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

Abstract:

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.