107 Supergene Pb-Cu-(Sb) mineral assemblage in abandoned epithermal deposit Rudno nad Hronom, Slovakia Jozef Vlasáč 1 , Tomáš Mikuš 1 , Martin Ondrejka 2 , Peter Žitňan 3,4 & Peter Tuček 5 1 Earth Science Institute, Slovak Academy of Sciences, Ďumbierska 1, 974 01 Banská Bystrica, Slovakia; vlasac@savbb.sk, mikus@savbb.sk 2 Department of Mineralogy, Petrology and Economic Geology, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, 842 15 Bratislava, Slovakia; martin.ondrejka@uniba.sk 3 Rudné Bane, Kammerhofská 7, 969 01, Banská Štiavnica, Slovakia; zitnan@rudnebane.sk 4 Department of Geology and Palaeontology, Faculty of Natural Sciences, Comenius University in Bratislava, Ilkovičova 6, 842 15 Bratislava, Slovakia; zitnan2@uniba.sk 5 Prospech Ltd., Križovatka 25, 969 01, Banská Štiavnica, Slovakia Abstract: An unusual assemblage of Pb-Cu-(Sb)-(Mn) supergene minerals, represented by mottramite, phosphohedyphane, mimetite, minerals of the segnitite-beudantite series, anglesite, cerussite, oxyplumboroméite, brochantite, devilline, gypsum and coronadite was recently identifed at the Priečna, Johan de Deo and Anna-Zubau epithermal ore veins near Rudno nad Hronom, Štiavnické vrchy Mts., Slovak Republic. Mottramite is a rare mineral at the Rudno deposit and this is the frst reported occurrence in the Western Carpathians. Also phosphohedyphane occurs only rarely at the deposit. The Pb 2+ <––––> Ca 2+ substitution between phosphohedyphane and pyromorphite was observed. An extensive substitution between As and S was recognised on the T site in the minerals of the beudantite – segnitite series. Anglesite and cerussite are relatively abundant supergene minerals, especially in the proximity of primary galena relicts. Secondary Cu sulphates (brochantite and devilline) are only secondary minerals found also in macroscopic size. Brochantite forms dark green tabular crystals up to 0.1 mm. Devilline oc- curs as a light green-blue acicular crystals grown on brochantite. Gypsum was found with this assemblage. Rare coronadite, Mn supergene mineral is also found at the Rudno nad Hronon locality. Key words: Western Carpathians, Neogene Banská Štiavnica stratovolcano, mottramite, phosphohedyphane, mimetite, seg- nitite-beudanite, devilline, brochantite, coronadite acta geologica slovaca, 13(1), 2021, 107–118 Manuscript received 2021-02-17 Revised version accepted 2021-05-25 1. INTRODUCTION Origin of secondary minerals is connected with hypogenous processes at ore deposits. Supergene Pb-Zn-Cu mineralisations in Western Carpathians are ofen subjects of mineralogical re- search, especially in the last two decades. From the base metal deposits or occurrences (Banská Štiavnica, Čavoj, Valaská Belá, Jasenie-Soviansko, Poniky-Drienok, Ochtiná – Mária-Margita and others) mimetite (Števko et al., 2015, 2018 a ), cerussite (e. g., Luptáková & Chovan, 2003; Števko & Bálintová, 2008; Števko et al., 2008, 2018a), pyromorphite (Števko et al., 2008, 2018 a ) and other lead secondary minerals – anglesite, wulfenite (cita- tions above) are known. Copper secondary mineral assemblage, represented by brochantite and devilline was recently described from the Cu deposits Špania Dolina – Piesky (Števko et al., 2013) but also from the base metal deposit Poniky – Drienok and Poniky – Farbište (Števko et al., 2011, 2018 a ) as well as from the epith- ermal deposit Hodruša-Hámre or Banská Štiavnica (Števko and Malíková 2014; Števko et al., 2018 b ). Te oxidation zone of the Rudno nad Hronom deposit is not well developed, nevertheless some interesting secondary minerals were recently recognised. Te primary epithermal precious metal (Au-Ag) and base-metal mineralisation was not object of this study. 2. HISTORY OF MINING Te name of the village implies the occurrence and exploitation of precious metals, but compared to other Central-Slovakian mining towns, Rudno nad Hronom is one of the poorest in terms of production. Gold and silver mines have existed here since 1331, but the main details on mining are recorded from the late 18 th century, when the old abandoned mines were reopened. How- ever, due to low profts, most adits were closed afer only three years of exploitation. Exploration works were unsuccessful and mining operated at a high defcient during the following years. As an example, in 1824 only 0.5 kg of gold and 34 kg of silver were recovered. Mining fnally ceased in 1876 (Bergfest, 1953). 3. GEOLOGICAL SETTINGS Te low sulphidation epithermal mineralisation occurs in the massif of Chlm hill in hydrothermally altered andesite between Rudno nad Hronom and the village of Brehy. Te deposit is formed of two groups of precious metal bearing, steeply dipping veins, striking N-S, 1-2 m thick and up to 1500 m long. Te veins are intensively altered (silicifcation and adularisation) and the hanging-wall has developed zone of the brecciated secondary quartzites (Lexa & Smolka, 2002). Te western part of the depos- it is formed by the Johan de Deo, Filip, Goldschram and Priečna vein. Te Anna vein structure occurs in the eastern part of the Chlm massif (Koděra et al., 1990). Te structure is developed along the total length of 1500 m (Smolka et al., 1988), but only a 200 m long segment at the junction of the so-called hanging-wall golden and footwall silver branch has been the subject of exploi- tation. Te thickness of the ore shoot reportedly reached 8–16 m; occasionally 42 m. Te Au-Ag mineralisation is developed