Fine Mineral Research Articles

Organic carbon fractional distribution and saturation in tropical soils of West African savannas with contrasting mineral composition

Savannas are dry tropical biomes characterized by high above- and belowground biomass production, but at the same time there is extensive C loss by fire regimes. Soil-mediated responses are crucial in biogeochemical cycling and the role of soil minerals may be important in controlling organic carbon (OC) storage and stabilization. The objective of this study was to determine OC fractional distribution and saturation capacity in three soil groups (Vertisols, Lixisols, Luvisols) that are characterized by specific and different 1:1 and 2:1 clay mineral dominance. For each soil group, top- and subsoils (0–10 cm, 40–60 cm) were sampled in protected Soudanian savannas across Burkina Faso and fractionated into free and aggregate-occluded particulate organic matter (fPOM, oPOM) and mineral-associated organic matter (mOM). The results showed that oPOM and mOM were significantly affected by soil groups and topsoil/subsoil layers. We consider this to be due to interactions with fine particles (clay, fine and medium silt), the presence of exchangeable Ca and Mg and extractable Al (D) and Fe (D) as revealed by significant positive correlations. We found that oPOM (13–29% of total OC) and mOM < 20 µm (54–76%) were the most important OC pools in these tropical savanna soils. Vertisols exhibited the highest OC contents and held three times more OC in the fine mineral fraction mOM < 20 µm than Lixisols and Luvisols. Luvisols were affected by mineral illuviation processes which lowered their OC contents. Overall, topsoils contained three times higher OC amounts of mOM < 20 µm than subsoils. Indications were found that all investigated topsoils are below OC saturation, likely due to prescribed fire and soil erosion effects, while the OC saturation deficit was important in Vertisols (−49 to −65%) and Lixisols (−41 to −45%). We conclude that tropical savanna soils have a high protective capacity for OC in top- and subsoils but require adequate management in order to increase OC storage.

Matching relation between matrix aspect ratio and applied magnetic induction for maximum particle capture in transversal high gradient magnetic separation

High gradient magnetic separation (HGMS) is widely applied in many industrial and scientific fields. Transversal high gradient magnetic separator applied in industry has relative higher magnetic leakage due to the large magnetic pole spacing and consequently low capacity as well as low recovery of fine minerals. Optimization of transversal HGMS is of great significance for improving mineral particle efficiency or reducing energy consumption. In this study, a new concept of matching relation between matrix aspect ratio and applied magnetic induction for maximum particle capture in transversal HGMS was proposed. Effect of matrix aspect ratio on particle capture was studied under equal matrix cross-section area and equal matrix horizontal axis using extended particle capture models for saturated and unsaturated matrices as well as model selection methodology. Particle motion trajectories under different circumstances were depicted and particle capture radii were determined and compared. Results showed that there existed matching relation between matrix aspect ratio and applied magnetic induction for maximum particle capture under the two cases considered. The matching relation is independent on particle and matrix size. Particle capture radius of matrices with the optimal aspect ratio can be much larger than that of conventional rod matrices. The matching relation can be used to configure the HGMS system for improving mineral recovery or reducing energy consumption.

High‐latitude dust deposition in snow on the glaciers of James Ross Island, Antarctica

AbstractHigh‐latitude dust (HLD) depositions on four glaciers of James Ross Island (the Ulu Peninsula) were analysed. The deposition rate on the selected glaciers varies from 11.8 to 64.0 g m−2, which is one order of magnitude higher compared to the glaciers in Antarctica or elsewhere in the world. A strong negative relationship between the sediment amount and altitude of a sampling site was found. This is most likely caused by the higher availability of aeolian material in the atmospheric boundary layer. General southerly and south‐westerly wind directions over the Ulu Peninsula – with exceptions based on local terrain configuration – help to explain the significantly lower level of sediment deposition on San Jose Glacier and the high level on Triangular Glacier. X‐ray fluorescence (XRF) spectrophotometry was used to estimate the relative proportions of the main and trace (lithophile) elements in the sediment samples. Both the sediment amount and the XRF results are analysed in a depth profile at each locality and compared among the glaciers, suggesting long‐range transport of fine mineral material from outside James Ross Island. The distribution of aeolian sediment among the glaciers corresponds well with the prevailing wind direction on the Ulu Peninsula. © 2020 John Wiley &amp; Sons, Ltd.

