The Mother Rock Alteration in Beppu Mine, Oita Prefecture

Abstract

The silica rock in Beppu mine is an replacement alteration product of the hornblende andesite by epithermal solutions.
The high grade ore is chiefly composed of opaline silica while low grade, ore contains alunite, kaolinite, limonite, hematite, sulphur, rutile and iron sulphide.
The mother rock alteration of Beppu mine is characterized by a zonal arrangement from the surface to downward as follows : silica rock, alunite clay, kaolinite clay, and original rock.
The chemical composition of the high grade ore is as follows:
SiO₂ AL₂O₃ Fe₂O₃+FeO CaO MgO K₂O Na₂O Ig. loss Total
90.00 1.82 0.20 0.40 tr. tr. tr. 7.95 100.37
The ore forming agent may have been an ascending hydrothermal sulphuric solution of vol canic origin.