Abstract
The radioactive springs related with the Hiroshima Granite, one of the largest batholith in Japan, are distributed near the contact between the granite and wall rocks. In the Kurobe geothermal field the hot springs are distributed near the contact, too. Similar distribution pattern was recognized in west-central Alaska (Miller et al., 1975). Structural studies on intrusive bodies revealed that the fractures are often present near the contact between the granite and wall rocks (e. g. Balk, 1937). They would be caused by the upward movement of the granitic pluton or by the high magma pressure. It was also pointed out that they would be of tension type (Balk, 1937; Koide and Bhattacharji, 1975). Some of the hot springs related with the granite may be tectonically controlled by such a fracture system.
