Hessite from the Sado Mine, Niigata Prefecture, Iapan

Abstract

The Sado mine, Niigata Prefecture, is composed of epithermal gold-silver veins genetically related to the Neogene volcanism. It is a very old and one of the large gold mines in Japan. Many gold and silver minerals such as electrum, native silver, hessite, argentite, stromeyerite, stephanite, pyrargyrite, polybasite, antimonpearceite, and cerargyrite (Br-bearing) were identified in the ore by microscopic observation, X-ray powder and fluorescence methods, and qualitative analysis by E.P.M.A. These minerals constitute so-called "Gin-guro" (black ore rich in silver). Hessite, the first finding in this mine, occurs in patchy or massive "Gin-guro" surrounded by aggregate of chalcedonic or white quartz with adularia. This "Gin-guro" part consists of large amounts of hessite and polybasite with small amounts of electrum and pyrite. A bromian cerargyrite occurs along its crack or drusy part.