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Article

Mineralogical and Geochemical Features of Coals and Clay Layers of the Karaganda Coal Basin

by
Aiman Kopobayeva
,
Altynay Amangeldikyzy
*,
Gulim Blyalova
and
Nazym Askarova
Department Geology and Exploration of Mineral Deposits, Abylkas Saginov Karaganda Technical University, N. Nazarbayev ave. 56/2, Karaganda 100027, Kazakhstan
*
Author to whom correspondence should be addressed.
Minerals 2024, 14(4), 349; https://doi.org/10.3390/min14040349
Submission received: 24 January 2024 / Revised: 23 March 2024 / Accepted: 24 March 2024 / Published: 27 March 2024
(This article belongs to the Section Mineral Deposits)
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Abstract

:
A comprehensive assessment of the critical elements contained in coal is essential for understanding the geological processes that affect the enrichment of these elements, which can then be used to fully utilize coal in an economically and environmentally friendly manner. In order to understand the geology of an area and the impact of demolition rock on the formation and enrichment of trace elements, as well as rare earth elements (REE) in coals, we have presented a range of recent geochemical and mineralogical data from the k7 coal seam in the Karaganda Formation of the Karaganda Coal Basin. The study revealed that the geochemical characteristics of coal-bearing deposits in the Karaganda Basin reflect the features of its geological evolution. Despite high tectonic activity and volcanic activity in the Paleozoic era, the specific composition of the rocks on the slopes and bases of coal-bearing valleys has determined the low potential for rare metals in the basin. It has been found that the coal in the Karaganda Basin is, in general, similar in terms of concentrations of most trace elements to the average for world coal. The main area of provenance of the trace elements was established using discriminant diagrams. It was established that the main source of the trace elements, including REEs in the basin coals, was the Tekturmas accretionary complex that represented the main upland (anticlinorium) during the coals’ formation. SEM studies identified micro-mineral forms that indicated the presence of trace elements of Zr, Ti, Se, and Fe in the samples of stratum k7.

1. Introduction

Due to the gradual depletion of traditional metallic mineral resources, their limited remaining reserves make it imperative to find new potential sources of these minerals. Coal, an important mineral and economic resource in numerous countries around the world, plays a significant role in the modern economy. Coal is distinguished by its lithological diversity, stages of sedimentation, and high content of organic substances. Coal can also very often be enriched with critical elements due to geological processes in the syngenetic and epigenetic periods [1,2,3,4]. The results of this research will guide the industrial processing of the most significant elements contained in coal and its combustion products. There is an increasing recognition of the significance of trace elements in coal, not only due to their environmental impact but also as a potential source of essential elements. The potential extraction of rare earth elements (hereafter referred to as REE) from coal deposits, including those from open-pit mines, is significant for industrial and commercial applications, as the processing of these elements included in coal can reduce the costs of disposal and minimize the harmful impact of waste on the environment. The studies in [3,5,6,7] suggest using the concentration coefficients (CCs) proposed by [6,8] to assess the enrichment of critical elements in coals. Elements such as lithium, rare-earth elements, and yttrium play important strategic roles in renewable energy, information technology, aerospace, and other developing strategic industries. Coal is significantly enriched with trace elements, including REEs, during the process of peat accumulation and at different metamorphic stages [4,6,9]; these elements remain in ash to a greater extent due to their low volatility during the combustion period. In the context of the rapid global growth in the requirements of the energy-generating industry, coal and its combustion products may provide a potential source of critical elements [2,6,10]. Thus, understanding the origin, processing mechanisms, and value of the industrial use of these critical elements has strategic significance. An additional motive for this research is the fact that, during recent decades, many deposits of Ge, Li, Sc, lanthanides, and other critical metals were discovered in relation to coal deposits in many countries [1,7,8,11]. The Karaganda coal basin is the main source of energy resources for Central Kazakhstan and its adjacent regions, and it is the largest in the Republic. A recognition of the importance of trace elements in coals is increasing not only due to their impact on the environment but also because they are a potential source of critical elements. In the last century, the trace elements in coal within the Karaganda coal basin have been studied during geological exploration operations with the use of an optical spectrograph to perform semiquantitative analysis of a limited number of elements. Therefore, there is a need for a comprehensive analysis of a large number of samples, which would provide a wider coverage of information on the distribution patterns of trace elements in coals. The results of a detailed geochemical and mineralogical study of the k7 coal seam are presented for the first time.
This study aimed to assess the geochemical and mineralogical characteristics of coals of the Karaganda coal basin based on modern analytical data via a study of the nature of their accumulation and identifying possible sources of income from the trace elements in the coal. The main purpose of this work is to determine the composition of the starting material, which served as a source for the enrichment of trace elements in coal, as well as to investigate the role of source-area composition factors on the enrichment of rare earth elements (REE). The main patterns of distribution and characteristics of trace element concentrations, including REEs, are presented, and the conditions and factors for their enrichment are identified. The features of the different forms of REE presence in coal and coal-bearing rocks have been studied, allowing for an assessment of their migration mechanisms and enrichment conditions. Based on the results of geochemical analysis, the factors influencing the movement of REEs were identified and the composition of the rocks framing the coal seams was determined, which influences the concentration of REEs in these seams. The latest mineralogical findings have allowed us to identify the ways in which these elements were transported to the paleo-basin during the syngenetic and epigenetic stages of the formation of these coal deposits.

