The Recent Geologic Exploration in the Hosokura Mine, Miyagi Prefecture

Abstract

The Hosokura mine, Miyagi prefecture, is one of the largest zinc and lead mines in Japan. The mine area is composed of propylite, rhyolite, rhyolitic rocks, dacitic rocks, green tuff and dacitic tuff of Miocene age. Most of the workable veins of fissure-filling type occur in the Hosokura formation. The formation is classified as follows :
(1) Upper tuff member
(2) Propylite group
(3) Lower tuff member
(4) Rhyclitic rocks
(5) Lowermost tuff member.
Most of the igneous rocks are lava flows within the pyroclastic members, but some propylites are intruding the formation. These rocks are stepped down towards the center by the N-W fault.
Development of ore shoots is controlled mainly by the following factors:
(1) Nature of host rocks
(2) Fissure patterns and features of N-W system faults
(3) Others.
Generally speaking, ore shoots occur within the upper tuff member, or in or near the igneous rocks.