Jungar Coalfield Research Articles

Distribution and modes of occurrence of Nb in subbituminous coal: A case study from the Jungar Coalfield, Ordos Basin, China

Niobium has been considered to be enriched in high-Al-Ga in north China coal and coal-hosted Nb(Ta)-Zr(Hf)-REY-Ga polymetallic deposits in the southwestern region of China. However, modes of occurrence and influencing factors of Nb in Al-Ga-rich coal in North China are rarely reported. This study investigated the distribution characteristics of Nb in the No.6 high-Al-Ga coal of the Jungar Coalfield in North China. The in-situ Nb concentration of selected minerals, including kaolinite, Ti-oxides, boehmite, and zircon, is further quantitatively characterized based on multiscale in-situ elemental analyses, including SEM-EDS and LA-ICP-MS spot and mapping analyses. The results showed that Nb is rich in the tonstein and mudstone partings among bulk samples and is highly concentrated in Ti-oxides, followed by zircon among the minerals. A certain amount of Nb is associated with kaolinite and boehmite with different modes of occurrence: vermicular kaolinite (65.94 ppm) > clastic kaolinite (25.43 ppm) > altered K-bearing kaolinite (18.11 ppm) > cryptocrystalline kaolinite (17.03 ppm) > clastic boehmite (9.08 ppm) > cryptocrystalline boehmite (7.97 ppm). The Nb-Nb/Ta and Zr/Hf-Nb/Ta ratios suggest that the primary source of Nb in the No.6 coal is the altered felsic volcanic ash and bauxite deposit. The high-Fe concentration in Ti-bearing minerals indicates that anatase may originate from the alteration of ilmenite with a process of Fe depletion and Nb enrichment. The enrichment of Nb in coal is attributed to the substitution of Nb for Ti in isomorphism in all Ti-oxides, high-Ti, and Ti-bearing minerals.

Study on the leaching behavior differences of rare earth elements from coal gangue through calcination-acid leaching

Critical metals in coal-based byproducts have been gradually regarded as one of the most important alternative resources due to the market parameters, strategic perspective, and advanced technology. In this study, the mechanism of calcination-acid leaching for rare earth elements (REY) recovery from coal gangue of Jungar coalfield was proposed based on the results of sample characteristics, extraction law, kinetic analysis, and typical mineral leaching. The micro-particles of bastnaesite and monazite were found and embedded in the kaolinite via micro-observation with SEM-EDS. Kaolinite in coal gangue calcined at 600 ℃ was transformed into highly positively reactive metakaolinite, enhancing the dissolution of aluminum (Al) and exposing the rare earth minerals encapsulated within the particles. Meanwhile, bastnaesite was thermally decomposed into rare earth oxides and rare earth fluorides. Rare earth oxides are more easily dissolved by acid, and the fluoride ions and the aluminum ions form a stable complex ion [AlF6]3-, which promotes the dissolution of rare earth fluoride. In addition, a high REY and Al recovery (78.8% of REY, and 88.5% of Al) came true from calcined coal gangue at optimal conditions. The leaching kinetics showed that REY leaching followed the hybrid control model of interfacial transfer and diffusion through solid layer, while Al leaching is controlled by chemical reaction. The leaching test of monazite shows that the leaching efficiency of LREY is higher than that of HREY indicating the leaching difference of LREY (82.3%) and HREY (61.3%) in coal gangue is mainly influenced by monazite. This may be related to the crystal structure and the radius of trivalent rare earth ions. This study provides a useful reference for the extraction of REY from coal gangue.

