Minerals

28 pages, 27259 KiB

Open AccessEditor’s ChoiceArticle

Data-Driven Predictive Modelling of Mineral Prospectivity Using Machine Learning and Deep Learning Methods: A Case Study from Southern Jiangxi Province, China

by Tao Sun, Hui Li, Kaixing Wu, Fei Chen, Zhong Zhu and Zijuan Hu

Minerals 2020, 10(2), 102; https://doi.org/10.3390/min10020102 - 24 Jan 2020

Cited by 142 | Viewed by 12141

Abstract

Predictive modelling of mineral prospectivity, a critical, but challenging procedure for delineation of undiscovered prospective targets in mineral exploration, has been spurred by recent advancements of spatial modelling techniques and machine learning algorithms. In this study, a set of machine learning methods, including [...] Read more.

Predictive modelling of mineral prospectivity, a critical, but challenging procedure for delineation of undiscovered prospective targets in mineral exploration, has been spurred by recent advancements of spatial modelling techniques and machine learning algorithms. In this study, a set of machine learning methods, including random forest (RF), support vector machine (SVM), artificial neural network (ANN), and a deep learning convolutional neural network (CNN), were employed to conduct a data-driven W prospectivity modelling of the southern Jiangxi Province, China. A total of 118 known W occurrences derived from long-term exploration of this brownfield area and eight evidential layers of multi-source geoscience information related to W mineralization constituted the input datasets. This provided a data-rich foundation for training machine learning models. The optimal configuration of model parameters was trained by a grid search procedure and validated by 10-fold cross-validation. The resulting predictive models were comprehensively assessed by a confusion matrix, receiver operating characteristic curve, and success-rate curve. The modelling results indicate that the CNN model achieves the best classification performance with an accuracy of 92.38%, followed by the RF model (87.62%). In contrast, the RF model outperforms the rest of ML models in overall predictive performance and predictive efficiency. This is characterized by the highest value of area under the curve and the steepest slope of success-rate curve. The RF model was chosen as the optimal model for mineral prospectivity in this region as it is the best predictor. The prospective zones delineated by the prospectivity map occupy 9% of the study area and capture 66.95% of the known mineral occurrences. The geological interpretation of the model reveals that previously neglected Mn anomalies are significant indicators. This implies that enrichment of ore-forming material in the host rocks may play an important role in the formation process of wolframite and can represent an innovative exploration criterion for further exploration in this area. Full article

(This article belongs to the Special Issue Geological Modelling, Volume II)

► Show Figures

Figure 1

17 pages, 5026 KiB

Open AccessEditor’s ChoiceArticle

Origin and Evolution of High-Mg Carbonatitic and Low-Mg Carbonatitic to Silicic High-Density Fluids in Coated Diamonds from Udachnaya Kimberlite Pipe

by Nikolai Gubanov, Dmitry Zedgenizov, Igor Sharygin and Alexey Ragozin

Minerals 2019, 9(12), 734; https://doi.org/10.3390/min9120734 - 28 Nov 2019

Cited by 17 | Viewed by 3808

Abstract

Microinclusions of high-density fluids (HDFs) were studied in coated diamonds from the Udachnaya kimberlite pipe (Siberian craton, Russia). The presence of C-centers in the coats testifies to their formation shortly before kimberlite eruption, whereas the cores have much longer mantle residence in chemically [...] Read more.

Microinclusions of high-density fluids (HDFs) were studied in coated diamonds from the Udachnaya kimberlite pipe (Siberian craton, Russia). The presence of C-centers in the coats testifies to their formation shortly before kimberlite eruption, whereas the cores have much longer mantle residence in chemically different mantle substrates, i.e., peridotite-type (P-type) and eclogite-type (E-type). The carbon isotope composition indicates an isotopically homogeneous carbon source for coats and a heterogeneous source for cores. Microinclusions in the coats belong to two groups: high-Mg carbonatitic and low-Mg carbonatitic to silicic. A relationship was found between high-Mg carbonatitic HDFs and peridotitic host rocks and between low-Mg carbonatitic to silicic and eclogites. The composition of high-Mg carbonatitic HDFs with a “planed” trace-element pattern can evolve to low-Mg carbonatitic to silicic during percolation through different mantle rocks. The compositional variations of microinclusions in the coats reflect this evolution. Full article

(This article belongs to the Special Issue Minerals of Kimberlites: An Insight into Petrogenesis and the Diamond Potential of Deep Mantle Magmas)

► Show Figures

Figure 1

45 pages, 48878 KiB

Open AccessEditor’s ChoiceArticle

Laser-Induced Breakdown Spectroscopy—An Emerging Analytical Tool for Mineral Exploration

by Russell S. Harmon, Christopher J.M. Lawley, Jordan Watts, Cassady L. Harraden, Andrew M. Somers and Richard R. Hark

Minerals 2019, 9(12), 718; https://doi.org/10.3390/min9120718 - 20 Nov 2019

Cited by 98 | Viewed by 15505

Abstract

The mineral exploration industry requires new methods and tools to address the challenges of declining mineral reserves and increasing discovery costs. Laser-induced breakdown spectroscopy (LIBS) represents an emerging geochemical tool for mineral exploration that can provide rapid, in situ, compositional analysis and high-resolution [...] Read more.

The mineral exploration industry requires new methods and tools to address the challenges of declining mineral reserves and increasing discovery costs. Laser-induced breakdown spectroscopy (LIBS) represents an emerging geochemical tool for mineral exploration that can provide rapid, in situ, compositional analysis and high-resolution imaging in both laboratory and field and settings. We demonstrate through a review of previously published research and our new results how LIBS can be applied to qualitative element detection for geochemical fingerprinting, sample classification, and discrimination, as well as quantitative geochemical analysis, rock characterization by grain size analysis, and in situ geochemical imaging. LIBS can detect elements with low atomic number (i.e., light elements), some of which are important pathfinder elements for mineral exploration and/or are classified as critical commodities for emerging green technologies. LIBS data can be acquired in situ, facilitating the interpretation of geochemical data in a mineralogical context, which is important for unraveling the complex geological history of most ore systems. LIBS technology is available as a handheld analyzer, thus providing a field capability to acquire low-cost geochemical analyses in real time. As a consequence, LIBS has wide potential to be utilized in mineral exploration, prospect evaluation, and deposit exploitation quality control. LIBS is ideally suited for field exploration programs that would benefit from rapid chemical analysis under ambient environmental conditions. Full article

(This article belongs to the Special Issue Novel Methods and Applications for Mineral Exploration)

► Show Figures

Graphical abstract

19 pages, 18842 KiB

Open AccessEditor’s ChoiceArticle

Acid and Thermal Treatment of Alkali-Activated Zeolite Foams

by Zdeněk Tišler, Kateřina Hrachovcová, Eliška Svobodová, Jan Šafář and Lenka Pelíšková

Minerals 2019, 9(12), 719; https://doi.org/10.3390/min9120719 - 20 Nov 2019

Cited by 17 | Viewed by 6152

Abstract

The foamed alkali-activated zeolite materials have been studied primarily in terms of mechanical and structural properties as potential substitutes for concrete and other building materials. However, they also have interesting textural and acid properties that make them much more useful, especially in the [...] Read more.

The foamed alkali-activated zeolite materials have been studied primarily in terms of mechanical and structural properties as potential substitutes for concrete and other building materials. However, they also have interesting textural and acid properties that make them much more useful, especially in the chemical industry. The aim of the study is to map in detail the influence of post-synthesis modifications of alkali-activated natural zeolite foams on their chemical, mechanical, and textural properties for possible use in catalytic and adsorption applications. Alkali-activated natural zeolite foam pellets were prepared by activation with mixed potassium hydroxide and sodium silicate activator and foamed using H₂O₂ solution. The foam pellets were post-synthetic modified by leaching with mineral and organic acids and calcination. The properties of the modified materials were characterised on the basis of XRF, XRD, N₂ physisorption, DRIFT, SEM, NH₃-TPD analyses, and the strength measurements. Our data showed that the basic clinoptilolite structure remains unchanged in the material which is stable up to 600 °C after acid leaching. In two-step leaching, the specific surface area increases to 350 m²/g and the leaching process allows the acid properties of the materials to be varied. Full article

(This article belongs to the Special Issue Alkali Activated Materials: Advances, Innovations, Future Trends)

► Show Figures

Graphical abstract

21 pages, 4918 KiB

Open AccessEditor’s ChoiceArticle

Grinding Kinetics of Slag and Effect of Final Particle Size on the Compressive Strength of Alkali Activated Materials

by Evangelos Petrakis, Vasiliki Karmali, Georgios Bartzas and Konstantinos Komnitsas

Minerals 2019, 9(11), 714; https://doi.org/10.3390/min9110714 - 19 Nov 2019

Cited by 37 | Viewed by 5243

Abstract

This study aims to model grinding of a Polish ferronickel slag and evaluate the particle size distributions (PSDs) of the products obtained after different grinding times. Then, selected products were alkali activated in order to investigate the effect of particle size on the [...] Read more.

This study aims to model grinding of a Polish ferronickel slag and evaluate the particle size distributions (PSDs) of the products obtained after different grinding times. Then, selected products were alkali activated in order to investigate the effect of particle size on the compressive strength of the produced alkali activated materials (AAMs). Other parameters affecting alkali activation, i.e., temperature, curing, and ageing time were also examined. Among the different mathematical models used to simulate the particle size distribution, Rosin–Rammler (RR) was found to be the most suitable. When piecewise regression analysis was applied to experimental data it was found that the particle size distribution of the slag products exhibits multifractal character. In addition, grinding of slag exhibits non-first-order behavior and the reduction rate of each size is time dependent. The grinding rate and consequently the grinding efficiency increases when the particle size increases, but drops sharply near zero after prolonged grinding periods. Regarding alkali activation, it is deduced that among the parameters studied, particle size (and the respective specific surface area) of the raw slag product and curing temperature have the most noticeable impact on the compressive strength of the produced AAMs. Full article

(This article belongs to the Special Issue Alkali Activated Materials: Advances, Innovations, Future Trends)

► Show Figures

Figure 1

31 pages, 5465 KiB

Open AccessEditor’s ChoiceReview

Spanish Bentonites: A Review and New Data on Their Geology, Mineralogy, and Crystal Chemistry

by Emilia García-Romero, Eva María Manchado, Mercedes Suárez and Javier García-Rivas

Minerals 2019, 9(11), 696; https://doi.org/10.3390/min9110696 - 11 Nov 2019

Cited by 33 | Viewed by 6691

Abstract

A review and a synthesis of the geological, mineralogical, and crystal chemical data available in the literature on active Spanish bentonitic exploitations were done, and at the same time, new data are provided from a set of representative samples from these deposits. They [...] Read more.

A review and a synthesis of the geological, mineralogical, and crystal chemical data available in the literature on active Spanish bentonitic exploitations were done, and at the same time, new data are provided from a set of representative samples from these deposits. They were located in three different areas with different geological origins: (1) Miocene sedimentary deposits from the Tajo Basin (Madrid–Toledo provinces) in the center of the Iberian Peninsula, where bentonites appear in two different units named for their colors (Green Clays and Pink Clays); (2) samples from Tamame de Sayago (Zamora province) originating from the hydrothermal alteration of granitic Variscan rocks; and 3) Miocene deposits originating from the hydrothermal alteration of volcanic or subvolcanic rocks from the Cabo de Gata volcanic area (Almería Province) in the southern part of Spain, where the three main deposits (Cortijo de Archidona, Los Trancos, and Morrón de Mateo) were studied. The bentonites from the Tajo Basin were formed mainly by trioctahedral smectites, and there were significant mineralogical differences between the Green and Pink Clays, both in terms of the contents of impurities and in terms of smectite crystallochemistry and crystallinity. The smectites from Tamame de Sayago were dioctahedral (montmorillonite–beidellite series), and they appeared with kaolinite, quartz, and mica in all possible proportions, from almost pure bentonite to kaolin. Finally, the compositions of the bentonites from the three studied deposits in Cabo de Gata were quite similar, and zeolites and plagioclases were the main impurities. The structural formulae of the smectites from Cortijo de Archidona and Los Trancos showed a continuous compositional variation in beidellite–montmorillonite, while in Morrón de Mateo, the smectites were mainly montmorillonite, although there was continuous compositional variation from Al montmorillonites to Fe–Mg-rich saponites. The variation in the smectite composition is due to the intrusion of a volcanic dome, which brings new fluids that alter the initial composition of the smectites. Full article

(This article belongs to the Special Issue Special Clays and Their Applications)

► Show Figures

Figure 1

18 pages, 3015 KiB

Open AccessEditor’s ChoiceArticle

Phlogopite-Forming Reactions as Indicators of Metasomatism in the Lithospheric Mantle

by Oleg Safonov, Valentina Butvina and Evgenii Limanov

Minerals 2019, 9(11), 685; https://doi.org/10.3390/min9110685 - 6 Nov 2019

Cited by 37 | Viewed by 6239

Abstract

Phlogopite is widely accepted as a major mineral indicator of the modal metasomatism in the upper mantle within a very wide P–T range. The paper reviews data on various phlogopite-forming reactions in upper-mantle peridotites. The review includes both descriptions of naturally occurring reactions [...] Read more.

