Geology and Cupriferous Pyrite Deposits (Besshi Type) of the Sanbagawa Metamorphic Zone including the Besshi and the Sazare Mines in Central Shikoku (III)

Abstract

As a result of the systematic study on the basis of the stratigraphical consideration, the following features have been recognized in the ore of the Besshi type.
1. In the texture of ore, the ore-forming minerals show the gefuge corresponding to the linier structure of this area.
2. The grain size of pyrite in ore grows in proportion to the metamorphic grade, showing a zonal distribution in this area.
3. Pyrrhotite is found throughout the Kawaguchi formation, and in the lower Minawa formation zincblende is rich in contrast with the ore-deposits in the other formations.
4. Concerning minor elements in ore, the result of chemical quantitative analysis has revealed the following :
It is observed the distribution of minor elements in ore characterizes each formation.
Name of formation Minor element
Pb Zn Ti Ni Co Sb As Sn
Kawaguchi * * * * *
lower * * *
Minawa middle *
upper *
Thus, these bedded ore-deposits belonging to the same horizon have common characters. Therefore, the writer has come to support the syngenetic theory, i, e., these ore-deposits had been deposited with other sediments in the submarine geosyncline of Sanbagawa in the course of the post-volcanic activities, and afterward the ore-deposits had suffered remarkable metamorphism, having been derived from the orogenic movements in the pre-Cretaceous period ; consequently, the bedded ore-deposits had been deformed and recrystallized with their motherrocks.
Standing on the above points, the writer has attempted to trace the special horizon including excellent ore-deposits, and has effectively found new ore-bodies and ore-shoots which, are controlled by the folding structure.
At present, the continuity of ore-body or ore-shoot has been confirmed for a distance from 2, 000 meters up to about 4, 500 meters.