Abstract
Five manganese nodules obtained from different locations with varying water depths of the Indian Ocean were analysed by k0-based instrumental neutron activation analysis (k0-INAA) method. A total of 22 elements were estimated including nineeee rare earth elements (REE). The accuracy of the method has been evaluated by analysing USGS manganese nodule reference material NOD P1. The nodules have been classified into hydrogenous and diagenetic on the basis of their Mn/Fe ratios. Data on elemental concentrations were used to explain the possible differences in the trace element distribution. The minor elements were found to be enriched in the hydrogenous nodules compared to the diagenetic one. An attempt was made to characterise the distribution of these minor elements in the light of known geochemical evidences of Pacific Ocean nodules. The dissimilarity of the geochemistry of Ce and Mn in the Indian Ocean nodules has been discussed. The manganese nodules under investigation exhibit a positive cerium anomaly, indicating an oxidising environment. The possible mechanism of incorporation of elements like REE into the iron oxyhydroxide phase has been discussed.
