and mechanisms of nonradioactive Cs(I) and Sr(II) analogs on bentonites of different chemical and mineral composition from solutions of Cs and Sr nitrates with pH 3, 7, and 10 units at constant ionic strength. The bentonites were [...] Read more.
This paper deals with adsorption regularities and mechanisms of nonradioactive Cs(I) and Sr(II) analogs on bentonites of different chemical and mineral composition from solutions of Cs and Sr nitrates with pH 3, 7, and 10 units at constant ionic strength. The bentonites were taken from the deposits Taganskoe (T), Dash-Salakhlinskoe (DS), Zyryanskoe (Z), and 10th Khutor (10H). The pH of bentonite aqueous suspensions, T and DS, exceeded 9 units. A less alkaline reaction was observed in bentonite suspensions Z and T with pH 8.94 and 7.70, respectively. Bentonites T and DS contained significant amounts of nonsilicate iron compounds, 1.0 and 0.5%, respectively. The recovery rate of the studied clays from aqueous solutions of Cs(I) and Sr(II) ions in concentrations from 0.25 to 5 mmol/L varied from 50% to 90% and decreased in the following order: “Ta-ganskoe” > “Dash-Salakhlinskoe” > “Zyryanskoe” > “10th Khutor” in the studied pH range. The main mechanism of Cs(I) and Sr(II) sorption in the studied pH range was cation fixation in the form of outer-sphere complexes on planar surfaces resulting from ion exchange. Increasing pH (pH > 6) enhanced pH-dependent positions, which allowed Cs(I) and especially Sr(II) ions to fix on them more firmly as inner-sphere complexes. At pH 9–10, Sr(II) could precipitate in the form of carbonates. The sorption of Cs(I) + and Sr(II) was accompanied by competitive interactions with proton at pH < 6 and Na+, Ca2+, Mg2+, and K+ cations at higher pH values. This competition was more apparent at concentrations of Cs(I)and Sr(II) in initial solutions < 0.5 mmol/L. The ability of bentonite T to sorb Cs(I) and Sr(II) in large amounts compared to the other bentonites was determined by high CEC values and charge of smectite T. Full article
(This article belongs to the Special Issue Environmental Applications of Chemically Modified Clay Minerals, Volume II)
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19 pages, 4187 KiB  
Review
Evolution of Sulfidic Legacy Mine Tailings: A Review of the Wheal Maid Site, UK
by Verity Fitch, Anita Parbhakar-Fox, Richard Crane and Laura Newsome
Minerals 2022, 12(7), 848; https://doi.org/10.3390/min12070848 - 1 Jul 2022
Cited by 2 | Viewed by 4097
Abstract
Historic tailings dams and their associated mine waste can pose a significant risk to human and environmental health. The Wheal Maid mine site, Cornwall, UK, serves as an example of the temporal evolution of a tailings storage facility after mining has ceased and [...] Read more.
Historic tailings dams and their associated mine waste can pose a significant risk to human and environmental health. The Wheal Maid mine site, Cornwall, UK, serves as an example of the temporal evolution of a tailings storage facility after mining has ceased and the acid-generating waste subjected to surficial processes. This paper discusses its designation as a contaminated land site and reviews our current understanding of the geochemistry, mineralogy, and microbiology of the Wheal Maid tailings, from both peer-reviewed journal articles and unpublished literature. We also present new data on waste characterisation and detailed mineral chemistry and data from laboratory oxidation experiments. Particularly of interest at Wheal Maid is the presence of pyrite-bearing “Grey Tailings”, which, under typical environmental conditions at the Earth’s surface, would be expected to have undergone oxidation and subsequently formed acidic and metalliferous mine drainage (AMD). The results identified a number of mechanisms that could explain the lack of pyrite oxidation in the Grey Tailings, including a lack of nutrients inhibiting microbial Fe(II) oxidation, passivation of pyrite mineral surfaces with tailings processing chemicals, and an abundance of euhedral pyrite grains. Such research areas need further scrutiny in order to inform the design of future tailings facilities and associated AMD management protocols. Full article
(This article belongs to the Special Issue Management of Abandoned Mine)
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36 pages, 6206 KiB  
Article
Electron Probe Microanalysis and Microscopy of Polishing-Exposed Solid-Phase Mineral Inclusions in Fuxian Kimberlite Diamonds
by Donggao Zhao
Minerals 2022, 12(7), 844; https://doi.org/10.3390/min12070844 - 30 Jun 2022
Cited by 1 | Viewed by 3738
Abstract
Solid-phase mineral inclusions in diamond (1–3 mm in diameter) from the No. 50 kimberlite diatreme of Liaoning Province, China, were exposed by polishing. A variety of silicate, carbonate and sulfide inclusions were recovered in the diamond. The common solid-phase inclusions are olivine, chromite, [...] Read more.
Solid-phase mineral inclusions in diamond (1–3 mm in diameter) from the No. 50 kimberlite diatreme of Liaoning Province, China, were exposed by polishing. A variety of silicate, carbonate and sulfide inclusions were recovered in the diamond. The common solid-phase inclusions are olivine, chromite, garnet and orthopyroxene; the rare phases include Ca carbonate, magnesite, dolomite, norsethite, pyrrhotite, pentlandite, troilite, a member of the linnaeite group, an unknown hydrous magnesium silicate and an Fe-rich phase. Abundance and composition of the solid-phase inclusions in diamond indicate that they belong to the peridotitic suite and are mainly harzburgitic. No eclogitic mineral inclusions were found in the diamond. The slightly lower Mg # of the olivine inclusions (peak at 93) than that of harzburgitic olivine inclusions worldwide (Mg # peak at 94), the higher Ni content (0.25–0.45 wt. %) of the olivine inclusions than those of olivine inclusions worldwide (0.30–0.40 wt. %), the higher Ti contents (up to 0.79 wt. %) in some chromite inclusions in diamond than those in chromite inclusions worldwide, the existence of carbonate inclusions in diamond, and the possible presence of hydrous silicate phases in diamond all indicate a metasomatic enrichment event in the source region of diamond beneath the North China craton, suggesting that the diamond probably formed by solid-state growth under metasomatic conditions with the presence of a fluid. Solid-state growth of diamond is also supported by abundant graphite inclusions in the diamond. Sulfide inclusions in diamond often coexist with chromite and olivine or are rich in Ni content, indicating that the sulfide inclusions belong to the peridotitic suite. From the chemical compositions, most sulfide inclusions in diamond from the No. 50 kimberlite were probably trapped as monosulfide crystals, although some may have been entrapped as melts. Full article
(This article belongs to the Special Issue Electron Microbeam and X-ray Techniques: Advances and Applications)
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13 pages, 33640 KiB  
Article
A New Approach Determining a Phase Transition Boundary Strictly Following a Definition of Phase Equilibrium: An Example of the Post-Spinel Transition in Mg2SiO4 System
by Takayuki Ishii, Artem Chanyshev and Tomoo Katsura
Minerals 2022, 12(7), 820; https://doi.org/10.3390/min12070820 - 28 Jun 2022
Cited by 8 | Viewed by 2765
Abstract
The Clapeyron slope is the slope of a phase boundary in P–T space and is essential for understanding mantle dynamics and evolution. The phase boundary is delineating instead of balancing a phase transition’s normal and reverse reactions. Many previous high pressure–temperature experiments determining [...] Read more.
