On the Precipitation Environment of a Kind of "Kuroko Deposit"

Abstract

There are two types of lead-zinc deposits in the Tertiary greentuff region of Japan. One is a vein-type deposit and tbe other is a massive black ore deposit, the so-called "Kuroko" deposit.
The author concluded that the original ore solutions for both types of deposits have alinost the same characteristics, but formed different types of deposits according to the geologic environment of their precipitation.
The rocks surrounding the vein deposits are mainly massive and easily fissured. On the other hand in the case of the massive black ore deposits, the country rocks consist of a tuffaceous shale of plastic character. These rocks became folded and, as a result of exogenetic forces, some bedding slips occurred so that the precipitation of the ore minerals probably took place in the enclosed cracks.
The author also discusses the analogous conditions of formation between the black ore deposits and some of the cupriferous pyritic bedded deposits in southwestern Japan.