Minerals

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21 pages, 3649 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Comparing the Performance of Hydrocyclones and High-Frequency Screens in an Industrial Grinding Circuit: Part I—Size Separation Assessments

by Bruna Silveira Costa, Maurício Guimarães Bergerman and Homero Delboni Júnior

Minerals 2024, 14(7), 707; https://doi.org/10.3390/min14070707 - 12 Jul 2024

Cited by 1 | Viewed by 1288

Abstract

Industrial ball milling circuits usually include hydrocyclones in a closed configuration to achieve a specified grinding size. Although hydrocyclones are relatively simple to operate, their classification performance is generally low, leading to significant fines recirculation within the circuit, consequently overgrinding the product. Conversely, [...] Read more.

Industrial ball milling circuits usually include hydrocyclones in a closed configuration to achieve a specified grinding size. Although hydrocyclones are relatively simple to operate, their classification performance is generally low, leading to significant fines recirculation within the circuit, consequently overgrinding the product. Conversely, high-frequency screening potentially shows a relatively higher separation efficiency, as the entrainment of fines to the coarse product is significantly reduced. The present work compares the performance of hydrocyclones—HC and high-frequency screens—HFS based on four surveys conducted in Nexa’s Vazante Zinc ore industrial grinding circuit in Vazante, Brazil, which processes zinc silicate ore. The comparisons included the partition of solids, water split, and particle size distributions. Whiten’s partition curve model was adopted to obtain the selected performance parameters through mass balancing the experimental data. The industrial surveys comprised three different size separation configurations, i.e., HC-Only, HFS-Only, and a combined HC-HFS setup. In all cases, the assessments consistently indicated higher separation performances with HFS compared to the HC operation. The final product associated with the HC+HFS configuration showed a narrower size distribution around the grinding size. Full article

(This article belongs to the Special Issue Advances in Mineral Processing and Extractive Metallurgy of Base and Precious Metals)

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20 pages, 4968 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Characterization of Incremental Markings in the Sagittal Otolith of the Pacific Sardine (Sardinops sagax) Using Different Imaging Modalities

by Kelsey C. James, Uwe Kierdorf, Victoria Cooley, Viktor Nikitin, Stuart R. Stock and Horst Kierdorf

Minerals 2024, 14(7), 705; https://doi.org/10.3390/min14070705 - 12 Jul 2024

Viewed by 4163

Abstract

Teleost fish possess calcium carbonate otoliths located in separate chambers (utriculus, sacculus, and lagena) of their membranous labyrinth. This study analyzed the surface topography of the sagittal otolith of the Pacific sardine (Sardinops sagax) and the daily and annual increments in [...] Read more.

Teleost fish possess calcium carbonate otoliths located in separate chambers (utriculus, sacculus, and lagena) of their membranous labyrinth. This study analyzed the surface topography of the sagittal otolith of the Pacific sardine (Sardinops sagax) and the daily and annual increments in these otoliths. The otolith surface, characterized by laser scanning confocal microscopy for the first time, consisted of a system of prominent ridges and valleys (grooves), but it is unclear whether these structures are functional or represent time-resolving markings reflecting growth periodicity. Within the first-year volume, daily increments, each consisting of an incremental (more mineralized) and a discontinuous (less mineralized) zone, were resolved by optical microscopy and backscattered electron (BSE) imaging in the scanning electron microscope (SEM). Daily growth increments could, however, not be resolved in volumes formed after the first year, presumably because otolith growth markedly slows down and spacing of incremental markings narrows in older fish. Throughout otolith growth, the crystalline network continues across the discontinuous zones. Fluorochrome labeling provides additional information on growth after the first year. Compared with optical and BSE imaging, synchrotron microComputed Tomography of intact otoliths (with 0.69 µm volume elements) was less able to resolve daily increments; X-ray phase contrast reconstructions provided more detail than reconstructions with absorption contrast. Future research directions are proposed. Full article

(This article belongs to the Special Issue Skeletal Tissues Mineralization)

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22 pages, 23827 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Role of Hydrocarbons in the Formation of Uranium Mineralization, Louzhuangzi District, Southern Junggar Basin (China)

by Zhong-Bo He, Bao-Qun Hu, Lin-Fei Qiu, Yun Wang, Hong Chen, Wei-Wei Jia, Yi-Fei Li, Hua-Li Ji and Man-Huai Zhu

Minerals 2024, 14(7), 709; https://doi.org/10.3390/min14070709 - 12 Jul 2024

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Abstract

In recent years, there have been important breakthroughs in the exploration for sandstone-hosted uranium (U) deposits in the Louzhuangzi district of the southern Junggar Basin. Between 2020 and 2023, a medium-sized sandstone-hosted uranium deposit production area was identified in the region. Only a [...] Read more.

In recent years, there have been important breakthroughs in the exploration for sandstone-hosted uranium (U) deposits in the Louzhuangzi district of the southern Junggar Basin. Between 2020 and 2023, a medium-sized sandstone-hosted uranium deposit production area was identified in the region. Only a few investigations have been conducted at the Louzhuangzi U deposit, including those analyzing its geological–tectonic evolution, basic geological features, hydrogeology, and ore-controlling factors. It is generally believed that uranium mineralization at the Louzhuangzi U deposit is controlled by a redox zone. Organic matter (referred to as OM hereafter) consisting of bitumen and carbonaceous debris is very common in the uranium ores (especially in high-grade ores) at the Louzhuangzi U deposit. However, the characteristics of the OM and its contribution to uranium’s mineralization have not been studied in detail. In this study, OM-rich U-ores, altered sandstone, and barren sandstone samples were collected for petrography, mineralogical, micro-spectroscopy, carbon, and sulfur isotope studies. The results of this study show that the distribution of U minerals and metal sulfides (pyrite, sphalerite, etc.) was strictly controlled by bitumen at the Louzhuangzi U deposit. The bitumen may have been formed by hydrocarbon-rich and U-rich ore-forming fluids, which were formed after hydrocarbon generation and expulsion in the underlying Jurassic coal-bearing source rocks. The fluids contained U, Zn, Fe, and other metal elements, which migrated together and then precipitated into the oxidized Toutunhe Formation sandstone through cracking and differentiation processes. Therefore, the results indicate that migrated hydrocarbons were involved in U mineralization, in addition to oxidation–reduction processes, in the Louzhuangzi district, south of the Junggar Basin (China). Full article

(This article belongs to the Special Issue Uranium: Geochemistry and Mineralogy)

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21 pages, 4452 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Crystallization Sequence of the Spodumene-Rich Alijó Pegmatite (Northern Portugal) and Related Metasomatism on Its Host Rock

by Idoia Garate-Olave, Encarnación Roda-Robles, Nora Santos-Loyola, Tania Martins, Alexandre Lima and Jon Errandonea-Martin

Minerals 2024, 14(7), 701; https://doi.org/10.3390/min14070701 - 9 Jul 2024

Cited by 1 | Viewed by 1946

Abstract

The Barroso–Alvão region is an excellent setting for studying Li mineralization associated with granitic pegmatites and developing Li exploration techniques. Among the distinguished pegmatite types in this pegmatite field, the spodumene-bearing dyke from Alijó is a representative example of an Iberian Li–Cs–Ta (LCT) [...] Read more.

The Barroso–Alvão region is an excellent setting for studying Li mineralization associated with granitic pegmatites and developing Li exploration techniques. Among the distinguished pegmatite types in this pegmatite field, the spodumene-bearing dyke from Alijó is a representative example of an Iberian Li–Cs–Ta (LCT) pegmatite currently under exploitation. In this work, we examine the internal evolution of the Alijó dyke and its external metasomatic effect on the surrounding metasediments, contributing to lithium exploration techniques. Electron microprobe analyses provided clues about the crystallization conditions and the degree of differentiation of the pegmatitic melt, whereas the external metasomatism induced by the spodumene-bearing pegmatite was studied through whole-rock geochemistry. The obtained results indicate that the primary crystallization of the studied dyke likely occurred at temperatures between 450–500 °C, with emplacement at shallow crustal levels of about 2–3 kbar. The high concentrations of trace elements such as Li, Cs, Rb, Be, Sn, Nb, Ta, Ge, U, and Tl in the pegmatitic melt suggests high availability of these elements, allowing their partitioning into an early exsolved fluid phase. The exsolution of this fluid phase, subtracting components such as F and B, from the pegmatitic melt would cause a significant undercooling of the melt. Moreover, the interaction of this expelled fluid with the country rock generated a metasomatic overprint in the surrounding metasedimentary host rocks. The metasomatic effect in Alijó is strongly influenced by the nature of the host metasediments, with a significantly higher grade of metasomatism observed in pelitic (mica-rich) samples compared to psammitic (mica-poor) samples collected at same distances from the dyke. The greisen developed close to the pegmatite contact reflects this metasomatic signature, characterized by the mobilization of at least B, F, Li, Rb, Cs, Sn, Be, Nb, Ta, and Tl. We cautiously suggest that whole rock Li concentrations greater than 300 ppm, combined with a minimum value of 1000 ppm for the sum of B, F, Li, Rb, Cs, and Sn in pelitic metasediments of Barroso–Alvão, may be indicative of a mineralized pegmatite in this region. Full article

(This article belongs to the Special Issue Rare Metal and Related Deposits: Geology, Geochemistry and Mineralization)

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16 pages, 7601 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Surface-Functionalized Nano-Montmorillonite and Its Application as Crude Oil Flow Improver

by Kechen Liu, Michal Slaný, Alena Golian-Struhárová, Hailong Wang, Liyuan Zhang, Jiyou Fu, Gang Chen and Yingna Du

Minerals 2024, 14(7), 696; https://doi.org/10.3390/min14070696 - 8 Jul 2024

Cited by 1 | Viewed by 1436

Abstract

In view of the problem of poor flowability in the production and transportation of high-wax crude oil and high-viscosity crude oil, crude oil flow improvers are commonly used to reduce their viscosity and pour point. Although polymer-based crude oil flow improvers are highly [...] Read more.

In view of the problem of poor flowability in the production and transportation of high-wax crude oil and high-viscosity crude oil, crude oil flow improvers are commonly used to reduce their viscosity and pour point. Although polymer-based crude oil flow improvers are highly effective in improving crude oil flowability, there are still problems such as high cost and the need for a large amount of solvent dilution when used. In this work, highly dispersed organic modified nano-montmorillonite was prepared by using Na-based montmorillonite and quaternary ammonium salts, and the influencing factors on the viscosity of the crude oil were investigated. The most effective modified nano-montmorillonite (B@MMT) can reduce the viscosity by 96.7% (21 °C) and depress the pour point by 15 °C. Furthermore, it has shown a high improvement in flowability in the other four different sources of crude oil, with viscosity reduction rates of 52.2, 93.4, 79.1 and 67.4%, respectively. B@MMT was characterized by FTIR, SEM, zeta potential and contact angle. Based on DSC and wax crystal structure analysis, the mechanism of the influence of B@MMT on crude oil viscosity and pour point was explored. Finally, the cost of B@MMT was estimated, and the result shows that, compared with the crude oil flow improver in use, B@MMT has considerable commercial competitive advantages. Full article

(This article belongs to the Special Issue Applications of Clay-Based Materials)

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18 pages, 11734 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Enhancing Rare Earth Element Recovery from Coal Ash Using High-Voltage Electrical Pulses and Citric Acid Leaching

by Tlek Ketegenov, Kaster Kamunur, Lyazzat Mussapyrova, Aisulu Batkal and Rashid Nadirov

Minerals 2024, 14(7), 693; https://doi.org/10.3390/min14070693 - 3 Jul 2024

Cited by 1 | Viewed by 1720

Abstract

The study investigates the application of high-voltage electrical pulses (HVEP) as a pretreatment to enhance the leaching efficiency of rare earth elements (REE) from coal ash (CA) produced from the combustion of Ekibastuz Basin coal in Almaty, Kazakhstan. HVEP treatment was applied to [...] Read more.

The study investigates the application of high-voltage electrical pulses (HVEP) as a pretreatment to enhance the leaching efficiency of rare earth elements (REE) from coal ash (CA) produced from the combustion of Ekibastuz Basin coal in Almaty, Kazakhstan. HVEP treatment was applied to the finest (<40 µm) non-magnetic fraction of CA under controlled conditions, optimizing discharge current, voltage, and treatment duration. Leaching experiments with 1 M citric acid at various solid-to-liquid ratios, temperatures, and durations were conducted on both treated and untreated samples. Results indicated that HVEP-treated CA significantly improved REE recovery rates compared to untreated samples, with optimal conditions achieving 74% cerium, 79% yttrium, and 77% lanthanum recovery. The leaching of untreated CA under the specified conditions allowed no more than 28% REE to be extracted into the solution. The leaching process was found to follow first-order kinetics, with the chemical reaction of metal dissolution being the rate-limiting step. Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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28 pages, 16832 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Tepsi Ultrabasic Intrusion, the Northern Part of the Lapland–Belomorian Belt, Kola Peninsula, Russia

by Andrei Y. Barkov, Andrey A. Nikiforov, Robert F. Martin, Sergey A. Silyanov and Boris M. Lobastov

Minerals 2024, 14(7), 685; https://doi.org/10.3390/min14070685 - 29 Jun 2024

Cited by 2 | Viewed by 1083

Abstract

The Tepsi ultrabasic body is located in the northeastern Fennoscandian Shield close to the junction of the Serpentinite Belt–Tulppio Belt (SB–TB) with suites of the Lapland–Belomorian Belt (LBB) of Paleoproterozoic age. The body is a deformed laccolith that has tectonic contacts with Archean [...] Read more.