The Clapeyron slope is the slope of a phase boundary in P–T space and is essential for understanding mantle dynamics and evolution. The phase boundary is delineating instead of balancing a phase transition’s normal and reverse reactions. Many previous high pressure–temperature experiments determining the phase boundaries of major mantle minerals experienced severe problems due to instantaneous pressure increase by thermal pressure, pressure drop during heating, and sluggish transition kinetics. These complex pressure changes underestimate the transition pressure, while the sluggish kinetics require excess pressures to initiate or proceed with the transition, misinterpreting the phase stability and preventing tight bracketing of the phase boundary. Our recent study developed a novel approach to strictly determine phase stability based on the phase equilibrium definition. Here, we explain the details of this technique, using the post-spinel transition in Mg2SiO4 determined by our recent work as an example. An essential technique is to observe the change in X-ray diffraction intensity between ringwoodite and bridgmanite + periclase during the spontaneous pressure drop at a constant temperature and press load with the coexistence of both phases. This observation removes the complicated pressure change upon heating and kinetic problem, providing an accurate and precise phase boundary. Full article
(This article belongs to the Special Issue In Situ Measurements of Physical Properties of Rocks, Minerals and Fluids at Extreme Conditions)
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17 pages, 1176 KiB  
Review
Sustainable Production of Rare Earth Elements from Mine Waste and Geoethics
by Marouen Jouini, Alexandre Royer-Lavallée, Thomas Pabst, Eunhyea Chung, Rina Kim, Young-Wook Cheong and Carmen Mihaela Neculita
Minerals 2022, 12(7), 809; https://doi.org/10.3390/min12070809 - 25 Jun 2022
Cited by 21 | Viewed by 6913
Abstract
The vulnerability of the rare earth element (REE) supply in a global context of increasing demands entails important economic and political issues, and has encouraged several countries to develop their own REE production projects. This study comparatively evaluated the production of REEs from [...] Read more.
The vulnerability of the rare earth element (REE) supply in a global context of increasing demands entails important economic and political issues, and has encouraged several countries to develop their own REE production projects. This study comparatively evaluated the production of REEs from primary and secondary resources in terms of their sustainability and contribution to the achievement of the Geoethics concept as responsibility towards oneself, colleagues, society, and the Earth system. Twelve categories of potential environmental and social impacts were selected: human health toxicity, global warming or climate change, terrestrial and aquatic eutrophication, acidification potential, particulate matter, resource depletion, water consumption, fresh water ecotoxicity, ionizing radiation, fossil fuel consumption, and ozone depletion. The results showed that the environmental impact of REE production from secondary sources is much lower relative to primary sources. A comparison of conventional and non-conventional REE resources showed that significant impact categories were related to particulate matter formation, abiotic resource depletion, and fossil fuel depletion, which could result from avoiding the tailings disposal before reuse. Based on these findings, governments and stakeholders should be encouraged to increase the recycling of secondary REE sources with Geoethics in mind, in order to balance the high demand of REEs while minimizing the overexploitation of non-renewable resources. Full article
(This article belongs to the Section Mineral Processing and Extractive Metallurgy)
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16 pages, 15762 KiB  
Article
Unravelling the Deformation of Paleoproterozoic Marbles and Zn-Pb Ore Bodies by Combining 3D-Photogeology and Hyperspectral Data (Black Angel Mine, Central West Greenland)
by Pierpaolo Guarnieri, Sam T. Thiele, Nigel Baker, Erik V. Sørensen, Moritz Kirsch, Sandra Lorenz, Diogo Rosa, Gabriel Unger and Robert Zimmermann
Minerals 2022, 12(7), 800; https://doi.org/10.3390/min12070800 - 23 Jun 2022
Cited by 7 | Viewed by 3360
Abstract
The Black Angel Zn-Pb ore deposit is hosted in folded Paleoproterozoic marbles of the Mârmorilik Formation. It is exposed in the southern part of the steep and inaccessible alpine terrain of the Rinkian Orogen, in central West Greenland. Drill-core data integrated with 3D-photogeology [...] Read more.
The Black Angel Zn-Pb ore deposit is hosted in folded Paleoproterozoic marbles of the Mârmorilik Formation. It is exposed in the southern part of the steep and inaccessible alpine terrain of the Rinkian Orogen, in central West Greenland. Drill-core data integrated with 3D-photogeology and hyperspectral imagery of the rock face allow us to identify stratigraphic units and extract structural information that contains the geological setting of this important deposit. The integrated stratigraphy distinguishes chemical/mineralogical contrast within lithologies dominated by minerals that are difficult to distinguish with the naked eye, with a similar color of dolomitic and scapolite-rich marbles and calcitic, graphite-rich marbles. These results strengthen our understanding of the deformation style in the marbles and allow a subdivision between evaporite-carbonate platform facies and carbonate slope facies. Ore formation appears to have been mainly controlled by stratigraphy, with mineralizing fluids accumulating within permeable carbonate platform facies underneath carbonate slope facies and shales as cap rock. Later, folding and shearing were responsible for the remobilization and improvement of ore grades along the axial planes of shear folds. The contact between dolomitic scapolite-rich and calcitic graphite-rich marbles probably represents a direct stratigraphic marker, recognizable in the drill-cores, to be addressed for further 3D-modeling and exploration in this area. Full article
(This article belongs to the Special Issue 3D-Modelling of Crustal Structures and Mineral Deposit Systems)
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34 pages, 5813 KiB  
Review
Geoenvironmental Model for Roll-Type Uranium Deposits in the Texas Gulf Coast
by Katherine Walton-Day, Johanna Blake, Robert R. Seal II, Tanya J. Gallegos, Jean Dupree and Kent D. Becher
Minerals 2022, 12(6), 780; https://doi.org/10.3390/min12060780 - 20 Jun 2022
Cited by 8 | Viewed by 4416
Abstract
Geoenvironmental models were formulated by the U.S. Geological Survey in the 1990s to describe potential environmental effects of extracting different types of ore deposits in different geologic and climatic regions. This paper presents a geoenvironmental model for roll-front (roll-type) uranium deposits in the [...] Read more.
Geoenvironmental models were formulated by the U.S. Geological Survey in the 1990s to describe potential environmental effects of extracting different types of ore deposits in different geologic and climatic regions. This paper presents a geoenvironmental model for roll-front (roll-type) uranium deposits in the Texas Coastal Plain. The model reviews descriptive and quantitative information derived from environmental studies and existing databases to depict existing conditions and potential environmental concerns associated with mining this deposit type. This geoenvironmental model describes how features of the deposits including host rock; ore and gangue mineralogy; geologic, hydrologic, and climatic settings; and mining methods (legacy open-pit and in situ recovery [ISR]) influence potential environmental effects from mining. Element concentrations in soil and water are compared to regulatory thresholds to depict ambient surface water and groundwater conditions. Although most open-pit operations in this region have been reclaimed, concerns remain about groundwater quality at three of the four former mills that supported former open-pit mines and are undergoing closure activities. The primary environmental concerns with ISR mining are (1) radon gas at active ISR operations, (2) radiation or contaminant leakage during production and transport of ISR resin or yellowcake, (3) uranium excursions into groundwater surrounding active ISR operations, and (4) contamination of groundwater after ISR mining. Although existing regulations attempt to address these concerns, some problems remain. Researchers suggest that reactive transport modeling and a better understanding of geology, stratigraphy, and geochemistry of ISR production areas could minimize excursions into surrounding aquifers and improve results of groundwater restoration. Full article
(This article belongs to the Special Issue Environmentally Sound In-Situ Recovery Mining of Uranium)
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13 pages, 2690 KiB  
Article
Bentonite Powder XRD Quantitative Analysis Using Rietveld Refinement: Revisiting and Updating Bulk Semiquantitative Mineralogical Compositions
by Jaime Cuevas, Miguel Ángel Cabrera, Carlos Fernández, Carlos Mota-Heredia, Raúl Fernández, Elena Torres, María Jesús Turrero and Ana Isabel Ruiz
Minerals 2022, 12(6), 772; https://doi.org/10.3390/min12060772 - 17 Jun 2022
Cited by 20 | Viewed by 8299
Abstract
Bentonite is a claystone formed by a complex mineralogical mixture, composed of montmorillonite, illite, and accessory minerals like quartz, cristobalite, feldspars, carbonates, and minor amounts of iron oxy-hydroxides. Bentonite presents complexity at various scales: (1): a single mineral may present different chemical composition [...] Read more.
