K-Ar ages of the Sanru and Koryu mines in Hokkaido, Japan

Abstract

K-Ar ages of adularia from epithermal gold-silver quartz veins of the Sanru and Koryu mines which belong to Kitami and South-western metallogenetic provinces in Hokkaido respectively, have been determined. Adularia occurs as band, 2 to 5mm in width, in crustified banding quartz associating with dark colored gold-silver bearing band (Ginguro). A K-Ar age of 12.4±0.6 Ma was obtained for adularia from the -120m level of the Juji vein, Sanru mine, whereas adularia from the 20m sublevel of the 60m level of the No. 1 vein, Koryu mine, gave a K-Ar age of 1.0±0.3 Ma. The former age corresponds to the Middle Miocene and suggests that one of mineralization of gold-silver in the Kitami metallogenetic province occurred that period. The age of 1.0±0.3 Ma for the Koryu mine is a youngest age for gold-silver mineralization in Japan according to all K-Ar age data for epithermal vein up to the present as given in Table 1, and it is significant to note that a hydrothermal mineralization which produced a gold-silver quartz vein in Hokkaido occurred in the Pleistocene age, as nearly the same time as that of the Hishikari and Ohra mines in the northern Kagoshima of Kyushu, Japan.