|Ferromanganese nodules from the Central Indian Ocean basin|
Jauhari, P.; Pattan, J.N. (2000). Ferromanganese nodules from the Central Indian Ocean basin, in: Cronan, D.S. (Ed.) Handbook of marine mineral deposits. pp. 171-195
In: Cronan, D.S. (Ed.) (2000). Handbook of marine mineral deposits. CRC Marine Science Series, 17. CRC Press: Boca Raton. ISBN 0-8493-8429-X. 406 pp., more
In: Kennish, M.J.; Lutz, P.L. (Ed.) CRC Marine Science Series., more
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The Central Indian Ocean Basin (CIOB), located between the Central Indian Ridge and the Ninety East Ridge receives sediments from the Ganges and Brahmaputra runoff, dispersed far south of the equator by turbidity currents. In order to delineate a mine site for ferromanganese nodules, extensive surveys were conducted in this area, which led to India being allocated a 150, 000 sq km area mine site for further developments related to ferromanganese nodule mining. Mapping of the basin by multibeam swath bathymetry (Hydrosweep) has revealed many new bottom relief features. These features have a strong influence on the movement and distribution of water masses, sediment transport, chemical activity, and enrichment of metals in the nodules and their distribution on the seafloor. Size of the nodules ranges from less than 2 cm to above 10 cm in more than 13 morphological facies in the basin. The highest abundance of nodules is generally associated with high relief areas like valleys, followed by hilltops and slopes. Abundance is least in abyssal plains. Nodules from the plains have the highest contents of Mn, Cu, and Ni, while those from hilltops have the lowest concentrations of these metals. There exists an inverse relationship between nodule abundance and their grade. Nodules are associated with practically all types of sediment, and their surface density varies from traces to more than 20 kg/m2 in the basin.Genetically, three types of nodules are discernible in the basin -Type A, enriched in Mn, Cu, Ni, and Zn are concentrated in siliceous sediments. They get their supply of metals through early diagenetic processes occurring in the sediments. These nodules are small in sire, rough surfaced, and contain todorokite as the dominant mineral phase. Type B, enriched in Fe and Co, are normally associated with red pelagic clays and are formed by accumulations mainly from sea water. These are represented by larger-sized nodules with smooth surfaces and containing δ-MnO2 as the principal mineral phase. The third, Type AB, are mixed phase and represent both processes. Rare earth elements in the nodules are contained in a single authigenic phase comprised of Fe, P, and Ti. 230Th and 230Thexe/232Th measurements on nodules from the siliceous ooze region show an accumulation rate of 1.2 mm/my for the nodule tops and 1.9 to 3.2 mm/my for the bottoms. Dendritic, collomorphic, laminated, and well-developed internal structures comprising alternating light-colored Mn- rich and dark-colored Fe-rich bands in sections of nodules have been observed under the ore microscope and scanning electron microscopeOrganisms belonging to seven different phyla and also a variety of biogenetic traces were observed on various geological features in the basin. These features highlight the importance of further ecological studies pertaining to the Environmental Impact Assesment prior to mining.