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In this study, major ions, isotopes and rare earth elements (REEs) were tested in groundwater from the coal-bearing sandstone aquifer of the Wolonghu coal mine in northern Anhui Province, and the elemental geochemical behavior and controlling factors in groundwater were discussed. The results indicate that the overall sandstone water is weakly alkaline, and the hydrochemical type is SO4-Na. The relationship between δD and δ18O suggests a hydraulic connection between the sandstone aquifer and the limestone aquifer. The composition characteristics of δ34SSO4 a nd δ18OSO4 indicate that the high concentration of SO42- in groundwater mainly comes from the dissolution of sulfate minerals. The content of rare earth elements (ΣREEs) in groundwater is controlled by pH value and carbonate complexation reaction, and it shows a relative enrichment feature of heavy rare earth elements (HREEs) after standardization with Post-Archean Australian Shales. Ce shows a slight negative anomaly and is mainly influenced by the redox environment, while the Eu anomaly is attributed to the dissolution of silicate minerals. Compared to groundwater quality before the mine closure, the weakening of hydraulic conditions led to an increase in ΣREEs, Ca2+, Mg2+, SO42-, and TDS concentrations accompanied by a significant decrease in HCO3- concentration. In addition, the difference between light rare earth elements (LREEs) decreased, whereas the differentiation between LREEs and HREEs gradually increased. Our findings provide valuable insights into the evolution of groundwater quality in abandoned mines and its genesis mechanism. The results could guide the utilization of groundwater resources in abandoned mines. [ABSTRACT FROM AUTHOR]

Taiyuan Formation limestone groundwater is the main aquifer threatening the safety of exploration under deep mining in the Huaibei coalfield. Therefore, acknowledging the hydrochemical characteristics and constructing reverse hydrogeochemical modeling are crucial for predicting and preventing mine water hazards. In this study, the mathematical statistical analysis, Piper threeline diagram, Gibbs diagram, ion proportional relationship, Chlorine-Alkali index, and the reverse hydrogeochemical modeling were employed for determining the hydrochemical characteristics and the formation mechanism. The results revealed that the hydrochemical types of groundwater samples were SO4.Cl-Ca.Mg and HCO3.Cl-Na, respectively. The water-rock interactions were primarily influenced by the leaching and the cation exchange, with these processes being more intense in the eastern region. Through reverse hydrogeochemical modeling, the water-rock interactions in the process of groundwater runoff were quantitatively verified, viz. the calcite and the dolomite were saturated and precipitating, while the gypsum and the halite were unsaturated and still dissolving. Furthermore, the simulations of mass transfer in groundwater runoff indicated that the dissolution and the leaching of gypsum, dolomite and halite, positive ion exchange, the precipitation of calcite, and the dissolution of CO2 gas predominantly occurred along four simulated flow paths. These results offered a scientific foundation for the prevention and controlling of mine water hazards in deep mining contexts. [ABSTRACT FROM AUTHOR]

The Qianyingzi Coalmine is located on the west of the Suxian Mining area of the Huaibei Coalfield, adjacent to the outer edge of the southern segment of the Xu-Su Arc Nappe Belt. Methods Based on the latest geological exploration and production data, this paper analysed the structural framework and coal-controlled structural patterns of the Qianyingzi Coalmine, divided the tectonic stages, and discussed the geotectonic background of the coalmine structures, Objective which provides an important geological basis for the understanding of the tectonic deformation and evolution of the coalmine, the geodynamic mechanism and the prediction of exploration directions. Results The results show that the Carboniferous-Permian coal-bearing formations in the mine are generally a gentle syncline with an NNE-trending axis. The faults in the mine are well developed, and the number of reverse faults is greater than that of normal faults. Both of these faults are mainly NE to NNE, followed by NS. The structural framework of this mine is significantly controlled by several large NS to NE-striking faults and is segmented from west to east by major faults, including the Nanping, F22, F17, DF200 and Shuangdui faults, which exhibit the characteristic of east and west zonation. The coal-controlled structural patterns in the mine can be classified into three types, namely, compressional, extensional and strike-slip. And the coal-controlled patterns can be further divided into nine subtypes, namely, thrust drag folds, hedge structures, pop-up structures, imbricate structures, grabens, horsts, step faults, positive flower structures and pinnated en-echelon structures. The analysis of structural combinations shows that the F17 fault has not only thrusting motion but also significant transcurrent activity. Conclusion The structural deformation of coal-bearing formation in the Qianyingzi Coalmine can be divided into five stages: the Fengjia Syncline with an NNE-trending axis, nearly NS-striking reverse faults, NNE-striking reverse-sinistral faults and NE-striking reverse faults, nearly NS-striking normal faults, and NW-SE-striking normal faults. Combined with the results of previous studies on the regional tectonic background, the first and second shortening structures in this mine are the results of foreland deformation during the convergence of the North China Craton and South China Plate and subsequent continent-continent collisional deformation during the Indosinian period. The third stage compresso-shear structures are related to the rapid oblique subduction of the Izanagi Plate toward the East Asian continental margin at the beginning of the Early Cretaceous in the Western Pacific. The fourth and fifth stage extensional structures developed against a strong extensional background in eastern China during the Early Cretaceous.