Resistance Properties to Chloride Ingress of Standard-Cured Concrete Made with an Admixture Incorporating Rich SiO2 and Al2O3

In regions where the concrete structures are exposed to a salty environment, the concrete requires high resistance to chloride-ion penetration. To achieve higher resistance against chloride ingress, a pozzolanic admixture incorporating a high volume of SiO2 and Al2O3 has been developed. The admixture is a fine mineral powder with a specific surface area of 13,000 m2/kg or higher. It is typically mixed with the concrete at a cement replacement level of 5–13 mass% (20–40 kg/m3). To demonstrate the applicability of the admixture to general ready-mix concretes, this study examined the fundamental properties of concrete cured under standard conditions regarding resistance against chloride ingress. Chloride immersion tests revealed high resistance against penetration of concrete produced with the admixture. Pore-size distribution analysis confirmed that the volume of pores less than 0.01 μm diameter increased whereas a decrease of large pores occurred (0.1 μm diameter or larger). The major contributor to the high resistance was found to be the immobilization of penetrating chloride ions by the formation of Friedel’s salt.

Native broad-leaved tree species play key roles on maintaining soil chemical and microbial properties in a temperate secondary forest, Northeast China

Silviculture of appropriate tree species can improve soil properties, subsequently ameliorating the productivity and ecological functions. However, it is not clear about the differences in the effects of tree species on soil properties in secondary forest ecosystems. In this study, four stands of 60–70 years secondary forests were chosen. Eight replicate individuals of five common native tree species: Acer mono, Quercus mongolica, Juglans mandschurica, Fraxinus rhynchophylla, and Fraxinus mandschurica were selected in each stand to test the effects of tree species on soil properties in a typical temperate secondary forest ecosystem in Northeast China. Forest floor, soil at three depths (0–10, 10–20 and 20–40 cm) were compared among five tree species. Our findings showed significant differences in soil mineral nitrogen (N) (i.e. NH4+-N and NO3–-N) and available phosphorus (P), microbial biomass C (MBC), microbial biomass N (MBN) and enzyme activities depending on the tree species. At 0–10 cm soil depth, F. mandschurica soils exhibited 18–28% higher mineral N than those A. mono, F. rhynchophylla, and Q. mongolica, 24–38% higher available P than Q. mongolica and F. rhynchophylla. Similarly, F. mandschurica soils showed 64–66% higher MBC and MBN than Q. mongolica, and 41–133% higher β-glucosidase enzyme activity than J. mandshurica, F. rhynchophylla, and Q. mongolica. At 10–20 cm soil depth, F. mandschurica exhibited higher soil mineral N and available P concentrations, MBC, enzyme activities of phenol oxidase, exoglucanase, and β-glucosidase than the other tree species. At 20–40 cm soil depth, there were no difference in soil mineral N and available P, MBC, MBN, and enzyme activities among five tree species. No differences were observed between the tree species in the C, N, and C/N ratio of forest floor; however, the C/N ratio of fine roots was lower for F. mandschurica than for Q. mongolica. Significant correlations were established between C/N ratio of fine roots and soil mineral N and available P, MBC and MBN, and phenol oxidase. This suggests that the high quality of F. mandschurica fine roots improved soil chemical and microbial properties. Nevertheless, these native tree species exhibited improving soil chemical and microbial properties, compared to larch plantation soils in secondary forest ecosystems. Therefore, we suggest that introduction of F. mandschurica followed by that of A. mono and J. mandshurica, and then Q. mongolica and F. rhynchophylla into larch plantations should be considered for restoring the degraded soils in plantations.

The Effect of Preparation Conditions on Microbubble Flotation Process of Ultra Clean Coal Using Box Behnken Design Model

