Geology and Ore Deposits of the Tatsumata and Akarimata Mines, Akita Prefecture

Abstract

The ore deposits of the Tatsumata and Akarimata mines are the complex veins composed of the xenothermal and epithermal type veins. The igneous activity related most closely to the formation of those ore deposits is the "volcanoplutonism" in the middle-late Nishikurozawa stage. During the activity in the Nishikurozawa stage liparite lavas flowed on one hand and the holocrystalline rocks intruded on the other. Location of the intrusion of holocrystalline rocks was governed by the folding structure. Formation of ore-shoot in fissure-filling vein was controlled by the shearing cracks due to thrusting or depression accompanying to the igneous intrusion and by the tension cracks formed by the lateral pressure accompanying to the folding movement. Therefore, the major veins occur always in dome or anticline in the complicated anticlinorium.