CHARACTERISTICS AND ORIGIN MODEL OF KAOLINITE ROCKS IN LATE-PALAEOZOIC COAL MEASURES, NORTH CHINA

The kaolinite rocks (including tonstein, flint clay and soft kaolin clay) are very abundant in the Late-Palaeozoic coal measures of North China The content of kaolinite minerals are in general more than 80% and up to 90%~ 100% in many good quality rocks. The accessory minerals include l/S mixed-layer clay mineral, NH4-illite, boemite, diaspore, chlorite, quartz,feldspar, feldspar, zircon, tourmaline and arutile. The Hinkley index (HI) varies with different kinds and origin of kaolinite, being the highest for the soft kaolin clay and the lowest for the terrigenous kaolinite. Geochemical studies show that the mother rocks are mainly related to the acid rocks. Three models of origin for the various types of kaolinite rocks were put forward in this paper.