AbstractWhen coal is widely used as fuel, it also produces lower combustion efficiency and environmental pollution due to direct utilization of coal. The demineralization of coal to prepare ultra clean coal can improve utilization value and reduce pollutant emissions. Thus, Taixi anthracite is chosen to prepare ultra clean coal by microbubble flotation method. Box Behnken design (BBD), a response surface model is introduced as a factorial design of experiments setup and used to find those parameters, which affect the ash content and yield of ultra clean coal and to adjust these parameters in order to achieve the optimized effect. Especially, their interaction effect of different factors in flotation process could be explored by the mathematical model. To explore the mechanism of preparing ultra clean coal, X‐ray fluorescence (XRF), X‐ray diffraction (XRD) and scanning electron microscopy energy dispersive spectroscopy (SEM‐EDS) results are analysed. Combining XRF with SEM‐EDS analysis, the concentrate is polluted by composite particles with particle size of less than 2 μm and organic matter accounting for more than 95 %. Through XRD and SEM‐EDS analysis, it can be shown that a small amount of fine clay minerals including kaolinite and illite agglomerate heterogeneously with coal particles during flotation and pollute concentrate. Further, the existence of composite particles and slime coatings were the main reason of limiting deep demineralization in microbubble flotation process.

Observability of Invisible Gold using BSE Imagery and Gold Recovery by Microwave-Nitric Acid Leaching

The aims of this study were to observe invisible gold, including that present in fine minerals, using back scattered electron (BSE) imagery, and to recover gold using microwave-nitric acid leaching experiments of powdered ore samples, including of invisible gold. As it is difficult to observe gold-bearing, fine minerals using a polarized microscope due to its resolution, BSE images and energy dispersive spectrometer (EDS) analyses were used in this study to easily identify brighter, fine minerals containing gold. As a microwave-nitric acid leaching test was applied to the powdered ore samples, arsenopyrite and pyrite were completely decomposed in a very short period of time. Both the nitric-acid leaching solution and insoluble residue were easily filtrated with three filter papers. In the nitric-acid leaching solution, Au was not dissolved at all, whereas Ag, Cu, and Zn were completely leached. When analyzing the insoluble residue, the first filter paper containing fine particles, as well as the second and third filtrated samples were used in the lead-fire assay respectively. All of the gold particles were effectively recovered from the samples during this experiment.

An experimental study on size distribution and zeta potential of bulk cavitation nanobubbles

Nanobubble flotation technology is an important research topic in the field of fine mineral particle separation. The basic characteristics of nanobubbles, including their size, concentration, surface zeta potential, and stability have a significant impact on the nanobubble flotation performance. In this paper, bulk nanobubbles generated based on the principle of hydrodynamic cavitation were investigated to determine the effects of different parameters (e.g., surfactant (frother) dosage, air flow, air pressure, liquid flow rate, and solution pH value) on their size distribution and zeta potential, as measured using a nanoparticle analyzer. The results demonstrated that the nanobubble size decreased with increasing pH value, surfactant concentration, and cavitation-tube liquid flow rate but increased with increasing air pressure and increasing air flow rate. The magnitude of the negative surface charge of the nanobubbles was positively correlated with the pH value, and a certain relationship was observed between the zeta potential of the nanobubbles and their size. The structural parameters of the cavitation tube also strongly affected the characteristics of the nanobubbles. The results of this study offer certain guidance for optimizing the nanobubble flotation technology.

Host minerals of Li–Ga–V–rare earth elements in Carboniferous karstic bauxites in southwest China

The Carboniferous karstic bauxite-bearing rock series in central Guizhou Province in southwest (SW) China is rich in trace elements, particularly Li, Ga, V, and rare earth elements (REEs), which have potential for comprehensive utilization as independent deposits or associated resources. However, the host minerals of Li, Ga, V, and REEs are not well-constrained because the sedimentary rocks are characteristics by complex mineral composition and fine mineral particles. This situation considerably hinders the compressive utilization of these trace elements in bauxite. Herein, laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) was successfully applied to element geochemistry analysis of hydrous minerals (diaspore/boehmite, kaolinite, and illite) in karstic bauxite samples, based on the principle that laser ablation data of all oxides were normalized to the sum of 100% minus the total volatile components of the mineral chemical formula. The analysis showed signal stabilization. Results indicated that the bivariate plots of selected elements had characteristics similar to statistical results of whole-rock samples from global bauxites, thereby indicating that the LA–ICP–MS analysis data were reliably but artificially herein. Combined with whole-rock geochemistry studies, the analysis results revealed that smectite may be the main host minerals of Li. Furthermore, Ga was enriched in diaspore/boehmite; V was mainly enriched in iron-bearing minerals, particularly chlorite; and REE-independent minerals, such as monazite, were the main host minerals of REEs in the Carboniferous karstic bauxite in SW China. This study contributed to the knowledge on the use of in-situ method for the element geochemistry investigation of hydrous minerals and sedimentary rocks.

