Metamorphic manganese mineralisation bound to the metacarbonate lenses at the Smolník - Malá Hekerová deposit in the Spišsko-gemerské Rudohorie Mts., Western Carpathians (Slovakia)

Abstract

Metamorphic manganese mineralisation recently studied at the Smolník - Malá Hekerová deposit is situated within the Early Paleozoic metamorphic volcano-sedimentary sequences of the Bystrý potok Formation (Gelnica Group, Gemericum), Spišsko-gemerské rudohorie Mountains, Slovakia. The manganese mineralisation is associated with metacarbonate bodies, within which Mn-rich calcite, spessartine, titanite, stilpnomelane, fluorapatite and pyrite have been identified. Stilpnomelane is enriched in Mn (up to 2.32 apfu) and Mg (up to 1.68 apfu), while being depleted in Ca, K, Ba and Na. It is considered a retrograde phase formed by the partial dissolution of spessartine. The carbonate-silicate bodies hosting the manganese mineralisation consist of rhodochrosite, kutnohorite, calcite, rhodonite group minerals, spessartine, tephroite, pyrosmalite-(Mn), magnetite, pyrophanite, clino-suenoite, clino-ferro-suenoite, actinolite, clinochlore, chamosite, caryopilite, greenalite, quartz, alabandite, pyrite, pyrrhotite, galena, sphalerite and chalcopyrite. This manganese assemblage is the result of multistage metamorphism during the Variscan and Alpine tectono-metamorphic evolution, which led to distinct mineral associations influenced by the release or incorporation of Fe-rich fluids, silicate alterations and recrystallisation. The multi-stage development is most evident in spessartine crystals, which exhibit chemically strongly distinguishable zones. The presence of significantly Fe-rich tephroite (with up to 31 mol% fayalite), pyrosmalite-(Mn) (with up to 2.39 apfu Fe), magnetite, pyrophanite, rhodochrosite and quartz inclusions in spessartine preserves the primary chemical composition of the later developing manganese ore. This suggests it formed concurrently with nearby magnetite lenses, as observed in the other Western Carpathian occurrences. Post-Variscan hydrothermal activity led to a greater accumulation of sulfides at the studied occurrence.