Cooperative Exploration Model of Coal–Lithium Deposit: A Case Study of the Haerwusu Coal–Lithium Deposit in the Jungar Coalfield, Inner Mongolia, Northern China

Lithium (Li) is an important strategic metal mineral resource, irreplaceable in the fields of modern industry, new energy technology, nuclear fusion, and energy storage devices. Li is an important supplement to traditional strategic metal mineral resources and has become an important avenue of mineral resource exploration. Therefore, there is an urgent need to establish a cooperative exploration model of coal and Li deposits to lay a theoretical foundation from the perspective of technical optimization and economic rationality. This study is based on the distribution characteristics of the Haerwusu coal–Li deposit, and the effectiveness of the response to exploration techniques, the economical and effective exploration techniques, the reasonable exploration engineering design, and resource estimation parameters is investigated. Therefore, the cooperative exploration model of the coal–Li deposit is established. The high-Li areas in the surface of the Haerwusu Li deposit is distributed near the B1 anticline or in the middle area between the X1 syncline and the B1 anticline, and the vertical distribution of Li content is irregular. The exploration techniques, exploration engineering design, and resource estimation are reviewed and optimized. According to the geological, geochemical, and geophysical conditions, a reasonable cooperative exploration model for coal–Li deposits is established from the two aspects of the coordination of multi-mineral exploration and the coordination of various exploration technologies. The determination of the coal–Li deposit cooperative exploration model has important practical significance for improving the resource security system.

Cooperative Exploration Model of Coal–Gallium Deposit: A Case Study of the Heidaigou Coal–Gallium Deposit in the Jungar Coalfield, Inner Mongolia, China

Gallium (Ga) is a typical scattered trace element that is irreplaceable in strategic sectors such as national defense, wireless communications, new materials, renewable energy, and healthcare. The coal–Ga deposit is an important complement to traditional Ga resources and has become a significant focus for Ga mineral resource exploration. Therefore, there is an urgent need to research the coal–Ga cooperative exploration model from both technical and economic perspectives. Taking the Heidaigou coal–Ga deposit as an example, the enrichment zone of coal–Ga is predominantly situated in the northern part of the exploration area, adjacent to the fault zone. The Ga concentration demonstrates a gradual decline from the north–central region towards the northeast and southeast. Similar vertical Ga distribution patterns are observed in adjacent drillings, with notably higher concentrations in the roof, floor, and parting layers. The cooperative exploration model for coal–Ga deposits is proposed based on the above features. The model employs a comprehensive set of cooperative technical methods, such as remote sensing, geological mapping, seismic exploration, drilling, petrogeochemistry, and well logging. The layout of exploration engineering and the concentration of Ga provide the basis for the estimation of Ga resources. Additionally, the model provides an important scientific basis for the improvement of the strategic coordination ability of Ga mineral resources.

Modes of occurrence of gallium in Al-Ga-rich coals in the Jungar Coalfield, Ordos Basin, China: Insights from LA-ICP-MS data

Owing to the concern about supply of Ga, it has been attracted much attention for the modes of occurrence of Ga in Al-Ga-rich coal-hosted deposits. However, the modes of occurrence of Ga in coal were mainly investigated using indirect methods, which may cause uncertainties. In this study, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) spot and mapping analysis were used to directly characterize the concentration of Ga within the host minerals including kaolinite and boehmite, and to investigate the distribution of Ga in organic matter in the Carboniferous Al-Ga-rich coal from the Haerwusu Mine in the Jungar Coalfield of the Ordos Basin, North China. Microscope observation and scanning electron microscope - energy dispersive spectrometry (SEM-EDS) analysis were performed, along with petrographical and mineralogical investigations. Eight types of kaolinite and three types of boehmite particles from coal, erosional-sourced mudstone, and tonstein were identified, classified, and selected for the determination of in-situ elemental compositions.The results showed that the concentration of Ga in the selected minerals varies, with the following order from highest to lowest: colloidal boehmite (90.38 ppm), low-Al (Al2O3/SiO2) clastic kaolinite (84.67 ppm), high-Al clastic kaolinite (55.49 ppm), Na-bearing kaolinite (49.94 ppm), fine-grained boehmite (47.13 ppm), high-Al cryptocrystalline kaolinite (40.25 ppm), low-Al cryptocrystalline kaolinite (38.78 ppm), and low-Al vermicular kaolinite (29.67 ppm), high-Al vermicular kaolinite (28.37 ppm), K-bearing kaolinite (19.44 ppm), and clastic boehmite and cell-filling kaolinite (below detection limit). LA-ICP-MS mapping demonstrated that a certain proportion of Ga could be associated with organic matter, concentrating on vitrinite. Notably, the concentration of Ga in clastic kaolinite and colloidal boehmite was found to be substantially higher compared to the whole-rock coal and erosional-sourced mudstone samples, indicative of their dominant host minerals for Ga. Conversely, the concentration of Ga in K-bearing or Na-bearing kaolinite which had experienced transformation from primary kaolinite is much lower than that in clastic kaolinite, while the concentration of Ga in fine-grained boehmite, which had altered from kaolinite, surpassed that of its corresponding kaolinite layer. These findings suggest that gallium could have undergone migration during the evolution or alteration of clay minerals.

