Hydrothermal alteration in the Kawarage and Doroyu areas, Akita Prefecture.

The Kawarage and Doroyu areas, where a geothermal field has been expected, are located in the southern part of the Yuzawa city, Akita Prefecture. Hotsprings, fumaroles and altered haloes formed by chemically geothermal fluids are found in these areas . The purpose of this study is to clarify the distribution and mineral associations of the alteration zones in both area. The results are as follows.1. The Kawarage area. The dimension of the alteration zone is about 1.5 and 0.5 Km along NW-SE and NE-SW, respectively. Silicified zone is widely spread around the Kawarage Sulfur deposit, and thinly enveloped by an argillized zone. The alteration minerals arranged from center to outer portion are sulfur, silica minerals, alunite, and montmorillonite. The amounts of quartz vary in each sampling piont, but quantitative analysis by X-ray diffraction method reveals that weight percentage of quartz is highest in the silicified zone.2. The Doroyu area. In contrast with The Kawarage area, the alteration zone in the Doroyu area has a smaller dimension of 0.5 and 0.2 Km wide, along NE-SW and NW-SE, respectively. It is composed of a narrow silicified zone and a wide argillized zone. The minerals in alteration zone distributed from its center to outer boundary are sulfur, silica minerals, alunite, kaolinite, and montmorillonite.