Mineralogy and chemistry of ferromanganese crusts from the Atlantic Ocean

The mineral and chemical compositions of a set of crust samples collected from the North, Central and South Atlantic were examined by means of analytical electron microscopy and ICP-MS, chemical, and microchemical elemental analysis. The dominant mineral phases of the crusts are vernadite, asbolane, and goethite, with minor ferrihydrite, and rare hematite and feroxyhyte. The samples show wide variability in major and trace elements; however, their characteristic geochemical signatures indicate hydrogenetic origin. A comparison between the compositions of oceanic hydrogenetic and hydrothermal crusts and metalliferous hydrothermal sediments from different ocean areas suggests that the geochemical approach may be insufficient in some cases and fail to identify a hydrothermal input in ferromanganese crusts of a mixed composition.