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

Identification and chemical characterisation of different microstructural features, present in the nodules from Central Indian Ocean Basin, have been carried out using atomic number (Z) contrast in the back-scattered electron (BSE) mode of SEM and EDS analysis. Three different kinds of Mn-Fe assemblages have been identified, namely, columnar and radial 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. Irrespective of morphological feature, Ni and Cu are found associated with Mn-rich regions. Co is found associated with Mn-rich regions in compact type of morphology and with Fe-rich regions in columnar and radial patterns. The regions present in different morphology were classified by Q-mode factor analysis of X-ray microanalysis data. Four significant factors, which explained 97% variance in the X-ray microanalysis data set, are based on the following elemental assemblages: Factor 1-Mn-Mg-Ni-Cu-Co-, Factor 2-Si-Al-Fe-K-Mg-Ti-, Factor 3-Fe-Co-Ti-Ca-Mn-, and Factor 4-Mn-Al-Ca-. The morphological features can be assigned genetic significance on the basis of elemental assemblages found in the factors.