MANGANESE (OR POLYMETALLIC) NODULES: Increasing global population, demand for metals and dwindling land resources, has come to such a pass that the next alternative source for the metals could be in the world oceans. Oceans are considered as a ‘warehouse’ for minerals, amongst others, polymetallic nodules (Ferromanganese nodules), phosphorites, hydrothermal sulphides, placer deposits and sand. The first discovery of polymetallic nodules was made by scientists onboard the research vessel “H M S Challenger” during 1873. In comparison, India (by the efforts of the National Institute of Oceanography, Goa) recovered nodules in the Arabian Sea during 1981 onboard “R.V.Gaveshani.” In 1982, India was recognised as a Pioneer Investor in deep seabed mining, by the United Nations Convention on the Law of Sea.
Subsequently, a massive effort was put in by India for exploration of polymetallic nodules in the Central Indian Ocean Basin (CIOB) by using a number of research vessels. This national programme (running into crores of rupees) is being funded by Department of Ocean Development, New Delhi.
To-date, India has surveyed an area of nearly 4 million sq km in the CIOB. This resulted in the identification of two mine sites, each 150,000 sq km area with equal commercial grade (Cu+Ni+Co wt%) and abundance (kg/sq m) of nodules. In 1984, India filed her claim with the Preparatory Commission (PRECOM) for the International Sea Bed Authority (ISBA). In 1987, India became the first country in the world to be allocated exclusive rights for further exploration.
One of the mine site (A) of 150, 000 sq km has been allotted to India and as per the condition of the ISBA, 50 % of the area has been relinquished to this body.
What are polymetallic nodules and the criteria for their formation?
Polymetallic nodules are Fe-Mn oxide deposits, potato shape, porous, black
earthy colour with size ranging from 2 to 10 cm in diameter.
Different shapes of polymetallic nodules .
Nodules occur at nearly 4 to 5 km depth in the deep oceans and they take one
million year to grow to one millimeter.
In the Indian Ocean, nodules occur in different basins such as CIOB Wharton Basin,
Crozet Basin, Madgascar Basin, Somali Basin, South Australian Basin and Arabian sea.
The prerequisite conditions to form the nodules are:
Low sedimentation rate
Availability of nucleus around which accretion of oxides takes place
Bottom currents of low velocity