Hypogene Alunite from Acid Alteration Zone in Hatchobaru Geothermal Field, Kyushu, Japan

Alteration minerals focused on alunite and other acid alteration minerals were examined in the northern part of the Hatchobaru geothermal field. Alunite minerals are widely distributed with more than 300 meters thickness. Alunite minerals have a wide range of δ³¹S from 0.5 to 23.7 per mil, indicating several different origins: supergene and hypogene origins. APS (Aluminium phosphate-sulfate) minerals in the core of the alunite minerals and the newly found acid alteration minerals such as zunyite, topaz, and andalusite suggest that volcanic acid sulfate solutions were once present to have formed the thick acid alteration zone at the Hatchobaru geothermal field.