Mineralogical and geochemical compositions of the Pennsylvanian coal in the Adaohai Mine, Daqingshan Coalfield, Inner Mongolia, China: Modes of occurrence and origin of diaspore, gorceixite, and ammonian illite

► High proportions of diaspore, ammonian illite, and gorceixite were found in coal. ► Diaspore was derived from gibbsite dehydration due to the heat of igneous intrusions. ► Ammonian illite formed by interaction of kaolinite and nitrogen released from coal. ► The calcite and dolomite were derived from the igneous fluids.