HYDROTHERMAL CLAY-MINERALS FOUND IN SEDIMENT CONTAINING YELLOWISH-BROWN MATERIAL FROM THE JAPAN BASIN

In a previous report, we suggested that the Fe-P mineral discovered in the yellowish-brown material from the deep-sea bottom in the eastern part of the Japan Basin could have been formed in situ under hydrother mal conditions. The present study of clay minerals in the muddy sedime nt containing the yellowish-brown material confirms the possibility of a submarine hydrothermal origin of these clay minerals, along with th e Fe-P mineral. Fe-smectites such as nontronite and ion-rich saponite and Fe-Mg chlorite indicated that Fe types rather than Mg type can be formed by slow alteration under submarine hydrothermal conditions at r elatively lower temperatures.