Phlogopite is widely accepted as a major mineral indicator of the modal metasomatism in the upper mantle within a very wide P–T range. The paper reviews data on various phlogopite-forming reactions in upper-mantle peridotites. The review includes both descriptions of naturally occurring reactions and results of experiments that model some of these reactions. Relations of phlogopite with other potassic phases, such as K-richterite, sanidine and K-titanates, are discussed. These data are taken as a basis for thermodynamic modeling of the phlogopite-forming reactions for specific mantle rocks in terms of log(a_H₂O) − log(a_K₂O) diagrams (pseudosections) using the Gibbs free energy minimization. These diagrams allow estimation of potassium-water activity relations during metasomatic transformations of mantle rocks, prediction sequences of mineral assemblages with respect to these parameters and comparison of metasomatic processes in the rocks of different composition. This approach is illustrated by examples from peridotite xenoliths from kimberlites. Full article

(This article belongs to the Special Issue Minerals of Kimberlites: An Insight into Petrogenesis and the Diamond Potential of Deep Mantle Magmas)

► Show Figures

Graphical abstract

14 pages, 1067 KiB

Open AccessEditor’s ChoiceArticle

Mineralogical Transformations of Heated Serpentine and Their Impact on Dissolution during Aqueous-Phase Mineral Carbonation Reaction in Flue Gas Conditions

by Clémence Du Breuil, Louis César-Pasquier, Gregory Dipple, Jean-François Blais, Maria Cornelia Iliuta and Guy Mercier

Minerals 2019, 9(11), 680; https://doi.org/10.3390/min9110680 - 3 Nov 2019

Cited by 15 | Viewed by 5818

Abstract

Mineral carbonation is known to be among the most efficient ways to reduce the anthropogenic emissions of carbon dioxide. Serpentine minerals (Mg₃Si₂O₅(OH)₄), have shown great potential for carbonation. A way to improve yield is to [...] Read more.

Mineral carbonation is known to be among the most efficient ways to reduce the anthropogenic emissions of carbon dioxide. Serpentine minerals (Mg₃Si₂O₅(OH)₄), have shown great potential for carbonation. A way to improve yield is to thermally activate serpentine minerals prior to the carbonation reaction. This step is of great importance as it controls Mg²⁺ leaching, one of the carbonation reaction limiting factors. Previous studies have focused on the optimization of the thermal activation by determining the ideal activation temperature. However, to date, none of these studies have considered the impacts of the thermal activation on the efficiency of the aqueous-phase mineral carbonation at ambient temperature and moderate pressure in flue gas conditions. Several residence times and temperatures of activation have been tested to evaluate their impact on serpentine dissolution in conditions similar to mineral carbonation. The mineralogical composition of the treated solids has been studied using X-ray diffraction coupled with a quantification using the Rietveld refinement method. A novel approach in order to quantify the meta-serpentine formed during dehydroxylation is introduced. The most suitable mineral assemblage for carbonation is found to be a mixture of the different amorphous phases identified. This study highlights the importance of the mineralogical assemblage obtained during the dehydroxylation process and its impact on the magnesium availability during dissolution in the carbonation reaction. Full article

(This article belongs to the Special Issue Geological and Mineralogical Sequestration of CO₂)

► Show Figures

Figure 1

12 pages, 4531 KiB

Open AccessEditor’s ChoiceArticle

Nanoscale Automated Quantitative Mineralogy: A 200-nm Quantitative Mineralogy Assessment of Fault Gouge Using Mineralogic

by Shaun Graham and Nynke Keulen

Minerals 2019, 9(11), 665; https://doi.org/10.3390/min9110665 - 29 Oct 2019

Cited by 16 | Viewed by 4228

Abstract

Effective energy-dispersive X-ray spectroscopy analysis (EDX) with a scanning electron microscope of fine-grained materials (submicrometer scale) is hampered by the interaction volume of the primary electron beam, whose diameter usually is larger than the size of the grains to be analyzed. Therefore, mixed [...] Read more.

Effective energy-dispersive X-ray spectroscopy analysis (EDX) with a scanning electron microscope of fine-grained materials (submicrometer scale) is hampered by the interaction volume of the primary electron beam, whose diameter usually is larger than the size of the grains to be analyzed. Therefore, mixed signals of the chemistry of individual grains are expected, and EDX is commonly not applied to such fine-grained material. However, by applying a low primary beam acceleration voltage, combined with a large aperture, and a dedicated mineral classification in the mineral library employed by the Zeiss Mineralogic software platform, mixed signals could be deconvoluted down to a size of 200 nm. In this way, EDX and automated quantitative mineralogy can be applied to investigations of submicrometer-sized grains. It is shown here that reliable quantitative mineralogy and grain size distribution assessment can be made based on an example of fault gouge with a heterogenous mineralogy collected from Ikkattup nunaa Island, southern West Greenland. Full article

(This article belongs to the Special Issue Applications of SEM Automated Mineralogy: From Ore Deposits over Processing to Secondary Resource Characterization)

► Show Figures

Graphical abstract

19 pages, 3453 KiB

Open AccessEditor’s ChoiceArticle

Improving the Quality of Ferruginous Chromite Concentrates Via Physical Separation Methods

by Sunil Kumar Tripathy, Y Rama Murthy, Veerendra Singh, Saeed Farrokhpay and Lev O. Filippov

Minerals 2019, 9(11), 667; https://doi.org/10.3390/min9110667 - 29 Oct 2019

Cited by 8 | Viewed by 6550

Abstract

The low chromium-to-iron ratio of chromite ores is an important issue in some chromite deposits. The value of the chromite ore is indeed dictated in the market by its iron, as well as its chromium content. In the present study, a chromite concentrate [...] Read more.

The low chromium-to-iron ratio of chromite ores is an important issue in some chromite deposits. The value of the chromite ore is indeed dictated in the market by its iron, as well as its chromium content. In the present study, a chromite concentrate was reprocessed by gravity (spiral concentrator) and magnetic separation to enhance the chromium-to-iron ratio. Also, detailed characterization studies including automated mineralogy were carried out to better understand the nature of the samples. Enhancing the chromium-to-iron ratio was achieved by using advanced spiral separators which will be discussed in this paper. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

► Show Figures

Figure 1

9 pages, 266 KiB

Open AccessEditor’s ChoiceArticle

Equations of State for the Deep Earth: Some Fundamental Considerations

by Frank D. Stacey

Minerals 2019, 9(10), 636; https://doi.org/10.3390/min9100636 - 17 Oct 2019

Cited by 12 | Viewed by 3673

Abstract

None of the 40+ equations that have been proposed to describe material properties at the pressures of the Earth’s core and mantle have escaped serious criticism. In this paper, some basic algebraic and thermodynamic constraints are reviewed, with the conclusion that the next [...] Read more.

None of the 40+ equations that have been proposed to describe material properties at the pressures of the Earth’s core and mantle have escaped serious criticism. In this paper, some basic algebraic and thermodynamic constraints are reviewed, with the conclusion that the next step should be a re-examination of the relationship between the dependence of the bulk modulus, K, on pressure, P, that is

K^{'} \equiv d K / d P

, and the normalized (dimensionless) pressure,

P / K

. A linear relationship between

1 / K^{'}

and

P / K

terminating at the infinite pressure asymptote, at which these quantities become equal, has been used for analysing properties at extreme pressure, but may be inadequate for calculations requiring precise derivatives of an equation of state. A new analysis indicates that

d (1 / K^{'}) / d (P / K)

increases with compression (or

P / K

), but there are, at present, no reliable equations representing this. Relationships between higher derivatives of K and the thermodynamic Grüneisen parameter offer the prospect of a resolution of the problem and hence a new generation of fundamentally-based equations of state. Although an earlier conclusion that a completely general ‘universal’ equation is not possible, in principle, is confirmed in this study, the fundamental relationships present strong constraints for the forms of other proposed equations. Full article

(This article belongs to the Special Issue Mineral Physics—In Memory of Orson Anderson)

16 pages, 5080 KiB

Open AccessEditor’s ChoiceArticle

Further Characterization of the RW-1 Monazite: A New Working Reference Material for Oxygen and Neodymium Isotopic Microanalysis

by Li-Guang Wu, Xian-Hua Li, Xiao-Xiao Ling, Yue-Heng Yang, Chao-Feng Li, You-Lian Li, Qian Mao, Qiu-Li Li and Benita Putlitz

Minerals 2019, 9(10), 583; https://doi.org/10.3390/min9100583 - 26 Sep 2019

Cited by 39 | Viewed by 5037

Abstract

The oxygen (O) and neodymium (Nd) isotopic composition of monazite provides an ideal tracer of metamorphism and hydrothermal activity. Calibration of the matrix effect and monitoring of the external precision of monazite O–Nd isotopes with microbeam techniques, such as secondary ion mass spectrometry [...] Read more.

The oxygen (O) and neodymium (Nd) isotopic composition of monazite provides an ideal tracer of metamorphism and hydrothermal activity. Calibration of the matrix effect and monitoring of the external precision of monazite O–Nd isotopes with microbeam techniques, such as secondary ion mass spectrometry (SIMS) and laser ablation-multicollector-inductively coupled plasma-mass spectrometry (LA-MC-ICPMS), require well-characterized natural monazite standards for precise microbeam measurements. However, the limited number of standards available is impeding the application of monazite O–Nd isotopes. Here, we report on the RW-1 monazite as a potential new working reference material for microbeam analysis of O–Nd isotopes. Microbeam measurements by electron probe microanalysis (EPMA), SIMS, and LA-MC-ICPMS at 10–24 µm scales have confirmed that it is homogeneous in both elemental and O–Nd isotopic compositions. SIMS measurements yield δ¹⁸O values consistent, within errors, with those obtained by laser fluorination techniques. Precise analyses of Nd isotope by thermal ionization mass spectrometry (TIMS) are consistent with mean results of LA-MC-ICPMS analyses. We recommend δ¹⁸O = 6.30‰ ± 0.16‰ (2SD) and ¹⁴³Nd/¹⁴⁴Nd = 0.512282 ± 0.000011 (2SD) as being the reference values for the RW-1 monazite. Full article

(This article belongs to the Special Issue Accessory Minerals in Silicic Igneous Rocks)

► Show Figures

Figure 1

18 pages, 3341 KiB

Open AccessEditor’s ChoiceArticle

Experimental Simulation of the Self-Trapping Mechanism for CO₂ Sequestration into Marine Sediments

by Hak-Sung Kim and Gye-Chun Cho

Minerals 2019, 9(10), 579; https://doi.org/10.3390/min9100579 - 24 Sep 2019

Cited by 17 | Viewed by 3893

Abstract

CO₂ hydrates are ice-like solid lattice compounds composed of hydrogen-bonded cages of water molecules that encapsulate guest CO₂ molecules. The formation of CO₂ hydrates in unconsolidated sediments significantly decreases their permeability and increases their stiffness. CO₂ hydrate-bearing sediments can, [...] Read more.

CO₂ hydrates are ice-like solid lattice compounds composed of hydrogen-bonded cages of water molecules that encapsulate guest CO₂ molecules. The formation of CO₂ hydrates in unconsolidated sediments significantly decreases their permeability and increases their stiffness. CO₂ hydrate-bearing sediments can, therefore, act as cap-rocks and prevent CO₂ leakage from a CO₂-stored layer. In this study, we conducted an experimental simulation of CO₂ geological storage into marine unconsolidated sediments. CO₂ hydrates formed during the CO₂ liquid injection process and prevented any upward flow of CO₂. Temperature, pressure, P-wave velocity, and electrical resistance were measured during the experiment, and their measurement results verified the occurrence of the self-trapping effect induced by CO₂ hydrate formation. Several analyses using the experimental results revealed that CO₂ hydrate bearing-sediments have a considerable sealing capacity. Minimum breakthrough pressure and maximum absolute permeability are estimated to be 0.71 MPa and 5.55 × 10⁻⁴ darcys, respectively. Full article

(This article belongs to the Special Issue Geological and Mineralogical Sequestration of CO₂)

► Show Figures

Figure 1

29 pages, 10051 KiB

Open AccessEditor’s ChoiceArticle

Emeralds from the Most Important Occurrences: Chemical and Spectroscopic Data

by Stefanos Karampelas, Bader Al-Shaybani, Fatima Mohamed, Supharart Sangsawong and Abeer Al-Alawi

Minerals 2019, 9(9), 561; https://doi.org/10.3390/min9090561 - 17 Sep 2019

Cited by 50 | Viewed by 10862

Abstract

The present study applied LA–ICP-MS on gem-quality emeralds from the most important sources (Afghanistan, Brazil, Colombia, Ethiopia, Madagascar, Russia, Zambia and Zimbabwe). It revealed that emeralds from Afghanistan, Brazil, Colombia and Madagascar have a relatively lower lithium content (⁷Li < 200 [...] Read more.

The present study applied LA–ICP-MS on gem-quality emeralds from the most important sources (Afghanistan, Brazil, Colombia, Ethiopia, Madagascar, Russia, Zambia and Zimbabwe). It revealed that emeralds from Afghanistan, Brazil, Colombia and Madagascar have a relatively lower lithium content (⁷Li < 200 ppmw) compared to emeralds from other places (⁷Li > 250 ppmw). Alkali element contents as well as scandium, manganese, cobalt, nickel, zinc and gallium can further help us in obtaining accurate origin information for these emeralds. UV-Vis spectroscopy can aid in the separation of emeralds from Colombia and Afghanistan from these obtained from the other sources as the latter present pronounced iron-related bands. Intense Type-II water vibrations are observed in the infrared spectra of emeralds from Madagascar, Zambia and Zimbabwe, as well as in some samples from Afghanistan and Ethiopia, which contain higher alkali contents. A band at 2818 cm⁻¹, supposedly attributed to chlorine, was observed only in emeralds from Colombia and Afghanistan. Samples with medium to high alkalis from Ethiopia, Madagascar, Zambia and Zimbabwe can also be separated from the others by Raman spectroscopy based on the lower or equal relative intensity of the Type I water band at around 3608 cm⁻¹ compared to the Type II water band at around 3598 cm⁻¹ band (with some samples from Afghanistan, Brazil and Russia presenting equal relative intensities). Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Gems)

► Show Figures

Figure 1

19 pages, 2229 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Recovery of Metals from Waste Lithium Ion Battery Leachates Using Biogenic Hydrogen Sulfide

by Giles Calvert, Anna H. Kaksonen, Ka Yu Cheng, Jonovan Van Yken, Barbara Chang and Naomi J. Boxall

Minerals 2019, 9(9), 563; https://doi.org/10.3390/min9090563 - 17 Sep 2019

Cited by 28 | Viewed by 6659

Abstract

Lithium ion battery (LIB) waste is increasing globally and contains an abundance of valuable metals that can be recovered for re-use. This study aimed to evaluate the recovery of metals from LIB waste leachate using hydrogen sulfide generated by a consortium of sulfate-reducing [...] Read more.