Tracking the Vegetation Change Trajectory over Large-Surface Coal Mines in the Jungar Coalfield Using Landsat Time-Series Data

Coal mining and ecological restoration activities significantly affect land surfaces, particularly vegetation. Long-term quantitative analyses of vegetation disturbance and restoration are crucial for effective mining management and ecological environmental supervision. In this study, using the Google Earth Engine and all available Landsat images from 1987 to 2020, we employed the Landsat-based Detection of Trends in Disturbance and Recovery (LandTrendr) algorithm and Support Vector Machine (SVM) to conduct a comprehensive analysis of the year, intensity, duration, and pattern of vegetation disturbance and restoration in the Heidaigou and Haerwusu open-pit coal mines (H-HOCMs) in the Jungar Coalfield of China. Our findings indicate that the overall accuracy for extractions of disturbance and restoration events in the H-HOCMs area is 83% and 84.5%, respectively, with kappa coefficients of 0.82 for both. Mining in Heidaigou has continued since its beginning in the 1990s, advancing toward the south and then eastward directions, and mining in the Haerwusu has advanced from west to east since 2010. The disturbance magnitude of the vegetation greenness in the mining area is relatively low, with a duration of about 4–5 years, and the restoration magnitude and duration vary considerably. The trajectory types show that vegetation restoration (R, 44%) occupies the largest area, followed by disturbance (D, 31%), restoration–disturbance (RD, 16%), disturbance–restoration (DR, 8%), restoration–disturbance–restoration (RDR), and no change (NC). The LandTrendr algorithm effectively detected changes in vegetation disturbance and restoration in H-HOCMs. Vegetation disturbance and restoration occurred in the study area, with a cumulative disturbance-to-restoration ratio of 61.79% since 1988. Significant restoration occurred primarily in the external dumps and continued ecological recovery occurred in the surrounding area.

Rare Earth Element Characteristics in Coal Ash from the Jungar Energy Gangue Power Plant, Inner Mongolia, China

The coal and coal-bearing measures in the Jungar Coalfield in Inner Mongolia are characterized by rare earth element (REE) enrichment. Combustion in coal-fired power plants can lead to further enrichment of REEs in coal ash, which serves as a new potential source for REE extraction and smelting. Further, investigating the content, modes of occurrence, and transformation behavior of REEs during coal combustion may help in better understanding REE differentiation during coal combustion and facilitate the development of economically feasible REE recovery technologies. Therefore, in this study, we analyzed coal ash from the Jungar Energy Gangue Power Plant in Inner Mongolia via inductively coupled plasma mass spectrometry, X-ray diffraction, and scanning electron microscopy combined with energy-dispersive spectroscopy. Our results showed that the REE content of the feed coal was 220 μg/g, slightly higher than the average for global coal. Additionally, fly ash had a higher REE content (898 μg/g) than bottom ash, and its rare earth oxide content was approximately 1152 μg/g, which meets the industrial requirements. Bottom and fly ashes contained similar minerals; however, their relative abundances were different. Specifically, mullite, quartz, calcite, and gypsum were slightly more abundant in fly ash than in bottom ash, whereas amorphous solids were slightly more abundant in bottom ash than in fly ash. Furthermore, fly ash, dominated by Si- and Al-rich minerals, was composed of irregular particles of different shapes and sizes. It also contained monazite and REE fluoro-oxides, which possibly originated from the feed coal and had mineral structures that remained unchanged during coal combustion. Thus, the REE fluoro-oxides possibly resulted from the conversion of bastnaesite in the feed coal during combustion and thereafter became attached to the edge of the Si–Al minerals in the fly ash.

