Structural Features and Ore Deposits of the Kishu Mine

Abstract

The copper deposits, consisting of chalcopyrite, pyrite, sphalerite, galena, quartz, calcite, sericite and others, in the main area of the Kishu Mine occur in the Okochi 'the Itaya and the Taketo formations of the Miocene Miyai Group. They are mainly composed of sandstone, and sandstone and shale.
The Miyai Group surrounding the main ore-bearing area has a general strike of N20-40°E and a dip of 10-30°E. The main ore-bearing area is situated in a dome of a large basin of the Miyai. Group. The long axis of the dome is parallel to the general strike of the Miyai Group.
Vein fissures of the main mining district are grouped in the following three sets according to the strike directions: i. e N-S, E-W and NW-SE. Intersections between two sets of fissures of the N-S group and the E-W or NW-SE group, can be regarded as the channelways of mineralizing solutions and mineralization centers. The most important intersection is situated in the vicinity of the dome where Josen No. 20 vein meets Josen 9-level North Cross-cut.
Five mineralization stages can be recognized. i.e Py, Cu-Py, Pb-Zn, Au-Ag and calcite stages. There are two types of copper ores. The one is associated with chlorite formed during the Cu-Py stage and the other with sericite formed during the Pb-Zn stage. The latter's deposition centers are generally beneath the former's.
Silicification, chloritization and sericitization are recongnized as wall-rock alterations.
The Cl^- content distribution in the deep seated ground-water in the mine well reflects in the geologic structure.
Filling temperatures of the minerals mainly measured by decrepitation method are 172-318°C in chalcopyrite, and 160-330°C in pyrite.