ON THE OXIDATION-STATES OF MN AND FE IN POLYMETALLIC OXIDE OXYHYDROXIDE CRUSTS FROM THE ATLANTIC-OCEAN/

A general study of the oxidation states of iron and manganese in selec ted polymetallic oxide/oxyhydroxide crusts was undertaken by means of Fe-57 Mossbauer X-ray and photoelectron spectroscopies, X-ray diffract ion, and electron spin resonance. Spectroscopic analyses allowed the d ifferentiation of these crusts from their origins: ''hydrogenous'' or ''hydrothermal''. This paper shows that polymetallic oxide/oxyhydroxid e crusts with high Mn:Fe ratios (greater than or equal to 34.4) contai n manganese in the form of todorokite. When the Mn:Fe ratios in the cr usts are less than or equal to 1, spectroscopic data indicate the occu rrence of Fe(III) and Mn(IV) in the forms of goethite and delta-MnO2, respectively. In addition, Mn(III) ions incorporated inside the goethi te structure to give alpha-Fe(III)I Mn-1-x(III)(x)OOH (where x represe nts the molar fractions: x = Mn/(Mn + Fe)) are strongly suspected in t hese ferromanganese deposits. This problem is addressed in the present work from crystallographic considerations. Copyright (C) 1996 Elsevie r Science Ltd