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Article

Geochemical Characteristics and Paleoenvironmental Significance of the Xishanyao Formation Coal from the Xiheishan Mining Area, Zhundong Coalfield, Xinjiang, China

by
Yongjie Hou
1,
Kaixuan Zhang
2,
Xiangcheng Jin
2,
Yongjia Xu
2,
Xiaotao Xu
3,4 and
Xiaoyun Yan
3,4,*
1
Key Laboratory of Xinjiang Coal Resources Green Mining, Ministry of Education, Xinjiang Institute of Engineering, Urumqi 830023, China
2
College of Geoscience and Survey Engineering, China University of Mining and Technology (Beijing), Beijing 100083, China
3
General Prospecting Institute of China National Administration of Coal Geology, Beijing 100039, China
4
China National Administration of Coal Geology, Beijing 100038, China
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(7), 686; https://doi.org/10.3390/min15070686 (registering DOI)
Submission received: 7 April 2025 / Revised: 17 June 2025 / Accepted: 20 June 2025 / Published: 27 June 2025
(This article belongs to the Special Issue Geochemical Controls on the Generation and Transformation of Carbon in Rocks)
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Abstract

The eastern Junggar Basin in Xinjiang, China is a key coal-bearing region dominated by the Middle Jurassic Xishanyao Formation. Despite its significance as a major coal resource base, detailed paleoenvironmental reconstructions of its coal seams remain limited. This study investigates the B1, B2, B3, and B5 coal seams of the Xishanyao Formation using X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) to assess geochemical indicators of the depositional environment during coal formation. The results show that the coal samples are characterized by high inertinite content and low vitrinite reflectance, indicative of low-rank coal. Slight enrichment of strontium (Sr) was observed in the B1, B2, and B5 seams, while cobalt (Co) showed minor enrichment in B3. Redox-sensitive elemental ratios (Ni/Co, V/Cr, and Mo) suggest that the peat-forming environment ranged from oxidizing to dysoxic conditions, with relatively high oxygen availability and strong hydrodynamic activity. A vertical trend of increasing paleosalinity and a shift from warm–humid to dry–hot paleoclimatic conditions was identified from the lower (B1) to upper (B5) coal seams. Additionally, the estimated atmospheric oxygen concentration during the Middle Jurassic was approximately 28.4%, well above the threshold for wildfire combustion. These findings provide new insights into the paleoenvironmental evolution of the Xishanyao Formation and offer a valuable geochemical framework for coal exploration and the assessment of coal-associated mineral resources in the eastern Junggar Basin.

1. Introduction

Coal remains a dominant fossil fuel in the global energy structure [1,2,3], particularly in countries such as China, where resources are abundant and heavily relied upon [1,4]. However, coal mining and utilization are often associated with significant environmental and health challenges, including land subsidence, ecological degradation, and the emission of pollutants such as CO2 and SO2, which contribute to global warming and acid rain [1,5]. Beyond its role as an energy resource, coal is also a geochemically complex material that contains nearly all naturally occurring elements [6]. The modes of elemental occurrence—organic, inorganic (mineral-bound), and organically associated—are strongly controlled by depositional environments and coal-forming processes [7,8]. Consequently, coal geochemistry provides valuable insights not only into resource quality but also into the paleoenvironmental and paleoclimatic conditions at the time of coal formation.
A wide range of geochemical proxies, including redox-sensitive trace element ratios (e.g., V/Cr, Ni/Co, Mo), sulfur content, and Sr/Ba ratios, have been widely applied to reconstruct redox conditions, paleosalinity, and depositional settings in coal-bearing sequences [9,10,11]. Moreover, the inertinite content—a maceral group strongly linked to wildfire events—is recognized as an effective proxy for estimating paleo-atmospheric oxygen concentrations [12,13]. When employed in a multi-proxy framework, these indicators allow for more robust reconstructions of paleoenvironmental and paleoclimatic evolution, providing critical geological context for coal formation and improving the predictability of coal and coal-associated mineral resources [10,11,12,13,14].
The Zhundong Coalfield, located in the eastern Junggar Basin, is one of the most important coal-producing regions in northwestern China. Although previous studies have investigated the geochemical characteristics and paleoenvironmental implications of coal seams in the broader Junggar Basin, research that integrates petrographic, geochemical, and elemental analyses remains limited—especially in the eastern part of the basin, where coal-bearing formations such as the Middle Jurassic Xishanyao Formation contain substantial untapped resources.
This study aims to address the above research gaps by investigating the B1, B2, B3, and B5 coal seams of the Xishanyao Formation in the Jiangjungebi Open-pit Coal Mine, Qitai County. Through a combination of maceral composition analysis, vitrinite reflectance measurements, and geochemical characterization via X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma mass spectrometry (ICP-MS), we reconstruct the redox conditions of peat-forming water bodies, paleosalinity trends, paleoclimate characteristics, and atmospheric oxygen levels (pO2) during coal formation. The findings contribute to a more comprehensive understanding of the paleoenvironmental evolution of the Xishanyao Formation and provide a scientific basis for efficient coal exploration and the sustainable utilization of coal-associated mineral resources in Xinjiang’s major coal base.

2. Geological Background

The Junggar Basin is located in northern Xinjiang, China, between the Altai Mountains and the Tianshan Mountains. As an important coal-bearing basin in the southern Central Asian Orogenic Belt, it has coal reserves of approximately 1.64 billion tons [15,16]. It lies at the convergence of the Siberian, Kazakhstan, and Tarim plates (Figure 1). From the Late Devonian to the Quaternary, the basin underwent complex tectonic evolution, including the Late Devonian–Early Carboniferous rift basin stage, the Late Carboniferous–Permian collisional foreland basin stage, the Triassic–Paleogene intracontinental sag basin stage, and the Neogene–Quaternary intracontinental subduction foreland basin stage [17,18]. The eastern Junggar Basin covers the area between the Kelameili Mountains and Bogda Mountains, spanning secondary structural units such as the Wucaiwan Sag, Shazhang Fault-Fold Belt, and Shishugou Sag (Figure 1) [18]. Late Paleozoic, Mesozoic, and Cenozoic strata are developed in this region, with the Middle Jurassic Xishanyao Formation as the main coal-bearing stratum, having a thickness of 79–290 m and displaying a sedimentary pattern of thickening southwestward and thinning northeastward [19]. The Xishanyao Formation consists of terrigenous deposits dominated by gray–white sandstone, gray–black mudstone, and coal seams, with braided river delta and lacustrine sedimentary systems. During the Middle Jurassic, the eastern Junggar Basin was in an extensional subsidence state, forming a large, shallow intracontinental sag coal basin [18]. From the late Middle Jurassic to Late Jurassic, influenced by peripheral block collisions, the basin entered a transpressive tectonic phase, which profoundly affected the coal-forming environment, causing variations in coal seam thickness and diversifying sedimentary environments [20,21,22]. These complex geological features—including multistage tectonic evolution, structural segmentation, and varied sedimentary environments—have directly influenced the spatial distribution, thickness variability, and geochemical characteristics of coal seams within the Xishanyao Formation in the eastern Junggar Basin.
In the Jiangjungebi No. 1 Open-pit Mine, the coal seams are numbered from top to bottom as B7, B5, B3’, B3, B2, and B1. Among them, three fully minable seams (thickness > 1.00 m) are B5, B3, and B1; the B2 seam is mostly minable; B3’ is locally minable, and B7 is unmineable. The six coal seams have a total average thickness of 50.49 m and an average clean coal thickness of 49.32 m. The average gangue thickness is 1.45 m, with a gangue ratio of 2.87%. The B5, B3, and B1 seams have a total average thickness of 49.58 m and an average clean coal thickness of 48.47 m. B5 is a fully minable seam with an average clean coal thickness of 21.49 m; B3 is a fully minable seam with an average clean coal thickness of 6.34 m; B1 is a fully minable seam with an average clean coal thickness of 20.43 m.
In the Jiangjungebi No. 2 Open-pit Mine, the B5, B3, and B2 seams in the Xishanyao Formation are identified as marker layers due to their significant thickness, continuity, and distinct characteristics. These seams share the following features: large thickness, stable stratigraphic position, and frequent occurrence as ultra-thick coal layers within the sequence. The B5 seam has a total thickness ranging from 0 to 30.43 m (average 18.00 m); the B3 seam ranging from 0 to 13.61 m (average 6.81 m); and the B2 seam ranging from 0 to 38.45 m (average 17.77 m) [20,21,22].

