Plucking minerals from the seabed is back on the agenda

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—potato-sized mineral agglomerations that litter vast tracts of Davy Jones’s locker. At first sight, these nodules are attractive targets for mining because, besides manganese, they are 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. Worries about shortages went away, and ocean mining returned whence it had come, to the pages of science-fiction novels.

Now it is back. As Mark Hannington of the GEOMAR-Helmholtz Centre for Ocean Research, in Germany, explained to the AAAS, prototype mining machines are already being tested, exploration rights divvied up between interested parties, and the legal framework put in place. Next week the International Seabed Authority, which looks after those parts of the ocean floor beyond coastal countries’ 200 nautical-mile exclusive economic zones, is issuing guidelines for the exploitation of submarine minerals. In Dr Hannington’s view, a gold rush is starting. And he was speaking only partly metaphorically.

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. This was the subject of a presentation by Stace Beaulieu of the Woods Hole Oceanographic Institution, in Massachusetts. The nature of that cost depends on the ecosystem. The deep-sea plains which host nodule fields tend not to be home to big animals, said Dr Beaulieu, but the 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.

Hydrothermal vents are an even more peculiar environment than nodule fields. Unlike almost every other ecosystem, they are based not on energy from the sun, but on chemicals—particularly hydrogen sulphide—dissolved in the ejected water that are used by specialised bacteria to power their metabolisms. This, and their isolation from one another in the manner of small oceanic islands, means vents are host to many distinct and rare species. Conservationists therefore care about them a lot.

That said, as Dr Beaulieu pointed out, vent life may be more robust than many people assume. One of the hazards of dwelling near an undersea volcano is that an eruption can destroy your home in an instant. The creatures that live around vents seem able to bounce back from such catastrophes fairly quickly, so a visit from a mining machine might not be such a disaster after all.