A SEM BACKSCATTERED ELECTRON MODE STUDY OF MICROSTRUCTURAL FEATURES OF FERROMANGANESE NODULES FROM CENTRAL INDIAN-OCEAN BASIN

Identification and chemical characterisation of different microstructu ral features, present in the nodules from Central Indian Ocean Basin, have been carried out using atomic number (Z) contrast in the back-sca ttered electron (BSE) mode of SEM and EDS analysis. Three different ki nds of Mn-Fe assemblages have been identified, namely, columnar and ra dial patterns, dendritic segregation, and compact type of morphology. The distribution of major (Mn, Fe and Si) and minor (Ni, Cu, Co, Ti, K , Ca, Mg etc) elements vis-a-vis different morphology and regions have been studied using X-ray mapping and line and point scans. Irrespecti ve of morphological feature, Ni and Cu are found associated with Mn-ri ch regions. Co is found associated with Mn-rich regions in compact typ e of morphology and with Fe-rich regions in columnar and radial patter ns. The regions present in different morphology were classified by Q-m ode factor analysis of X-ray microanalysis data. Four significant fact ors, which explained 97% variance in the X-ray microanalysis data set, are based on the following elemental assemblages: Factor 1-Mn-Mg-Ni-C u-Co-, Factor 2-Si-Al-Fe-K-Mg-Ti-, Factor 3-Fe-Co-Ti-Ca-Mn-, and Facto r 4-Mn-Al-Ca-. The morphological features can be assigned genetic sign ificance on the basis of elemental assemblages found in the factors.