3. Sample Collection and Experimental Methods

In accordance with the Chinese National Standard GB/T 482-2008 [24], a total of 27 samples were collected from fresh exposed coal seams at the working faces of the Jiangjungebi No. 1 Open-pit Coal Mine and Jiangjungebi No. 2 Open-pit Coal Mine, located in Xiheishan Mining Area of the Eastern Junggar Coalfield, Xinjiang. The samples were taken from the B1, B2, B3, and B5 seams of the Middle Jurassic Xishanyao Formation, which are the major coal-bearing strata in the region.
From top to bottom, the samples collected from the Jiangjungebi No. 1 Open-pit Coal Mine include JJGB1-B1-R, JJGB1-B1-C1, JJGB1-B1-C2, JJGB1-B1-C3, JJGB1-B1-C4, JJGB1-B1-C5, JJGB1-B1-F, JJGB1-B3-R, JJGB1-B3-C1, JJGB1-B3-F, JJGB1-B5-C0, JJGB1-B5-C1, JJGB1-B5-C2, JJGB1-B5-C3 and JJGB1-B5-F. Similarly, samples collected from the Jiangjungebi No. 2 Open-pit Coal Mine include JJGB2-B5-C0, JJGB2-B5-C1, JJGB2-B5-F, JJGB2-B3-C0, JJGB2-B3-C1, JJGB2-B3-C2, JJGB2-B3-P1, JJGB2-B3-F, JJGB2-B2-R, JJGB2-B2-C1, JJGB2-B2-C2 and JJGB2-B2-F.
Sampling was conducted along vertical stratigraphic profiles at intervals representing distinct coal benches. Each sample weighed approximately 5–10 kg, all samples were stored in clean and uncontaminated plastic bags immediately after collection to avoid contamination and oxidation. Each sample was ground to a particle size of less than 75 μm (200 mesh) and stored for subsequent geochemical analysis, including major, trace and rare earth elements (REEs).
All the coal and non-coal samples were ashed at 815 °C; the high-temperature ashes (HTAs) were then analyzed by X-ray fluorescence spectrometry (XRF, S8 Tiger, Bruker, Ettlingen, Germany) in order to determine the concentrations of major element. The concentrations of trace elements in each coal bench sample were determined by inductively coupled plasma mass spectrometry (ICP-MS, iCAP™ Q, Thermo Fisher Scientific, Waltham, MA, USA).
The concentrations of trace elements in the samples were determined by ICP-MS, following the procedures described by Dai et al. (2011) [25]. Prior to analysis, 50 ± 0.5 mg of each sample (200 mesh) was digested using a mixture of hydrofluoric acid (HF) and nitric acid (HNO3) in closed Teflon vessels to ensure complete dissolution of silicate and sulfide phases. All elemental concentration data were processed using arithmetic means.

4. Results

4.1. Maceral Composition and Vitrinite Reflectance

Under microscopic observation, organic matter constitutes 90.50%–95.60% of the total components, averaging 93.17%. The organic components are dominated by inertinite, accounting for 43.6%–92.8% (avg. 60.63%), followed by vitrinite at 7.2%–52.2% (avg. 37.06%), and minor semivitrinite at 0.0%–3.8% (avg. 2.07%). No liptinite or coke was observed (Table 1).
The vitrinite group is primarily composed of matrix vitrinite and detrital vitrinite (both non-structured). Matrix vitrinite exhibits a dark gray oil-immersion reflectance color, lacks cellular structure, and shows impurities and uneven surfaces with slight protrusion. Detrital vitrinite particles are small and irregularly distributed. Semivitrinite consists mainly of matrix semivitrinite, appearing gray under oil-immersion reflectance with faint protrusion and generally no cellular structure. Inertinite is dominated by fusinite and semifusinite, with occasional detrital inertinite showing white oil-immersion reflectance and moderate protrusion. No liptinite components were identified.

4.2. Vitrinite Reflectance

The maximum reflectance test results in nine coal samples of B1, B3 and B5 in Xiheishan Mining Area of eastern Junggar Basin are shown in Table 1. The range of reflectance in the B1 is 0.42%; the range of maximum reflectance in the B2 is between 0.38% and 0.49% and the average is 0.42%; the range of maximum reflectance in the B3 is between 0.26% to 0.48% and the mean is 0.39%; the range of maximum reflectance in the B5 is between 0.29% to 0.56%, the mean is 0.45%.

4.3. Major Element Oxides

The concentrations of major elements oxides and loss on ignition in coal bench samples, as well as average values for Chinese coals [1], are given in Table 2.
The concentration coefficient of major elements is defined as the ratio of the thickness-weighted average content in coal to the corresponding element content in Chinese coals. This coefficient reflects the depletion or enrichment of major elements in coal. According to the classification proposed by Dai et al. [4], concentration coefficients are categorized into six classes: depletion (<0.5), normal (0.5–2), slight enrichment (2–5), enrichment (5–10), strong enrichment (10–100), and extreme enrichment (>100).
In comparison with average values for Chinese coals [1], the percentages of CaO and MnO in JJGB2-B2 are enrichment. The remaining major-element oxides have values close to or lower than the corresponding average values for Chinese coals (Figure 2).

