Ferenc Š., Mikuš T., Kopáčik R., Vlasáč J. & Hoppanová E., 2022: Cu-(U) mineralisation in the copper sandstones at Šafárka occurrence near Novoveská Huta (Spišská Nová Ves), Spišsko-gemerské Rudohorie Mts., Western Carpathians, Gemeric Unit, eastern Slovakia. Acta Geologica Slovaca, 14, 2, 87–101.

Cu-(U) mineralisation in the copper sandstones at Šafárka occurrence near Novoveská Huta (Spišská Nová Ves), Spišsko-gemerské Rudohorie Mts., Western Carpathians, Gemeric Unit, eastern Slovakia

Štefan Ferenc¹, Tomáš Mikuš², Richard Kopáčik¹, Jozef Vlasáč² & Eva Hoppanová¹

¹Department of Geography and Geology, Faculty of Natural Sciences, Matej Bel University, Tajovského 40, 974 01 Banská Bystrica, Slovakia, stefan.ferenc@umb.sk
²Earth Science Institute of the Slovak Academy of Sciences, Ďumbierska 1, 974 11 Banská Bystrica, Slovakia

Abstract

Several occurrences of copper sandstone mineralisation type occur in the Permian volcano-sedimentary sequences of the Northern Gemeric Unit (Spišsko-gemerské Rudohorie Mts.). The object of presented mineralogical research was Cu-(U) mineralisation in the copper sandstones at the Šafárka occurrence, located about 4 km SE of Novoveská Huta (part of Spišská Nová Ves district town). Cu-(U) mineralisation was formed in fine-grained psammites of greenish-grey colour. The surface of the samples is limonitised, with coatings of green Cu and U supergene minerals. The main rock-forming mineral is quartz. Carbonate (probably authigenic), muscovite and fragments of sericite shales or highly altered volcanics are present to a lesser extent. Accessories represent K-feldspar, tourmaline and leucoxenised Fe-Ti oxides. Rock matrix is formed mainly by sericite and fine-grained quartz. Ore minerals (chalcopyrite, pyrite – also var. bravoite, tennantite-(Fe), uranium-bearing leucoxene) form disseminations and veinlets in sandstones. Supergene minerals of Fe, Cu, and U (chalcocite, yarrowite, uranophane-α, goethite, malachite, baryte, anglesite, and cinnabar) fill microscopic cavities and cracks in the rock. Based on the chemical composition, the studied pyrite can be divided into several groups: a) pyrite with a minimum content of admixtures (composition almost corresponding to the formula FeS₂; b) As-bearing pyrite; and c) Ni- and Co-bearing bravoite. Arsenic most likely enters the anionic position of pyrite by the substitution As^1- ––> S^1- and is probably present in solid solution. Zonality of bravoite is caused by ranging in Ni content and the corresponding fluctuations in Fe content (negative correlation), at a relatively constant Co content. Studied bravoite represents a nice example of the preferred concentration of Ni at the edges of the crystals and growth zones. Formation of uranophane-α documents the neutralisation of the environment during weathering of sandstones. Precipitation of baryte and anglesite caused an increase in the pH of the environment (from acid to the slightly basic), which allowed the precipitation of uranophane-α and malachite.

Key words: Western Carpathians, Gemeric Unit, Permian, sandstones, copper, uranium, red-ox conditions

Manuscript received: 2022-02-10

Revised version accepted: 2022-08-23