Foraminifera Fossils in Ferruginous Chert of the Kosaka Mine

Abstract

The Uchinotai ore-deposits of the Kosaka mine belong to "Kuroko (black ore)" type deposits, which are bedded sulfide and sulfate ore-deposits in the volcanic rocks and pyroclastic. strata of Miocene. The ore-deposits consist of siliceous ore, gypsum ore, cupriferous pyrite ore (yellow ore), cupriferous galena and sphalerite ore (black ore) in ascending order. These deposits are overlain by the sericitized. tuff with subordinated bedded red rook.
The red rocks in the sericitized tuff is observed as a thick stratified bed in one place and an aggregate of lenticular rocks in the other. The rock is generally called "ferruginous quartz". It is divided into. the following three groups by the appearance, in ascending order ; compact ferruginous quartz, shagreen ferruginous quartz and ferruginous clay. The red rock is often laminated and contain some Foraminifera, a mixed fauna of arenaceous species and calcareous ones. Some geologists believe that the bedded red rock is a replacement material accompanied by the formation of the Kuroko ore deposits. However, judging from the lamination and fossils tound init, t seems to be a marine sediment of the Miocene Nishikurosawa stage. This conclusion suggests that the "Kuroko" ore deposits of the Uchinotai mine were syngenetically formed by the material derived from submarine volcanism.