4.4. Trace Elements

The concentrations of trace elements and average values for world low-rank coals [28] are given in Table 3. The Method Detection Limit (MDL) of the trace elements determined by ICP-MS are given in Table 4. The Concentration Coefficient (CC), defined as the ratio of the thickness-weighted average concentration of trace elements in coal to the average concentration of corresponding elements in global low-rank coals [28], is used to assess whether trace elements in coal are relatively enriched or depleted. According to the classification of element enrichment coefficients proposed by Dai et al. (2015) [29], CC is divided into six levels: CC ≤ 0.5 indicates depleted; 0.5 < CC ≤ 2 indicates normal; 2 < CC ≤ 5 indicates slight enrichment; 5 < CC ≤ 10 indicates enrichment; 10 < CC ≤ 100 indicates significant enrichment; and CC > 100 indicates unusual enrichment.
Compared with the average values for low-rank coals [28], in the JJGB1—B1 coal seam, Sr exhibits the most significant enrichment with a CC of 2.23 (slight enrichment), while Ga, Ge, Mo, V, Cr, Co, Ni, Cu, Zn, and Pb have CC values of 0.20, 0.32, 0.05, 0.12, 0.31, 0.33, 0.34, 0.24, 0.09, and 0.23, respectively, indicating depletion. In the JJGB2—B2 coal seam, Sr and Co show slight enrichment (CC = 2.50, 2.03, respectively). Sc, Cr, Ni, Y, In, and Th have CC values of 0.51, 0.57, 1.41, 0.54, 1.09, and 0.79 (normal). The remaining elements have a CC < 0.5, indicating depletion. The concentration of Co, Ni, and Cu in the JJGB2-B3 coal seam is slight enrichment than that of the average value for world low-rank coals, with a CC of 2-5 (CC = 4.42, 2.23, 2.03, respectively). The trace elements with a CC < 0.5 only include Be, Ge, Cd, Tl, Bi, and U; on the other hand, the remaining elements, with a concentration coefficient of 0.5–2, have concentrations close to the corresponding averages for the world low-rank coals. While the concentrations of Co, Sr, and Mo in the JJGB1-B3 coal seam are close to the corresponding averages for the world low-rank coals, with a CC of 0.5–2, the remaining elements are depleted (CC < 0.5). The concentrations of Ni, Sr, and In in the JJGB2-B5 coal seam are close to the corresponding averages for the world low-rank coals, with a CC of 0.5–2; the remaining elements are depleted (CC < 0.5). The concentrations of Cr, Ni, Rb, Sr, Zr, and In in the JJGB1-B5 coal seam are close to the corresponding averages for the world low-rank coals, with a CC of 0.5–2; the remaining elements are depleted (CC < 0.5) (Figure 3).

4.5. Rare Earth Elements and Yttrium

The content of rare earth elements (REEs) in specific samples is utilized to standardize the REE content within coal. In this research, samples were chosen to normalize the rare earth element (REE) content of coal because coal bears a closer resemblance to the natural properties of the upper crust. According to the classification approach put forward by Seredin and Dai [4], the rare earth elements were divided into three groups: light rare earth elements (LREEs), middle rare earth elements (MREYs), and heavy rare earth elements (HREEs). The content levels of rare earth elements and yttrium in coal seam samples are presented in Table 5, along with the content levels of rare earth elements.
For the 17 coal samples, the average total rare earth element (∑REE) content is 22.69 μg/g. The values for individual samples vary from 4.59 μg/g to 56.49 μg/g. Significantly, this average is much lower than that of world low-rank coals (65.27 μg/g) and Chinese coals (138 μg/g). In the parting samples, the average total REE content stands at 96.40 μg/g. This figure is on a par with the average content of world low-rank coals, yet it is still considerably lower than that of Chinese coals. Regarding the floor and roof samples, their average total REE content levels are 137.88 μg/g and 135.71 μg/g respectively. Evidently, these values are substantially higher than those of the coal and parting samples. The REE content in coal is mainly affected by the input of terrestrial clasts. The ash yield of coal is in the range of 3.12%–45.56%, with an average value of 10.87%, which is relatively low. This implies that during the coal-forming process, there was a severe shortage of terrestrial clastic supply, resulting in an extremely low REE content in the coal.

5. Discussion

5.1. Redox Environment

In natural aquatic environments, the redox state of water bodies can be subdivided into five types based on dissolved oxygen content and hydrogen sulfide concentration: oxidizing, suboxic, dysoxic, anoxic, and euxinic [30,31,32,33]. Elements sensitive to redox conditions, such as Ni, Mo, Co, V, and U, exhibit varying enrichment levels under different redox states. Therefore, the redox conditions of paleosedimentary environments can be reconstructed using the concentrations or ratios of these elements [34,35].
Elemental ratios like V/Cr and Ni/Co are widely used to assess the redox state of peat swamp waters [10,36]. Jones and Manning (1994) [36], in their study of paleo-aqueous redox conditions in the Norwegian North Sea, established the following criteria: V/Cr < 2: Oxidizing environment; V/Cr = 2–4.24: Dysoxic environment; V/Cr > 4.24: Suboxic/Anoxic environment. They also proposed Ni/Co as a key indicator: Ni/Co < 5: Oxic environment; Ni/Co = 5–7: Dysoxic environment; Ni/Co > 7: Suboxic/Anoxic environment [36]. Although the burial and diagenetic histories of the North Sea and the Xiheishan Mining Area in the eastern Junggar Basin are distinct, the fundamental redox behavior of trace elements such as V, Cr, Ni, and Co remains governed by universal geochemical principles. These elements respond to oxygen availability in consistent and predictable ways across different depositional systems. Previous studies in in the eastern Junggar Basin have successfully applied the Jones and Manning criteria to reconstruct redox conditions in coal-bearing strata, demonstrating its applicability beyond marine settings [23]. Therefore, while acknowledging geological differences, the adoption of these ratio thresholds is justified by their geochemical robustness and precedent in similar non-marine coal-forming environments.
Geochemical analysis of coal samples from the B1, B2, B3, and B5 seams of the Xishanyao Formation in the Xiheishan Mining Area (eastern Junggar Basin) shows that most V/Cr ratios are below 2, with a smaller number falling between 2 and 4.24, indicating oxidizing to dysoxic conditions in the peat-forming environment. Similarly, Ni/Co ratios are predominantly below 5, with a minority ranging from 5 to 7, also suggesting oxidizing to dysoxic depositional conditions. Furthermore, when plotted on the Ni/Co–V/Cr and Ni/Co–Mo diagrams proposed by Rimmer (2004) [9,10,11], the majority of data points from the Jiangjungebi Open-pit Coal Mine cluster within the oxidizing and suboxic zones (Figure 4), corroborating the trace element ratio results.
These interpretations are further supported by previous studies in the Wucaiwan Mining Area, also located in the eastern Junggar Basin, which reported repeated lake-level fluctuations and changes in depositional systems during the Middle Jurassic [37,38,39,40]. Such environmental dynamics likely enhanced water movement and oxygenation within the peat swamp. Taken together, both our results and previous research suggest that the peat swamp waters during coal formation in the study area were characterized by strong hydrodynamic activity and elevated free oxygen content, leading to predominantly oxidizing to dysoxic conditions.

5.2. Ancient Salinity Characteristics

Paleosalinity plays a pivotal role in reconstructing sedimentary paleogeographic environments and paleoclimatic conditions, holding significant practical value [41,42,43,44]. Current methods for reconstructing paleosalinity include the use of boron (B), barium (Ba), Sr/Ba ratios, and isotopic techniques. Barium exhibits high reactivity with sulfate ions in seawater, rapidly precipitating as barite (BaSO4). Due to its large ionic radius and low hydration energy, Ba is readily adsorbed by clay minerals. Consequently, Ba concentrations are typically elevated in continental and transitional facies sediments but markedly lower in marine environments [45].
Coal and rock samples from the study area exhibit distinct Sr/Ba ratios, which reflect differences in depositional salinity. The coal samples show relatively high Sr/Ba values, with an average of 7.42 (range: 1.92–18.87), suggesting deposition under saline or weakly marine-influenced conditions. In contrast, the associated mudstones and siltstones exhibit much lower Sr/Ba ratios, averaging 0.61 (range: 0.18–1.01), indicative of a continental freshwater to brackish water environment (Figure 5).
The Sr/Ba ratio has been widely used as a paleosalinity indicator in sedimentary geochemistry [46,47]. In natural waters, both Sr and Ba occur primarily as bicarbonate complexes. However, Sr remains more mobile in solution due to the higher solubility of SrSO4 compared to BaSO4. As salinity increases, Ba precipitates first as BaSO4, leading to a relative enrichment of Sr in the residual solution. Thus, higher Sr/Ba ratios typically reflect higher salinity or marine influence, while lower ratios correspond to freshwater depositional settings.
The contrasting Sr/Ba values observed in this study reflect a salinity gradient between the peat-forming swamp environment and the adjacent clastic sedimentary system, supporting the interpretation of variable hydrological and geochemical conditions during coal formation in the Xishanyao Formation.

