Cobalt-rich ferromanganese crusts from the Central Pacific

Ferromanganese crusts coat most hard substrates on seamounts, ridges, and plateaus in the centralPacific basin. Crusts from less than 2500 m water depth are rich in Mn, Co, Ni, Pb, and Pt. Samples we collected from the EEl of the Hawaiian, Johnston, Palmyra, and Marshall Islands are discussed. Necker Ridge in the Hawaiian EEl has the greatest average crust thickness of 4 em. The dominant mineral in all crusts is o-Mn02' Substrate rocks are dominantly volcanic breccia. Slumping and turbidity currents on the flanks of the submarine edifices partly control crust thicknesses by burial and dissolution or erosion. Regional variations in crust chemistry and mineralogy can be related to various oceanographic and geologic conditions. Of the areas examined in Some detail, the EEl of Johnston, Palmyra, and the Marshall Islands hold the greatest economic potential.