The Banska Stiavnica Au-Ag-base metals, epithermal deposit is located in southern-central Slovakia (Slovak Republic), within the western Carpathians Neogene neovolcanic belt.
It has been mined for Ag, Au, Pb, Zn & Cu since the 8th century and has yielded >100 tonnes of Au and 1500 to 2000 t of Ag. Proven reserves in 1999 were 1.5 Mt @ 2.2% Pb, 3.2% Zn, 42 g/t Ag, 4.8 g/t Au, while probable reserves are of the order of 47 Mt.
The deposit occurs within a concentrically zoned volcanic caldera complex in which an early Miocene granodiorite-quartz diorite pluton has intruded pre-Cenozoic sediments, with associated magmatic andesites and rhyolite lavas. The intrusives have been variously dated at 17 to 16 Ma and 13 to 11 Ma, while the rhyolite lavas are 11.6 ±0.3 Ma.
The first phase of pre-caldera hydrothermal mineralisation comprised stockwork-disseminated base metals with advanced argillic alteration and was associated with the intrusion of quartz-diorite porphyries and granodiorite.
Post caldera hydrothermal systems are represented by 16 to 11 Ma quartz and quartz-carbonate veins with precious and base metal mineralisation accompanied by linear zones of quartz-carbonate-sericite alteration. The economic mineralisation is temporally related to this second phase and numerous quartz-diorite porphyry dykes that occur along the margin of the intrusive granodiorite stock in the central part of the caldera.
Ore is present in around 120 quartz-carbonate veins, each 0.8 up to 10 to 15 m in thickness, that extend over strike lengths of 5 to 7 km and vertical interval of 700 to 900 m. Four main mineralisation zones are recognised from bottom to top, as follows: 1). Cu zone, 2). lower Pb-Zn zone, 3). upper Pb-Zn zone, and 4). the uppermost Au-Ag zone. The mineral paragenesis has been determined to comprise: a). quartz-hematite, b). sphalerite, c). rhodonite-carbonate-quartz, d). galena-chalcopyrite, and e). Ag bearing sulfosalt-barite. Economic grades accompanied stages b), d), and e).
(Source: Porter GeoConsultancy, www.portergeo.com.au, 2000)