Selenium-Rich Ag–Au Mineralization at the Kremnica Au–Ag Epithermal Deposit, Slovak Republic

Abstract

Selenium-rich Au–Ag mineralization has been discovered in the Kremnica ore district, central Slovakia. The mineralization is hosted by a single quartz–dolomite vein hosted by Neogene propyllitized andesites of the Kremnica stratovolcano. Ore mineralogy and crystal chemistry of individual ore minerals have been studied here. The early base-metal ore mineralization composed of pyrite, sphalerite, and chalcopyrite lacks selenium, whereas the superimposed Au–Ag paragenesis is Se-enriched. The Au–Ag alloys, uytenbogaardtite, minerals of the galena–clausthalite series, acanthite–naumannite series, diaphorite, miargyrite, pyrargyrite–proustite, polybasite group, minerals of the tetrahedrite group and andorite branch (andorite IV, andorite VI, Ag-excess fizélyite), freieslebenite, and rare Pb–Sb sulphosalts (scaiinite, robinsonite, plagionite) have been identified here. Besides selenides, the most Se-enriched phases are miargyrite, proustite–pyrargyrite, and polybasite–pearceite, whose Se contents are among the highest reported worldwide. In addition, one new phase has been found, corresponding to a Se-analogue of pearceite containing 2.08–3.54 apfu Se. The style of mineralization, paragenetic situation, and chemical trends observed in individual minerals are comparable to those of Au–Ag low-sulphidation epithermal Au–Ag mineralizations of the Kremnica and neighboring Štiavnica and Hodruša-Hámre ore districts. However, the pronounced enrichment in selenium is a specific feature of the studied vein only.