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

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 bee n studied at three different types of deposit, mostly by fluid inclusion and stable isotope techniques. 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 (~550 m) from fluids of mixed magmatic and meteoric origin. 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 (~270-140°C) related to decrease in erosion level from ~500 to ~50 m. 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 to <380°C) accompanied by Ferich salt melt. Gold precipitated in a high-temperature but low-pressure subvolcanic environment.

Mineralogical and physico–chemical properties of bentonites from the Jastrabá Formation (Kremnické vrchy Mts., Western Carpathians)

“…(Konečný et al 1983). The results of K-Ar isotope dating of Kraus et al 1994;Koděra et al 2014). Bentonite deposits: Stará Kremnička -Jelšový potok (1); Stará Kremnička III (2); Lutila I (3); Lutila -Pod Klapou (4); Bartošova Lehôtka (5); Kopernica (6) and Dolná Ves (7).…”

“…The thickness of bentonite beds ranges from a few metres up to 50 m (Šamajová et al 1992). The bentonite beds are often interbedded with limnic/lacustrine silicites which are formed by SiO 2 discharge from the subsurface hydrothermal fluids upon reaching the local limnic/lacustrine basins (Koděra et al 2014). The previous studies have reported that bentonite deposits of the Jastrabá Fm.…”

“…The results of recent studies have shown a strong effect of subsurface hydrothermal fluids (deeply-circulating, mostly meteoric waters, driven by heat from the contemporaneous rhyolite magma chamber) on the bentonitization of rhyolitic volcanoclastics from the Jastrabá Fm. (Demko et al 2010;Koděra et al 2014).…”

Gold-transporting hydrothermal fluids in the Earth's crust: an introduction

“…One is dedicated to currently exploited deposits of the Central Slovakia Volcanic field and another to a sedimentary-hosted epithermal prospect from the Tertiary Eastern Rhodopes (Bulgaria). The Rozália, Kremnica, and Biely Vrch mines studied by Koděra et al (2014) are three epithermal-porphyry deposits of economic importance currently exploited in the Central Slovakia Volcanic field of the Carpathian arc, one of the most important AuAg mining regions of Europe since the 14th -15th century. The peculiarity of these Neogene deposits is that they form different styles of Au deposits within two coalescent stratovolcanoes (Š tiavnica and Javorie).…”

“…At Kremnica and Rozália, the mineralization is hosted by coupled sets of transtension/extension faults filled with quartz, carbonates and sulphides (pyrite, galena, sphalerite, chalcopyrite, proustite, pyrargyrite), while at Biely Vrch the deposit is made of a Au-bearing stockwork of quartz, sulphides and Fe-Ti oxide crosscutting an hydrothermally altered rock rich in kaolinite, pyrophyllite, chlorite and K-feldspar. Koděra et al (2014) constrain the properties of the Au-transporting ore fluids of these deposits using a dataset made of fluid inclusion microthermometry, oxygen and carbon isotope analyses, and quantification of clay mineral abundance of altered rocks by XRD analyses. These data are used in conjunction with age relationships and well-constrained field relationships to propose a genetic model of the three deposits.…”