First insights into mineralogy, geochemistry, and isotopic signatures of the Upper Triassic high-sulfur coals from the Thai Nguyen Coal field, NE Vietnam

This paper represents the first integrated research on the mineralogical, geochemical and stable isotope characteristics of the Upper Triassic high-sulfur coals from the Khanh Hoa open-pit mine, Thai Nguyen Coalfield, NE Vietnam. Formed in a marine-influenced carbonate succession, the Khanh Hoa coal is characterized by medium ash yield, low volatile matter yield, and high sulfur content. Minerals in the Khanh Hoa coal are predominantly composed of authigenic calcite in the upper portion; and pyrite, quartz, with minor amounts of tobelite ([(NH4), K] (Si, Al)4Al2O10(OH)2), gypsum in the middle and lower portions. The high-sulfur Khanh Hoa coal is enriched in an As-Mo-Sb-U-Cs-P assemblage, which presents both an organic and inorganic mode of occurrence, and is largely ascribed to hydrothermal fluids. The 613C values of the Khanh Hoa coal range from - 24.77%0 to -22.80%0 (avg. -23.33%0), reflecting a change in sedimentation pattern (from transgressive to high stand system upwards). The 615N values of the Khanh Hoa coal range from 2.41%0 to 3.73%0 (avg. 3.30%0), possibly resulted from influenced by seawater influence and a redox environment. The mineralogical, geochemical and isotopic characteristics reflected that the high-sulfur Khanh Hoa coal was formed/preserved in marine-influenced anoxic environment, with low detrital input, and strong activities of multi-stage hydrothermal solutions.

Automated summary

This study presents the first integrated research on the mineralogical, geochemical, and stable isotope characteristics of high-sulfur coals from the Khanh Hoa open-pit mine in the Thai Nguyen Coalfield of NE Vietnam. The coal formation is attributed to marine influences and is characterized by medium ash yield, low volatile matter yield, and high sulfur content. The mineralogical, geochemical, and isotopic characteristics suggest that the high-sulfur Khanh Hoa coal was formed/preserved in a marine-influenced anoxic environment.