Chemistry and possible resource potential of cobalt rich ferromanganese crust from Afanasiy-Nikitin seamount in the Indian Ocean
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Samples of ferromanganese encrustations (fe-Mn crusts) dredged from the upper flank of the Afanasiy-Nikitin seamount, above the Carbonate Compensation Depth (CCD) in the Northern Central Indian Ocean (NCIO) were analysed for Al, Fe, Mn, Ca, Ba, Cu, Ni, Co, Zn and V and found to be rich in Co (upto 0.88%) mineralogically, the studied Fe-Mn crust samples contain poorly crystalline d-MnO sub(2) and minor amount of Carbonate Fluorapatite (CFA) and feldspars. The low Mn/Fe ratios (less than 2), d-MnO sub(2) dominant mineralogy and the interlement associations show that these crusts are formed by slow hydrogenetic precipitation of colloidal Fe-Mn oxyhydroxides. Fe, Mn, Co, Zn and V exhibit matually strong positive association (r greater than 0.7) indicating their incorporation into the Fe-Mn crust during the hydrogenetic precipitation. The Al on the other hand, appears to be independent and diluant for hydrogenetic component. Therefore, the Al in the Fe-Mn crusts might be due to the presence of fine lithogeneous detritus intermixed with hydrogenetic component. Another detrital indicator element 'Ti', instead of showing the affinity to Al exhibits affinity towards hydrogenetic oxide elements suggesting a possible incorporation into Fe-Mn crust analogous to other transition metals.
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