Recent exploration of the Fukazawa kuroko deposits and some interesting modes of occurrence of the ores

Abstract

The Fukazawa deposits are located in the central part of the Hokuroku basin, Akita Prefecture. They are stratabound kuroko deposits occurring in volcanics of Miocene age. Kuroko ore is a main constituent of the Fukazawa deposits, and Oko, Keiko and Sekko ores, which are common in many other kuroko deposits, are seldom contained in the deposits. The stratiform orebody has a considerably greater lateral extension than thickness and occurs immediately under a thick basalt flow.
Some interesting modes of occurrence have been observed in the deposits. In the Manjakuzawa No. 2 ore-body, basalt is interstratified with kuroko ore and divided into small irregular or ellipsoidal masses like a stack of pillows at the end of the flow. This suggests that the basalt flowed into unconsolidated sediments and ores.
The upper Yellow ore (Oko) occurring within the hanging wall layered tuff and basalt in the Fukazawa deposits has been considered to be an evidence of post-kuroko mineralization. Mineralization lasted probably after main kuroko mineralization. This type of ore of the Tsunokakezawa No. 1 orebody and intensely silicified zone with chalcopyrite and pyrite in the foot wall lithic tuff may have been formed by the later mineralization.