Effects of Fine Minerals on Pulp Rheology and the Flotation of Diaspore and Pyrite Mixed Ores

In this study, the effects of four fine minerals, which were fine diaspore (FDIA), kaolinite, illite, and pyrophyllite (D50 is about 4.55 μm, D80 is about 10.78 μm), on the pulp rheology of the diaspore and pyrite mixed ores (D50 is about 120.53 μm, D80 is about 187.36 μm) and the recovery of pyrite were investigated through flotation tests, pulp rheology measurements, and sedimentation tests. It was found that fine minerals could change the pulp rheology and affect the pyrite recovery. The apparent viscosity of the mixed ores slurry increased with the addition of FDIA, kaolinite, and illite and the pyrite recovery decreased in varying degrees. When the addition was 15 wt.%, the recovery of pyrite decreased from 92.3% to 60.8%, 81.4%, and 84.7%, respectively. The addition of pyrophyllite had a significant deteriorating effect on flotation. When the addition of pyrophyllite was 5 wt.%, the pyrite recovery was reduced to 49.2%, and when the addition was further increased to 15 wt.%, the pyrite recovery reduced to 28.5%. However, the effect of pyrophyllite addition on the pulp rheology of the mixed ore was not remarkable. Pyrophyllite affected pyrite recovery not only by affecting the rheological behavior of the pulp, but also because pyrophyllite was adsorbed on the surface of pyrite and diaspore, producing hetero-aggregation, which made it difficult for the pyrite particles to collide with the bubbles effectively. This was the main reason for the reduction of pyrite recovery. Generally, the order in which the reduction of pyrite recovery was affected by the additions of fine minerals was pyrophyllite &gt; FDIA &gt; kaolinite &gt; illite.

Influence of limestone flour on properties of expanded clay concrete

The article enlightens the influence of limestone flour as a fine mineral additive on the physical and mechanical characteristics of expanded clay concrete. It was determined that when this component is applied in an amount of 5%, the strength increases by 16 %, and in combination with a hyperplasticizer– by 25% compared to a non-additive specimen. It is also worth noting that when the content of limestone flour is 10% by weight of cement, the performance values do not decrease.

Influence of calcium sulphoaluminoferrite on the cement stone structure

Usually to obtain expansive cements sulphoaluminate clinker or mix aluminate clinker with calcium sulphates (gypsum, hemihydrate, anhydrate) are used. This paper deals with the composition and properties of solid solution of calcium sulphoaluminoferrite. It was studied an influence of calcium sulphoaluminoferrite on structure and properties cement phases. For these cements ettringite is an important hydration product. The investigation of hydration and properties of sulphomineral cements shows that ettringite are formed thus providing expansion of cement stone. Study of the hydration processes of the calcium sulfoaluminoferrite mineral in gypsum solution showed that the hydration of fine mineral fractions (less than 28 μm) occurs during partial dissolution with crystallization of small ettringite crystals from solution. Sulphoaluminoferrite mineral is characterized by the growth of large prismatic ettringite crystals with their subsequent cleavage in fractions of 45–63 μm. Research showed that for expanding additives based on calcium sulfoaluminoferrite, a polyfraction composition combining only small fractions is preferable.

Development of a mathematical model of a vibrating polyfrequency screen as a dynamic system with distributed parameters

A mathematical model of a vibrating polyfrequency screen as a dynamic system with distributed parameters has been developed. The dynamic system of solids of finite sizes was chosen as the design scheme for the screen: framework, sieves with bulk material and impactors, the contact interaction of which occurs through two-side bonds and collisions on surface areas that have elastic-damping coverings. It is shown that a change in the amplitude of the exciting force has a significant effect on the dynamics of vibration impactors of a polyfrequency vibrating. There is an amplitude value at which the impactor passes from the mode without interacting with elastic bonds to the vibro-impact mode. The impactor movements begin to change disproportionately altered by the exciting force amplitude. It is shown that the start of the impactors in the screen substantially depends on the exciting force. Changes in the amplitude of the exciting force make it possible to achieve chaotic oscillations of impactors, which in turn leads to oscillations of screen surfaces with a continuous frequency spectrum, i.e. to the operation mode of the screen, which is most appropriate for dehydration and separation of fine mineral fractions.

