Horizontal strain rate in relation to vein formation of the Hishikari golddeposits, southern Kyushu, Japan

The Hishikari deposits comprise the Honko (Main), Yamada, and Sanjin deposi ts. The horizontal strain in the direction (approx. N40 degreesW) normal to the general NE-SW strike of the Hishikari vein system was calculated, base d on the measured total vein widths to the distance along three crosscuts. Veins were assumed to accompany no significant fault displacement in the ca lculation. Veins in the eastern and the middle parts of the Honko-Sanjin de posits spatially occupy 3.2% and 1.3%, respectively, and veins in the Yamad a deposit occupy 6.7%. Significant local variation of strain is observed in some areas. Reported K-Ar ages on adularia-quartz veins indicate the durat ion of vein opening to be 2.6x10(5) yr in the Honko-Sanjin deposits and 5.9 x10(5) yr in the Yamada deposit. Horizontal strain rates were calculated to be 5.0-12x10(-8) yr(-1) through the Hishikari deposits. The calculated str ain rates at the Hishikari deposits are roughly comparable to the regions! horizontal strain rate in the Recent. Widespread extensional movement in so uthern Kyushu seems to have been able to provide sufficient strain for the formation of the Hishikari deposits, rather than contribution of local move ments.