Hydrothermal fluids in epithermal and porphyry Au deposits in the Central Slovakia Volcanic Field

Abstract

Abstract The Neogene Central Slovakia Volcanic Field in the Carpathian arc contains various Au deposits, hosted by central zones of large andesite stratovolcanoes. Fluids involved in mineralization have been studied at three different types of deposit, mostly by fluid inclusion and stable isotope techniques. The Rozália mine in the Štiavnica stratovolcano hosts intermediate sulphidation-style Au–Ag epithermal mineralization in subhorizontal veins related to hydrothermal activity during an early stage of caldera collapse. Associated fluids of low salinity underwent extensive boiling at 280–330 °C on transition from suprahydrostatic towards hydrodynamic conditions at shallow depths ( c. 550 m) from fluids of mixed magmatic and meteoric origin. The Kremnica ore field hosts a large system of low sulphidation-style Au–Ag veins contemporaneous with rhyolite magmatism and situated on resurgent horst faults. Fluids were of low salinity, predominantly of meteoric origin, and showed gradual decrease in temperature along the system ( c. 270–140 °C) related to a decrease in erosion level from c. 500 to c. 50 m. The Biely Vrch Au-porphyry deposit in the Javorie stratovolcano is associated with quartz stockwork in diorite porphyry intrusion. The major type of ore-bearing fluid was high temperature magmatic vapour (720–<380 °C) accompanied by Fe-rich salt melt. Gold precipitated in a high-temperature but low-pressure subvolcanic environment. Supplementary material: Stable isotope data and fluid inclusion microthermometric data are available at http://www.geolsoc.org.uk/SUP18752 .