Acta Musei Moraviae

Primary gold mineralization from Hory near Předín, western Moravia

In the Předín ore district, gold was exploited between 13th and 16th century. Gold-bearing quartz veins penetrate Moldanubian sillimanite-biotite gneisses and quartzites at three sites near Hory village (localities “Štůlně”, “Malý Štítek” and “Zákopy”). The Předín district is characterized by simple mineral assemblages in quartz veins. Fine-grained, ochre-coloured quartz or rarely limonitized white quartz are the typical gold-bearing ores (Štůlně, Malý Štítek). At Zákopy, the gold-bearing white translucent quartz forms tiny veinlets in the quartzite. Besides gold, the only commonly occurring ore mineral is pyrite. Rare primary accessory phases include acanthite, galena, chalcopyrite and unidentified Ni, As, S-bearing phase. Limonite, barite and goethite are supergene minerals. Gold typically fills infrequent small vugs in quartz. It commonly contains 17–34 wt. % Ag which is the only element present in elevated amount. Sporadically, isometric inclusions or tiny veinlets of gold significantly depleted in silver (1.5–4.2 wt. % Ag) were observed. Fluid inclusions were studied in quartz gangues. Only aqueous fluid inclusions were identified, the fluid system is H₂O-MgCl₂-NaCl with bulk salinity between 2.4 and 9.9 wt. % NaCl eq. The temperatures of homogenization range between 129 and 259 °C for primary inclusions. Both the relatively low homogenization temperatures and apparent absence of volatiles in fluid inclusions are distinctly different from the other gold-bearing mineralizations in Moldanubicum. The origin of goldbearing fluids is probably related to the late-magmatic and/or late-metamorphic fluids, however, the available data do not allow definite conclusion.