| Title | Hypogene Acid Alteration at Unzen Jigoku Steaming Ground, Unzen Volcano, Kyushu, Japan |
|---|---|
| Authors | Sachihiro Taguchi, Yumi Kubo, Soichiro Yoshii, Yoko Tanaka, Hitoshi Chiba |
| Year | 2008 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | hypogene, silicified rock, advanced argillic alteration, steaming ground, Unzen, Kyushu, Japan |
| Abstract | Advanced argililic alteration zones (Alinite zone, and Kaolin zone) are dominant in and around the Unzen Jigoku due to the present acid-sulfate steam-heated waters. However, silicified rock mainly composed of quartz is distributed at the Old-Hachiman area in the Jigoku. Fluid inclusions from quartz veins in the rock suggest that the rock was formed in two phase conditions under 170 to 220°C at least a depth of about 100m. Moreover, dickite occurs from a kaolin zone surrounding the silicified rock at the southwest of the rock. Some of sulfur isotope data of alunite minerals occurred near the silicified rock indicate a hypogene origin, although many of alunite minerals were formed under steam-heated water. Such alteration features conclude that the silicified rock at the Old-Hachiman area was formed under a volcanic acid fluid environment about 200°C, which was eroded out at least 100m and located at the present surface. |