Maceral and Organic Geochemical Characteristics of the No. 6 Coal Seam from the Haerwusu Surface Mine, Inner Mongolia, China

Haerwusu Surface Mine of the Jungar Coalfield is a large coal mine. Its coal formation environments have not been reported in detail. In order to reconstruct the paleoenvironment of the peat formation, nine samples were collected, and were analyzed using microscope, column chromatography, gas chromatography (GC), and gas chromatography–mass spectrometry (GC–MS). According to the results of the microscopic analysis, the average random vitrinite reflectance ( Rr) is 0.73%, indicating a low rank bituminous coal. Vitrinite group is the predominant macerals with an average content of 54.54%, followed by inertinite group with an average of 35.99%. The higher inertinite contents indicate widespread wildfire events during the peat formation. The distribution pattern of n-alkanes, the cross plot between Pr/ n-C17 and Ph/ n-C18, the lower saturated/aromatic hydrocarbon ratios (0.22–0.68) and the presence of cadalene, retene, simonellite indicates that the organic matter is predominantly terrestrial higher plants with a small amount of aquatic organisms. The ternary diagram of Pr/Ph, Pr/ n-C17 and Ph/ n-C18 and the relative abundance of fluorene, dibenzofuran and dibenzothiophene indicate a continental–oceanic alternative facies. The higher contents of combustion-derived PAHs are also indicative of widespread wildfire events during peat formation.

Multiscale in-situ elemental characterization of critical elements in low rank coal, implications for modes of occurrence

This study investigated the distribution characteristics and modes of occurrence of rare elements (Li, V, Co, Mo, Ni, Sb, W, Nb), dispersed elements (Ga, Ge), and rare earth elements (REEs) in two selected coal samples: the Al-Li-Ga-rich coal from the Jungar Coalfield in the Ordos Basin, China, and the Ge-rich coal from the Shengli Coalfield in the Erlian Basin, China. Multiscale in-situ elemental characterization techniques, including BSE-EDS, EMPA mapping, and LA-ICP-MS mapping, were used for this purpose. The results showed that in the Al-Li-Ga-rich Jungar coal, Li was mainly associated with kaolinite with various origins, dominated by epigenetic kaolinite, followed by syngenetic kaolinite. Gallium was highly concentrated in organic matter, led by collodetrinite, followed by collotelinite. The majority of Nb was associated with organic matter, while a minority was distributed in Al-bearing minerals, including boehmite and epigenetic and syngenetic kaolinite. In the Ge-rich Shengli coal, Ge, W, and Sb were consistently distributed in coal and concentrated in organic matter, mainly semifusinite. V was widespread in organic matter, including textinite, fusinite, and semifusinite. Cobalt, Mo, and Ni occurred in a similar distribution and were associated with organic matter, led by collodetrinite in the Al-Ga-rich coal and cutinite in the Ge-rich coal. REEs, except for La and Ce, were associated with organic matter, led by vitrinite in Al-Ga-rich coal and huminite in Ge-rich coal. Lanthanum and Ce were highly concentrated in La, Ce-rich minerals, even if they were widespread in organic matter as well. The visualized results of this study confirm most of the previous findings obtained from indirect analyses but also reveal some differences. Gallium was rarely detected in Al-rich minerals such as boehmite and kaolinite, but highly concentrated in organic matter. Lithium was detected in both epigenetic and syngenetic kaolinite. Ge, W, and Sb were organically associated and concentrated in semifusinite in Shengli Ge-rich coal. Overall, this study provides a way to determine the modes of occurrence of trace elements in organic matter in coal, and these findings could be applied to coal from other geological backgrounds.