The natural balance system of deep groundwater is disturbed by coal mining and drainage depressurization, leading to temporal and spatial changes in microbial communities in different aquifers. Herein, groundwater samples of Permian coal measures sandstone aquifer and Carboniferous Taiyuan Formation limestone aquifer with depths of 600 and 750 m are collected from the mine hydrological holes in Huaibei coalfield, and 16S rRNA gene V4 region sequencing method is used to test and analyze the microbial community diversity of deep groundwater. The operational taxonomic units (OTUs) numbers of coal measure water and Taiyuan limestone water samples range from 968−3071 and 820−3894, respectively, with the average values being 1980.43 and 1847.81 respectively. ACE, Shannon and Chao values show that coal measure water > Taiyuan limestone water. Simpson index shows that coal measure water < Taiyuan limestone water, indicating that coal measure water > Taiyuan limestone water, regarding the diversity of microbial community composition in groundwater. Main dominant bacteria phylum in Taiyuan limestone water and coal measure water are Proteobacteria, Bacteroidota and Planctomycetota; their relative abundance ranging 41.48%−97.36%, 0.57%–48.01%, 0.13%–15.29%, respectively. Main dominant bacteria genera in coal measure water are Thiovirga, Hydrogenophaga, and Flavobacterium; their relative abundance accounting for 5.98%, 4.39% and 3.43%, respectively of the total bacteria in the coal measure water. Hydrogenopaga, Acinetobacter and Thiobacillus are the main dominant bacteria genera in Taiyuan limestone water, their relative abundance being 11.13%, 4.72% and 4.40% respectively. Unique OTUs in coal measure and Taiyuan limestone aquifers number 1759 and 4107, respectively. F−, K+ and ORP are the main environmental factors affecting the bacterial community in groundwater. K+ impacts the abundance of the bacterial community in the Taiyuan limestone water to a greater extent than that of coal measure water. Contrarily, F− affects the bacterial community in the coal measure water and Taiyuan limestone water is similar. As the aquifer depth increases, so does the influence of F− and K+ on the microbial community abundance. The increase of F− concentration of typical pollutants in Huaibei Coal strengthens some bacterial communities, resulting in changes in microbial community composition. The groundwater pollution caused by coal mining also enriches Thiothrix in the ash water. Huaibei coal measure water and Taihui limestone water are the main water filling sources for coal mining in Huaibei coalfield. Knowledge of the deep underground of the coalfield and how different water microbial community change, has been improved by this work, thereby providing a new method for identifying the water source of coal mine gushing (outburst), and a guarantee for the prevention and control of water disasters in coal mines.

The main threat source of coal mining in the lower formation of Huaibei Coalfield is limestone water from the coal seam floor (including the Carboniferous Taiyuan Formation and the Ordovician limestone water), and some well flooding accidents occur from time to time. For the control of water disaster in the limestone floor, at present, the ground directional drilling high-pressure grouting technology is mostly used for carrying out the regional reinforcement and reconstruction of the third layer of thin limestone (referred to as “three ashes”) in the Taiyuan Formation of the coal seam floor. Therefore, it seals the karst cracks of the three ashes and blocks the vertical water channel passing through the three ashes. However, with the implementation of large-scale high-pressure grouting project, the groundwater flow field in the injected aquifer will be disturbed. Because of the coupling effect of a large amount of slurry water, the groundwater chemical field will inevitably be seriously disturbed. Taking the limestone aquifer of the Taiyuan Formation (hereinafter referred to as “Taihui water”) in the Taoyuan Coalmine of the Huaibei Coalfield as the research object, based on the constant component monitoring data statistics, Piper diagram, ion combination ratio, and saturation index analysis, this paper studies the hydrogeochemical evolution law of the Taihui water before grouting, during grouting and after grouting (i.e. “three periods before, during and after regional grouting”). The results show that ① in the three periods, Na++K+, HCO3 −, Cl− in the Taihui water first decrease and then increase. Ca2+, SO4 2− and pH values first increase and then decrease, while Mg2+, TDS decrease as a whole. In the grouting control area, Ca2+ and SO4 2− are relatively high and alkalinity is relatively high, while Na++K+ and HCO3 − are relatively low. Before grouting, SO4·Cl−Na and SO4·Cl−Na·Ca (mixed type) are the main types. Since regional grouting, SO4·Cl−Na·Ca and SO4·Cl−Na are the main types in the Taihui water, and the proportion of mixed water increases. ② During grouting, the dissolution of carbonate and sulfate, the desalfation and the cation exchange in the Taihui water are weakened, the dissolution of calcite and dolomite is enhanced, and the mixing effect of the precipitates water of cement slurry is obvious. After grouting, the dissolution of carbonate and sulfate, desulphation and cation exchange are gradually enhanced, the dissolution of calcite and dolomite is gradually weakened, and the mixing effect of precipitates water is weakened. One year after the completion of grouting, the hydrochemical effect is gradually recovered toward the state before grouting, but it has not yet recovered to the state before grouting. It can be seen that the regional grouting treatment has a relatively obvious impact on the disturbance of the chemical field of the Taihui water. ③ The saturation index of dolomite and calcite in the Taihui water is large, and most of them are in precipitation state. The saturation index of gypsum and rock salt is small, and they mostly exist in the state of dissolution. In the three periods, the saturation indexes of calcite, dolomite and gypsum in the Taihui water increase first and then decrease, in which dolomite is more obvious, while the rock salt saturation index does not change significantly. The saturation index of most minerals has a strong positive correlation with pH value, while the saturation index of gypsum has a strong positive correlation with TDS. ④ Due to the mixing of the water from the grouting slurry with high pH value, the original ion balance is broken, which leads to the reduction of the correlation of the conventional indicators of the Taihui water since the regional grouting, and the correlation is lower after the grouting than that during the grouting.