Bentonite is a claystone formed by a complex mineralogical mixture, composed of montmorillonite, illite, and accessory minerals like quartz, cristobalite, feldspars, carbonates, and minor amounts of iron oxy-hydroxides. Bentonite presents complexity at various scales: (1): a single mineral may present different chemical composition within the same quarry (e.g., feldspars solid solutions); (2): montmorillonite presents variability in the cation-exchange distribution while illite may be presented as mixed-layer with smectite sheets; and (3): hardness and crystal size are larger in accessory minerals than in clay minerals, preventing uniform grinding of bentonite. The FEBEX bentonite used is originally from Almería (Spain), and it is a predominantly calcium, magnesium, and sodium bentonite. This Spanish FEBEX bentonite has been hydrothermally altered at laboratory scale for 7–14 years. A thermal gradient was generated by heating a disk of pressed iron powder, simulating the metal waste canister, in contact with the compacted bentonite sample. Hydration was forced from the opposite direction. XRD recorded patterns were very similar. In order to minimize the bias of XRD semi-quantitative determination methods, Rietveld refinement was performed using BGMN software and different structural models. Confidence in the quantification of the main phases allows us to convincingly detect other subtle changes such as the presence of calcite in the hydration front, right at the interface between the saturated and unsaturated bentonite, or the presence of goethite, and not hematite, in the saturated bentonite, near the source of hydration. Smectite component was 72 ± 3% and the refinement was consistent with the presence of ~10% illite, comparable with previous characterizations. Full article
(This article belongs to the Special Issue Structure and Crystallochemistry of Clay Minerals)
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30 pages, 35980 KiB  
Article
Ductile vs. Brittle Strain Localization Induced by the Olivine–Ringwoodite Transformation
by Julien Gasc, Blandine Gardonio, Damien Deldicque, Clémence Daigre, Arefeh Moarefvand, Léo Petit, Pamela Burnley and Alexandre Schubnel
Minerals 2022, 12(6), 719; https://doi.org/10.3390/min12060719 - 4 Jun 2022
Cited by 5 | Viewed by 3177
Abstract
As it descends into the Earth’s mantle, the olivine that constitutes the lithosphere of subducting slabs transforms to its high-pressure polymorphs, wadsleyite and ringwoodite, in the so-called transition zone. These transformations have important rheological consequences, since they may induce weakening, strain localization, and, [...] Read more.
As it descends into the Earth’s mantle, the olivine that constitutes the lithosphere of subducting slabs transforms to its high-pressure polymorphs, wadsleyite and ringwoodite, in the so-called transition zone. These transformations have important rheological consequences, since they may induce weakening, strain localization, and, in some cases, earthquakes. In this study, germanium olivine (Ge-olivine) was used as an analogue material to investigate the rheology of samples undergoing the olivine–ringwoodite transformation. Ge-olivine adopts a ringwoodite structure at pressures ~14 GPa lower than its silicate counterpart does, making the transformation accessible with a Griggs rig. Deformation experiments were carried out in a new-generation Griggs apparatus, where micro-seismicity was recorded in the form of acoustic emissions. A careful analysis of the obtained acoustic signal, combined with an extensive microstructure analysis of the recovered samples, provided major insights into the interplay between transformation and deformation mechanisms. The results show that significant reaction rates cause a weakening via the implementation of ductile shear zones that can be preceded by small brittle precursors. When kinetics are more sluggish, mechanical instabilities lead to transformational faulting, which stems from the unstable propagation of shear bands localizing both strain and transformation. The growth of these shear bands is self-sustained thanks to the negative volume change and the exothermic nature of the reaction, and leads to dynamic rupture, as attested by the acoustic emissions recorded. These micro-earthquakes share striking similarities with deep focus earthquakes, which may explain several seismological observations such as magnitude frequency relations and the occurrence of deep repeating earthquakes and foreshocks. Full article
(This article belongs to the Special Issue Mantle Strain Localization—How Minerals Deform at Deep Plate Interfaces)
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47 pages, 12420 KiB  
Article
Restoration Insights Gained from a Field Deployment of Dithionite and Acetate at a Uranium In Situ Recovery Mine
by Paul Reimus, James Clay and Noah Jemison
Minerals 2022, 12(6), 711; https://doi.org/10.3390/min12060711 - 2 Jun 2022
Cited by 6 | Viewed by 3037
Abstract
Mining uranium by in situ recovery (ISR) typically involves injecting an oxidant and a complexing agent to mobilize and extract uranium in a saturated ore zone. This strategy involves less infrastructure and invasive techniques than traditional mining, but ISR often results in persistently [...] Read more.
Mining uranium by in situ recovery (ISR) typically involves injecting an oxidant and a complexing agent to mobilize and extract uranium in a saturated ore zone. This strategy involves less infrastructure and invasive techniques than traditional mining, but ISR often results in persistently elevated concentrations of U and other contaminants of concern in groundwater after mining. These concentrations may remain elevated for an extended period without remediation. Here, we describe a field experiment at an ISR facility in which both a chemical reductant (sodium dithionite) and a biostimulant (sodium acetate) were sequentially introduced into a previously mined ore zone in an attempt to establish reducing geochemical conditions that, in principle, should decrease and stabilize aqueous U concentrations. While several lines of evidence indicated that reducing conditions were established, U concentrations did not decrease, and in fact increased after the amendment deployments. We discuss likely reasons for this behavior, and we also discuss how the results provide insights into improvements that could be made to the restoration process to benefit from the seemingly detrimental behavior. Full article
(This article belongs to the Special Issue Environmentally Sound In-Situ Recovery Mining of Uranium)
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15 pages, 3977 KiB  
Article
A Kinetic Monte Carlo Approach to Model Barite Dissolution: The Role of Reactive Site Geometry
by Inna Kurganskaya, Nikolay Trofimov and Andreas Luttge
Minerals 2022, 12(5), 639; https://doi.org/10.3390/min12050639 - 18 May 2022
Cited by 10 | Viewed by 2687
Abstract
Barite (Ba[SO4]) is one of the promising candidates for sequestration of radioactive waste. Barite can incorporate radium (Ra) and form ideal solid solutions, i.e., (Ba,Ra)[SO4]. Together with isostructural celestite (Sr[SO4]), ternary solid solutions, (Ba,Sr,Ra)[SO4], may [...] Read more.