Flocculation-dewatering prediction of fine mineral tailings using a hybrid machine learning approach.

Polymer-assisted flocculation-dewatering of mineral processing tailings (MPT) is crucial for its environmental disposal. To reduce the number of laboratory experiments, this study proposes a novel and hybrid machine learning (ML) method for the prediction of the flocculation-dewatering performance. The proposed ML method utilizes principle component analysis (PCA) for the dimension-reduction of the input space. Then, ML prediction is performed using the combination of particle swarm optimisation (PSO) and adaptive neuro-fuzzy inference system (ANFIS). Monte Carlo simulations are used for the converged results. An experimental dataset of 102 data instances is prepared. 17 variables are chosen as inputs and the initial settling rate (ISR) is chosen as the output. Along with the raw dataset, two new datasets are prepared based on the cumulative sum of variance, namely PCA99 with 9 variables and PCA95 with 7 variables. The results show that Monte Carlo simulations need to be performed for over 100 times to reach the converged results. Based on the statistic indicators, it is found that the ML prediction on PCA99 and PCA95 is better than that on the raw dataset (average correlation coefficient is 0.85 for the raw dataset, 0.89 for the PCA99 dataset and 0.88 for the PCA95 dataset). Overall speaking, ML prediction has good prediction performance and it can be employed by the mine site to improve the efficiency and cost-effectiveness. This study presents a benchmark study for the prediction of ISR, which, with better consolidation and development, can become important tools for analysing and modelling flocculate-settling experiments.

Features of the Structure Formation of Silicate Bricks Obtained with the Use of Solid Waste Produced by JSC "Berezniki Soda Plant"

The results of studying the structure formation features of silicate bricks obtained with the use of solid waste produced by JSC "Berezniki soda plant" are presented in this article. Various samples, such as sludge from the "closed" sump with a moisture content of 5 %, sludge from the open sump surface with a moisture content of 35 %, moistened sludge from the open sump with a moisture content of 70 %, were taken from the sludge collectors for the research. It was established the building lime meeting the requirements of GOST 9179 can be received by means of heat treatment at 950 °C of the dehydrated slime selected from the closed settler. By results of silicate brick samples forming parameters and their structure optimization it was found that the use of lime from soda production solid waste as part of lime-silica autoclave hardening binder allows to obtain silicate bricks samples, characterized by the strength grade M200. Samples microstructure studies obtained using the methods of electron microscopic and x-ray phase analysis showed that silicate samples produced with the use of soda production waste are characterized by a cementing substance heterogeneous structure and an insufficient number of tobermorite group low-basic calcium hydrosilicates formed during autoclaving. This is due to the waste material composition, namely the presence of reactive-passive components and impurities. Increasing the structural strength of samples made with the use of soda production wastes is possible due to raising the lime-silica binder specific surface area and the binder modification with fine mineral additives.

ПОЛУЧЕНИЕ ВЯЖУЩИХ КОМПОЗИЦИЙ ДЛЯ БЕТОНОВ В ЦЕНТРОБЕЖНОЙ ПОМОЛЬНОЙ МЕЛЬНИЦЕ

Abstract. The results of studies on the grinding of waste wet magnetic separation of ferruginous quartz-ites of the Lebedinsky mining and processing plant in a centrifugal grinding unit are given, their grinding features are established. Binder compositions are obtained at different ratios of cement and wet magnetic separation waste in a centrifugal grinding mill at different grinding modes. The features of grinding process-es are studied, the technological and physicomechanical properties of the obtained binding compositions are determined. The data obtained indicate that the use of mineral filler up to 10% provides compaction of the structure due to the presence of fine mineral filler, which will reduce the consumption of Portland cement to 10%. During mechanical activation of the compositions of binding compositions, a sharp increase in the con-centration of surface defects occurs, due to the violation of contacts between crystals with the rupture of sili-con-oxygen valence bonds. The activity of the wet magnetic separation waste of ferruginous quartzites is ap-parently due to the presence of a large number of exchange centers on their surface, a significant part of which are Bronsted acids and bases. The processes of hydration and the formation of cement with the use of binders requires further detailed study.