With industrial development and innovation, the demand for key metal minerals dominated by rare earth elements is increasing day by day. More experts believe that coal measures mineral resources have the potential to obtain key metal minerals, and such resources have therefore received high attention at home and abroad. Huaibei coalfield in China is rich in coal resources. In order to study the geochemical characteristics of trace elements in its coal and judge the industrial potential of rare metals, No. 5 coal, No. 8 coal and No. 10 coal in Zhuzhuang Coal Mine were selected as the research objects. The samples were analyzed by means of industrial analysis, XRF and ICP-MS. The results show that compared with the world coal, most trace elements in Zhuzhuang Coal Mine are highly enriched, such as Li, Cr, Co, etc. Compared with 5 coal and 8 coal, the concentration of trace elements in 10 coal is low, and the contents of V, Mn, Rb and Cs belong to the normal range. Through the analysis of w (Al2O3)/ w (TiO2) ratio and element geochemical characteristics, it is concluded that the sedimentary source area of the study area is felsic source rock, the paleosalinity from Shanxi formation to Lower Shihezi Formation changes from marine facies to saline water facies, and the paleoclimate is a warm and humid reduction environment. In addition, rare earth elements are enriched in light and medium rare earth elements, and Eu, Y positive anomalies and Ce negative anomalies all show that the sedimentary environment of Zhuzhuang mine is affected by seawater and magmatic hydrothermal solution. Therefore, the abnormal enrichment of trace elements in Zhuzhuang Coal Mine may be affected by the sedimentary environment, seawater and hydrothermal solution. In addition, the study area is relatively rich in rare earth elements, and its total content is close to or even higher than the industrial grade. Through the comparison of REY prospect coefficient (Coutl) and a variety of sediment minerals, it is considered that the rare earth elements of coal 5 and coal 8 in the sample of the study area are promising as REY raw materials, while the effect of coal 10 is poor.

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The project implementation of water inrush and its treatment ensures the safe mining of coal mines, but also causes certain disturbance to the hydrogeochemistry of primary limestone water. Based on the water inrush event in Taoyuan Coal Mine of Huaibei coalfield in 2013, the water rock interaction mechanism of Taiyuan Formation limestone water (namely, ‘Taihui water’) was discussed. The results showed that: (1) the relationship of cation mass concentration before and after water inrush was Na+ + K+ > Ca2+ > Mg2+; the correlation of anionic mass concentration before water inrush was SO42− > HCO3− > Cl−, while it was HCO3− > SO42− > Cl− after the event. Before the event, the main water quality types were SO4•Cl-Ca and SO4•Cl-Na; after the event, they mainly included HCO3-Na and SO4•Cl-Na; (2) There is a strong positive correlation between mineral saturation index and pH value, that is, minerals are easy to dissolve under acidic conditions, while alkaline conditions will inhibit the dissolution and transformation of minerals; (3) The hydrogeochemical processes of limestone aquifer mainly included cation exchange, carbonate dissolution, pyrite oxidation, sulfate and silicate dissolution. HIGHLIGHTS The hydrogeochemical characteristics of Taiyuan Formation limestone water disturbed by water inrush of collapse column was analyzed.; Based on saturation index, ion combination ratio and correlation analysis method, the evolution of hydrogeochemistry under the influence of water inrush was discussed.; The relationship between saturation index and TDS and pH value was studied.;

This research focused on the hazardous elements in the main coal seam of Huaibei coalfield, China. Through collecting 20 feed coal samples from different coal seams of nine coal mines in the region, and combining with XRF, XRD, ICP-MS, and sequential chemical extraction, the mineral composition and the contents of major elements and HEs for feed coal were analyzed. Compared with previous research results, the enrichment characteristics of HEs in feed coal were revealed. The leaching behaviors of Se, Hg, and Pb in feed coal and coal ash under different leaching conditions were analyzed in depth by using a leaching device independently developed. Results showed that, compared with Chinese coals and World coals, the content of other elements, except Se, Sb, Hg, and Pb, in feed coal of Huaibei coalfield were at the "Normal" level, and no "Low" level elements were found; as the acidity of leaching solution decreased, the relative leaching rate of Se (LSe) was gradually increasing, while the LHg and LPb were not obvious; the LSe in feed coal and coal ash had a great relationship with the modes of occurrence of Se. The difference in the Hg content in the ion exchange state in feed coal may be an important reason for the difference in Hg leaching behavior. However, the content of Pb in feed coal had little influence on its leaching behavior. The modes of occurrence of Pb determined that the LPb in feed coal and coal ash was not high. The LSe increased with the increase in acidity of leaching solution and leaching time. The leaching time was the main influencing factor of the LHg and LPb. [ABSTRACT FROM AUTHOR]

The hydrogeochemistry of geothermal fluids provides insight into the occurrence, formation, and circulation of geothermal resources. We collected 13 geothermal water (> 34 °C) and 11 common groundwater samples (< 20 °C) from the Qingdong coal mine in China. The geothermal water samples had higher TDS, Ca2+, and SO42− contents, by 1.22-, 1.28-, and 1.25-fold, respectively. The hydrochemical facies of the geothermal water samples was 92% SO4·Cl–Ca.Mg and 8% SO4·Cl–Na, whereas the common groundwater samples was 73% SO4·Cl–Ca.Mg and 27% SO4·Cl–Na. Moreover, hydrogen and oxygen isotopic analysis revealed that atmospheric precipitation and water–rock interaction were the sources of the geothermal water. The chemical composition of the geothermal water is dominated by ion-exchange interactions and the dissolution of carbonates and silicates. Overall, geothermal water in the study area is characterized by optimal hydrodynamic conditions and more intense ion-exchange interactions than common groundwater. Moreover, the formation of geothermal water is controlled by hydrogeological and structural conditions, and by the infiltration of atmospheric precipitation, heating by deep circulation, and transportation by water-conducting faults (F11) to shallow coal strata. These results will facilitate the development of geothermal resources and the construction of green ecological mines, which will provide considerable economic and social benefits. [ABSTRACT FROM AUTHOR]