Barite (Ba[SO4]) is one of the promising candidates for sequestration of radioactive waste. Barite can incorporate radium (Ra) and form ideal solid solutions, i.e., (Ba,Ra)[SO4]. Together with isostructural celestite (Sr[SO4]), ternary solid solutions, (Ba,Sr,Ra)[SO4], may exist in natural conditions. Our fundamental understanding of the dissolution kinetics of isostructural sulfates is critically important for a better risk assessment of nuclear waste repositories utilizing this mineral for sequestration. So far, the barite-water interface has been studied with experimental methods and atomistic computer simulations. The direct connection between the molecular scale details of the interface structure and experimental observations at the microscopic scale is not yet well understood. Here, we began to investigate this connection by using a kinetic Monte Carlo approach to simulate the barite dissolution process. We constructed a microkinetic model for the dissolution process and identified the reactive sites. Identification of these sites is important for an improved understanding of the dissolution, adsorption, and crystal growth mechanisms at the barite–water interface. We parameterized the molecular detachment rates by using the experimentally observed etch pit morphologies and atomic step velocities. Our parameterization attempts demonstrated that local lattice coordination is not sufficient to differentiate between the kinetically important sites and estimate their detachment rates. We suggest that the water structure and dynamics at identified sites should substantially influence the detachment rates. However, it will require more work to improve the parameterization of the model by means of Molecular Dynamics and ab initio calculations. Full article
(This article belongs to the Special Issue Ion Adsorption at Mineral–Water Interfaces)
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12 pages, 3996 KiB  
Article
Extraction of Gold and Copper from Flotation Tailings Using Glycine-Ammonia Solutions in the Presence of Permanganate
by Huan Li, Elsayed Oraby, Jacques Eksteen and Tanmay Mali
Minerals 2022, 12(5), 612; https://doi.org/10.3390/min12050612 - 12 May 2022
Cited by 14 | Viewed by 6847
Abstract
This study presents the novel idea of a cyanide-free leaching method, i.e., glycine-ammonia leaching in the presence of permanganate, to treat a low-grade and copper-bearing gold tailing. Ammonia played a key role as a pH modifier, lixiviant and potential catalyst (as cupric ammine) [...] Read more.
This study presents the novel idea of a cyanide-free leaching method, i.e., glycine-ammonia leaching in the presence of permanganate, to treat a low-grade and copper-bearing gold tailing. Ammonia played a key role as a pH modifier, lixiviant and potential catalyst (as cupric ammine) in this study. Replacing ammonia with other pH modifiers (i.e., sodium hydroxide or lime) made the extractions infeasibly low (<30%). The increased additions of glycine (23–93 kg/t), ammonia (30–157 kg/t) and permanganate (5–20 kg/t) enhanced gold and copper extractions considerably. Increasing the solids content from 20 to 40% did not make any obvious changes to copper extraction. However, gold leaching kinetics was slightly better at lower solids content. It was indicated that the staged addition of permanganate was unnecessary under the leaching conditions. Recovery of gold by CIL was shown to be feasible, and it improved gold extraction by 15%, but no effect was observed for copper extraction. Percentages of 76.5% gold and 64.5% copper were extracted in 48 h at 20 g/L glycine, 10 kg/t permanganate, 20 g/L carbon, pH 10.5 and 30% solids. Higher extractions could be potentially achieved by further optimization, such as by increasing permanganate addition, extending leaching time and ultra-fine grinding. Full article
(This article belongs to the Special Issue Hydrometallurgy of Base and Precious Metals)
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20 pages, 1343 KiB  
Review
Overview on the Development of Intelligent Methods for Mineral Resource Prediction under the Background of Geological Big Data
by Shi Li, Jianping Chen and Chang Liu
Minerals 2022, 12(5), 616; https://doi.org/10.3390/min12050616 - 12 May 2022
Cited by 29 | Viewed by 6123
Abstract
In the age of big data, the prediction and evaluation of geological mineral resources have gradually entered a new stage, intelligent prospecting. This review briefly summarizes the research development of textual data mining and spatial data mining. It is considered that the current [...] Read more.
In the age of big data, the prediction and evaluation of geological mineral resources have gradually entered a new stage, intelligent prospecting. This review briefly summarizes the research development of textual data mining and spatial data mining. It is considered that the current research on mineral resource prediction has integrated logical reasoning, theoretical models, computational simulations, and other scientific research models, and has gradually advanced toward a new model. This type of new model has tried to mine unknown and effective knowledge from big data by intelligent analysis methods. However, many challenges have come forward, including four aspects: (i) discovery of prospecting big data based on geological knowledge system; (ii) construction of the conceptual prospecting model by intelligent text mining; (iii) mineral prediction by intelligent spatial big data mining; (iv) sharing and visualization of the mineral prediction data. By extending the geological analysis in the process of prospecting prediction to the logical rules associated with expert knowledge points, the theory and methods of intelligent mineral prediction were preliminarily established based on geological big data. The core of the theory is to promote the flow, invocation, circulation, and optimization of the three key factors of “knowledge”, “model”, and “data”, and to preliminarily constitute the prototype of intelligent linkage mechanisms. It could be divided into four parts: intelligent datamation, intelligent informatization, intelligent knowledgeization, and intelligent servitization. Full article
(This article belongs to the Special Issue GIS, AI, and Modelling of Mineralization Process and Prospectivity)
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20 pages, 3363 KiB  
Review
The Challenges and Prospects of Recovering Fine Copper Sulfides from Tailings Using Different Flotation Techniques: A Review
by Muhammad Bilal, Ilhwan Park, Vothy Hornn, Mayumi Ito, Fawad Ul Hassan, Sanghee Jeon and Naoki Hiroyoshi
Minerals 2022, 12(5), 586; https://doi.org/10.3390/min12050586 - 6 May 2022
Cited by 29 | Viewed by 12037
Abstract
Flotation is a common mineral processing method used to upgrade copper sulfide ores; in this method, copper sulfide mineral particles are concentrated in froth, and associated gangue minerals are separated as tailings. However, a significant amount of copper is lost into tailings during [...] Read more.
Flotation is a common mineral processing method used to upgrade copper sulfide ores; in this method, copper sulfide mineral particles are concentrated in froth, and associated gangue minerals are separated as tailings. However, a significant amount of copper is lost into tailings during the processing; therefore, tailings can be considered secondary resources or future deposits of copper. Particle–bubble collision efficiency and particle–bubble aggregate stability determines the recovery of target particles; this attachment efficiency plays a vital role in the selectivity process. The presence of fine particles in the flotation circuit is because of excessive grinding, which is to achieve a higher degree of liberation. Complex sulfide ores of markedly low grade further necessitate excessive grinding to achieve the maximum degree of liberation. In the flotation process, fine particles due to their small mass and momentum are unable to collide with rising bubbles, and their rate of flotation is very slow, further lowering the recovery of target minerals. This collision efficiency mainly depends on the particle–bubble size ratio and the concentration of particles present in the pulp. To overcome this problem and to maintain a favorable particle–bubble size ratio, different techniques have been employed by researchers to enhance particle–bubble collision efficiency either by increasing particle size or by decreasing bubble size. In this article, the mechanism of tailing loss is discussed in detail. In addition, flotation methods for fine particles recovery such as microbubble flotation, column flotation, nanobubble flotation, polymer flocculation, shear flocculation, oil agglomeration, and carrier flotation are reviewed, and their applications and limitations are discussed in detail. Full article
(This article belongs to the Special Issue Sustainable Production of Metals for Low-Carbon Technologies)
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17 pages, 5241 KiB  
Article
In Situ Study on Dehydration and Phase Transformation of Antigorite
by Shuang Liang, Yuegao Liu and Shenghua Mei
Minerals 2022, 12(5), 567; https://doi.org/10.3390/min12050567 - 30 Apr 2022
Viewed by 2912
Abstract
Antigorite is the main carrier of water in Earth’s subduction zones. The dehydration processes of antigorite were investigated by carrying out in situ phase transition experiments using a dynamic diamond anvil cell, with a time-resolved Raman scattering system, at 0.3–10 GPa and 396–1100 [...] Read more.