Lithium ion battery (LIB) waste is increasing globally and contains an abundance of valuable metals that can be recovered for re-use. This study aimed to evaluate the recovery of metals from LIB waste leachate using hydrogen sulfide generated by a consortium of sulfate-reducing bacteria (SRB) in a lactate-fed fluidised bed reactor (FBR). The microbial community analysis showed Desulfovibrio as the most abundant genus in a dynamic and diverse bioreactor consortium. During periods of biogenic hydrogen sulfide production, the average dissolved sulfide concentration was 507 mg L⁻¹ and the average volumetric sulfate reduction rate was 278 mg L⁻¹ d⁻¹. Over 99% precipitation efficiency was achieved for Al, Ni, Co, and Cu using biogenic sulfide and NaOH, accounting for 96% of the metal value contained in the LIB waste leachate. The purity indices of the precipitates were highest for Co, being above 0.7 for the precipitate at pH 10. However, the process was not selective for individual metals due to simultaneous precipitation and the complexity of the metal content of the LIB waste. Overall, the process facilitated the production of high value mixed metal precipitates, which could be purified further or used as feedstock for other processes, such as the production of steel. Full article

(This article belongs to the Special Issue The Processing of Alternative and Urban Ores)

► Show Figures

Figure 1

25 pages, 4019 KiB

Open AccessEditor’s ChoiceArticle

Implications of Hf Isotopes for the Evolution of the Mantle Source of Magmas Associated with the Giant El Teniente Cu-Mo Megabreccia Deposit, Central Chile

by Charles R. Stern, Kwan-Nang Pang, Hao-Yang Lee, M. Alexandra Skewes and Alejandra Arévalo

Minerals 2019, 9(9), 550; https://doi.org/10.3390/min9090550 - 12 Sep 2019

Cited by 8 | Viewed by 3751

Abstract

We have determined the Hf isotopic compositions of 12 samples associated with the giant El Teniente Cu-Mo megabreccia deposit, central Chile. The samples range in age from ≥8.9 to 2.3 Ma and provide information about the temporal evolution of their magmatic sources from [...] Read more.

We have determined the Hf isotopic compositions of 12 samples associated with the giant El Teniente Cu-Mo megabreccia deposit, central Chile. The samples range in age from ≥8.9 to 2.3 Ma and provide information about the temporal evolution of their magmatic sources from the Late Miocene to Pliocene. Together with previously published data, the new analysis indicates a temporal decrease of 10 ε_Hf(t) units, from +11.6 down to +1.6, in the 12.7 m.y. from 15 to 2.3 Ma. These variations imply increasing incorporation of continental crust through time in the magmas that formed these rocks. The fact that the samples include mantle-derived olivine basalts and olivine lamprophyres suggests that these continental components were incorporated into their mantle source, and not by intra-crustal contamination (MASH). We attribute the increase, between the Middle Miocene and Pliocene, of crustal components in the subarc mantle source below El Teniente to be due to increased rates of subduction erosion and transport of crust into the mantle. The deposit formed above a large, long-lived, vertically zoned magma chamber that developed due to compressive deformation and persisted between ~7 to 4.6 Ma. Progressively more hydrous mantle-derived mafic magmas feed this chamber from below, providing heat, H₂O, S and metals, but no unique “fertile” Cu-rich magma was involved in the formation of the deposit. As the volume of these mantle-derived magmas decreased from the Late Miocene into the Pliocene, the chamber crystallized and solidified, producing felsic plutons and large metal-rich magmatic-hydrothermal breccias that emplaced Cu and S into the older (≥8.9 Ma) mafic host rocks of this megabreccia deposit. Full article

(This article belongs to the Special Issue Role of Magmatic Activity in Generation of Ore Deposits)

► Show Figures

Figure 1

20 pages, 2501 KiB

Open AccessEditor’s ChoiceReview

Polymineralic Inclusions in Megacrysts as Proxies for Kimberlite Melt Evolution—A Review

by Yannick Bussweiler

Minerals 2019, 9(9), 530; https://doi.org/10.3390/min9090530 - 30 Aug 2019

Cited by 17 | Viewed by 4894

Abstract

Polymineralic inclusions in megacrysts have been reported to occur in kimberlites worldwide. The inclusions are likely the products of early kimberlite melt(s) which invaded the pre-existing megacryst minerals at mantle depths (i.e., at pressures ranging from 4 to 6 GPa) and crystallized or [...] Read more.

Polymineralic inclusions in megacrysts have been reported to occur in kimberlites worldwide. The inclusions are likely the products of early kimberlite melt(s) which invaded the pre-existing megacryst minerals at mantle depths (i.e., at pressures ranging from 4 to 6 GPa) and crystallized or quenched upon emplacement of the host kimberlite. The abundance of carbonate minerals (e.g., calcite, dolomite) and hydrous silicate minerals (e.g., phlogopite, serpentine, chlorite) within polymineralic inclusions suggests that the trapped melt was more volatile-rich than the host kimberlite now emplaced in the crust. However, the exact composition of this presumed early kimberlite melt, including the inventory of trace elements and volatiles, remains to be more narrowly constrained. For instance, one major question concerns the role of accessory alkali-halogen-phases in polymineralic inclusions, i.e., whether such phases constitute a common primary feature of kimberlite melt(s), or whether they become enriched in late-stage differentiation processes. Recent studies have shown that polymineralic inclusions react with their host minerals during ascent of the kimberlite, while being largely shielded from processes that affect the host kimberlite, e.g., the assimilation of xenoliths (mantle and crustal), degassing of volatiles, and secondary alteration. Importantly, some polymineralic inclusions within different megacryst minerals were shown to preserve fresh glass. A major conclusion of this review is that the abundance and mineralogy of polymineralic inclusions are directly influenced by the physical and chemical properties of their host minerals. When taking the different interactions with their host minerals into account, polymineralic inclusions in megacrysts can serve as useful proxies for the multi-stage origin and evolution of kimberlite melt/magma, because they can (i) reveal information about primary characteristics of the kimberlite melt, and (ii) trace the evolution of kimberlite magma on its way from the upper mantle to the crust. Full article

(This article belongs to the Special Issue Minerals of Kimberlites: An Insight into Petrogenesis and the Diamond Potential of Deep Mantle Magmas)

► Show Figures

Figure 1

26 pages, 7386 KiB

Open AccessEditor’s ChoiceArticle

Age and Origin of Silicocarbonate Pegmatites of the Adirondack Region

by Jeffrey Chiarenzelli, Marian Lupulescu, George Robinson, David Bailey and Jared Singer

Minerals 2019, 9(9), 508; https://doi.org/10.3390/min9090508 - 23 Aug 2019

Cited by 10 | Viewed by 6101

Abstract

Silicocarbonate pegmatites from the southern Grenville Province have provided exceptionally large crystal specimens for more than a century. Their mineral parageneses include euhedral calc–silicate minerals such as amphibole, clinopyroxene, and scapolite within a calcite matrix. Crystals can reach a meter or more in [...] Read more.

Silicocarbonate pegmatites from the southern Grenville Province have provided exceptionally large crystal specimens for more than a century. Their mineral parageneses include euhedral calc–silicate minerals such as amphibole, clinopyroxene, and scapolite within a calcite matrix. Crystals can reach a meter or more in long dimension. Minor and locally abundant phases reflect local bedrock compositions and include albite, apatite, perthitic microcline, phlogopite, zircon, tourmaline, titanite, danburite, uraninite, sulfides, and many other minerals. Across the Adirondack Region, individual exposures are of limited aerial extent (<10,000 m²), crosscut metasedimentary rocks, especially calc–silicate gneisses and marbles, are undeformed and are spatially and temporally associated with granitic pegmatites. Zircon U–Pb results include both Shawinigan (circa 1165 Ma) and Ottawan (circa 1050 Ma) intrusion ages, separated by the Carthage-Colton shear zone. Those of Shawinigan age (Lowlands) correspond with the timing of voluminous A-type granitic magmatism, whereas Ottawan ages (Highlands) are temporally related to orogenic collapse, voluminous leucogranite and granitic pegmatite intrusion, iron and garnet ore development, and pervasive localized hydrothermal alteration. Inherited zircon, where present, reflects the broad range of igneous and detrital ages of surrounding rocks. Carbon and oxygen isotopic ratios from calcite plot within a restricted field away from igneous carbonatite values to those of typical sedimentary carbonates and local marbles. Collectively, these exposures represent a continuum between vein-dyke and skarn occurrences involving the anatexis of metasedimentary country rocks. Those of Ottawan age can be tied to movement and fluid flow along structures accommodating orogenic collapse, particularly the Carthage-Colton shear zone. Full article

(This article belongs to the Special Issue Minerals of the Southern Grenville Province)

► Show Figures

Figure 1

23 pages, 7820 KiB

Open AccessEditor’s ChoiceReview

Tools and Workflows for Grassroots Li–Cs–Ta (LCT) Pegmatite Exploration

by Benedikt M. Steiner

Minerals 2019, 9(8), 499; https://doi.org/10.3390/min9080499 - 20 Aug 2019

Cited by 45 | Viewed by 21822

Abstract

The increasing demand for green technology and battery metals necessitates a review of geological exploration techniques for Li–Cs–Ta (LCT) pegmatites, which is applicable to the work of mining companies. This paper reviews the main controls of LCT pegmatite genesis relevant to mineral exploration [...] Read more.

The increasing demand for green technology and battery metals necessitates a review of geological exploration techniques for Li–Cs–Ta (LCT) pegmatites, which is applicable to the work of mining companies. This paper reviews the main controls of LCT pegmatite genesis relevant to mineral exploration programs and presents a workflow of grassroots exploration techniques, supported by examples from central Europe and Africa. Geological exploration commonly begins with information gathering, desktop studies and Geographic Information System (GIS) data reviews. Following the identification of prospective regional areas, initial targets are verified in the field by geological mapping and geochemical sampling. Detailed mineralogical analysis and geochemical sampling of rock, soil and stream sediments represent the most important tools for providing vectors to LCT pegmatites, since the interpretation of mineralogical phases, deportment and liberation characteristics along with geochemical K/Rb, Nb/Ta and Zr/Hf metallogenic markers can detect highly evolved rocks enriched in incompatible elements of economic interest. The importance of JORC (Joint Ore Reserves Committee) 2012 guidelines with regards to obtaining geological, mineralogical and drilling data is discussed and contextualised, with the requirement of treating LCT pegmatites as industrial mineral deposits. Full article

(This article belongs to the Special Issue Novel Methods and Applications for Mineral Exploration)

► Show Figures

Figure 1

16 pages, 2976 KiB

Open AccessEditor’s ChoiceArticle

Niobium Mineralogy of Pliocene A₁-Type Granite of the Carpathian Back-Arc Basin, Central Europe

by Monika Huraiová, Patrik Konečný and Vratislav Hurai

Minerals 2019, 9(8), 488; https://doi.org/10.3390/min9080488 - 15 Aug 2019

Cited by 7 | Viewed by 4578

Abstract

A₁-type granite xenoliths occur in alkali basalts erupted during Pliocene–Pleistocene continental rifting of Carpathian back-arc basin (Central Europe). The Pliocene (5.2 Ma) peraluminous calc-alkalic granite contains unusually high concentrations of critical metals bound in Nb, Ta, REE, U, Th-oxides typical for [...] Read more.

A₁-type granite xenoliths occur in alkali basalts erupted during Pliocene–Pleistocene continental rifting of Carpathian back-arc basin (Central Europe). The Pliocene (5.2 Ma) peraluminous calc-alkalic granite contains unusually high concentrations of critical metals bound in Nb, Ta, REE, U, Th-oxides typical for silica-undersaturated alkalic granites, and syenites: columbite-Mn, fergusonite-Y, oxycalciopyrochlore, Nb-rutile, and Ca-niobate (fersmite or viggezite). In contrast, it does not contain allanite and monazite—the main REE-carriers in calc-alkalic granites. The crystallization of REE-bearing Nb-oxides instead of OH-silicates and phosphates was probably caused by strong water deficiency and low phosphorus content in the parental magma. Increased Nb and Ta concentrations have been inherited from the mafic parental magma derived from the metasomatized mantle. The strong Al- and Ca-enrichment probably reflects the specific composition of the mantle wedge modified by fluids, alkalic, and carbonatitic melts liberated from the subducted slab of oceanic crust prior to the Pliocene-Pleistocene rifting. Full article

(This article belongs to the Special Issue Accessory Minerals in Silicic Igneous Rocks)

► Show Figures

Figure 1

23 pages, 5630 KiB

Open AccessEditor’s ChoiceArticle

Hydrothermal Alteration of Eudialyte-Hosted Critical Metal Deposits: Fluid Source and Implications for Deposit Grade

by Mathijs A. J. van de Ven, Anouk M. Borst, Gareth R. Davies, Emma J. Hunt and Adrian A. Finch

Minerals 2019, 9(7), 422; https://doi.org/10.3390/min9070422 - 10 Jul 2019

Cited by 12 | Viewed by 6959

Abstract

Eudialyte-hosted critical metal deposits potentially represent major sources of rare earth elements (REE), zirconium and niobium. Here, we study the chemical and isotopic composition of fresh and altered eudialyte in nepheline syenite from the Ilímaussaq Complex, Greenland, one of the world’s largest known [...] Read more.