2. Geological Setting

In this research, the authors studied Karaganda’s coal-bearing basin, which is known for its metalliferous coals, with relatively active paleotectonics during the Paleozoic era [12,13,14,15,16]. There are rare-metal granites with a developed weathering crust in their basement and margins.
The Karaganda coal basin (Figure 1a) is located in the western part of the Central Asian orogenic belt in restraint and corresponds to the middle part of the laterally elongated synclinorium that occupies a specific position in the structure of Central Kazakhstan. The basin is located in the area connecting the regions of the Caledonian and Hercynian folds, i.e., between the Hercynian Dzhungaro–Balkhash geosyncline in the south and the Caledonian solidification zone in the north. The Devonian marginal volcanogenic belt stretches along this area; its occurrence was facilitated by the presence of a system of deep-seated faults, which are accompanied by contortion, crushing, and schistosity of the rocks. The Karaganda synclinorium is a complex but relatively unified large laterally oriented syncline structure formed by Devonian volcanogenic sedimentation rocks and coal-bearing series of the Carboniferous age. As a result of late Hercynian block movements, the Karaganda synclinorium was divided along the longitudinal faults into separate blocks, which represent graben synclines divided into deeply eroded upheavals. The western part of the Karaganda synclinorium is formed by predominantly Devonian volcanogenic rocks.
The overlying Karaganda coal basin was formed within the Karaganda synclinorium as a result of a deep downwarping of the southern margin of the described zone during the Hercynian tectogenesis. From the Dzhungaro–Balkhash geosyncline, which occupies the southwestern part of Central Kazakhstan, it is separated by two anticlinoria: the Spassk anticlinorium and the Tekturmass anticlinorium. The Spassk anticlinorium directly flanks the basin in the south. The Tekturmass anticlinorium is located to the south; it was formed in the early Givetian age as advanced forms of the Hercynian folded structure.
Magmatic rocks are widely spread in the geological structure of the basement and flanks of the Karaganda basin. They are represented by intrusive complexes of the Ordovic (diabasic porphyry and quartz diorites) and Devonian (granodiorites, leucocratic granites, granosyenites, syenite porphyry, and granite porphyry), as well as Devonian subvolcanic formations (dacitic porphyry). All Devonian formations belong to the area of volcanogenic formations of the Coblentzian–Givetian age, and form, as a rule, bodies with small dimensions that are related to the first stage of the Devonian magmatism.
In providing a more detailed analysis of the paleogeographic conditions of the period in which the productive coal strata of the Karaganda basin accumulated, it should be noted that positive movements during the late Tournaisian and early Visean ages resulted in the eastern part of the foredeep (in particular, at the basin territory), replacing the typically marine carbonaceous sediments in the upper Tournaisian with the clayey rocks of Terekty layers and lower part of Akkuduk series that were formed under lagoon conditions. In the area of the Dzhungaro–Balkhash geosyncline, this upheaval was accompanied by an activation of volcanic activity, which is reflected by the widespread thin interlayers of tuffs in clayey sediments of the lower Visean age and within and beyond the area of the Karaganda basin. The complexity of the tectonic position, the diversity of the local geochemical background, and the numerous geological conditions of formation of the Karaganda coal basin territory motivated the interest in studying the metal content and the main geological factors that impacted IE enrichment in coals. To this end, the authors of this paper performed complex mineralogical and geochemical research on the coals and clayey interlayers (hereinafter referred to as CIs) of stratum k7 (the sedimentary sequence is shown in Figure 1b), and their results are presented below.