Antigorite is the main carrier of water in Earth’s subduction zones. The dehydration processes of antigorite were investigated by carrying out in situ phase transition experiments using a dynamic diamond anvil cell, with a time-resolved Raman scattering system, at 0.3–10 GPa and 396–1100 K. Three typical phase transformation reactions occurred within the P–T range of this study, corresponding to three reaction products. At low pressures (<0.7 GPa), antigorite transfers to talc and forsterite; as the temperature increases, the talc disappears and a combination of forsterite and clinoenstatite occurs. At moderate pressures (1.8–7.5 GPa), antigorite dehydrates into forsterite and clinoenstatite as temperatures increase; with the continuous increase in pressure, the dehydration products become clinoenstatite and phase A. At high pressures (>8.6 GPa), the products of the dehydration phase transition of antigorite are consistently clinoenstatite and phase A. Compared with the previous studies carried out by large-volume presses (such as a multi anvil press and a piston-cylinder press), the reaction to produce phase A occurs at higher P–T conditions, and the stable temperature region for talc as a dehydration product is narrower. Moreover, large quantities of pores with 5–10 μm in diameter formed in dehydration products, supporting the hypothesis that intermediate-depth earthquakes may result from dehydration embrittlement. The precise phase boundary determined by this in situ study provides a better understanding of the dehydration phase transition behavior and geological phenomena exhibited by antigorite under different pressure and temperature conditions. Full article
(This article belongs to the Section Crystallography and Physical Chemistry of Minerals & Nanominerals)
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33 pages, 4834 KiB  
Review
Review on the Development and Utilization of Ionic Rare Earth Ore
by Xianping Luo, Yongbing Zhang, Hepeng Zhou, Kunzhong He, Caigui Luo, Zishuai Liu and Xuekun Tang
Minerals 2022, 12(5), 554; https://doi.org/10.3390/min12050554 - 28 Apr 2022
Cited by 63 | Viewed by 8730
Abstract
Rare earth, with the reputation of “industrial vitamins”, has become a strategic key metal for industrial powers with increasingly significant industrial application value. As a unique rare earth resource, ionic rare earth ore (IREO) has the outstanding advantages of complete composition, rich resource [...] Read more.
Rare earth, with the reputation of “industrial vitamins”, has become a strategic key metal for industrial powers with increasingly significant industrial application value. As a unique rare earth resource, ionic rare earth ore (IREO) has the outstanding advantages of complete composition, rich resource reserves, low radioactivity, and high comprehensive utilization value. IREO is the main source of medium and heavy rare earth raw materials, which are in great demand all over the world. Since the discovery of IREO, it has attracted extensive attention. Scientists in China and the around world have carried out a lot of research and practical work and achieved a series of important breakthroughs. This paper introduces the discovery process, metallogenic causes, deposit characteristics, and the prospecting research progress of IREO, so as to deepen the understanding of the global distribution of ionic rare earth resources and the prospecting direction of ionic rare earth deposits. The leaching principle of IREO, the innovation of leaching process, the influencing factors and technological development of in situ leaching process, and the technical adaptability of in situ leaching process are reviewed. The development of leachate purification and rare earth extraction technology is summarized. We aim to provide guidance for the industrial development of IREO through the above review analysis. Additionally, the problems existing in the development of IREO are pointed out from the aspects of technology, economy, and the environment. Ultimately, a series of suggestions are put forward, such as the development of ammonium free extraction technology in the whole exploitation process of in situ leaching and leachate purification and rare earth precipitation, research on enhancing of seepage and mass transfer process, and research on the development of new technologies for impurity removal of leachate and extraction of rare earth, so as to promote the development of green and efficient exploitation new technologies and sustainable development of ionic rare earth ore. Full article
(This article belongs to the Special Issue Recovery of Rare Earth Elements Minerals)
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23 pages, 4262 KiB  
Article
Mining and Metallurgical Waste as Potential Secondary Sources of Metals—A Case Study for the West Balkan Region
by Robert Šajn, Ivica Ristović and Barbara Čeplak
Minerals 2022, 12(5), 547; https://doi.org/10.3390/min12050547 - 27 Apr 2022
Cited by 43 | Viewed by 6973
Abstract
The aim of this paper is to present a chemical composition and quantities of mining and processing waste landfills material developed during historical mining and smelting. After detailed inspection, it was found that approximately 2.6 gigatons of the waste had been deposited at [...] Read more.
The aim of this paper is to present a chemical composition and quantities of mining and processing waste landfills material developed during historical mining and smelting. After detailed inspection, it was found that approximately 2.6 gigatons of the waste had been deposited at 1650 sites, covering almost 65 km2. More than half of this material, 55%, is characterized as conventional mining waste, 37% belongs to the processing tailings, and 8% to metallurgical waste. Most of these tailing sites are unclaimed, presenting a source of contamination for nearby communities. According to the literature data collected and additional chemical analyses, in accordance with zero-waste philosophy, about 42 promising locations (c. 270 million tons) could be selected, where various advanced eco-innovative methods of recovery could possibly apply. The areas with the highest prospective recovery are Serbia and Kosovo. In accordance with the metal prices achieved in March 2022, it is estimated that the recovery of tailings could bring up to 18,100 million USD, which is much more compared to the prices of March 2020—10,600 million USD—when the commodity market was governed by the COVID-19 restrictions. In addition to the commercial value of the metals, the environmental aspect should not be forgotten after the application of reuse and recycling concepts. Full article
(This article belongs to the Special Issue Selected Papers from the 8th and 9th International Conference on Mining and Environmental Protection)
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23 pages, 5608 KiB  
Article
Apatite, Ca10(PO4)6(OH,F,Cl)2: Structural Variations, Natural Solid Solutions, Intergrowths, and Zoning
by Kaveer S. Hazrah and Sytle M. Antao
Minerals 2022, 12(5), 527; https://doi.org/10.3390/min12050527 - 23 Apr 2022
Cited by 7 | Viewed by 8607
Abstract
Thirty-three samples from natural apatite (Ap) solid solutions, ideal structural formula [9]Ca12[7]Ca23([4]PO4)3[3](F,OH,Cl), (Z = 2) were examined with electron-probe microanalysis, synchrotron high-resolution powder X-ray diffraction (HRPXRD), and Rietveld refinements. Apatite [...] Read more.
