| Abstract |
Oyasu-Uenotai area is one of geothermal fields where is now in exploration. The area is located at southern inland of Akita Prefecture about 20 km north of the Onikobe Geothermal Plant and also about 90 km south of the Kakkonda Geothermal Plant. According to Naka et al. (1987) and unpublished data in the Akita Geothermal Energy Co. Ltd., an area of about 5 km2 has been investigated geologically, geophysically, geochemically and also through exploratory drilling. The inv~stigation found a fracture zone at a depth of 1200 ~ 1850 m where the temperature is in a range of 280 ~ 335°C. Steam only issued from most of the exploratory wells, while mixture of steam and hot water is obtained some wells in the north-eastern area, where the content of hot water is 20 ~ 30 ~o after flashing under near atmospheric pressure. In this study, the hydrogen and oxygen isotopic ratios of thermal water from the exploratory wells were measured and the results were discussed in comparison with the isotopic feature of meteoric water and natural thermal water in the vicinity, to estimate the origins of thermal water in this area. The measurements of isotopic ratios were carried out with conventional methods, and the results were presented as 0 values relative to the SMOW standard. |