Minerals

21 pages, 15203 KiB

Open AccessArticle

Geological and 3D Image Analysis toward Protecting a Geosite: The Case Study of Falakra, Limnos, Greece

by Ioannis K. Koukouvelas, Aggeliki Kyriou, Konstantinos G. Nikolakopoulos, Georgios Dimaris, Ioannis Pantelidis and Harilaos Tsikos

Minerals 2025, 15(2), 148; https://doi.org/10.3390/min15020148 - 31 Jan 2025

Abstract

The Falakra geosite is located at the northern shoreline of the island of Limnos, Greece, and exhibits an array of unusual geomorphological features developed in late Cenozoic sandstones. Deposition of the primary clastic sediments was overprinted by later, low-temperature hydrothermal fluid flow and [...] Read more.

The Falakra geosite is located at the northern shoreline of the island of Limnos, Greece, and exhibits an array of unusual geomorphological features developed in late Cenozoic sandstones. Deposition of the primary clastic sediments was overprinted by later, low-temperature hydrothermal fluid flow and interstitial secondary calcite formation associated with nearby volcanic activity. Associated sandstone cannonballs take center stage in a landscape built by joints, Liesengang rings and iron (hydr)oxide precipitates, constituting an intriguing site of high aesthetic value. The Falakra geosite is situated in an area with dynamic erosion processes occurring under humid weather conditions. These have evidently sculpted and shaped the sandstone landscape through a complex interaction of wave- and wind-induced erosional processes aided by salt spray wetting. This type of geosite captivates scientists and nature enthusiasts due to its unique geological and landscape features, making its sustainable conservation a significant concern and topic of debate. Here, we provide detailed geological and remote sensing mapping of the area to improve the understanding of geological processes and their overall impact. Given the significance of the Falakra geosite as a unique tourist destination, we emphasize the importance of developing it under sustainable management. We propose the segmentation of the geosite into four sectors based on the corresponding geological features observed on site. Sector A, located to the west, is occupied by a lander-like landscape; to the southeast, sector B contains clusters of cannonballs and concretions; sector C is characterized by intense jointing and complex iron (hydr)oxide precipitation patterns, dominated by Liesengang rings, while sector D displays cannonball or concretion casts. Finally, we propose a network of routes and platforms to highlight the geological heritage of the site while reducing the impact of direct human interaction with the outcrops. For constructing the routes and platforms, we propose the use of serrated steel grating. Full article

(This article belongs to the Special Issue Application of UAV and GIS for Geosciences, 2nd Edition)

11 pages, 3068 KiB

Open AccessArticle

The Adjustment for Entrainment Behavior of Kaolinite in Coal Flotation

by Chengyong Liu, Wenzhe Gu, Haijun Zhang, Quanzhi Tian, Hainan Wang, Yuejin Zhou and Zhicheng Liu

Minerals 2025, 15(2), 147; https://doi.org/10.3390/min15020147 - 31 Jan 2025

Abstract

The entrainment of gangue particles always increases the ash content of coal flotation concentrate. In the present work, the adjustment for entrainment of kaolinite in coal flotation was studied focusing on the parameters including solid concentration and frother dosage. The results indicated that [...] Read more.

The entrainment of gangue particles always increases the ash content of coal flotation concentrate. In the present work, the adjustment for entrainment of kaolinite in coal flotation was studied focusing on the parameters including solid concentration and frother dosage. The results indicated that the ash contents of concentrates were always higher in the early or late stage (flotation time: 0–30 s or 120–180 s) than that in the middle stage (flotation time: 30–120 s). This is mainly because of the mechanical entrainment in the early stage and the entrainment caused by water transportation in the later stage. It has been confirmed that reducing the feed solid concentration and frother dosage effectively decrease mechanical entrainment in the early stage. Furthermore, better flotation results can be obtained under a high solid concentration and frother dosage in the late stage of the flotation process. Therefore, a novel two-stage flotation process was proposed for the coal flotation. A better flotation performance (combustible recovery: 91.28%; ash content: 4.09%) can be achieved by two-stage flotation, compared to the flotation results (combustible recovery: 93.12%; ash content: 5.16%) of the one-stage flotation process. Full article

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

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20 pages, 3711 KiB

Open AccessArticle

Innovative Cut-and-Fill Mining Method for Controlled Surface Subsidence and Resourceful Utilization of Coal Gangue

by Yongqiang Zhao, Yingming Yang, Zhiqiang Wang, Qingheng Gu, Shirong Wei, Xuejia Li and Changxiang Wang

Minerals 2025, 15(2), 146; https://doi.org/10.3390/min15020146 - 31 Jan 2025

Abstract

Existing coal filling mining technologies face significant challenges of controlled surface subsidence, efficient utilization of waste rock in coal mines, and a shortage of adequate filling materials. This study introduces an innovative cut-and-fill mining method designed to strategically partition the goaf into cutting [...] Read more.

