Manganese Crusts and Nodules from the Hawaiian Ridge1

Manganese stains, crusts, and nodules are widely distributed on the insular slopes of the Hawaiian ridge. The thickness of the manganese crusts depends on depth of water, water circulation, and the age and lithology of the substrate, and varies from absent to stains off the island of Hawaii to a maximum of 5 cm in the vicinity of Midway. Scanning electron microscope studies indicate that the internal structure of the manganese crusts is relatively featureless compared with that of deep-sea manganese nodules. Reconsideration of ages of manganese deposits from the Hawaiian archipelago indicates that the rates of accretion of manganese crusts are probably in the same range as those of deep-sea deposits and that the crusts do not accrete at a much faster rate than deep-sea deposits as previously suggested. Iron staining is observed in the volcanic substrates and becomes more apparent with the increasing age of the substrate. There appears, however, to be no evidence that iron oxide is a ubiquitous control factor in initiating manganese crustal growth. Because of the terrain and the rocky nature of the substrate, diagenetic processes within the sediment column probably play no major role in controlling the composition of manganese crusts on the flanks of the island ridge. terraces are identified on the Hawaiian ridge (Stearns 1966, 1967, Mathewson 1971, Morgenstein 1974). These terraces act as traps to downward-moving rubble on which the manganese oxides accrete. The Waho Terrace at 1100 meters, which is generally recognizable throughout the archipelago, contains the most extensive crustal deposits. The manganese deposits of the Hawaiian archipelago have recently attracted interest as a potential economic resource, particularly for cobalt, and a pr~liminary report on their distribution, mineralogy, and composition has been prepared (Frank et al. 976). We present here a short account of the morphology, internal structure, and co' position, and the role of iron oxides in initiating manganese crustal growth in thes deposits. The samples described here are hose collected from the Hawaiian chain so theast of Midway (Frank et al. 1976) an do not include those collected during e 1976 RfV Kana Keoki cruises to the leeward Hawaiian and Emperor Seamoun chains, which are still being studied.