Provenance of multi-stage volcanic ash recorded in the Late Carboniferous coal in the Jungar Coalfield, North China, and their contribution to the enrichment of critical metals in the coal

The origins of partings within the Late Carboniferous No. 6 coal in the Jungar Coalfield, North China, and their relationship to the enrichment of critical metals in the coal, is poorly understood. This study combines UPb ages and LuHf isotope data of zircon, whole-rock geochemistry, LA–ICP–MS elemental mapping, and selective chemical extraction experiments to investigate the provenance of the partings and the occurrence mode of critical metals in the partings collected from the exploration area in the northwest of the Jungar Coalfield. It was found that the zircons in the kaolinite-dominant partings yielded a single age group of ca. 300 Ma at the latest Carboniferous (Gzhelian), indicating that the partings are alteration products of air-fall volcanic ash (tonsteins). The zircons are characterized by negative εHf(t) values and a continental arc tectonic setting, suggesting a genetic connection between the volcanic ash and the Late Paleozoic continental arc that existed in the Inner Mongolia Paleo-Uplift, related to the southward subduction of the Paleo-Asian oceanic plate beneath the northern margin of the North China Block. During the devitrification of volcanic glasses to kaolinite in the mires, the incompatible elements, such as Nb, Ta, Zr, Hf, and rare earth elements (REEs and Y, REY), preserved in the volcanic glasses were leached out as they are incompatible with the crystal lattice of kaolinite. Niobium and Ta, similar to Ti in ionic radii, were preferentially incorporated into fine-grained Ti oxides as reprecipitated products in the alteration process of volcanic ash. The enrichment of Nb, Ta, and Ti in organic matter in the tonsteins suggests that they have some mobility during alteration of volcanic ash and could be, to some extent, transported into the enclosing peats. Zirconium, Hf, and REY were fixed by organic matter admixed with the volcanic ash after their deposition in the mires. Meanwhile, they could also be transported into the enclosing peats, as no secondary minerals formed could substantially retain them. Although Li and Ga were able to be incorporated into the crystal lattice of kaolinite during their crystallization, they could also be transported into the enclosing peats due to their fluid-mobile nature. Both the leaching of a voluminous amount of volcanic ash contacting with the peats and the input of the volcanic ash as an admixture into the peats contributed to the enrichment of critical metals in the Late Carboniferous coal in the Jungar Coalfield.

Distribution of Li, Ga, Nb, and REEs in coal as determined by LA-ICP-MS imaging: A case study from Jungar coalfield, Ordos Basin, China

Previous studies on modes of occurrence of Li, Ga, and Nb in coal are primarily based upon statistical analyses due to the low concentrations of these elements and the lack of methods of direct analysis. Laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) can be used for the in-situ determination of trace elements in minerals. The strong heterogeneity and diversity of macerals lead to a lack of suitable internal calibration elements required for LA-ICP-MS-based analysis of trace elements in coal, making the determination of trace elements in organic matter in coal challenging. In this study, the previously investigated high-Al and Li-Ga-Nb enriched No. 6 coal in the Haerwusu Mine of the Jungar Coalfield, Ordos Basin, China, was chosen for revealing the distribution and modes of occurrence of Li, Ga, Nb, and rare earth elements (REEs; REY if Y included) in coal, using the LA-ICP-MS method of mapping (imaging) technology. The results indicate that the majority of Ga and Nb present within the coal was concentrated within a specific collotelinite layer. Gallium and Nb have an organic association and are rare within minerals (i.e., clay minerals and boehmite). Lithium is homogeneously distributed throughout the clay minerals in the collodetrinite. Most of the La and Ce in the coal are concentrated in La- and Ce-enriched minerals, including monazite, bastnaesite, and lanthanite. The other REEs are concentrated in the Ga- and Nb-enriched collotelinite, along with small amounts of La and Ce. A similar characterization processing may be used to determine the modes of occurrences of trace elements in other organic-rich rocks or fine-grained sediments.

