Study of kaolinite rock in coal bearing stratum, North China

Abstract

The proved reserves of kaolinite in coal measures in China is very rich, most of which are excellent industrial materials and are associated with the Permo-Carboniferous strata of North China. There are three types of kaolinite rocks in the present research area: the first type (be called tonsteins) occurs in the roofs, partings and floors of coal seams, normally called tonsteins, which are thinner and widespread; the second type, usually 2~6 m thick, is not adjacent to coal seams, usually in the lower part of coal measures of Upper Permian, similar to the flint clay in North America; the third type is soft kaolin clay of 0.5~5 m in thickness and associated with surficial weathered coals. Results of XRD, IR, DTA and SEM studies show that the content of kaolinite minerals is in general more than 70% and up to 90%~100% in some good quality rocks. The elements of Mo, W, Zr, Hf, Th, Ag and Sb are very rich in kaolinite rocks in the study area, with their average contents being higher than those in the earth's crust, basalt and granite. It is suggested that tonsteins formed from the in situ alteration of air fall volcanic ashes, second type of kaolinite have formed mainly on the adjacent landmass, but some crystallization of gels within the basin is not ruled out, the third type of kaolinite is related to weathering of coals.