Eudialyte-hosted critical metal deposits potentially represent major sources of rare earth elements (REE), zirconium and niobium. Here, we study the chemical and isotopic composition of fresh and altered eudialyte in nepheline syenite from the Ilímaussaq Complex, Greenland, one of the world’s largest known eudialyte-hosted deposits. Late-magmatic hydrothermal alteration caused partial replacement of primary magmatic eudialyte by complex pseudomorph assemblages of secondary Zr-, Nb-, and REE-minerals. Three secondary assemblage types are characterised by the zirconosilicates catapleiite, gittinsite and zircon, respectively, of which the catapleiite type is most common. To investigate elemental exchange associated with alteration and to constrain the nature of the metasomatic fluids, we compare trace elements and Sm/Nd isotope compositions of unaltered eudialyte crystals and their replaced counterparts from five syenite samples (three catapleiite-type, one gittinsite-type, and one zircon-type assemblage). Trace element budgets for the catapleiite-type pseudomorphs indicate a 15–30% loss of REE, Ta, Nb, Zr, Sr and Y relative to fresh eudialyte. Moreover, the gittinsite- and zircon-type assemblages record preferential heavy REE (HREE) depletion (≤50%), suggesting that the metasomatic fluids mobilised high field strength elements. Initial Nd isotope ratios of unaltered eudialyte and catapleiite- and gittinsite-type pseudomorphs are indistinguishable, confirming a magmatic fluid origin. However, a higher initial ratio and stronger HREE depletion in the zircon-type pseudomorphs suggests a different source for the zircon-forming fluid. Although alteration reduces the metal budget of the original eudialyte volume, we infer that these elements re-precipitate nearby in the same rock. Alteration, therefore, might have little effect on overall grade but preferentially separates heavy and light REE into different phases. Targeted processing of the alteration products may access individual rare earth families (heavy vs. light) and other metals (Zr, Nb, Ta) more effectively than processing the fresh rock. Full article

(This article belongs to the Special Issue Rare Earth Deposits and Challenges of World REE Demand for High-Tech and Green-Tech at the Beginning of the 3^rd Millennium)

► Show Figures

Figure 1

24 pages, 8562 KiB

Open AccessEditor’s ChoiceArticle

The Genetic Association between Quartz Vein- and Greisen-Type Mineralization at the Maoping W–Sn Deposit, Southern Jiangxi, China: Insights from Zircon and Cassiterite U–Pb Ages and Cassiterite Trace Element Composition

by Li-Li Chen, Pei Ni, Bao-Zhang Dai, Wen-Sheng Li, Zhe Chi and Jun-Yi Pan

Minerals 2019, 9(7), 411; https://doi.org/10.3390/min9070411 - 4 Jul 2019

Cited by 43 | Viewed by 7869

Abstract

The large-scale Maoping W–Sn deposit in the Gannan metallogenic belt of the eastern Nanling Range, South China, spatially associated with the Maoping granite pluton, hosts total ore reserves of 103,000 t WO₃ and 50,000 t Sn. Two different types of mineralization developed [...] Read more.

The large-scale Maoping W–Sn deposit in the Gannan metallogenic belt of the eastern Nanling Range, South China, spatially associated with the Maoping granite pluton, hosts total ore reserves of 103,000 t WO₃ and 50,000 t Sn. Two different types of mineralization developed in this deposit: Upper quartz vein-type mineralization, mostly within the Cambrian metamorphosed sandstone and slate, and underneath greisen-type mineralization within the Maoping granite. Cassiterites from both types of mineralization coexist with wolframite. Here we report for the first time in situ U–Pb data on cassiterite and zircon of the Maoping deposit obtained by LA-ICP-MS. Cassiterite from quartz vein and greisen yielded weighted average ²⁰⁶Pb/²³⁸U ages of 156.8 ± 1.5 Ma and 156.9 ± 1.4 Ma, respectively, which indicates that the two types of mineralization formed roughly at the same time. In addition, the two mineralization ages are consistent with the emplacement age of the Maoping granite (159.0 ± 1.5 Ma) within error, suggesting a close temporal and genetic link between W–Sn mineralization and granitic magmatism. The two types of mineralization formed at the same magmatic-hydrothermal event. Cassiterite from both types of mineralization shows high Fe, Ta, and Zr contents with a low Zr/Hf ratio, suggesting that the ore-forming fluid should be derived from the highly differentiated Maoping granite pluton. Cassiterite in greisen has higher contents of Nb and Ta but a lower concentration of Ti compared with that in quartz vein, indicating that the formation temperature of greisen-type mineralization is little higher than that of quartz-vein-type mineralization. Full article

(This article belongs to the Special Issue Integrated Chronology Studies of Ore Deposits)

► Show Figures

Figure 1

13 pages, 2261 KiB

Open AccessEditor’s ChoiceArticle

Iron Control in Atmospheric Acid Laterite Leaching

by Ville Miettinen, Jarno Mäkinen, Eero Kolehmainen, Tero Kravtsov and Lotta Rintala

Minerals 2019, 9(7), 404; https://doi.org/10.3390/min9070404 - 30 Jun 2019

Cited by 23 | Viewed by 5241

Abstract

Iron control in the atmospheric acid leaching (AL) of nickel laterite was evaluated in this study. The aim was to decrease acid consumption and iron dissolution by iron precipitation during nickel leaching. The combined acid leaching and iron precipitation process involves direct acid [...] Read more.

Iron control in the atmospheric acid leaching (AL) of nickel laterite was evaluated in this study. The aim was to decrease acid consumption and iron dissolution by iron precipitation during nickel leaching. The combined acid leaching and iron precipitation process involves direct acid leaching of the limonite type of laterite followed by a simultaneous iron precipitation and nickel leaching step. Iron precipitation as jarosite is carried out by using nickel containing silicate laterite for neutralization. Acid is generated in the jarosite precipitation reaction, and it dissolves nickel and other metals like magnesium from the silicate laterite. Leaching tests were carried out using three laterite samples from the Agios Ioannis, Evia Island, and Kastoria mines in Greece. Relatively low acid consumption was achieved during the combined precipitation and acid leaching tests. The acid consumption was approximately 0.4 kg acid per kg laterite, whereas the acid consumption in direct acid leaching of the same laterite samples was approximately 0.6–0.8 kg acid per kg laterite. Iron dissolution was only 1.5–3% during the combined precipitation and acid leaching tests, whereas in direct acid leaching it was 15–30% with the Agios Ioannis and Evia Island samples and 80% with the Kastoria sample. Full article

(This article belongs to the Special Issue Recent Advances in Hydro- and Biohydrometallurgy)

► Show Figures

Figure 1

7 pages, 585 KiB

Open AccessEditor’s ChoiceCommunication

The Atomic Arrangement of Cr-rich Tourmaline from the #1 Mine, Balmat, St. Lawrence County, New York, USA

by Steven G. Dannenberg, Devany Di Paolo, Alix M. Ehlers, Kyle P. McCarthy, Mark T. Mancini, Matthew B. Reuter, Dennis M. Seth, Zihui Song, Maria I. Valladares, Xuanfu Zhu, John M. Hughes and Marian V. Lupulescu

Minerals 2019, 9(7), 398; https://doi.org/10.3390/min9070398 - 28 Jun 2019

Cited by 4 | Viewed by 4262

Abstract

Chromium-bearing tourmalines are rare. Chromium-rich tourmaline from the northwestern part of the Adirondack Mountains in the Adirondack Lowlands is among the most chromium-rich tourmalines found to date. The mineral, with >21.0 wt. % Cr₂O₃, is from the marble-hosted talc–tremolite–cummingtonite [...] Read more.

Chromium-bearing tourmalines are rare. Chromium-rich tourmaline from the northwestern part of the Adirondack Mountains in the Adirondack Lowlands is among the most chromium-rich tourmalines found to date. The mineral, with >21.0 wt. % Cr₂O₃, is from the marble-hosted talc–tremolite–cummingtonite schist in the #1 mine in Balmat, St. Lawrence County, New York. The atomic arrangement of the sample (a = 16.0242(3) Å, c = 7.3002(2) Å) was refined to R1 = 0.0139. The composition, from chemical analyses and optimization of the formula, is ^X(Ca_0.22Na_0.69K_0.01) ^Y(Cr³⁺_1.68Mg_0.80Ti_0.13V_0.06Mn_0.02Fe_0.02Li_0.29) ^Z(Al_3.11Cr³⁺_1.18Mg_1.70Fe_0.01) ^T(Si_5.93Al_0.07) B₃O₂₇ OH_3.99 F_0.01. There has been extensive debate over the ordering of Cr³⁺ between the tourmaline Y and Z octahedral sites. Recent work has suggested that, at low concentrations (<~1.03 apfu), the substituent Cr³⁺ is ordered into the Y-site, whereas, at greater concentrations, the substituent is disordered over both octahedral sites. An analysis of nine recently published, high-precision structures of chromium-bearing tourmaline, in combination with the Adirondack tourmaline, suggests that structural changes to the Y-site at low concentrations of Cr³⁺ induce changes in the Z-site that make it more amenable to incorporation of the Cr³⁺ substituents by increasing <Z–O>. The bond lengths change to lower the bond-valence sum of Cr³⁺ in the Z-site of the chromium-dravite, making that site more amenable to the substituent. Calculations suggest that the Z-site begins to accept substituent Cr³⁺ when the bond valence sum of that ion in Z reduces to a value of ~3.36 valence units. Full article

(This article belongs to the Special Issue Minerals of the Southern Grenville Province)

► Show Figures

Figure 1

18 pages, 11970 KiB

Open AccessEditor’s ChoiceReview

The Orson Anderson Era of Mineral Physics at Lamont in the 1960s

by Robert Cooper Liebermann

Minerals 2019, 9(6), 342; https://doi.org/10.3390/min9060342 - 4 Jun 2019

Cited by 5 | Viewed by 4628

Abstract

From 1964 to the early 1970s, Orson Anderson led a research program at the Lamont Geological Observatory in the newly-emerging field of “mineral physics”. In collaboration with colleagues Edward Schreiber and Naohiro Soga, Orson exploited the techniques of physical acoustics to study the [...] Read more.

From 1964 to the early 1970s, Orson Anderson led a research program at the Lamont Geological Observatory in the newly-emerging field of “mineral physics”. In collaboration with colleagues Edward Schreiber and Naohiro Soga, Orson exploited the techniques of physical acoustics to study the behavior of the sound velocities of minerals at elevated pressures and temperatures. This research program also included semi-empirical studies of the relationships between the bulk modulus and the molar volume of solids, the use of lattice dynamics to calculate the elastic moduli of cubic structures as a function of pressure to predict instabilities, and theoretical investigations of the Lagrangian and Eulerian formulations of finite strain equations of state. Full article

(This article belongs to the Special Issue Mineral Physics—In Memory of Orson Anderson)

► Show Figures

Figure 1

14 pages, 3668 KiB

Open AccessEditor’s ChoiceArticle

Elemental Compositions of Smectites Reveal Detailed Sediment Provenance Changes during Glacial and Interglacial Periods: The Southern Drake Passage and Bellingshausen Sea, Antarctica

by Young Kyu Park, Jae Il Lee, Jaewoo Jung, Claus-Dieter Hillenbrand, Kyu-Cheul Yoo and Jinwook Kim

Minerals 2019, 9(5), 322; https://doi.org/10.3390/min9050322 - 26 May 2019

Cited by 12 | Viewed by 5809

Abstract

Variations in clay mineral assemblages have been widely used to understand changes in sediment provenance during glacial and interglacial periods. Smectite clay minerals, however, have a range of various elemental compositions that possibly originated from multiple different sources. Therefore, it might be crucial [...] Read more.

Variations in clay mineral assemblages have been widely used to understand changes in sediment provenance during glacial and interglacial periods. Smectite clay minerals, however, have a range of various elemental compositions that possibly originated from multiple different sources. Therefore, it might be crucial to distinguish the various types of smectites by analyzing their elemental composition in order to verify the sediment provenances with certainty. This hypothesis was tested for the clay mineral characteristics in a marine sediment core from the southern Drake Passage (GC05-DP02). Rare earth elements and

ε_{N d}

data had previously indicated that fine grained detritus was supplied from the Weddell Sea to the core site during interglacial periods, when the sediments contained more Al-rich smectite (montmorillonite). Indeed, marine sediments collected close to the Larsen Ice Shelf on the eastern Antarctic Peninsula continental shelf, western Weddell Sea embayment, show more Al-rich smectite components as compared with other possible West Antarctic sources, such as the Ross Sea embayment or King George Island, South Shetland Islands. Furthermore, two types of smectite (Al-rich and Al-poor) were identified in core GC360 from the Bellingshausen Sea shelf, suggesting that during glacial periods some sediment is derived from subglacial erosion of underlying pre-Oligocene sedimentary strata containing predominantly Al-rich montmorillonite. This finding reveals different sources for smectites in sediments deposited at site GC360 during the last glacial period and during the present interglacial that show only minor differences in smectite contents. For the interglacial period, two groups of smectite with a wide range of Al-rich and Mg–Fe-rich were identified, which indicate delivery from two different sources: (1) the detritus with high contents of Mg–Fe-rich smectite supplied from Beethoven Peninsula, southwestern Alexander island and (2) the detritus with higher contents of Al-rich smectite (montmorillonite) possibly derived from the subglacial reworking of pre-Oligocene sedimentary strata. These results demonstrate that the elemental compositions of smectites can be used to differentiate the sources of smectites in marine sediments, which is an important tool to define sediment provenance in detail, when down-core changes observed in clay mineral assemblages are interpreted. Full article

(This article belongs to the Special Issue Clays and Micro-Organisms: From Nature to Industry)

► Show Figures

Figure 1

23 pages, 7679 KiB

Open AccessEditor’s ChoiceArticle

A Bat-Optimized One-Class Support Vector Machine for Mineral Prospectivity Mapping

by Yongliang Chen, Wei Wu and Qingying Zhao

Minerals 2019, 9(5), 317; https://doi.org/10.3390/min9050317 - 23 May 2019

Cited by 37 | Viewed by 3802

Abstract

One-class support vector machine (OCSVM) is an efficient data-driven mineral prospectivity mapping model. Since the parameters of OCSVM directly affect the performance of the model, it is necessary to optimize the parameters of OCSVM in mineral prospectivity mapping. Trial and error method is [...] Read more.