Years mining activities have changed the distribution characteristics of groundwater hydrochemical field, which may lead to the deterioration of groundwater quality and the occurrence of mine water inrush disasters. The study of groundwater hydrogeochemical evolution can provide a theoretical basis for the prevention of mine water inrush disaster and the rational utilization and protection of groundwater. Using the Piper trigram, Person correlation analysis matrix, Gibbs diagram, ion proportion coefficient diagram, and mineral saturation index to study the hydrogeochemical evolution mechanism of Taiyuan Formation limestone water before grouting (2010) and after grouting (2020) in this study. The results show that the concentrations of anion and cation in the limestone water of Taiyuan Formation have the same change trend before and after grouting in the study area, the anion concentration changes to SO42-> HCO4- >Cl-, the cation concentration changes to Na+ + K+ > Ca2 +> Mg2+. The correlation coefficient between most ions of limestone water after grouting is reduced. The hydrogeochemical type is gradually transformed from Na+ + K+ -SO42- type to Mg2+-SO42- type and Ca2+-SO42- type. Rock weathering and cation exchange are the main factors affecting the hydrogeochemical characteristics of limestone water. The higher concentration of SO42-is related to the dissolution of gypsum and the oxidation of pyrite. [ABSTRACT FROM AUTHOR]

The Huaibei coalfield is an important coal base and one of the hot spots of coalbed methane development in China. Therefore, a detailed understanding of gas occurrence in the Huaibei coalfield is of great significance. This paper analyzes the gas occurrence from the perspective of multiple-level tectonic control, i.e., the regional tectonic level, the coalfield tectonic level, the mining area tectonic level, and the coal mine tectonic level. This study deduces that gas occurrence in the Huaibei coalfield is characterized by multiple-level tectonic control. At the regional level, the Huaibei coalfield is located in the southeast margin of the North China plate, affected by the tectonic evolution of the North China plate and by the evolution of the Dabie–Tanlu–Sulu orogenic belt. Therefore, the regional geological tectonic is complex, leading to the high gas content and serious gas hazard. At the coalfield level, gas occurrence in the Huaibei coalfield is controlled by east–west faults, NNE faults, and the Xuzhou–Suzhou arc nappe tectonic, which results in the highest gas occurrence in the Suxian mining area, followed by the Linhuan mining area and the Suixiao mining area, while the lowest amount of gas occurs in the Guoyang mining area. At the mining area level, considering the Suxian mining area as an example, the gas occurrence is controlled by the distance from the Tancheng–Lujiang fault zone and the intensity of tectonic compression, i.e., coal mine gas in the east is the highest, followed by coal mines in the south, while coal mine gas in the west is the lowest. At the coal mine level, gas occurrence is controlled by the buried depth of the coal seam, the tensional normal fault, magmatic activity, and uplift and erosion of strata. Finally, the findings of this study may help in the prevention of gas hazard and the exploration and development of coalbed methane in the Huaibei coalfield and other coalfields of similar geological characteristics. [ABSTRACT FROM AUTHOR]

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This research focused on the hazardous elements in the main coal seam of Huaibei coalfield, China. Through collecting 20 feed coal samples from different coal seams of nine coal mines in the region, and combining with XRF, XRD, ICP-MS, and sequential chemical extraction, the mineral composition and the contents of major elements and HEs for feed coal were analyzed. Compared with previous research results, the enrichment characteristics of HEs in feed coal were revealed. The leaching behaviors of Se, Hg, and Pb in feed coal and coal ash under different leaching conditions were analyzed in depth by using a leaching device independently developed. Results showed that, compared with Chinese coals and World coals, the content of other elements, except Se, Sb, Hg, and Pb, in feed coal of Huaibei coalfield were at the “Normal” level, and no “Low” level elements were found; as the acidity of leaching solution decreased, the relative leaching rate of Se (LSe) was gradually increasing, while the LHg and LPb were not obvious; the LSe in feed coal and coal ash had a great relationship with the modes of occurrence of Se. The difference in the Hg content in the ion exchange state in feed coal may be an important reason for the difference in Hg leaching behavior. However, the content of Pb in feed coal had little influence on its leaching behavior. The modes of occurrence of Pb determined that the LPb in feed coal and coal ash was not high. The LSe increased with the increase in acidity of leaching solution and leaching time. The leaching time was the main influencing factor of the LHg and LPb.

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The effects of a water inrush event on the chemical composition of groundwater in a coal measures sandstone aquifer that is important for water supply was investigated at the Taoyuan coal mine in the Huaibei region in China. Changes in groundwater quality caused by the inrush event were investigated using statistical techniques, a Piper trilinear diagram, saturation index, ion combination ratios and a fuzzy comprehensive evaluation method. These investigations indicated that Na+ + K+ and SO42− were the main cation and anion, and the average contents were 272 mg/L and 732 mg/L before water inrush, and 394 mg/L and 779 mg/L after water inrush, respectively. The concentrations of anions in groundwater before the inrush event were in the order SO42− > HCO3− > Cl− and the cation concentrations were in the order Na+ + K+ > Ca2+ > Mg2+. The chemical composition of groundwater was mainly SO4·Cl–Ca·Mg before water inrush event, and SO4·Cl–Na and Na–HCO3–Cl after this event. According to the saturation index method, gypsum, calcite, magnesite, and aragonite controlling the chemical composition of groundwater were reactive minerals in groundwater system. The oxidation of pyrite, dissolution of sulfate and carbonate minerals were main geochemical process before and after the event; while the oxidation of pyrite and cation exchange were enhanced after the water inrush event. The fuzzy comprehensive evaluation results showed that the type V water accounted for a large proportion of poor-quality groundwater. Groundwater quality in the aquifer near the mine generally deteriorated after the water inrush event. [ABSTRACT FROM AUTHOR]