Existing coal filling mining technologies face significant challenges of controlled surface subsidence, efficient utilization of waste rock in coal mines, and a shortage of adequate filling materials. This study introduces an innovative cut-and-fill mining method designed to strategically partition the goaf into cutting and filling zones. In the cutting zone, in situ filling materials are employed to construct waste rock column supports adjacent to the filling zone, thereby achieving controlled surface subsidence. This approach is integrated with long-wall mining operations and implemented using advanced, comprehensive equipment. FLAC3D simulations were conducted to investigate the patterns of stress distribution, surface deformation, and plastic zone formation within the mining field. With the implementation of the cut-and-fill mining balance, key observations include a reduction in maximum principal stress near the center of the goaf, an increasing trend in minimum principal stress, regular displacement distributions, and intact plastic zones positioned vertically away from the stope and horizontally close to the center of the stope. Compared to traditional caving methods, the cut-and-fill technique significantly reduces maximum vertical displacement, by nearly 95%, and maximum horizontal displacement, by approximately 90%. Additionally, it minimizes energy accumulation, lowers overall energy release, and prolongs the release period. Importantly, this method facilitates the resourceful utilization of approximately 800 million tons of waste rock, potentially leading to an estimated reduction of 500 million tons in CO₂ emissions. By achieving a balance of three effects—harmonizing coal extraction and filling capacity, aligning the supply and demand of filling materials, and optimizing the balance between filling costs and mining benefits—this method provides a sustainable and eco-friendly solution for the coal mining industry. The findings of this study are crucial for guiding the industry towards more environmentally responsible practices. Full article

(This article belongs to the Special Issue Advances in Mine Backfilling Technology and Materials)

23 pages, 1777 KiB

Open AccessArticle

Resistance Characteristics of Cemented High-Concentration Backfill in a Bending Pipeline: A Numerical Simulation

by Jinping Guo, Zheng Qiu, Xiaolin Wang, Qinghua Gu, Haiqiang Jiang and Shunman Chen

Minerals 2025, 15(2), 145; https://doi.org/10.3390/min15020145 - 31 Jan 2025

Abstract

With the advancement of backfill mining technology, cemented high-concentration backfill (CHB), composed of solid particles, such as high-concentration tailings or waste rock mixed with a small amount of binder, has gained widespread applications due to its superior filling performance. Given the complexity of [...] Read more.

With the advancement of backfill mining technology, cemented high-concentration backfill (CHB), composed of solid particles, such as high-concentration tailings or waste rock mixed with a small amount of binder, has gained widespread applications due to its superior filling performance. Given the complexity of the backfill pipeline network, studying the characteristics of pipe transportation is crucial. The local resistance in bending pipes represents an important parameter for CHB pipeline transportation. However, existing research on the local resistance characteristics of bending pipes lacks comprehensiveness and depth. This study proposes a novel definition of the local resistance coefficient as the ratio of pressure loss per unit length of a bend pipe compared to that of a straight pipe. Utilizing the computational fluid dynamics (CFD) method the impact of six different factors on the local resistance coefficient of the bending pipe is investigated: flow velocity, pipe diameter, slurry concentration, binder content, turning radius, and bending angle. The results indicate that the local resistance coefficient positively correlates with the flow velocity and pipe diameter but negatively correlates with the slurry concentration, turning radius, and bending angle. Among these factors, the slurry concentration exerts the most significant influence on the local resistance coefficient. The recommended approach to control the local resistance coefficient in the mine is to use CHB with a 76% solid fraction at a 1.5 m/s flow velocity, along with pipe parameters of a 0.15 m diameter, a 2.5 m turning radius, and bending angles between 90° and 150°. The findings provide a valuable reference for determining the optimal parameters for bend pipes and CHB and facilitate the theoretical calculation of resistance in complex filling pipeline networks. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling: 2nd Edition)

29 pages, 20123 KiB

Open AccessReview

Secrets from the Depths of Space and Earth: Unraveling Newly Discovered High-Pressure Polymorphs in Meteorites and Diamond Inclusions

by Dmitry Pushcharovsky and Luca Bindi

Minerals 2025, 15(2), 144; https://doi.org/10.3390/min15020144 - 31 Jan 2025

Abstract

Significant recent discoveries of a large group of high-pressure (HP) minerals are reviewed. These minerals can be classified into two genetic types: those formed in shocked meteorites and impact craters and those formed under static P-T conditions and found as inclusions in diamonds. [...] Read more.

Significant recent discoveries of a large group of high-pressure (HP) minerals are reviewed. These minerals can be classified into two genetic types: those formed in shocked meteorites and impact craters and those formed under static P-T conditions and found as inclusions in diamonds. Of particular interest are the HP-polymorphic modifications of minerals such as olivine, ilmenite, ulvöspinel, wollastonite, and feldspars. Some examples include asimowite, poirierite, ohtaniite, liuite, wangdaodeite, tschaunerite, breyite, davemaoite, lingunite, and liebermannite. Special attention is also devoted to new dense hydrous silicates, which show much better stability than other known hydrous minerals to act as water reservoirs in the early stage of Earth’s geological history. The crystal structures and compositions of these new HP-minerals provide valuable insights into the complex petrology of deep geospheres, otherwise not obtainable in laboratory experiments. Using such a rich database, further steps became appropriate and possible toward the directions of a more advanced knowledge of evolution, composition, and structure of Earth. Full article

(This article belongs to the Special Issue Crystal Structures and Phase Transitions of Minerals at Extreme Conditions, 2nd Edition)

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28 pages, 2401 KiB

Open AccessArticle

Mineral Composition and Elemental Oxide Changes in Heat-Affected Soils and the Implications on Heavy Metal Immobilization by Sewage Sludge

by Veronica Mpode Ngole-Jeme, Constance Sebola and Christophe Nsaka Ntumba

Minerals 2025, 15(2), 143; https://doi.org/10.3390/min15020143 - 31 Jan 2025

Abstract

This paper investigated how increased soil temperatures affect soil mineralogy and major and trace element oxide concentrations and the implications of these effects on the mobility of potentially toxic elements (PTEs) in heat-affected soils amended with sewage sludge. The aim was to determine [...] Read more.