One-class support vector machine (OCSVM) is an efficient data-driven mineral prospectivity mapping model. Since the parameters of OCSVM directly affect the performance of the model, it is necessary to optimize the parameters of OCSVM in mineral prospectivity mapping. Trial and error method is usually used to determine the “optimal” parameters of OCSVM. However, it is difficult to find the globally optimal parameters by the trial and error method. By combining OCSVM with the bat algorithm, the intialization parameters of the OCSVM can be automatically optimized. The combined model is called bat-optimized OCSVM. In this model, the area under the curve (AUC) of OCSVM is taken as the fitness value of the objective function optimized by the bat algorithm, the value ranges of the initialization parameters of OCSVM are used to specify the search space of bat population, and the optimal parameters of OCSVM are automatically determined through the iterative search process of the bat algorithm. The bat-optimized OCSVMs were used to map mineral prospectivity of the Helong district, Jilin Province, China, and compared with the OCSVM initialized by the default parameters (i.e., common OCSVM) and the OCSVM optimized by trial and error. The results show that (a) the receiver operating characteristic (ROC) curve of the trial and error-optimized OCSVM is intersected with those of the bat-optimized OCSVMs and (b) the ROC curves of the optimized OCSVMs slightly dominate that of the common OCSVM in the ROC space. The area under the curves (AUCs) of the common and trial and error-optimized OCSVMs (0.8268 and 0.8566) are smaller than those of the bat-optimized ones (0.8649 and 0.8644). The optimal threshold for extracting mineral targets was determined by using the Youden index. The mineral targets predicted by the common and trial and error-optimized OCSVMs account for 29.61% and 18.66% of the study area respectively, and contain 93% and 86% of the known mineral deposits. The mineral targets predicted by the bat-optimized OCSVMs account for 19.84% and 14.22% of the study area respectively, and also contain 93% and 86% of the known mineral deposits. Therefore, we have 0.93/0.2961 = 3.1408 < 0.86/0.1866 = 4.6088 < 0.93/0.1984 = 4.6875 < 0.86/0.1422 = 6.0478, indicating that the bat-optimized OCSVMs perform slightly better than the common and trial and error-optimized OCSVMs in mineral prospectivity mapping. Full article

(This article belongs to the Special Issue Novel Methods and Applications for Mineral Exploration)

► Show Figures

Figure 1

38 pages, 8289 KiB

Open AccessEditor’s ChoiceArticle

Spatial and Temporal Controls on the Distribution of Indium in Xenothermal Vein-Deposits: The Huari Huari District, Potosí, Bolivia

by Lisard Torró, Joan Carles Melgarejo, Laura Gemmrich, Diva Mollinedo, Malena Cazorla, Álvaro Martínez, Núria Pujol-Solà, Júlia Farré-de-Pablo, Antoni Camprubí, David Artiaga, Belén Torres, Pura Alfonso and Osvaldo Arce

Minerals 2019, 9(5), 304; https://doi.org/10.3390/min9050304 - 17 May 2019

Cited by 25 | Viewed by 7080

Abstract

The Huari Huari deposit, Potosí Department in SW Bolivia, hosts polymetallic stratiform and vein mineralization of Miocene age with significant concentrations of the critical metal indium (In). Vein mineralization records document early crystallization of quartz and cassiterite followed by prominent associations of sulfides [...] Read more.

The Huari Huari deposit, Potosí Department in SW Bolivia, hosts polymetallic stratiform and vein mineralization of Miocene age with significant concentrations of the critical metal indium (In). Vein mineralization records document early crystallization of quartz and cassiterite followed by prominent associations of sulfides and sulfosalts. The earliest sulfide was arsenopyrite, followed by pyrrhotite, and progressively giving way to pyrite as the main iron sulfide, whereas Cu–Ag–Pb sulfosalts constitute late hypogene associations. Sphalerite is the chief ore mineral, and its crystallization is extended during most of the mineralization lifespan as evidenced by its initial cocrystallization with pyrrhotine, then with pyrite, and finally with Ag–Pb sulfosalts. The composition of sphalerite varies from early to late generations with a continuous decrease in FeS that attests to a decrease in temperature, which is constrained to vary from ~450 to <200 °C, and/or an increase in f(S₂), both congruent with the described paragenetic sequence. Indium concentrated mostly in the structure of Fe-rich sphalerite (up to 3.49 wt. %) and stannite (up to 2.64 wt. %) as limited solid solutions with roquesite in the (Zn,Fe)S–Cu₂FeSnS₄–CuInS₂ pseudoternary system. In sphalerite, In shows a strong positive correlation with Cu at Cu/In = 1, suggesting its incorporation via a (Cu⁺ + In³⁺) ↔ 2Zn²⁺ coupled substitution, and it does not correlate with Fe. In stannite, In shows a moderate, negative correlation with Cu and Sn, and an In³⁺ ↔ (Cu⁺ + ½ Sn⁴⁺) coupled substitution is suggested. Coexisting sphalerite and stannite yielded the highest In concentrations and crystallized at temperatures between 350 and 250 °C. Copper activity probably played a major role in the accumulation of In in the structure of sphalerite since In-bearing sphalerite coexisted with the deposition of stannite, shows high concentrations of Cu (up to 0.13 atoms per formula unit (a.p.f.u.)) in its structure, and hosts exsolutions of stannite and chalcopyrite. Distribution on the district scale of In suggests an input of hydrothermal fluids richer in Cu in the central position of the mineralizing system, represented by the Antón Bravo vein. Full article

(This article belongs to the Special Issue Mineral Deposits of Critical Elements)

► Show Figures

Figure 1

14 pages, 3470 KiB

Open AccessEditor’s ChoiceArticle

Numerical Simulation of Flow Field Characteristics and Separation Performance Test of Multi-Product Hydrocyclone

by Yuekan Zhang, Peikun Liu, Lanyue Jiang, Xinghua Yang and Junru Yang

Minerals 2019, 9(5), 300; https://doi.org/10.3390/min9050300 - 16 May 2019

Cited by 5 | Viewed by 3712

Abstract

A traditional hydrocyclone can only generate two products with different size fractions after one classification, which does not meet the fine classification requirements for narrow size fractions. In order to achieve the fine classification, a multi-product hydrocyclone with double-overflow-pipe structure was designed in [...] Read more.

A traditional hydrocyclone can only generate two products with different size fractions after one classification, which does not meet the fine classification requirements for narrow size fractions. In order to achieve the fine classification, a multi-product hydrocyclone with double-overflow-pipe structure was designed in this study. In this work, numerical simulation and experimental test methods were used to study the internal flow field characteristics and distribution characteristics of the product size fraction. The simulation results showed that in contrast with the traditional single overflow pipe, there were two turns in the internal axial velocity direction of the hydrocyclone with the double-overflow-pipe structure. Meanwhile, the influence rule of the diameter of the underflow outlet on the flow field characteristics was obtained through numerical simulation. From the test, five products with different size fractions were obtained after one classification and the influence rule of the diameter of the underflow outlet on the size fraction distribution of multi-products was also obtained. This work provides a feasible research idea for obtaining the fine classification of multiple products. Full article

(This article belongs to the Special Issue Physical Separation and Enrichment)

► Show Figures

Figure 1

12 pages, 1389 KiB

Open AccessEditor’s ChoiceArticle

Laboratory Scale Investigations on Heap (Bio)leaching of Municipal Solid Waste Incineration Bottom Ash

by Jarno Mäkinen, Marja Salo, Jaakko Soini and Päivi Kinnunen

Minerals 2019, 9(5), 290; https://doi.org/10.3390/min9050290 - 11 May 2019

Cited by 14 | Viewed by 4351

Abstract

Municipal solid waste incineration bottom ash (MSWI BA) is the main output of the municipal solid waste incineration process, both in mass and volume. It contains some heavy metals that possess market value, but may also limit the utilization of the material. This [...] Read more.

Municipal solid waste incineration bottom ash (MSWI BA) is the main output of the municipal solid waste incineration process, both in mass and volume. It contains some heavy metals that possess market value, but may also limit the utilization of the material. This study illustrates a robust and simple heap leaching method for recovering zinc and copper from MSWI BA. Moreover, the effect of autotrophic and acidophilic bioleaching microorganisms in the system was studied. Leaching yields for zinc and copper varied between 18–53% and 6–44%, respectively. For intensified copper dissolution, aeration and possibly iron oxidizing bacteria caused clear benefits. The MSWI BA was challenging to treat. The main components, iron and aluminum, dissolved easily and unwantedly, decreasing the quality of pregnant leach solution. Moreover, the physical nature and the extreme heterogeneity of the material caused operative requirements for the heap leaching. Nevertheless, with optimized parameters, heap leaching may offer a proper solution for MSWI BA treatment. Full article

(This article belongs to the Special Issue Recent Advances in Hydro- and Biohydrometallurgy)

► Show Figures

Figure 1

15 pages, 7877 KiB

Open AccessEditor’s ChoiceArticle

Geostatistical Determination of Ore Shoot Plunge and Structural Control of the Sizhuang World-Class Epizonal Orogenic Gold Deposit, Jiaodong Peninsula, China

by Si-Rui Wang, Li-Qiang Yang, Jian-Gang Wang, En-Jing Wang and Yong-Lin Xu

Minerals 2019, 9(4), 214; https://doi.org/10.3390/min9040214 - 4 Apr 2019

Cited by 24 | Viewed by 8147

Abstract

The Jiaodong Peninsula in eastern China is the third largest gold-mining area and one of the most important orogenic gold provinces in the world. Ore shoots plunging in specific orientations are a ubiquitous feature of the Jiaodong lode deposits. The Sizhuang gold deposit, [...] Read more.

The Jiaodong Peninsula in eastern China is the third largest gold-mining area and one of the most important orogenic gold provinces in the world. Ore shoots plunging in specific orientations are a ubiquitous feature of the Jiaodong lode deposits. The Sizhuang gold deposit, located in northwestern Jiaodong, is characterized by orebodies of different occurrences. The orientation of ore shoots has remained unresolved for a long time. In this paper, geostatistical tools were used to determine the plunge and structural control of ore shoots in the Sizhuang deposit. The ellipses determined by variogram modeling reveal the anisotropy of mineralization, plus the shape, size, and orientation of individual ore shoots. The long axes of the anisotropy ellipses trend NE or SEE and plunge 48° NE down the dip. However, individual ore shoots plunge almost perpendicular to the plunge of the ore deposit as a whole. This geometry is interpreted to have resulted from two periods of fluid flow parallel to two sets of striations that we identified on ore-controlling faults. Thrust-related lineations with a sinistral strike-slip component were associated with early-stage mineralization. This was overprinted by dextral and normal movement of the ore-controlling fault that controlled the late-stage mineralization. This kinematic switch caused a change in the upflow direction of ore-forming fluid, which in turn controlled the orientation of the large-scale orebodies and the subvertical plunge of individual ore shoots. Thus, a regional transition from NW-to-SE-trending compression to NW-to-SE-trending extension is interpreted as the geodynamic background of the ore-forming process. This research exemplifies an effective exploration strategy for studying the structural control of the geometry, orientation, and grade distribution of orebodies via the integration of geostatistical tools and structural analysis. Full article

(This article belongs to the Special Issue Polymetallic Metallogenic System)

► Show Figures

Figure 1

31 pages, 7721 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Volcanic-Derived Placers as a Potential Resource of Rare Earth Elements: The Aksu Diamas Case Study, Turkey

by Eimear Deady, Alicja Lacinska, Kathryn M. Goodenough, Richard A. Shaw and Nick M. W. Roberts

Minerals 2019, 9(4), 208; https://doi.org/10.3390/min9040208 - 30 Mar 2019

Cited by 16 | Viewed by 9121

Abstract

Rare earth elements (REE) are essential raw materials used in modern technology. Current production of REE is dominated by hard-rock mining, particularly in China, which typically requires high energy input. In order to expand the resource base of the REE, it is important [...] Read more.

Rare earth elements (REE) are essential raw materials used in modern technology. Current production of REE is dominated by hard-rock mining, particularly in China, which typically requires high energy input. In order to expand the resource base of the REE, it is important to determine what alternative sources exist. REE placers have been known for many years, and require less energy than mining of hard rock, but the REE ore minerals are typically derived from eroded granitic rocks and are commonly radioactive. Other types of REE placers, such as those derived from volcanic activity, are rare. The Aksu Diamas heavy mineral placer in Turkey has been assessed for potential REE extraction as a by-product of magnetite production, but its genesis was not previously well understood. REE at Aksu Diamas are hosted in an array of mineral phases, including apatite, chevkinite group minerals (CGM), monazite, allanite and britholite, which are concentrated in lenses and channels in unconsolidated Quaternary sands. Fingerprinting of pyroxene, CGM, magnetite and zircon have identified the source of the placer as the nearby Gölcük alkaline volcanic complex, which has a history of eruption throughout the Plio-Quaternary. Heavy minerals were eroded from tephra and reworked into basinal sediments. This type of deposit may represent a potential resource of REE in other areas of alkaline volcanism. Full article

(This article belongs to the Special Issue Rare Earth Deposits and Challenges of World REE Demand for High-Tech and Green-Tech at the Beginning of the 3^rd Millennium)

► Show Figures

Graphical abstract

32 pages, 9000 KiB

Open AccessFeature PaperEditor’s ChoiceReview

X-ray Microcomputed Tomography (µCT) for Mineral Characterization: A Review of Data Analysis Methods

by Pratama Istiadi Guntoro, Yousef Ghorbani, Pierre-Henri Koch and Jan Rosenkranz

Minerals 2019, 9(3), 183; https://doi.org/10.3390/min9030183 - 15 Mar 2019

Cited by 62 | Viewed by 12102

Abstract

The main advantage of X-ray microcomputed tomography (µCT) as a non-destructive imaging tool lies in its ability to analyze the three-dimensional (3D) interior of a sample, therefore eliminating the stereological error exhibited in conventional two-dimensional (2D) image analysis. Coupled with the correct data [...] Read more.

