The Ever-Present Human: digging deep into the sea

hydrothermal vents. image from http://oceanservice.noaa.gov/facts/vents.html

In the 1960s and 1970s, amid worries about dwindling natural resources, several big companies looked into the idea of mining the ocean floor. They proved the principle by collecting hundreds of tonnes of manganese nodules…rich in cobalt, copper and nickel. As a commercial proposition, though, the idea never caught on. Working underwater proved too expensive and prospectors discovered new mines on dry land.

The International Seabed Authority, which looks after those parts of the ocean floor beyond coastal countries’ 200 nautical-mile exclusive economic zones, has issued guidelines for the exploitation of submarine minerals.

One of the most advanced projects is that of Nautilus Minerals, a Canadian firm. In January 2016 Nautilus took delivery of three giant mining machines (two rock-cutters and an ore-collector) that move around the seabed on tracks, like tanks. It plans to start testing these this year. If all goes well the machines could then start operating commercially in Nautilus’s concession off the coast of Papua New Guinea, which prospecting shows contains ore with a copper concentration of 7%. (The average for terrestrially mined ore is 0.6%.) This ore also contains other valuable metals, including gold.

This approach (which is also that taken by firms such as Neptune Minerals, of Florida, and a Japanese consortium led by Mitsubishi Heavy Industries) is different from earlier efforts. It involves mining not manganese nodules, but rather a type of geological formation unknown at the time people were looking into those nodules—submarine hydrothermal vents. These rocky towers, the first of which was discovered in 1977, form in places where jets of superheated, mineral-rich water shoot out from beneath the sea floor. They are found near undersea volcanoes and along the ocean ridges that mark the boundaries between Earth’s tectonic plates. They generally lie in shallower waters than manganese nodules, and often contain more valuable substances, gold among them.

They are not, though, as abundant as manganese nodules, so if and when the technology for underwater mining is proved, it is to nodules that people are likely to turn eventually. These really are there in enormous numbers. According to Dr Hannington, the Clarion-Clipperton fracture zone, a nodule field that stretches from the west coast of Mexico almost to Hawaii, contains by itself enough nickel and copper to meet global demand for several decades, and enough cobalt to last a century.

Mining, whether on land or underwater, does come at an environmental cost, though… [T]he sediments the nodules are found in play host to microscopic critters that would be most upset by the process of trawling that is needed to bring the nodules to the surface. They might take decades to recover from it.

Excerpts from :Oceanography: Fruits de mer, Economist, Feb. 25, 2017

 

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