K-Ar Ages of the dike rocks in the Kamioka Pb-Zn sharn deposits in the Hida terrain, Japan

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The Kamioka deposits are composed of skam type lead-zinc orebodies formed by the replacement of limestone, a member of Hida metamorphic rocks, and there are many variety of dikes and small stocks which occur in and around the deposits. The Kamioka deposits are estimated to have formed from a hydrothermal events related to the Mesozoic magmatism.<BR>In order to clarify the related igneous activity, we carried out K-Ar age determination for representative dikes in the mining area. From the data, the dikes and stocks are roughly divided into two groups, that is late Cretaceous to early Paleogene (55-65Ma) and Cretaceous to some older (90-125Ma). The former age is equivalent to the age of Shiroji(63.8-67.5Ma for sericites, NAGASAWA and SHIBATA, 1985) mineralization of the Kamioka deposits.<BR>Although the igneous rocks clearly related to the mineralization in the Kamioka area have not been identified, it is concluded that the former young dikes belong to a group of late Cretaceous acidic magmatism locating beneath this area that is estimated to be a related magmatism to the mineralization of the Kamioka deposits (SAKAI, 1963; SHIMAZAKI and KUSAKABE, 1990; Among others).
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