The Tepsi ultrabasic body is located in the northeastern Fennoscandian Shield close to the junction of the Serpentinite Belt–Tulppio Belt (SB–TB) with suites of the Lapland–Belomorian Belt (LBB) of Paleoproterozoic age. The body is a deformed laccolith that has tectonic contacts with Archean rocks. Its primary textures and magmatic parageneses are widely preserved. Fine-grained olivine varies continuously from Fo_90.5 to Fo_65.4. The whole-rock variations in MgO, Fe₂O₃, SiO₂, and other geochemical data are also indicative of a significant extent of differentiation. Compositional variations were examined in the grains of calcic and Mg-Fe amphiboles, clinochlore, micas, plagioclase, members of the chromite–magnetite series, ilmenite, apatite, pentlandite, and a number of other minor mineral species. Low-sulfide disseminated Ni-Cu-Co mineralization occurred sporadically, with the presence of species enriched in As or Bi, submicrometric grains rich in Pt and Ir, or diffuse zones in pentlandite enriched in (Pd + Bi). We recognize two series: the pentlandite series (up to 2.5–3 wt.% Co) and the cobaltpentlandite series (~1 to ~8 apfu Co). The latter accompanied serpentinization. The two series display differences in their substitutions: Ni ↔ Fe and Co → (Ni + Fe), respectively. Relative enrichments in H₂O, Cl, and F, observed in grains of apatite (plus high contents of Cl in hibbingite or parahibbingite), point to the abundance of volatiles accumulated during differentiation. We provide the first documentation of scheelite grains in ultrabasic rocks, found in evolved olivine-rich rocks (Fo_77–72). We also describe unusual occurrences of hypermagnesian clinopyroxene associated with tremolite and serpentine. Abundant clusters of crystallites of diopside display a microspinifex texture. They likely predated serpentinization and formed owning to rapid crystallization in a differentiated portion of a supercooled oxidized melt or, less likely, fluid, after bulk crystallization of the olivine. We infer that the laccolithic Tepsi body crystallized rapidly, in a shallow setting, and could thus not form megacycles in a layered series or produce a well-organized structure. Our findings point to the existence of elevated PGE-Au-Ag potential in numerous ultrabasic–basic complexes of the SB–TB–LBB megastructure. Full article

(This article belongs to the Special Issue From Mantle to Market: Platinum Group Elements and Minerals and Their Geological Significance)

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15 pages, 3423 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Preparation of Humic Acid from Weathered Coal by Mechanical Energy Activation and Its Properties

by Xiujuan Feng, Rilong Xiao, Sékou Mohamed Condé, Chengliang Dong, Yanping Xun, Dalong Guo, Hui Liu, Kunpeng Liu and Mingzhi Liang

Minerals 2024, 14(7), 648; https://doi.org/10.3390/min14070648 - 25 Jun 2024

Cited by 1 | Viewed by 2160

Abstract

Humic acid (HA) is rich in functional groups with high activity, which can effectively improve the soil environment. The large reserves of weathered coal in China provide sufficient raw material guarantee for HA extraction and utilization. At present, the activation side of weathered [...] Read more.

Humic acid (HA) is rich in functional groups with high activity, which can effectively improve the soil environment. The large reserves of weathered coal in China provide sufficient raw material guarantee for HA extraction and utilization. At present, the activation side of weathered coal is still the main technical difficulty that restricts HA extraction. In this study, the weathered coal from Inner Mongolia was used as the raw material, and the mechanical energy was used to activate the weathered coal through a planetary ball mill, which improved the extraction rate of HA and optimized the molecular structure and composition of HA. The effects of four parameters, namely, ball material ratio, ball milling time, ball milling speed, and ball size, on the free HA content of weathered coal were investigated, the HA was extracted by alkaline extraction method, and the activated weathered coal and the extracted HA were characterized. The results showed that a ball material ratio of 9:1, a ball milling speed of 200 r/min, a ball milling time of 200 min, a milling ball size of Ф5:Ф10:Ф15 = 48:42:45 and 56:42:37 are the optimal parameters for the mechanical energy activation, and the HA extraction rate of activated weathered coal under these conditions reached 82.3%, which was 15% higher than that of the unactivated one. Moreover, the aroma of the ball-milled weathered coal increased, the content of oxygenated functional groups increased, and the molecular weight and aroma of HA increased. This provides scientific theoretical guidance for the preparation of HA with high aromaticity and large molecular weight from weathered coal. Full article

(This article belongs to the Special Issue Waste Minerals, Sediments and Their Environmental Mineralogy)

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20 pages, 9384 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Petrogenetic Implications of the Lithium-Rich Tongtianmiao Granite Pluton, South China: Evidence from Geochemistry and Geochronology

by Xinhui Yu, Yongzhang Zhou, Wei Cao, Hanyu Wang, Can Zhang, Lifeng Zhong, Wu Wei, Zhiqiang Wang, Jianying Yao, Zhiqiang Chen and Qinghe Xu

Minerals 2024, 14(7), 637; https://doi.org/10.3390/min14070637 - 21 Jun 2024

Viewed by 1425

Abstract

The South China Block, a region renowned for its extensive granite distribution and rich metal deposits, serves as a natural laboratory for the study of granite-related mineralization. This research focuses on the Tongtianmiao granite pluton, which is located at the intersection of the [...] Read more.

The South China Block, a region renowned for its extensive granite distribution and rich metal deposits, serves as a natural laboratory for the study of granite-related mineralization. This research focuses on the Tongtianmiao granite pluton, which is located at the intersection of the Qin-Hang and Nanling metallogenic belts and has been confirmed as a significant lithium mineral resource. Despite its discovery and ongoing development, the lithium-rich Tongtianmiao pluton has been understudied, particularly concerning its petrogenesis, which has only recently come to the forefront of scientific inquiry. By integrating an array of petrogeochemical data with geochronological studies derived from zircon and monazite dating, this study provides insights into the magmatic processes related to lithium enrichment in the Tongtianmiao granites. The Tongtianmiao granites are classified as A-type granites characterized by high SiO₂ contents (69.18–78.20 wt.%, average = 74.08 wt.%), K₂O + Na₂O contents (4.59–8.34 wt.%, average = 6.86 wt.%), A/CNK > 1.2, and low concentrations of Ca, Mg, and Fe. These granites are enriched in alkali metals such as Li, Rb, and Cs but are significantly depleted in Ba, Sr, and Eu. They show no significant fractionation of light or heavy rare-earth elements but present characteristic tetrad effects. A finding of this study is the identification of multiple ages from in situ zircon U–Pb dating, which implies a prolonged history of magmatic activity. However, given the high uranium content in zircons, which could render U–Pb ages unreliable, emphasis is placed on the monazite U–Pb ages. These ages cluster at approximately 172.1 ± 1.1 Ma and 167.9 ± 1.6 Ma, indicating a Middle Jurassic period of granite formation. This timing correlates with the retreat of the Pacific subduction plate and the associated NE-trending extensional fault activity, which likely provided favorable conditions for lithium enrichment. The study concluded that the Tongtianmiao granites were formed through partial melting of crustal materials and subsequent underplating by mantle-derived materials, and were contaminated by strata materials. This process resulted in the formation of highly differentiated granite through magmatic differentiation and external forces. These findings have significant implications for understanding the petrogenesis of lithium-rich granites and are expected to inform future exploration endeavors in the Tongtianmiao pluton. Full article

(This article belongs to the Special Issue In-Situ Microanalytical Techniques in Geological and Geochronological Research)

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12 pages, 4631 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Surface Wettability Analysis from Adsorption Energy and Surface Electrical Charge

by Chen Zhang, Xuming Wang, Lixia Li, Jan D. Miller and Jiaqi Jin

Minerals 2024, 14(6), 628; https://doi.org/10.3390/min14060628 - 20 Jun 2024

Cited by 2 | Viewed by 1809

Abstract

Surface wettability is determined by the attraction of a liquid phase to a solid surface. It is typically quantified by using contact angle measurements at mineral surfaces in the case of the flotation of mineral particles. Contact angle research to describe wettability has [...] Read more.

Surface wettability is determined by the attraction of a liquid phase to a solid surface. It is typically quantified by using contact angle measurements at mineral surfaces in the case of the flotation of mineral particles. Contact angle research to describe wettability has been investigated at different scales by sessile drop measurements, molecular dynamic simulation, and atomic force microscopy. In this study, the density functional theory (DFT) was employed for predicting the surface free energy and contact angles of a well-known hydrophobic phyllosilicate mineral talc and a well-known hydrophilic phyllosilicate mineral muscovite based on the calculated interfacial energy and surface charge. The results revealed that the predicted contact angle at the atomic scale was larger than the experimental value, and identified two interactions: electrostatic interaction and hydrogen bonding, between the hydrophilic muscovite surface and the water layer, while a water-exclusion zone of 3.346 Å was found between the hydrophobic talc surface and the first water layer. This investigation gives a new perspective for wettability determination at the atomic scale. Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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20 pages, 2190 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Quantification of Feldspar and Quartz Nucleation Delay in a Hydrous Peraluminous Granitic Melt

by Maude Bilodeau and Don R. Baker

Minerals 2024, 14(6), 611; https://doi.org/10.3390/min14060611 - 15 Jun 2024

Viewed by 1217

Abstract

A modified model based on classical nucleation theory was applied to a natural hydrous peraluminous pegmatite composition and tested against crystallization experiments in order to further investigate the quantification of nucleation delay in felsic melts. Crystallization experiments were performed in a piston-cylinder apparatus [...] Read more.

A modified model based on classical nucleation theory was applied to a natural hydrous peraluminous pegmatite composition and tested against crystallization experiments in order to further investigate the quantification of nucleation delay in felsic melts. Crystallization experiments were performed in a piston-cylinder apparatus at 630 MPa and temperatures between 650 and 1000 °C for durations ranging from 0.3 to 211 h. Experimental run products were investigated by scanning electron microscopy paired with energy dispersive spectroscopy analyses of both crystalline and quenched liquid phases, the results of which were compared to an established theoretical nucleation delay model from the literature. The experiments showed good agreement (within a factor of 5) with the model for quartz, while it showed moderate agreement (within a factor of 10) with the model for sodic feldspar. Other crystals also nucleated, demonstrating abundant features of disequilibrium. Our research further demonstrates the potential of the model to predict nucleation delay, showing promising results for the quantification of the nucleation delay of quartz and feldspar in natural felsic melts, thus adding to previously published studies on hydrous, metaluminous, felsic melts and dry basaltic melts. Full article

(This article belongs to the Special Issue Pegmatites as Hosts of Critical Metals: From Petrogenesis to Mineral Exploration)

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20 pages, 4455 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Bulk and Surface Characterization of Distinct Hematite Morphology: Implications for Wettability and Flotation Response

by Lívia Marques Faustino, Belinda McFadzean, José Tadeu Gouvêa Junior and Laurindo de Salles Leal Filho

Minerals 2024, 14(6), 609; https://doi.org/10.3390/min14060609 - 14 Jun 2024

Cited by 1 | Viewed by 1977

Abstract

To understand why hematite of different genesis behave diversely in flotation systems, this study assesses the flotation response at pH 5 of bulk (morphology, texture, Crystal Preferential Orientation (CPO)) plus interfacial (surface area, zeta potential, immersion enthalpy, contact angle, induction time) characteristics of [...] Read more.

To understand why hematite of different genesis behave diversely in flotation systems, this study assesses the flotation response at pH 5 of bulk (morphology, texture, Crystal Preferential Orientation (CPO)) plus interfacial (surface area, zeta potential, immersion enthalpy, contact angle, induction time) characteristics of species formed under distinct metamorphic conditions: low-strain deformation (Hematite-1) versus high-strain deformation (Hematite-2). Hematite-2 (predominantly composed of specular and lamellar morphologies) shows (001) CPO and exhibits fewer Fe sites on its surface that undergo doubly coordinated Fe-OH when exposed to moisture. This results in a less reactive surface associated with a less ordered adsorbed water layer than Hematite-1, which is predominantly composed of granular and sinuous hematite. Those characteristics lead to a naturally hydrophobic behavior characterized by the exothermic energy below the Critical Immersion Enthalpy (

- {∆ H}_{i m m}

< 200 mJ/m²), lower values of zeta potential due to attenuated dissociation of Fe-OH_(surf), lower induction time (47 ms vs. 128 ms), higher contact angle (39° vs. 13°), and higher flotation recovery (21% vs. 12%) than Hematite-1. Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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16 pages, 12704 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Provenance Studies of Natural Stones Used in Historical Buildings of the Peninsula de Barbanza, Galicia, Spain (North-Western Iberia)

by Ana C. Hernández, Jorge Sanjurjo-Sánchez, Carlos Alves and Carlos A. M. Figueiredo

Minerals 2024, 14(6), 595; https://doi.org/10.3390/min14060595 - 5 Jun 2024

Viewed by 1163

Abstract

Traditionally, the building stones used in the architectural heritage of Galicia (Spain) during the past were mainly extracted from quarries located in the surrounding areas of the historical buildings. Thus, a great variety of monuments were built with the same type of granite [...] Read more.

