5:15 PM - 6:30 PM
[HRE12-P01] Exploration of multiple geothermal resources in southern Yuzawa area, Akita prefecture
Keywords:geothermal resources
Multiple geothermal resource exploration was conducted in the southern part of Yuzawa city, Akita prefecture.
The Sanzugawa caldera is distributed around this area, and in this caldera, there are basement rocks of pre-tertiary granitic and metamorphic rocks from the lower part, and the Doroyu and Torageyama formations are distributed in the upper part. In particular, the Torageyama formation is composed of partially fused tuff and is widely distributed in this area. The upper part of the Torageyama formation includes the Sanzugawa formation, the Kabutoyama formation, and the Takamatsudake volcanic rocks. In this study, we carried out Thermoluminescence measurements and identification of alteration minerals.
Thermoluminescence geothermal prospecting is a method of analyzing the luminescence produced by heating quartz particles in igneous rocks, and is used to evaluate the thermal effects of the rocks.
Alteration minerals can be broadly classified into acidic, neutral, and alkaline alteration minerals. The alkaline alteration zone was observed in Yunomatazawa in the western part of this area. Pyrophyllite was also found in the middle reaches of the Minasegawa, and it can be assumed that there was strong acidic alteration in this area. Furthermore, acidic and alkaline alteration minerals are distributed locally, while neutral alteration minerals are distributed over a wide area.
As a result of TL measurement, low TL values were detected near the lower reaches of the Minasegawa, and the surrounding streams were also found to have low TL values. Furthermore, the TL values decreased as the elevation decreased from Torageyama to Minasegawa. This indicates that there is a strong thermal influence from Torageyama to Minasegawa.
We developed a thermal structure model of the subsurface in this area by coupling the decay rate equation of TL with temperature and the unsteady heat conduction model to estimate the location of the heat source. The heat source was modeled as a heat source on a uniform flat plate, with a source temperature of 700℃ and initial surface and subsurface temperatures of 15℃. The TL values at the surface were best explained when the heat sources were located at a depth of 5000 m near Toragesawa and 4000 m downstream of the Minasegawa. In the middle reaches of the Toragesawa river, the TL values are consistent with the case where the heat source is located at 4500 m below the ground surface. From the above, it can be inferred that the subsurface thermal structure in the target area is not a uniform heat source, but a shallow heat source in parts.
The Sanzugawa caldera is distributed around this area, and in this caldera, there are basement rocks of pre-tertiary granitic and metamorphic rocks from the lower part, and the Doroyu and Torageyama formations are distributed in the upper part. In particular, the Torageyama formation is composed of partially fused tuff and is widely distributed in this area. The upper part of the Torageyama formation includes the Sanzugawa formation, the Kabutoyama formation, and the Takamatsudake volcanic rocks. In this study, we carried out Thermoluminescence measurements and identification of alteration minerals.
Thermoluminescence geothermal prospecting is a method of analyzing the luminescence produced by heating quartz particles in igneous rocks, and is used to evaluate the thermal effects of the rocks.
Alteration minerals can be broadly classified into acidic, neutral, and alkaline alteration minerals. The alkaline alteration zone was observed in Yunomatazawa in the western part of this area. Pyrophyllite was also found in the middle reaches of the Minasegawa, and it can be assumed that there was strong acidic alteration in this area. Furthermore, acidic and alkaline alteration minerals are distributed locally, while neutral alteration minerals are distributed over a wide area.
As a result of TL measurement, low TL values were detected near the lower reaches of the Minasegawa, and the surrounding streams were also found to have low TL values. Furthermore, the TL values decreased as the elevation decreased from Torageyama to Minasegawa. This indicates that there is a strong thermal influence from Torageyama to Minasegawa.
We developed a thermal structure model of the subsurface in this area by coupling the decay rate equation of TL with temperature and the unsteady heat conduction model to estimate the location of the heat source. The heat source was modeled as a heat source on a uniform flat plate, with a source temperature of 700℃ and initial surface and subsurface temperatures of 15℃. The TL values at the surface were best explained when the heat sources were located at a depth of 5000 m near Toragesawa and 4000 m downstream of the Minasegawa. In the middle reaches of the Toragesawa river, the TL values are consistent with the case where the heat source is located at 4500 m below the ground surface. From the above, it can be inferred that the subsurface thermal structure in the target area is not a uniform heat source, but a shallow heat source in parts.