Heavy metals in the collapsed lake of Zhuxianzhuang Mine in the typical coal mine of Huaibei Coalfield were selected as the research object. Differences, sources and human health risks of heavy metals such as Cu, Cd, Cr, Ni, Pb, V, Zn and Mn in four seasons of lake water were analyzed. Among them, the content of V element was the highest in all four seasons (1.80~7.04mg/l), while the content of Cd was the lowest (0.03~1.92mg/l). In addition, the elements of the super background value are: V, Ni, Cu, and Cr, wherein the V content exceeds the background value multiple of 4.3 to 12.93. Principal component analysis (PCA) results show that the three principal components share 81.6% of the variance contribution rate. Finally, the results of lake water health risk assessment showed that the risk of non-carcinogenicity of 8 heavy metals was: Cu>Cd>Cr>Ni>Pb>V>Zn>Mn. The Cr element is the main carcinogenic risk element in the lake water of the study area, and the risk value is concentrated at 1.16E-08~7.54E-07. Among the exposed population, the hazard index (HI) of Mn was 49.21 times that of adults. In general, the hazard index value is <1, and the cancer risk is within acceptable levels (1E-06). But from the perspective of public health and safety, we need to maintain further observation and research on these elements. [ABSTRACT FROM AUTHOR]

Taking insight into genetic mechanisms of coalbed methane (CBM) can provide an effective approach for evaluating the value of CBM resources. In this study, the geo-temperature and the thermal subsidence history were used to investigate the effect of the present geothermal field characteristic on the genetic mechanisms of CBM at the Huaibei Coalfield. The results showed that the Permian coal strata in the study areas had a relatively low geo-temperature (

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The composition characteristics of altered coals in the Huaibei Coalfield, China, was investigated through a comparative analysis between altered and unaffected coals from the Wolonghu, Taoyuan and Renlou coal mines. Results indicated that the altered coals in Wolonghu coal mine are mostly anthracite coals, with a maximum vitrinite reflectance of 1.6–3.9% (average of 2.9%). Coals from Wolonghu coal mine were mainly consisted of vitrinite (66.2–97.0%), followed by inertinite (2.0–4.0%) and exinite (0.4–6.9%). Differences in volatile matter content were observed between the altered coals in Wolonghu coal mine and unaffected coals from neighboring coal mines, implying that the chemical composition and maturity of coals were changed after magmatic alteration. In addition, differences in hydrogen element were noted among the coals from Wolonghu, Renlou and Taoyuan coal mines, and the phenomenon of “deficient in hydrogen element” was observed in Wolonghu coals. The aliphatic hydrocarbon structure parameters suggested that the aliphatic chain lengths of Wolonghu coals are shorter than those of coal samples from the Renlou and Taoyuan coal mines. In addition, maturity is positively correlated with hydrogen enrichment degree, but negatively related with aliphatic hydrocarbon structure. Coals from Renlou and Taoyuan coal mines showed great weight loss with various heating rates at temperatures of 0–1000 °C, whereas those from Wolonghu coal mine had less weight loss.

Taking insight into genetic mechanisms of coalbed methane (CBM) can provide an effective approach for evaluating the value of CBM resources. In this study, the geo-temperature and the thermal subsidence history were used to investigate the effect of the present geothermal field characteristic on the genetic mechanisms of CBM at the Huaibei Coalfield. The results showed that the Permian coal strata in the study areas had a relatively low geo-temperature (< 50°C), high vitrinite reflectance (Ro,max; 0.75%-1.2%) and a coal rank typical of intermediate-high metamorphic bituminous. Comprehensive analyses of the characteristics of the present geothermal field indicate that the CBM at the Huaibei Coalfield are dominated by secondary biogenic gases. Furthermore, the genetic mechanism towards CBM was further proposed based on the tectonic evolution history: (1) Tectonic thrusting contributed to Ro,max values ranging from 0.5% to 3.0%, with maximum geo-temperatures of 140-180°C, which resulted in the generation of thermogenic CBM. (2) An extensional regime contributed to gradual uplift of the Permian coal-bearing strata, with the gradual escape of CBM at burial depths greater than 700m. (3) A large number of faults and hydrodynamic environments greatly promoted the microbial degradation of the early thermogenic gases, resulting in generation of secondary biogenic gases. [ABSTRACT FROM AUTHOR]

Sunan mining area was selected as investigated area from Huaibei coalfield to study the accumulation and enrichment characteristics of heavy metals in soil and plant. This study focused on heavy metal content characteristics about surface and profile soil, maize plant bioconcentration transfer characteristics and health risk assessment of heavy metals. The results indicated that the mean content of heavy metals (Cd, Cr, Pb, Ni, Zn and Cu) were 0.26, 52.69, 24.09, 29.77, 57.00 and 26.09mg/kg in surface soil, respectively. Cr exceeded the secondary standard of national environment quality standard for soil in China with the proportion of 50%, while other heavy metals did not exceed the corresponding standard. Single factor pollution index showed that 8.33% of Ni and Cd samples belonged to the warning limit pollution level respectively, and other heavy metals were at clear. Profile heavy metal vertical migration characteristics revealed that except for Pb, other heavy metals showed an obvious trend of vertical migration in different degrees. Among organs of maize plant (e.g. roots, stems, leaves), Zn content was highest, while Cd content was lowest. The bioconcentration factor( BCF) and transfer factor (TF)of Cd were relatively larger, and maize plant root tended to absorb more Cd from the soil firstly, and then transferred to the upper part of the ground. Health risk assessment results suggested that the health risk of six heavy metals to children was much higher than that of adults, and Cr contribution were the largest among them. [ABSTRACT FROM AUTHOR]

