1975 Volume 25 Issue 130 Pages 195-207
Furutobe mine is located in the northern part of Akita Prefecture. The deposit of the mine is known as one of the typical Kuroko deposits occurring in the acidic pyroclastic rocks of Miocene age. The deposit shows following characters :
(1) A definite succession, siliceous ore, yellow ore, black ore, and ferruginous chert in ascending order, is seen in the deposit.
(2) Bedded sulphide ore occurring at the upper part of the deposit contains various fragments of ores and rocks.
Modes of occurrence of the siliceous ore and the results of its exploration are reported in this paper.
Siliceous ore is divided into two types on the basis of modes of occurrence and host rocks. One type of the siliceous ore occurs in rhyolite (lower siliceous ore zone) and the other in rhyolitic pyroclascic rocks (upper siliceous ore zone). The lower siliceous ore zone has cylindrical or tabular shape standing vertically. In the ore zone, a zonal distribution of ore-forming minerals, chalcopyrite zone, chalcopyrite-pyrite zone, and pyrite zone from center to periphery of the ore body is recognized. Silicification gradually becomes strong as approching to the central part of the mineralized zone. Clay minerals occurring in the mineralized zone are sericite and inter-stratified sericite/montmorillonite. Sericite is found mainly in the central part and interstratified sericite/montmorillonite is observed in general in the outer part of the ore zone.
The exploration was conducted on the basis of geological and mineralogical investigation and some ore bodies and bonanzas have been found in the lower siliceous ore zone.
