K-Ar ages of Chitose, Todoroki and Teine Au-Ag vein-type deposits, Southwest Hokkaido, Japan

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K-Ar age determination for adularia and sericite from three Au-Ag vein-type deposits (Chitose, Todoroki and Teine) in southwest Hokkaido has been carried out. Adularias in a gangue and a hydrothermally altered rock from the Bifuehonpi vein in the Chitose deposits showed almost same K-Ar age, 3.47±0.08 Ma and 3.30±0.08 Ma, respectively. Therefore, it is considered that the K-Ar age of the hydrothermally altered rock is comparable to the age of mineralization.<BR>Adularia and sericites from the Daikoku No.3 vein in the Chitose deposits gave K-Ar ages of 3.48±0.08 to 3.43±0.12 Ma as same as the Bifue-honpi vein. The Shuetsu and Chuetsu veins in the Todoroki deposits showed ages of 2.08±0.05 Ma and 3.05±0.08 to 2.09±0.07 Ma, respectively. K-Ar ages of 4.00±0.13 and 4.00±0.19 Ma were obtained from the Toriyabe vein in the Teine deposits. These results indicate that three deposits of the Chitose, Todoroki and Teine mines were formed during the Pliocene time.<BR>The estimated mineralization ages of vein-type deposits of the Chitose, Todoroki, Teine, Inakuraishi, Ohe, Toyoha and Koryu mines are coincident with ages of Pliocene to Pleistocene andesite lavas which overlie these deposits. This may imply that the magmatic activity yielded not only the andesite lavas but generated hydrothermal solutions also which is related to the formation of the ore deposits beneath the lavas.
資源地質学会の論文