The impact of coal mining activities on the structure of groundwater microbial communities in coal mining areas has gradually received academic attention. In this study, hydrochemical analysis and sequencing of the V4 region of the 16S rRNA gene were carried out using groundwater samples from the fourth aquifer in the loose layer of Cenozoic, the sandstone fissure aquifer in the coal measure strata of Permian, the Carboniferous Taiyuan Formation limestone aquifer, and the Ordovician limestone aquifer, at depths of 250 m, 600 m, 750 m, and 1000 m in monitoring wells. Results showed that the operational taxonomy units (OTUs) in the deep groundwater ecosystem were clustered distinguishably between the contaminated and the uncontaminated aquifers. The microbial community alpha-diversity of groundwater was significantly correlated with depth, and the richness of microbial community composition decreased with increasing depth. Proteobacteria (34.41%–97.41%), was found to be the dominant phylum, Gammaproteobacteria (10.05%–92.06%) was the dominant class and " Unassigned " (4.12%–64.72%) was dominant at the genus level. The number of endemic bacteria in the four aquifers was 1, 33, 99 and 11, respectively. It was also found that F−, oxidation-reduction potential (ORP), and TOC were the main environmental variables affecting the groundwater all OTUs, abundant OTUs, and rare OTUs, respectively. These results indicate that the activity of rare OTU subcommunities increases gradually with increasing aquifer depth and that mining significantly enriched Thiovirga in deep groundwater. In addition, it was found that with the increase of depth, the effect of ORP on microbial community abundance decreased. This study deepens our understanding of the evolution characteristics of microbial communities in deep groundwater in coal mining areas. The unique characteristics of microbial communities characteristics of four aquifers with different depths provide a microbial perspective for understanding the characteristics of deep aquifers. [Display omitted] • Hydrochemical analysis was carried out on aquifer groundwater samples. • Microbial community diversity was significantly affected by depth. • Microbial community composition became richer with increasing depth. • Proteobacteria was found to be the dominant phylum. • Gammaproteobacteria was the dominant class. [ABSTRACT FROM AUTHOR]

Selenium, a toxic element, is highly enriched in the coals of the Huaibei coal deposit, China. For this study, Se content along with rock-forming and trace element abundances was determined in 123 coal and 19 rock samples collected from the main coal seams in seven coal mines in the Huaibei coalfield. This was done to investigate the Se geochemistry in the Huaibei coals. Compared with average Chinese coal and other coals around the world, the Huaibei coals are enriched in Se by a factor of five. Differences in the boron content in the sequence of Huaibei coal seams show that the depositional environment of the formations hosting the coal seams evolved from a delta front to a prodelta setting and then to a delta plain environment. Selenium is distributed unevenly both horizontally and vertically in the Huaibei coal deposit. Pearson correlation coefficients between Se with several elements (Ca, Fe, and S) indicate that iron-bearing clay minerals and carbonates are the dominant carriers of Se in coals of the Lower Shihezi Formation. Selenium in coals from No. 3 and No. 10 coal seams are mainly associated with sulfide minerals. The well-developed faults in Huaibei coalfield may have contributed to the enrichment of Se in Huaibei coals. [ABSTRACT FROM AUTHOR]

The Huaibei coalfield is in the East China Economic Area, which is rich in coal and gas resources. However, hundreds of coal and gas outburst accidents have occurred because of the complex geological structures of the coalfield. Based on theoretical analysis and field statistics, the characteristics of regional geological structures and the coal measure strata evolution in the Huaibei coalfield were researched, and gas resource distribution and gas parameters were statistically analyzed to determine the dominant controlling factors of gas occurrence and gas dynamic disaster. The results indicated that the Huaibei coalfield has undergone complex tectonic evolution, causing obvious differences in gas storage in different blocks of different mining areas, which exhibits a pattern of high amounts of gas in the south and east, and low amounts of gas in the north and west. The coal seam and gas occurrence have a bipolar distribution in the coalfield caused by multiple tectonic movements, and they are deeply buried. Horizontal tectonic stress plays a dominant role in gas outburst, and the thermal evolution and trap effects of magma intrusion increase the possibility and extent of gas outburst. Considering coal seam and gas occurrence characteristics in the coalfield, we propose a new technology for deep coal reservoir reconstruction which combined present underground regional gas control methods and surface well extraction methods. The technology has three effects: developing gas resources, improving coal mining safety level and reducing greenhouse gas emissions, which has been practiced to be effective in coal mines in the Huaibei coalfield. [ABSTRACT FROM AUTHOR]

Discussed the origins of coalbed methane in Luling Coal Mine of Huaibei coalfield from the aspects of carbon and hydrogen isotope of methane, the quantitative relationship between δ5D(CH4), δD(H2O) and the source of coalbed produced water. The results reveal that the methane is predominant (up to 97%) and is thought as extremely dry. δ13C(CH4) from -67.6‰ to -64.2‰ and δD(CH4) from -206‰ to -224‰, so it is in the range of biogenic gas. Quantitative relationship between δ D(CH4) and δ D(H2O) indicates that the methane mainly generated by carbon dioxide is biogenic methane. Hydrogen and oxygen of water sample falls near the meteoric water line, indicating they are all from precipitation, so it meets the condition of water supply for generation of biogenic methane. Therefore, integrating the above three aspects of qualitative and quantitative analysis and the history of tectono-thermal, that the extant methane is secondary microbial origin in Luling Coal Mine of Huaibei coalfield is concluded. [ABSTRACT FROM AUTHOR]

