A sem-edax study of sea nodules from central Indian-ocean basin

Abstract

SEM/SE/EDAX analysis for the elements Mn, Fe, Ni, Co, Cu, Ti, Si, Al, Mg, K, Ca, Na, Cl and S was carried out at various points on the polished section of a nodule from Central Indian Ocean basin. Linear regression analysis of chemical composition data confirmed the positive correlation of Ni, Cu and Mg with Mn, Ti with Fe and Si with Al. Co showed positive correlations with both Mn and Fe but significant correlation was observed only with Mn. Dissolution behaviour of elements in sequential extraction (i.e. selective sequential removal of exchangeable ions, Mn-fraction. organic matter, and Fe-fraction) was used to verify the elemental correlation observed in linear regression analysis. A very small amount of minor elements was found to be present in easily exchangeable form. The positive associaton of Ni and Mg with Mn, and Ti with Fe was corroborated by the close correspondence between dissolution behaviour of minor and respective major element, Multiple association of Cu with Mn-fraction and organic matter appears to be due to the complex behaviour of cuprous ion formed during reductive dissolution of manganese bearing phases. Association of Co with Mn- and Fe- fraction and perhaps organic matter is indicated by its leaching behaviour in sequential extraction. Q-mode factor analysis of SEM/SE/EDAX data resulted in four significant factors: (i) Factor 1 : Mn-Ni-Cu-Mg-Co-, diagenetic; (ii) Factor 2A : Si-Fe-Al-K-Ti-, siliceous ooze; (iii) Factor 2B : Si-Al-K-Na-Ca-, detrital; and (iv) Factor 3 : Fe-Ti-Co-Ca-Mn-, hydrogenetic. The association of Fe with Si suggests that biological silica has a role to play in the fractionation of manganese and iron.