Traditionally, the building stones used in the architectural heritage of Galicia (Spain) during the past were mainly extracted from quarries located in the surrounding areas of the historical buildings. Thus, a great variety of monuments were built with the same type of granite but with different degrees of weathering depending on local conditions, geological context (facies), and period of construction. The main purpose of this work is to evaluate the probable origin of the construction materials of six historical buildings on the Barbanza Peninsula, Galicia (Spain), based on the degree of weathering and petrographic-mineralogical characteristics. The evaluation was performed on six different samples of granite according to the geological context in outcrops of places where there are old quarries. We used X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), and petrographic microscopy (PM) to attempt to address whether the origin is really local to the Barbanza Peninsula or whether the stone was brought from more distant places, based on our knowledge of the geological context of the study area. Based on the chemical, textural, and mineralogical analyses obtained, the material used for construction has a local origin and comes from small quarries spread over a wide area within the Peninsula itself. Barbanza-type granite is the most abundant within the geological context of the area and also the most used as a construction material. Other types of granites identified are the Confurco Granite and other granitoids of the Noya complex. The Chemical Alteration Index (CIA) shows low to moderate weathering in the granites, fitting petrographic observations. In monuments, samples show higher concentrations of Na and K due to salt crystallization. They show microcracks due to extraction, cutting, and finishing processes and common alteration processes of the main minerals, such as sericitization of plagioclase and chloritization of biotite. This work consists of a multidisciplinary study focused on the geological perspective for the identification and preservation of historic quarries. Knowledge of the original material also presents a unique opportunity for the restoration and/or reconstruction of monuments, which allows for the maintenance of their conceptual and constructive homogeneity. 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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10 pages, 2223 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Hydroclimate and Paleoenvironmental Variability from the Tonle Sap Lake Basin during the Angkor Period

by Xinnan Zhao, Jian Wang, Wei Zhao and Hai Cheng

Minerals 2024, 14(6), 581; https://doi.org/10.3390/min14060581 - 31 May 2024

Viewed by 984

Abstract

The profound impact of the Khmer Empire on Southeast Asia renders the Angkor Period particularly significant in guiding contemporary societies to advocate and promote policies that respond to climate change. We present a new continuous multi-proxy speleothem dataset from Tonle Sap Lake Basin, [...] Read more.

The profound impact of the Khmer Empire on Southeast Asia renders the Angkor Period particularly significant in guiding contemporary societies to advocate and promote policies that respond to climate change. We present a new continuous multi-proxy speleothem dataset from Tonle Sap Lake Basin, investigating hydroclimate variability and the paleoenvironment of Cambodia during the Angkor Period from the 9th to 15th centuries. In addition, two important climatic events on a decadal scale are clearly reconstructed. The first is the reduction of precipitation between 800 and 1000 AD and the relatively significant drought that the regional environment may have experienced from 950 to 1000 AD. The second is the anomalous wet period between 1000 and 1200 AD, during which the Southern Oscillation Index also reached its negative peak after a thousand years. The wet and dry conditions are highly consistent with the El Niño-dominated and northward Intertropical Convergence Zone. Full article

(This article belongs to the Special Issue Stalagmite Geochemistry and Its Paleoenvironmental Implication)

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25 pages, 6966 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Further on the Choice of Space Group for Scapolite Group Members and Genetic Considerations about the Si-Al Ordering in Their Framework Construction

by Vladislav Kostov-Kytin, Milen Kadiyski and Rositsa Nikolova

Minerals 2024, 14(6), 556; https://doi.org/10.3390/min14060556 - 28 May 2024

Cited by 2 | Viewed by 1577

Abstract

This paper poses a major question regarding the choice of space group for scapolite mineral group members. An artificial boundary is typically drawn between space groups I4/m and P4₂/n when solving the structures of scapolites within the [...] Read more.

This paper poses a major question regarding the choice of space group for scapolite mineral group members. An artificial boundary is typically drawn between space groups I4/m and P4₂/n when solving the structures of scapolites within the marialite–meionite series. The authors debate if solving the crystal structure in lower symmetries is justified. The choice of space group here is attributed to Si-Al ordering of the framework, and it is shown that the interstitial framework cations and anions have an accompanying role in that decision. Some answers on the ranges and limits of distribution of space groups of scapolite members in the marialite–meionite series, and the manifestations of violation of the Lowenstein rule or the so-called aluminum avoidance rule are presented. Modern physical methods (SEM-EDS and SXDA) are employed in the study to properly analyze the solid solution series in detail. New crystal–chemical data are reported for scapolite samples from different localities. An analysis was made for the types of possible Al-O-Al bonds that can occur in the structures at different Al:Si ratios and their influence on Al-Si ordering. Finally, genetic considerations about Al-Si ordering in the framework construction during the mineral formation processes are proposed. Full article

(This article belongs to the Special Issue Crystal Structure, Mineralogy, and Geochemistry of Scapolite)

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19 pages, 2575 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Recycling Feldspar Mining Waste as Buffering Agent for Acid Mine Drainage Mitigation

by Giovanni Grieco, Giuseppe Cocomazzi, Stefano Naitza, Micol Bussolesi, Matteo Luca Deidda, Elena Silvia Ferrari and Enrico Destefanis

Minerals 2024, 14(6), 552; https://doi.org/10.3390/min14060552 - 27 May 2024

Cited by 1 | Viewed by 1119

Abstract

Acid mine drainage (AMD) prevention or remediation is a major issue of the environmental management of sulfide-bearing active and abandoned mining sites, the main sources of acidic waters being wastes and tailings. The present work intends to check a circular economy approach to [...] Read more.

Acid mine drainage (AMD) prevention or remediation is a major issue of the environmental management of sulfide-bearing active and abandoned mining sites, the main sources of acidic waters being wastes and tailings. The present work intends to check a circular economy approach to such issues in the mining region of Sardinia, where environmental pollution, due to AMD, is a major concern. Tests were conducted on basic drainage-producing feldspar mining wastes that could be recycled as buffering agents of sulfide-bearing tailings. Among the sulfide-bearing abandoned mining sites investigated, Furtei epithermal gold deposit tailings are the most polluting and those that can better test the buffering agent efficacy. Buffering test results show that buffering to near-neutral conditions can be attained following steps similar to those of pure calcite buffer. The buffering potential of the recycled waste is due to both the buffer calcite content, which provides short-term buffering, enhanced by feldspar content that can provide long-term buffering. Buffered waters show a dramatic decrease in the concentration of most of the metals present in the leachate, down to conditions that meet the requirements for the discharge of industrial waters according to Italian legislation. Full article

(This article belongs to the Section Environmental Mineralogy and Biogeochemistry)

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26 pages, 7119 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Genesis of the Sartohay Podiform Chromitite Based on Microinclusions in Chromite

by Xingying Wen and Yongfeng Zhu

Minerals 2024, 14(6), 530; https://doi.org/10.3390/min14060530 - 21 May 2024

Cited by 1 | Viewed by 1281

Abstract

Here, we present a petrographic and microanalytical study of microinclusions in chromite from podiform chromitites hosted by the Sartohay ophiolitic mélange in west Junggar, northwestern China, to investigate the parental magma evolution and chromitite genesis. These silicate inclusions comprise olivine, enstatite, diopside, amphibole, [...] Read more.

Here, we present a petrographic and microanalytical study of microinclusions in chromite from podiform chromitites hosted by the Sartohay ophiolitic mélange in west Junggar, northwestern China, to investigate the parental magma evolution and chromitite genesis. These silicate inclusions comprise olivine, enstatite, diopside, amphibole, and Na-phlogopite. Their morphological characteristics suggest that most inclusions crystallized directly from the captured melt, with a few anhydrous inclusions (olivines and pyroxenes) as solid silicates trapped during the chromite crystallization. Equilibrium pressure–temperature conditions of coexisting enstatite–diopside inclusions are 8.0–21.6 kbar, and 874–1048 °C. The high Na₂O and TiO₂ contents of hydrous minerals indicate that the parental magma of chromitites was hydrous and enriched in Mg, Na, Ca, and Ti. The calculated Al₂O₃ content and FeO/MgO ratio of the parental melts in equilibrium with chromite showed MORB affinity. However, the TiO₂ values of parental melts, TiO₂ contents of chromite, and estimated fO₂ values for chromitites (1.3–2.0 log units above the FMQ buffer) evoked parental MORB-like tholeiitic melts. The composition of olivine inclusion was determined, and it was revealed that the primary melts of the Sartohay podiform chromitites had MgO contents of ~22.7 wt %. This aligns with the observed high magnesian signature in mineral inclusions (Fo = 96–98 in olivine, Mg^# = 0.91–0.97 in diopside, and Mg^# = 0.92–0.97 in enstatite). We propose that Sartohay podiform chromitites initially formed through the mixing/mingling of primary hydrous Mg-rich melt and the evolved MORB-like melt derived from the melt–peridotite reaction in the upper mantle. In this process, the continuous crystallization of chromite captured micro-silicate mineral inclusions, finally leading to the formation of the Sartohay podiform chromitites. Full article

(This article belongs to the Section Crystallography and Physical Chemistry of Minerals & Nanominerals)

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14 pages, 3682 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Selective Recovery of Gold from E-Waste Recycling Plants’ Waste Fractions: Waste-to-Resource Transition

by Svetlana Zueva, Nicolò Maria Ippolito, Marco Passadoro, Pietro Romano, Francesco Ferella and Francesco Vegliò

Minerals 2024, 14(5), 518; https://doi.org/10.3390/min14050518 - 16 May 2024

Viewed by 3410

Abstract

Electronic waste grows globally at a rate of 5% annually, which makes electronic waste recycling (WEEE recycling) an urgent task aimed at achieving (i) environmental protection and (ii) the preservation of mineral resources through the re-introduction of strategic metals into the market. As [...] Read more.

Electronic waste grows globally at a rate of 5% annually, which makes electronic waste recycling (WEEE recycling) an urgent task aimed at achieving (i) environmental protection and (ii) the preservation of mineral resources through the re-introduction of strategic metals into the market. As it turns out, WEEE recycling produces further waste, called WEEE secondary waste, which still contains valuable metals such as gold, silver, and copper. This study assessed the economic viability of recovering these metals and identified the most promising targets and approaches. WEEE secondary waste produced at a plant in southern Europe was sampled and examined for this purpose. The study methods included an ANOVA (analysis of variance) and an OCCP (orthogonal central composition plan). Over 90% gold, silver, and copper extraction was achieved with hydrochloric acid leaching in sodium hypochlorite with sodium chlorite as an oxidizing agent at 60 °C. The significance of the variation in the response for each factor, calculated using the Yates algorithm, demonstrates that by excluding sodium chloride and optimizing the doses of hydrochloric acid and sodium hypochlorite, gold can be selectively recovered through the leaching process. The scenario of HCl (2.5M)/NaClO (5%) leaching results in the maximum extraction effect of Au (91.6%) at the lowest concentrations of Ag and Cu (37–44%). Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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16 pages, 3817 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Preparation and Properties of Expansive Backfill Material Based on Municipal Solid Waste Incineration Fly Ash and Coal Gangue

by Zhen Wang, Honglin Liu, Yuanxin Zhang, Zhiwen Chen, Rumeng Zhao, Yongyong Jia, Mingchao Yong and Guodong Li

Minerals 2024, 14(5), 513; https://doi.org/10.3390/min14050513 - 14 May 2024

Cited by 1 | Viewed by 1408

Abstract

To realize the large-scale utilization of municipal solid waste incineration (MSWI) fly ash in the field of building materials and to reduce the cost of coal mine backfill mining, the effects of the mixing ratio of cementitious materials, the particle size distribution of [...] Read more.

