Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Karel Žák, Lukáš Ackerman, František Veselovský, Jan Pašava, Petr Dobeš, Martin Svojtka, Robert A. Creaser

Multistage hydrothermal vein mineralization in low-grade metamorphosed rocks: Chříč locality, Teplá-Barrandian Unit, Bohemian Massif, Czech Republic

Journal of Geosciences, volume 68 (2023), issue 4, 281 - 299

DOI: http://doi.org/10.3190/jgeosci.381

A small and isolated hydrothermal vein-type Sb deposit is hosted by a lamprophyre dike which penetrated Neoproterozoic to early Cambrian volcanosedimentary successions near Chříč in the Teplá-Barrandian Unit, Czech Republic. Hydrothermal minerals were formed in several consecutive mineralization stages, separated by long pauses in hydrothermal fluid flow. Early Stage I is characterized by the formation of carbonates of dolomite-ankerite series (Carb I) and arsenopyrite with an imprecise Re-Os age of ~570 to 510 Ma. Stage I was followed by tectonic movements and brecciation. The second mineralization stage (Stage II) is characterized by the precipitation of quartz (Qtz I) and Sb minerals (predominantly stibnite) while the third stage (Stage III) is marked by the presence of carbonates of dolomite-ankerite series (Carb II) and quartz (Qtz II) along with Cu, Zn, Pb, Ag and Fe sulfides. Lead isotope data of galena indicate a Variscan age of Stages II-III. These stages were followed by precipitation of another generation of carbonate of dolomite-ankerite series (Carb III, Stage IV), quartz (Qtz III, Stage V) and formation of Sb supergene minerals. The earlier reported occurrence of gold was not confirmed in the studied rock samples but three types of gold particles of variable fineness, with one of them indicating a local origin, were found in the heavy mineral concentrate from a local creek. Elevated Au concentrations were found in arsenopyrite and pyrite. The ore-forming hydrothermal fluid of the mineralization stage III was of H₂O-CO₂ type with minor CH₄ admixture, medium salinity, and temperatures in the range of 258-350 °C with an observed temperature decrease from Stage II to Stage V. Oxygen isotope data of Carb II correspond to high δ¹⁸O_fluid values (~ +7.5 ‰ VSMOW) with a decrease in the fluid δ¹⁸O to later stages. An important part of the carbonate carbon was derived from decomposition of organic matter or its high-temperature reaction with hydrothermal fluid. Considering the wide variation in δ³⁴S values of sulfides and elevated Sb contents in the TBU black shales, we anticipate that the origin of the Chříč mineralization is closely associated with a metal and carbon-sulfur remobilization from the TBU volcanosedimentary successions in response to Cadomian and Variscan tectonothermal events.