This paper investigated how increased soil temperatures affect soil mineralogy and major and trace element oxide concentrations and the implications of these effects on the mobility of potentially toxic elements (PTEs) in heat-affected soils amended with sewage sludge. The aim was to determine the efficiency of sewage sludge as an immobilizer of PTEs in heat-affected PTE-contaminated soils. Soil samples were heated to 150 °C, 300 °C, 500 °C, and 750 °C and later amended with stabilized sewage sludge at different rates. The concentrations of arsenic (As), chromium (Cr), cobalt (Co), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) in the different geochemical fractions of the soils were determined before heating, after heating, and after sewage sludge application. Increased soil temperatures affected the mineral assemblage and the concentrations of some major and trace element oxides and the degree of weathering of the soils. These changes were, however, insignificant. The segregation of PTEs into the different soil geochemical fractions before and after heating varied. High soil temperatures resulted in an increase in PTE concentrations in the non-residual fractions of the soil (F1, F2, and F3) with a consequent increase in their mobility. The application of sewage sludge to heated and unheated soils reduced PTE concentrations in the F1 and F2 fractions of both soils, whereas it increased PTE concentrations in the F3 and F4 fractions by up to 30% for As and Cu, 20% for Cd, 25% for Co, 60% for Cr and Ni, 50% for Pb, and 55% for Zn. Significant immobilization of the PTEs was observed in the heat-affected soils that received higher amount of sewage sludge. Fire events could increase the mobility of PTEs in soils, but sewage sludge could still effectively immobilize these PTEs, although it needs to be applied at higher application rates. Full article

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

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43 pages, 28833 KiB

Open AccessArticle

Volcanic Response to Post-Pan-African Orogeny Delamination: Insights from Volcanology, Precise U-Pb Geochronology, Geochemistry, and Petrology of the Ediacaran Ouarzazate Group of the Anti-Atlas, Morocco

by Mohamed Achraf Mediany, Nasrrddine Youbi, Mohamed Ben Chra, Oussama Moutbir, Ismail Hadimi, João Mata, Jörn-Frederik Wotzlaw, José Madeira, Miguel Doblas, Ezz El Din Abdel Hakim Khalaf, Rachid Oukhro, Warda El Moume, Jihane Ounar, Abdelhak Ait Lahna, Moulay Ahmed Boumehdi and Andrey Bekker

Minerals 2025, 15(2), 142; https://doi.org/10.3390/min15020142 - 31 Jan 2025

Abstract

Post-collisional volcanism provides valuable insights into mantle dynamics, crustal processes, and mechanisms driving orogen uplift and collapse. This study presents geological, geochemical, and geochronological data for Ediacaran effusive and pyroclastic units from the Taghdout Volcanic Field (TVF) in the Siroua Window, Anti-Atlas Belt. [...] Read more.

Post-collisional volcanism provides valuable insights into mantle dynamics, crustal processes, and mechanisms driving orogen uplift and collapse. This study presents geological, geochemical, and geochronological data for Ediacaran effusive and pyroclastic units from the Taghdout Volcanic Field (TVF) in the Siroua Window, Anti-Atlas Belt. Two eruptive cycles are identified based on volcanological and geochemical signatures. The first cycle comprises a diverse volcanic succession of basalts, basaltic andesites, andesites, dacites, and rhyolitic crystal-rich tuffs and ignimbrites, exhibiting arc calc-alkaline affinities. These mafic magmas were derived from a lithospheric mantle metasomatized by subduction-related fluids and are associated with the gravitational collapse of the Pan-African Orogen. The second cycle is marked by bimodal volcanism, featuring tholeiitic basalts sourced from the asthenospheric mantle and felsic intraplate magmas. These units display volcanological characteristics typical of facies models for continental basaltsuccessions and continental felsic volcanoes.s. Precise CA-ID-TIMS U-Pb zircon dating constrains the volcanic activity to 575–557 Ma, reflecting an 18-million-year period of lithospheric thinning, delamination, and asthenospheric upwelling. This progression marks the transition from orogen collapse to continental rifting, culminating in the breakup of the Rodinia supercontinent and the opening of the Iapetus Ocean. The TVF exemplifies the dynamic interplay between lithospheric and asthenospheric processes during post-collisional tectonic evolution. Full article

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

12 pages, 1105 KiB

Open AccessArticle

Cyanide Storage on Ferroan Brucite (Mg_xFe_1−x(OH)₂): Implications for Prebiotic Chemistry

by Ellie K. Hara and Alexis S. Templeton

Minerals 2025, 15(2), 141; https://doi.org/10.3390/min15020141 - 31 Jan 2025

Abstract

Cyanide is a crucial reagent for the synthesis of biomolecules in prebiotic chemistry. However, effective organic synthesis requires cyanide to be concentrated. One proposed mechanism for cyanide storage and concentration on Early Earth involves the formation of aqueous ferrocyanide complexes. In basic pH [...] Read more.

