Precious-metal ore mineralizations in central Slovak volcanic field
Final Report Abstract
According to bulk chemical analysis, the Au content reaches up to 116 g/t and Ag up to 1110 g/t. The mineralisation is hosted by partially hydrothermally brecciated, silicified, and sericitized andesitic-dacitic subvolcanic rocks and is very different depending on the sites. In Banská Belá, the Ag minerals are acanthite, polybasite-pearceite, pyrargyrite, stephanite, rare proustite and freibergite and form mostly inclusions in pyrite. In Rabenstein, pyrargyrite and freibergite are the dominant Ag carriers and occur as intergrowths with galena and chalcopyrite. In Kopanice, the main Ag mineral is acanthite and often rimmed by an unnamed Ag-Fe(Ni) or AgSe(Te) sulfide. At Treiboltz, hessite and benleonardite (both tellurides) are the dominant Ag minerals, both associated with galena. In Nová Baná, the main Ag carriers are pyrargyrite and miargyrite. Electrum and uytenbogaardtite occur in all sites except for Treiboltz. The precipitation of the precious metal minerals always appears to be postdate the formation of the base-metal sulfides. Some of them were most likely formed by processes of secondary enrichment in the cementation zone. Analyses of fluid inclusions indicate fluids with low salinity (0-3 wt% NaCl eq.), which is typical for low sulfidation epithermal systems. Homogenisation temperatures varied mostly between 190 and 240 °C, depending on the part of the vein system. Abundant co-existence of liquid- and vapor-rich inclusions in several samples indicates boiling offluids,which was the likely reason for precipitation of gold. Assuming hydrostatic pressures, boiling occurred from 12 to 35 bars, corresponding to paleodepth of boiling 130 to 400 m, reflecting variable erosion level of individual parts of the vein system.
Publications
- (2014): Mineralogy of the Medieval Ag-Au occurrences Banská Belá, Treiboltz, Rabenstein, and Kopanice in the Banská Štiavnica ore district (Slovakia). N. Jb. Miner. Abh. (J. Min. Geochem.) 191/3
Berkh, K., Majzlan, J., Chovan, M., Kozák, J., Bakos, F.
(See online at https://doi.org/10.1127/0077-7757/2014/0259)