5.3. Paleoclimatic Characteristics

The enrichment of elements in coal is closely linked to paleoclimatic conditions, and thus the geochemical information of coal elements can reflect paleoclimatic changes to some extent [4,41]. Previous studies indicate that Sr exhibits low stability during weathering, with its content rapidly decreasing in warm, humid, and intensely weathered environments. The Sr/Cu ratio, sensitive to paleoclimatic variations, is widely used as an indicator of paleoclimate and holds critical significance for characterizing climatic changes during coal formation [48,49]. Lerman et al. (1995) [47] proposed that the following: Sr/Cu = 1.3–5: Relatively warm–humid climate; Sr/Cu > 5: Relatively dry–hot climate.
Additionally, empirical formulas derived from studies on Sr content and paleo-water temperature are used to calculate paleo-water temperatures: Y = 2578 − 80.8T [23], where Y represents Sr content (μg/g) and T denotes paleo-water temperature (°C) [50,51,52]. For the B1, B2, B3, and B5 coal seams in the Xishanyao Formation of the Xihishan Mining Area (eastern Junggar Basin), Sr/Cu ratios in most coal samples exceed 5 (Figure 6). Calculated paleo-water temperatures of the peat swamp range from 11 to 32 °C (avg. 29.49 °C) (Figure 7).
These results suggest that the depositional environment of the Xishanyao Formation was characterized by relatively high water temperatures and a dry–hot paleoclimate during the coal-forming period. Furthermore, the vertical variation in Sr/Cu ratios across the B1, B2, B3, and B5 coal seams shows a gradual upward increase, from the lower B1 seam through the middle B3 seam to the upper B5 seam. This trend suggests a progressive shift in paleoclimate from relatively warm and humid conditions in the lower strata to increasingly dry and hot conditions in the upper strata. This interpretation is consistent with previous studies on the Xishanyao Formation in the eastern Junggar Basin, which have similarly inferred an upward transition toward a more arid paleoenvironment during the Middle Jurassic coal-forming period [23,50,51,52,53].

5.4. Characteristics of the Atmospheric Oxygen Content

Inertinite, as a hallmark product of ancient wildfire events [12,54,55], shows a strong correlation with atmospheric oxygen levels (pO2), making it a widely accepted proxy for reconstructing paleo-atmospheric oxygen concentrations [13,23]. The formation and preservation of inertinite require sufficient oxygen levels to sustain wildfire combustion. Experimental studies indicate that wildfires cannot occur when pO2 falls below approximately 16%, while modern wildfires occur under current atmospheric conditions of ~21% oxygen [23].
Glasspool and Scott [56], and later Glasspool et al. [57], compiled an extensive global dataset of inertinite content from coal seams spanning the Phanerozoic and proposed a quantitative model linking inertinite volume percentage to atmospheric pO2 [13,23,53,56]. This model uses three calibration points to establish an S-shaped (sigmoidal) curve:
pO2 = 16% corresponds to 0% inertinite, representing the lower threshold for wildfire activity;
pO2 = 21% corresponds to 4.27 ± 0.64% inertinite, based on modern peats from diverse environments;
pO2 = 28 ± 2% corresponds to a peak inertinite content of 50 ± 2%, inferred from Late Paleozoic coal seams.
The relationship is expressed using a cosine-based S-curve:
I = (0.5 − 0.5 × cos[π(o − omin)/(omax − omin)])
(where I is the inertinite content, o is the oxygen level, omin = 16%, omax ≈ 30%–33% depending on assumptions) [56]
In this study, the Middle Jurassic coal samples from the Xishanyao Formation in the Xiheishan Mining Area show an average inertinite content of 63.56 vol.% (on a mineral-matter-free basis). Applying the calibration curve from Glasspool et al. [57], this value corresponds to an estimated atmospheric pO2 of approximately 28.4%, suggesting an oxygen-rich environment favorable for frequent and intense wildfires during the coal-forming period.
This elevated oxygen level is consistent with the observed high inertinite content and supports the interpretation of a dry–hot paleoclimate with strong wildfire activity during the Middle Jurassic in the eastern Junggar Basin.

6. Conclusions

(1) The Ni/Co–V/Cr and Ni/Co–Mo diagrams suggest that the coal-forming peat swamps of the Xishanyao Formation were deposited under oxidizing to dysoxic redox conditions. These conditions likely reflect elevated free oxygen levels and relatively strong hydrodynamic activity during peat accumulation.
(2) The Sr/Ba and Sr/Cu ratios exhibit a general upward trend from the lower to the upper coal seams, suggesting a gradual increase in paleosalinity. This geochemical pattern indicates that the peat swamp environment evolved from a weakly brackish to a slightly saline continental setting, rather than representing purely freshwater or marine conditions.
(3) The average inertinite content in the B1, B2, B3, and B5 coal seams of the Xiheishan Mining Area is 63.56 vol.%. Applying the established relationship between inertinite abundance and atmospheric oxygen concentration, we estimate that pO2 during the Middle Jurassic reached approximately 28.4%, which is consistent with environmental conditions favorable for frequent wildfires under a dry–hot paleoclimate.

Author Contributions

Methodology, X.J. and X.X.; Software, K.Z.; Data curation, Y.X.; Writing—original draft, Y.H.; Writing—review & editing, X.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Xinjiang Province Major Science and Technology Project grant number 2022A03014-1, Xinjiang Uygur Autonomous Region “Tianchi Talents” Introduction Program grant number 2024XGYTCYC10 and Doctoral Start-up Fund Project of Xinjiang Institute of Engineering grant number 2024XGYBQJ07.