Cyanide is a crucial reagent for the synthesis of biomolecules in prebiotic chemistry. However, effective organic synthesis requires cyanide to be concentrated. One proposed mechanism for cyanide storage and concentration on Early Earth involves the formation of aqueous ferrocyanide complexes. In basic pH conditions, cyanide will spontaneously form ferrocyanide complexes in the presence of aqueous Fe(II). While ferrocyanide aqueous complex formation is well defined, the potential for Fe(II)-bearing minerals to react with cyanide to form ferrocyanide complexes or store cyanide on the mineral surface has yet to be explored under prebiotically relevant conditions. In this study, we demonstrate that when cyanide interacts with ferroan brucite (Mg_xFe_1−x(OH)₂), cyanide will both form aqueous and mineral-surface-adsorbed ferrocyanide implying that there are two reservoirs that cyanide will partition into. In addition, we found that cyanide decreased the amount of hydrogen gas produced by the oxidation of ferroan brucite, indicating that cyanide alters the mineral’s redox reactivity. The cyanide adsorbed on brucite can be released by a decrease in pH, which leads to the dissolution of ferroan brucite, thus releasing the adsorbed cyanide. Our findings suggest that iron-bearing minerals may represent an overlooked storage reservoir of cyanide on Hadean Earth, potentially playing a significant role in cyanide availability for prebiotic chemistry. Full article

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

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17 pages, 1551 KiB

Open AccessArticle

Bioavailable and Bioaccessible Fractions of Potentially Toxic Elements in Copper Mining Wastes in the Southeastern Amazon

by Gabriela Vilhena de Almeida Pereira, Wendel Valter da Silveira Pereira, Sílvio Junio Ramos, José Tasso Felix Guimarães, Watilla Pereira Covre, Yan Nunes Dias and Antonio Rodrigues Fernandes

Minerals 2025, 15(2), 140; https://doi.org/10.3390/min15020140 - 30 Jan 2025

Abstract

The Brazilian Amazon presents several artisanal and industrial Cu mines that generate significant amounts of waste. The objective of this study was to evaluate the risks to the environment and human health based on the bioavailable and bioaccessible concentrations of potentially toxic elements [...] Read more.

The Brazilian Amazon presents several artisanal and industrial Cu mines that generate significant amounts of waste. The objective of this study was to evaluate the risks to the environment and human health based on the bioavailable and bioaccessible concentrations of potentially toxic elements (PTEs; Ba, Co, Cr, Cu, Mo, Ni, Pb, and Zn) in artisanal and industrial Cu mining areas in the Carajás Mineral Province (CMP), eastern Amazon. For this purpose, samples (0–20 cm depth) were collected from natural forest soils (considered as a reference), as well as areas where artisanal mining wastes (artisanal overburden–AO and artisanal rock waste–AR) and industrial mining tailings (IT) were deposited. Total PTE concentrations were obtained via acid digestion, bioavailable concentrations were obtained via sequential extraction, and oral bioaccessible concentrations were obtained via the simple bioaccessibility extraction test. Environmental indices were obtained from PTE concentrations. The results indicated contamination by elements such as Mo, Cr, Ni, and Cu, mainly in AR, which had the highest contamination levels. Sequential extraction revealed that most PTEs are in residual form, suggesting low environmental risk from the bioavailable fraction. The bioaccessible concentrations of Cr and Ni were associated with health risks for children in AR. The results of this study will be important for protecting the environment and public health in artisanal mining areas in the region. Full article

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

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21 pages, 6342 KiB

Open AccessArticle

Characteristics of Fluid Inclusions and Hydrocarbon Accumulation Stages of Carbonate Rock Reservoir: A Case Study from the Majiagou Formation Ordovician, Central and Eastern Ordos Basin

by Yanzhao Liu, Zhanli Ren, Kai Qi, Xinyun Yan, Beile Xiong, Jian Liu, Junfeng Ren, Guangyuan Xing, Mingxing Jia, Juwen Yao and Hongwei Tian

Minerals 2025, 15(2), 139; https://doi.org/10.3390/min15020139 - 30 Jan 2025

Abstract

The Ordovician carbonate formations in the Ordos Basin provide a crucial stratigraphic unit for prospective oil and gas exploration. Significant progress has been made in the exploration of natural gas within the Ordovician subsalt formations. Nonetheless, understanding its accumulating properties requires additional investigation. [...] Read more.

