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Mineral matter, including minerals and non-mineral elements, in coal is of great significance for geological evolution, high-value coal utilization, and environment protection. The minerals and elemental geochemistry of Late Permian coals from the M8 coal seam, Shihao mine, Songzao coalfield in Chongqing, were analyzed to evaluate the sediment source, sedimentary environment, hydrothermal fluids, and utilization prospects of critical metals. The average total sulfur (4.21%) was high in coals, which mainly exists in the forms of pyritic sulfur. Kaolinite, pyrite, calcite, quartz, illite and illite/smectite (I/S) mixed layers, and anatase predominated in coals, with trace amounts of chlorite, ankerite, and siderite. Epigenetic cell- and fracture-filling pyrite, veined calcite, and ankerite were related to hydrothermal fluids and/or pore water after the diagenesis stage. Compared to the world's hard coals, As and Cd are enriched in the Shihao M8 coals, and Li, Cr, Co, Zr, Mo, Pb, and Tb are slightly enriched. These high contents of sulfophile elements may be related to seawater intrusion. The terrigenous clastics of the Shihao M8 coals originated from the felsic–intermediate rocks atop the Emeishan Large Igneous Provinces (ELIP) (Kangdian Upland), while the roof and floor samples were derived from Emeishan high-Ti basalt. Through the combination of sulfur contents and indicator parameters of Fe2O3 + CaO + MgO/SiO2 + Al2O3, Sr/Ba and Y/Ho, the depositional environment of peat swamp was found to be influenced by seawater. Although the critical elements in coal or coal ash did not reach the cut-off grade for beneficial recovery, the concentration of Li and Zr were high enough in coal ash. [ABSTRACT FROM AUTHOR]

The indicative significance of organic matter in fossil fuels, particularly polycyclic aromatic compounds (PACs), is a current research hotspot. Petrology, minerals, and organic matter in Late Permian coals from the Moxinpo (MXP) mine located in Chongqing, southwestern China, were analyzed to evaluate the coal rank, coal-forming material source and thermal maturity of organic matter, and sedimentary environment of the peat swamp. Vitrinite and inertinite were dominated by collotelinite, collodetrinite, inertodetrinite, fusinite, and semifusinite. Owing to the high maturity of the coals, liptinite was not observed under the microscope. Clay (kaolinite) and pyrite were the primary minerals in the MXP coals, followed by calcite, quartz, trace amounts of anatase, gypsum, xenotime, and bastnaesite. The minerals in the MXP coals were authigenic primarily in the epigenetic stage. The extract yield of organic matter in coals was low (0.30%), and the saturated and aromatic fractions accounted for approximately 60% of the extractable organic matter. Low ratios of saturated to aromatic compounds reflected the terrestrial higher plants input and high maturity level of the coals. The extracted yield in the host rock samples was much lower than in the coals, while the proportion of saturated hydrocarbons was relatively high. The marine-continental transitional sedimentary environment, distribution of n -alkanes, ∑ C 21 − /∑ C 22 + , and pristane (Pr)/ n -C 17 vs. phytane (Ph)/ n -C 18 indicated that the organic matter originated from the input of terrestrial higher plants and was accompanied by the contribution of marine lower phytoplankton and aquatic organisms. The coal-forming environment of the coal seam was reductive according to the Pr/Ph and sulfur-containing compounds of dibenzothiophenes and benzonaphthothiophenes. The thermodynamic stability controls the presence of polycyclic aromatic hydrocarbons in extractable organic matter. Isomeric compounds with high stability had higher concentrations, such as 2-methylnaphthalene, 2,6 + 2,7-DMN, 4- methylbiphenyl, and 2- methylphenanthrene. [Display omitted] • Macerals were primarily vitrinite and inertinite, while liptinite was absent. • Minerals were dominated by kaolinite, pyrite, calcite, and quartz in the MXP coal. • Organic matter in coals was dominated by the input of terrestrial higher plants. • Coal-forming environment was a reductive and marine-continental transitional environment. • Concentration of isomer compounds was controlled by thermodynamic stability. [ABSTRACT FROM AUTHOR]

