Exploration at the Northwestern Area of the Hosokura Mine, Miyagi Prefecture

Abstract

The Hosokura Mine is situated 84 km north of the Sendai City, Miyagi Prefecture. The area is located geologically at the eastern margin of so-called "green tuff region" in Northeast Japan. The ore deposits of this mine are lead-zinc fissure filling veins of epithermal or mesothermal type.
In this paper, geological features of fissure systems and ore shoots of Oiwake veins located at the northwestern margin of the Hosokura Mine are described. They are summarized as follows ;
(1) The geology of this area consists of massive propylite, brecciated propylite, tuff breccia or sandy tuff (Hosokura lower formation) and tuff breccia, pumiceous or sandy tuff (Hosokura upper formation) in ascending order.
(2) Two fissure systems, NW-SE and NE-SW are developed in the area. The NE-SW fissure system forms the Oiwake veins reported in this paper.
(3) Ore shoots of the Oiwake veins are developed along a major fault, Hanzashinpi fault. Several notable ore shoots are recognized at the uppermost part of Hosokura lower forma-tion as well.
It is considered that the exploration plannings for Oiwake area in the future should be based on the facts mentioned above.