The Ordovician carbonate formations in the Ordos Basin provide a crucial stratigraphic unit for prospective oil and gas exploration. Significant progress has been made in the exploration of natural gas within the Ordovician subsalt formations. Nonetheless, understanding its accumulating properties requires additional investigation. Clarifying the formation periods of the carbonate rock reservoirs in the Majiagou Formation of the basin can furnish a theoretical foundation for advanced exploration of carbonate rock oil and gas. This study uses fluid inclusion petrography, laser Raman spectroscopy, and microscopic temperature measurement methods, along with information about the basin’s history of burial and thermal evolution, to look at the oil and gas charging periods of Majiagou Formation reservoir in the central-eastern basin. The results show that there are two stages of hydrocarbon inclusions. The first stage has blue fluorescence and temperature peaks between 85 and 95 °C in the central basin and between 105 and 115 °C in the eastern basin. For the second stage, no fluorescence can be observed. Meanwhile, the temperature peaks are between 175 and 185 °C in the central basin, and between 165 and 175 °C in the eastern basin. In the central part of the basin, oil charging began in the Late Triassic (231–203 Ma) and reached the gas generation stage in the Late Early Cretaceous (121–112 Ma), peaking in natural gas charging. In contrast, the reservoirs in the eastern part of the basin experienced a primary oil charging stage in the Early Jurassic (196–164 Ma) and entered the gas generation stage in the Late Early Cretaceous (110–101 Ma). The hydrocarbon charging process in the study area is mainly controlled by the thermal evolution history of the basin. The study determines that the central basin enters the threshold of hydrocarbon generation earlier than the eastern basin, leading to earlier oil and gas charging. Full article

(This article belongs to the Topic Formation Mechanism and Quantitative Evaluation of Deep to Ultra-Deep High-Quality Reservoirs)

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20 pages, 15795 KiB

Open AccessArticle

Chromogenic Mechanism and Formation of Zonal Genesis of Raspberry-Red Grossular from the Sierra de Cruces Range, Mexico

by Siyuan Wu, Siyi Zhao, Yi Zhao and Chenxi Zhang

Minerals 2025, 15(2), 138; https://doi.org/10.3390/min15020138 - 30 Jan 2025

Abstract

The raspberry-red grossular, discovered in the Sierra de Cruces in Coahuila, Mexico, is characterized by its zoned coloration, featuring a pink rim and a black mantle with a sharp color transition at the border. However, there is a notable lack of definitive and [...] Read more.

The raspberry-red grossular, discovered in the Sierra de Cruces in Coahuila, Mexico, is characterized by its zoned coloration, featuring a pink rim and a black mantle with a sharp color transition at the border. However, there is a notable lack of definitive and systematic identification characteristics pertaining to its special zones. The mineral chemical composition and chromogenic mechanism remain unsupported by empirical validation derived from specific experimental data. In this study, the gemological properties, chemical composition, and spectral characteristics are systematically analyzed to explore the chromogenic mechanism and formation of zonal genesis. The results of the X-ray diffraction pattern, Raman spectrum, and major elements’ composition show that the raspberry-red grossular samples are grossular with high purity. Mn ions are a direct coloring factor of the pink rim of the grossular samples, while Fe ions are chromogenic elements of the black mantle. The MnO content of the pink rim ranges from 0.15 wt% to 1.72 wt%. The FeO content of the black mantle ranges from 3.11 wt% to 5.09 wt%, which is generally higher than that of other parts. The trace element compositions reveal that the rim and core of samples were formed in an oxidative environment (δEu = 0.43–2.41), which could be derived from the hydrothermal metasomatic skarn (δ¹⁸O = 11.03–12.14); the mantles of samples were formed in a reducing environment (δEu = 0.42–0.85), which is consistent with the magmatic skarn (δ¹⁸O = 11.40–11.66). They also show that the surrounding rocks provide part of the compositional sources for the raspberry-red grossular and interact with the black mantle, which affects the formation of the pink rim. This study offers geological and mineral compositional insights, addressing a significant void in the study of raspberry-red grossular, and lays the foundation for follow-up investigations. Full article

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

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26 pages, 6510 KiB

Open AccessArticle

Magnetite Texture and Geochemistry in the Takab Ore Deposit (NW Iran): Implications for a Complex Hydrothermal Evolution

by Christiane Wagner, Omar Boudouma, Nicolas Rividi, Beate Orberger, Ghasem Nabatian, Maryam Honarmand and Iman Monsef

Minerals 2025, 15(2), 137; https://doi.org/10.3390/min15020137 - 29 Jan 2025

Abstract

The massive magnetite deposit from Takab (NW Iran) is hosted in amphibolite layers intercalated with the chemical and terrigenous sediments of the Takab BIF. A comprehensive textural and chemical study allowed three types of magnetite (Mt) to be distinguished. Mt1 forms large (≤1 [...] Read more.

