ABSTRACT

Ferromaganese encrustations of hydrogeneous types have been known together with manganese nodule for their Ni-Cu metal content. However, ferromanganese crust formed on ancient volcanoes and have a chemistry quite different than those associated with nodules. They have a high level of cobalt (∼1.5%) and platinum (∼1g/ton) in addition to a series of other elements such as, cerium and titanium, which are of strategic significance in terms of "new metals". Based on the criteria of exploration, potential areas within the Indian Ocean most ideally suitable for the development of the crust have been suggested. The substrata rocks over which the cobalt rich crust have been formed are volcanic breccias, hydroclastic basalts, phosphorite, limestone, volcanoclastic sandstone, mudstone and chert. Several areas in the Indian Ocean have a geological environment which is favourable for the formation of thick ferromanganese crusts. These areas could be grouped into:

  • Old seamounts (More than 20 million years of age).

  • Areas with a well developed oxygen minimum zone.

  • Areas of strong, oxygen-rich, near-bottom currents, and

  • Areas where seamount flanks are ideally between 500 to 1500m water depth, in the equatorial zone (between 15–20° latitude each side of the equator).

In such exploration campaign, one has to

  • Avoid areas with atolls and coral reefs.

  • Avoid areas near continents.

  • Select area with flat top of the seamounts for better picking/sampling and eventual detailed exploration to mining prospects.

  • Select areas with an average crust thickness of more than 4 cm and a cobalt grade of more than 0.8%.

  • Select microphotographic areas with the wide-spread occurrence of crust, and eliminate areas of slumps, talus deposits and sediment cover.

Based on these criteria, in the Indian Ocean, areas close to India worth considering for exploration are (1). Lakshadweep islands, only seamounts without reefs, (2) Southern tip of Kerala state, (3) Seamounts between 93° -96° E and 10° -13° N. The area could be extended to the south of the Ninety-East Ridge, as well as other potential areas well within the EEZ of India.

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