Exceptional Tl-bearing manganese oxides from Zalas, Krakow area, southern Poland

Abstract In the Permian rhyodacite quarry at Zalas near Krakow, southern Poland, thallium-bearing Mn oxides occur in a small fault zone cutting Middle Jurassic sandy limestone poorly encrusted by an oxidized polymetallic mineralization. The encrustation comprises sulphides (pyrite, chalcopyrite, chalcocite, covellite, galena, marcasite), native bismuth, hematite, goethite, cuprite, mottramite, iodargyrite, unrecognized Cu sulphates and Bi oxychlorides as supergene minerals, barite and rare tiny grains of gold. It is most likely connected with rejuvenation of Early-Paleozoic faults during the Alpine orogeny on the Oligocene–Miocene boundary. Rare Tlbearing Mn oxides occur in an outside zone of the encrustations, filling small fractures and voids in limestone forming the fault breccia. Tl contents, reaching 20.82wt% as Tl2O, exceed by more than two orders of magnitude those reported in similar minerals before, making the oxides unique on a world scale. The Tl-bearing Mn oxides from Zalas reflect intensive weathering of an older Tl-bearing sulphide mineralization in an arid climate, involving saline fluids delivered to the groundwater system as the nappe structure of the Carpathians was developing during the Sava tectonic phase Oligocene/Miocene boundary.