Relation of Tectonic Movement and Igneous Activity to the Mineralization in the Tomii Mining Field, Tochigi Prefecture, Japan

Abstract

The ore deposits of the Tomii Mine are localized under the control of a horst structure or some uplifts which were caused by the doming elongated north 20°east trend. Particularly, it is considered that the forming of fracture patterns of each vein group was based on local uplifts. And it determinedthe character of each ore body that fractures developed step by step, and the ore solution ascended asthe pulsatile action consisted with the doming.
There were some eruptions of liparitic complex as the last phase of intermittent igneous activities in the Tomii mining field. They were followed by mineralization at three different stages. It is inferredthat the ore solution was related originally to the source of activities of liparite eruptions, but theopening of fractures and the ascending of ore solutions were not caused by these igneous activities but by the doming.