Post-Caldera Epithermal Veins of the Štiavnica Stratovolcano

Abstract The post-caldera system of epithermal veins that extends over an area of 100 km2 in the central zone of the Štiavnica stratovolcano includes 120 veins, with the major veins reaching a length of 8 km. Their position in the evolution of the stratovolcano, mineralogy, alteration zoning and genetic aspects are discussed by Lexa et al. (1999) — reprinted in this volume. Here we concentrate on the aspects of the system which are not covered in that paper, including structural aspects, subdivision into mineralization types and a detailed description of the two epithermal veins to be visited. The system of epithermal veins formed on faults of the Hodruša-Štiavnica resurgent horst in the central part of the caldera. Thus, their evolution was controlled by the structural evolution of the horst. According to structural relationships, radiometric dating of associating rhyolites and radiometric dating of the epithermal veins itself, the uplift of the horst lasted almost 2 Myr, during the Middle Sarmatian to Early Pannonian (roughly 12.5 to 10.7 Ma; Lexa et al., 1999). The regional stress field during this time was dominated by strong NW-SE extension, with the maximum stress axis mostly in a subvertical position, but occasionally also in a sub-horizontal NE-SW orientation (Nemcok et al., in press). This configuration of the stress field is reflected in dip-slip as well as oblique movements on the veins. While the strong extension led eventually to the formation of low-angle and lystric vein structures with a decreasing dip with the increasing depth, the dextral lateral