3. Sample Collection and Methods

3.1. Sample Collection and Preparation

For a more detailed study of the geochemical features and understanding of the mechanisms of enrichment of trace elements in the coal-bearing deposits of the Karaganda syncline, we extracted samples in three operating mines located in the study area, the k7 formation. These mines—Saranskaya, Aktasskaya, and Kuzembaev—are located directly at the base of the formation. The sample collection was conducted using the channel-sample method (vertical sampling) from layers of coal and host rocks with a thickness of 0.05–0.20 m, and 35 sections were passed. The distance between the sections varies from ~500 m to 800 m. The distance between the first and last sections is ~2.9 km. In total, 175 samples of coal, clay interlayers, and coal–clay interlayer contact zones were conducted. Five samples were used in each section to trace the lateral and vertical changes in the mineralogical and geochemical features of the k7 formation. The selected samples of the Karaganda coal basin underwent sample preparation, namely, the samples weighing 1.5–2 kg were crushed to prepare composite samples weighing 250 g and were then subjected to various analyses.

3.2. Experimental Analytical Methods

3.2.1. ICP-OES and ICP-MS Analysis

The selected samples from the Karaganda basin were subjected to the following laboratory analytical studies in an accredited leading laboratory at the Federal State Budget Enterprise of Science Far East Geological Institute of the Far Eastern Branch of the Russian Academy of Sciences (FEGI FEB RAS). The samples of clayey interlayers and coals were analyzed using the Inductively Coupled Plasma–Atomic Emission Spectroscopy and Inductively Coupled Plasma Spectroscopy methods using an Agilent 7500 spectrometer (Agilent Techn, Santa Clara, CA, USA) (ICP-OES and ICP-MS). The ICP-OES method was used to determine the contents of Ti, Al, Fe, Mn, Mg, Ca, Na, K, and P in terms of oxides; the ICP-MS method was used to determine the contents of Li, Be, S, Al, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Rb, Sr, Sn, Sb, Te, Y, Mo, Ag, Zr, Cd, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Tl, Pb, Bi, Th, and U. Additionally, to assess the repeatability of the results and their accuracy, a part of the samples (10 samples) was analyzed in parallel. To assess the accuracy of the research results, standard samples of the composition of CLB-1 and SARM 19 coals from the US Geological Survey were analyzed with each batch of samples.

3.2.2. Electron Microscopic Analysis

The distribution of minerals, the form, and the morphological specifics of the coal and clayey interlayers were studied using an analytical scanning electron microscope along with X-ray energy-dispersive spectroscopy (XEDS). Electron microscopic analysis of the samples was performed in the laboratory for micro- and nano-research using a Tescan Lyra 3 XMH (Brno—Kohoutovice, Czech Republic) two-beam scanning electron microscope and AZtec X-Max 80 Standard EDS (Abingdon, Oxfordshire, England). This method allows for mineral forms to be identified and photographed at micron and nanometer sizes, and their ultimate composition to be identified. As a result of using the highly localized analytical scanning electron microscope (XEDS) method, the morphometry of solid-phase components in the presented samples was characterized, the content of chemical elements was defined, and an automated search of the mineral phases was conducted with set characteristics using AZtecFeature 3.1 software modules. This included the electronic documentation of images captured in various modes under the scanning electron microscope and the definition of the composition of the obtained X-ray-dispersive spectra. Based on the data, tables were compiled for the content of separate trace elements, and various geochemical and petrochemical diagrams were built to represent the average content of trace elements with reference to their clarkes in hard coals, clayey interlayers, and their interfaces.

