The main dolomite deposits in Gifu Prefecture occur, from west to east, at Kasuga-mura and Yokokura, Kuze-mura areas in Ibi-gun, and Miyama-mura area in Yamagata-gun, along with their outskirts. They are situated on an arc whose radius measures 50 to 60 km from Nagoya City, its center. It should also be noted that such pure limestone deposits as at Mino Akasaka and Saraji are located inside the said arc, almost parallel to them.
Many of these deposits are found in large limestone beds as in Mt. Ibuki, Mt. Funafuse, Mt. Kita and so on, although some exceptions are found in their smaller extensions and also in slate, chert and the like, not accompanied by limestone.
These limestone deposits have in them many fusulinids, while dolomite deposits are featured with
Parafusulina zones. Therefore, it is considered they belong to the geological age of the middle Permian.
The dye test disclosed that the crystals of the mineral are mostly 0.1 mm in size, a little bigger than those found at Kuzuu, Tochigi Proefecture, although not a few are of the same size.
The dolomite in Japan is a little different from that of foreign lands in that pores among crystals are packed up with calcite, and accordingly, very compact.
As for the dolomite in Kasuga area, Gifu Prefecture, it is considered that parts of the deposits have undergone thermal metamorphism by the injection of granite, and that it has been re-crystalized.
Three mines are in operation now, each of which is producing from 2, 000 to 8, 000 tons a month. It is of the grade MgO 17to 19 % and SiO
2 0.5 to 1.5 %. The mineral is mostly used for refractory substances for iron and steel works.
Special attention should be paid to the fact that the dolomite from Kasuga area contains least Fe
2O
3 in Japan-at 0.005%-on an average. For this reason, it is in great demand from the glass industry. Another recent use of the dolomite is agricultural dolomitic lime.
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