Some findings on recent exploration of the Shirogane veins, Akenobe mine.

Abstract

The vein-deposits in the Akenobe mine have been cited as one of the best-known examples of the polymetallic vein-type mineralization with the characteristic of the remarkable mineral zonings. They occur in formations of slate, basic tuff and basic lava of middle to late Permian Maizuru Group.
The total amount of crude ores ever produced is estimated more than 13, 000, 000 tons (Cu 1.09% Zn 2.0% Sn 0.37%) from over a hundred veins, about 30 veins of which are still workable. Recent production and exploration tend to be moved to lower and outer parts of mineralized area. It is recognized that mineral zoning pattern which has been identified in upper and central parts of the area is still applicable.
The Shirogane veins, located at the southeastern fringe of the mineralized area, are proved to be:
(1) rich in Pb-Zn at near surface and upper part of the veins, on the other hand, rich in Cu-Zn at lower part;
(2) composed of two veins intersecting each other, Shirogane No.1 vein and Shirogane No.2 vein, the former at the lower part showing the precipitation from the ore solution rich in Cu-Zn and the latter from the ore solutions rich in Cu-Zn firstly and rich in Zn secondly;
(3) zoned vertically, Pb-Zn—Cu-Zn—Cu-Sn zones in descending order, however, vertical interval of Cu-Zn zone seems to be longer compared with that of average Cu-Zn zone in the Akenobe mine.
Adding those findings, it is also confirmed in Shirogane No.2 vein that ores are brecciated by fault displacement occurred in the period between the first Cu-Zn rich mineralization and the second Zn rich mineralization, and that ore-breccias are generally rimmed and cemented by quartz and sphalerite precipitated from later Zn rich solution.