K-Ar ages of several hydrothermal ore deposits in the Shakotan Peninsula, Southwest Hokkaido, Japan

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Various types of hydrothermal ore deposits; copper-lead-zinc vein, manganese vein, manganese strata-bound, barite vein, pyrite vein and Kuroko, are distributed in the Shakotan Peninsula, southwest Hokkaido. K-Ar ages for sericite separated from hydrothermally altered rocks collected from the individual types of ore deposits are as follows; copper-lead-zinc vein (10.22 to 1.99 Ma), manganese vein (6.29 to 3.14 Ma), pyrite vein (2.39 Ma) and barite vein (4.85 Ma). A Kuroko deposit yields 12.27 Ma and a manganese strata-bound deposit, 6.53 Ma.<BR>Newly and previously obtained K-Ar age data, and geological information for the hydrothermal ore deposits in the Shakotan-Shikotsu district suggest that the major ore mineralization are grouped into three epochs; Middle Miocene Kuroko, Late Miocene vein (copper-lead-zinc) and Plio-Pleistocene vein (gold-silver, copper-lead-zinc and manganese). The Late Miocene mineralization is related to the activity of acidic intrusive rocks. The Plio-Pleistocene mineralization age is coincident with that of andesite lavas overlying the vein-type deposits.
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