抄録
Alteration halos of the Hachimantai Appi geothermal area is divided into alunite, kaolinite and smectite zones from 273 samples. Zonal arrangements are reformed by landslide and overlapping of more than two hydrothermal events are recognized. Thermoluminescence (TL) age determination of 12 altered rocks shows that the age of older event is expected around 0.9-0.5 Ma and that of younger is 0.3-0.1 Ma. Heat source volcanoes are identified by TL dating of 8 volcanic rocks. Ages of 4 samples from southern mountainous area are 0.31-0.37 Ma whereas those of 4 samples from northern slope are 0.58-0.72 Ma. It shows very good correlation with underground temperature profile. Lineaments identified from JERS-1 SAR images and colored aerial photographs show E-W directional structure and fractures for fluid flow. Regional geothermal model is constructed from age data and distribution of volcanoes. Promising geothermal areas can select by precise age determination of both alteration and volcanic rocks. Conditions for such potential drilling sites are as follows; (1) The occurrence of volcanism from 0.5-0.3 Ma, and extending to younger volcanoes around 0.1 Ma. (2) The presence of pyrophyllite and other high temperature minerals in the alteration zones. (3) The occurrence of more than two hydrothermal events, the most recent being younger than 0.3 Ma.