To realize the large-scale utilization of municipal solid waste incineration (MSWI) fly ash in the field of building materials and to reduce the cost of coal mine backfill mining, the effects of the mixing ratio of cementitious materials, the particle size distribution of aggregates, and the amount and mass concentration of cementitious materials on the properties of backfill materials were experimentally investigated, and the microstructure of the hydration products was analyzed. The results showed that as the mass ratio of MSWI fly ash to bottom ash increased, the rate of expansion of the cementitious system continued to increase, and the compressive strength of the cementitious system continued to decrease. The Al (aluminum) and AlN (aluminum nitride) in the fly ash reacted with water to generate gas, causing the expansion of the cementitious materials; NaOH increased the alkalinity of the solution, which promoted the formation of more bubbles, thereby improving the expansion performance of the cementitious material. When the content of NaOH was 0.9%, the sample rate of expansion could reach 15.9%. The addition of CaCl₂ promoted the early hydration reaction of the cementitious material, forming a dense microstructure, thus improving the early strength and rate of expansion of the cementitious material. The compressive strength of the backfill body increased as the fractal dimension of the aggregate particles increased, and the particle grading scheme of group S1 was optimal. The 1-day, 3-day, and 28-day strengths of the backfill body of group S1 reached 0.72 MPa, 1.43 MPa, and 3.26 MPa, respectively. It is recommended to choose a backfill paste concentration ranging between 78.5% and 80% and a reasonable amount of cementitious material between 20% and 25%. After the MSWI fly ash was prepared as a backfill material, the leaching of potentially harmful elements in the fly ash was greatly reduced, and the concentration of dioxin was reduced to 13 ng TEQ/kg. This was attributed to the dilution of the cement, the physical encapsulation of gel products, and the isomorphous replacement of Ca²⁺ in calcium aluminate chloride hydrate. Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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15 pages, 7670 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Controls on Soft Tissue and Cellular Preservation in Late Eocene and Oligocene Vertebrate Fossils from the White River and Arikaree Groups of Nebraska, South Dakota, and Wyoming

by John E. Gallucci, Grace Woolslayer, Kelsey Barker, Brian Kibelstis, Allison R. Tumarkin-Deratzian, Paul V. Ullmann, David E. Grandstaff and Dennis O. Terry, Jr.

Minerals 2024, 14(5), 497; https://doi.org/10.3390/min14050497 - 8 May 2024

Viewed by 2552

Abstract

Previous studies on microtaphonomy have identified multiple types of organic microstructures in fossil vertebrates from a variety of time periods and past environmental settings. This study investigates potential taphonomic, paleoenvironmental, and paleoclimatic controls on soft tissue and cellular preservation in fossil bone. To [...] Read more.

Previous studies on microtaphonomy have identified multiple types of organic microstructures in fossil vertebrates from a variety of time periods and past environmental settings. This study investigates potential taphonomic, paleoenvironmental, and paleoclimatic controls on soft tissue and cellular preservation in fossil bone. To this end, fifteen vertebrate fossils were studied: eight fossils collected from the Oligocene Sharps Formation of the Arikaree Group in Badlands National Park, South Dakota, and seven fossils from formations in the underlying White River Group, including the Oligocene Brule Formation of Badlands National Park, and the Eocene Chadron Formation of Flagstaff Rim, Wyoming; Toadstool Geologic Park, Nebraska; and Badlands National Park, South Dakota. A portion of each fossil was demineralized to identify any organic microstructures preserved within the fossils. We investigated several factors which may have influenced cellular/soft tissue decay and/or preservation pathways, including taxonomic identity, paleoclimatic conditions, depositional environment, and general diagenetic history (as interpreted through thin section analysis). Soft tissue microstructures were preserved in all fossil samples, and cellular structures morphologically consistent with osteocytes were recovered from 11 of the 15 fossil specimens. Preservation of these microstructures was found to be independent of taxonomy, paleoclimate regime, apatite crystallinity, depositional environment, and general diagenetic history, indicating that biogeochemical reactions operating within microenvironments within skeletal tissues, such as within individual osteocyte lacunae or Haversian canals, may exert stronger controls on soft tissue and biomolecular decay or stabilization than external environmental (or climatic) conditions. Full article

(This article belongs to the Special Issue Recent Advances in Bone Diagenesis)

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22 pages, 15317 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A New Insight into the Genesis of Graphite Deposits in Madagascar Using U–Pb Zircon Dating and Electron Microprobe Analysis

by Ming-Jian Yang, Yong-Jun Di, Da Zhang, Da-Tian Wu, Ye Fang and Xin-Ming Zhang

Minerals 2024, 14(5), 484; https://doi.org/10.3390/min14050484 - 2 May 2024

Cited by 2 | Viewed by 2346

Abstract

Madagascar is globally recognized as an important producer of high-quality flaky graphite. However, current research on graphite deposits in Madagascar remains insufficient. Previous studies have linked the genesis of Madagascan graphite deposits to the metamorphism of sedimentary organic matter. Here, we provide a [...] Read more.

Madagascar is globally recognized as an important producer of high-quality flaky graphite. However, current research on graphite deposits in Madagascar remains insufficient. Previous studies have linked the genesis of Madagascan graphite deposits to the metamorphism of sedimentary organic matter. Here, we provide a case study of graphite deposits in Madagascar, combining new data from the Ambahita graphite deposit (AMG) in southern Madagascar with data from the Antanisoa graphite deposit (ANG) in central Madagascar and the Vohitasara graphite deposit (VOG) on the east coast of Madagascar. We note that the mineral assemblages of graphite-bearing rocks in the AMG, ANG, and VOG are not typical of metamorphic mineral assemblages but rather the results of filling and metasomatism by mantle-derived fluids that occurred after peak metamorphism. Electron microprobe analysis indicates that the graphite of the AMG, VOG, and ANG is usually associated with phlogopite or Mg-biotite; the phlogopite shares a common genesis with other widespread phlogopite deposits across Madagascar. We reveal that the distribution of graphite deposits in Madagascar is primarily controlled by ductile shear zones between blocks. Ductile shear zones that extend deep into the mantle can provide an ideal migration channel and architecture for the emplacement of mantle-derived fluids. The graphite mineralization formed no earlier than the peak metamorphism (490 Ma) and no later than the intrusion of pegmatite veins (389 ± 5 Ma). The distribution of graphite deposits, graphite orebody morphologies, mineral associations, and geochemical data suggest that the genesis of graphite deposits in Madagascar is linked to mantle-derived fluid filling rather than the metamorphism of sediments, as previously suggested. These findings have important implications for similar deposits in Madagascar and potentially globally. Full article

(This article belongs to the Special Issue Microbeam Analysis Characterization in Petrogenesis and Ore Deposit)

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17 pages, 1764 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effect of Fractionation Columns on the Elution of Rare Earth Elements Recovered from Acid Mine Drainage

by Gabriela Cordeiro Silva, Clauson Souza, Pedro Augusto Possa Vicente Sacramento Ferreira, Liliani Pacheco Tavares Nazareth and Ana Claudia Queiroz Ladeira

Minerals 2024, 14(5), 451; https://doi.org/10.3390/min14050451 - 25 Apr 2024

Viewed by 1491

Abstract

Rare earth elements (REE) can be found in expressive contents in different secondary sources, such as acid mine drainage (AMD). This work evaluated separation of light and heavy rare earth elements (REE) from an acid mine drainage (AMD) generated in a former uranium [...] Read more.

Rare earth elements (REE) can be found in expressive contents in different secondary sources, such as acid mine drainage (AMD). This work evaluated separation of light and heavy rare earth elements (REE) from an acid mine drainage (AMD) generated in a former uranium mine in Brazil by using ion exchange. This AMD presents pH 3.50, total REE content of 97 mg L⁻¹ and 1.3 g L⁻¹ of sulfate and was used in the REE loading experiments. Loading experiments were carried out in columns using a commercial strong acid cation (SAC) exchange resin. Elution was performed with 0.01 mol L⁻¹ NH₄EDTA in systems with one, two and three columns. Regarding the loading step, the resin presented a total loading capacity of 0.58 mmol g⁻¹. The resin proved to be more selective for light REE with adsorption efficiency of 78% and 48% for heavy REE. Regarding elution, high efficiencies between 90 and 100% were achieved for REE. The final REE solution is approximately 10 times more concentrated in the liquor related to the acid mine water. Better fractionation results were achieved for the system with three columns. Although the complete separation of the REE into pure elements was not possible, two distinct fractions of heavy and light REE could be obtained, and La was completely separated from the other REE. In order to improve fractionation and separate the REE into individual ones, the concentrated fractions can proceed to subsequent ion exchange systems. Full article

(This article belongs to the Special Issue Characterization and Management of Mine Waters)

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18 pages, 3115 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Influences of O₂ Availability on the Microbial Activities and Fe Transformations in the Iron Formation Caves of the Southern Espinhaço Range, Brazil

by Melissa K. Mulford, Anela Mukherjee, Augusto S. Auler, Hazel A. Barton and John M. Senko

Minerals 2024, 14(4), 425; https://doi.org/10.3390/min14040425 - 20 Apr 2024

Viewed by 1511

Abstract

Over 3000 iron formation caves (IFCs) have formed in erosion-resistant Fe(III)-rich rocks throughout Brazil. Microbial Fe(III) reduction occurs in IFCs, where a microbe-rich, Fe(III)-depleted paste (sub muros) is found behind an Fe(III)-(hydr)oxide crust in the ceiling/walls. Microbial Fe(III) reduction in sub [...] Read more.

Over 3000 iron formation caves (IFCs) have formed in erosion-resistant Fe(III)-rich rocks throughout Brazil. Microbial Fe(III) reduction occurs in IFCs, where a microbe-rich, Fe(III)-depleted paste (sub muros) is found behind an Fe(III)-(hydr)oxide crust in the ceiling/walls. Microbial Fe(III) reduction in sub muros appears to be responsible for the transformation of Fe(III) to more soluble Fe(II), which is removed, leading to cave formation. This process of biospeleogenesis is likely controlled by O₂ availability, which is linked to seasonal changes. Here, we studied the effects of alternating anoxia/oxia on the microbial community and on Fe solubility in banded iron formation (BIF), a rock type consisting of layered Fe(III)-oxide and silicate. Incubations of synthetic pore water, pulverized BIF, and sub muros were prepared and incubated under anoxia, during which BIF-Fe(III) reduction proceeded. During the Fe(III) reduction period, Firmicutes and/or Alphaproteobacteria were enriched, and genes involved in Fe(III) and sulfate reduction were detected in the metagenomes. Fe(II) oxidation genes, which were detected in the fresh sub muros, were not found. Upon the addition of atmospheric O₂, Fe(III) reduction was arrested, and incomplete Fe(II) oxidation occurred. Betaproteobacteria, Gammaproteobacteria, and Chloroflexi increased in relative abundance following aeration, and Fe(III) reduction genes were still identified. Our results demonstrate that the sub muros microbial community retains the ability to reduce Fe(III) and drive speleogenesis despite fluctuations in O₂ levels. Full article

(This article belongs to the Section Biomineralization and Biominerals)

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19 pages, 39343 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Conditions and Mechanism of Crystallization of Hydrous W-Fe Oxides with a Pyrochlore-Type of Structure (Elsmoreite Group) in the Oxidation Zone of Ore Deposits

by Mihail Tarassov and Eugenia Tarassova

Minerals 2024, 14(4), 422; https://doi.org/10.3390/min14040422 - 19 Apr 2024

Cited by 1 | Viewed by 1684

Abstract

The purpose of the article is to elucidate the conditions and mechanism of crystallization of W-Fe oxide minerals with a pyrochlore-type structure (formerly ferritungstite, now elsmoreite group minerals) based on (1) a study of representative samples of secondary tungsten minerals from the oxidation [...] Read more.

The purpose of the article is to elucidate the conditions and mechanism of crystallization of W-Fe oxide minerals with a pyrochlore-type structure (formerly ferritungstite, now elsmoreite group minerals) based on (1) a study of representative samples of secondary tungsten minerals from the oxidation zone of the Grantcharitsa tungsten deposit (Bulgaria) and (2) laboratory experiments under conditions suggested by the study of natural samples. It has been shown that crystallization of W-Fe pyrochlores occurs easily and effectively when treating WO₃·xFe₂O₃·nH₂O compounds (meymacite and tungstite) with W-Fe-containing solutions with pH 2.5–6.5 (70 °C); at the same time, direct crystallization (direct low-temperature hydrothermal synthesis) of these phases from aqueous solutions is unlikely. The crystallization of W-Fe pyrochlores under natural and laboratory conditions occurs through the oriented attachment of their nanocrystals to the {111} faces of growing crystals. The nucleation of such nanocrystals occurs in the bulk of the solution as a result of the interaction of the W-Fe solution with the W-(Fe) oxide hydrate precursor. The Fe/W ratio in the resulting W-Fe pyrochlore phase depends on the Fe/W ratio in the solution and precursor, as well as on the pH of the solution. Full article

(This article belongs to the Special Issue Mineral Evolution and Mineralization during Weathering)

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17 pages, 3673 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Application of Stacking Ensemble Learning in Predicting Copper’s Flotation Concentrate Grade

by Chengzhe Yin and Leming Ou

Minerals 2024, 14(4), 424; https://doi.org/10.3390/min14040424 - 19 Apr 2024

Cited by 1 | Viewed by 1221

Abstract

Addressing issues such as a low operational condition recognition efficiency, strong subjectivity, and significant fluctuations in Outotec X fluorescence analysis data in copper flotation production, a copper concentrate grade classification model is constructed based on image processing technology and the Stacking ensemble learning [...] Read more.