Thirty-three samples from natural apatite (Ap) solid solutions, ideal structural formula [9]Ca12[7]Ca23([4]PO4)3[3](F,OH,Cl), (Z = 2) were examined with electron-probe microanalysis, synchrotron high-resolution powder X-ray diffraction (HRPXRD), and Rietveld refinements. Apatite has space group P63/m for the general chemical formula above. In Ap, the two different Ca sites are generally occupied by Ca, Mn, Sr, Na, or REE3+ cations; the P site is occupied by P, Si, or S, and the X is occupied by F, OH, Cl, O2−, or (CO3)2− anions. However, it may be possible for CO32− + F− anions to partially replace PO43− groups. In this study, the unit-cell parameters a, c, and c/a ratio, vary smoothly and non-linearly with the unit-cell volume, V. The data falls on two distinct trend lines. The average <P-O>[4] distance is nearly constant across the Ap series, whereas the average <O-P-O>[6] angle decreases linearly. The coordination numbers for the atoms are given in square brackets in the general chemical formula above. The average <Ca1-O>[9], <Ca2-O>[6], <Ca2-O,X>[7], and Ca2-X distances change non-linearly with increasing V. Although Cl− anion is larger than OH− and F− anions, the c unit-cell parameter in F-Ap is larger than that in Cl-Ap. In Cl-Ap, the Ca2 polyhedra are larger than in F-Ap, so the O and Cl anions are under-bonded, which cause the Ca1 polyhedra to contract and charge balance the anions. Alternatively, the Ca1 polyhedra are smaller in Cl-Ap than in F-Ap, so the Ca1 polyhedra in Cl-Ap cause the c axis to contract compared to that in F-Ap. Full article
(This article belongs to the Section Crystallography and Physical Chemistry of Minerals & Nanominerals)
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28 pages, 2980 KiB  
Review
Accessing Metals from Low-Grade Ores and the Environmental Impact Considerations: A Review of the Perspectives of Conventional versus Bioleaching Strategies
by Rosina Nkuna, Grace N. Ijoma, Tonderayi S. Matambo and Ngonidzashe Chimwani
Minerals 2022, 12(5), 506; https://doi.org/10.3390/min12050506 - 20 Apr 2022
Cited by 48 | Viewed by 16489
Abstract
Mining has advanced primarily through the use of two strategies: pyrometallurgy and hydrometallurgy. Both have been used successfully to extract valuable metals from ore deposits. These strategies, without a doubt, harm the environment. Furthermore, due to decades of excessive mining, there has been [...] Read more.
Mining has advanced primarily through the use of two strategies: pyrometallurgy and hydrometallurgy. Both have been used successfully to extract valuable metals from ore deposits. These strategies, without a doubt, harm the environment. Furthermore, due to decades of excessive mining, there has been a global decline in high-grade ores. This has resulted in a decrease in valuable metal supply, which has prompted a reconsideration of these traditional strategies, as the industry faces the current challenge of accessing the highly sought-after valuable metals from low-grade ores. This review outlines these challenges in detail, provides insights into metal recovery issues, and describes technological advances being made to address the issues associated with dealing with low-grade metals. It also discusses the pragmatic paradigm shift that necessitates the use of biotechnological solutions provided by bioleaching, particularly its environmental friendliness. However, it goes on to criticize the shortcomings of bioleaching while highlighting the potential solutions provided by a bespoke approach that integrates research applications from omics technologies and their applications in the adaptation of bioleaching microorganisms and their interaction with the harsh environments associated with metal ore degradation. Full article
(This article belongs to the Special Issue Current Status of Low-Grade Minerals and Mine Wastes Recovery: Reaction Mechanism, Mass Transfer, and Process Control)
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30 pages, 10711 KiB  
Article
Stratigraphy, Paleogeography and Depositional Setting of the K–Mg Salts in the Zechstein Group of Netherlands—Implications for the Development of Salt Caverns
by Alexandre Pichat
Minerals 2022, 12(4), 486; https://doi.org/10.3390/min12040486 - 16 Apr 2022
Cited by 15 | Viewed by 6160
Abstract
The 1 km thick evaporitic Permian Zechstein group in the Netherlands is subdivided into 5 halite rich evaporitic sequences including K–Mg salts (polyhalite, kieserite, sylvite, carnallite and bischofite) for which the position in the Zechstein stratigraphy is still poorly constrained. Understanding the repartition [...] Read more.
The 1 km thick evaporitic Permian Zechstein group in the Netherlands is subdivided into 5 halite rich evaporitic sequences including K–Mg salts (polyhalite, kieserite, sylvite, carnallite and bischofite) for which the position in the Zechstein stratigraphy is still poorly constrained. Understanding the repartition of K–Mg salts is especially important for the development of salt caverns which require a salt as pure as possible in halite. By compiling well log and seismic data in the offshore and onshore domains of the Netherlands, regional cross-sections and isopach maps were performed in order to update the lithostratigraphy of the Zechstein group by including the K–Mg salts. Results enable (i) to propose paleogeographic maps representing the spatial repartition and the thickness variations of one to two K–Mg rich intervals in each evaporite cycle, (ii) to constrain the depositional setting of the different type of salts and the hydrological conditions which influenced the Zechstein stratigraphic architecture and (iii) to develop over the Netherlands risking maps assessing the risk of encountering K–Mg salts in salt pillows or salt diapirs eligible in term of depth and thickness for the development of salt caverns. Full article
(This article belongs to the Special Issue Sedimentology, Petrography, Geochemistry and Geobiology of Marine Evaporitic Rocks)
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17 pages, 3188 KiB  
Article
Molecular Dynamics Simulation and Cryo-Electron Microscopy Investigation of AOT Surfactant Structure at the Hydrated Mica Surface
by Daniel M. Long, Jeffery A. Greathouse, Guangping Xu and Katherine L. Jungjohann
Minerals 2022, 12(4), 479; https://doi.org/10.3390/min12040479 - 14 Apr 2022
Cited by 6 | Viewed by 3625
Abstract
Structural properties of the anionic surfactant dioctyl sodium sulfosuccinate (AOT or Aerosol-OT) adsorbed on the mica surface were investigated by molecular dynamics simulation, including the effect of surface loading in the presence of monovalent and divalent cations. The simulations confirmed recent neutron reflectivity [...] Read more.
Structural properties of the anionic surfactant dioctyl sodium sulfosuccinate (AOT or Aerosol-OT) adsorbed on the mica surface were investigated by molecular dynamics simulation, including the effect of surface loading in the presence of monovalent and divalent cations. The simulations confirmed recent neutron reflectivity experiments that revealed the binding of anionic surfactant to the negatively charged surface via adsorbed cations. At low loading, cylindrical micelles formed on the surface, with sulfate head groups bound to the surface by water molecules or adsorbed cations. Cation bridging was observed in the presence of weakly hydrating monovalent cations, while sulfate groups interacted with strongly hydrating divalent cations through water bridges. The adsorbed micelle structure was confirmed experimentally with cryogenic electronic microscopy, which revealed micelles approximately 2 nm in diameter at the basal surface. At higher AOT loading, the simulations reveal adsorbed bilayers with similar surface binding mechanisms. Adsorbed micelles were slightly thicker (2.2–3.0 nm) than the corresponding bilayers (2.0–2.4 nm). Upon heating the low loading systems from 300 K to 350 K, the adsorbed micelles transformed to a more planar configuration resembling bilayers. The driving force for this transition is an increase in the number of sulfate head groups interacting directly with adsorbed cations. Full article
(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)
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20 pages, 5530 KiB  
Article
Role of Volatiles in the Evolution of a Carbonatitic Melt in Peridotitic Mantle: Experimental Constraints at 6.3 GPa and 1200–1450 °C
by Aleksei Kruk and Alexander Sokol
Minerals 2022, 12(4), 466; https://doi.org/10.3390/min12040466 - 11 Apr 2022
Cited by 2 | Viewed by 2218
Abstract
Reconstruction of the mechanisms of carbonatitic melt evolution is extremely important for understanding metasomatic processes at the base of the continental lithospheric mantle (CLM). We have studied the interaction between garnet lherzolite and a carbonatitic melt rich in molecular CO2 and H [...] Read more.
