Modes of Occurrence and Origin of Minerals in Permian Coals from the Huainan Coalfield, Anhui, China

Minerals in coal provide useful information for not only paleo-environments of peat accumulation, but also for geological evolution during later diagenesis and/or epigenesis. This paper reports new data on coal quality and the mineralogical and geochemical compositions of 17 unaltered (by intrusion)...

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Main Authors: Yuan Li, Wenhui Huang, Bo Jiu, Qilong Sun, Qingsong Che
Format: Article
Language:English
Published: MDPI AG 2020-04-01
Series:Minerals
Subjects:
Online Access:https://www.mdpi.com/2075-163X/10/5/399
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author Yuan Li
Wenhui Huang
Bo Jiu
Qilong Sun
Qingsong Che
author_facet Yuan Li
Wenhui Huang
Bo Jiu
Qilong Sun
Qingsong Che
author_sort Yuan Li
collection DOAJ
description Minerals in coal provide useful information for not only paleo-environments of peat accumulation, but also for geological evolution during later diagenesis and/or epigenesis. This paper reports new data on coal quality and the mineralogical and geochemical compositions of 17 unaltered (by intrusion) coal samples collected from the Huainan coalfield, providing new insight into the origins and modes of occurrence of the minerals in coal and their geological evolution. The results showed that the studied coal samples were low rank bituminous coal, with low ash yield (11.92–38.31%, average 24.80%) and high volatile content (25.13–43.43%, average 37.29%). Minerals in the coal mainly included kaolinite and quartz; varying proportions of calcite, siderite, ankerite, and pyrite; and traces of chlorite, zircon, strontianite, apatite, and gorceixite. Typical modes of mineral occurrence could be used to determine the formation stage of minerals. The detrital mineral, occurring as sub-angular to rounded discrete fragments or thin layers intimately admixed with organic matter at particular horizons, was of terrigenous origin, deposited during peat accumulation. Cell infillings, as well as nodule siderites and polycrystalline aggregates of pyrite, precipitated during the syngenetic to early diagenetic stages. Cleat infillings, compressed cell infillings, and fracture infillings precipitated in the epigenetic stage. However, the stage of mineral formation of the pore infilling was difficult to determine. Combined with coal quality, mineralogy, and geochemical analysis, the sedimentary environment of Shanxi Formation was affected by seawater, and Fe-rich hydrothermal fluids filled into the No. 3 coal seam in the epigenetic stage. The sedimentary environment of the No. 8 coal seam had widespread reduction and acid conditions due to basin subsidence, and sulfate-rich hydrothermal fluids may have been formed during the peat deposition stage. In contrast, the peat accumulation environment of the Upper Shihezi Formation was oxidized with a low pH condition. Alkaline fluid then flowed into the No. 13-1 coal seam in the epigenetic stage.
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spelling doaj.art-67cc73bc8e194b5ca56e310a6a0ad3b62023-11-19T23:03:55ZengMDPI AGMinerals2075-163X2020-04-0110539910.3390/min10050399Modes of Occurrence and Origin of Minerals in Permian Coals from the Huainan Coalfield, Anhui, ChinaYuan Li0Wenhui Huang1Bo Jiu2Qilong Sun3Qingsong Che4School of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, ChinaSchool of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, ChinaSchool of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, ChinaSchool of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, ChinaSchool of Energy Resources, China University of Geosciences (Beijing), Beijing 100083, ChinaMinerals in coal provide useful information for not only paleo-environments of peat accumulation, but also for geological evolution during later diagenesis and/or epigenesis. This paper reports new data on coal quality and the mineralogical and geochemical compositions of 17 unaltered (by intrusion) coal samples collected from the Huainan coalfield, providing new insight into the origins and modes of occurrence of the minerals in coal and their geological evolution. The results showed that the studied coal samples were low rank bituminous coal, with low ash yield (11.92–38.31%, average 24.80%) and high volatile content (25.13–43.43%, average 37.29%). Minerals in the coal mainly included kaolinite and quartz; varying proportions of calcite, siderite, ankerite, and pyrite; and traces of chlorite, zircon, strontianite, apatite, and gorceixite. Typical modes of mineral occurrence could be used to determine the formation stage of minerals. The detrital mineral, occurring as sub-angular to rounded discrete fragments or thin layers intimately admixed with organic matter at particular horizons, was of terrigenous origin, deposited during peat accumulation. Cell infillings, as well as nodule siderites and polycrystalline aggregates of pyrite, precipitated during the syngenetic to early diagenetic stages. Cleat infillings, compressed cell infillings, and fracture infillings precipitated in the epigenetic stage. However, the stage of mineral formation of the pore infilling was difficult to determine. Combined with coal quality, mineralogy, and geochemical analysis, the sedimentary environment of Shanxi Formation was affected by seawater, and Fe-rich hydrothermal fluids filled into the No. 3 coal seam in the epigenetic stage. The sedimentary environment of the No. 8 coal seam had widespread reduction and acid conditions due to basin subsidence, and sulfate-rich hydrothermal fluids may have been formed during the peat deposition stage. In contrast, the peat accumulation environment of the Upper Shihezi Formation was oxidized with a low pH condition. Alkaline fluid then flowed into the No. 13-1 coal seam in the epigenetic stage.https://www.mdpi.com/2075-163X/10/5/399minerals in unaltered coalmode of mineral occurrencegeological significancePermian coalHuainan coalfield
spellingShingle Yuan Li
Wenhui Huang
Bo Jiu
Qilong Sun
Qingsong Che
Modes of Occurrence and Origin of Minerals in Permian Coals from the Huainan Coalfield, Anhui, China
Minerals
minerals in unaltered coal
mode of mineral occurrence
geological significance
Permian coal
Huainan coalfield
title Modes of Occurrence and Origin of Minerals in Permian Coals from the Huainan Coalfield, Anhui, China
title_full Modes of Occurrence and Origin of Minerals in Permian Coals from the Huainan Coalfield, Anhui, China
title_fullStr Modes of Occurrence and Origin of Minerals in Permian Coals from the Huainan Coalfield, Anhui, China
title_full_unstemmed Modes of Occurrence and Origin of Minerals in Permian Coals from the Huainan Coalfield, Anhui, China
title_short Modes of Occurrence and Origin of Minerals in Permian Coals from the Huainan Coalfield, Anhui, China
title_sort modes of occurrence and origin of minerals in permian coals from the huainan coalfield anhui china
topic minerals in unaltered coal
mode of mineral occurrence
geological significance
Permian coal
Huainan coalfield
url https://www.mdpi.com/2075-163X/10/5/399
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AT bojiu modesofoccurrenceandoriginofmineralsinpermiancoalsfromthehuainancoalfieldanhuichina
AT qilongsun modesofoccurrenceandoriginofmineralsinpermiancoalsfromthehuainancoalfieldanhuichina
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