Search

• NME are involved in the mineral transformation with the ashing temperature increasing. • The Ca for calcite formation in ash (500 °C) was sourced from the non-mineral Ca in coal. • The increase of ashing temperature causes the change of mineral crystallinity in coal. • NME are altered into crystalline minerals during the ashing process affected by temperature. Investigation of mode of occurrence and chemical transformation of non-mineral elements (NME) is of benefit to solve sintering and slagging during utilization of coal. To better understand the mineral phase transition and thermal behavior of NME during ashing process, lignite in Hailar basin and its ash obtained at different ashing temperatures are analyzed by the sequential selective leaching (SSL), X-ray fluorescence (XRF), X-ray diffraction (XRD) and field emission-scanning electron microscopy with energy-dispersive X-ray spectrometry (SEM-EDS). The results show that the phases of minerals in coals changed and the NME are involved in the mineral phase transformation with the increase of ashing temperature. In particular, non-mineral calcium presented as sulfate minerals (gypsum, bassanite or anhydrite) in the ashes of 120 °C, 350 °C and 815 °C, while changed into calcite in the 500 °C ashes. It may be due to the carbon dioxide generated by the oxidation of organic matter reacted with the non-mineral calcium that gradually released in coal under the high temperature (≥500 °C) and pressure. The transformation mechanism of non-mineral calcium implies an interaction between organic matter and mineral matter in the ashing process. [ABSTRACT FROM AUTHOR]

The coal-hosted Ge deposit (Early Cretaceous) at Wulantuga, Inner Mongolia, northern China, is one of the largest Ge deposits in the world. Although the origin, modes of occurrence, and spatial distribution of Ge in this deposit have been investigated by several studies, the provenance and pathways of Ge from the source to the deposit are largely unknown. In this study, we investigated the 87Sr/86Sr values in the high-Ge coal of the Wulantuga deposit and the stratigraphically-equivalent low-Ge coal of the No. 1 Pit, both from the Shengli Coalfield, Inner Mongolia, northern China. In addition to an organic association, Sr and Ca in the high-Ge and low-Ge coals also occur in gypsum. The water-soluble Sr (i.e., in gypsum) in the high-Ge coal (Ge concentrations: 45–1170 ppm, 273 ppm on average, whole coal basis) has 87Sr/86Sr values in the range of 0.710411 to 0.710633 (with an average of 0.710478). In contrast, the low-Ge coal (Ge concentrations: up to 4.23 ppm, 0.45 ppm on average, whole coal basis) has lower 87Sr/86Sr values in two sub-groups, a low range of 0.709896–0.71005 (with an average of 0.709736) and a high range of 0.710173–0.710547 (with an average of 0.710329 and dominantly in the range of 0.710173–0.710406). The higher 87Sr/86Sr values in the high-Ge coals indicate that the highly-elevated concentration of Ge is associated with a local source of radiogenic Sr. The enrichment of Ge in the coal is due to several consecutive processes. Surface waters penetrated deeply into granite and dissolved at least partially more soluble phases of the granite. The Ge-rich solution flowed over ground or underground into the Shengli Coalfield and Ge precipitated in the peat, the precursor of the coal investigated in the coalfield. The 87Sr/86Sr values of the water-soluble fraction, the elemental compositions of high-Ge and low-Ge coals, and the geomorphological setting of the coalfield point to the Hercynian granodiorite intrusion on the nearby SE margin of the Shengli Coalfield as the primary source of Ge in the Wulantuga coal-hosted Ge deposit. In addition to serving as an indicator of the mode of formation of the coal-hosted Ge deposit, the 87Sr/86Sr values and their spatial distribution can provide an indication for the hydrological pathways of the mineralising fluid. • The Sr in gypsum in the high-Ge coals has 87Sr/86Sr values from 0.710411 to 0.710633. • The Sr in gypsum in the low-Ge coal has lower 87Sr/86Sr values, 0.709896–0.710547. • The higher 87Sr/86Sr values in the high-Ge coals indicate a grantic Ge source. [ABSTRACT FROM AUTHOR]

