K-Ar ages of gold mineralization and argillization in the Arita-Hasami area, western Kyushu, Japan.

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Clay deposits for pottery stone and epithermal gold bearing quartz veins occur with their close relations in fossil geothermal zones of the Arita-Hasami area in western Kyushu, Japan. They are hosted mainly by late Pliocene rhyolitic rocks and partly by Miocene sedimentary rocks. To characterize hydrothermal activity in the area, we examined the K-Ar ages of hydrothermal mineralization and the homogenization temperatures of fluid inclusions from quartz veins in the area with mineral zonation mapping based on hydrothermal mineral assemblages.<BR>Four mineral zones were clarified in the area; cristobalite-smectite zone (Zone I), quartz-smectite zone (Zone II), interstratified clay mineral zone (Zone III) and sericite-chlorite zone (Zone IV). Two sericites from a clay deposit in Arita gave 2.12±0.06 and 2.19±0.05 Ma, and four sericites from clay deposits in Hasami gave 1.49±0.04, 1.51±0.04, 1.72±0.04 and 1.72±0.04 Ma, respectively, in age. Adularia from the gold deposit in Hasami was 1.75±0.04 Ma. Fluid inclusion studies indicate that the mineralization temperatures are about 250°C and suggest that quartz formed during boiling of fluid in the Hasami gold deposit.<BR>The time span between the rhyolite volcanism and the subsequent hydrothermal mineralization is larger than 0.5 Ma, requiring reexamination of the autometasomatism model for the process of clay mineralization of the intrusive rhyolite.
資源地質学会の論文