The main advantage of X-ray microcomputed tomography (µCT) as a non-destructive imaging tool lies in its ability to analyze the three-dimensional (3D) interior of a sample, therefore eliminating the stereological error exhibited in conventional two-dimensional (2D) image analysis. Coupled with the correct data analysis methods, µCT allows extraction of textural and mineralogical information from ore samples. This study provides a comprehensive overview on the available and potentially useful data analysis methods for processing 3D datasets acquired with laboratory µCT systems. Our study indicates that there is a rapid development of new techniques and algorithms capable of processing µCT datasets, but application of such techniques is often sample-specific. Several methods that have been successfully implemented for other similar materials (soils, aggregates, rocks) were also found to have the potential to be applied in mineral characterization. The main challenge in establishing a µCT system as a mineral characterization tool lies in the computational expenses of processing the large 3D dataset. Additionally, since most of the µCT dataset is based on the attenuation of the minerals, the presence of minerals with similar attenuations limits the capability of µCT in mineral segmentation. Further development on the data processing workflow is needed to accelerate the breakthrough of µCT as an analytical tool in mineral characterization. Full article

(This article belongs to the Special Issue Mineral Liberation)

► Show Figures

Figure 1

18 pages, 3649 KiB

Open AccessEditor’s ChoiceArticle

Occurrence of Graphite-Like Carbon in Podiform Chromitites of Greece and Its Genetic Significance

by Maria Economou-Eliopoulos, George Tsoupas and Vasilis Skounakis

Minerals 2019, 9(3), 152; https://doi.org/10.3390/min9030152 - 3 Mar 2019

Cited by 9 | Viewed by 4680

Abstract

The role of post-magmatic processes in the composition of chromitites hosted in ophiolite complexes, the origin of super-reduced phases, and factors controlling the carbon recycling in a supra-subduction zone environment are still unclear. The present contribution compiles the first scanning electron microscope/energy-dispersive (SEM/EDS) [...] Read more.

The role of post-magmatic processes in the composition of chromitites hosted in ophiolite complexes, the origin of super-reduced phases, and factors controlling the carbon recycling in a supra-subduction zone environment are still unclear. The present contribution compiles the first scanning electron microscope/energy-dispersive (SEM/EDS) data on graphite-like amorphous carbon, with geochemical and mineral chemistry data, from chromitites of the Skyros, Othrys, Pindos, and Veria ophiolites (Greece). The aim of this study was the delineation of potential relationships between the modified composition of chromite and the role of redox conditions, during the long-term evolution of chromitites in a supra-subduction zone environment. Chromitites are characterized by a strong brittle (cataclastic) texture and the presence of phases indicative of super-reducing phases, such as Fe–Ni–Cr-alloys, awaruite (Ni₃Fe), and heazlewoodite (Ni₃S₂). Carbon-bearing assemblages are better revealed on Au-coated unpolished sections. Graphite occurs in association with hydrous silicates (chlorite, serpentine) and Fe²⁺-chromite, as inclusions in chromite, filling cracks within chromite, or as nodule-like graphite aggregates. X-ray spectra of graphite–silicate aggregates showed the presence of C, Si, Mg, Al, O in variable proportions, and occasionally K and Ca. The extremely low fO₂ during serpentinization facilitated the occurrence of methane in microfractures of chromitites, the precipitation of super-reducing phases (metal alloys, awaruite, heazlewoodite), and graphite. In addition, although the origin of Fe–Cu–Ni-sulfides in ultramafic parts of ophiolite complexes is still unclear, in the case of the Othrys chromitites, potential reduction-induced sulfide and/or carbon saturation may drive formation of sulfide ores and graphite-bearing chromitites. The presented data on chromitites covering a wide range in platinum-group element (PGE) content, from less than 100 ppb in the Othrys to 25 ppm ΣPGE in the Veria ores, showed similarity in the abundance of graphite-like carbon. The lack of any relationship between graphite (and probably methane) and the PGE content may be related to the occurrence of the (Ru–Os–Ir) minerals in chromitites, which occur mostly as oxides/hydroxides, and to lesser amounts of laurite, with pure Ru instead activating the stable CO₂ molecule and reducing it to methane (experimental data from literature). Full article

(This article belongs to the Special Issue Spinel Group Minerals)

► Show Figures

Figure 1

7 pages, 1132 KiB

Open AccessEditor’s ChoiceArticle

Selective Separation of Hematite by a Synthesized Depressant in Various Scales of Anionic Reverse Flotation

by Arash Tohry, Reza Dehghan, Saeed Chehreh Chelgani, Jan Rosenkranz and Omid Ali Rahmani

Minerals 2019, 9(2), 124; https://doi.org/10.3390/min9020124 - 20 Feb 2019

Cited by 8 | Viewed by 4361

Abstract

Demand for high-quality iron concentrate is significantly increasing around the world. Thus, the development of the techniques for a selective separation and rejection of typical associated minerals in the iron oxide ores, such as phosphorous minerals (mainly apatite group), is a high priority. [...] Read more.

Demand for high-quality iron concentrate is significantly increasing around the world. Thus, the development of the techniques for a selective separation and rejection of typical associated minerals in the iron oxide ores, such as phosphorous minerals (mainly apatite group), is a high priority. Reverse anionic flotation by using sodium silicate (SS) as an iron oxide depressant is one of the techniques for iron ore processing. This investigation is going to present a synthesized reagent “sodium co-silicate (SCS)” for hematite depression through a reverse anionic flotation. The main hypothesis is the selective depression of hematite and, simultaneously, modification of the pulp pH by SCS. Various flotation experiments, including micro-flotation, and batch flotation of laboratory and industrial scales, were conducted in order to compare the depression selectivity of SS versus SCS. Outcomes of flotation tests at the different flotation scales demonstrated that hematite depression by SCS is around 3.3% higher than by SS. Based on flotation experiment outcomes, it was concluded that SCS can modify the pH of the process at ~9.5, and the plant reagents (including NaOH, Na₂CO₃, and SS gel) can be replaced by just SCS, which can also lead to a higher efficiency in the plant. Full article

(This article belongs to the Special Issue Flotation Reagents)

► Show Figures

Figure 1

17 pages, 2920 KiB

Open AccessEditor’s ChoiceArticle

Carbon Sources and the Graphitization of Carbonaceous Matter in Precambrian Rocks of the Keivy Terrane (Kola Peninsula, Russia)

by Ekaterina Fomina, Evgeniy Kozlov, Kirill Lokhov, Olga Lokhova and Vladimir Bocharov

Minerals 2019, 9(2), 94; https://doi.org/10.3390/min9020094 - 8 Feb 2019

Cited by 9 | Viewed by 4978

Abstract

The Precambrian rocks of the Keivy Terrane reveal five types of carbonaceous matter (CM): Fine-grained, flaky, nest, vein, and spherulitic. These types differ in their distribution character, carbon isotope composition, and graphitization temperatures calculated by the Raman spectra of carbonaceous material (RSCM) geothermometry. [...] Read more.

The Precambrian rocks of the Keivy Terrane reveal five types of carbonaceous matter (CM): Fine-grained, flaky, nest, vein, and spherulitic. These types differ in their distribution character, carbon isotope composition, and graphitization temperatures calculated by the Raman spectra of carbonaceous material (RSCM) geothermometry. Supracrustal rocks of the Keivy Terrane contain extremely isotopically light (δ¹³C_PDB = –43 ± 3‰) carbon. Presumably, its source was a methane–aqueous fluid. According to temperature calculations, this carbon matter and the host strata underwent at least two stages of metamorphism in the west of the Keivy Terrane and one stage in the east. The CM isotope signatures of several samples of kyanite schists (δ¹³C_PDB = –33 ± 5‰) are close to those of oils and oil source rocks, and they indicate an additional carbon reservoir. Thus, in the Keivy territory, an oil-and-gas bearing basin has existed. Heavy carbon (δ¹³C_PDB = −8 ± 3‰) precipitated from an aqueous CO₂-rich fluid is derived from either the lower crust or the mantle. This fluid probably migrated from the Keivy alkaline granites into the surrounding rocks previously enriched with “methanogenic” carbon. Full article

(This article belongs to the Special Issue Mineralogy of Natural Graphite)

► Show Figures

Figure 1

16 pages, 5972 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Controls on the Distribution of Invisible and Visible Gold in the Orogenic Gold Deposits of the Yangshan Gold Belt, West Qinling Orogen, China

by Nan Li, Jun Deng, David I. Groves and Ri Han

Minerals 2019, 9(2), 92; https://doi.org/10.3390/min9020092 - 4 Feb 2019

Cited by 9 | Viewed by 6840

Abstract

Six orogenic gold deposits constitute the Yangshan gold belt in the West Qinling Orogen. Gold is mostly invisible in solid solution or in the sulfide lattice, with minor visible gold associated with stibnite and in quartz-calcite veins. Detailed textural and trace-element analysis of [...] Read more.

Six orogenic gold deposits constitute the Yangshan gold belt in the West Qinling Orogen. Gold is mostly invisible in solid solution or in the sulfide lattice, with minor visible gold associated with stibnite and in quartz-calcite veins. Detailed textural and trace-element analysis of sulfides in terms of a newly-erected paragenetic sequence for these deposits, together with previously published data, demonstrate that early magmatic-hydrothermal pyrite in granitic dike host-rocks has much higher Au contents than diagenetic pyrite in metasedimentary host rocks, but lower contents of As, Au, and Cu than ore-stage pyrite. Combined with sulfur isotope data, replacement textures in the gold ores indicate that the auriferous ore-fluids post-dated the granitic dikes and were not magmatic-hydrothermal in origin. There is a strong correlation between the relative activities of S and As and their total abundances in the ore fluid and the siting of gold in the Yangshan gold ores. Mass balance calculations indicate that there is no necessity to invoke remobilization processes to explain the occurrence of gold in the ores. The only exception is the Py_1-2 replacement of Py_1m, where fluid-mediated coupled dissolution-reprecipitation reactions may have occurred to exchange Au between the two pyrite phases. Full article

(This article belongs to the Special Issue Polymetallic Metallogenic System)

► Show Figures

Figure 1

14 pages, 4153 KiB

Open AccessEditor’s ChoiceArticle

Fingerprinting Paranesti Rubies through Oxygen Isotopes

by Kandy K. Wang, Ian T. Graham, Laure Martin, Panagiotis Voudouris, Gaston Giuliani, Angela Lay, Stephen J. Harris and Anthony Fallick

Minerals 2019, 9(2), 91; https://doi.org/10.3390/min9020091 - 3 Feb 2019

Cited by 7 | Viewed by 4836

Abstract

In this study, the oxygen isotope (δ¹⁸O) composition of pink to red gem-quality rubies from Paranesti, Greece was investigated using in-situ secondary ionization mass spectrometry (SIMS) and laser-fluorination techniques. Paranesti rubies have a narrow range of δ¹⁸O values between [...] Read more.

In this study, the oxygen isotope (δ¹⁸O) composition of pink to red gem-quality rubies from Paranesti, Greece was investigated using in-situ secondary ionization mass spectrometry (SIMS) and laser-fluorination techniques. Paranesti rubies have a narrow range of δ¹⁸O values between ~0 and +1‰ and represent one of only a few cases worldwide where δ¹⁸O signatures can be used to distinguish them from other localities. SIMS analyses from this study and previous work by the authors suggests that the rubies formed under metamorphic/metasomatic conditions involving deeply penetrating meteoric waters along major crustal structures associated with the Nestos Shear Zone. SIMS analyses also revealed slight variations in δ¹⁸O composition for two outcrops located just ~500 m apart: PAR-1 with a mean value of 1.0‰ ± 0.42‰ and PAR-5 with a mean value of 0.14‰ ± 0.24‰. This work adds to the growing use of in-situ methods to determine the origin of gem-quality corundum and re-confirms its usefulness in geographic “fingerprinting”. Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Gems)

► Show Figures

Figure 1

41 pages, 23058 KiB

Open AccessEditor’s ChoiceArticle

Gem Corundum Deposits of Greece: Geology, Mineralogy and Genesis

by Panagiotis Voudouris, Constantinos Mavrogonatos, Ian Graham, Gaston Giuliani, Vasilios Melfos, Stefanos Karampelas, Vilelmini Karantoni, Kandy Wang, Alexandre Tarantola, Khin Zaw, Sebastien Meffre, Stephan Klemme, Jasper Berndt, Stefanie Heidrich, Federica Zaccarini, Anthony Fallick, Maria Tsortanidis and Andreas Lampridis

Minerals 2019, 9(1), 49; https://doi.org/10.3390/min9010049 - 15 Jan 2019

Cited by 18 | Viewed by 13264

Abstract

Greece contains several gem corundum deposits set within diverse geological settings, mostly within the Rhodope (Xanthi and Drama areas) and Attico-Cycladic (Naxos and Ikaria islands) tectono-metamorphic units. In the Xanthi area, the sapphire (pink, blue to purple) deposits are stratiform, occurring within marble [...] Read more.