Igneous intrusions can bring hydrothermal fluids, metals, and ligands to the surrounding host sequences, changing their physical, textural and chemical features to some extent depending on the degree of thermal exposure. However, regarding hydrothermally-altered coals, previous studies have predominately focused on variations in coal quality, chemistry and mineralogy, despite the growing research on stable and radioactive isotopes within coal-bearing sequences. The Pennsylvanian coal from the Daqingshan Coalfield, Inner Mongolia, China, was thermally affected by a granitic intrusion in the eastern part of the coalfield during the Yanshanian Orogeny, between the Late Jurassic and Early Cretaceous. The investigated Hailiushu, Datanhao, and Adaohai mines in present study are distributed in Daqingshan Coalfield from west to east. The Adaohai Mine is located to the southwest of the intrusion point, at a distance of approximately 50 km. The Hailiushu and Adaohai mines are about10 km apart, and the Datanhao Mine is located between them. With decreasing distance to the intrusion, there is an increase in vitrinite reflectance values (from 0.84% through 1.17% to 1.58%) and a decrease in the volatile matter content (from 44.57% through 31.31% to 19.60%) in the studied three coal mines. The present study revealed that the westernmost Hailiushu coals have the most negative δ 13C org values (from −24.8 ‰ to −23.5 ‰; −24.3 ‰ on average). In contrast, with the distance from the intrusion decreases, the δ 13C org values of coals from the Datanhao mine range from −24.8 ‰ to −23.5 ‰ (−24.2 ‰ on average). The δ 13C org values of the easternmost Adaohai coals range from −23.8 ‰ to −22.8 ‰, (−23.3 ‰ on average), about 1 ‰ less negative than those in the Datanhao and Hailiushu coals. It is not just the maceral composition that causes the difference in organic carbon isotopes, but the loss of 12C-enriched volatiles due to the thermal effects associated with the igneous intrusion. This hypothesis was further supported by Rock-Eval analysis on the organic matter: the average T max of the Hailiushu, Datanhao, and Adaohai coals increases but generation of hydrocarbons and pyrolysable carbon decrease as approaching the intrusion. Moreover, fracture/cleat-filling carbonates are more abundant in the Adaohai coals than in the Datanhao and Hailiushu coals. The δ 13C PDB (from −14.2 ‰ to 1.7 ‰) and δ 18O PDB (from −16.9 ‰ to −7.0 ‰) of these vein carbonates all indicate a hydrothermal origin. Hydrothermal fluids derived from igneous intrusions is also responsible for the elevated 87Sr/86Sr ratios (0.711392–0.717643) in the carbonate mineral in the thermally altered coals. • δ 13C org values are less negative in coals closer to the igneous intrusion. • The closer the coal to the intrusion, the less pyrolyzable the organic matter. • C O isotopes show that the coal seam was intensely hydrothermally-altered. • High 87Sr/86Sr values for carbonates indicate an igneous rock origin for the Sr. [ABSTRACT FROM AUTHOR]

In this contribution, we report the palynology, organic petrography and carbon isotopes for the #16 Seam in the Lower Cretaceous Yimin Formation of the Hailar Basin, Inner Mongolia, China. Eighteen palynological samples were collected from the coal seam as well as from intraseam partings and the immediate roof. Microfloras comprise a diverse assemblage of ferns, conifers, horsetails, lycopsids, bryophytes, ginkgoes and cycads. Conifer pollen is common, especially representative of Pinaceae (Pinuspollenites) as well as Cheirolepidiaceae (Classopollis) and Araucariaceae (Araucariacites, Chasmatosporite s); however, this material is interpreted as mostly derived from an upland source rather than from the mire-forming vegetation. An overrepresentation of conifer pollen may explain the relatively poor abundance and diversity of ginkgo and cycad pollen, compared to what is found in the macrofossil record. The palynological assemblage found in Seam #16 indicates a Barremian to Aptian age. Maceral composition, ash yields, and δ13C org signature of the coal suggest peat accumulation was controlled by a rising water table from flooding of the mire, coupled with significant ground (peat) fires and/or surface wildfires. These conditions resulted in high levels of detrital mineral matter and charcoal input, the latter represented by inertodetrinite in the coals. The top of the coal seam is characterised by a higher ash yield, lower δ13C org values and increased sphagnacean spores, which suggest the gradual drowning of the palaeomire. Although angiosperms were present in the Hailar Basin during the time that Seam #16 was accumulating, they are absent from the pollen found in this study. This may indicate that they were not yet adapted to the extreme conditions of the mire (e.g., acidity, anoxia), and unable to compete with the established mire vegetation. • Abundant fossil charcoal in the Seam #16 shows fire as an important part of palaeomire ecology. • Ash yields and δ13C org values indicate that flooding terminated the palaeomire. • Some pollen was likely derived from upland conifer forests and transported into the mire. • The absence of angiosperms reflects the harsh, palaeomire conditions. [ABSTRACT FROM AUTHOR]