Alteration around Fukazawa kuroko deposits, Akita prefecture, with special reference to zonal distribution of alteration minerals in hanging-wall rocks.

Abstract

Around 2, 000 samples were taken from 48 drill holes perforated near Fukazawa Kuroko deposits to determine the alteration minerals by X-ray diffractmeter. The zonal arrangement of the alteration minerals was clarified in both the hangingwall and the footwall. In both walls, the amount of montmorillonite was revealed to decrease and that of sericite to increase towards the ore deposits, and zeolitic minerals (such as mordenite and analcime) to occur only in the parts far away from the ore deposits.
In hangingwall, montmorillonite-lack zone was found just above the ore deposits like as a ring. Montmorillonite in the inner part of the ring shows low d₀₀₁ values that suggest high Na content. On the other hand, montmorillonite in the outer part of the ring shows rather high d₀₀₁ values that do not mean high Na content. DATE, et all (1979) showed the existence of the dacite very poor in Na₂O just below the ore deposits. It is likely that, some amounts of Na₂O that was leached from the dacite and its pyroclastic rocks below the ore deposits seem to be settled in Na-montmorillonite just above the ore deposits after the formation of the ore deposits.