Data Availability Statement

No new data were created or analyzed in this study.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. Location of the Junggar Basin (a), regional geological map of eastern Junggar Basin (b), coal-bearing strata of the Middle Jurassic Xishanyao Formation (c) (after Xu et al., 2024) [23].
Figure 1. Location of the Junggar Basin (a), regional geological map of eastern Junggar Basin (b), coal-bearing strata of the Middle Jurassic Xishanyao Formation (c) (after Xu et al., 2024) [23].
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Minerals 15 00686 g002
Figure 2. Concentration coefficients of major elements in the investigated coal samples, normalized by average concentrations of elements in common Chinese coals [1].
Figure 2. Concentration coefficients of major elements in the investigated coal samples, normalized by average concentrations of elements in common Chinese coals [1].
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Minerals 15 00686 g003
Figure 3. Concentration coefficients (CCs) of trace elements in the investigated samples, normalized by average trace element concentrations in the world low coals reported [28].
Figure 3. Concentration coefficients (CCs) of trace elements in the investigated samples, normalized by average trace element concentrations in the world low coals reported [28].
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Minerals 15 00686 g004
Figure 4. Redox discrimination diagrams for the coal-forming swamp in the Xishanyao Formation of the Xiheishan Mining Area, eastern Junggar Basin ((a) Ni/Co vs. V/Cr plot; (b) Ni/Co vs. Mo plot).
Figure 4. Redox discrimination diagrams for the coal-forming swamp in the Xishanyao Formation of the Xiheishan Mining Area, eastern Junggar Basin ((a) Ni/Co vs. V/Cr plot; (b) Ni/Co vs. Mo plot).
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Minerals 15 00686 g005
Figure 5. Paleosalinity discrimination diagram for the coal-forming swamp in the Xishanyao Formation of the Xihishan Mining Area, eastern Junggar Basin.
Figure 5. Paleosalinity discrimination diagram for the coal-forming swamp in the Xishanyao Formation of the Xihishan Mining Area, eastern Junggar Basin.
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Figure 6. Sr/Cu paleoclimatic discrimination of the investigated samples.
Figure 6. Sr/Cu paleoclimatic discrimination of the investigated samples.
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Figure 7. Paleowater temperature discrimination of the investigated samples.
Figure 7. Paleowater temperature discrimination of the investigated samples.
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Table 1. Maceral composition and vitrinite reflectance of coal samples from the Xishanyao Formation Coal from the Xiheishan Mining Area, Zhundong Coalfield.
Table 1. Maceral composition and vitrinite reflectance of coal samples from the Xishanyao Formation Coal from the Xiheishan Mining Area, Zhundong Coalfield.
Coal
Seam		Number of
Samples		Maceral Content (Vol.%, mmf)Maximum Vitrinite
Reflectance (%)
Vitrinite +
Semi − Vitrinite		Inertinite
B51111.4–52.3
38.59		47.60–88.6
61.28		0.29–0.56
0.45
B3917.6–55.9
38.49		43.6–82.4
61.44		0.26–0.48
0.39
B2611.2–49.2
30.8 		50.7–88.8
69.1		0.38–0.49
0.42
B137.2–55.5
32.74		49.6–92.8
67.1		0.41–0.44
0.42
Note: mmf represents mineral-matter-free, the number below each range represents the average value. The maceral composition and vitrinite reflectance in coal are from the “Xinjiang Zhundong coalfield Qitai County General Gobi No. 1 open-pit coal mine exploration report”, “Xinjiang Zhundong coalfield Qitai County General Gobi No. 2 open-pit coal mine exploration report” [26,27].
Table 2. Major element oxides and ignition loss of the study samples (%; on whole coal/rock basis).
Table 2. Major element oxides and ignition loss of the study samples (%; on whole coal/rock basis).
SamplesThickness
(m)		LithologyLOISiO2TiO2Al2O3Fe2O3MnOMgOCaONa2OK2OP2O5
JJGB2-B5-C00.5coal96.390.85 0.01 0.59 0.41 0.01 0.58 0.89 0.24 0.02 0.01
JJGB2-B5-C10.5coal95.940.49 0.01 0.22 1.68 0.04 0.43 0.93 0.22 0.03 0.01
JJGB2-B5-F0.5coal43.6335.27 0.65 15.04 1.63 0.01 0.82 0.47 0.69 1.74 0.03
JJGB2-B3-R0.5coal96.251.21 0.15 0.43 0.12 0.00 0.55 0.93 0.34 0.02 0.00
JJGB2-B3-C10.5coal78.3312.93 0.36 5.80 0.57 0.01 0.48 0.78 0.47 0.27 0.01
JJGB2-B3-C20.5coal83.698.91 0.24 4.53 0.83 0.01 0.43 0.76 0.45 0.15 0.01
JJGB2-B3-C30.5parting39.9246.48 1.03 10.12 0.54 0.01 0.39 0.47 0.55 0.48 0.02
JJGB2-B3-F0.5coal11.1170.49 1.40 10.65 4.59 0.05 0.31 0.21 0.43 0.73 0.03