4. Results

Using the analysis results obtained via the ICP-MS method, the average content of trace elements in the coals in the three mines was normalized to world coals [17] (Figure 2), and in clays, it was normalized to the clarke for sedimentary rocks according to [18] (Figure 3). It is established that there are predominantly near-clarke values for IE in the coals of stratum k7. Micro-element concentrations are close to the average values for world coals (0.5 < CC < 2) for elements such as Li, Sc, V, Cu, Ag, Te, and Hf. It was found that the content of most trace elements in the coals of the Karaganda basin is low, and their concentration is close to the corresponding average for world coal.
Characteristics of insignificant enrichment of the clayey interlayers with microelements are shown in Figure 3. According to the obtained data, the IE content in the clayey interlayers in the three mines is represented by a generally uniform distribution within the stratum researched. The concentrations of some elements (Li, Ga) are close to the average values for global sedimentary rocks (2 < CC < 5), and there is also enrichment with Se (5 < CC < 10). At the same time, the elements Li, Be, Ga, Se, Ag, Bi, and Th exceed clarke contents laterally (Figure 3). There are increased contents of Be, Ga, Bi, and Th in clayey interlayers compared to the content of the same elements in coals.
Through the investigations, a significant increase in Se over the clarke (5 < CC < 10) was identified in the CIs, and some of its minerals were identified. Multiple grains of lead selenide–clausthalite (PbSe) (Figure 4), selenium-containing galena (PbSeS) (Figure 5a), and single grains of PbS (Se, Bi) (Figure 5b) are detected. Clausthalite has also been detected [19] in brecciated coal (in fusinite and semifusinite) and [20] in bituminous coals of Jiu Valley, Petroşani basin (southern Carpathian Mountains), Se-galena has been found [21] in coals of stratum No. 6 of the Junger Coalfield (Ordos Basin, China) through SEM, and all grains are found in cavities in fusinite.
Lateral variations in element concentrations have been assessed, which allows the impact of the source area rocks on the basin to be identified [22]. Lateral variability in IE content within the Karaganda basin was assessed on stratum k7, which is accessible for sampling at multiple sites along over 6 km. Stratum k7 is a production stratum and is currently being mined throughout the basin at many points. The average trace element contents in coals for the three mines in which the samples were taken are presented in Table 1.
The peculiarities of the distribution of trace elements in the coals of the basin are determined by a number of factors that manifest at different scale levels and form both common features of the geochemical spectrum of the coals of the basin and local patterns of the appearance of element-enriched coals within individual layers, formations, and deposits. One of the main factors controlling the enrichment of trace elements in coals is the source area composition factor. The influence of the composition of rocks in the source area on the formation of the geochemical background of the Karaganda coal basin is expressed through the peculiarities of the geochemical speciation of the basin’s coals. By interpreting the data obtained, a range of trace element distribution patterns in the research area can be traced. The accumulation levels and the heterogeneous distribution of elements in the formation indicate the influence of the peculiarities of the metallogeny and geochemistry of the source area. A clear spatial and geochemical relationship made it possible to define and identify five groups of elements evenly distributed in the transverse direction; they are presented below (Figure 6, Figure 7, Figure 8 and Figure 9). The groups contain elements whose patterns of lateral distribution are similar.
In the first group, a gradual increase in element content is established from the west to the northeast, i.e., from the Saranskaya mine to the Kuzembayev mine, and the lowest element contents are found in the Aktasskaya mine. This group comprises the following elements: light REEs (Nb, Ce, La, Pr), heavy REEs (Yb, Lu, Er, Tm), and Ag. It is necessary to note that the heavy REEs Er and Tm are present at almost the same level at the Saranskaya and Kuzembayev mines.
In the second group, an increase in element content is observed from the northeast to the west. Peak values are found at the Saranskaya mine, and minimal contents are found at the Aktasskaya mine; for Y, the lowest value is found at the Kuzembayev mine. This group includes heavy REEs (Gd, Tb, Dy, Ho) and a number of light REEs (Sm, Eu) and transition elements (W, Y).
The third group combines the lateral distribution patterns that are characterized by an increased content of elements at the Aktasskaya mine compared to the values at the other two mines. Here, elements of various groups (Sc, Ba, Se, V, Sb, Tl, Ga, Li, Cs, As) are present, as well as transition elements (Cr, Ni, Zn, Mo) and an alkaline-earth element (Sr).
In the fourth group, an increase in the content of Pb, Zr, U, Th, Hf, and Bi is established from the west to the northeast. Vice versa, in the fifth group, there is a decrease in the content of Co and Te from the west to the northeast. The analysis of the lateral distribution has shown that the REE content decreases distinctly from the margins to the center.
Another specific geochemical feature of the Karaganda basin is the enrichment of other femic elements (Sc and V) in coals. Their content in coals is in excess of the clarke values within 1- to 2-fold (Table 1). The highly correlated dependence of Sc on both TiO2. (r = 0.6) and V (r = 0.6) in coals, CIs, and their contacts (Figure 10) indicates that their sources are are rocks of the basic composition [24,25].
