Ferromanganese micronodules from Bengal Fan

Abstract

The occurrence of ferromanganese micronodules, hitherto unreported from any fan-valley system of the world, has been recorded from over 0.22 million km sup(2) area located in the middle fan region of the Bay of Bengal. Their abundance is higher in the eastern bay than in the western bay. Botryoidal and spheroidal are the two dominant morphological forms observed in the eastern and the western bay respectively. The bulk chemical analysis of the micronodules reveals that they have 24.1% Mn, depleted Fe (1.10%), Ni I0.089%), Zn (0.150%) and Co (0.01%), and a Mn/Fe ratio of 21.1. Todorokite in association with quartz, feldspar and phillipsite is observed in the nodules. The preliminary results suggest that Mn released from the smectite clay mineral and early diagenesis are the responsible for their formation