The massive magnetite deposit from Takab (NW Iran) is hosted in amphibolite layers intercalated with the chemical and terrigenous sediments of the Takab BIF. A comprehensive textural and chemical study allowed three types of magnetite (Mt) to be distinguished. Mt1 forms large (≤1 mm) inhomogeneous grains surrounded and locally invaded by magnetite Mt2. Oscillatory zoning is present in Mt1 and Mt2. Mt3 forms bands aligned along fracture planes. Mt3 may contain hematite relicts and is porous in proximity to hematite. Mt1 shows variable and higher Si (up to 1.4 wt. %), Al, Ca, and Mg and lower Fe content (68 wt. %) than Mt2. Mt3 has the lowest Si (<0.3 wt. %) and highest Fe (71 wt. %) contents. The temperature of formation decreases from Mt1 (600 °C) to Mt2 (500–550 °C) and Mt3 (380–440 °C). Mt1 likely formed in a reducing Si-rich environment. The close spatial relationship, sharp compositional boundaries, similar crystallographic structure of Mt1 and Mt2, and porosity in Mt2 suggest a fluid-assisted coupled dissolution of Mt1 and precipitation of Mt2 (CDR process). Microfracturing allowed the penetration of oxidizing fluid and the formation of platy hematite bands. Mt3 (mushketovite) formed after hematite by interaction with a reducing lower temperature fluid through a redox transformation. Full article

(This article belongs to the Special Issue Geochemistry and Genesis of Hydrothermal Ore Deposits)

13 pages, 3416 KiB

Open AccessArticle

Palaeostomate Bryozoans from Glacial Erratics in the Tvären Region, Sweden

by Baopeng Song, Yue Liang, Lars E. Holmer, Luke C. Strotz, Junye Ma and Zhifei Zhang

Minerals 2025, 15(2), 136; https://doi.org/10.3390/min15020136 - 29 Jan 2025

Abstract

The post-impact fauna of the Dalby Limestone of Tvären Bay has been extensively examined, with the exception of the Palaeostomate bryozoan taxa present. Here, we report three palaeostomate bryozoans found in limestone boulders recovered from glacial deposits on Ringsö Island derived from Tvären [...] Read more.

The post-impact fauna of the Dalby Limestone of Tvären Bay has been extensively examined, with the exception of the Palaeostomate bryozoan taxa present. Here, we report three palaeostomate bryozoans found in limestone boulders recovered from glacial deposits on Ringsö Island derived from Tvären Bay, Sweden. The bryozoan fauna includes Pachydictya bifurcata, Hallopora sp., and Trematoporid sp. indet. Pachydictya bifurcata has bifoliate zoaria with two layers of zooecia oriented in opposite directions along the mesotheca. Hallopora sp. is characterized by the presence of mesozooecia, tubular autozooecia with rounded apertures, thin walls, and possessing diaphragms. The zoaria of Trematoporid sp. indet are loosely arranged and slightly ambiguous, but lack further identifying features. The report of Pachydictya bifurcata herein represents an extension of its stratigraphic range within the late Ordovician. These findings enhance our understanding of the bryozoan diversity in the region, providing the first detailed report of the presence of these taxa in this geological context. Full article

(This article belongs to the Special Issue Biomineralization and Biominerals: Lessons from Mineral-Producing Organisms, 2nd Edition)

20 pages, 1724 KiB

Open AccessArticle

Slag Substitution Effect on Features of Alkali-Free Accelerator-Reinforced Cemented Paste Backfill

by Ibrahim Cavusoglu

Minerals 2025, 15(2), 135; https://doi.org/10.3390/min15020135 - 29 Jan 2025

Abstract

Cemented paste backfill (CPB) improves underground stability by filling mine voids, but the high cost of cement presents economic challenges for miners. While alternative binders and admixtures have been explored, the combined impact of slag substitution and alkali-free (AF) accelerators on CPB performance [...] Read more.

Cemented paste backfill (CPB) improves underground stability by filling mine voids, but the high cost of cement presents economic challenges for miners. While alternative binders and admixtures have been explored, the combined impact of slag substitution and alkali-free (AF) accelerators on CPB performance is not yet fully understood. This study investigates the influences of slag substitution and AF accelerators on the performance of CPB through a comprehensive experimental approach. CPB samples were prepared with slag substitution ratios of 25%, 50%, and 75%, maintaining a fixed AF accelerator content of 0.4%. Various test techniques, including unconfined comprehensive strength (UCS), mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and thermal analysis (TG/DTA), were employed to study their mechanical and microstructural properties. Monitoring tests were also conducted to thoroughly assess the performance of CPB, including suction (self-desiccation), electrical conductivity (EC), and volumetric water content (VWC) tests. The results showed that the PCI50–SL50–0.4AF sample exhibited 2.3 times higher strength than the control sample for 28 days, with this improvement attributed to enhanced pozzolanic reactions contributing to better microstructural compactness. Monitoring tests revealed accelerated hydration kinetics and reduced water content in slag-reinforced CPB, highlighting the significant role of AF accelerator in facilitating rapid setting and improving early-age mechanical strength. Microstructural findings revealed that porosity decreased and C–S–H gel formation increased in the specimen containing slag and AF accelerators, contributing to increased strength and durability. These findings highlight the potential usage of slag and AF accelerators to enhance CPB’s mechanical, microstructural, and hydration properties, offering significant benefits for mining operations by improving backfill performance, while contributing to environmental sustainability through reduced cement consumption and associated CO₂ emissions. Full article

(This article belongs to the Special Issue Cemented Mine Waste Backfill: Experiment and Modelling: 2nd Edition)

25 pages, 20095 KiB

Open AccessArticle

Interpreting the Complexity of Sulfur, Carbon, and Oxygen Isotopes From Sulfides and Carbonates in a Precious Metal Epithermal Field: Insights From the Permian Drake Epithermal Au-Ag Field of Northern New South Wales, Australia

by Hongyan Quan, Ian Graham, Rohan Worland, Lewis Adler, Christian Dietz, Emmanuel Madayag, Huixin Wang and David French

Minerals 2025, 15(2), 134; https://doi.org/10.3390/min15020134 - 29 Jan 2025

Abstract

The Drake Goldfield, also known as Mount Carrington, is located in north-eastern New South Wales, Australia. It contains a number of low–intermediate-sulfidation epithermal precious metal deposits with a current total resource of 724.51 metric tons of Ag and 10.95 metric tons of Au. [...] Read more.