No mineral forms of scandium were found when investigations were performed on the samples from the Karaganda coal basin using scanning electron microscopy. Singular inclusions of Sc (<1%) were found in zircon grains in coal samples (Figure 11a) and in samples extracted at the coal and CI interface (Figure 11b). According to the data in [25,26,27], an absence of minerals in coals and the presence of an admixture of scandium, with its increased chemical content, may indicate a hydrogen mechanism of scandium formation in the coals of the basin with an organic association.
The high S content found in the coal of the Karaganda coal basin may be a result of bacterial activity, which is impacted by an increase in sulfate ion content in seawater [28,29]. A large amount of pyrite in the coal and CIs of stratum k7 is mainly found in the form of massive and framboidal grains and pyritized tissue (Figure 12).
The presence of pyrite of syngenetic origin often indicates that seawater penetrated the coal strata and provided a sulfur source for the formation of sulfide minerals [11,30,31]. This is confirmed by earlier studies [32] related to identifying the paleogeography of the basin. These studies state that regressive and transgressive conditions in the territory followed each other right down to the Oligocene. In the period of coal formation (Visean age), the basin territory was dominated by sea level oscillations. According to [33,34] the Sr/Ba ratio, which is ˃1.0 for the coal samples of stratum k7 (on average ~2.38), the impact of seawater during the formation and enrichment of the basic sediments is indicated.
Magmatic processes have accompanied the entire history of the geological formation of the Karaganda synclinorium; therefore, subvolcanic bodies, intrusive rocks, and volcanic formations are widespread around the basin, on the flanks, and in the basement of the basin.
The second half of the Givetian age, before the period of accumulation of productive coal strata in the Karaganda basin (late Tournaisian age and early Visean age), is represented by the occurrence of a new stage in the tectonic development of Central Kazakhstan. Positive movements (specifically near the basin margin) resulted in the formation of the main upheaval of the Tekturmas anticlinorium. Debris material was produced from this upheaval, within which increased erosion occurred due to uplift [32]. The Tekturmas anticlinorium (or TAC) [35] comprises magmatic rocks with a predominantly average basic composition and serpentine mélange with blocks of sediment and magmatic rocks. The main formations are peridotites, gabbro, andesites, basalts, and sediments. The metamorphosed equivalents of the above-mentioned formations are related to the formation of serpentine mélange. Mélange consists of lizardite, chrysotile–lizardite–harzburgite hyaloplasm, and blocks of dunites, lherzolites, pyroxenite, dolerites, and gabbro [35].
Table 2 shows the average content of the main oxides in coals and CIs, and the average composition of TAC rocks, presenting the supposed main source of the IE in the coals and CIs of the Karaganda coal basin. The main oxides in the studied coals are SiO2 (8.06% on average), Al2O3 (4.97% on average), CaO (1.65%), and Fe2O3 (1.61% on average).
Table 3 demonstrates the average content of REEs in the coals and CIs of the Karaganda basin and in the TAC magmatic rocks. Distribution diagrams for the main oxides (Figure 13) demonstrate a similar picture of their distribution in coals, CIs, and TAC magmatic rocks.
REE enrichment in coal strata is conditioned by the specifics of the provenance area composition, and there are clear differences between the composition of the clayey rocks and coals and TAC magmatic rocks (Figure 14). According to the geochemical classification diagram suggested in [6] and normalized to the average REE concentrations and to UCC [36], coal shows a heavy REE enrichment and an (H)-type pattern, while the CIs exhibit light REE enrichment and an L-type pattern. There is a weak negative Eu-anomaly. The Tekturmass magmatic rocks and coal show significant heavy REE enrichment. According to earlier studies [32], the source of sediments in this area is mainly the TAC, i.e., upheaval dividing the Karaganda coal basin and the Devonian volcanic–plutonic belt, which is represented by the mountains located to the south of the basin being studied. The magmatic rocks are widely developed there (consistent with the results of this paper) and Devonian magmatic rocks surround the basin.
When plotted on La/Yb–ΣREE source rocks [37,38], all classified samples of coal, CIs, and contacts from stratum k7 mainly fall within the field of the sedimentary rocks (argillites) (Figure 15).
A Winchester–Floyd discrimination diagram [39] (Figure 16) was used to project samples to further verify that the source rocks originated from the areas of coal and CI formation. The results demonstrate that most sampling points fall within the area of trachyandesite, trachyte, and basanite nephelinite. The results of the diagrams (Figure 15 and Figure 16) demonstrate the different compositions of the source areas.
When using the classification diagram (Figure 16), it is necessary to consider the more significant removal of zirconium from ash horizons compared with titanium during the decomposition of the primary mineral substance [40,41]. This conclusion is based on the identified factors of uniform and sometimes quite significant enrichment of zirconium in coals located near clayey interlayers (tonsteins) that come into direct contact with [40,41]. It is also based on multiple findings of corroded zircon crystal in coals and CIs (Figure 17).
Furthermore, a significant amount of rutile was found in coals and CIs according to the SEM results.
The scanning electron microscopy method was used to identify its morphology in coals and CIs of the Karaganda coal basin. Thus, it is found that Ti is contained in the micro-mineral phase (rutile) (TiO2). Grains with different morphology dimensions of TiO2 were found in coals, CIs, and samples used at the coal and CI interface (Figure 18), and the frequent and uniform distribution of grains in the Karaganda coal basin indicates a predominance of its mineral form.

