Geological controls on the quality of coals from the West Shandong mining district, Eastern China

The basic coal quality parameters, coal petrology, mineralogy and geochemis try were investigated for coal seams 2, 3 and 4 (Permian Shanxi Formation) and 11, 12, 13 and 15 (Carboniferous Taiyuan Formation) of the Xinwen and F eicheng coal fields in the West Shandong mining district, East China. Rank parameters indicate a high volatile C to B bituminous rank for the Shandong coal. Coal from the Zhaizhen and Cha Zhuang mines is characterised by high vitrinite and low-middle inertinite and liptinite contents. Inertinite con tents show an increase towards the top of the stratigraphic sequence from c oal seams 15, 13 and 11 to coal seams 4 and 2. This trend may be related to a stratigraphic trend characterised by the evolution of relatively more re ducing conditions of the synsedimentary coal forming environment in the ear ly Taiyuan coals (marine-influenced lower delta plain) to more oxidising pa leoenvironments of the Upper Shanxi coal seams (upper delta plain). Major m ineral phases present in the Shandong coal are quartz, kaolinite, pyrite an d calcite. Traces of other primary minerals (dolomite, ankerite, illite, op al, feldspars and marcasite) and weathering products (gypsum, melanterite a nd hematite) can be found in several coal seams. The Lower Permian coal sea ms (two to four) have a lower mineral content (8-14% ash db) than the Upper Carboniferous coal seams (15-37% ash db), owing to the lower proportions o f quartz and sulphide mineral. The occurrence and distribution of the diffe rent minerals in the Shandong coal indicates a paragenetic sequence charact erised by an early syngenetic stage (detrital minerals, framboidal, euhedra l and massive cell-filling pyrite, ankerite, neomorphic quartz and kaolinit e), middle and late syngenetic stages (radial and fibrous marcasite aggrega tes, massive pyrite) and an epigenetic stage (carbonates and sulphides as c leat filling). A clear differentiation exists between the Shanxi and the Ta iyuan coal seams, based on the higher sulphide contents of the Taiyuan coal (3.3 to 6.2%, S db) compared with the Shanxi coal (0.4 to 0.8% S db). This differentiation is related to marine influence on the depositional environ ment of coal seams 11 to 15, which has been reported by earlier studies. Ve rtical variations of the abundance of major and trace elements are discusse d on the basis of this differentiation. An epigenetic external enrichment o f Ge, Mo and U at the top of most of the coal seams is observed, and major and trace element affinities are deduced for the West Shandong coal. (C) 19 99 Elsevier Science B.V. All rights reserved.