Characterization of Co-Rich Ferromanganese Crust Fields within the Johnston Island EEZ (Central Pacific)

The consolidated mineral deposits of ferromanganese crusts occur, in general, on summit and slope regions of seamounts and show Co, Ni and Mn concentrations which might be of economic interest. Two generations of growth are observed from which the older one is somewhat enriched in Pt. The depth range of high quality crust fields regarding metal concentration, thickness, and local coverage lies between 1,000 and 2,200 m. The research work carried out on the Midpac-3 cruise (November and December 1986) included dredging operations, TV-controlled grab sampling, sediment and water sampling, underwater photography and television record by the Ocean Floor Observation System (OFOS), and current meter deployments. Bottom photos in combination with video tapes recorded during all of the underwater camera stations and bathymetric mapping by the seabeam system have been used to carry out a first resource assessment. The local environment and geological situation with regard to crust abundance, microtopography, and obstacle frequency will be presented.