Pliocene to Pleistocene Volcanism and Related Vein-Type Mineralization in Sapporo-Iwanai District, Southwest Hokkaido, Japan

Abstract

Several epithermal vein-type deposits accompany andesite lavas called "flat lava" in Sapporo-Iwanai district, northern part of southwest Hokkaido, which is situated at the junction between the northeast Honshu Arc and the Kuril Arc. These "flat lavas" have been dated to be of Pliocene and Pleistocene age by K-Ar method, and the compilation of Pliocene to Holocene lavas in the district has revealed a sequential alignment of three NW-SE volcanic chains of Early Pliocene, Late Pliocene and Pleistocene.
The mineralization ages of vein-type deposits such as Inakuraishi, Ohe, Toyoha and Koryu are coincident with ages of the "flat lavas" which overlie these deposits. This may imply that the magmatic activity resulted in the "flat lavas" was also concerned in generation of hydrothermal solutions which brought ore deposition. under the lavas.
These deposits are located at the intersection between the NW-SE volcanic chains and a E-W dextral strike-slip shear zone extended from the Kuril Arc. They are considered to have been formed since the Pliocene under the overlapped tectonic setting of the volcanism of the northeast Honshu Arc and the structural movement of the Kuril Arc. In this respect, the arc-arc junction may be one of the most suitable sites for vein-type mineralization.