Greece contains several gem corundum deposits set within diverse geological settings, mostly within the Rhodope (Xanthi and Drama areas) and Attico-Cycladic (Naxos and Ikaria islands) tectono-metamorphic units. In the Xanthi area, the sapphire (pink, blue to purple) deposits are stratiform, occurring within marble layers alternating with amphibolites. Deep red rubies in the Paranesti-Drama area are restricted to boudinaged lenses of Al-rich metapyroxenites alternating with amphibolites and gneisses. Both occurrences are oriented parallel to the ultra-high pressure/high pressure (UHP/HP) Nestos suture zone. On central Naxos Island, colored sapphires are associated with desilicated granite pegmatites intruding ultramafic lithologies (plumasites), occurring either within the pegmatites themselves or associated metasomatic reaction zones. In contrast, on southern Naxos and Ikaria Islands, blue sapphires occur in extensional fissures within Mesozoic metabauxites hosted in marbles. Mineral inclusions in corundums are in equilibrium and/or postdate corundum crystallization and comprise: spinel and pargasite (Paranesti), spinel, zircon (Xanthi), margarite, zircon, apatite, diaspore, phlogopite and chlorite (Naxos) and chloritoid, ilmenite, hematite, ulvospinel, rutile and zircon (Ikaria). The main chromophore elements within the Greek corundums show a wide range in concentration: the Fe contents vary from (average values) 1099 ppm in the blue sapphires of Xanthi, 424 ppm in the pink sapphires of Xanthi, 2654 ppm for Paranesti rubies, 4326 ppm for the Ikaria sapphires, 3706 for southern Naxos blue sapphires, 4777 for purple and 3301 for pink sapphire from Naxos plumasite, and finally 4677 to 1532 for blue to colorless sapphires from Naxos plumasites, respectively. The Ti concentrations (average values) are very low in rubies from Paranesti (41 ppm), with values of 2871 ppm and 509 in the blue and pink sapphires of Xanthi, respectively, of 1263 ppm for the Ikaria blue sapphires, and 520 ppm, 181 ppm in Naxos purple, pink sapphires, respectively. The blue to colorless sapphires from Naxos plumasites contain 1944 to 264 ppm Ti, respectively. The very high Ti contents of the Xanthi blue sapphires may reflect submicroscopic rutile inclusions. The Cr (average values) ranges from 4 to 691 ppm in the blue, purple and pink colored corundums from Naxos plumasite, is quite fixed (222 ppm) for Ikaria sapphires, ranges from 90 to 297 ppm in the blue and pink sapphires from Xanthi, reaches 9142 ppm in the corundums of Paranesti, with highest values of 15,347 ppm in deep red colored varieties. Each occurrence has both unique mineral assemblage and trace element chemistry (with variable Fe/Mg, Ga/Mg, Ga/Cr and Fe/Ti ratios). Additionally, oxygen isotope compositions confirm their geological typology, i.e., with, respectively δ¹⁸O of 4.9 ± 0.2‰ for sapphire in plumasite, 20.5‰ for sapphire in marble and 1‰ for ruby in mafics. The fluid inclusions study evidenced water free CO₂ dominant fluids with traces of CH₄ or N₂, and low CO₂ densities (0.46 and 0.67 g/cm³), which were probably trapped after the metamorphic peak. The Paranesti, Xanthi and central Naxos corundum deposits can be classified as metamorphic sensu stricto (s.s.) and metasomatic, respectively, those from southern Naxos and Ikaria display atypical magmatic signature indicating a hydrothermal origin. Greek corundums are characterized by wide color variation, homogeneity of the color hues, and transparency, and can be considered as potential gemstones. Full article

(This article belongs to the Special Issue Mineralogy and Geochemistry of Gems)

► Show Figures

Figure 1

12 pages, 1876 KiB

Open AccessEditor’s ChoiceArticle

Crystallization Behaviour of Iron-Hydroxide Sulphates by Aging under Ambient Temperature Conditions

by Amalia Jiménez, Ana Hernández and Manuel Prieto

Minerals 2019, 9(1), 27; https://doi.org/10.3390/min9010027 - 5 Jan 2019

Cited by 11 | Viewed by 5438

Abstract

The crystallization behaviour of jarosite and schwertmannite has been studied by precipitation-aging experiments performed using different parent-solution concentrations at acidic conditions and ambient temperature. Schwertmannite exhibits low crystallinity and is the only mineral identified during low-concentration (LC) experiments. However, in high-concentration (HC) experiments, [...] Read more.

The crystallization behaviour of jarosite and schwertmannite has been studied by precipitation-aging experiments performed using different parent-solution concentrations at acidic conditions and ambient temperature. Schwertmannite exhibits low crystallinity and is the only mineral identified during low-concentration (LC) experiments. However, in high-concentration (HC) experiments, a relatively rapid Ostwald ripening process leads to the transformation of schwertmannite into natrojarosite. The presence of sodium modifies the morphology and stability of the obtained phases. TEM observations reveal that schwertmannite particles consist of disoriented nanodomains (~6 nm) spread in an amorphous mass. In contrast, natrojarosite particles exhibit a single-domain, highly crystalline core, with the crystallinity decreasing from core to rim. The thermal behaviour of these phases depends on both their composition and their degree of crystallinity. TG and DTG analyses show that, below 500 °C, the amount of structural water is clearly higher in schwertmannite than in natrojarosite. The present results highlight the role of the ripening processes in epigenetic conditions and could be important in interpreting the formation of jarosite in Earth and Martian surface environments. Full article

(This article belongs to the Special Issue Chemical-Physical Properties of Minerals and Minerogenesis in Supergene Environment)

► Show Figures

Figure 1

21 pages, 6148 KiB

Open AccessEditor’s ChoiceArticle

Counter-Current Leaching of Low-Grade Laterites with Hydrochloric Acid and Proposed Purification Options of Pregnant Solution

by Christiana Mystrioti, Nymphodora Papassiopi, Anthimos Xenidis and Konstantinos Komnitsas

Minerals 2018, 8(12), 599; https://doi.org/10.3390/min8120599 - 18 Dec 2018

Cited by 19 | Viewed by 7002

Abstract

A hydrochloric acid hydrometallurgical process was evaluated for Ni and Co extraction from a low-grade saprolitic laterite. The main characteristics of the process were (i) the application of a counter-current mode of operation as the main leaching step (CCL), and (ii) the treatment [...] Read more.

A hydrochloric acid hydrometallurgical process was evaluated for Ni and Co extraction from a low-grade saprolitic laterite. The main characteristics of the process were (i) the application of a counter-current mode of operation as the main leaching step (CCL), and (ii) the treatment of pregnant leach solution (PLS) with a series of simple precipitation steps. It was found that, during CCL, co-dissolution of Fe was maintained at very low levels, i.e., about 0.6%, which improved the effectiveness of the subsequent PLS purification step. The treatment of PLS involved an initial precipitation step for the removal of trivalent metals, Fe, Al, and Cr, using Mg(OH)₂. The process steps that followed aimed at separating Ni and Co from Mn and the alkaline earths Mg and Ca, by a combination of repetitive oxidative precipitation and dissolution steps. Magnesium and calcium remained in the aqueous phase, Mn was removed as a solid residue of Mn(III)–Mn(IV) oxides, while Ni and Co were recovered as a separate aqueous stream. It was found that the overall Ni and Co recoveries were 40% and 38%, respectively. About 45% of Ni and 37% of Co remained in the leach residue, while 15% Ni and 20% Co were lost in the Mn oxides. Full article

(This article belongs to the Special Issue Recent Advances in Hydro- and Biohydrometallurgy)

► Show Figures

Figure 1

21 pages, 6548 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Petrographic Characteristics and Physico-Mechanical Properties of Aggregates on the Quality of Concrete

by Petros Petrounias, Panagiota P. Giannakopoulou, Aikaterini Rogkala, Panagiotis M. Stamatis, Paraskevi Lampropoulou, Basilios Tsikouras and Konstantin Hatzipanagiotou

Minerals 2018, 8(12), 577; https://doi.org/10.3390/min8120577 - 8 Dec 2018

Cited by 53 | Viewed by 7784

Abstract

This paper examines the effect of the aggregate type on concrete strength, and more specifically, how the petrographic characteristics of various aggregate rocks as well as their physico-mechanical properties influences the durability of C 25/30 strength class concrete. The studied aggregate rocks were [...] Read more.

This paper examines the effect of the aggregate type on concrete strength, and more specifically, how the petrographic characteristics of various aggregate rocks as well as their physico-mechanical properties influences the durability of C 25/30 strength class concrete. The studied aggregate rocks were derived from Veria-Naousa and Edessa ophiolitic complexes as well as granodiorite and albitite rocks from their surrounding areas in central Macedonia (Greece). Concretes were produced with constant volume proportions, workability, mixing and curing conditions using different sizes of each aggregate type. Aggregates were mixed both in dry and water saturated states in concretes. Six different types of aggregates were examined and classified in three district groups according to their physicomechanical properties, petrographic characteristics and surface texture. The classification in groups after the concrete compressive strength test verified the initial classification in the same three groups. Group I (ultramafic rocks) presented the lowest concrete strengths, depending on their high alteration degree and the low mechanical properties of ultramafic aggregates. Group II (mafic rocks and granodiorite) presented a wide range of concrete strengths, depending on different petrographic characteristics and mechanical properties. Group III (albite rocks) presented the highest concrete strengths, depending on their lowest alteration degree and their highest mechanical properties. Therefore, mineralogy and microstructure of the coarse aggregates affected the final strength of the concrete specimens. Full article

(This article belongs to the Special Issue Petrography of Construction Materials: Compositional, Mineralogical and Textural Features)

► Show Figures

Figure 1

25 pages, 9270 KiB

Open AccessEditor’s ChoiceArticle

Geochemistry and Mineralogy of Rare Earth Elements (REE) in Bauxitic Ores of the Catalan Coastal Range, NE Spain

by Nils Reinhardt, Joaquín A. Proenza, Cristina Villanova-de-Benavent, Thomas Aiglsperger, Telm Bover-Arnal, Lisard Torró, Ramon Salas and Annika Dziggel

Minerals 2018, 8(12), 562; https://doi.org/10.3390/min8120562 - 1 Dec 2018

Cited by 49 | Viewed by 8582

Abstract

Karst bauxite deposits are currently investigated as a new resource for rare earth elements (REE) in order to avoid present and future supply shortfalls of these critical metals. The present work focuses on the geochemistry and mineralogy of the REE in karst bauxite [...] Read more.

Karst bauxite deposits are currently investigated as a new resource for rare earth elements (REE) in order to avoid present and future supply shortfalls of these critical metals. The present work focuses on the geochemistry and mineralogy of the REE in karst bauxite deposits of the Catalan Coastal Range (CCR), NE-Spain. It is revealed that the studied bauxitic ores have a dominant breccia and local ooido-pisoidic and pelitomorphic texture. The bauxitic ores are mostly composed of kaolinite and hematite, as well as of lesser amounts of boehmite, diaspore, rutile and calcite. The mineralogy and major element composition indicate incomplete bauxitization of an argillaceous precursor material possibly derived from the erosion of the Mesozoic Ebro massif paleo-high. The studied bauxites are characterized by ∑REE (including Sc, Y) between 286 and 820 ppm (av. 483 ppm) and light REE to heavy REE (LREE/HREE) ratios up to 10.6. REE are mainly concentrated in phosphate minerals, identified as monazite-(Ce) and xenotime-(Y) of detrital origin and unidentified REE-phosphates of a possible authigenic origin. REE remobilization presumably took place under acidic conditions, whereas REE entrapment in the form of precipitation of authigenic rare earth minerals from percolating solutions was related to neutral to slightly alkaline conditions. During the bauxitization process no significant REE fractionation took place and the REE distribution pattern of the bauxitic ores was governed by the REE budget of the precursor material. Finally, adsorption as a main REE scavenging mechanism in the studied CCR bauxite deposits should not be considered, since the presented data did not reveal significant REE contents in Fe-and Mn-oxyhydroxides and clay minerals. Full article

(This article belongs to the Special Issue Mineral Deposits of Critical Elements)

► Show Figures

Figure 1

13 pages, 2893 KiB

Open AccessEditor’s ChoiceArticle

“Zero-Waste”: A Sustainable Approach on Pyrometallurgical Processing of Manganese Nodule Slags

by Marcus Sommerfeld, David Friedmann, Thomas Kuhn and Bernd Friedrich

Minerals 2018, 8(12), 544; https://doi.org/10.3390/min8120544 - 23 Nov 2018

Cited by 38 | Viewed by 9159

Abstract

A continuously growing demand for valuable non-ferrous metals and therefore an increase in their prices at the metal exchanges makes it necessary and profitable to investigate alternative metal resources. Polymetallic deep-sea nodules contain cobalt, copper, manganese, molybdenum and nickel, and are highly abundant [...] Read more.

A continuously growing demand for valuable non-ferrous metals and therefore an increase in their prices at the metal exchanges makes it necessary and profitable to investigate alternative metal resources. Polymetallic deep-sea nodules contain cobalt, copper, manganese, molybdenum and nickel, and are highly abundant on the sea floor. Developing a metallurgical process to recover the metal content from manganese nodules can close the predicted supply gap of critical metals like cobalt. This paper investigated a potential extraction process for valuable metals from manganese nodules supplied by the German Federal Institute for Geosciences and Natural Resources. The samples originated from the German license area of the Clarion-Clipperton Zone in the Pacific Ocean. Due to a low concentration of valuable metals in nodules, a pyrometallurgical enrichment step was carried out to separate cobalt, copper, molybdenum and nickel in a metallic phase. The manganese was discarded in the slag and recovered in a second smelting step as ferromanganese. To aid the experiments, FactSage^TM was used for thermodynamic modeling of the smelting steps. To increase metal yields and to alter the composition of the metal alloys, different fluxes were investigated. The final slag after two reduction steps were heavy-metal free and a utilization as a mineral product was desired to ensure a zero-waste process. Full article

(This article belongs to the Special Issue Marine Minerals of the Deep Sea: Mineralogy, Crystallography and Their Use for Tailored Processing and Metal Extraction)

► Show Figures

Figure 1

21 pages, 45558 KiB

Open AccessEditor’s ChoiceArticle

Underground Vertical Seismic Profiling with Conventional and Fiber-Optic Systems for Exploration in the Kylylahti Polymetallic Mine, Eastern Finland

by Marko Riedel, Calin Cosma, Nicoleta Enescu, Emilia Koivisto, Kari Komminaho, Katri Vaittinen and Michał Malinowski

Minerals 2018, 8(11), 538; https://doi.org/10.3390/min8110538 - 20 Nov 2018

Cited by 25 | Viewed by 6982

Abstract

Seismic reflection methods have been used for the exploration of mineral resources for several decades. However, despite their unmatched spatial resolution and depth penetration, they only have played a minor role in mineral discoveries so far. Instead, mining and exploration companies have traditionally [...] Read more.