Abstract: Eighteen semianthracite samples of the No. 9 coal seam in the Gequan Mine, Xingtai Coalfield, China were investigated, primarily by microscope and organic geochemical methods. The petrological results showed that the vitrinite random reflectance (R o) is 2.36% and the maceral group was dominated by vitrinite. The gas chromatograms (GC) of the saturates display a monomodal or bimodal outline of n-alkane peaks, generally from n-C10 to n-C31, resulting in two ranges of ∑(C1–C21)/∑(C22–C34) values. Most of the coal samples exhibit consistently similar parameters, such as pristane/n-C17 and phytane/n-C18 ratios, whereas samples with different Pr/Ph values may have been the result of varied redox depositional conditions. The distributions of the polycyclic aromatic compounds (PACs) identified in the aromatics were generally similar due to the similar high rank of the coal samples. Under the high thermal maturity, the PACs with greater thermodynamic stabilities (including 2-methylnaphthalene, 2,6- and 2,7-dimethylnaphthalenes, 2- and 3-methylphenanthrenes, and 2,6- and 2,7-dimethylphenanthrenes) were present at higher concentrations than those of less thermodynamically stable PACs. A portion of these PACs most likely originated from a secondary generation. The generally higher contents of dibenzothiophenes and benzonaphthothiophenes were most likely generated under the control of hydrothermal fluids. However, the coal-forming environment may also have played a role for higher contents of dibenzothiophenes and benzonaphthothiophenes. [Copyright &y& Elsevier]

Today wildfire is an important disturbance in many continental ecosystems, and it is assumed that with ongoing climate changes the frequencies and impacts of wildfires will increase in many regions. One way to obtain information about the potential long term influences of wildfires on ecosystems and the climate system itself is to study palaeo-wildfires. A total of 140 Jurassic samples, including 122 coal samples and 18 rock samples from roof and floor of coal seams, were collected from 4 coalfields in Northwestern China. The samples were analyzed by macropetrography, microscopy, scanning electron microscopy, gas chromatography, and gas chromatography–mass spectrometry to study the evidences of wildfires and their impact on the paleoclimate. High contents of pyrogenic inertinites (charcoal), natural char and natural coke particles observed in the samples which indicate that widespread wildfire events occurred in the early Middle Jurassic in all over Northwestern China. Additionally, high-molecular-weight polycyclic aromatic hydrocarbons were detected in the coal samples. These aromatic compounds were formed under high temperature and provide further evidence of wildfires. According to a carbon emission model for modern forest fires, the total carbon and gas emissions from wildfires in peat swamps of the Middle Jurassic in Northwest China were calculated by the data from 21,575 coal samples of number of 1567 drill core samples. The total carbon released from peat-swamp forest wildfires was at least 1207 Gt, corresponding to emissions of CO 2 , CO and CH 4 of 1926 Gt, 163 Gt, and 8.8 Gt, respectively. The huge amount of CO 2 released by forest fires in the peat swamp systems of the Middle Jurassic in Northwestern China alone was equivalent to 64.20% of the total CO 2 in the atmosphere at present (3000Gt). The large amounts of greenhouse gases released by wildfires must have led to long-term changes in the atmospheric composition and have caused global warming, which could have the reason of affected the paleoclimate. • High contents of charcoal indicate that wildfire events occurred in the early Middle Jurassic. • The main types of wildfires were surface fires and ground fires, with less crown fires. • The oxygen levels could have reached from 27% to 29% in the Middle Jurassic. • The greenhouse gases released by wildfires in the Middle Jurassic in Northwest China reached at least 2097.6 Gt • Greenhouse gases released by wildfires might have affected the paleoclimate and paleoecosystems. [ABSTRACT FROM AUTHOR]

The Dongying depression is an important oil-producing area in northeastern China, where the Paleogene Shahejie Formation is the main oil-bearing feature. Although petroleum migration and accumulation in the Dongying depression have been extensively studied, the charging history is still unclear. This paper defines the timeframe of petroleum migration on the basis of a comprehensive investigation of fluid inclusions coupled with basin modeling. According to the petrography and microthermometry of the fluid inclusions, types of fluid inclusion with low-peak-range distributions of the homogenization temperature (T h) (85–95 °C for the Niuzhuang sag and 90–105 °C for the Lijin sag) and high-peak-range T h distributions (105–120 °C for the Niuzhuang sag and 115–130 °C for the Lijin sag) were identified. By recovering the burial and thermal histories of Niuzhuang and Lijin sags with pressure–volume–temperature–composition simulation and one-dimensional basin modeling, it can be inferred that the trapping pressures of two types of hydrocarbon inclusions were higher than the corresponding paleopressure. (42.4 and 42.0 MPa, respectively), indicating rapid hydrocarbon charging resulting from abnormally high pressure. Two hydrocarbon charging events associated with the regional tectonic evolution of the Dongying depression, namely, continuous deposition and tectonics in the Paleogene Dongying Formation (Ed) and rapid deposition and tectonics in the Paleogene Minghuazhen Formation (Em), were inferred. The direction of oil charging was traced from the center to the margin in the north, and from the center to the central fault in the southeastern part of the depression in general, as indicated by the molecular maturity parameters, which roughly coincided with the abnormal pressure. • The investigation of fluid inclusions showed two oil-charging episodes in Sha 3 reservoirs. • The basin modeling suggested each reservoir was charged during the Late Paleogene and Early Neogene respectively. • The oils are charged along with the central faults and from the center to the edge of the depression. [ABSTRACT FROM AUTHOR]

