日本のカオリソ質粘土資源

抄録

Kaolin clays produced in Japan is classified into refractory-clay and kaolin. And the former, moreover, is divided into shale-clay, Kibushi-clay, Gaerome-clay and hydrothermal refractory-clay. Among these kaolin clays, Kibushi-and Gaerome-clays are most important and their output exceeds 60% of that of all kaolin clays.
Genetically, they are divided as follows; hydrothermal, residual, sedimentary and diagenetic. Particularly, sedimentary type deposits are the most predominant and hydrothermal type ones next to it.
Hydrothermal clay deposits are distributed being confined to both the late-Cretaceous acid volcanic zone and the Miocene-Pleistocene volcanic zone. Kaolin, pyrophylliteand sericite clays occur in these deposits with close relation to each other. Three deposits, Itaya, Hiraki and Omura mines, are very outstanding as kaolin clay deposits. But most of them show very complicated occurrence controlled by various geologic features andare rather small in scale.
Sedimentary kaolin clay deposits, which comprise shale-clay, Kibushi-clay and Gaerome-clay, occur in the Palaeogene and the Pliocene coal-or lignite-bearing formations. It is very characteristic that they always occur in the basal parts of these formations. Chemical features of these clays indicate Pliocene was more favorable age in climatic condition for formation of kaolinic weathering crust.
However, supply of kaolin clays does not meet the demands in Japan. About 50% of kaolin, which is used mainly for paper and porcelain, is imported from the United States and other countries. The output of refractory clays has increased steadily. But the results of analysis of production statistics suggest some of refractory-clays, particularly Kibushi-clay, will be exhausted in near future.