Reconstruction of the mechanisms of carbonatitic melt evolution is extremely important for understanding metasomatic processes at the base of the continental lithospheric mantle (CLM). We have studied the interaction between garnet lherzolite and a carbonatitic melt rich in molecular CO2 and H2O in experiments at 6.3 GPa and 1200–1450 °C. The interaction with garnet lherzolite and H2O-bearing carbonatite melt leads to wehrlitization of lherzolite, without its carbonation. Introduction of molecular CO2 and H2O initiates carbonation of olivine and clinopyroxene with the formation of orthopyroxene and magnesite. Partial carbonation leads to the formation of carbonate–silicate melts that are multiphase saturated with garnet harzburgite. Upon complete carbonation of olivine already at 1200 °C, melts with 27–31 wt% SiO2 and MgO/CaO ≈ 1 are formed. At 1350–1450 °C, the interaction leads to an increase in the melt fraction and the MgO/CaO ratio to 2–4 and a decrease in the SiO2 concentration. Thus, at conditions of a thermally undisturbed CLM base, molecular CO2 and H2O dissolved in metasomatic agents, due to local carbonation of peridotite, can provide the evolution of agent composition from carbonatitic to hydrous silicic, i.e., similar to the trends reconstructed for diamond-forming high density fluids (HDFs) and genetically related proto-kimberlite melts. Full article
(This article belongs to the Section Crystallography and Physical Chemistry of Minerals & Nanominerals)
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12 pages, 3926 KiB  
Article
Preparation and Swelling Inhibition of Mixed Metal Hydroxide to Bentonite Clay
by Bowen Zhang, Qingchen Wang, Yan Wei, Wei Wei, Weichao Du, Jie Zhang, Gang Chen and Michal Slaný
Minerals 2022, 12(4), 459; https://doi.org/10.3390/min12040459 - 8 Apr 2022
Cited by 20 | Viewed by 3691
Abstract
In this paper, mixed metal hydroxide (MMH) was prepared via MgCl2 and AlCl3 by the co-precipitation method and characterized by XRD, TGA laser and particle size analysis. The inhibitory effect of MMH on the swelling of clay was evaluated by linear [...] Read more.
In this paper, mixed metal hydroxide (MMH) was prepared via MgCl2 and AlCl3 by the co-precipitation method and characterized by XRD, TGA laser and particle size analysis. The inhibitory effect of MMH on the swelling of clay was evaluated by linear expansion, mud ball, laser particle size analysis, X-ray diffraction analysis and TGA. The linear expansion experiment showed that MMH with a ratio of Mg:Al = 3:1 displayed a strong inhibitory effect on bentonite expansion when 0.3% MMH was added to the drilling fluid, demonstrating better inhibition than 4.0% KCl. Within 48 h, only a few cracks were visible on the mud ball surface in the 0.3% MMH suspension, which indicates that MMH can inhibit wet bentonite for deep hydration. X-ray diffraction and particle size analyses of bentonite were conducted before and after MMH was added to illustrate the inhibition. MMH also displayed high temperature resistance in water-based drilling fluid as a shear strength-improving agent, and its dynamic plastic ratio and shear force were stable after aging at 200 °C for 16 h. Full article
(This article belongs to the Special Issue Coupled Processes in Clays: Experiments, Modeling, Applications)
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16 pages, 1416 KiB  
Article
Effect of Structural Fe Reduction on Water Sorption by Swelling and Non-Swelling Clay Minerals
by Christos Vasilopanagos, Cédric Carteret, Stephen Hillier, Anke Neumann, Harry J. L. Brooksbank and Hugh Christopher Greenwell
Minerals 2022, 12(4), 453; https://doi.org/10.3390/min12040453 - 7 Apr 2022
Cited by 4 | Viewed by 3128
Abstract
Ferruginous clay minerals in saturated soils and within hydrocarbon deposits often exist in a reduced state. Upon introduction of dissolved oxygen, or other oxidants, the clay minerals oxidise and changes in mineral surface charge and sorption capacity occur, resulting in changes in hydration [...] Read more.
Ferruginous clay minerals in saturated soils and within hydrocarbon deposits often exist in a reduced state. Upon introduction of dissolved oxygen, or other oxidants, the clay minerals oxidise and changes in mineral surface charge and sorption capacity occur, resulting in changes in hydration as well as flux of intercalated species. Here we examine the sorption of water to the Fe-containing clay minerals nontronite NAu-2 (23 wt% Fe) and illite IMt-2 (7 wt% Fe) as a function of Fe oxidation state and exchangeable cations by means of water vapour volumetry and N2 surface area analysis. The clay minerals were chemically reduced using sodium dithionite. Sorption isotherms of water vapour and nitrogen, controlled relative humidity diffractograms, and chemical analyses were recorded. The results show that, after reduction using sodium dithionite, increased amounts of water vapour and nitrogen were adsorbed to the high Fe content nontronite, despite decreased interlayer separation. Little change was observed for the non-swelling and low Fe content illite. Sodium from the reducing agent was found to exchange with calcium present in the starting clay minerals, and sodium balanced the additional mineral charge generated during reduction. The findings presented in this study deliver improved understanding of sorption at the surface of the reduced clay minerals, which aid constrain the role of clay mineral interfaces in subsurface environments. Full article
(This article belongs to the Special Issue Feature Papers in Clays and Engineered Mineral Materials)
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18 pages, 8484 KiB  
Article
Deep-Learning-Based Automatic Mineral Grain Segmentation and Recognition
by Ghazanfar Latif, Kévin Bouchard, Julien Maitre, Arnaud Back and Léo Paul Bédard
Minerals 2022, 12(4), 455; https://doi.org/10.3390/min12040455 - 7 Apr 2022
Cited by 43 | Viewed by 6243
Abstract
A multitude of applications in engineering, ore processing, mineral exploration, and environmental science require grain recognition and the counting of minerals. Typically, this task is performed manually with the drawback of monopolizing both time and resources. Moreover, it requires highly trained personnel with [...] Read more.
A multitude of applications in engineering, ore processing, mineral exploration, and environmental science require grain recognition and the counting of minerals. Typically, this task is performed manually with the drawback of monopolizing both time and resources. Moreover, it requires highly trained personnel with a wealth of knowledge and equipment, such as scanning electron microscopes and optical microscopes. Advances in machine learning and deep learning make it possible to envision the automation of many complex tasks in various fields of science at an accuracy equal to human performance, thereby, avoiding placing human resources into tedious and repetitive tasks, improving time efficiency, and lowering costs. Here, we develop deep-learning algorithms to automate the recognition of minerals directly from the grains captured from optical microscopes. Building upon our previous work and applying state-of-the-art technology, we modify a superpixel segmentation method to prepare data for the deep-learning algorithms. We compare two residual network architectures (ResNet 1 and ResNet 2) for the classification and identification processes. We achieve a validation accuracy of 90.5% using the ResNet 2 architecture with 47 layers. Our approach produces an effective application of deep learning to automate mineral recognition and counting from grains while also achieving a better recognition rate than reported thus far in the literature for this process and other well-known, deep-learning-based models, including AlexNet, GoogleNet, and LeNet. Full article
(This article belongs to the Section Mineral Exploration Methods and Applications)
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21 pages, 18453 KiB  
Article
Automated Quantitative Characterization REE Ore Mineralogy from the Giant Bayan Obo Deposit, Inner Mongolia, China
by Taotao Liu, Wenlei Song, Jindrich Kynicky, Jinkun Yang, Qian Chen and Haiyan Tang
Minerals 2022, 12(4), 426; https://doi.org/10.3390/min12040426 - 30 Mar 2022
Cited by 17 | Viewed by 4381
Abstract
Rare earth elements (REEs) are considered critical elements in modern society due to their irreplaceable role in new innovative and energy technologies. The giant carbonatite-related Bayan Obo deposit contributes most REE resources in the world’s market, while its origin is still unclear because [...] Read more.
