Finding of the Radiolarian Fossils in the 'Oxide Bed' of the Hanaoka Mine

Abstract

The ore deposits of the Hanaoka mine are of the 'Kuroko' type. The 'Kuroko' deposits generally occus as bedded or tabular bodies in the Tertiary formation in Japan. In the 'Kuroko' area, the following rocks are found in ascending order: dacite, pyrite-bearing siliceous rock, gypsum ore-body. pyrite ore-body, chalcopyrite-pyrite ore-body, chalcopyrite-barite-galena-sphalerite ore-body and oxide bed. The oxide bed consists characteristically of manganite and hematite. The principal mineral assemblages of the oxide bed are as follows: 1) manganite-'pink colored montmorillonite' or montmorillonite alone, 2) hematite-quartz in nodule and sericite-quartz in host. The radiolarian fossils were found to be rather commoner in the siliceous part than in the clayey part of the bed. Judging from the existence of many radiolarian fossils, the oxide bed might be deposited like ferruginous chert in sea water. Close field relationship of the 'Kuroko' deposit with the oxide bed suggests that the former is of the submarine exhalative sedimentary type.