Maceral and Organic Geochemical Characteristics of the No. 6 Coal Seam from the Haerwusu Surface Mine, Inner Mongolia, China

Haerwusu Surface Mine of the Jungar Coalfield is a large coal mine. Its coal formation environments have not been reported in detail. In order to reconstruct the paleoenvironment of the peat formation, nine samples were collected, and were analyzed using microscope, column chromatography, gas chromatography (GC), and gas chromatography–mass spectrometry (GC–MS). According to the results of the microscopic analysis, the average random vitrinite reflectance (Rr) is 0.73%, indicating a low rank bituminous coal. Vitrinite group is the predominant macerals with an average content of 54.54%, followed by inertinite group with an average of 35.99%. The higher inertinite contents indicate widespread wildfire events during the peat formation. The distribution pattern of n-alkanes, the cross plot between Pr/n-C17 and Ph/n-C18, the lower saturated/aromatic hydrocarbon ratios (0.22–0.68) and the presence of cadalene, retene, simonellite indicates that the organic matter is predominantly terrestrial higher plants with a small amount of aquatic organisms. The ternary diagram of Pr/Ph, Pr/n-C17 and Ph/n-C18 and the relative abundance of fluorene, dibenzofuran and dibenzothiophene indicate a continental–oceanic alternative facies. The higher contents of combustion-derived PAHs are also indicative of widespread wildfire events during peat formation.