Addressing issues such as a low operational condition recognition efficiency, strong subjectivity, and significant fluctuations in Outotec X fluorescence analysis data in copper flotation production, a copper concentrate grade classification model is constructed based on image processing technology and the Stacking ensemble learning algorithm. Firstly, a feature extraction model for copper concentration flotation foam images is established, extracting color, texture, and size statistical features to build a feature dataset. Secondly, to avoid redundancy in the feature data, which could reduce model accuracy, a combined correlation feature selection is employed for dimensionality reduction, with the filtered feature subset being used as the model input. Finally, to fully leverage the strengths of each model, a Stacking ensemble learning copper concentrate grade classification model is constructed with support vector machine (SVM), random forest (RF), and adaptive boosting (AdaBoost) as base models and logistic regression (LR) as the meta-model. The experimental results show that this ensemble model achieves good recognition for different grade categories, with a precision, recall, and F1 score of 90.01%, 89.85%, and 89.93%, respectively. The accuracy of this Stacking ensemble model, with a 7% improvement over Outotec X fluorescence analysis, demonstrates a potential to meet the daily production needs of beneficiation plants. Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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15 pages, 1713 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Stability of CO₂ Fluid in Eclogitic Mantle Lithosphere: Thermodynamic Calculations

by Yulia G. Vinogradova and Anton Shatskiy

Minerals 2024, 14(4), 403; https://doi.org/10.3390/min14040403 - 15 Apr 2024

Viewed by 1256

Abstract

Findings of solid and liquefied CO₂ in diamonds from kimberlites and placers have indicated its presence in the form of a fluid phase in the Earth’s mantle at depths of 150–250 km. However, this is inconsistent with the results of experiments and [...] Read more.

Findings of solid and liquefied CO₂ in diamonds from kimberlites and placers have indicated its presence in the form of a fluid phase in the Earth’s mantle at depths of 150–250 km. However, this is inconsistent with the results of experiments and existing thermodynamic calculations. To clarify this, we carried out thermodynamic modeling of garnet–CO₂ and bimineral eclogite–CO₂ systems using the Perple_X v. 7.1.3 software package, which establishes the most thermodynamically favorable assemblages for a given bulk composition of the system, unlike previous calculations, for which the phase relationships were simply assumed. The key difference between our results and previously known data is the presence of a region of partial carbonation. In this region, the garnet and clinopyroxene of the new compositions, CO₂ fluid, carbonates, kyanite, and coesite are in equilibrium. The calculations revealed that unlike endmember systems (pyrope–CO₂ and diopside–CO₂) in the eclogite–CO₂ system, the carbonation and decarbonation lines do not coincide, and the Grt+Cpx+CO₂ and Carb+Ky+Coe+Cpx fields are separated by the Grt+Cpx+CO₂+Carb+Ky+Coe region, which extends to pressures exceeding 4.3–6.0 GPa at 1050–1200 °C. This should extend the CO₂ stability field in the eclogitic mantle to lower temperatures. Yet, owing to the short CO₂ supply in the real mantle, the CO₂ fluid should be completely spent on the carbonation of eclogite just below the eclogite + CO₂ field. Thus, according to the obtained results, the CO₂ fluid is stable in the eclogitic mantle in the diamond stability field at temperatures exceeding 1250 °C and pressures of 5–6 GPa. Full article

(This article belongs to the Section Crystallography and Physical Chemistry of Minerals & Nanominerals)

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21 pages, 3280 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Rare-Earth Element Phase Associations in Four West Virginia Coal Samples

by Rachel Yesenchak, Shikha Sharma, Christina Lopano and Scott Montross

Minerals 2024, 14(4), 362; https://doi.org/10.3390/min14040362 - 29 Mar 2024

Cited by 2 | Viewed by 1982

Abstract

Rare-earth elements are critical components of technologies used in renewable energy, communication, transportation, and national defense. Securing supply chains by developing domestic rare-earth resources, including coal and coal byproducts, has become a national priority. With some of the largest coal reserves in the [...] Read more.

Rare-earth elements are critical components of technologies used in renewable energy, communication, transportation, and national defense. Securing supply chains by developing domestic rare-earth resources, including coal and coal byproducts, has become a national priority. With some of the largest coal reserves in the country, states within the Appalachian Basin can play a key role in supplying these elements. Understanding rare-earth element phase associations and the processes that lead to enrichment in these coals will inform resource prospecting and recovery techniques. This study used sequential leaching in addition to scanning electron microscopy and energy-dispersive X-ray spectroscopy to identify rare-earth element modes of occurrence in WV coals. The results indicate that heavier elements have a stronger association with organic matter and that phosphate minerals are primary sources of both heavy and light rare-earth elements. However, these phases are shielded by a resistant aluminosilicate matrix that can impede the recovery of rare-earth elements using traditional methods. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: "Critical and Strategic Minerals")

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16 pages, 2684 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Machine-Learning Analysis of the Canadian Royalties Grinding Circuit

by Antonio Di Feo, Nasseh Khodaie, Matthieu Girard and Simon Michaud

Minerals 2024, 14(4), 356; https://doi.org/10.3390/min14040356 - 28 Mar 2024

Viewed by 1314

Abstract

This work aimed to understand the relationships between grinding variables and the P80 (80% passing size) of a grinding circuit (feed to flotation). Canadian Royalties want to obtain and reduce variations in the P80, which is currently 65 micrometres. Thus, principal component analysis [...] Read more.

This work aimed to understand the relationships between grinding variables and the P80 (80% passing size) of a grinding circuit (feed to flotation). Canadian Royalties want to obtain and reduce variations in the P80, which is currently 65 micrometres. Thus, principal component analysis (PCA), part of machine learning, was utilized to better understand the factors that significantly influence the P80. PCA is meant to be used as a guideline for plant metallurgists to determine how the grinding circuit factors influence P80; thus, the variables can be manipulated to lower P80 fluctuations. PCA revealed that the head grade of the ore (pentlandite (Pn), chalcopyrite (Cp), pyrrhotite (Po) and non-sulphide gangue (NSG)) and the primary ball mill power were weakly correlated with P80. However, the ore level in the silo, flowrate to cyclones, cyclone pressure, percent solids and the feed tonnage rate to the primary ball mill were strongly correlated with P80. This information can be used to develop a strategy to control the P80 of the grinding circuit and provide a more consistent grind size to the flotation circuit, which can positively impact metallurgical performance. Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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22 pages, 7342 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Computed Tomography of Scheelite Ore, Kara, Australia: Morphological Characterisation and Modal Mineralogy

by Leonard T. Krebbers, Julie A. Hunt and Bernd G. Lottermoser

Minerals 2024, 14(4), 345; https://doi.org/10.3390/min14040345 - 27 Mar 2024

Cited by 1 | Viewed by 3602

Abstract

Metal ores are mineralogically characterised to understand their genesis in order to allow informed decisions on mineral processing and to recognise likely environmental risks upon mining. However, standard mineralogical techniques generate only two-dimensional information at best, which in addition may be subject to [...] Read more.

Metal ores are mineralogically characterised to understand their genesis in order to allow informed decisions on mineral processing and to recognise likely environmental risks upon mining. However, standard mineralogical techniques generate only two-dimensional information at best, which in addition may be subject to sampling and stereological errors. By contrast, computed tomography (CT) is a non-destructive imaging technique that allows three-dimensional analysis of solid materials. In the present study, two ore types of the Kara Fe-W deposit (Australia) were characterised using CT to examine their mineral texture and modal mineralogy as well as scheelite distribution and ore grade (WO₃). The results show that scheelite is primarily associated with hydrous phases (e.g., epidote, chlorite, amphibole) and occurs as massive or disseminated mineral as well as vein-fill at minor and trace concentrations. This study demonstrates that CT of scheelite ore enables accurate 3D texture visualisation (volume, grain size distribution) and yields valid quantitative data on modal mineralogy and WO₃ grade of individual ore samples. Consequently, CT analysis of scheelite-bearing ore provides information relevant for ore genesis studies and comminution strategies for the possible recovery of scheelite as a by-product from metalliferous ores. Full article

(This article belongs to the Special Issue Microanalysis Applied to Mineral Deposits)

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15 pages, 10804 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Isolation and Characterization of Indigenous Ureolytic Bacteria from Mindanao, Philippines: Prospects for Microbially Induced Carbonate Precipitation (MICP)

by Kryzzyl M. Maulas, Charla S. Paredes, Carlito Baltazar Tabelin, Mark Anthony Jose, Einstine M. Opiso, Takahiko Arima, Ilhwan Park, Walubita Mufalo, Mayumi Ito, Toshifumi Igarashi, Theerayut Phengsaart, Edrhea Villas, Sheila L. Dagondon, Ephrime B. Metillo, Mylene M. Uy, Al James A. Manua and Mylah Villacorte-Tabelin

Minerals 2024, 14(4), 339; https://doi.org/10.3390/min14040339 - 26 Mar 2024

Cited by 4 | Viewed by 4339

Abstract

Microbially induced carbonate precipitation (MICP), a widespread phenomenon in nature, is gaining attention as a low-carbon alternative to ordinary Portland cement (OPC) in geotechnical engineering and the construction industry for sustainable development. In the Philippines, however, very few works have been conducted to [...] Read more.

Microbially induced carbonate precipitation (MICP), a widespread phenomenon in nature, is gaining attention as a low-carbon alternative to ordinary Portland cement (OPC) in geotechnical engineering and the construction industry for sustainable development. In the Philippines, however, very few works have been conducted to isolate and identify indigenous, urease-producing (ureolytic) bacteria suitable for MICP. In this study, we isolated seven, ureolytic and potentially useful bacteria for MICP from marine sediments in Iligan City. DNA barcoding using 16s rDNA identified six of them as Pseudomonas stutzeri, Pseudomonas pseudoalcaligenes, Bacillus paralicheniformis, Bacillus altitudinis, Bacillus aryabhattai, and Stutzerimonas stutzeri but the seventh was not identified since it was a bacterial consortium. Bio-cementation assay experiments showed negligible precipitation in the control (without bacteria) at pH 7, 8, and 9. However, precipitates were formed in all seven bacterial isolates, especially between pH 7 and 8 (0.7–4 g). Among the six identified bacterial species, more extensive precipitation (2.3–4 g) and higher final pH were observed in S. stutzeri, and B. aryabhattai, which indicate better urease production and decomposition, higher CO₂ generation, and more favorable CaCO₃ formation. Characterization of the precipitates by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and attenuated total reflectance Fourier transform spectroscopy (ATR-FTIR) confirmed the formation of three carbonate minerals: calcite, aragonite, and vaterite. Based on these results, all six identified indigenous, ureolytic bacterial species from Iligan City are suitable for MICP provided that the pH is controlled between 7 and 8. To the best of our knowledge, this is the first report of the urease-producing ability and potential for MICP of P. stutzeri, P. pseudoalcaligenes, S. stutzeri, and B. aryabhattai. Full article

(This article belongs to the Special Issue Biomineralization and MICP in Wastewater, Reclaimed Water and Seawater)

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22 pages, 5606 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fluorite and Gibbsite Solubility Controls the Vertical Transport of Fluoride and Aluminum during Rainwater Percolation through Ashfall Deposits in La Palma (Canary Islands, Spain)

by Javier Sánchez-España, Ana M. Nieto Castillo, M. Pilar Mata, Javier Martínez-Martínez and Jose F. Mediato

Minerals 2024, 14(4), 338; https://doi.org/10.3390/min14040338 - 26 Mar 2024

Viewed by 1268

Abstract

This study addresses the in situ mobility of fluoride and aluminum in two different ashfall deposits accumulated during the 2021 eruption of the Tajogaite volcano (La Palma, Canary Islands, Spain), which were exposed to contrasting conditions of ambient humidity and precipitation. We selected [...] Read more.

This study addresses the in situ mobility of fluoride and aluminum in two different ashfall deposits accumulated during the 2021 eruption of the Tajogaite volcano (La Palma, Canary Islands, Spain), which were exposed to contrasting conditions of ambient humidity and precipitation. We selected one site to the east of the volcanic emission center, located near the top of Cumbre Vieja Ridge and exposed to continuous humidity and rain, and another site to the west of the volcano situated in a lowland and characterized by much drier conditions. The mobility of fluoride and aluminum is markedly different at both sites, with the first sequence suggesting a downwards migration of Al and F, and the second sequence showing no sign of mobility. The migration of aluminum and fluorine results from the dissolution of different fluoride salts (mostly AlF₃ and CaF₂, as suggested by scanning electron microscopy) followed by vertical transport as ionic complexes (AlF₃, AlF₂⁺, AlF₄⁻) during the percolation of rainwater through the ashfall deposits. Geochemical calculations suggest that the mobility of fluorine at neutral to alkaline conditions (pH 7.0–9.0) is likely limited by the solubility of fluorite (CaF₂), whereas at slightly acidic conditions (pH < 6.5), the aqueous concentration of aluminum seems to be controlled by the solubility of gibbsite (Al(OH)₃). This study demonstrates that aluminum and fluoride can be transported from volcanic ash to the underlying soil or groundwater, which is an environmental concern that should be followed in the future. Full article

(This article belongs to the Section Environmental Mineralogy and Biogeochemistry)

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33 pages, 11185 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Evaluation of Coarse Gold-Bearing Conglomerate Mineralisation at Beatons Creek, Pilbara, Western Australia: Sampling for Resource Development and Grade Control

by Simon C. Dominy, Janice C. Graham and Ian M. Glacken

Minerals 2024, 14(4), 337; https://doi.org/10.3390/min14040337 - 25 Mar 2024

Cited by 2 | Viewed by 1809

Abstract

Many styles of gold mineralisation are challenging to sample because of the presence of coarse gold and a high spatial heterogeneity. The coarse gold-bearing conglomerates of the Beatons Creek deposit provide some challenges related to the presence of gold particles up to 8 [...] Read more.