JJGB2-B2-R0.5coal42.542.01 0.57 10.97 1.32 0.01 0.57 0.36 0.50 1.18 0.02
JJGB2-B2-C10.5coal96.550.84 0.02 0.77 0.04 0.00 0.59 0.93 0.25 0.01 0.00
JJGB2-B2-C20.5coal54.440.52 0.01 0.49 0.35 0.41 0.46 43.23 0.07 0.00 0.01
JJGB2-B2-F0.5sandstone16.7851.75 1.58 27.13 1.42 0.01 0.28 0.15 0.37 0.50 0.03
JJGB1-B1-R0.5sandstone15.5564.89 0.56 10.66 5.64 0.07 0.46 0.20 0.37 1.57 0.03
JJGB1-B1-C10.5coal96.540.75 0.01 0.30 0.73 0.02 0.45 0.98 0.19 0.03 0.00
JJGB1-B1-C20.5coal96.880.47 0.01 0.35 0.65 0.02 0.44 0.98 0.18 0.02 0.00
JJGB1-B1-C30.5coal96.510.93 0.03 0.76 0.04 0.00 0.57 1.00 0.14 0.01 0.00
JJGB1-B1-C40.5coal92.752.89 0.04 1.14 0.87 0.01 0.56 1.16 0.49 0.07 0.01
JJGB1-B1-C50.5coal86.85.37 0.16 4.25 0.85 0.01 0.61 1.48 0.44 0.02 0.01
JJGB1-B1-F0.5sandstone9.0265.32 1.05 20.87 1.13 0.01 0.43 0.07 0.35 1.71 0.03
JJGB1-B3-R0.5sandstone20.3153.52 0.88 16.82 4.76 0.07 0.81 0.34 0.56 1.87 0.08
JJGB1-B3-C10.5coal91.294.11 0.11 1.92 0.82 0.01 0.45 0.80 0.42 0.06 0.00
JJGB1-B3-F0.5sandstone9.7875.38 1.85 11.34 0.38 0.01 0.23 0.17 0.45 0.38 0.03
JJGB1-B5-R0.5coal66.8721.23 0.30 6.73 1.63 0.03 0.84 1.14 0.61 0.60 0.02
JJGB1-B5-C10.5coal94.340.90 0.01 0.36 2.65 0.06 0.46 0.92 0.26 0.03 0.01
JJGB1-B5-C20.5coal96.710.61 0.01 0.25 0.66 0.03 0.47 1.01 0.22 0.02 0.01
JJGB1-B5-C30.5coal94.870.42 0.01 0.26 2.87 0.06 0.44 0.84 0.19 0.02 0.01
JJGB1-B5-F0.5sandstone38.4239.46 0.66 15.77 1.60 0.01 0.90 0.52 0.64 1.97 0.05
JJGB2-B5-av 0.67 0.01 0.40 1.04 0.02 0.51 0.91 0.23 0.03 0.01
JJGB2-B3-av 7.68 0.25 3.59 0.51 0.00 0.48 0.82 0.42 0.15 0.01
JJGB2-B2-av 0.68 0.02 0.63 0.19 0.21 0.52 22.08 0.16 0.01 0.01
JJGB1-B1-av 2.08 0.05 1.36 0.63 0.01 0.53 1.12 0.29 0.03 0.01
JJGB1-B3-av 4.11 0.11 1.92 0.82 0.01 0.45 0.80 0.42 0.06 0.01
JJGB1-B5-av 5.79 0.08 1.90 1.95 0.05 0.55 0.98 0.32 0.17 0.01
China 1-- 8.47 0.33 5.98 4.85 0.02 0.22 1.23 0.16 0.19 0.09
JJGB2-B5-CC 0.08 0.04 0.06 0.72 0.62 0.98 0.40 0.62 0.05 0.45
JJGB2-B3-CC 0.91 0.75 0.54 0.35 0.12 0.93 0.36 1.14 0.30 0.30
JJGB2-B2-CC 0.08 0.06 0.09 0.14 5.20 1.01 9.68 0.43 0.01 0.38
JJGB1-B1-CC 0.25 0.16 0.21 0.44 0.35 1.01 0.49 0.77 0.06 0.29
JJGB1-B3-CC 0.49 0.32 0.29 0.57 0.21 0.86 0.35 1.13 0.13 0.20
JJGB1-B5-CC 0.68 0.25 0.29 1.35 1.16 1.06 0.43 0.86 0.34 0.48
1 Average concentrations of elements in common Chinese coals [1].
Table 3. Trace element concentrations in the JJGB coal (ug/g).
Table 3. Trace element concentrations in the JJGB coal (ug/g).
SampleLiBeScVCrCoNiCuZnGaGeRbSrYZrNb
JJGB2-B5-C01.68 0.08 0.63 1.44 1.89 0.62 3.97 1.10 0.67 0.37 0.03 1.26 230.35 1.07 3.37 0.14
JJGB2-B5-C13.83 0.04 1.03 0.99 1.62 1.56 9.78 0.31 0.93 0.86 0.06 0.79 223.96 2.84 3.61 0.14
JJGB2-B5-F25.35 2.14 18.71 105.75 43.79 6.73 19.78 43.58 50.80 19.64 0.89 89.04 178.35 34.09 144.28 5.70
JJGB2-B3-C05.45 0.16 2.43 11.81 17.22 9.45 14.49 65.61 19.92 2.34 0.23 2.48 275.65 10.10 24.99 1.08
JJGB2-B3-C19.43 0.36 4.48 29.78 17.37 17.98 19.73 12.11 5.59 7.10 0.50 12.23 196.78 8.08 64.61 2.70
JJGB2-B3-C27.07 0.42 5.88 32.98 22.99 28.21 25.97 13.85 12.46 11.18 2.02 7.33 203.17 8.47 56.31 2.50
JJGB2-B3-P118.04 0.81 10.42 66.91 65.00 17.21 19.12 27.66 17.56 17.56 1.21 18.13 146.55 21.28 201.07 9.38
JJGB2-B3-F23.99 1.36 10.34 84.33 98.67 3.99 15.69 26.15 21.92 21.56 1.68 31.25 89.88 25.75 333.15 14.38
JJGB2-B2-R19.24 2.75 11.15 86.48 37.98 9.80 16.12 24.04 33.20 17.57 4.94 58.18 147.90 20.94 139.98 7.30
JJGB2-B2-C17.25 0.11 3.31 1.16 14.66 10.84 10.32 3.82 2.00 1.97 0.05 3.57 349.60 6.75 6.77 0.37
JJGB2-B2-C20.86 0.13 0.84 1.55 2.30 6.21 14.98 BDLBDL1.19 0.12 0.81 249.40 2.60 2.41 0.30
JJGB2-B2-F90.02 1.96 11.71 168.79 152.93 4.83 43.80 15.06 19.21 36.09 2.50 27.17 76.15 21.82 452.27 25.53
JJGB1-B1-R13.04 0.64 5.53 33.40 35.42 6.23 12.85 18.84 29.36 11.74 1.43 43.23 59.30 14.01 185.91 5.84
JJGB1-B1-C12.03 0.04 BDL0.84 1.79 4.12 5.78 0.56 5.09 0.26 0.02 0.51 253.26 1.08 2.40 0.16
JJGB1-B1-C21.35 0.04 0.57 0.63 2.21 0.32 1.87 1.05 BDL0.30 0.01 0.55 245.11 1.39 3.30 0.11
JJGB1-B1-C33.50 0.04 1.51 1.43 3.03 0.40 0.97 3.15 BDL0.53 0.02 1.22 267.40 2.59 8.15 0.37
JJGB1-B1-C43.19 0.11 0.72 4.58 5.45 1.36 3.65 1.32 0.28 1.10 0.07 2.35 228.71 2.05 9.48 0.36
JJGB1-B1-C530.46 0.38 2.64 7.92 12.71 2.15 9.82 12.95 0.60 3.49 3.42 0.43 346.28 4.42 55.35 2.03
JJGB1-B1-F34.75 1.27 9.94 122.03 73.21 18.00 43.97 39.30 35.47 26.74 1.71 67.79 53.48 14.35 236.27 15.48
JJGB1-B3-R24.78 1.87 14.90 110.73 61.36 10.51 24.29 31.89 207.08 19.81 1.68 70.15 101.19 29.13 190.29 9.26
JJGB1-B3-C13.37 0.18 2.70 10.82 9.69 13.93 17.68 11.71 7.90 2.26 0.19 2.59 221.55 4.42 21.43 0.75
