Subsurface High Temperature Hypogene Acid Alteration at the Hatchobaru Geothermal Field, Kyushu, Japan

Abstract

Alteration minerals and their distribution were examined in the northern part of the Hatchobaru geothermal field, especially alunite and other acid alteration minerals. Alunite minerals are widely distributed with more than 300 meters thickness at the northern part of the field. Alunite minerals have a wide range of 6 34S from 0 to 24 per mil, indicating several different origins. Newly found acid minerals such as zunyite, topaz, and andalusite suggest that volcanic acid sulfate solutions were once present and was responsible for the formation of the thick acid alteration zone at the Hatchobaru geothermal field.