The Drake Goldfield, also known as Mount Carrington, is located in north-eastern New South Wales, Australia. It contains a number of low–intermediate-sulfidation epithermal precious metal deposits with a current total resource of 724.51 metric tons of Ag and 10.95 metric tons of Au. These deposits occur exclusively within the Drake Volcanics, a 60 × 20 km NW-SE trending sequence of Late Permian volcanics and related epiclastics. Drilling of the Copper Deeps geochemical anomaly suggests that the volcanics are over 600 m thick. The Drake Volcanics are centered upon a geophysical anomaly called “the Drake Quiet Zone” (DQZ), interpreted to be a collapsed volcanic caldera structure. A total of 105 fresh carbonate samples were micro-drilled from diamond drillcores from across the field and at various depths. A pXRD analysis of these carbonates identified five types as follows: ankerite, calcite, dolomite, magnesite, and siderite. Except for three outlier values (i.e., −21.32, −19.48, and 1.42 ‰), the δ¹³C_VPDBgenerally ranges from−15.06 to −5.00 ‰, which is less variable compared to the δ¹⁸O_VSMOW, which varies from −0.92 to 17.94 ‰. μ-XRF was used to analyze the elemental distribution, which indicated both syngenetic/epigenetic relationships between calcite and magnesite. In addition, a total of 53 sulfide samples (primarily sphalerite and pyrite) from diamond drillcores from across the Drake Goldfield were micro-drilled for S isotope analysis. Overall, these have a wide range in δ³⁴S_CDT values from −16.54 to 2.10 ‰. The carbon and oxygen isotope results indicate that the fluids responsible for the precipitation of carbonates from across the Drake Goldfield had complex origins, involving extensive mixing of hydrothermal fluids from several sources including those of magmatic origin, meteoric fluids and fluids associated with low-temperature alteration processes. Sulfur isotope ratios of sulfide minerals indicate that although the sulfur was most likely derived from at least two different sources; magmatic sulfur was the dominant source while sedimentary-derived sulfur was more significant for the deposits distal from the DQZ, with the relative importance of each varying from one deposit to another. Our findings contribute to a greater understanding of Au-Ag formation in epithermal environments, particularly in collapsed calderas, enhancing exploration strategies and models for ore deposition. Full article

(This article belongs to the Special Issue New Discovery and Exploration Methods of Porphyry and Epithermal Mineral Deposits)

13 pages, 23223 KiB

Open AccessArticle

Selective Flotation Separation of Chalcopyrite from Copper-Activated Pyrite and Pyrrhotite Using Oxidized Starch as Depressant

by Guangxing Bai, Chunyuan Huang, Yonghao Li and Ming Zhang

Minerals 2025, 15(2), 133; https://doi.org/10.3390/min15020133 - 29 Jan 2025

Abstract

The disadvantages of using lime to depress the flotation of copper-activated pyrite and pyrrhotite are well known. In this study, oxidized starch, prepared by the ozone nanobubble technology, was employed as an eco-friendly depressant for copper-activated pyrite and pyrrhotite in the flotation of [...] Read more.

The disadvantages of using lime to depress the flotation of copper-activated pyrite and pyrrhotite are well known. In this study, oxidized starch, prepared by the ozone nanobubble technology, was employed as an eco-friendly depressant for copper-activated pyrite and pyrrhotite in the flotation of chalcopyrite. Single mineral flotation showed that oxidized starch inhibited the flotation of copper-activated pyrite and pyrrhotite at pH 5.5 while having no significant impact on chalcopyrite flotation. Zeta potential and adsorption measurements, together with XPS analysis and EDTA extraction, were conducted to understand the mechanism underpinning the selective depression behavior of oxidized starch. It was found that oxidized starch had a stronger affinity for copper-activated pyrite and pyrrhotite than for chalcopyrite. The depression of pyrite and pyrrhotite by oxidized starch was due to the combined effect of the formation of hydrophilic Cu-starch complex and the oxidation of Cu(I) on their surfaces. Further, oxidized starch was examined in the flotation of an actual bulk sulfur concentrate where a comparable depression performance to that of lime was shown. This investigation may contribute to the greening of the chalcopyrite flotation process by demonstrating the promising potential of oxidized starch for copper-activated pyrite and pyrrhotite depression. Full article

(This article belongs to the Special Issue Flotation of Fine-Grained Minerals)

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23 pages, 7270 KiB

Open AccessArticle

Stylolites in Carbonate Rocks: Morphological Variability According to the Host Rock Texture

by Silvana Magni, Juan Diego Martín-Martín, Paul D. Bons and Enrique Gomez-Rivas

Minerals 2025, 15(2), 132; https://doi.org/10.3390/min15020132 - 29 Jan 2025

Abstract

Stylolites are ubiquitous structures in carbonates that present a variety of morphologies. Besides being important structures in terms of rock compaction and deformation, stylolites control limestone permeability, which is influenced by their morphology and arrangement in connected networks. This study characterizes stylolite morphological [...] Read more.

