On the Successful Exploration at the Lower Part of the Mozumi Mining Area, the Kamioka Mines (No.2)

Abstract

As a result of the intensive exploration, based upon the studies of geological structure and mode of mineralization, more than ten new ore-bodies were discovered in the external zone around the known mineralized tracts of the Mozumi mining area, the Kamioka mines. At present, the zone involves the following ore-bodies : S No.6 to No.9, E No.2 to No.4, NE Nos.1 and 2, N No.21 to 23 and so on.
The discovery of these ore-bodies has brought about 2, 500, 000 tons of crude ores. In the near future another 4, 000, 000 tons of probable ore reserves may be expected.
On geological structure of the area, the followings have been clarified;
1) It is most probable that there is a large synclinorium in the Mozumi mining area. Consequently, it is considered that two major groups of ore-bodies, the Ikenoyama and the Nakagoya, might be emplaced in the limestone bed belonging to the same horizon.
2) The mode of distribution of the Tetori Members and Hida gneiss complex and geological relationship between them have been disclosed.
3) The geological significance of Kita No.20 fault can be well understood.
4) The three blocks consisting of gneiss complex were discriminated and also their mutual geological relationships have been clarified, namely,
a) The first block of the Ikenoyama area is situated at the hanging-wall side of the Kita No. 20 fault.
b) The second block is bounded by the Yokoyama overthrust and the Kita No.20 fault.
c) The third block develops at the foot-wall side of the Yokoyama overthrust, and is covered by the Tetori Member on the surface.
On the mode of mineralization, the following facts have been clarified ;
1) The zonal distribution of ores in each ore body is clearly recognized, from the center outward as follows :
Ore veins and stringers→Shiroji high-grade ore→Pb-Zn Mokuji ore→Cu-bearing Mokuji ore→Barren Mokuji.
2) From the field relations, it seems reasonable to consider that the mineralization is closely related to the igneous activity of the Namaridani granite prophyry which develops north to the mineralized zone.
3) The role of fissures for mineralization has been clearly disclosed. At the higher level, fissures relating to the Nanagohi fault played an important role as channelways of ore-forming fluid ; the same as at the lower level these relating to the Kita No.20 fault must be considered as the main channelways.
Summarizing the above, it is inferred that the mineralized zone may be enlarged downwards with increasing depth.