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ABSTRACT: Marine Mineral Resources of the Central Indian Basin: Ferromanganese Nodules and Crusts

Prattipati S. Rao, Ravindra R. Nair

The Central Indian basin and adjacent Carlsberg Ridge were sampled and surveyed extensively to understand the distribution, origin, and resource potential of ferromanganese nodules and crusts. The northernmost and western parts of the basin are covered with terrigenous and calcareous sediments, respectively; these two areas have relatively

higher sedimentation rates and less abundance of nodules. Areas with a relief of a few hundred meters have high abundance and patchy distribution of nodules whereas areas of low relief have less abundance with a regular distribution. Variations in composition, morphology, and internal microstructures correspond to the genetic type of nodule and the local topography. The underlying sediment type has a profound influence on the mineralogy and metal concentrations of the nodules. Todorokite is the main manganese mineral in the rough surface nodules from the siliceous sediments and contains higher concentrations of Mn, Ni, and Cu owing to the supply of the metals during early diagenesis. The smooth surface nodules on pelagic red clays are rich in Fe and Co with ^dgr-MnO2 as the dominant mineral and formed from colloidal particles precipitated as authigenic metal oxyhydroxides. The nodules, especially from the siliceous sediments, are similar in composition and origin to those of the North Pacific. In contrast, crusts formed on seamounts and as abyssal hardgrounds are markedly different in composition from the Co-rich crusts of the North Pacific. The relative depletion of Co in the Indian Ocean crusts is attributed to their formation in deeper waters.

AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990