Abstract
Shaanxi is among the provinces with abundant coal resources in North China. These enormous coal resources (approx. 4143 Gt) are widely distributed in the Ordos Basin and its marginal fold belts. The main coal-bearing strata consist of the late Carboniferous Taiyuan Formation, the early Permain Shanxi Formation, the late Triassic Wayaobao Formation, and the middle Jurassic Yan’an Formation, which were respectively deposited in coastal plains and a lagoon environment, a continental environment, an inland open lake and a confined lake environment. The Permo-Carboniferous coals are low volatile bituminous and characterized by relatively high vitrinite content, which decreases from south to north, and from the lower coal seams upwards. By contrast, the late Triassic and middle Jurassic coals are highly volatile bituminous, but are respectively characterized by relatively high vitrinite and high inertinite content. Minerals in the Permo-Carboniferous coals, the late Triassic coals, and the middle Jurassic coals, are respectively dominated by kaolinite and calcite, quartz and kaolinite, and quartz and calcite. Furthermore, contemporary coals deposited in different coal fields or even different mines of the same coal field present different mineral characteristics. The Permain Shanxi Formation coals from the Shanbei C-P coalfield in the north of Shaanxi Province are characterized by higher kaolinite and lower carbonate contents compared to those from the Weibei C-P coalfield in the south of Shaanxi Province. The distinctive mineralogical characteristics of coals formed in different coalfields and different geological ages were ascribed to integrated influences of different terrigenous detrital input from sediment provenance, sedimentary settings (e.g., subsidence rate, sea transgression, and regression process), and hydrothermal activities.
Highlights
As an important part of the Ordos Basin, Shaanxi Province has become one of the most significant bases for coal resource exploitation in China, with estimated coal reserves of approx. 4143 Gt [1]
After formation of the late Paleozoic coal seam, the subsidence rate was low in the northern area where the coalification is low, whereas the subsidence rate was high in the southern area where the coalification is high [40]
Vitrinite is the dominant maceral in the Permo-Carboniferous coals, with an increasing tendency from the north to the south, probably due to the slow subsidence in the northern area and the marine transgression from the southwest towards the northeast of the Permo-Carboniferous epicontinental basin in North China
Summary
As an important part of the Ordos Basin, Shaanxi Province has become one of the most significant bases for coal resource exploitation in China, with estimated coal reserves of approx. 4143 Gt [1]. As an important part of the Ordos Basin, Shaanxi Province has become one of the most significant bases for coal resource exploitation in China, with estimated coal reserves of approx. (a) Location of Ordos basin; (b) distribution of the main coal fields and locations of sampling sites in Shaanxi Provence. The composition, abundance, distribution, and modes of occurrence of minerals in coals may provide significant geologic information on coal depositional conditions, coalbearing sequence formation, regional geological history, and associated diagenetic and epigenetic processes affecting coal formation [8,9,10,11,12,13,14,15,16,17,18,19]. Typical mineral phases are important carriers of critical elements (e.g., Ga, Li, Zr, Hf, Nb, Ta, rare earth elements and Y, etc.) and toxic elements (e.g., S, As, F, Hg) in coal [13,21,25,26,27,28]
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