Mechanism for nucleation and growth of manganese nodules

FERROMANGANESE oxide crusts and concretions cover vast areas of the sea floor 1,2 and the relatively high concentrations of cobalt, nickel and copper in manganese nodules, together with the high population densities of polymetallic nodules on certain sea beds, such as the North Pacific Equatorial Belt 3 , mean that these marine sediments are potential ore deposits. A fact that is often overlooked, however, is that in many sedimentary environments most of the manganese and iron does not accumulate in the form of ferromanganese nodules, but instead is distributed throughout the sediment in the form of dispersed microscopic concretions 4 . A fundamental problem in accounting for the origin and distribution of polymetallic nodules is to explain the nucleation and growth of the host ferromanganese oxide phases. We demonstrate here that crystal-structure relationships between host manganese (IV) oxide and iron (III) oxide hydroxide phases control the authigenesis, mineralogy and metal enrichments of manganese nodules.