Acta Musei Moraviae

Limonitized quartzites with Fe-Mn-Ba-Co ore mineralization in Svratka Dome, Moravicum, south of Maršov near Tišnov

The presented iron-bearing quartzites with oxidic Fe-Mn-Ba-Co mineralisation are situated south of Maršov near Tišnov in crystalline complex of the Svratka Dome (Moravicum). Brightly colored quartz-rich rocks mainly appear in the vicinity of “Skalky” hillock (elevation 482.6 m) and in woodland “Na salaši”, “Habří” and “Bílá skála” near Šmelcovna settlement in Bílý potok creek valley. The geological mapping has provided distribution of the studied rocks in the vicinity of a tectonic contact (Dřínová overthrust) between phyllites of the Bílý potok Unit (Moravicum) and cataclazed to mylonitized gneiss of the Deblín group (Brunovistulicum). Limonitized quartzites and accompanying barite-quartz breccias form morphologically substantial ridges or only isolated boulders and blocks. Quartzites are largely affected by multiphase alteration – silicification, “limonitization” and hematitization with Fe, Mn and Ba import and/or redistribution. It cannot be ruled out that quartzites are relicts of Devonian clastic rocks, later distinctly affected by Late Variscan hydrothermal barite mineralization. The existence of hydrothermal barite veins penetrating the quartzite as well as Devonian limestones of Lažánky-Heroltice belt is remarkable. The individual oxidic Mn-rich mineral phases as a hollandite, cryptomelane, coronadite, including thein transitional phases, pyrolusite and goethite in quartzite were detected. The intense silicification and Fe-Mn distributions related to weathering of surrounding rocks (in part kaolinization) under suitable climatic conditions during Mesozoic or Tertiary are highly probable. Isolated black manganese (± Co) concretions occur at places of appearance of the studied rocks and originated from the similar oxide mineralization but in a different environment.