Seismic reflection methods have been used for the exploration of mineral resources for several decades. However, despite their unmatched spatial resolution and depth penetration, they only have played a minor role in mineral discoveries so far. Instead, mining and exploration companies have traditionally focused more on the use of potential field, electric and electromagnetic methods. In this context, we present a case study of an underground Vertical Seismic Profiling (VSP) experiment, which was designed to image a (semi-)massive sulfide deposit located in the Kylylahti polymetallic mine in eastern Finland. For the measurement, we used a conventional VSP with three-component geophones and a novel fiber-optic Distributed Acoustic Sensing (DAS) system. Both systems were deployed in boreholes located nearby the target sulfide deposit, and used in combination with an active seismic source that was fired from within the underground tunnels. With this setup, we successfully recorded seismic reflections from the deposit and its nearby geological contrasts. The recording systems provided data with a good signal-to-noise ratio and high spatial resolution. In addition to the measurements, we generated a realistic synthetic dataset based on a detailed geological model derived from extensive drilling data and petrophysical laboratory analysis. Specific processing and imaging of the acquired and synthetic datasets yielded high-resolution reflectivity images. Joint analysis of these images and cross-validation with lithological logging data from 135 nearby boreholes led to successful interpretation of key geological contacts including the target sulfide mineralization. In conclusion, our experiment demonstrates the value of in-mine VSP measurements for detailed resource delineation in a complex geological setting. In particular, we emphasize the potential benefit of using fiber-optic DAS systems, which provide reflection data at sufficient quality with less logistical effort and a higher acquisition rate. This amounts to a lower total acquisition cost, which makes DAS a valuable tool for future mineral exploration activities. Full article

(This article belongs to the Special Issue Seismic Methods in Mineral Exploration)

► Show Figures

Figure 1

18 pages, 9161 KiB

Open AccessEditor’s ChoiceArticle

Petrology of Chromitites in the Higashi-Akaishi Ultrahigh-Pressure (UHP) Peridotite Complex, Japan: Toward Understanding of General Features of the UHP Chromitites

by Makoto Miura, Shoji Arai, Tomoyuki Mizukami, Vladimir R. Shmelev and Satoko Ishimaru

Minerals 2018, 8(11), 525; https://doi.org/10.3390/min8110525 - 11 Nov 2018

Cited by 6 | Viewed by 5003

Abstract

Ultrahigh-pressure (UHP) chromitites containing UHP minerals such as coesite and diamond have been reported from some ophiolites in Tibet and the Polar Urals. Their nature, i.e., origin, P-T path and abundance, however, are still controversial and left unclear. Here we describe chromitites in [...] Read more.

Ultrahigh-pressure (UHP) chromitites containing UHP minerals such as coesite and diamond have been reported from some ophiolites in Tibet and the Polar Urals. Their nature, i.e., origin, P-T path and abundance, however, are still controversial and left unclear. Here we describe chromitites in the Higashi-akaishi (HA) ultramafic complex in the Cretaceous Sanbagawa metamorphic belt, Japan, which experienced UHP condition (up to 3.8 GPa) at the peak metamorphism via subduction, in order to understand the nature of UHP chromitites. The HA peridotites typically contain garnets and are associated with eclogites, and their associated chromitites are expected to have experienced the UHP metamorphism. The Higashi-akaishi (HA) chromitites show banded to massive structures and are concordant to foliation of the surrounding peridotite. Chromian spinels in the chromitite and surrounding peridotites were sometimes fractured by deformation, and contain various inclusions, i.e., blade- and needle-like diopside lamellae, and minute inclusions of pyroxenes, olivine, and pargasite. The peculiar UHP minerals, such as coesite and diamond, have not been found under the microscope and the Raman spectrometer. Spinels in the HA chromitites show high Cr#s (0.7 to 0.85), and low Ti contents (<0.1 wt %), suggesting a genetic linkage to an arc magma. The HA chromitites share the basic petrographic and chemical features (i.e., diopside lamellae and arc-related spinel chemistry) with the UHP chromitites from Tibet and the Polar Urals. This suggests that some of the characteristics of the UHP chromitite can be obtained by compression, possibly via deep subduction, of low-P chromitite. Full article

(This article belongs to the Special Issue Petrology, Geochemistry and Mineralogy of the Mantle as Tools to Read Messages from the Earth’s Interior)

► Show Figures

Figure 1

18 pages, 5486 KiB

Open AccessEditor’s ChoiceArticle

Copper in Natural Oxide Spinels: The New Mineral Thermaerogenite CuAl₂O₄, Cuprospinel and Cu-Enriched Varieties of Other Spinel-Group Members from Fumaroles of the Tolbachik Volcano, Kamchatka, Russia

by Igor V. Pekov, Fedor D. Sandalov, Natalia N. Koshlyakova, Marina F. Vigasina, Yury S. Polekhovsky, Sergey N. Britvin, Evgeny G. Sidorov and Anna G. Turchkova

Minerals 2018, 8(11), 498; https://doi.org/10.3390/min8110498 - 1 Nov 2018

Cited by 21 | Viewed by 6835

Abstract

This paper is the first description of natural copper-rich oxide spinels. They were found in deposits of oxidizing-type fumaroles related to the Tolbachik volcano, Kamchatka, Russia. This mineralization is represented by nine species with the following maximum contents of CuO (wt.%, given in [...] Read more.

This paper is the first description of natural copper-rich oxide spinels. They were found in deposits of oxidizing-type fumaroles related to the Tolbachik volcano, Kamchatka, Russia. This mineralization is represented by nine species with the following maximum contents of CuO (wt.%, given in parentheses): a new mineral thermaerogenite, ideally CuAl₂O₄ (26.9), cuprospinel, ideally CuFe³⁺₂O₄ (28.6), gahnite (21.4), magnesioferrite (14.7), spinel (10.9), magnesiochromite (9.0), franklinite (7.9), chromite (5.9), and zincochromite (4.8). Cuprospinel, formerly known only as a phase of anthropogenic origin, turned out to be the Cu-richest natural spinel-type oxide [sample with the composition (Cu_0.831Zn_0.100Mg_0.043Ni_0.022)_Σ0.996(Fe³⁺_1.725Al_0.219Mn³⁺_0.048Ti_0.008)_Σ2.000O₄ from Tolbachik]. Aluminum and Fe³⁺-dominant spinels (thermaerogenite, gahnite, spinel, cuprospinel, franklinite, and magnesioferrite) were deposited directly from hot gas as volcanic sublimates. The most probable temperature interval of their crystallization is 600–800 °C. They are associated with each other and with tenorite, hematite, orthoclase, fluorophlogopite, langbeinite, calciolangbeinite, aphthitalite, anhydrite, fluoborite, sylvite, halite, pseudobrookite, urusovite, johillerite, ericlaxmanite, tilasite, etc. Cu-bearing spinels are among the latest minerals of this assemblage: they occur in cavities and overgrow even alkaline sulfates. Cu-enriched varieties of chrome-spinels (magnesiochromite, chromite, and zincochromite) were likely formed in the course of the metasomatic replacement of a magmatic chrome-spinel in micro-xenoliths of ultrabasic rock under the influence of volcanic gases. The new mineral thermaerogenite, ideally CuAl₂O₄, was found in the Arsenatnaya fumarole at the Second scoria cone of the Northern Breakthrough of the Great Tolbachik Fissure Eruption. It forms octahedral crystals up to 0.02 mm typically combined in open-work clusters up to 1 mm across. Thermaerogenite is semitransparent to transparent, with a strong vitreous lustre. Its colour is brown, yellow-brown, red-brown, brown-yellow or brown-red. The mineral is brittle, with the conchoidal fracture, cleavage is none observed. D(calc.) is 4.87 g/cm³. The chemical composition of the holotype (wt.%, electron microprobe) is: CuO 25.01, ZnO 17.45, Al₂O₃ 39.43, Cr₂O₃ 0.27, Fe₂O₃ 17.96, total 100.12 wt.%. The empirical formula calculated on the basis of 4 O apfu is: (Cu_0.619Zn_0.422)_Σ1.041(Al_1.523Fe³⁺_0.443Cr_0.007)_Σ1.973O₄. The mineral is cubic, Fd-3m, a = 8.093(9) Å, V = 530.1(10) Å³. Thermaerogenite forms a continuous isomorphous series with gahnite. The strongest lines of the powder X-ray diffraction pattern of thermaerogenite [d, Å (I, %) (hkl)] are: 2.873 (65) (220), 2.451 (100) (311), 2.033 (10) (400), 1.660 (16) (422), 1.565 (28) (511) and 1.438 (30) (440). Full article

(This article belongs to the Special Issue New Mineral Species and Their Crystal Structures)

► Show Figures

Figure 1

74 pages, 66542 KiB

Open AccessEditor’s ChoiceReview

Modular Crystal Chemistry of Thallium Sulfosalts

by Emil Makovicky

Minerals 2018, 8(11), 478; https://doi.org/10.3390/min8110478 - 24 Oct 2018

Cited by 21 | Viewed by 6319

Abstract

Complex sulfides of thallium with As, Sb, or Bi and with other cations (‘thallium sulfosalts’) are a large group of crystal structures with extreme variability. Incorporation of the large Tl⁺ cation in them is solved in several different ways: housing of Tl [...] Read more.

Complex sulfides of thallium with As, Sb, or Bi and with other cations (‘thallium sulfosalts’) are a large group of crystal structures with extreme variability. Incorporation of the large Tl⁺ cation in them is solved in several different ways: housing of Tl in columns of capped trigonal coordination prisms, which form separate walls in the structure (in different combinations with Pb and/or Sb), regular alternation of large Tl with small cations (As), presence of structural arrays of Tl coordination polyhedra paralleled by arrays of As coordination pyramids with a frequency ratio 1:2, omission derivatives with cavities for Tl accommodation and formation of layer structures with thallium concentrated into separate (inter)layers of different types. The first principle leads to a large family of sartorite homologues and rare lillianite homologues, as well as to the chabournéite group. The second one to the hutchinsonite family, omission derivatives form the routhierite and galkhaite groups, and the 1:2 periodicity ratio principle results in several outstanding structures from different groups. Layer structures consist of two-component and three-component layer combinations. Close cation-cation interactions are present but rare. Full article

(This article belongs to the Special Issue Thallium: Mineralogy, Geochemistry and Ore Processes)

► Show Figures

Figure 1

33 pages, 5173 KiB

Open AccessEditor’s ChoiceArticle

Decoding of Mantle Processes in the Mersin Ophiolite, Turkey, of End-Member Arc Type: Location of the Boninite Magma Generation

by Satoko Ishimaru, Yuji Saikawa, Makoto Miura, Osman Parlak and Shoji Arai

Minerals 2018, 8(10), 464; https://doi.org/10.3390/min8100464 - 18 Oct 2018

Cited by 8 | Viewed by 5862

Abstract

The Mersin ophiolite, Turkey, is of typical arc type based on geochemistry of crustal rocks without any signs of mid-ocean ridge (MOR) affinity. We examined its ultramafic rocks to reveal sub-arc mantle processes. Mantle peridotites, poor in clinopyroxene (<1.0 vol.%), show high Fo [...] Read more.

The Mersin ophiolite, Turkey, is of typical arc type based on geochemistry of crustal rocks without any signs of mid-ocean ridge (MOR) affinity. We examined its ultramafic rocks to reveal sub-arc mantle processes. Mantle peridotites, poor in clinopyroxene (<1.0 vol.%), show high Fo content of olivine (90–92) and Cr# [=Cr/(Cr + Al) atomic ratio] (=0.62–0.77) of chromian spinel. NiO content of olivine is occasionally high (up to 0.5 wt.%) in the harzburgite. Moho-transition zone (MTZ) dunite is also highly depleted, i.e., spinel is high Cr# (0.78–0.89), clinopyroxene is poor in HREE, and olivine is high Fo (up to 92), but relatively low in NiO (0.1–0.4 wt.%). The harzburgite is residue after high-degree mantle melting, possibly assisted by slab-derived fluid. The high-Ni character of olivine suggests secondary metasomatic formation of olivine-replacing orthopyroxene although replacement textures are unclear. The MTZ dunite is of replacive origin, resulted from interaction between Mg-rich melt released from harzburgite diapir and another harzburgite at the diapir roof. The MTZ dunite is the very place that produced the boninitic and replacive dunite. The MTZ is thicker (>1 km) in Mersin than in MOR-related ophiolite (mostly < 500 m), and this is one of the features of arc-type ophiolite. Full article

(This article belongs to the Special Issue Petrology, Geochemistry and Mineralogy of the Mantle as Tools to Read Messages from the Earth’s Interior)

► Show Figures

Figure 1

13 pages, 2654 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Importance of Magmatic Water Content and Oxidation State for Porphyry-Style Au Mineralization: An Example from the Giant Beiya Au Deposit, SW China

by Xinshang Bao, Liqiang Yang, Wenyan He and Xue Gao

Minerals 2018, 8(10), 441; https://doi.org/10.3390/min8100441 - 10 Oct 2018

Cited by 25 | Viewed by 4612

Abstract

The Beiya Au deposit is the largest Cenozoic Au deposit in the Jinshajiang-Ailaoshan porphyry metallogenic belt. Numerous studies document that high water content and fO₂ are vital factors for the generation of Au mineralization. In this belt, only the Wandongshan and [...] Read more.

The Beiya Au deposit is the largest Cenozoic Au deposit in the Jinshajiang-Ailaoshan porphyry metallogenic belt. Numerous studies document that high water content and fO₂ are vital factors for the generation of Au mineralization. In this belt, only the Wandongshan and Hongnitang districts are considered to be of economic importance, while the other districts, such as Bailiancun, are barren. So in order to reveal the importance of water content and oxidation state for Beiya porphyry-style Au mineralization, the amphiboles and zircons compositions are used to evaluate the physicochemical conditions (e.g., pressure, temperature, fO₂, and water content) of the Wandongshan ore-fertile porphyries and Bailiancun ore-barren porphyries observed in the Beiya Au deposit. The results show that the water content of the Wandongshan parent magma (≤4.11 ± 0.4 wt %) are slightly higher than those of the parent magma at Bailiancun (≤3.91 ± 0.4 wt %), while the emplacement pressure of the Wandongshan parent magma (31.5–68.6 MPa) is much lower than that of the parent magma at Bailiancun (142.3–192.8 MPa), indicating that the Wandongshan magma reached water saturation earlier. In addition, the Wandongshan porphyries crystallized from more oxidized magma (average of ΔFMQ = +3.5) with an average temperature of 778 °C compared to the Bailiancun porphyries (average of ΔFMQ = +1.5) with a mean magmatic temperature of 770 °C. The Ce⁴⁺/Ce³⁺ ratio of zircon in the Wandongshan ore-related intrusions (average Ce⁴⁺/Ce³⁺ of 62.00) is much higher than that of the Bailiancun barren porphyries (average Ce⁴⁺/Ce³⁺of 23.15), which further confirmed Wandongshan ore-related magma is more oxidized than the Bailiancun barren magma. Therefore, melts that are more enriched in water and with a high oxidation state will be more fertile to form an economic porphyry-style Au system. Full article

(This article belongs to the Special Issue Polymetallic Metallogenic System)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Editor’s Choice Articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI