Occurrences and characterization of alunite group minerals from the Lece-Radan Oligo-Miocene volcanic complex (Serbia)

Abstract

The Lece-Radan area of the Oligo-Miocene magmatic complex (former Tethyan active margin, southern Serbia) contains more or less altered volcanic and/or pyroclastic rocks of predominant andesitic, andesitic-dacitic, to dacitic composition. Alteration seen at exposures varies in type and intensity. Samples with documented alunitization were collected from hydrothermally altered zones embedded within local geological units of Oligo-Miocene age. Mineralogical-chemical study has confirmed for the first time the presence of alunite group minerals (thirty-one occurrences) in this area. The minerals of the alunite group described exhibit different compositions that are remarkably consistent with both different alteration types and host lithologies. Six samples characterized in detail show the following solid solutions: Alu52Nal43Sch5, Alu48Nal40Sch12, Nal48Alu35Sch17, Nal44Alu35Sch21, Alu36Sch33Nal31 and Sch46Alu27Nal27 (Alu, Nal and Sch refer to alunite, natroalunite and schlossmacherite, respectively). The cross-cutting alunite-bearing fracture pattern and its density indicate a high-sulphidation epithermal palaeoenvironment. The alunite discovery is consistent with the structural setting (fracture frequency) emphasizing its dominant role in controlling the local mineralization.