JJGB1-B3-F24.34 0.78 10.41 93.32 74.94 2.02 8.77 22.59 15.81 19.62 1.34 15.01 69.61 27.26 341.33 16.42
JJGB1-B5-C09.75 0.55 3.98 25.43 30.51 4.95 9.86 8.72 11.21 6.03 0.49 20.50 198.61 7.56 61.72 2.65
JJGB1-B5-C11.67 0.11 0.35 1.45 1.38 0.75 5.74 0.29 0.58 0.44 0.05 1.18 218.75 0.72 2.99 0.18
JJGB1-B5-C21.63 0.03 0.80 0.65 1.69 0.72 3.46 2.15 BDL0.55 0.02 2.64 242.37 1.83 3.58 0.12
JJGB1-B5-C32.30 0.04 0.88 1.29 1.42 0.96 9.45 BDL17.98 0.79 0.03 0.13 224.00 1.19 2.66 0.08
JJGB1-B5-F27.26 1.83 13.17 111.86 46.66 12.15 23.25 38.06 39.38 21.86 1.11 89.93 168.74 29.68 173.08 7.38
World a10.00 1.20 4.1022.0015.00 4.209.00 15.00 18.00 5.50 2.00 10.00 120 8.60 35.00 3.30
JJGB2-B5-WA0.28 0.05 0.20 0.06 0.12 0.26 0.76 0.05 0.04 0.11 0.02 0.10 1.89 0.23 0.10 0.04
JJGB2-B3-WA0.73 0.26 1.04 1.13 1.28 4.42 2.23 2.03 0.70 1.25 0.46 0.73 1.88 1.03 1.39 0.63
JJGB2-B2-WA0.41 0.10 0.51 0.06 0.57 2.03 1.41 0.13 0.06 0.29 0.04 0.22 2.50 0.54 0.13 0.10
JJGB1-B1-WA0.81 0.10 0.27 0.14 0.34 0.40 0.49 0.25 0.07 0.21 0.36 0.10 2.23 0.27 0.45 0.18
JJGB1-B3-WA0.34 0.06 0.18 0.09 0.09 0.73 0.36 0.33 0.09 0.14 0.09 0.02 0.92 0.14 0.11 0.07
JJGB1-B5-WA0.38 0.15 0.37 0.33 0.58 0.44 0.79 0.19 0.41 0.36 0.07 0.61 1.84 0.33 0.51 0.23
SampleMoCdInSnSbCsBaLaYbHfTaTlPbBiThU
JJGB2-B5-C00.18 0.04 0.034 0.13 0.03 0.08 117.60 1.20 0.09 0.09 0.02 0.01 0.61 0.09 0.37 0.13
JJGB2-B5-C10.21 0.04 0.004 0.05 0.03 0.05 12.33 2.63 0.21 0.09 0.02 0.02 0.86 0.05 1.11 0.27
JJGB2-B5-F0.52 0.43 0.099 1.78 0.45 7.92 264.99 25.70 3.77 3.85 0.47 0.49 10.41 0.37 6.60 2.05
JJGB2-B3-C00.94 0.07 0.020 0.42 0.34 0.14 81.79 5.76 1.26 0.58 0.12 0.05 8.32 0.77 3.70 1.27
JJGB2-B3-C11.69 0.10 0.018 0.69 0.70 1.41 97.94 6.42 0.98 1.73 0.29 0.06 4.08 0.07 1.89 0.66
JJGB2-B3-C21.27 0.10 0.020 0.57 1.16 0.75 91.09 4.33 0.88 1.49 0.19 0.07 5.87 0.08 1.63 0.80
JJGB2-B3-P11.27 0.31 0.051 1.69 0.67 2.49 144.67 11.12 2.75 5.02 0.65 0.15 5.10 0.23 4.48 1.75
JJGB2-B3-F1.89 0.51 0.052 2.89 1.17 4.37 185.89 13.29 3.34 8.21 1.00 0.15 5.52 0.12 6.53 2.45
JJGB2-B2-R0.57 0.22 0.066 1.68 1.80 6.22 148.53 15.61 2.25 3.90 0.59 0.32 12.26 0.21 5.24 2.07
JJGB2-B2-C10.15 0.02 0.008 0.24 0.06 0.14 50.00 4.29 0.79 0.20 0.04 0.03 4.42 0.05 5.04 1.60
JJGB2-B2-C20.11 0.01 0.038 0.06 0.09 0.07 25.32 2.03 0.19 0.08 0.13 0.06 0.76 0.08 0.16 0.20
JJGB2-B2-F1.03 0.63 0.147 5.35 1.64 3.76 86.63 12.35 2.75 12.1 2.41 0.13 19.74 0.55 18.36 7.23
JJGB1-B1-R0.84 0.33 0.038 1.42 0.93 1.79 333.41 13.22 2.01 4.72 0.60 0.25 5.58 0.09 4.51 1.53
JJGB1-B1-C10.09 0.02 BDL0.34 0.04 0.03 37.47 0.95 0.10 0.06 0.01 BDL0.84 0.01 0.40 0.12
JJGB1-B1-C20.27 0.02 0.002 0.29 BDL0.03 43.03 0.94 0.17 0.06 BDL0.06 0.63 0.00 0.39 0.16
JJGB1-B1-C30.04 0.07 BDL0.11 BDL0.07 58.36 1.70 0.32 0.21 0.02 BDL1.05 0.01 1.59 0.41
JJGB1-B1-C40.17 0.04 0.004 0.09 BDL0.17 39.64 1.49 0.22 0.23 0.01 0.01 0.91 0.00 0.60 0.25
JJGB1-B1-C50.01 0.08 0.030 0.43 0.68 0.10 20.86 4.31 0.48 1.51 0.21 BDL5.44 0.11 6.36 1.33
JJGB1-B1-F1.33 0.66 0.101 2.93 1.36 6.80 230.20 18.59 1.87 6.68 1.19 0.45 23.77 0.34 12.85 4.50
JJGB1-B3-R1.16 0.50 0.173 1.92 0.82 5.18 295.14 27.05 3.17 5.30 0.72 0.32 17.44 0.33 6.62 2.26
JJGB1-B3-C12.16 0.04 0.014 0.20 0.13 0.31 76.85 3.71 0.46 0.55 0.04 0.03 3.28 0.08 0.83 0.28
JJGB1-B3-F1.87 0.48 0.048 2.71 0.83 2.22 137.65 10.77 3.83 8.78 1.23 0.10 6.56 0.13 6.75 2.76
JJGB1-B5-C00.51 0.11 0.020 0.54 0.20 1.62 103.65 8.98 0.94 1.74 0.21 0.09 3.23 0.04 2.47 0.73
JJGB1-B5-C10.17 0.02 0.065 0.03 0.01 0.10 17.15 0.57 0.08 0.09 0.02 BDL0.34 0.10 0.28 0.08
JJGB1-B5-C20.12 0.02 0.002 0.01 0.07 0.14 32.22 1.86 0.23 0.10 0.01 BDL0.96 0.01 0.48 0.18
JJGB1-B5-C30.20 0.05 0.004 0.01 BDL0.02 13.11 1.58 0.15 0.07 BDL0.01 1.52 0.01 0.80 0.19
JJGB1-B5-F0.74 0.32 0.094 2.34 0.45 8.73 218.14 23.56 3.36 5.04 0.64 0.48 9.06 0.34 7.58 2.35
World a2.20 0.24 0.02 0.79 0.84 0.98 150 10.00 1.001.20 0.26 0.68 6.60 0.84 3.30 2.60
JJGB2-B5-CC0.09 0.16 0.90 0.11 0.03 0.07 0.43 0.19 0.15 0.08 0.08 0.03 0.11 0.08 0.22 0.08
JJGB2-B3-CC0.59 0.38 0.92 0.71 0.87 0.78 0.60 0.55 1.04 1.05 0.77 0.09 0.92 0.36 0.73 0.35
JJGB2-B2-CC0.06 0.05 1.09 0.19 0.09 0.11 0.25 0.32 0.49 0.12 0.33 0.06 0.39 0.08 0.79 0.35
JJGB1-B1-WA0.05 0.19 0.34 0.32 0.17 0.08 0.27 0.19 0.26 0.34 0.19 0.02 0.27 0.03 0.57 0.17
JJGB1-B3-WA1.35 0.05 0.22 0.06 0.10 0.02 0.17 0.08 0.19 0.11 0.03 0.03 0.23 0.22 0.06 0.06
JJGB1-B5-WA0.11 0.22 1.08 0.19 0.08 0.48 0.28 0.32 0.35 0.42 0.22 0.03 0.23 0.05 0.31 0.11
a Average concentrations of elements in the world low-rank coals [28].
Table 4. Method Detection Limit (MDL) of the trace elements determined by ICP-MS.
Table 4. Method Detection Limit (MDL) of the trace elements determined by ICP-MS.