Many styles of gold mineralisation are challenging to sample because of the presence of coarse gold and a high spatial heterogeneity. The coarse gold-bearing conglomerates of the Beatons Creek deposit provide some challenges related to the presence of gold particles up to 8 mm and gold particle clusters (up to 500 mm³) at low in situ grades (<2 g/t Au). Novo has attempted to address these issues over the last six years of exploration, resource development and mining. The Beatons Creek open pit operation was the first Pilbara conglomerate-hosted gold deposit to go into production. Between January 2021 and September 2022, it produced 2.5 Mt at 1.2 g/t Au for 87,300 oz Au recovered. Gold is present within a matrix of multiple, narrow-stacked oxide and fresh (sulphide) conglomeritic reef horizons, which are interbedded with unmineralised conglomerate, sandstones and grits. It is strongly associated with detrital pyrite and authigenic nodules. Several sampling techniques have been applied across the project, including diamond core and RC drilling, trench channel sampling and bulk sampling. Assay methods applied include fire assay, screen fire assay, LeachWELL™ and more recently PhotonAssay™. The dominant sampling protocol applied for resource development and grade control utilised 0.5 m length RC samples; a 50% rig split (c. 8.5 kg) and laboratory crushing to 3 mm, followed by a 2.5 kg split and total assay via PhotonAssay™. For part of the 2022 RC programme, the detectORE™ technique was used to screen primary RC samples and reduce the feed to the laboratory. Novo operated a sampling and assay programme that aimed to reduce the impact of coarse gold on sample and assay preparation biases and to improve estimation. Full article

(This article belongs to the Section Mineral Exploration Methods and Applications)

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14 pages, 6131 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Eddavidite, Cu₁₂Pb₂O₁₅Br₂, a New Mineral Species, and Its Solid Solution with Murdochite, Cu₁₂Pb₂O₁₅Cl₂

by Melli Rosenblatt, Marcus J. Origlieri, Richard Graeme III, Richard Graeme IV, Douglas Graeme and Robert T. Downs

Minerals 2024, 14(3), 307; https://doi.org/10.3390/min14030307 - 15 Mar 2024

Viewed by 1825

Abstract

Eddavidite is a new mineral species (IMA2018-010) with ideal formula, Cu₁₂Pb₂O₁₅Br₂, and cubic Fm

\bar{3}

m symmetry: a = 9.2407(9) Å; V = 789.1(2) Å³; Z = 2. Eddavidite is the bromine [...] Read more.

Eddavidite is a new mineral species (IMA2018-010) with ideal formula, Cu₁₂Pb₂O₁₅Br₂, and cubic Fm

\bar{3}

m symmetry: a = 9.2407(9) Å; V = 789.1(2) Å³; Z = 2. Eddavidite is the bromine analog of murdochite, Cu₁₂Pb₂O₁₅Cl₂, with which it forms a solid solution series. The type locality is the Southwest mine, Bisbee, Cochise County, Arizona, U.S.A. Eddavidite also occurs in the Ojuela mine, Mapimí, Durango, Mexico. Eddavidite occurs as domains within mixed murdochite–eddavidite crystals. The empirical formula, normalized to 12 Cu apfu, is Cu₁₂(Pb_1.92Fe_0.06Si_0.06)(O_15.08F_0.02)-(Br_0.99Cl_0.89☐_0.12). Type locality samples contain up to 67% eddavidite component, while Ojuela mine samples contain up to 62%. Mixed eddavidite–murdochite crystals show forms {100} and {111}; the habit grades from cubic through cuboctahedral to octahedral. Mixed eddavidite–-murdochite crystals exhibit good cleavage on {111}. Eddavidite is black, opaque with submetallic luster, and visually indistinguishable from intergrown murdochite. Its Mohs hardness is 4; d_meas. = 6.33 g/cm³, d_calc. = 6.45 g/cm³. The crystal structure, refined to R = 0.0112, consists of corner-sharing square planar CuO₄ units, arranged in Cu₁₂O₂₄ metal oxide clusters, which encapsulate Br atoms. PbO₈ cubes share edges with Cu₁₂O₂₄ clusters in a continuous framework. Eddavidite incorporates bromine remaining after desiccation of paleo-seawater at its two known localities, which were both once situated along the Western Interior Seaway. Full article

(This article belongs to the Collection New Minerals)

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15 pages, 13206 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Immobilization Forms of Cadmium and Mercury in a Potassium-Activated Metakaolin-Based Geopolymer

by Pramesti Prihutami, Raudhatul Islam Chaerun, Yusuke Ohya, Tsubasa Otake, Ryosuke Kikuchi and Tsutomu Sato

Minerals 2024, 14(3), 311; https://doi.org/10.3390/min14030311 - 15 Mar 2024

Cited by 3 | Viewed by 1969

Abstract

Previous studies of cadmium and mercury immobilization in geopolymers have produced inconsistent results due to their different pozzolans, metal concentrations, and mixing procedures. Understanding the effects of these parameters on heavy metal immobilization is key to predicting their long-term stability. In this study, [...] Read more.

Previous studies of cadmium and mercury immobilization in geopolymers have produced inconsistent results due to their different pozzolans, metal concentrations, and mixing procedures. Understanding the effects of these parameters on heavy metal immobilization is key to predicting their long-term stability. In this study, cadmium and mercury were incorporated into a metakaolin-based K-activated geopolymer by three mixing procedures and concentrations of 0.02–1.00 wt.%. The samples were then immersed in water for 90 d to determine their stability. The results show that mercury is readily leached from the geopolymer, but cadmium is retained. Adding the heavy metals in salt form converts the metals into cadmium hydroxide and mercury oxide that reside at the bottom of the geopolymer. Mixing the salts with water forms soluble heavy metals prior to geopolymerization. This procedure produces more-homogeneous geopolymers. Cadmium is associated with silicate and aluminate, giving a better stability, whereas mercury forms mercury oxide. Different cadmium and mercury concentrations do not change the metal speciation as mercury is affected by relativistic contribution. Full article

(This article belongs to the Special Issue Environmental Mineralogy, 2nd Edition)

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18 pages, 2471 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Linear Correlations of Gibbs Free Energy of REE Phosphates (Monazite, Xenotime, and Rhabdophane) and Internally Consistent Binary Mixing Properties

by Ruiguang Pan, Alexander P. Gysi, Artas Migdisov, Lei Gong, Peng Lu and Chen Zhu

Minerals 2024, 14(3), 305; https://doi.org/10.3390/min14030305 - 14 Mar 2024

Cited by 3 | Viewed by 2052

Abstract

Rare Earth Elements (REE) phosphates (monazite, xenotime, and rhabdophane) are critical REE-bearing minerals typically formed in hydrothermal and magmatic ore deposits. The thermodynamic properties of those REE minerals are crucial to understanding the solubility, speciation, and transport of REE complexes. However, the standard-state [...] Read more.

Rare Earth Elements (REE) phosphates (monazite, xenotime, and rhabdophane) are critical REE-bearing minerals typically formed in hydrothermal and magmatic ore deposits. The thermodynamic properties of those REE minerals are crucial to understanding the solubility, speciation, and transport of REE complexes. However, the standard-state Gibbs free energy of formation (∆G°_f) values reported for these minerals in the literature vary by up to 25 kJ mol⁻¹. Here, we present linear free energy relationships that allow the evaluation and estimation of the ∆G°_f values at 25 °C and 1 bar for the three minerals from the ionic radius (r_REE³⁺) and the non-solvation Gibbs free energy contribution to the REE³⁺ aqua ion (∆G°_n_{, REE}³⁺): ∆G°_f_,monazite − 399.71 r_REE³⁺ = 1.0059 ∆G°_n_,REE³⁺ − 2522.51; ∆G°_f_,xenotime − 344.08 r_REE³⁺ = 0.9909 ∆G°_n_,REE³⁺ − 2451.53; and ∆G°_f_,rhabdophane − 416.17 r_REE³⁺ = 1.0067 ∆G°_n_{, REE}³⁺ − 2688.86. Moreover, based on the new dataset derived for REE end-members, we re-fitted the binary Margules parameter (W) from previous theoretical calculations into linear correlations: W + 0.00204 ∆G°^’_n_,monazite = 39.3549 ∆V + 0.0641; W + 0.00255 ∆G°^’_n_,xenotime = 25.4885 ∆V − 0.0062. The internally consistent thermodynamic properties of these REE phosphates are incorporated into the computer program Supcrtbl, which is available online at Zhu’s research website. Full article

(This article belongs to the Section Mineral Geochemistry and Geochronology)

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23 pages, 24301 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Numerical Simulation and Optimization of Screening Process for Vibrating Flip-Flow Screen Based on Discrete Element Method–Finite Element Method–Multi-Body Dynamics Coupling Method

by Ningning Xu, Xinwen Wang, Dongdong Lin and Weiran Zuo

Minerals 2024, 14(3), 278; https://doi.org/10.3390/min14030278 - 6 Mar 2024

Cited by 4 | Viewed by 2048

Abstract

Vibrating flip-flow screens are widely employed in the deep screening processes of coal washing, solid waste treatment, metallurgy, and other fields, playing a crucial role in enhancing product quality and production efficiency. The screen surface and material movement of vibrating flip-flow screens are [...] Read more.

Vibrating flip-flow screens are widely employed in the deep screening processes of coal washing, solid waste treatment, metallurgy, and other fields, playing a crucial role in enhancing product quality and production efficiency. The screen surface and material movement of vibrating flip-flow screens are highly complex, and there is currently insufficient understanding of their screening mechanism, limiting further optimization and application. In this paper, the Discrete Element Method (DEM), Finite Element Method (FEM), and Multi-Body Dynamics (MBD) were integrated to establish a numerical coupling model for vibrating flip-flow screens, considering material loads, screen surface deformation, and screen machine dynamics. The Response Surface Method was utilized to analyze the significant impact of relative amplitude, tension amount, amplitude of driving screen frame, vibration frequency, and screen surface inclination on screening efficiency and material velocity. The results indicate that the most significant factor influencing the screening of flip-flow screens is the screen surface inclination. Based on a BP neural network, a five-degree-of-freedom inclination surrogate model for flip-flow screens was established. The whale algorithm was employed for multi-objective optimization of the surrogate model, resulting in a screen surface inclination distribution that meets the requirements of different operating conditions. Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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18 pages, 35994 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Case History of Graphite Exploration in North Norway Integrating Various Geophysical Surveys

by Vikas Chand Baranwal, Jan Steinar Rønning, Bjørn Eskil Larsen, Yang Su, Bo Zhang, Yunhe Liu, Xiuyan Ren, Håvard Gautneb and Jomar Gellein

Minerals 2024, 14(3), 266; https://doi.org/10.3390/min14030266 - 2 Mar 2024

Cited by 5 | Viewed by 2853

Abstract

Graphite is considered to be one of Europe’s most critical minerals. It is necessary for the transition from hydrocarbon fuel to electricity due to its use in batteries that power electronic devices and electric transport. In the past, high-quality exposed graphite was found [...] Read more.

Graphite is considered to be one of Europe’s most critical minerals. It is necessary for the transition from hydrocarbon fuel to electricity due to its use in batteries that power electronic devices and electric transport. In the past, high-quality exposed graphite was found in Norway without today’s advanced geophysical and geological methods. Norway is a key destination in Europe for graphite production. With an increasing demand for graphite, there have been efforts to systematically survey the country using modern geophysical and geological methods to find hidden graphite deposits. Among the various geophysical survey methods, electrical and electromagnetic (EM) methods are the first choice for the exploration of graphite due to the material’s high electrical conductivity. Airborne surveys are often used to cover a large area for a regional reconnaissance survey to locate the sites with potential mineral deposits before performing ground geophysical and geological surveys. Therefore, frequency-domain helicopter EM (HEM) and airborne magnetic surveys were performed in Northern Norway to locate interesting anomalies which were followed by ground surveys such as electrical resistivity tomography (ERT), charged-potential (CP), self-potential (SP), ground EM, and geological surveys. Some locations were also investigated with drilling and petrophysical core-sample analysis. In this paper, we present helicopter EM and magnetic data, 3D inversion of HEM data, and a successful ground follow-up survey result from the Vesterålen district in Northern Norway. The HEM survey identified previously known and new graphite occurrences, both partially exposed or buried, which were confirmed using ground surveys, drilling, and laboratory analysis of the samples. Full article

(This article belongs to the Special Issue Using Geophysical Inversion for Mineral Exploration: Methods and Applications)

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23 pages, 3152 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Deformation and Transformation Textures in the NaMgF₃ Neighborite—Post-Perovskite System

by Estelle E. Ledoux, Michael Jugle, Stephen Stackhouse and Lowell Miyagi

Minerals 2024, 14(3), 250; https://doi.org/10.3390/min14030250 - 28 Feb 2024

Viewed by 1508

Abstract

The D″ region of the lower mantle, which lies just above the core–mantle boundary, is distinct from the bulk of the lower mantle in that it exhibits complex seismic heterogeneity and seismic anisotropy. Seismic anisotropy in this region is likely to be largely [...] Read more.

