Composition and origin of high-alumina coal in Jungar coalfield

Based on the analysis of tectonic background and coal-accumulating environment of Jungar coalfield, the coal petrological characteristics, inorganic mineral composition, distribution and occurrence regularity of coal and gangue in No.6 coal of the Junger coalfield are studied, and the genesis is determined byutilizing the research methods of coal petrology, mineralogy and geochemistry.The study shows that the average contents of the inertinite, vitrinite and exinite in the maceral of No.6 coal in the study area are 59 %, 28 % and 13 %, respectively.Compared with the Late Paleozoic coals in other areas of North China, the content of the inertinite is high, which reflects an adequate supply of surface water during the formation of No.6 coal seam.The main inorganic minerals in coal and gangue are kaolinite and boehmite, associated with quartz, calcite, siderite, pyrite, anhydrite, anatase and svanbergite.The vertical changes of the mineral composition and main chemical elements of No.6 coal indicate that the middle of the coal seam is rich in boehmite, while the upper and lower parts are rich in kaolinite.There are three origins of kaolinite: colloidal precipitation crystallization, terrestrial transport sedimentation and volcanic ash alteration.And there are two origins of boehmite: alumina colloidal precipitation crystallization and desilication alteration of kaolinite.