Stylolites are ubiquitous structures in carbonates that present a variety of morphologies. Besides being important structures in terms of rock compaction and deformation, stylolites control limestone permeability, which is influenced by their morphology and arrangement in connected networks. This study characterizes stylolite morphological parameters, such as length, thickness, filling by insoluble material, spacing and connectivity, to provide quantitative data on the relationships between stylolite morphology and carbonate host rock textures. A collection of thin sections from a variety of lithologies and geological settings was analyzed, showing that the stylolite length, thickness and morphology are interrelated and are controlled by the host rock textures. The results show that stylolite linearity, calculated as the ratio between the straight length and the length measured along the stylolite trace, varies according to the stylolite type. Higher stylolite thickness is observed in mud-dominated textures compared to grain-dominated ones but is independent of the stylolite type. There is no clear trend in terms of the amount of insoluble material collected by the stylolites and the rock texture or stylolite type. Analysis of stylolite spacing reveals that heterogeneity in grain size, grain sorting and composition controls stylolite formation. Full article

(This article belongs to the Special Issue Stylolites: Development, Properties, Inversion and Scaling)

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36 pages, 7505 KiB

Open AccessArticle

Advancing Iron Ore Grade Estimation: A Comparative Study of Machine Learning and Ordinary Kriging

by Mujigela Maniteja, Gopinath Samanta, Angesom Gebretsadik, Ntshiri Batlile Tsae, Sheo Shankar Rai, Yewuhalashet Fissha, Natsuo Okada and Youhei Kawamura

Minerals 2025, 15(2), 131; https://doi.org/10.3390/min15020131 - 29 Jan 2025

Abstract

Mineral grade estimation is a vital phase in mine planning and design, as well as in the mining project’s economic assessment. In mining, commonly accepted methods of ore grade estimation include geometrical approaches and geostatistical techniques such as kriging, which effectively capture the [...] Read more.

Mineral grade estimation is a vital phase in mine planning and design, as well as in the mining project’s economic assessment. In mining, commonly accepted methods of ore grade estimation include geometrical approaches and geostatistical techniques such as kriging, which effectively capture the spatial grade variation within a deposit. The application of machine-learning (ML) techniques has been explored in the estimation of mineral resources, where complex correlations need to be captured. In this paper, the authors developed four machine-learning regression models, i.e., support vector regression (SVR), random forest regression (RFR), k-nearest neighbour (KNN) regression, and extreme gradient boost (XGBoost) regression, using a geological database to predict the grade in an Indian iron ore deposit. When compared with ordinary kriging (R² = 0.74; RMSE = 2.09), the RFR (R² = 0.74; RMSE = 2.06), XGBoost (R² = 0.73; RMSE = 2.12), and KNN (R² = 0.73; RMSE = 2.11) regression models produced similar results. The block model predictions generated using the RFR, XGBoost, and KNN models show comparable accuracy and spatial trends to those of ordinary kriging, whereas SVR was identified as less effective. When integrated with geological methods, these models demonstrate significant potential for enhancing and optimizing mine planning and design processes in similar iron ore deposits. Full article

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

9 pages, 1401 KiB

Open AccessArticle

Pyrite–Coal Depressants Interactions During Coal Reverse Flotation

by You Zhou, Zijuan Xie, Boris Albijanic, Arturo A. García-Figueroa, Sheila Devasahayam, Bogale Tadesse and Rensheng Li

Minerals 2025, 15(2), 130; https://doi.org/10.3390/min15020130 - 29 Jan 2025

Abstract

This work investigates coal desulfurization by using reverse flotation. In this method, pyrite (the only source of sulfur in the studied coal) was separated from the meta-bituminous coal by using three different coal depressants (starch, dextrin and humic acid). A novel variable elimination [...] Read more.

This work investigates coal desulfurization by using reverse flotation. In this method, pyrite (the only source of sulfur in the studied coal) was separated from the meta-bituminous coal by using three different coal depressants (starch, dextrin and humic acid). A novel variable elimination approach was used to determine the contribution of the depressant type and the depressant concentration on the desulfurization performance. The results showed that the pyrite recoveries are influenced by the depressant type while the highest pyrite recovery was achieved in the presence of humic acid. Therefore, humic acid should be used in flotation rougher and scavenger cells in which the aim is to achieve high pyrite recovery. By contrast, the pyrite grades are affected significantly by the depressant concentration. Considering that the aim in flotation cleaner cells is to achieve high pyrite grade, any of the studied coal depressants can be successfully used but at high concentrations. This work demonstrated that the selection of flotation depressants depends on the type of flotation cells used in coal desulfurization. Full article

(This article belongs to the Special Issue Surface Chemistry and Reagents in Flotation)

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