Geochronology, mineralogy, and geochemistry of tonsteins from the Pennsylvanian Taiyuan Formation of the Jungar Coalfield, Ordos Basin, North China

Altered volcanic ashes occur worldwide in coal-bearing sequences. The Carboniferous is one of the important coal-forming periods but the altered volcanic ashes within coals in China of this geological age have not been well studied. In this study, the nature of the partings in the No. 9 coal seam of the Pennsylvanian Taiyuan Formation from the Yaogou Mine, Jungar Coalfield, Ordos Basin, North China, was comprehensively investigated. Fifteen partings were identified as altered volcanic ashes based on the typical features, including thin but persistent bands, sharp contacts with the enclosing coals, vermicular and book-like kaolinite, angular quartz, and euhedral primary zircons, while some muscovite and detrital zircon grains in the samples indicate minor contribution of terrigenous debris. Two UPb zircon ages from the altered volcanic ashes at the top and bottom of the No. 9 coal constrain that the Taiyuan Formation in the studied area falls within the Gzhelian Stage of the Late Pennsylvanian. All the altered volcanic ashes were defined as tonsteins due to the relative abundances of kaolinite (> 50%). Furthermore, the TiO2/Al2O3 values suggest that the tonsteins have three magmatic origins, which were mostly felsic, with less intermediate and mafic. The trace elements of the enclosing coals, detrital intra-seam clay beds, floor, and roof were mainly sourced from the felsic-intermediate rocks. However, the elevated concentrations of Li, Ga, Zr, Nb, In, Sn, Hf, Ta, Pb, and Th may be related to the leaching of the tonsteins by (acidic) groundwater or hydrothermal solutions. This is supported by the dominant MREY enrichment patterns with positive Gd anomalies of the coals.

Extraction of lithium from coal gangue by a roasting-leaching process

ABSTRACT Lithium is an important strategic metallic element, which plays a vital role in the production of batteries. Coal gangue has been regarded as a promising resource of lithium. In this study, the coal gangue collected from Jungar coalfield contains 437 ppm of lithium, which is significantly higher than the average content of coal (31.8 ppm) in China. Lithium extraction from the coal gangue was systematically investigated via the integrated process of roasting and acid leaching with the mechanism analysis. The majority (94%) of lithium was extracted when raw samples are roasted at 400°C for 20 min before 4 h leaching with 2 mol/L hydrochloric acid at 60°C, which represented the optimal conditions. X-Ray Diffraction patterns and surface microscopic analysis of the roasting samples showed that thermal decomposition of kaolinite, as the carrier minerals of lithium in the gangue, happened during the roasting, resulting in the easy release of lithium by acid leaching. It was found that diffusion is the dominant control factor of lithium leaching based on the kinetic analysis. In this paper, an integrated process of roasting and leaching with moderate conditions was developed and performed for lithium extraction from coal gangue.

New Insight into the Depositional Age of No. 6 Coal in Heidaigou Mine, Late Paleozoic Jungar Coalfield, Inner Mongolia, China

