Epithermal Be-Mn mineralization at the Banska Hodrusa deposit: the first occurrence of helvin in the Western Carpathians

During the exploration activities of Slovenska banska s.r.o. on the 14^th and 16^th horizons of the Rozalia mine, a new type of Be-mineralization was discovered, represented by helvine, which is directly associated with Mn-mineralization on the Karolina-type veins. The aim of this work is the mineralogical and geochemical characteristics of this mineralization, as well as the preliminary interpretation of its genesis using the microthermal study of fluid inclusions in helvin and quartz. The helvinite mineral is typically found in granites, pegmatites and skarns. It is also rarely found in epithermal deposits such as Cavnic in Romania, Sweet Home and Sunnyside mine in Colorado or Pachapaqui mine and Caylloma area in Peru), where it is also associated with rhodonite and Mn-carbonates. The studied mineralization with helvin represents a new type of mineralization in the area of the Rozalia mine, and it is also the first occurrence of helvin in the Western Carpathians and the first recorded Be mineral on the epithermal type of mineralization in Slovakia. In addition to helvine, other minerals such as axinite-(Mn), epidote and johannsenite, which have not been described on Karolina-type veins, were also identified in the studied samples. The temperatures and salinities of the fluids from which helvin crystallized (268 - 309 grad C, 2.4 - 5.6 wt % NaCl equiv.) are similar to those from which the associating quartz crystallized and correspond to the data published by Kubac et al. (2018) for quartz from the entire Karolina vein system. Beryllium in hydrothermal fluids in epithermal systems is probably transported mainly in the form of fluoride complexes, the solubility of which decreases with temperature. The increased content of Mn and Be exclusively in the early stages of the development of the deposit indicates a connection with the preferential fractionation of these elements from the source magma into fluids after the beginning of their exsolution in the magma chamber below the stratovolcano. The authors do not assume a source of Be from the surrounding andesite. (authors)