Mineralization of the Arakawa No.4 Vein of the Kushikino Mine, Kagoshima Prefecture, Japan

Abstract

Mineralization of the Arakawa No. 4 vein, one of the representative veins in the Kushikino mine, was investigated. Four periods of mineralization are recognized. They are, from earlier to later stages, period I (quartz-calcite zone), period II (high grade "Ginguro" ore zone containing polybasite, electrum, pyrite and tetrahedrite), period III (brecciated quartz-calcite-clay zone), period IV (banded "Ginguro" zone containing polybasite, electrum and pyrite). Period II can be divided into earlier one (period IIa containing polybasite and pyrite) and later one (period IIb containing electrum, polybasite, pyrite, sphalerite and chalcopyrite). No compositional variations were found in electrum and tetrahedrite. On the other hand, decrease of iron content of sphalerite, and increases of selenium contents of polybasite and naumannite-acanthite series minerals from earlier to later stage were observed. Filling temperature of fluid inclusions decreases slightly from earlier to later periods; 240-200°C for period I, 240-180°C for period II and 220-170°C for period IV. Based on the variations in the iron content of sphalerite and filling temperatures of fluid inclusions, sulfur fugacity for period II is estimated to be 10^-11-10^-13 atm. Decreasing of temperature under the relatively oxidizing environments can explain the variations of selenium contents of polybasite and naumannite-acanthite series minerals.