Abstract: Since the early 1980s, fifteen outbursts have occurred in the Huaibei Coalfield of China. These outbursts were reported to be associated with sills. To study the effect of sill intrusions on coal seam and their relationship to methane outbursts, eleven samples from the No. 10 coal seam were taken from the Wolonghu Mine at various distances from a diorite sill. Comparisons were made between unaltered and heat-affected coals using petrographic and chemical data, micropore characteristics, adsorption properties of coal, and gas outburst indexes from field. Approaching the intrusion, vitrinite reflectance levels increased from 2.74% to 5.03%, and the thermal aureole of the sill ~60m (from the sill boundary to sample 9). Three zones along this gradient were identified as corresponding to (1) thermal evolution zone No. 1 (0–5m from sill), (2) thermal evolution zone No. 2 (5–60m from sill), and (3) unaltered zone. The methane adsorption capacity of coal samples in the thermal evolution zone No. 2 was generally higher than in the two other zones, and the unaltered zone higher than the thermal evolution zone No. 1. It is concluded that the contact-metamorphism decreased the adsorption capacity of coal and the thermal evolution of sill increased it. The trap effect of sill, combined with the mudstone and siltstone roof and floor of the No. 10 coal seam, provided a seal for the formation of a gas pocket. Abnormally high formation pressures at the No. 10 coal seam led to two outbursts. [Copyright &y& Elsevier]

The geothermal history and the tectonic subsidence history of the Huaibei-Huainan coalfields were reconstructed by using the vitrinite reflectance data, and their correlative restriction on coalbed gas generation of Huaibei-Huainan coalfields and Qinshui coal basin was discussed. The burial, thermal, and maturity histories of are similar between Huaibei coalfield and Huainan coalfield, obviously different from those of Qinshui coal basin. Based on the tectono-thermal evolution characters of Huaibei-Huainan coalfields and Qinshui basin, the process of coalbed gas generation can be divided into three stages: (1) During Early Mesozoic, both in Huaibei-Huainan and Qinshui, the buried depth of Permian coal seams increased rapidly, which resulted in strong metamorphism and high burial temperature of coal seams. At this stage, the coal rank was mainly fat coal, and locally reached coking coal. These created an environment favoring the generation of thermogenic gas. (2) From Late Jurassic to Cretaceous, in the areas of Huaibei-Huainan, the strata suffered from erosion and the crust became thinning, and the Permian coal-bearing strata were uplifted to surface. At this stage, the thermogenic gas mostly escaped. Conversely, in Qinshui basin, the cover strata of coal seams kept intact during this stage, and the thermogenic gas were mostly preserved. Furthermore, with the interaction of magmatism, the burial temperature of coal seams reached higher peak value, and it was suitable for the secondary generation of thermogenic gas. (3) From Paleogene onward, in area of Huainan-Huaibei, the maturity of coal and burial temperature were propitious to the generation of secondary biogenic gases. However, in Qinshui basin, the maturity of coal went against genesis of second biogenic gas or thermogenic gas. By comparison, Huaibei-Huainan coalfields are dominated by thermogenic gas with a significant biogenic gas and hydrodynamic overprint, whereas Qinshui basin is dominated mainly by thermogenic gas. [ABSTRACT FROM AUTHOR]

Abstract: Zircon fission-track (ZFT) analysis was performed on 12 samples, which were collected at the depths between 300 m and 1133 m in different structural units of the Huaibei coalfield in eastern China. The ZFT dating and decomposition results indicate the age populations can be divided into three periods, which are 213 ± 21 Ma–230 ± 21 Ma, 252 ± 32 Ma–304 ± 21 Ma and 378 ± 39 Ma–933 ± 16 Ma. These periods are less than, close to and greater than the depositional age, respectively. The continental collision between the north and south China plates impacted on its thermal and structural evolution strongly, but it is possible the burial and magmatism merely resulted in partial annealing on ZFT. Obvious differences of structural and thermal evolution exist in both the EW and NS directions. And the differences in the EW direction were mainly resulted from the tectonic movements in late Indosinian and Yanshanian, but the NS direction differences were on account of the magmatic activity in Yanshanian. [ABSTRACT FROM AUTHOR]

Based on an analysis of the present geo-temperature field and the thermal conductivity ( K) of 62 samples from the central-south area of the Huaibei coalfield in eastern China, we calculated the heat flow and plotted its distribution map. The results show that the average heat flow in the research area is about 60 mW/m. It is different from other major energy basins in the North China Plate, but has close relationship with the regional geology and the deep geological setting. The heat flow is comparatively higher in the southeastern, central, and northwestern areas than in the northeastern and southwestern areas. The geo-temperature distribution map of the bottom interface of the Permian coal measure was drawn by calculating its embedding depth and geo-temperature gradients. Finally, the present gas generation condition of the Permian coal measure is discussed by associating with the temperature condition, the vitrinite reflectance ( R ), the metamorphism of coal and tectonic-burial evolution. The study indicates all present characters of the Permian coal measure, such as lower present temperature, higher R value, middle-high rank coals, and uplift and extension events after the coal measure sediment, are favorable for the generation of secondary biogenic gas, but not thermogenic gas or primary biogenic gas. [ABSTRACT FROM AUTHOR]

Abstract: The Huaibei Coalfield, Anhui Province, China, is one of the largest coalfields in China. The coals of Permian age are used mainly for power generation. Coal compositions and 47 trace elements of the No. 10 Coal of the Shanxi Formation, the No. 7, 5, and 4 Coals of the Lower Shihezi Formation, and the No. 3 Coal of the Upper Shihezi Formation from the Huaibei Coalfield were studied. The results indicate that the Huaibei coals have low ash, moisture, and sulfur contents, but high volatile matter and calorific value. The ash yield increases stratigraphically upwards, but the volatile matter and total sulfur contents show a slight decrease from the lower to upper seams. Magmatic intrusion into the No. 5 Coal resulted in high ash, volatile matter, and calorific value, but low moisture value in the coal. Among the studied 47 trace elements, Ba, Co, Cr, Cu, Hg, Mo, Ni, Pb, Sb, Th, U, V, and Zn are of environmental concerns. Four elements Hg, Mo, Zn, and Sb are clearly enriched in the coals as compared with the upper continental crust. [Copyright &y& Elsevier]