This paper provides new geochemical data focusing on valuable elements in the coal, parting, and floor samples in the No. 5 coal seam of the Taiyuan Formation from the Wujiawan mine, Datong coalfield, northern China. The minerals mainly consist of kaolinite, calcite, and pyrite, as well as trace amounts of quartz and illite. The No. 5 coal is enriched in Li, Ga, high field strength elements (HFSEs), and rare earth elements and yttrium (REY) when compared with world hard coals. Of particular interest is the high average concentration of Li (67.66 μg/g), which is around seven times higher than the value for world hard coals. Lithium, Ga, and HFSEs have strong inorganic affinities, whereas REY have organic affinities. The main carrier of Li, Ga, and HFSEs is aluminosilicate minerals, while REY appear to occur with organophosphorus. These HFSEs are enriched, both in the parting and in the adjacent coal samples. This suggests that these elements are likely to leach out during the diagenetic process. The distribution patterns of REY, along with the ratio of Al2O3/TiO2 and the figure of Zr/TiO2 vs. Nb/Y are suggestive of their derivation from felsic parent material. In the northern and eastern part of the Datong coalfield, there are several regions where the Li content is higher than the mineable grade, in particular in the northern Datong coalfield where there is a mine with an Li content of 294.6 μg/g. This is significantly higher than the mineable grade. Therefore, there is a potential for financially viable recovery of Li in these coals of the Datong coalfield. [ABSTRACT FROM AUTHOR]

The Chang 6, Chang 8, and Chang 9 reservoirs of the Upper Triassic Yanchang Formation in the Zhenjing area of the Ordos Basin are characterized by low porosity, low permeability, high oil saturation, and large oil reserves, which indicate huge tight oil potential. To comprehensively investigate the hydrocarbon contributors and charging history, fluid inclusions were systemically studied coupled with basin modeling and oil geochemical analysis. According to the petrographic characteristics, two episodes of fluid inclusions occurred in each of the three reservoirs. Microthermometry analysis suggests that the hydrocarbon inclusions of the first episode in each reservoir are distributed mainly along overgrowth quartz or secondary microcracks and exhibit light yellow or light brown fluorescence; the coeval aqueous inclusions display low homogenization temperature (Th) peaks with 80–100 °C. The hydrocarbon inclusions of the second episode in each reservoir are mainly distributed in microcracks that cut across or within quartz grains and exhibit light green or bluish-green fluorescence; the coeval aqueous inclusions are characterized by high Th peaks with 110–120 °C. The different characteristics of the two episodes of the fluid inclusions imply the existence of two episodes of hydrocarbon charging events. The burial and geothermal histories of the various reservoirs were reconstructed using one-dimensional basin modeling and pressure–volume–temperature–composition (PVTX) simulation coupled with the authigenic illite K–Ar dating. The reconstruction implied the time of the two hydrocarbon charging episodes to be Early Cretaceous and Late Cretaceous. Oil-source correlation studies illustrate that the Chang 6, Chang 8, and Chang 9 crude oils all originate from the Chang 7 source rock. The migration characteristics and directions were comprehensively analyzed by using maturity parameters. This explanation of the charging history and oil migration pathway of the Upper Triassic Yanchang Formation in the Zhenjing area provides a theoretical basis for further exploration. • Each reservoir was charged during the Early and Late Cretaceous, respectively. • The crude oils in all reservoirs originated primarily from the Chang 7 source rocks. • The oils are charged along with the faults and the W-dipping monocline. [ABSTRACT FROM AUTHOR]