5. Conclusions

The research on the geochemical characteristics and determination of the composition of the k7 formation coals of the Karaganda coal basin presented in this paper showed that the coals of the k7 stratum and its GP formation have slightly higher contents of Li, Sc, Be, Ga, Se, Ag, Bi, and Th, exceeding the clarke values of coals and sedimentary rocks. SEM analysis identified some selenium-containing minerals, such as clausthalite, Se-galena, and titanium minerals (rutile); zircon with Sc impurity; and pyrite.
A series of geochemical methods allowed for the identification of the composition of the source material that served as a source of trace element enrichment in the coals. When studying the lateral distribution of trace elements, five groups were identified for the regular distribution, which indicates different provenance areas and roles of the source-area composition factor around the basin. The provenance source of the k7 coal seam is mainly from intermediate and basic rocks with a small amount of ancient sedimentary rock. All the above data indicate that source area rocks have basic, intermediate, and alkali compositions. These observations are supported by the regional geology of the basin margins.
A number of geochemical factors confirmed the role of seawater and that the coals were accumulated in coastal marine conditions. It is shown that the main source of the trace elements, including REEs in the basin coals, was the Tekturmas accretionary complex, which was the main upland (anticlinorium) process during coal formation.
In conclusion, it should be noted that a comprehensive assessment of critical element contents in coals is extremely important for understanding the geological processes impacting their enrichment. This would allow the coal to be used in an economical and environmentally friendly manner.

Author Contributions

Conceptualization, methodology, validation, resources, writing, editing, and formal analysis: A.K. and A.A.; investigation, A.K., A.A., G.B. and N.A.; funding acquisition: A.K.; project administration: A.K. and A.A. All authors have read and agreed to the published version of the manuscript.

Funding

This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (grant no. AP13067779).

Data Availability Statement

All data from this study are available within the article.

Acknowledgments

The authors are thankful to the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan for supporting and funding the research of young scientists grant no. AP13067779, thanks to which decisive analyses were conducted and the results reflected in this work were obtained. The authors are also grateful to the team of the FEGI FEB RAS for their support and high-quality analytical work.

Conflicts of Interest

The authors declare no conflicts of interest.

