1988 Volume 38 Issue 207 Pages 57-62
In the Inakuraishi-Ohe mining district, there are successive mineralizations from the kuroko-type to polymetallic and iron sulfide vein-type deposits. These sequence can be estimated based on the stratigraphic horizons of their host rocks, the extent of the hydrothermal alteration haloes, and the whole-rock K-Ar dating of the alteration zone. The mineralization ages of the Inakuraishi and Ohe polymetallic vein-type deposits were determined by the K-Ar dating on the sericitized host rocks juxtaposed with these veins. The whole-rock K-Ar ages of the sericitized andesitic rocks of the early Miocene Lower Furubira Formation from the Inakuraishi mine were 4.9±0.2 to 2.7±0.2Ma. On the other hand, the sericitized quartz diorite of probably late Miocene age from the Ohe mine gave the K-Ar age of 3.4±0.3Ma. This quartz diorite is considered to be related to the mineralizations of the Inakuraishi and Ohe deposits. It is suggested that the mineralizations of the Inakuraishi and Ohe deposits had taken place in late Miocene to Pliocene time after the intrusion of quartz diorite. Especially the main mineralizations of both deposits appear to have occurred in Pliocene time.
