Nature

This week, scientists at the University of Tokyo announced a discovery that threatened to break China's control over the world's supply of rare-earth metals, used to build electronics: They found the metals in vast expanses of mud on the floor of the Pacific Ocean in 78 sites. Predictably, the news made a worldwide media splash. A close look at the deep-sea mining industry, however, suggests that miners in China will not be out of work soon. And the world has known about metals on the ocean floor for decades.

Rare-earth magnets and other components are used in electronic devices from computers to electric cars, and demand has surged in the last decade. Mines in China supply nearly all of the world's rare-earths metal, and the Chinese government uses its near monopoly as political leverage: It was accused of halting rare-earth exports to Japan during a territorial dispute last year, and also announced a restriction of worldwide rare-earth exports, which sent chills through markets and tech companies. The United States, Canada, Brazil and other countries possess reserves, and the U.S. used to produce a sizeable percentage of the world supply before shutting many mines because of environmental concerns. Those deposits may be exploited in the next few years, though China's huge deposits and existing infrastructure guarantee that it will lead production for the near future.

So it's no surprise that the Japanese study, which appears in the journal Nature Geoscience, sparked excitement. The researchers took core samples at 78 sites around Hawaii, Tahiti and other locations in the eastern South Pacific and central North Pacific, finding rare-earth concentrations of about 0.2 percent. At that concentration, they reported, just 1 square kilometer of sea-floor mud could provide one-fifth of the world's annual rare-earth consumption, making it a "highly promising huge resource for these elements."

Without context, though, that kind of statement is misleading, says Frank Sansone, an oceanography professor at the University of Hawaii, Manoa. "It's not just something that you can glibly say, 'Oh, this is a huge amount of rare earth,'" he says. "It would be difficult to exploit. There's a big difference between saying that the elements exist in large amounts and being able to appropriately, economically and environmentally extract that material."

John Wiltshire, director of the Hawaii Undersea Research Laboratory, also at the University of Hawaii, Manoa, puts it even more bluntly. "The truth of the matter is, nobody's going to mine in the deep sea—even if somebody massively funds this—for a minimum of a decade," he says. The startup cost could run from $1 to $2 billion.

It's not that we don't know how to work in the deep sea, Wiltshire points out. Telegraph cables were first laid across the ocean floor 150 years ago, and at least three industries—telecommunications, oil drilling and diamond mining—have become adept at deep-sea engineering. Today, telecom cables are buried in deep trenches to guard against accidents such as damage by fishing trawlers. Oil rigs drill thousands of feet into the sea floor from floating platforms. And a handful of companies mine diamonds in several hundred feet of water off the coast of Namibia in southwest Africa; they drop remote-controlled seafloor crawlers to the ocean floor that, like pool cleaners, inhale sediment that is pumped to an overhead ship through a hose.

Deep-sea rare-earth deposits aren't new, either. Wiltshire, Sansone and many other researchers have been studying mineral deposits—including rare-earth mineral deposits—on the ocean floor since their careers began. "I published a paper on this 25 years ago. The first papers that indicated rare-earth minerals go back 30 or 35 years," Wiltshire says. "People have been talking about mining manganese nodules since the 1960s," Manganese nodules are conglomerates of metallic particles—rare-earth metals and others—stripped from the water over eons, and they were the hot undersea mining topic of decades past. Manganese nodule mining even provided cover for a bit of Cold War intrigue in 1974, when a $350 million deep-sea drilling ship built by one of Howard Hughes' companies supposedly went looking for a deposit to develop. In fact, the ship was being used by the CIA to look for a Soviet nuclear sub that had sunk off Oahu in the 1960s.

Today, though, as in the 1970s, cost and time remain enormous hurdles to mining these deposits. Wiltshire says a proposed deep-sea mine off the coast of Papua New Guinea illustrates the challenges that would face anyone looking to start a rare-earth operation in the Pacific Ocean. Nautilus Minerals plans to build a $157 million ship to support what could be the world's only deep-sea gold and copper mine. The ship, floating about three miles above the seafloor, will need to be gigantic: 680 feet long, with a deadweight capacity of more than 20,000 tons and bunks for up to 160 people.

Nautilus plans to unleash three remote-controlled devices on the sea floor: two cutters and a collector, adapted from technologies used in the oil and cable-trenching industries. An as-yet-undesigned pump system will lift the ore from the seafloor to the ship. "They've already spent about $400 million, the boat will be a couple hundred million," Wiltshire says. "A complete operation for Nautilus will easily be a billion."

The question, then, for any company that would seek to lease these areas (from the Pacific nations which possess the rights) and mine rare earths from the ocean bottom is: Is it worth all this trouble and expense? At 0.2 percent concentration of rare earths, the deep-sea deposits pale in comparison to ore deposits on land, which can have 5 to 10 percent concentrations. All things being equal, it's easier to collect minerals from mud than from ore. But things are not equal, because this mud is beneath three miles of water.

Experts do not discount the notion that we may someday mine rare-earth metals in the deep sea; perhaps the buzzwords of the year 2040 will be "Autonomous Underwater Mining Vehicle." But if you're wondering where rare-earth components in computer chips and solar cells will come from for the next decade, the answer is clear—China.

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