Description and chemical composition of ferromanganese encrustations and deposits in the Atlantic Ocean from R/V Atlantis II cruises 20, 42, 60, 85; R/V Chain cruise 35; R/V Knorr cruise 61 and RRS Shackleton cruise 75/1 stations

Chemical and mineralogical compositions of ferromanganese oxide coatings on rocks dredged from the New England Seamounts, the Sierra Leone Rise and the Mid-Atlantic Ridge near the Equator have been determined in an investigation of regional differences in Atlantic ferromanganese deposits. Most encrustations are clearly of hydrogenous origin, consisting mainly of todorokite and delta MnO2, but several recovered from the equatorial fracture zones may be hydrothermal accumulations. Differences in the chemistry of the water column and in growth rates of the ferromanganese coatings may be important in producing this regional contrast in composition. Fine-scale changes in element abundances within the encrustations indicate that the nature of the substrate has little influence on compositional variations.

Chemical composition of Lake George (New York) iron-manganese nodules and underlying sediment

Lake George, New York, is the site of a new discovery of iron-manganese nodules. These nodules occur at a water depth between 21 and 36 m along a stretch of lake extending for about 5 mi north and south of the Narrows, a constricted island-dotted area which separates the north and south Lake George basins. Nodules occur on or within the uppermost 5 cm of a varved glacial clay. Some areas are solidly floored with a carpet of nodules in areas where active currents keep the nodules exposed. The nodules form around nuclei which consist of clay and less commonly of spore capsules, detrital particles, or bark. By their shape we recognize three types of nodules: spherical, discoidal, and lumps. On X-ray examination all nodules show small goethite peaks; in one nodule the manganese mineral birnessite was identified. Manganese and part of the iron appears to be in X-ray amorphous ferromanganese compounds. The Lake George nodules are enriched in iron with respect to marine nodules but are lower in manganese. They have a higher trace element concentration than nodules from other known freshwater lake occurrences, but a lower concentration than marine nodules.