K-Ar ages of vein-type deposits in the Otaru-Shikotsu districi, Southwest Hokkaido, Japan
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Various hydrothermal ore deposits such as gold-silver vein-type, copper-lead-zinc vein-type, Kuroko, and massive barite are distributed in the Otaru-Shikotsu district, Southwest Hokkaido. K-Ar mineral ages for hydrothermally altered rocks from the gold-silver vein-type deposits of Teine, Sapporo, Maruyama, Nakanosawa, and Eniwa and copper-lead-zinc vein-type deposits of Higashi-Kucchan, Shin-Otoyo, Jozankei, and Toyotomi were determined to estimate their mineralization ages.<BR>Sericites from the Teine, Sapporo, and Maruyama deposits gave age values of 4.35±0.12, 5.19±0.13, and 3.63±0.12 Ma, respectively, while potassium feldspars-from the Nakanosawa and Eniwa deposits gave those of 3.18±0.08 and 2.14±0.05 Ma, respectively. These results indicate that gold-silver vein-type deposits were formed during the Pliocene epoch. On the other hand, a Late Miocene mineralization was obtained for the Higashi-Kucchan, Jozankei, and Toyotomi copper-lead-zinc vein-type deposits.<BR>Comparison of the newly-obtained age data and reported ones suggest that the hydrothermal ore deposits in the Otaru-Shikotsu district were formed in three stages, namely: Middle Miocene (Kuroko), Late Miocene (copper-lead-zinc vein-type and massive barite), and Plio-Pleistocene (gold-silver and copper-lead-zinc vein-type). The Late Miocene miner-alizations are related to quartz porphyry activity. The Plio-Pleistocene mineralization age is coincident with that of andesite lavas overlying the gold-silver and copper-lead-zinc vein-type deposits.
- 資源地質学会の論文
資源地質学会 | 論文
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