Deep-sea exploration started in the 1960s, but mining was not viable then. However, new interest has been sparked by rising demand for precious metals, mainly from Asian and other developing countries, and rising commodity prices.
Anglo American, through its majority stake in De Beers, sucks up diamonds from the ocean floor on the coast of South Africa and Namibia.
These diamonds were carried out to sea by the Orange River and swept up the coast or ashore by tide and wind. Most lie in shallow water, so scooping them up is fairly simple.
On the same sea bed, miners intend to extract phosphates. It will be the first time in the world that phosphates are taken from the sea, where the heaviest accumulation of phosphorous material is believed to be.
Namibian Marine Phosphate plans to mine the Sandpiper project phosphate deposit as soon as 2014.
Project manager David Wellbeloved said it is a high-grade deposit of about 1.8billion tons of phosphates that could provide phosphate, mainly used in agricultural fertiliser, for the next 200 years.
He said the mine will play an important role in boosting food production, especially in rapidly developing sub-Saharan Africa.
Wellbeloved and his team are waiting for environmental clearances to start construction of the ocean-mine that will take about 18 to 24 months to complete.
Even though ocean mining is not a new concept in Namibia, the project has met opposition from community and environmental organisations.
Phosphorus accumulation on the ocean floor comes from underground hydrothermal volcanic activity and deposition of organic material.
Wellbeloved said Sandpiper was formed mainly by the Benguela current depositing skeletons, plankton and other organic material on the coast line. He said specific ocean worms and larvae, as well as the fishing industry, need to be protected.
"All mining, whether on land or in the ocean, has an impact on the environment. One has to find the best way to mitigate this. According to experts who have assessed the project and rate of development and mining, the environmental impact of the Sandpiper project will not be significant and could be mitigated," he said.
At full production, the project would supply about 10% of the global phosphate market. The biggest land-based phosphate producers in Africa now are Egypt and Morocco.
"This project will be a world first. We will be mining an enormous and unique deposit," said Wellbeloved.
He would know as he has been involved in mining project development for about 30 years, with two of his sons following in his footsteps.
Canadian-headquartered company Nautilus Minerals is developing the Solwara 1 project in Papua New Guinea's territorial waters, believed to contain about 100000 tons of copper, as well as gold. If all goes to plan these mineral riches could be mined from next year.
Miners search far and wide for mineral wealth, as the world's resources continue to shrink and the population gets larger, miners are looking towards oceans - and even space.
Nautilus believes that up to a third of the world's minerals can eventually come from the sea floor.
Russia and China have been the countries most interested in ocean mining. Russia has been grubbing around on the sea bed for years and has found four massive sulphide deposits in as many years.
China is less sure what it is looking for but has become interested in the southern Indian Ocean, as well as the zone in the North Pacific where most of the manganese-nodule licences have been granted.
Ocean-formed mineral formations excite miners as they are often large, tens of metres thick and the metals are highly concentrated.
Technology to mine these deposits has become available, with much of it adapted from the long-established deep-sea oil industry.
The biggest challenge is industry regulation. The most noteworthy regulations on deep-sea mining are the United Nations Conventions on the Law of the Sea, which came into force in 1994.
The conventions set up the International Seabed Authority, which regulates deep-sea mining ventures outside each nation's 370km-deep exclusive economic zone.
However, there are still no environmental legal codes in place for deep-sea mining outside these economic zones, which explains why the only places where companies have dipped more than a toe in the water are in exclusive economic zones, which are not just shallower than many parts of the distant ocean but also within the legal ambit of a national authority.
In another dimension, new company Planetary Resources recently unveiled plans to mine near-Earth asteroids for water and metals.
Co-founder Peter Diamandis is a key figure in the personal space flight industry, having created many space-related businesses and organisations. He also founded an educational non-profit institute seeking radical breakthroughs for the benefit of humanity.
As history has repeatedly shown, if there are valuable minerals and resources, adventurous pioneers will set out to find them - even if they have to battle extreme conditions and risk life and limb.