Microbially mediated iron ore formation, Silicic Superunit, Rudabanya, Hungary

The mineralogical, petrological, geochemical and textural characterization of the Triassic Bodvaszilas Sandstone in the Rudabanya open pit and Aggtelek Mts. is summarized based on our investigations. The pore-filling carbonate cement in the Lower Triassic Badvaszilas Sandstone Formation of a proximal basin series (Rudabanya) was formed as the result of syngenetic and early diagenetic two step microbially mediated Fe mineralization (Fe-oxide formation by chemo-lithoautotrophic Fe-oxidizing microbes (FeOB) in a suboxic neutrophylic environment, and Fe-carbonate by heterotrophic microbes in a suboxic to anaerobic environment based on mineralized microbially produced textural evidences). The carbonate in the higher parts of the formation (transition between the Bodvaszilas Sandstone and the overlying formation, Szin Marl) was formed by the same metasomatic processes that produced the siderite ore in the Middle Triassic limestones and dolomites. These processes led to partial or complete Fe replacement of the syngenetic carbonate layers. Microbially mediated Fe enrichment also occurred at distal basin position in the Bodvaszilas Sandstone (Aggtelek Mts.). The formation later underwent deep burial diagenesis. (C) 2015 Elsevier B.V. All rights reserved.