Acta Musei Moraviae

Hydrothermal mineralization in sandstones of Variegated Godula Member at the locality Bystrý potok (Moravskoslezské Beskydy Mts.)

Tiny hydrothermal veinlets hosted by Upper Cretaceous siliciclastic flysch sediments of the Variegated Godula Member (Godula Development, Silesian Unit, Outer West Carpathians) have been studied from mineralogical, fluid inclusion and stable isotope points of view. The occurrence of mineralization composed of quartz, and three populations of calcite containing isolated grains and aggregates of galena and chlorite (chamosite) is restricted only to sandstone beds. Fluid inclusions hosted by quartz trapped a heterogeneous mixture of aqueous solution and vapour phase at temperature of ~120 °C, whereas calcitehosted fluid inclusions enclosed homogeneously trapped aqueous fluids (Th = 111–155 °C). The salinities are generally low, between 1.1 and 2.6 wt. % NaCl eq. The highly positive fluid δ18O values (+6.2 to +9.5 ‰ SMOW) and variable fluid δ¹³C values (-4.3 to -9.5 ‰ PDB) have been found. The origin of the hydrothermal minerals is interpreted to be in “diagenetic” fluids that have been probably generated during deeper burial and/or subsequent tectonic deformations of the host clay-rich sedimentary rocks.