Study on Zonal Distribution in Ore Veins of the Tomii Mine, Tochigi Prefecture, Japan

Abstract

The author's discussion on the genesis of zonal distribution in ore veins of the Tomii Mine is mainly based on the observation of the Honpi Vein.
The vein was divided into four zones, namely, (1) uppermost zone consisting of gold-bearing quartz vein, (2) upper zone consisting of gold-and bismuthinite-bearing ore, (3) middle zone consisting of ore of relatively concentrated bismuth and copper, and (4) lower zone consisting of pyrite ore. This zoning was formed by the mineralization of early stage. The zone of barite molded quartz which formed by the mineralization of middle stage overlapped the lower zone, and the zone of zincblende formed by the mineralization of late stage overlapped the middle zone.
Some factors of this zonal distribution in veins of the mine are summarized as follows ; (1) zonality due to the overlap of different ores by the mineralizations of time-separated stages, (2) zonality due to the overlap of different ore deposition phases in a mineralization, (3) zonality due to physico-chemical. conditions of the mineral deposition, and (4) zonality due to inter-ore metasomatic conditions.
It is inferred that the zonal distribution in ore veins of the mine resulted from the aforesaid factors combined together, and was mainly composed of different ore deposition phases. Therefore, it falls under the "poly-ascendent zoning" by J. Kutina.