Supergénny jarosit v metalydite na lokalite Betliar-Turecká (Slovenská republika)

Jarosite was identified for the first time in the metalydite of the Bystrý potok Formation ofthe Gelnica Group in the Southern Gemeric Unit of the Western Carpathians (Slovakia) atthe locality Betliar-Turecká. In metalydite, jarosite forms granular aggregates with smalltabular to pseudocubic crystals, occurring as pseudomorphs after pyrite or as crystalswithin muscovite interlayers. Pyrite was not preserved in the studied metalydite as it wascompletely replaced by secondary jarosite. Pyrite is present as an accessory mineral in theaccompanying graphitic-muscovite phyllites, locally in the metalydite. The sulphur necessaryfor jarosite formation comes from the breakdown of pyrite, while the source of potassiumis muscovite. During the supergene process, low pH fluids attack muscovite, releasing K+needed for jarosite formation. Chemical composition investigated by EPMA and based onthe Raman spectroscopy showed that, jarosite is typical with dominant Fe3+ in the intervalof 2.86–2.97 apfu and K+ in the range of 0.76–0.94 apfu. It contains minor amounts of Na+up to 0.13 apfu, H3O+ up to 0.11 apfu, As5+ up to 0.08 apfu and Pb2+ up to 0.01 apfu. Thesource of sodium in the jarosite is probably derived from muscovite, as no feldspars or clayminerals have been identified in the metalydite. The arsenic in the jarosite is probably sourcedfrom arsenic-rich pyrite, while the source of lead may be attributed to galena, relatedto hydrothermal processes within nearby metamorphic manganese mineralization. Thephosphorus in the jarosite likely originates from accessory apatite, which is found withinthe surrounding acidic metavolcanoclastics and phyllites that host the metalydite horizons.