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Minerals 14 00349 g001aMinerals 14 00349 g001b
Figure 1. (a) The geological structure of the Karaganda coal basin (highlighted in bold) and the studied area. A fragment of the map of the M-43-V sheet, scale 1:500, 000 (Serykh, 2007). 1—polymictic grauwacki, medium (j2-3); 2—polymictic grauwacki, sour (l4-j1); 3—monzogranite (K granite) (μγ4c22-4); 4—leukogranite (lγ1c6-p1); 5—K-Na granosyenite (γξ2c7-p2); 6—monzogranodiorite (K granodiorite) (μγδ3c22-4); 7—petroclastic grauwacki, medium sodium (c); 8—Na trachyandesite (ταd5-6, ταc2-4); 9—Na trachydacite (τϚd5-6); 10—K trachyriodacite (τλϚd5-6); 11—K trachyandesibasalt (ταβd5-6); 12—trachybasalt (τβd5-6); 13—Na and K-Na trachyandesibasalt porphyrites (ταβπd5-6); 14—Na and K-Na trachyandesite porphyrites (ταπd5-6); 15—trachyriolite porphyry (τλπd5-6) and ayuriolite porphyry (υλπd5-6); 16—trachybasalt porphyrite (τβπd5-6); 17—Na and K-Na trachyriodacite porphyries (τλζπd5-6); 18—Na, K-Na, and K trachydacite porphyries (τζπd5-6); 19—K-Na quartz monzonite (qμd5-6, qμc7-p2); 20—K-Na syenogranites (εγ3d5-6); 21—basalt (βo4-5); 22—andesibasalt (αβo4-6); 23—ayulit (νo1); 24—basalt and tholeiitic porphyrites (βπo4-6). (b) Sedimentary sequence of Karaganda coal basin.
Figure 1. (a) The geological structure of the Karaganda coal basin (highlighted in bold) and the studied area. A fragment of the map of the M-43-V sheet, scale 1:500, 000 (Serykh, 2007). 1—polymictic grauwacki, medium (j2-3); 2—polymictic grauwacki, sour (l4-j1); 3—monzogranite (K granite) (μγ4c22-4); 4—leukogranite (lγ1c6-p1); 5—K-Na granosyenite (γξ2c7-p2); 6—monzogranodiorite (K granodiorite) (μγδ3c22-4); 7—petroclastic grauwacki, medium sodium (c); 8—Na trachyandesite (ταd5-6, ταc2-4); 9—Na trachydacite (τϚd5-6); 10—K trachyriodacite (τλϚd5-6); 11—K trachyandesibasalt (ταβd5-6); 12—trachybasalt (τβd5-6); 13—Na and K-Na trachyandesibasalt porphyrites (ταβπd5-6); 14—Na and K-Na trachyandesite porphyrites (ταπd5-6); 15—trachyriolite porphyry (τλπd5-6) and ayuriolite porphyry (υλπd5-6); 16—trachybasalt porphyrite (τβπd5-6); 17—Na and K-Na trachyriodacite porphyries (τλζπd5-6); 18—Na, K-Na, and K trachydacite porphyries (τζπd5-6); 19—K-Na quartz monzonite (qμd5-6, qμc7-p2); 20—K-Na syenogranites (εγ3d5-6); 21—basalt (βo4-5); 22—andesibasalt (αβo4-6); 23—ayulit (νo1); 24—basalt and tholeiitic porphyrites (βπo4-6). (b) Sedimentary sequence of Karaganda coal basin.
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Figure 2. Concentration coefficients (CCs) for microelements in the coals of stratum k7.
Figure 2. Concentration coefficients (CCs) for microelements in the coals of stratum k7.
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Figure 3. Concentration coefficients (CCs) for microelements in the clayey interlayers of stratum k7.
Figure 3. Concentration coefficients (CCs) for microelements in the clayey interlayers of stratum k7.
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Figure 4. Clausthalite in a CI sample.
Figure 4. Clausthalite in a CI sample.
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Figure 5. Grains of selenium-containing galena (a) in a CI sample and (b) in a sample used at the coal and CI contact.
Figure 5. Grains of selenium-containing galena (a) in a CI sample and (b) in a sample used at the coal and CI contact.
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Figure 6. Diagrams of lateral variability in elements from W to NE (Group 1).
Figure 6. Diagrams of lateral variability in elements from W to NE (Group 1).
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Figure 7. Diagrams of lateral variability in elements from NE to W (Group 2).
Figure 7. Diagrams of lateral variability in elements from NE to W (Group 2).
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Figure 8. Diagrams of lateral variability in elements (Group 3).
Figure 8. Diagrams of lateral variability in elements (Group 3).
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Figure 9. Diagrams of lateral variability in average element content in coals by mines—(a) W to NE (Group 4) and (b) NE to W (Group 5).
Figure 9. Diagrams of lateral variability in average element content in coals by mines—(a) W to NE (Group 4) and (b) NE to W (Group 5).
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Figure 10. Correlation diagrams for Sc/TiO2 (a) and Sc/V (b).
Figure 10. Correlation diagrams for Sc/TiO2 (a) and Sc/V (b).
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Figure 11. Zircon grains in a coal sample with Th and Sc impurities (a) and the interface (KH-53п) between coal and CI with Sc impurities (b).
Figure 11. Zircon grains in a coal sample with Th and Sc impurities (a) and the interface (KH-53п) between coal and CI with Sc impurities (b).
