Fluid Inclusion Study of Ores from the Fukazawa Mine, Hokuroku District, Akita Prefecture

Abstract

Fluid-inclusion thermometry of sphalerite and quartz from the Fukazawa mine indicates that the minerals formed in the temperature range of 250°C to 350°C from a fluid with a salinity that varied from 2.1 to 5.2 weight percent NaCl equivalent. Homogenization temperature and salinity are positively correlated for sphalerite and some quartz. The slope of a regression line through data points from one sample is equivalent to the slope of a line of constant density suggesting that density may have been a factor in controlling the temperature-salinity gradient. Local thermal and chemical gradients may have helped in the formation of zones of chalcopyritization. Chalcopyrite-bearing fluid inclusions in sphalerite have hotter homogenization temperatures (350°C) than any other inclusions measured and may contain fluids responsible for chalcopyritization.