Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Martin Števko, Matej Rybárik, Peter Koděra, Pavol Myšľan, Ján Prcúch, Tomáš Mikuš

Helvine and associated minerals from the Banská Hodruša Au-Ag-Pb-Zn-Cu deposit, Slovakia: on the origin of beryllium and boron in epithermal systems

Journal of Geosciences, volume 70 (2025), issue 2, 87 - 104

DOI: http://doi.org/10.3190/jgeosci.0037.25

An unusual hydrothermal Mn-Be mineralization was recently discovered at the Banská Hodruša intermediate-sulfidation epithermal deposit, Slovakia. Mn-Be mineralization occurs in dense stockwork of the stage 2 quartz-rhodonite-rhodochrosite veins (Karolína type) and it is represented by helvine, minerals of the rhodonite and epidote group, johannsenite-diopside series and axinite-(Mn) accompanied by minor Mn-rich clinochlore, adularia, pyrite, sphalerite, chalcopyrite, hematite as well as abundant younger Ca-rich rhodochrosite and calcite and rarely also anhydrite. Helvine from the Banská Hodruša deposit is compositionally close to the end member (content of Mn is between 3.50 to 3.98 apfu) with only minor presence of genthelvine (Zn up to 0.22 apfu) and danalite (Fe up to 0.20 apfu) constituents. Rare occurrence of hydrothermal axinite-(Mn) containing dominant Mn (1.83 to 2.10 apfu) and only subordinate amounts of Fe (up to 0.29 apfu) and Mg (0.11 apfu) is also notable. Beryllium and boron at the Banská Hodruša deposit were likely introduced by magmatic-hydrothermal fluids with increased activity of manganese. Homogenisation temperatures and salinities obtained from fluid inclusions hosted directly in helvine and associated quartz are typical for intermediate sulfidation epithermal deposits (259 to 309 °C, 1.9 to 6.3 wt. % NaCl eq.) with a slightly increased salinities compared to most fluid inclusions at the studied deposit. Persistent boiling is probably responsible for increased salinity of fluids and fractionation of Be and B in residual fluids which were trapped in cavities and fissures in veins. The resulting increased activities of Be and B along with cooling are probably responsible for the precipitation of helvine, axinite-(Mn) and associated minerals.