Geology and Ore Deposits of the Hirota Mine

Abstract

Thd Hirota mine is located approximately 20 kilometers to the south of the Matsuyama City in the Ehime Prefecture.
The geology of this mine is made of the Sanbagawa-crystalline schists and the overlying Tertiary formations of conglomerate and andestic basalt, intrued by andesite and liparite.
The ore deposits are the bedded cupriferous pyritic ore deposits occurring in the green schists and are composed chiefly of pyrite and chalcopyrite with a small amount of pyrrhotite, magnetite, sphalerite and galena.
The mode of occurrence of ore deposits is concordant with the structure of country rocks. The following characteristics of the ore deposits are notable:
1. The horizon of ore deposits is limited within the green schist.
2. Close to the ore deposits, there is hematite-quartz schist beds which form a direct wall rock in some places.
3. Ore shoots are formed in the syncline.
4. Lineations and the folding axes agrees well eack other, suggesting that there is an intimate correlation between the ore shoot and the lineation.
5. The natures of the ore in the deposits are massive, banded and disseminated ores successively from the lower to the upper horizon of the deposits succession remains unchanged over the wide area.
6. Exploration works have been undertaken under the working hypothesis of the syngenetic origin, with good results.