Journal of

GEOsciences

  (Formerly Journal of the Czech Geological Society)

Original paper

Pavol Myšľan, Martin Števko, Tomáš Mikuš

Mineralogy of metamorphic magnetite-manganese ores at the Prakovce - Zimná Voda prospect (Spišsko-gemerské rudohorie Mts., Slovakia): The occurrence of REE-bearing allanite-subgroup minerals ferriakasakaite and ferriallanite

Journal of Geosciences, volume 69 (2024), issue 4, 231 - 249

DOI: http://doi.org/10.3190/jgeosci.400

Manganese mineralization was discovered at the Zimná Voda occurrence near Prakovce located in the Spišsko-gemerské rudohorie Mountains, eastern Slovakia. The mineralization is hosted in the Early Paleozoic metamorphic rocks of the Gemeric Unit in the Western Carpathians and it represents the only occurrence of metamorphosed manganese mineralization discovered within the Drnava Formation (Devonian). Manganese minerals are directly associated with magnetite bodies forming isolated lenses of a strata-bound oxidic Fe-ores. The manganese mineralization underwent metamorphism during the Variscan and Alpine tectonometamorphic events, resulting in two types of distinct mineral assemblages. The older assemblage includes rhodonite-ferrorhodonite series, rhodochrosite, kutnohorite, spessartine, fluorapatite and quartz with magnetite impregnations. These assemblages are intersected by younger mineral assemblages present in veins and vugs. This later assemblage consists of rhodochrosite, kutnohorite, baryte, clino-suenoite to clino-ferro-suenoite, minerals of the epidote supergroup, quartz and relatively rare sulfidic mineralization including pyrite, galena, sphalerite and cobaltite along with hübnerite. This stage also features the formation of garnets predominantly composed of the andradite molecule, with locally preserved spessartine remnants in the garnet centres. The subsequent younger post-Variscan metamorphic event is characterized by a high influx of rare earth elements (REE), leading to the formation of a rare ferriallanite-(Ce), ferriallanite-(La), ferriakasakaite-(La) and ferriakasakaite-(Ce). Allanite-subgroup minerals form a strongly zonal polycrystalline dark brown aggregates with size up to 50 μm, generated from hydrothermal fluids affecting the mineral composition of the late-stage mineral assemblage.