Occurrence
Nodules lie on the seabed sediment, often partly or completely buried. They vary greatly in abundance, in some cases touching one another and covering more than 70% of the sea floor. The total amount of polymetallic nodules on the sea floor was estimated at 500 billion tons by Alan A. Archer of the London Geological Museum in 1981. They can occur at any depth, even in lakes, but the highest concentrations have been found on vast abyssal plains in the deep ocean between 4,000 and 6,000 m (13,000 and 20,000 ft).
Polymetallic nodules were discovered in 1868 in the Kara Sea, in the Arctic Ocean of Siberia. During the scientific expeditions of the HMS Challenger (1872–1876), they were found to occur in most oceans of the world. Nodules of economic interest have been found in three areas:
- North central Pacific Ocean
- Peru Basin in the southeast Pacific, and
- Center of the north Indian Ocean.
The most promising of these deposits in terms of nodule abundance and metal concentration occur in the Clipperton Fracture Zone of the eastern equatorial Pacific between Hawaii and Central America.
Read more about this topic: Manganese Nodule
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