Geology and Ore Deposits of the Yanahara Mine with Reference to Structural Control

Abstract

Among geologic units in the Yanahara area, clayslate, volcanic rocks, diabase and epi-quartz diorite of Triassic age are of outstanding importance. Diorite, breccia-liparite and dyke rocks, and locally Tertiary and Recent sediments are also present.
The old volcanic rocks which include lavas and tuffs are intercalated in the lower part of the clayslate, and are the most fruitful mother rocks for high grade pyritic deposits of the Yanahara Mine. We call. this unit of volcanic rocks the "complex zone", because of its high complexity in petrological as well as structural features.
The ore shoots are restricted to the "complex zone", where veins containing them swell. The particular shapes of ore deposits are probably related to some tectonic movements in the area.
As a guide to new ore deposits, the above concepts should be very useful during future prospecting.