History of the exploration and development at the Chiemon vein swarm in the Akenobe polymetallic vein-type deposit

Abstract

An exploration program conducted by Akenobe Mining Co., Ltd. has resulted in a discovery and development of the Chiemon copper-zinc-tin vein swarm localized at the southwestern part of the Akenobe vein-type deposit. The Chiemon vein swarm has salient characteristics as follows: (1) it is far from known veins in the Akenobe deposit; (2) it has many ore shoots in the lower part; (3) it consists of many branchs or parallel veins; (4) it is essentially blind.
A history of the development of the Chiemon vein swarm to date is summarized below:
(1) In 1955, a crosscut at -2 level (340 m above sea level) was undertaken first in the Chiemon area, but his program was stopped in 1959 because of its poor mineralization.
(2) In 1969, a crosscut was again opened at -4 level (280 m above sea level), and the remarkable mineralization was found at the lower elevation. During the period from 1969 to 1972, active exploration works including underground geological survey, crosscutting, drifting, raising and diamond drilling were operated mainly between -4 and -8 levels.
(3) Based on the results of this exploration, during the period from 1973 to 1980, the exploration and development works were carried out between -9 and -14 levels. It realized that the Chiemon vein swarm was predominant mainly below -10 level.
(4) Since 1981, a trackless system has been introduced to prospect and develop for the levels deeper than -14 level (the present bottom is -17 level) in the Chiemon area.
Our exploration philosophy for the Chiemon vein swarm is summarized as follows.
(1) Based on the analysis of the post-ore movement caused by major faults, an exploration target of the Chiemon area is extended to -20 level.
(2) Assay maps indicate that ore shoots generally pitch toward south. This fact suggests that ore shoots were situated in deeper levles in the Chiemon area.
(3) It is neccessary for the exploration to pay special attention to two remakable mineralizations distinguished in the Chiemon vein swarm, an earlier chalcopyrite-sphalerite stage and a later cassiterite-ferberite-quartz stage.
(4) Vein fractures and ore shoots of the Chiemon vein swarm are developed mainly in the basic lava of brittle nature (the upper Permian Maizuru Group).
(5) Chiemon No. 4 vein, a champion of the swarm, is considered to have been a channel way of ascending ore solution. Most or other veins are localized around this champion vein as branchs or parallel veins.
(6) For the complicated vein system, systematic short hole (less than 50 m) and shallow hole (100-200 m) drilling operations many useful indications to the exploration program.
Current ore reserves of the Chiemon vein swarm have totalled about 2, 000, 000 metric tons of minable ore, averaging 1.78% of copper, 6.25% of zinc and 0.42% tin. Based on geology of the ore deposit, it is highly expected that ore reserves of the Chiemon vein swarm (including the Monju vein swarm) will be increased more than 1, 000, 000 metric tons by future exploration and development works.