Coal deposits can provide novel stratigraphic markers for reconstructing the evolution history of a sedimentary basin and correlating sedimentary successions. Age dating was conducted on zircons harvested from the No. 6 coal seam within the Heidaigou Mine, Inner Mongolia. Two-kilogram samples were taken, and the recovered zircons were analyzed for U–Pb isotopic and rare earth elements (REE). The REE results of the zircon grains showed that all the zircon grains were enriched in heavy rare earth elements (HREE) but depleted in light rare earth elements (LREE). In addition, zircons from the No. 6 coal seam had strongly positive Ce (Ce/Ce* = 2.4–224.6) and strongly negative Eu anomalies (Eu/Eu* = 0.1–0.6). Combined with the clear oscillatory zones in the cathodoluminescence images, all the zircon grains of the No. 6 coal were characteristic of zircons with magmatic origins. The 206Pb/238U ages of 34 zircon grains produced a narrow age population of 303–286 Ma, with a weighted average age of 293.0 ± 1.5 Ma (mean-squared weighted deviation = 1.5). Therefore, we infer that the No. 6 coal in the Heidaigou Mine was deposited during the Early Permian, and the Carboniferous–Permian boundary should be located stratigraphically lower than the No. 6 coal. The zircon U–Pb geochronology is a useful tool to determine the depositional ages of non-marine-influenced coal.

Thermal activation and structural transformation mechanism of kaolinitic coal gangue from Jungar coalfield, Inner Mongolia, China

The benefits of industrial solid waste as a supplementary cementitious material in the manufacture of eco-efficient cement are evident in the context of sustainable and green development. Coal gangue from the Jungar coalfield, Inner Mongolia, China, was characterized and activated thermally at 500 °C–1000 °C. This study investigated the effects of thermal activation conditions on the phase and structural changes of the minerals in coal gangue. The pozzolanic activity of the thermally activated coal gangue was evaluated using both direct and indirect methods. The experimental results show that the coal gangue had a silicoaluminous nature mainly comprising of kaolinite. The pozzolanic activity of coal gangue depends on the phase and structural transformation of kaolinite during calcination. Highest pozzolanic activity is reached when calcined at 800 °C for 2 h, with lime consumption and strength activity index up to 1039 mg g−1 and 1.1, respectively. The high pozzolanic activity of metakaolinite was attributed mainly to the formation of a five-coordinated Al sheet and the less polymerized Si sheet after dehydroxylation under calcination.

Leaching behavior of Li and Ga from granitic rocks and sorption on kaolinite: Implications for their enrichment in the Jungar Coalfield, Ordos Basin

The granite collected from the Yinshan Mountain and kaolinite has been selected for the leaching and adsorption experiment, respectively, aiming to clarify the enrichment processes of Li and Ga during the deposition. Results suggest both Li and Ga could be leached out from granite by using different acid solutions of different pH and kaolinite can adsorb Li and Ga with varying degrees. Lithium and Ga had the highest leaching ratio when pH = 1. Special geological events (e.g. volcanic eruptions and wildfires), which could result in very low pH values of water in peatland, may have accelerated the release of Li and Ga from the source rocks. Kaolinite has the highest adsorption fraction was obtained at pH = 8. The different characteristics of Li and Ga displayed in the leaching and adsorption experiments probably result from the different occurrences and enrichment processes of Li and Ga in the coals. Lithium was probably enriched before the Li carriers (e.g. kaolinite) had been transported into paleomires because of its high leaching ratio and high adsorption fraction under neutral and alkaline conditions, whereas Ga was more likely concentrated by kaolinite and other carriers after it had been transported into the peat mires.© 2022 China Geology Editorial Office.

Composition and origin of high-alumina coal in Jungar coalfield

Composition and origin of high-alumina coal in Jungar coalfield

Genesis of Kaolinite Deposits in the Jungar Coalfield, North China: Petrological, Mineralogical and Geochemical Evidence