Abstract: Sequential extraction tests using a Flow Injection Mercury System (FIMS) were done on 34 samples collected from the number 3, 4, 5, 7, and 10 coal seams in the Huaibei Coalfield; average total mercury (Hg) concentrations for the seams were 0.13, 0.18, 0.54, 0.34, and 0.19 mg/kg respectively. The average value for all of the coal samples was 0.26 mg/kg, which is higher than most Chinese and U.S. coals. Six modes of Hg occurrence were recognized, including: water-leachable, ion-exchangeable, organic-bound, carbonate-bound, silicate-bound, and sulfide-bound Hg. With rare exception, little Hg was found in water-soluble, ion-exchangeable or carbonate-bound forms. Sulfide-bound Hg and organic-bound Hg dominated seams 3, 4, and 10, whereas silicate-bound Hg dominated seams 5 and 7. The relatively high Hg values observed in seams 5 and 7, especially in parting samples, are attributed to Hg enrichment by magmatic intrusions. [Copyright &y& Elsevier]

Abstract: The rare earth elements (REEs) in coals are important because of: (a) REE patterns can be an indicator of the nature of source rocks of the mineral matter as well as sedimentary environments; (b) REEs abundance in coal may have industrial-significance. In this study, a total of thirty-four samples of Permian coal, partings, roof, and floor were collected from the Huaibei Coalfield, Anhui Province, China. Abundances of rare earth elements (REEs) and other elements in the samples were determined by inductively coupled-plasma mass spectrometry (ICP-MS) and inductively coupled-plasma atomic emission spectrometry (ICP-AES). The results show that the REEs are enriched in coals in the Huaibei Coalfield as compared with Chinese and U.S. coals and the world coal average. Coals in the Lower Shihezi Formation (No. 7, 5, and 4 Coals) and Upper Shihezi Formation (No. 3) have higher REE abundances than the coals in Shanxi Formation (No. 10). Magmatic intrusion resulted in high enrichment of REEs concentrations in No. 5 and 7 Coals. The REE abundances are positively correlated with the ash content. The mineral matter in these coals is mainly made up of clay minerals and carbonates. The REEs are positively correlated with lithophile elements including Si, Al, Ti, Fe, and Na, which are mainly distributed in clay minerals, indicating that REEs are contained mainly in clay minerals. The REE abundances in coals normalized by the ash are higher than that in partings. REEs abundances of coals cannot be accounted for by the REE content in the mineral matter, and some REEs associated with organic matter in coals. [Copyright &y& Elsevier]

The composition characteristics of altered coals in the Huaibei Coalfield, China, was investigated through a comparative analysis between altered and unaffected coals from the Wolonghu, Taoyuan and Renlou coal mines. Results indicated that the altered coals in Wolonghu coal mine are mostly anthracite coals, with a maximum vitrinite reflectance of 1.6–3.9% (average of 2.9%). Coals from Wolonghu coal mine were mainly consisted of vitrinite (66.2–97.0%), followed by inertinite (2.0–4.0%) and exinite (0.4–6.9%). Differences in volatile matter content were observed between the altered coals in Wolonghu coal mine and unaffected coals from neighboring coal mines, implying that the chemical composition and maturity of coals were changed after magmatic alteration. In addition, differences in hydrogen element were noted among the coals from Wolonghu, Renlou and Taoyuan coal mines, and the phenomenon of "deficient in hydrogen element" was observed in Wolonghu coals. The aliphatic hydrocarbon structure parameters suggested that the aliphatic chain lengths of Wolonghu coals are shorter than those of coal samples from the Renlou and Taoyuan coal mines. In addition, maturity is positively correlated with hydrogen enrichment degree, but negatively related with aliphatic hydrocarbon structure. Coals from Renlou and Taoyuan coal mines showed great weight loss with various heating rates at temperatures of 0–1000 °C, whereas those from Wolonghu coal mine had less weight loss. [ABSTRACT FROM AUTHOR]

The Taiyuan formation limestone water in the Huaibei coalfield is not only the water source for coal mining, but also the water source for industry and agriculture in mining areas. Its hydrogeochemical characteristics and water quality are generally concerning. In this paper, conventional ion tests were carried out on the Taiyuan formation limestone water of 16 coal mines in the Sunan and Linhuan mining areas of the Huaibei coalfield. Piper trigram, Gibbs diagram and an ion scale coefficient map were used to analyze the hydrogeochemical characteristics of the Taiyuan formation limestone water. The water quality was evaluated in a fuzzy comprehensive manner. The results show that the main cation and anion contents in the Taiyuan formation limestone water were Na + > Mg 2+ > Ca 2+ > K + , SO 4 2 - > HCO 3 - > Cl - . There were differences in the hydrogeochemical types of the Taiyuan formation limestone water in the two mining areas; HCO 3 -Na type water was dominant in the Sunan mining area and SO 4 ·Cl-Na type water was dominant in the Linhuan mining area. The chemical composition of the Taiyuan formation limestone water is mainly affected by the weathering of the rock and is related to the dissolution of the evaporated salt and the weathering of the silicate. The fuzzy comprehensive evaluation results show that the V-type water accounts for a large proportion of the Taiyuan formation limestone water in the study area and the water quality is poor. This study provides a basis for the development and utilization of the Taiyuan formation limestone water and water environmental protection in the future.