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

Metamorphic manganese mineralization recently studied at the Smolník – Malá Hekerová deposit is located within the Early Paleozoic metamorphic volcano-sedimentary sequences of the Bystrý potok Formation, Gelnica Group of the Gemeric Unit, in the Spišsko-gemerské rudohorie Mountains, eastern Slovakia. The manganese mineralization is closely associated with metacarbonate bodies, where Mn-rich calcite, spessartine, titanite, stilpnomelane, fluorapatite and pyrite have been identified. Stilpnomelane contains increased Mn (up to 2.32 apfu ) and Mg (up to 1.68 apfu ), while being depleted in Ca, K, Ba and Na. Stilpnomelane is considered a retrograde phase, formed by the partial dissolution of spessartine under the lower greenschist facies conditions. The carbonate-silicate bodies of manganese mineralization 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 a result of multistage metamorphism during the Variscan and Alpine tectono-metamorphic evolution, resulting in characteristic mineral assemblages influenced by release or incorporation of Fe-enriched fluids, alteration of silicates and recrystallization of newly generated phases. Polycyclic development is most evident in spessartine crystals, which display chemically distinguishable zones reflecting the multi-stage metamorphic development of manganese mineralization. The presence of significantly Fe-rich tephroite (up to 31 mol.% fayalite), pyrosmalite-(Mn) (up to 2.39 apfu Fe), magnetite, pyrophanite, rhodochrosite and quartz inclusions considered as residual phases in spessartine preserves the primary chemical composition of the later developing manganese ore. This suggests its concurrent forming with nearby magnetite lenses, as well as observed at the other Western Carpathian occurrences. Post-Variscan hydrothermal activity, influenced by suitable host rocks, led to the larger accumulation of sulfides in low-pressure and low-temperature metamorphic manganese occurrences in the Western Carpathians.