Primary hematite in neoarchean to paleoproterozoic banded iron formations

Abstract

Banded iron formations (BIFs) are chemical sedimentary rocks formed throughout the first two billion years of Earth’s life history. They are characterized by alternating iron- and silica-rich bands. Iron oxides (i.e., hematite and magnetite) and chert are major minerals of BIFs. It was extensively accepted that the chert was transformed from amorphous silica or silica colloids flocculated with ferric oxyhydroxides, whereas the hematite and magnetite were derived from Fe(III) oxyhydroxide precursors. Ferrous iron oxidization was supposed having occurred in the seawaters from which BIFs deposited, via anaerobic iron-oxidizing bacteria …