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Figure 12. Pyrite minerals of stratum k7.
Figure 12. Pyrite minerals of stratum k7.
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Figure 13. Distribution of the main oxides in coals, CIs, and TAC magmatic rocks.
Figure 13. Distribution of the main oxides in coals, CIs, and TAC magmatic rocks.
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Figure 14. Distribution of the REEs in coals, CIs, and TAC magmatic rocks.
Figure 14. Distribution of the REEs in coals, CIs, and TAC magmatic rocks.
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Figure 15. Discrimination diagram La/Yb–ΣREE to determine sources of debris material in coal stratum k7.
Figure 15. Discrimination diagram La/Yb–ΣREE to determine sources of debris material in coal stratum k7.
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Figure 16. Winchester–Floyd diagram to identify sources of debris materials for the rocks studied from coal stratum k7.
Figure 16. Winchester–Floyd diagram to identify sources of debris materials for the rocks studied from coal stratum k7.
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Figure 17. Zircon grains in samples of coal (a,b) and CIs (c).
Figure 17. Zircon grains in samples of coal (a,b) and CIs (c).
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Figure 18. TiO2 grains in the composition: (a) in coal; (b) clayey interlayer; (c) coal and clayey interlayer contact.
Figure 18. TiO2 grains in the composition: (a) in coal; (b) clayey interlayer; (c) coal and clayey interlayer contact.
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Table 1. Average trace element contents (ppm) in coals of the Karaganda basin.
Table 1. Average trace element contents (ppm) in coals of the Karaganda basin.
ElementSaranskayaAktasskayaKuzembayev Coal Clarke *ElementSaranAktasskayaKuzembayevCoal Clarke *
Li10.96420.6415.6414.00Hf1.0531.071.361.20
Be0.2940.360.342.00Ta0.0530.070.080.30
Sc4.2466.595.703.70W0.2410.190.231.00
V30.15953.0533.2228.00Tl0.0090.090.010.58
Cr2.5882.872.4017.00Pb2.7353.653.879.00
Co3.1343.062.936.00Bi0.0740.090.121.10
Ni2.6692.812.0917.00Th1.0991.121.323.20
Cu14.98321.2316.6216.00U0.3490.410.491.90
Zn12.09613.8611.6428.00Ge0.3160.360.332.50
Ga2.6984.893.616.20Te0.1060.070.030.05
As0.2514.300.199.00La5.6344.645.9611.00
Se1.0633.321.331.60Ce12.35210.6513.2923.00
Rb1.3983.711.4418.00Pr1.5051.341.623.50
Sr62.41380.8854.85100.00Nd6.9976.227.2111.00
Y 9.5817.697.968.20Sm1.6661.521.642.40
Zr41.63843.9651.1136.00Eu0.3940.360.380.43
Nb 0.7650.990.904.00Gd1.8081.581.692.70
Mo 0.3112.840.112.10Tb0.2670.240.260.31
Ag0.1440.130.320.10Dy1.5861.281.482.10
Cd0.0630.100.080.20Ho0.3190.260.310.57
Sn0.5030.600.541.40Er0.9150.760.920.85
Sb0.0320.290.051.00Tm0.1350.110.140.31
Cs0.1230.200.121.10Yb0.8680.680.991.00
Ba22.02170.6724.99150.00Lu0.1390.110.140.20
* Clarkes of trace elements in coals according to [23].
Table 2. Average content of the main oxides (%) in coals and CIs of the Karaganda basin and in TAC magmatic rocks.
Table 2. Average content of the main oxides (%) in coals and CIs of the Karaganda basin and in TAC magmatic rocks.
SampleSiO2TiO2Al2O3Fe2O3MgOCaOMnONa2OK2O
Average for TAC48.231.06514.312.6657.092511.1750.18252.6350.495
Average for CI39.680.5031.024.310.680.520.060.671.01
Average for Coal *8.060.184.911.610.201.650.020.090.11
* Note: The coal analysis is on a whole coal basis.
Table 3. Average content of REEs (ppm) normalized by UCC in coals and CIs of the Karaganda basin and in TAC magmatic rocks.
Table 3. Average content of REEs (ppm) normalized by UCC in coals and CIs of the Karaganda basin and in TAC magmatic rocks.
RocksLaCePrNdSmEuGdTbDyYHo ErTmYbLu
Coals 0.180.180.210.260.350.430.440.390.410.380.370.370.380.380.40
CI0.680.610.560.580.640.540.620.430.430.370.390.440.520.550.63
Magmatic Rocks0.260.300.370.440.550.790.700.900.951.020.940.830.730.680.63
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Kopobayeva, A.; Amangeldikyzy, A.; Blyalova, G.; Askarova, N. Mineralogical and Geochemical Features of Coals and Clay Layers of the Karaganda Coal Basin. Minerals 2024, 14, 349. https://doi.org/10.3390/min14040349

AMA Style

Kopobayeva A, Amangeldikyzy A, Blyalova G, Askarova N. Mineralogical and Geochemical Features of Coals and Clay Layers of the Karaganda Coal Basin. Minerals. 2024; 14(4):349. https://doi.org/10.3390/min14040349

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Kopobayeva, Aiman, Altynay Amangeldikyzy, Gulim Blyalova, and Nazym Askarova. 2024. "Mineralogical and Geochemical Features of Coals and Clay Layers of the Karaganda Coal Basin" Minerals 14, no. 4: 349. https://doi.org/10.3390/min14040349

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