Stable isotope and fluid inclusion study of epithermal polymetallic mineralization near Štěpánov nad Svratkou (Svratka Dome, Moravicum)


Authors: Malý K, Dobeš P

Published in: Bulletin of Geosciences, volume 76, issue 1; pages: 15 - 22;

Keywords: Moravicum, Svratka Dome, polymetallic mineralization, stable isotopes, fluid inclusions,

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Two types of polymetallic mineralization in the surroundings of Štěpánov nad Svratkou in the NW part of the Olešnice Group (Svratka Dome of the Moravicum) were studied: 1) Pb-Zn(-Sb) type of mineralization with sphalerite, galena, quartz, Mg-Fe carbonates and rarer Sb minerals and barite; 2) Cu-Pb(-Zn) type of mineralization represented by chalcopyrite, galena, quartz, calcite, barite and abundant secondary Cu minerals. The calculated δ34Sfluid values for both the types of mineralization range between +9 and +11 ‰ CDT, and indicate that sulfur of the hydrothermal fluid comes from country rocks. The calculated δ13Cfluid values vary from -9 to -3 ‰ PDB for the Pb-Zn(-Sb) mineralization and from -9 to -5 ‰ PDB for the Cu-Pb(-Zn) mineralization. The carbon of the surrounding marbles and the carbon of the original organic matter of graphitic rocks are assumed to be the source of carbon of this isotopic composition. Water of the hydrothermal fluid had the isotopic composition of δ18Ofluid between +3 and +12 ‰ SMOW for the Pb-Zn(-Sb) mineralization and between -7 and +9 ‰ SMOW for the Cu-Pb(-Zn) mineralization. Stable isotope and fluid inclusion data suggest that the Pb-Zn(-Sb) type of mineralization formed at temperatures of up to 250 °C and pressures of about 50 MPa from water-rich hydrothermal fluid with moderate salinity. The Cu-Pb(-Zn) mineralization formed from low-salinity H2O-type fluid at temperatures of up to 130 °C and pressures not exceeding 10 MPa. The waning stage of the hydrothermal system is characterized by infiltration of lower salinity and temperature fluids with low δ18O values. Based on the obtained data, hydrothermal ore-bearing fluids were high δ18O fluids, which isotopically equilibrated with metamorphic rocks at high temperatures (metamorphic waters s. l.). Meteoric waters took part in the formation of late stage of Cu-Pb(-Zn) mineralization. The genetic connection of the mineralization with a magmatic body or with tectonic lines of higher order is improbable.