A mile beneath the ocean's waves waits a buried cache beyond any treasure hunter's wildest dreams: gold, copper, zinc, and other valuable minerals.

Scientists have known about the bounty for decades, but only recently has rising demand for such commodities sparked interest in actually surfacing it. The treasure doesn't lie in the holds of sunken ships, but in natural mineral deposits that a handful of companies are poised to begin mining sometime in the next one to five years.

The deposits aren't too hard to find—they're in seams spread along the seafloor, where natural hydrothermal vents eject rich concentrations of metals and minerals.

These underwater geysers spit out fluids with temperatures exceeding 600ºC. And when those fluids hit the icy seawater, minerals precipitate out, falling to the ocean floor.

The deposits can yield as much as ten times the desirable minerals as a seam that's mined on land.

While different vent systems contain varying concentrations of precious minerals, the deep sea contains enough mineable gold that there's nine pounds (four kilograms) of it for every person on Earth, according to the National Oceanic and Atmospheric Administration's (NOAA) National Ocean Service.

At today's gold prices, that's a volume worth more than $150 trillion.

Can an Industry Be Born?

But a fledgling deep-sea mining industry faces a host of challenges before it can claim the precious minerals, from the need for new mining technology and serious capital to the concerns of conservationists, fishers, and coastal residents.

The roadblocks are coming into view in the coastal waters of Papua New Guinea, where the seafloor contains copper, zinc, and gold deposits worth hundreds of millions of dollars and where one company, Nautilus Minerals, hopes to launch the world's first deep-sea mining operation.

Animation: How Robots Could Mine Seafloor

Source: Nautilus Minerals

Last year, the Papua New Guinean government granted the Canadian firm a 20-year license to mine a site 19 miles (30 kilometers) off their coast, in the Bismarck Sea in the southwestern Pacific Ocean. The company plans to mine the site, known as Solwara 1, by marrying existing technologies from the offshore oil and gas industry with new underwater robotic technologies to extract an estimated 1.3 million tons of minerals per year.

Samantha Smith, Nautilus's vice president for corporate social responsibility, says that ocean floor mining is safer, cleaner, and more environmentally friendly than its terrestrial counterpart.

"There are no mountains that need to be removed to get to the ore body," she says. "There's a potential to have a lot less waste ... No people need to be displaced. Shouldn't we as a society consider such an option?"

But mining a mile below the sea's surface, where pressure is 160 times greater than on land and where temperatures swing from below freezing to hundreds of degrees above boiling, is trickier and more expensive than mining on terra firma.

Nautilus says it will employ three remote-controlled construction tools that resemble giant underwater lawn mowers to cut the hard mineral ore from the seafloor and pump it a mile up to a surface vessel.

That vessel would be equipped with machinery that removes excess water and rock and returns it to the mining site via pipeline, an effort aimed at avoiding contaminating surface waters with residual mineral particles. The company would then ship the rock to a concentrator facility to remove the mineral from the ore.

An Unknown Impact

At least that's the plan.

But the ocean floor is still a mysterious place, seldom visited by humans, compounding the known difficulties of working at sea.

Scientists weren't even able to prove the existence of underwater hydrothermal vents until 1977.

That year, an expedition of geologists, geochemists, and geophysicists from the Woods Hole Oceanographic Institute, Oregon State University, the Massachusetts Institute of Technology, Stanford University, and the U.S. Geological Survey proved their existence in the Galápagos rift with cameras and a manned dive in the submersible Alvin.

The animal-rich landscape and huge temperature shifts came as a surprise.

"When the first people went down there, and saw these things, they had no idea," says Mike Coffin, a geophysicist and executive director of the Institute for Marine and Antarctic Studies at the University of Tasmania in Australia. "The submersible had windows that could melt at temperatures lower than what was coming out of the vent."

And, in contrast to the desert-like landscape that the scientists expected, it turns out that hydrothermal vents are home to lots of life: snails the size of tennis balls, seven-foot-long (two-meter-long) tubeworms, purple octopi, and all-white crabs and skates.

It turns out that, far from the sun's life-giving light, the same minerals now eyed by the mining industry support lively communities.

Now some researchers fear that deep-sea mining could jeopardize those communities by altering their habitats before the systems have been fully explored and explained.

"We're still just grappling with this reality of commercialization of the deep sea," says Cindy Van Dover, director of Duke University's Marine Lab. "And scrambling to figure out what we need to know."

Van Dover was aboard the first manned biological exploration of the hydrothermal vents in 1982 and was the only woman to pilot the submersible Alvin. Despite the strides that have been made in understanding the deep sea, she says, it's still a young science.

When it comes to the impacts of mining on any deep-sea life, "there's a particular type of research that needs to be done," she says. "We haven't yet studied the ecosystem services and functions of the deep sea to understand what we'd lose.

"We don't yet know what we need to know," Van Dover says.

Conservationists also say they want to know more about the vent ecosystems and how they will be mined.

"The whole world is new to the concept of deep-sea mining," says Helen Rosenbaum, coordinator of the Deep Sea Mining Campaign, a small activist group in Australia that campaigns against mining the Solwara 1 site.

"This is going to be the world's first exploitation of these kinds of deep resources. The impacts are not known, and we need to apply precautionary principles," she says. "If we knew what the impacts were going to be, we could engage in a broad-based debate."

Rosenbaum says some communities in Papua New Guinea are raising concerns about the sustainability of local livelihoods in the face of mining and say they aren't receiving the information they need.

The Deep Sea Mining Campaign is especially concerned about the impacts of toxic heavy metals from the mining activities on local communities and fish. The group claims that the Environmental Impact Statement for the Solwara 1 mine hasn't effectively modeled the chemistry of the metals that would be stirred up by the mining process or the ocean currents that could transport them closer to land.

"The Solwara 1 project is scheduled to be a three-year project," Rosenbaum says. "The mining company thinks they'll be out of there before there are problems with heavy metal uptake. We might not see the effects for several years."

A report released in November 2012 by the Deep Sea Mining Campaign ties exploratory pre-mining activities and equipment testing by Nautilus to "cloudy water, dead tuna, and a lack of response of sharks to the age-old tradition of shark calling."

Shark calling is a religious ritual in which Papau New Guineans lure sharks from the deep and catch them by hand.

Another concern for Deep Sea Mining Campaign: Papua New Guinea's government has a 30 percent equity share in the minerals as part of a seabed lease agreement with Nautilus.

The company and government are currently involved in a lawsuit over these finances, but the Deep Sea Mining Campaign says government investment could compromise its regulatory efforts.

Mining for Dollars

Nautilus' Smith insists that the company has taken a careful and transparent approach. "The biggest challenge the company faces," she says, "is funding."

Fluctuations in commodity pricing, the high cost of working underwater, and financial disagreements with the Papua New Guinean government have been setbacks for Nautilus.

Last November, the company announced that it had suspended construction of its mining equipment in order to preserve its financial position. Smith says that Nautilus is still committed to finding a solution for its work in Papua New Guinea, and that the company could still extract minerals as early as 2014.

Other companies around the world are also exploring the possibility of mining throughout the South Pacific.

The International Seabed Authority, which regulates use of the seafloor in international waters in accordance with the United National Convention on the Law of the Sea, has granted 12 exploratory permits to various governments—including India, France, Japan, Russia, China, Korea, and Germany—in roughly the last decade.

And as long as the promise of riches await, more firms and governments will be looking to join the fray.