Acta Musei Moraviae

Furutobeite and betekhtinite from the ore deposit Horní Benešov in the Nízký Jeseník Mts. – Czech Republic

The occurrence of two rare Pb-Ag-Cu-Fe sulphides, furutobeite and betekhtinite, is described from the Devonian Zn-Pb stratiform deposit of Horní Benešov. Both minerals were found within post-metamorphic veinlets (cutting the pyrite-sphalerite-galena stratiform ore) associated with galena, digenite (both forming myrmekitic intergrowths), covellite, pearceite, stromeyerite, tennantite, quartz and barytocalcite. Aggregates of furutobeite, up to 0.4 mm, display significant substitution of Ag for Cu (0.21–1.05 apfu Ag), and slightly elevated content of Zn (0.09–0.17 apfu). Betekhtinite grains, up to X0 μm in diameter, exhibit also elevated Ag and Zn contents (0.09–0.11 and 0.01–0.08 apfu, respectively). The fluid inclusion study of associated quartz indicates the long-lasting fluid activity, which is manifested by the presence of three types of low-temperature (< 200 °C) aqueous fluids in primary fluid inclusions: 1) low-salinity Na-Mg-Cl „metamorphic“ fluids; 2) high-salinity Ca-Na-Cl fluids with high NaCl/CaCl₂ ratio; 3) high-salinity Ca-Na-Cl fluids with low NaCl/CaCl₂ ratio. The role of high-salinity aqueous solutions for remobilization of heavy metals from the stratiform ores, is emphasized generativy giving rise to the Ag-Cu-enriched vein assemblage.