Geology and Ore deposits of the Hosokura Mine, Miyagi Prefecture

Abstract

The Hosokura mine is one of the largest zinc and lead mines in Japan and is located in the Miyagi prefecture.
The mine area is composed of propylite, rhyolitic rocks, dacite, green tuff and dacitic tuff which belong to the Tertiary period.
Most of the veins occur in the propylite and rhyolitic rocks and some occur in the green tuff, and these veins were, formed as an epithermal fissure-filling deposit in the Miocene epoch.
Writers apply the idea of the "Strain Ellipse" to the original fractures in Hosokura, and classify them into the the tension fractures and the shear fractures. The tension fractures which are comparatively simple and stable are prevalent in the central part of the propylite, and shear fractures which are more complicated and unstable than the former are prevalent along the marginal parts of the propylite.
It is considered that these fractures were controlled by the intruded igneous bodies and were formed by the compressive stress.