K-Ar Ages of the Sericite and Kaolin Deposits in the Chugoku District, Southwest Japan

Abstract

The K-Ar ages of sericites collected from sericite and kaolin deposits in the Chugoku district were determined and their formation stages were discussed.
Sericites from sericite deposits are dated as follows; Ohgin (31.1 Ma), Iwaya (36.4 Ma), Nabeyama (45.6 Ma), Yoshida (48.5 Ma), Unnan (50.3 Ma), Igi (50.6 Ma), Hida (56.9 Ma), Ohguni (61.4 Ma) and Kumano (77.5 Ma).
Sericites from Komaki, Kohtachi and Toyosaka kaolin deposits are dated at 55.6 Ma, 76.5 Ma and 79.5 Ma, respectively.
The results indicate that the formation ages of sericite and kaolin deposits are comparable to or slightly younger than those of respective hosts or nearby granitic rocks whose age data are available at the present. Therefore, the mineralization stages of these clay deposits appear to be concluded to correspond with the hydrothermal stages of granitic activities in the Chugoku district during the period from Late Cretaceous to Palaeogene.