The D″ region of the lower mantle, which lies just above the core–mantle boundary, is distinct from the bulk of the lower mantle in that it exhibits complex seismic heterogeneity and seismic anisotropy. Seismic anisotropy in this region is likely to be largely due to the deformation-induced texture (crystallographic preferred orientation) development of the constituent mineral phases. Thus, seismic anisotropy can provide a marker for deformation processes occurring in this dynamic region of the Earth. Post-perovskite-structured (Mg,Fe)SiO₃ is believed to be the dominant mineral phase in many regions of the D”. As such, understanding deformation mechanisms and texture development in post-perovskite is important for the interpretation of observed seismic anisotropy. Here, we report on high-pressure diamond anvil cell deformation experiments on NaMgF₃ neighborite (perovskite structure) and post-perovskite. During deformation, neighborite develops a 100 texture, as has been previously observed, both in NaMgF₃ and MgSiO₃ perovskite. Upon transformation to the post-perovskite phase, an initial texture of {130} at high angles to compression is observed, indicating that the {100} planes of perovskite become the ~{130} planes of post-perovskite. Further compression results in the development of a shoulder towards (001) in the inverse pole figure. Plasticity modeling using the elasto-viscoplastic self-consistent code shows this texture evolution to be most consistent with deformation on (001)[100] with some contribution of glide on (100)[010] and (001)<110> in NaMgF₃ post-perovskite. The transformation and deformation mechanisms observed in this study in the NaMgF₃ system are consistent with the behavior generally observed in other perovskite–post-perovskite systems, including the MgSiO₃ system. This shows that NaMgF₃ is a good analog for the mantle bridgmanite and MgSiO₃ post-perovskite. Full article

(This article belongs to the Special Issue Phase Transitions and Physical Properties of Minerals under Extreme Conditions of Pressure and Temperature)

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23 pages, 19609 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Transformation of the Geological Environment under the Influence of Liquid Radioactive Waste (Russian Experience in Studying Historical Nuclear Disposal)

by Victoria Krupskaya, Sergey Zakusin and Mikhail Chernov

Minerals 2024, 14(3), 252; https://doi.org/10.3390/min14030252 - 28 Feb 2024

Viewed by 1424

Abstract

Due to various historical events, in the Russian Federation, in addition to the radioactive waste storage facilities used in world practice, there are various nuclear and radiation hazardous facilities that require special procedures for monitoring and decommissioning. One of these facilities is the [...] Read more.

Due to various historical events, in the Russian Federation, in addition to the radioactive waste storage facilities used in world practice, there are various nuclear and radiation hazardous facilities that require special procedures for monitoring and decommissioning. One of these facilities is the disposal site for LRW on the territory of the JSC Siberian Chemical Plant, where specially prepared waste is injected into sand reservoirs lying at depths of 300–350 m between clayey strata. This study examines in detail the features of the lithological and mineral composition of reservoir sands and aquitards. The processes of environmental transformation in reservoir sands, which lead to changes in the composition and structure of rocks, were characterized. These processes manifest themselves in the form of the development of leaching zones and their “healing” with newly formed smectite, the destruction of terrigenous grains, including the development of cracks, and the growth of newly formed smectite in the pore space of reservoirs. The forms of occurrence and localization of authigenic smectite formed as a result of technogenic impact are described. It has been shown that, despite the obvious impact of highly reactive solutions accompanying liquid radioactive waste, the insulating properties of the geological environment are maintained and even improved to some extent. Full article

(This article belongs to the Special Issue Adsorption Properties and Environmental Applications of Clay Minerals)

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18 pages, 3761 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Determining the Metabolic Processes of Metal-Tolerant Fungi Isolated from Mine Tailings for Bioleaching

by Rosina Nkuna and Tonderayi S. Matambo

Minerals 2024, 14(3), 235; https://doi.org/10.3390/min14030235 - 26 Feb 2024

Cited by 3 | Viewed by 1881

Abstract

This study examined the metal tolerance and organic acid-producing capabilities of fungal isolates from South African tailings to assess their potential for future bioleaching applications. Four isolates were chosen for additional examination based on their capacity to generate organic acids and tolerance to [...] Read more.

This study examined the metal tolerance and organic acid-producing capabilities of fungal isolates from South African tailings to assess their potential for future bioleaching applications. Four isolates were chosen for additional examination based on their capacity to generate organic acids and tolerance to metals. In terms of tolerance to Al, Zn, Ni, and Cr, these four isolates—Trichoderma, Talaromyces, Penicillium_3, and Penicillium_6—displayed varying degrees of resistance, with Trichoderma displaying a better metal tolerance index. The growth rates under metal stress varied among the isolates, with Trichoderma displaying the highest growth rates. In high-performance liquid chromatography results, citric acid emerged as the primary organic acid produced by the four isolates, with Trichoderma achieving the highest yield in the shortest timeframe. Gas chromatography–mass spectrometry results showed that the citric acid cycle is one of the main pathways for organic acid production, though other pathways related to lipid biosynthesis and carbohydrate metabolism also play significant roles. Three compounds involved in furfural breakdown were abundant. Using KEGG, a link between these compounds and the citric acid cycle was established, where their breakdown generates an intermediate of the citric acid cycle. Full article

(This article belongs to the Special Issue Bioremediation of Contaminants in Mine Areas)

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20 pages, 12869 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Grinding of Australian and Brazilian Iron Ore Fines for Low-Carbon Production of High-Quality Oxidised Pellets

by Wuju Zhang, Qi Zhou, Jian Pan, Deqing Zhu and Congcong Yang

Minerals 2024, 14(3), 236; https://doi.org/10.3390/min14030236 - 26 Feb 2024

Cited by 3 | Viewed by 2698

Abstract

Oxidised pellets have become an indispensable high-quality charge for blast furnaces. Nevertheless, high-quality pellet feeds are becoming scarcer and scarcer. To broaden the range of sources of pellet feeds and reduce the production cost of pellets, more steel mills are predicted to use [...] Read more.

Oxidised pellets have become an indispensable high-quality charge for blast furnaces. Nevertheless, high-quality pellet feeds are becoming scarcer and scarcer. To broaden the range of sources of pellet feeds and reduce the production cost of pellets, more steel mills are predicted to use coarse iron ore fines with a relatively low iron grade and low impurities for the preparation of desirable pellet feeds through a typical wet grinding–settling–filtering process. In this work, the grinding, settling and filtering behaviour of Brazilian and Australian iron ore fines are studied and compared, with the aim of discovering the internal relationship between the mineralogical characteristics of different iron ore types and their grinding–settling–filtering performance. Additionally, the effects of ore blending on pellet preparation were investigated. The results show that, usually, the higher the hardness of the iron ore, the more grinding energy is required. Australian and Brazilian ore fines exhibit good grindability, with a Bond work index of about 10–15 kW·h/t. Furthermore, ore blending can reduce grinding energy consumption and improve settling and filtration rates, and the addition of finely ground Australian ores improves the balling performance of pellet mixtures. At the same bentonite content, the ball drop strength of the three blends with added Australian ore is significantly higher than that of the base blend, and the fired pellets obtained from Blend 1, Blend 2 and Blend 3 blends exhibit good metallurgical properties. Full article

(This article belongs to the Special Issue Advances in Pyrometallurgy of Minerals and Ores)

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15 pages, 2175 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Inversion for 3D Conductivity and Chargeability Models Using EM Data Acquired by the New Airborne TargetEM System in Ontario, Canada

by Leif H. Cox, Michael S. Zhdanov and Alexander Prikhodko

Minerals 2024, 14(3), 237; https://doi.org/10.3390/min14030237 - 26 Feb 2024

Cited by 3 | Viewed by 1710

Abstract

This paper introduces an original approach to the joint inversion of airborne electromagnetic (EM) data for three-dimensional (3D) conductivity and chargeability models using hybrid finite difference (FD) and integral equation (IE) methods. The inversion produces a 3D model of physical parameters, which includes [...] Read more.

This paper introduces an original approach to the joint inversion of airborne electromagnetic (EM) data for three-dimensional (3D) conductivity and chargeability models using hybrid finite difference (FD) and integral equation (IE) methods. The inversion produces a 3D model of physical parameters, which includes conductivity, chargeability, time constant, and relaxation coefficients. We present the underlying principles of this approach and an example of a high-resolution inversion of the data acquired by a new active time domain airborne EM system, TargetEM, in Ontario, Canada. The new TargetEM system collects high-quality multicomponent data with low noise, high power, and a small transmitter–receiver offset. This airborne system and the developed advanced inversion methodology represent a new effective method for mineral resource exploration. Full article

(This article belongs to the Section Mineral Exploration Methods and Applications)

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23 pages, 14713 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effect of Low Viscosity Contrast between Quartz and Plagioclase on Creep Behavior of the Mid-Crustal Shear Zone

by Hiroto Endo, Katsuyoshi Michibayashi, Takamoto Okudaira and David Mainprice

Minerals 2024, 14(3), 229; https://doi.org/10.3390/min14030229 - 24 Feb 2024

Cited by 4 | Viewed by 1889

Abstract

Ultramylonites are among the most extreme fault rocks that commonly occur in the mid-crustal brittle–plastic transition and are mainly characterized by intensely sheared fine-grained microstructures and well-mixed mineral phases. Although the deformation mechanism of ultramylonites is key to understanding the rheological behavior of [...] Read more.

Ultramylonites are among the most extreme fault rocks that commonly occur in the mid-crustal brittle–plastic transition and are mainly characterized by intensely sheared fine-grained microstructures and well-mixed mineral phases. Although the deformation mechanism of ultramylonites is key to understanding the rheological behavior of the mid-crustal shear zone, their microstructural development is still controversial owing to their intensely fine-grained textures. To investigate the possible crustal deformation mechanisms, we studied 13 mylonites obtained from the Kashio shear zone along the Median Tectonic Line that is the largest strike-slip fault in Japan. In particular, we investigated various mixed quartz–plagioclase layers developed within tonalitic mylonite, which are representative of the common mean grain size and crystal fabric of quartz among the studied samples. A high-quality phase-orientation map obtained by electron backscattered diffraction showed not only a wide range of quartz–plagioclase mixing (10%–80% in quartz modal composition) but also revealed a correlation between grain size reduction and crystal fabric weakening in quartz, indicating a change in the deformation mechanism from dislocation creep to grain-size-sensitive creep in the mixed quartz-plagioclase layers. In contrast, plagioclase showed an almost consistent fine grain size and weak to random crystal fabrics regardless of modal composition, indicating that grain size-sensitive creep is dominant. Combined with laboratory-determined flow laws, our results show that the Kashio shear zone could have developed under deformation mechanisms in which the viscosities of quartz and plagioclase are nearly comparable, effectively within 10¹⁷–10¹⁹ Pa·s, thereby possibly enabling extensive shearing along the Median Tectonic Line. Full article

(This article belongs to the Section Crystallography and Physical Chemistry of Minerals & Nanominerals)

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14 pages, 3657 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Microwave Treatment of Minerals and Ores: Heating Behaviors, Applications, and Future Directions

by Jin Chen, Xinpei Li, Lei Gao, Shenghui Guo and Fei He

Minerals 2024, 14(3), 219; https://doi.org/10.3390/min14030219 - 21 Feb 2024

Cited by 12 | Viewed by 4868

Abstract

The application of microwave technology in mineral metallurgy is a transformative approach to ore processing that offers new ideas about the current progressive depletion of resources and the environmental impact of mineral processing. This review delves into the principles, applications, and future directions [...] Read more.

The application of microwave technology in mineral metallurgy is a transformative approach to ore processing that offers new ideas about the current progressive depletion of resources and the environmental impact of mineral processing. This review delves into the principles, applications, and future directions of microwave treatment in mineral and ore processing. Microwave technology, characterized by its unique advantages such as rapid and uniform heating, selective heating, and energy efficiency, stands in contrast to traditional heating methods. It directly interacts with materials at the molecular level, enabling volumetric heating. The review encompasses a wide range of applications, including ore pre-treatment, drying, mineral processing, hydrometallurgy, smelting, and reduction. It highlights the role of microwave treatment in enhancing metal recovery, reducing energy consumption, and improving processing speeds. Future research directions are identified, focusing on enhanced equipment design, process optimization, integration with conventional methods, and technological innovations. The comprehensive overview assists researchers, engineers, and decision-makers in understanding the potential of microwave technology in mineral metallurgy, emphasizing its contribution to innovation and sustainability in the sector. Full article

(This article belongs to the Special Issue Microwave Treatment of Minerals and Ores: Heating Behaviours, Applications and Future Directions)

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28 pages, 7482 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Coupled Microstructural EBSD and LA-ICP-MS Trace Element Mapping of Pyrite Constrains the Deformation History of Breccia-Hosted IOCG Ore Systems

by Samuel Anthony King, Nigel John Cook, Cristiana Liana Ciobanu, Kathy Ehrig, Yuri Tatiana Campo Rodriguez, Animesh Basak and Sarah Gilbert

Minerals 2024, 14(2), 198; https://doi.org/10.3390/min14020198 - 15 Feb 2024

Cited by 4 | Viewed by 2849

Abstract

Electron backscatter diffraction (EBSD) methods are used to investigate the presence of microstructures in pyrite from the giant breccia-hosted Olympic Dam iron–oxide copper gold (IOCG) deposit, South Australia. Results include the first evidence for ductile deformation in pyrite from a brecciated deposit. Two [...] Read more.

