The Marine Geochemistry and Genesis of ferromanganese nodules from Central Indian Ocean Basin (CIOB)

Saurabh KUMAR Barman, Banaras Hindu University, Varanasi, India

The area under consideration is situated in Central Indian Ocean Basin (CIOB). The samples have been obtained from the area lying between latitude 8.5ºS to 12º S and longitude 75º E to 78.5º E while water depth ranging between 4,500–5,500m. Nodules contain many metals above crustal abundances and hence aptly called Fe-Mn nodules. Mn concentration is more in nucleus of nodule and its concentration decreases towards periphery. Fe-components shows a reverse trend and is more concentrated towards peripheral part of nodule.

The 3-phases mainly oxide/hydroxides, sulphide & aluminosilicates constitute Fe-Mn nodules or polymetallic nodules. Oxyhydroxides of Fe and Mn dominate over aluminosilicate fraction & most of transition metals are co-hosted by these two phases. The medhod adopted in present study involve analysis of major and minor elememts using UV spectrophotometer & atomic absorption photometer (AAS). Studies indicate that Fe shows negative correlation with Mn, Zn, Cu, Ni, CaO, MgO, Na2O, and K2O. Similarly, Mn also show negative correlation with TiO2, P2O5, SiO2, Al2O3, CaO, MgO, Na2O, K2O, Sr. Furthermore, Cu also shows Negative correlation with TiO2, P2O5, SiO2, Al2O3, Sr. In addition, Ni has similar relation with Pb, TiO2, SiO2, Al2O3, Sr, P2O5, Na2O.

On the other hand many of metals viz. Ni shows positive correlation with Mn, Cu, Co, Zn, Mn/Fe. Similarly, Cu shows positive correlation with Mn, Co, Pb, Mn/Fe. Furthermore, Mn also shows similar relation with Zn. In addition to this Fe has similar relation with Sr, P2O5, Pb, SiO2, and Al2O3. Similar relation have been observed between the following pairs viz. Al2O3-SiO2, MgO-CaO, K2O-Na2O, P2O5-TiO2, TiO2-Pb, Sr-CaO, Sr-MgO, P2O5-CaO & P2O5-MgO.

Chemical partitioning technique generalizes two distinct co-existing associative phase with Mn and Fe as controlling factors viz. Mn–Ni–Cu & Fe–Co–Zn. Cu and Ni are intimately associated with Mn both in chemical partitioning experiments and in nodule chemistry examinations. Mn/Fe ratio and various ternary diagrams ( Cu+Ni+Co ) x10–Mn–Fe ; Cu–Zn–Ni ; Al–Mn–Fe & Si–M –Fe suggest that these nodules belong to typical nodules oxide– hydroxide field and is hydrogenetic.

The above inter elemental relationship helps in distinguish major elemental association group.