Cobalt-Rich Crusts: Recognition and Preliminary Evaluations

Cobalt-rich ferromanganese oxide crusts were not routinely distinguished from manganese nodules before the 1980s but came to be recognized as a distinct class of deposits (at least from the resource point of view) during that decade. They coat exposed rock substrates on seamounts and island slopes. They contain up to 2% cobalt and elevated concentrations of some other elements relative to their concentrations in manganese nodules. They were first recognized in the Atlantic Ocean on the Blake Plateau and, in the central and western Pacific Ocean, in the Hawaiian Archipelago, and on features such as the Line Islands Ridge and the Mid-Pacific Mountains, and off some of the former US Trust Territories. Early resource evaluations indicated that they were comparable with manganese nodules in value, but presented greater difficulties in mining than the latter as they are generally firmly attached to their hard rock substrates.