Electron backscatter diffraction (EBSD) methods are used to investigate the presence of microstructures in pyrite from the giant breccia-hosted Olympic Dam iron–oxide copper gold (IOCG) deposit, South Australia. Results include the first evidence for ductile deformation in pyrite from a brecciated deposit. Two stages of ductile behavior are observed, although extensive replacement and recrystallization driven by coupled dissolution–reprecipitation reaction have prevented widespread preservation of the earlier event. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) element maps of pyrite confirm that many pyrite grains display compositional zoning with respect to As, Co, and Ni, but that the zoning is often irregular, patchy, or otherwise disrupted and are readily correlated with observed microstructures. The formation of ductile microstructures in pyrite requires temperatures above ~260 °C, which could potentially be related to heat from radioactive decay and fault displacements during tectonothermal events. Coupling EBSD methods with LA-ICP-MS element mapping allows a comprehensive characterization of pyrite textures and microstructures that are otherwise invisible to conventional reflected light or BSE imaging. Beyond providing new insights into ore genesis and superimposed events, the two techniques enable a detailed understanding of the grain-scale distribution of minor elements. Such information is pivotal for efforts intended to develop new ways to recover value components (precious and critical metals), as well as remove deleterious components of the ore using low-energy, low-waste ore processing methods. Full article

(This article belongs to the Special Issue Microanalysis Applied to Mineral Deposits)

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20 pages, 15919 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Temporal Distribution of the Host Rocks to Gold, the Archean Witwatersrand Basin, South Africa

by Neil Phillips, Julian Vearncombe, Dave Craw and Arthur Day

Minerals 2024, 14(2), 199; https://doi.org/10.3390/min14020199 - 15 Feb 2024

Cited by 4 | Viewed by 3727

Abstract

The hosts to gold around the Witwatersrand Basin span over 400 my, through 14 km of stratigraphy in a variety of host rocks and in tectonic settings that include periods of rifting, thermal subsidence, foreland basin, flood basalt outpouring, graben development, and further [...] Read more.

The hosts to gold around the Witwatersrand Basin span over 400 my, through 14 km of stratigraphy in a variety of host rocks and in tectonic settings that include periods of rifting, thermal subsidence, foreland basin, flood basalt outpouring, graben development, and further thermal subsidence. A geological model that assumes placer processes to explain this diversity implies a super-long-lived and special source of the detrital gold, transport, and highly effective sorting processes over a time span of 400 my. There is no evidence of a special source and sorting over such a long time period. In the Phanerozoic, this would be equivalent to the special source and sorting processes operating continually over an equivalent period of geological time spanning from the Devonian up until the present day; this is as yet recognised nowhere else on the planet. With regard to the geological model that assumes a placer process, this is untenable because of these scientific shortcomings and its lack of success in exploration. A better use of funds may be to consider alternative approaches and epigenetic models in exploration. Full article

(This article belongs to the Special Issue Geological, Structural, Geochemical, Hyperspectral, and Geostatistical Modeling for Mineral Exploration)

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33 pages, 4723 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Beneficiation of High-Density Tantalum Ore in the REFLUX™ Concentrating Classifier Analysed Using Batch Fractionation Assay and Density Data

by Simon M. Iveson, Nicolas Boonzaier and Kevin P. Galvin

Minerals 2024, 14(2), 197; https://doi.org/10.3390/min14020197 - 14 Feb 2024

Cited by 1 | Viewed by 1721

Abstract

A laboratory-scale REFLUX™ Concentrating Classifier was operated in continuous mode to beneficiate a sub 0.100 mm tantalum ore with a head grade of 0.56 wt.% Ta. The unit incorporated a lower section with a reduced diameter to accommodate a low yield. At a [...] Read more.

A laboratory-scale REFLUX™ Concentrating Classifier was operated in continuous mode to beneficiate a sub 0.100 mm tantalum ore with a head grade of 0.56 wt.% Ta. The unit incorporated a lower section with a reduced diameter to accommodate a low yield. At a yield to underflow product of 4.0 wt.%, a product grade of 13.3 wt.% was achieved (23.7 upgrade) at a recovery of 88.3%. Samples of the feed, product and reject were then fractionated in a batch REFLUX™ Classifier unit using dense lithium heteropolytungstate (LST) solution into 11 fractions. Each of these fractions was then screened into seven size intervals and analysed by pycnometry and X-ray fluorescence (XRF). Most of the material was found to reside in four relatively narrow density bands. A new analysis based on the recovery of selected tracer elements showed that the partition curve had good closure at both ends and that the density cut point and Ep both increased with decreasing particle size. For the +0.045 mm material, the density cut point was estimated to be around 3952 kg/m³ with an Ep of 317 kg/m³, but it was expected that this new method could overestimate Ep. An alternative novel approach for estimating the partition performance was developed. This method estimated the cut point and Ep values to be 3764 kg/m³ and 107 kg/m³, respectively. However, sensitivity analysis found that due to the near total absence of material in the density range from 3400 kg/m³ to 4700 kg/m³, the Ep could likely lie anywhere in the range from 0 to 250 kg/m³. The methodology proved useful in establishing these limitations in the analysis. Full article

(This article belongs to the Section Mineral Processing and Extractive Metallurgy)

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29 pages, 7624 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Chemical and Textural Peculiarities of Zircon from Peralkaline Granites and Quartz-Bearing Syenites

by Karel Breiter, Jindřich Kynický and Zuzana Korbelová

Minerals 2024, 14(2), 187; https://doi.org/10.3390/min14020187 - 10 Feb 2024

Viewed by 1930

Abstract

Zircon from four plutons of peralkaline granites and quartz-bearing syenites, differing in geotectonic positions, petrological and mineralogical compositions, and contents of volatile and trace elements, was studied using SEM, CL, and EPMA with the intention to define typical textural and chemical features of [...] Read more.

Zircon from four plutons of peralkaline granites and quartz-bearing syenites, differing in geotectonic positions, petrological and mineralogical compositions, and contents of volatile and trace elements, was studied using SEM, CL, and EPMA with the intention to define typical textural and chemical features of zircon from peralkaline rocks. In strongly peralkaline Na-pyroxene-bearing rocks represented by the Khan Bogd and Khalzan Buregte plutons (Mongolia), the primary zircon is scarce or missing. Most zircon grains are secondary, originating in hydrothermal stage from primary Zr silicates. They often form globular or radial aggregates. Chemical compositions of zircon in these rocks typically show high contents of Y, moderate contents of REE (thus high Y/Yb values) together with low contents of U and Th and low analytical totals. In mildly peralkaline mica-bearing rocks represented by Ivigtut stock (Groenland) and Madeira pluton (Brazil), the exclusive primary Zr mineral is zircon, mostly of orthomagmatic origin. Its analytical totals approach 100 wt%, enrichment in HREE, resulting in low Y/Yb values, is typical. Zircon populations from two types of peralkaline granitoids can be distinguished from each other and from zircon from S-type granites based on combination of the Zr/Hf, Y/Yb, and U/Th values, or on the Y-Hf-P ternary diagram. Full article

(This article belongs to the Section Mineral Geochemistry and Geochronology)

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15 pages, 2827 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Interactions of Perrhenate (Re(VII)O₄⁻) with Fe(II)-Bearing Minerals

by Anthony W. N. Kilber, Maxim I. Boyanov, Kenneth M. Kemner and Edward J. O’Loughlin

Minerals 2024, 14(2), 181; https://doi.org/10.3390/min14020181 - 7 Feb 2024

Cited by 3 | Viewed by 1774

Abstract

Rhenium (Re) is an extremely rare element, with a crustal abundance of approximately 0.4 parts per billion (ppb) and a sea water concentration of 8.3 parts per trillion (ppt). However, Re concentrations in anoxic marine sediments range from 2 to 184 ppb, which [...] Read more.

Rhenium (Re) is an extremely rare element, with a crustal abundance of approximately 0.4 parts per billion (ppb) and a sea water concentration of 8.3 parts per trillion (ppt). However, Re concentrations in anoxic marine sediments range from 2 to 184 ppb, which is attributed to reduction of the highly soluble perrhenate ion (Re(VII)O₄⁻) to insoluble Re(IV) species. Anoxic sediments typically contain Fe(II) and sulfide species, which could potentially reduce Re(VII) to Re(IV). In this study, we examined the interactions of KReO₄ with magnetite (Fe₃O₄), siderite (FeCO₃), vivianite (Fe₃(PO₄)₂•8H₂O), green rust (mixed Fe(II)/Fe(III) layered double hydroxide), mackinawite (FeS), and chemically reduced nontronite (NAu-1) using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to determine the valence state and speciation of Re. Uptake of Re by green rust was rapid, with ~50% associated with the solids within 2 days. In contrast, there was <10% uptake by the other Fe(II) phases over 48 days. Reduction of Re(VII) to Re(IV) was only observed in the presence of green rust, producing clusters of bidentate-coordinated Re(IV)O₆ octahedra.. These results suggest that except for green rust, the potential for other Fe(II)-bearing minerals to act as reductants for ReO₄⁻ in sedimentary environments requires further investigation. Full article

(This article belongs to the Special Issue Redox Reactivity of Iron Minerals in the Geosphere, 2nd Edition)

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22 pages, 6645 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Mineral Chemistry of Olivine, Oxy-Spinel, and Clinopyroxene in Lavas and Xenoliths from the Canary, Azores, and Cape Verde Islands (Macaronesia, North Atlantic Ocean): New Data and Comparisons with the Literature

by Federica Zaccarini, Giorgio Garuti, Reinhard Moser, Constantinos Mavrogonatos, Panagiotis Voudouris, Adriano Pimentel and Sabrina Nazzareni

Minerals 2024, 14(2), 161; https://doi.org/10.3390/min14020161 - 1 Feb 2024

Viewed by 2802

Abstract

An electron microprobe study was carried out on olivine, clinopyroxene, and oxy-spinel occurring in basalts and dunite xenoliths from the archipelagos of the Azores, the Canary Islands, and Cape Verde. By comparing our results with previously published data from the volcanic islands of [...] Read more.

An electron microprobe study was carried out on olivine, clinopyroxene, and oxy-spinel occurring in basalts and dunite xenoliths from the archipelagos of the Azores, the Canary Islands, and Cape Verde. By comparing our results with previously published data from the volcanic islands of Macaronesia, we confirmed the validity of the compositions of olivine, clinopyroxene, and oxy-spinel as geochemical tracers. The origin of olivine, i.e., crystallized in the lithospheric mantle or in volcanic rocks, was successfully discriminated. Olivine from Lanzarote dunite xenoliths, which represent fragments of the mantle transported to the surface by host magmas, exhibited higher Fo% values (Fo_91.02 to Fo_91.94) and a different distribution of minor elements Ca, Ni, and Mn (CaO up to 0.42 wt%, NiO 0.07–0.41 wt%, MnO 0.06–0.3 wt%) when compared with olivine occurring as phenocrysts in basaltic lavas from the Macaronesian islands. The highly variable forsterite contents (Fo_75.1 to Fo_94.4) in olivine from gabbro and peridotite xenoliths found across the islands of Macaronesia were attributed to fractional crystallization that started in a deep magma reservoir, suggesting that these xenoliths represent cumulate rocks and not mantle fragments. Alternatively, these xenoliths may have been affected by the interaction with metasomatic fluids. The composition of clinopyroxene phenocrysts was used to decipher formation conditions under extensional tectonics. Their composition suggests that the host lavas have an alkaline to calc-alkaline signature. Furthermore, clinopyroxene euhedral shapes and compositions suggest an origin by fractional crystallization in a closed magmatic system. The composition alone of oxy-spinel from Macaronesian basalts and xenoliths was not sufficient to draw conclusions about the geodynamic environment where they were formed. Nevertheless, the relationship between oxy-spinel and olivine crystallized in equilibrium was successfully used as oxybarometers and geothermometers. The oxy-spinel–olivine pairs show evidence that the basaltic lavas were crystallized from melts with higher oxygen fugacity and different cooling histories than those of the mantle xenoliths, as the latter crystallized and re-equilibrated much slower than the basalts. Full article

(This article belongs to the Special Issue Submarine Volcanism, Related Hydrothermal Systems and Mineralizations)

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