Rare earth elements (REEs) are considered critical elements in modern society due to their irreplaceable role in new innovative and energy technologies. The giant carbonatite-related Bayan Obo deposit contributes most REE resources in the world’s market, while its origin is still unclear because of the complicated and diverse REE ore mineralogy and texture. Thescanning electron mircroscopy SEM)-based automated mineralogy allows for the numeric assessment of rocks and ores’ compositional and textural properties. Here, we use TIMA (TESCAN Integrated Mineral Analyzer) to quantitatively characterize REE ore mineralogy from the deep drill core within the H8 unit (“dolomite marble”) to better understand the deposit. The mineral composition, occurrence, and Ce elemental deportment of the borehole ores at different depths (i.e., 1107 m, 1246 m, 1406 m, 1546 m, and 1682 m) were obtained. The results show that the main types of ores in the investigated samples can be divided into banded REE-Fe ores, banded REE ores, disseminated REE-Fe ores, and veined REE ores. REE and gangue minerals vary significantly in abundance and occurrence. Monazite-(Ce) and bastnäsite-(Ce) are the primary REE host minerals, and both contribute the most to the REE budget. Other REE minerals, such as parisite-(Ce)/synchysite-(Ce), cerite-(Ce), huanghoite-(Ce)/cebaite-(Ce), and aeschynite-(Ce), are significant contributors. The gangue minerals generally include fluorite, barite, magnetite, pyrite, quartz, magnesio-arfvedsonite, and minerals of the biotite and apatite groups, among others. Combined with the newly published mineral-scale chronological and isotopic geochemical analyses, it is reasonable to conclude that the later hydrothermal fluids remobilized and redistributed the original Mesoproterozoic carbonatitic REE minerals and formed a high variable ore mineral assemblage. Furthermore, it is demonstrated that the mineralogical study using TIMA can provide accurate and reliable mineralogy data for the comprehensive interpretation of the complex REE ores, and extend our understanding of the deposit. Full article
(This article belongs to the Special Issue Ore Mineralogy and Geochemistry of Rare Metal Deposits)
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29 pages, 4586 KiB  
Article
Development and Description of a Composite Hydrogeologic Framework for Inclusion in a Geoenvironmental Assessment of Undiscovered Uranium Resources in Pliocene- to Pleistocene-Age Geologic Units of the Texas Coastal Plain
by Andrew P. Teeple, Kent D. Becher, Katherine Walton-Day, Delbert G. Humberson and Tanya J. Gallegos
Minerals 2022, 12(4), 420; https://doi.org/10.3390/min12040420 - 29 Mar 2022
Cited by 5 | Viewed by 3620
Abstract
A previously completed mineral resources assessment of the Texas Coastal Plain indicated the potential for the future discovery of uranium resources. Geoenvironmental assessments that include the hydrogeologic framework can be used as a tool to understand the potential effects of mining operations. The [...] Read more.
A previously completed mineral resources assessment of the Texas Coastal Plain indicated the potential for the future discovery of uranium resources. Geoenvironmental assessments that include the hydrogeologic framework can be used as a tool to understand the potential effects of mining operations. The hydrogeologic framework for this study focused on the composite hydrogeologic unit of the tract permissive for the occurrence of uranium consisting of the upper part of the Miocene-age Fleming Formation/Lagarto Clay, Pliocene-age Goliad and Pleistocene-age Willis Sands, Pleistocene-age Lissie and Beaumont Formations, and Holocene-age alluvial sediments (fluvial alluvium and eolian sand deposits). This composite hydrogeologic unit, which contains the Chicot and Evangeline aquifers of the Gulf Coast aquifer system, is intended for inclusion in a regional-scale geoenvironmental assessment of as yet undiscovered uranium resources. This article provides (1) a brief literature review describing the geologic and hydrogeologic settings, (2) the methodology used to develop a composite hydrogeologic framework, and (3) descriptions and maps of the land-surface altitude, composite hydrogeologic unit base and midpoint depth, water-level altitude, depth of water, unsaturated and saturated zone thickness, and transmissivity and hydraulic conductivity. A composite hydrogeologic unit, created by combining geologic and hydrogeologic data and maps for individual geologic and hydrogeologic units, is intended for use as a tool in a geoenvironmental assessment to evaluate potential contaminant migration through various avenues. Potential applications include using the hydrogeologic framework as an input into a geoenvironmental assessment to help estimate the potential for (1) runoff of contaminants into surface water, (2) infiltration of contaminants into the groundwater (aquifers), or (3) movement of contaminants from the mining area through wind, groundwater-flow, or streamflow in a given permissive tract. The procedures outlined in this paper also provide a method for developing hydrogeologic frameworks that can be applied in other areas where mining may occur. Full article
(This article belongs to the Special Issue Environmentally Sound In-Situ Recovery Mining of Uranium)
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16 pages, 3854 KiB  
Article
Steady-State Microstructures of Quartz Revisited: Evaluation of Stress States in Deformation Experiments Using a Solid-Medium Apparatus
by Ichiko Shimizu and Katsuyoshi Michibayashi
Minerals 2022, 12(3), 329; https://doi.org/10.3390/min12030329 - 6 Mar 2022
Viewed by 2835
Abstract
Dynamically recrystallizing quartz is believed to approach a steady-state microstructure, which reflects flow stress in dislocation creep. In a classic experimental study performed by Masuda and Fujimura in 1981 using a solid-medium deformation apparatus, two types of steady-state microstructures of quartz, denoted as [...] Read more.
Dynamically recrystallizing quartz is believed to approach a steady-state microstructure, which reflects flow stress in dislocation creep. In a classic experimental study performed by Masuda and Fujimura in 1981 using a solid-medium deformation apparatus, two types of steady-state microstructures of quartz, denoted as S and P, were found under varying temperature and strain rate conditions. However, the differential stresses did not systematically change with the deformation conditions, and unexpectedly high flow stresses (over 700 MPa) were recorded on some experimental runs compared with the applied confining pressure (400 MPa). Internal friction in the sample assembly is a possible cause of reported high differential stresses. Using a pyrophyllite assembly similar to that used in the previous work and setting up paired load cells above and below the sample assembly, we quantified the frictional stress acting on the sample and corrected the axial stress. The internal friction changed in a complicated manner during pressurization, heating, and axial deformation at a constant strain rate. Our results suggest that Masuda and Fujimura overestimated the differential stress by about 200 MPa in their 800 °C runs. Crystallographic fabrics in the previous experimental sample indicated that the development of elongated quartz grains, which are characteristics of Type-S microstructures, was associated with preferential growth of unfavorably oriented grains during dynamic recrystallization. Full article
(This article belongs to the Special Issue Microstructures in Quartz: Indicators for Kinematics and the Conditions for Ductile Deformation in Tectonites)
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