Acta Musei Moraviae

Gold and associated minerals from the Mír and Na barytě adits near Štěpánov nad Svratkou (Štěpánov Ore District, Czech Republic)

A mineralogical study of newly collected samples of Cu-Pb(-Zn) ore mineralization from the Mír and Na barytě adits in the Štěpánov Ore District (Czech Republic) clarified of elevated contents of Au, which were encountered in previous chemical analyses of the bulk ore. Small inclusions of Au-Ag alloys were found to be enclosed in early quartz and associated chalcopyrite. Some gold grains are zoned. The cores are formed by gold (50.1–74.2 at. % Au), whereas the rarely found rims have composition of Au-rich silver (47.9–22.8 at. % Au). In addition, pyrite, galena and sphalerite are minor ore minerals in the studied samples. The supergene phases are represented by stilpnosiderite, limonite, malachite, brochantite, and Cu-sulphides (chalcocite, djurleite, digenite/roxbyite, anilite, geerite). The origin of Ag,Sb-rich rims of gold grains could be related to aktivity Ag,Sb-bearing fluids, which operated during crystallization of late mineral assemblage of the same vein containing calcite, baryte, galena and tetrahedrite-group minerals. The new compositional data collected from accompanying minerals are partly different from published data and point out that a detailed revision of mineralogy of hypogene mineralization of this ore vein is necessary.