ElementLiBeScVCrCoNiCuZnGaGeRbSrYZrNb
MDL0.0060.0030.0030.0120.0090.0030.0090.0660.0030.0030.0060.0030.0060.0090.0120.006
ElementMoCdInSnSbCsBaLaYbHfTaTlPbBiThU
MDL0.0060.0030.0030.0060.0090.0030.0330.0030.0060.0030.0030.0030.0060.0150.0060.003
ElementCePrNdSmEuGdTbDyHoErTmLu
MDL0.0030.0030.0150.0030.0090.0030.0060.0030.0060.0030.0030.006
Table 5. Content levels of rare earth elements in coal seam samples from the coal mine (μg/g).
Table 5. Content levels of rare earth elements in coal seam samples from the coal mine (μg/g).
SamplesScYLaCePrNdSmEuGdTbDyHoErTmYbLuREY 1
JJGB2-B5-C00.63 1.07 1.20 2.32 0.22 0.82 0.18 0.09 0.22 0.03 0.20 0.04 0.12 0.02 0.09 0.02 7.27
JJGB2-B5-C11.03 2.84 2.63 4.56 0.62 2.34 0.44 0.09 0.55 0.09 0.47 0.10 0.27 0.04 0.21 0.03 16.3
JJGB2-B5-F18.7 34.1 25.7 58.4 7.27 29.9 6.84 1.83 8.29 1.21 6.34 1.33 3.74 0.56 3.77 0.56 209
JJGB2-B3-C02.43 10.1 5.76 14.5 1.37 5.21 1.17 0.29 1.44 0.29 1.87 0.41 1.26 0.19 1.26 0.18 47.7
JJGB2-B3-C14.48 8.08 6.42 13.1 1.49 5.73 1.20 0.33 1.41 0.23 1.38 0.30 0.93 0.14 0.98 0.16 46.3
JJGB2-B3-C25.88 8.47 4.33 10.5 1.14 4.61 1.09 0.36 1.27 0.26 1.48 0.33 0.93 0.15 0.88 0.14 41.8
JJGB2-B3-P110.4 21.3 11.1 23.0 2.69 10.7 2.40 0.67 3.22 0.53 3.50 0.78 2.50 0.41 2.75 0.44 96.4
JJGB2-B3-F10.3 25.8 13.3 27.2 3.07 11.6 2.61 0.76 3.12 0.66 4.06 0.98 3.06 0.52 3.34 0.59 111
JJGB2-B2-R11.2 20.9 15.6 38.9 3.79 14.7 3.13 0.84 3.68 0.63 3.61 0.77 2.25 0.34 2.25 0.35 123
JJGB2-B2-C13.31 6.75 4.29 12.6 0.89 3.22 0.67 0.14 0.87 0.18 1.20 0.26 0.78 0.13 0.79 0.13 36.2
JJGB2-B2-C20.84 2.60 2.03 4.19 0.48 1.90 0.46 0.13 0.51 0.09 0.48 0.10 0.26 0.04 0.19 0.03 14.3
JJGB2-B2-F11.7 21.8 12.4 31.5 3.48 13.6 3.06 0.67 3.28 0.62 3.73 0.82 2.58 0.40 2.75 0.45 113
JJGB1-B1-R5.53 14.0 13.2 26.7 3.26 12.0 2.26 0.66 2.62 0.40 2.36 0.55 1.78 0.29 2.01 0.33 88.0
JJGB1-B1-C1BDL1.08 0.95 1.71 0.19 0.67 0.15 0.05 0.18 0.03 0.18 0.04 0.12 0.02 0.10 0.02 5.49
JJGB1-B1-C20.57 1.39 0.94 1.62 0.21 0.92 0.19 0.05 0.22 0.03 0.22 0.04 0.16 0.01 0.17 0.02 6.75
JJGB1-B1-C31.51 2.59 1.70 2.91 0.45 1.85 0.39 0.10 0.48 0.07 0.52 0.10 0.31 0.04 0.32 0.04 13.4
JJGB1-B1-C40.72 2.05 1.49 3.38 0.41 1.80 0.42 0.10 0.48 0.06 0.38 0.07 0.23 0.02 0.22 0.02 11.9
JJGB1-B1-C52.64 4.42 4.31 9.15 0.97 3.29 0.61 0.12 0.78 0.13 0.75 0.16 0.49 0.07 0.48 0.08 28. 5
JJGB1-B1-F9.94 14.4 18.6 38.0 3.85 13.8 2.52 0.59 2.90 0.47 2.58 0.55 1.78 0.28 1.87 0.31 112
JJGB1-B3-R14.9 29.1 27.1 60.5 7.01 28.2 6.11 1.58 6.61 1.08 5.66 1.12 3.21 0.46 3.17 0.47 196
JJGB1-B3-C12.70 4.42 3.71 7.91 1.03 4.13 0.87 0.25 0.98 0.15 0.80 0.16 0.48 0.06 0.46 0.06 28.2
JJGB1-B3-F10.4 27.3 10.8 21.9 2.44 9.43 2.17 0.60 2.71 0.58 4.06 0.99 3.29 0.56 3.83 0.65 102
JJGB1-B5-C03.98 7.56 8.98 18.3 2.16 7.96 1.47 0.38 1.74 0.25 1.35 0.28 0.91 0.12 0.94 0.15 56.5
JJGB1-B5-C10.35 0.72 0.57 1.32 0.18 0.64 0.15 0.06 0.16 0.04 0.14 0.04 0.09 0.03 0.08 0.03 4.59
JJGB1-B5-C20.80 1.83 1.86 2.98 0.46 1.67 0.32 0.06 0.37 0.05 0.30 0.06 0.22 0.02 0.23 0.04 11.3
JJGB1-B5-C30.88 1.19 1.58 3.30 0.31 1.05 0.19 0.03 0.25 0.03 0.21 0.04 0.14 0.01 0.15 0.02 9.37
JJGB1-B5-F13.2 29.7 23.6 54.5 6.27 25.3 5.69 1.46 6.15 1.03 5.50 1.15 3.30 0.49 3.36 0.50 181
1: REY represents earth elements and yttrium.
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Hou, Y.; Zhang, K.; Jin, X.; Xu, Y.; Xu, X.; Yan, X. Geochemical Characteristics and Paleoenvironmental Significance of the Xishanyao Formation Coal from the Xiheishan Mining Area, Zhundong Coalfield, Xinjiang, China. Minerals 2025, 15, 686. https://doi.org/10.3390/min15070686

AMA Style

Hou Y, Zhang K, Jin X, Xu Y, Xu X, Yan X. Geochemical Characteristics and Paleoenvironmental Significance of the Xishanyao Formation Coal from the Xiheishan Mining Area, Zhundong Coalfield, Xinjiang, China. Minerals. 2025; 15(7):686. https://doi.org/10.3390/min15070686

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Hou, Yongjie, Kaixuan Zhang, Xiangcheng Jin, Yongjia Xu, Xiaotao Xu, and Xiaoyun Yan. 2025. "Geochemical Characteristics and Paleoenvironmental Significance of the Xishanyao Formation Coal from the Xiheishan Mining Area, Zhundong Coalfield, Xinjiang, China" Minerals 15, no. 7: 686. https://doi.org/10.3390/min15070686

APA Style

Hou, Y., Zhang, K., Jin, X., Xu, Y., Xu, X., & Yan, X. (2025). Geochemical Characteristics and Paleoenvironmental Significance of the Xishanyao Formation Coal from the Xiheishan Mining Area, Zhundong Coalfield, Xinjiang, China. Minerals, 15(7), 686. https://doi.org/10.3390/min15070686

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