The microstructure and wear behaviour of garnet particle reinforced Al matrix composites

Composites containing different size range of garnet reinforced in LM13 alloy were prepared by liquid metallurgy route. Wear tests of composites were done at a constant sliding velocity of 1.6 m/s for a sliding distance of 3000 m at different loads varying from 9.8 to 49 N. The particle size variation of garnet mineral and its content used as reinforcement significantly influenced the microstructure, microhardness and wear behaviour of the composites. The wear rate of fine size garnet mineral reinforced composites is low as compared to composites reinforced with coarse size garnet mineral particles at all loads. The wear rate of 15 wt.% fine size garnet mineral reinforced composite is minimum even at higher load (49 N) when compared to the cast iron used in brake drum of vehicles.

Chemometric Optimisation of a Copper Sulphide Tailings Flocculation Process in the Presence of Clays

The presence of fine and ultra-fine gangue minerals in flotation plants can contribute to sub-optimal valuable ore recovery and incomplete water recycling from thickeners, with the performance of the latter equipment relying on adequate flocculation. In order to study the dependence of the flocculation process on the suspension-flocculant mixing conditions, a series of experiments—chosen using chemometric analysis—were carried out by varying mixing conditions, solid concentration, water salinity and flocculant dosage. To this purpose, two different tailings (both featuring coarse and fine content) were considered and a response surface methodology based on a Doehlert experimental design was used. The results suggest that the operational conditions to optimise the flocculated tailings settling rate and the suspended solids that report to a thickener overflow are not necessarily the same. This is a reasonable outcome, given that the settling rate depends on the coarse aggregates generated in the slurry, while the overflow solids content is governed both by either fine particle content (and its characteristics) or small aggregates. It is inferred that to maximise dewatering performance two stages should be involved—a separate treatment of the thickener overflow to remove fine content and thickening at optimal flocculant dosage to enhance this process.

X-ray CT observations of selective damage of mineralised synthetic particles by high voltage pulses

High voltage pulse (HVP) selective weakening and selective breakage of mineralised particles have been previously reported. It was hypothesised that these effects were a consequence of metalliferous grains-induced electrical breakdown, but no microscale evidence was presented to test the hypothesis. In the present study, synthetic particles made of grout were cast with a single grain of metalliferous mineral embedded, or with many grains of fine metalliferous mineral dispersed, or with no metalliferous mineral present at all (the barren particle). HVP tests were performed in which a pair of synthetic particles consisting of a mineralised particle and a barren particle were subjected to one pulse loading. The HVP products were examined by X-ray Computed Tomography (X-ray CT) to extract the cracks/micro-cracks and domain breakdown channel propagation behavior. X-ray CT images showed that the majority of the cracks/micro-cracks were generated in the metalliferous grain(s) embedded synthetic particles, whereas no cracks/micro-cracks were observed in the barren particles. The X-ray CT images also confirmed that the electrical breakdown channels traveled through the metalliferous grains rather than through the grain boundary between the grout and the metalliferous grain, which had a detrimental effect upon the integrity of the metalliferous grains. The effect of metalliferous grain-induced HVP selective damage of mineralised particles is used to elucidate the mechanisms of HVP selective weakening and selective breakage of mineralised particles.

Geochemistry, mineralogy and genesis of rare metal (Nb-Ta-Zr-Hf-Y-REE-Ga) coals of the seam XI in the south of Kuznetsk Basin, Russia

The research describes the detailed mineralogical and geochemical characteristics of rare-metal Nb-Ta-Zr-Hf-Y-REE-Ga ores found in Permian coals in the layer XI in the south of the Kuznetsk Basin. The concentrations and distribution of ore, and related elements, were studied in the coal seam section and along the seam strike. Spatial and genetic relationships of the mineralization in the coal were found to be related to the presence of an altered volcanogenic pyroclastic horizon of REE-enriched pantellerite composition. The highest concentrations of basic ore elements in the coal are associated with the contact zones above and below the volcanogenic horizon. The ore matter is mainly concentrated in the fine mineral phases, composed mainly of Zr-Nb-Ti-Fe oxides, fine zircons, rare-earth carbonates (bastnesite) and phosphates (monazite, xenotime, goyacite). Resource estimates are made of the rare metals. Confirmation of the connection between the complex rare-metal mineralization and the alkaline volcanogenic pyroclastics significantly expands the prospects of revealing further such mineralization in the coals of East and Central Asia.