AbstractPetrological, mineralogical and geochemical studies carried out on kaolinite deposits in Haerwusu surface mine, Jungar Coalfield, northern Ordos Basin, North China, define their characteristics, ore genesis and economic interest. Based on the crystalline size, two different types of kaolinite rocks, cryptocrystalline and grainy, were identified under the microscope. XRD data show that kaolinite is the predominant mineral, associated with boehmite, magnesite, anatase, pyrite, diaspore and calcite. However, high boehmite content (mean 70%) shows up in the middle layers. Kaolinite minerals present homogeneous shape and a good crystallinity (HI = 0.96–1.26). Geochemical studies show that the SiO2/Al2O3 molar ratio of kaolinite is close to the theoretical value, and the contents of Na2O, K2O, CaO, MgO are less, suggesting a strong chemical weathering environment. The REE and Eu anomalies show a close relationship between kaolinite and the Yinshan Oldland granite. A Ce anomaly reflects a continental sedimentary environment with shallow water. A temperature range of 26.7–34°C was calculated on the basis of the isotopic signatures (δ18O, δD) of the kaolinite rocks. All these data indicate that the formation of the kaolinite is caused mainly by the dissolution, coagulation, precipitation and recrystallization of aluminosilicate clastics in acidic conditions. The formation of boehmite in the middle layers indicates that the source rocks have changed. Boehmite is mainly formed by dehydration and compaction of an aluminum‐rich colloid which transported into peat swamp during diagenesis. In addition, it formed by desiliconization of kaolinite under acidic conditions. Due to its high kaolinite content (up to 90%) and low iron mineral content (less than 1%), and good crystallinity, kaolinite deposits occurred at Haerwusu surface mine probably have great economical value in the future.

Leaching behavior of Li and Ga from granitic rocks and sorption on kaolinite: Implications for their enrichment in the Jungar Coalfield, Ordos Basin

The granite collected from the Yinshan Mountain and kaolinite has been selected for the leaching and adsorption experiment, respectively, aiming to clarify the enrichment processes of Li and Ga during the deposition. Results suggest both Li and Ga could be leached out from granite by using different acid solutions of different pH and kaolinite can adsorb Li and Ga with varying degrees. Lithium and Ga had the highest leaching ratio when pH = 1. Special geological events (e.g. volcanic eruptions and wildfires), which could result in very low pH values of water in peatland, may have accelerated the release of Li and Ga from the source rocks. Kaolinite has the highest adsorption fraction was obtained at pH = 8. The different characteristics of Li and Ga displayed in the leaching and adsorption experiments probably result from the different occurrences and enrichment processes of Li and Ga in the coals. Lithium was probably enriched before the Li carriers (e.g. kaolinite) had been transported into paleomires because of its high leaching ratio and high adsorption fraction under neutral and alkaline conditions, whereas Ga was more likely concentrated by kaolinite and other carriers after it had been transported into the peat mires.© 2022 China Geology Editorial Office.

The net primary productivity of early Permian peatland and their control factors: evidenced by the no. 6 coal seam of Jungar coalfield in North China

Purpose The purpose of this paper is to take the early Permian no.6 coal seam in Jungar coalfield of North China as an example, this paper studied the net primary productivity (NPP) level of the early Permian peatland and its relationship with the atmospheric environment at that time, analyzed the influence of the atmospheric environment, and discussed its control factors. Design/methodology/approach First, geophysical logging signals were used for a spectrum analysis to obtain the Milankovitch cycle parameters in the no. 6 coal seam, including the eccentricity (95 ka); obliquity (35.6 ka); and precession (21.2 ka). These were then used to calculate the accumulation rate of the residual carbon in the no. 6 coal seam, which was determined to be between 49.44 and 50.57 gC/(m2 · a). The carbon loss could be calculated according to the density and residual carbon content of the no. 6 coal seam. Then, the total carbon accumulation rate of the peatland was further derived as being between 64.91 and 66.40 gC/(m2 · a). Also, the NPP of the peatland was determined to be between 129.82 and 132.8 gC/(m2 · a). Finding The result showed that the NPP of the early Permian peatland area was lower than that of the Holocene at the same latitude, and also lower than that of the later Permian of South China. Originality/value This study’s comprehensive analysis indicated that the temperature and humidity conditions, along with the oxygen and carbon dioxide levels in the atmosphere, were the main control factors of the NPP of the early Permian peatland. Also, wildfires were found to play a role.