Canadian mining firm Nautilus Minerals says it plans to lead the way with the world's first commercial deep-sea mining project, scheduled to get underway within the next few years off the coast of Papua New Guinea.

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Only recently has deep-sea mining become technologically and financially feasible, thanks to using remotely operated subs and other technologies developed for deepwater oil and gas production. Proponents say higher ore grades mean deep-sea mining would be more cost-effective than land-based operations, with a smaller ecological footprint that would be less visible.

But these are uncharted waters, says Cindy van Dover, director of the Duke University Marine Laboratory in Beaufort, N.C. "We do not know where the tipping points are with regard to how much damage deep-sea systems can sustain and still maintain the health of the ocean," she says.

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One likely test case is Nautilus's Solwara 1 Project, which will target a massive sulfide deposit 1,500 meters deep in the Bismarck Sea northeast of New Guinea. Nautilus estimates the site could produce more than 72,500 metric tons of copper and more than 4.5 metric tons of gold. The copper ore grade--the concentration of a valuable mineral within an ore--averages nearly 8 percent, compared with 0.6 percent on land in 2015, says Nautilus chief executive Mike Johnston.

To collect this treasure Nautilus has designed a trio of huge, remote-controlled underwater machines that would not look out of place in a Terminator movie. Two "cutters"--weighing 308 and 250 metric tons, respectively--will crawl across the seafloor on tank treads and grind the ore into slurry using spinning toothed wheels. A 2,200-metric-ton collecting machine will feed the slurry into an enclosed pumping system to the surface. Operators in a support vessel control the cutters and collecting machine using joysticks, sonar and live streaming video. Onboard the support vessel the slurry will be drained and transferred to another ship for processing in China. The wastewater will be filtered of impurities and pumped back down to the seafloor.

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Richard Steiner, a conservation biologist and former University of Alaska professor who is not involved in the Solwara project, is unconvinced. "There's no question this will pose massive environmental impacts," he says--from bright lights, noise and potential toxic leaks to sediment plumes that could clog the filters many kinds of sea life use for feeding. The deep ocean is the largest and least understood biological habitat on Earth and deep-sea vents--discovered as recently as 1977--may be one of the rarest of all ecosystems, says Steiner, who heads up the conservation consultancy Oasis Earth. Only about 300 vent sites are known and estimates of the total number that exists range between 500 and 5,000.

Impact reports that use land-based mines as a benchmark are comparing apples and oranges, Steiner says--and our environmental track record in deepwater oil and gas recovery is not exactly inspiring. The deep ocean is unforgiving, even to experts; in 2014 Woods Hole's Nereus robotic sub imploded in the Kermadec Trench, a 10-kilometer-deep rut in the Pacific Ocean floor where two tectonic plates meet northeast of New Zealand. "There's a dangerous combination of ignorance, arrogance, greed and very poor scientific understanding," Steiner says. "Humans are terrestrial primates; we just don't get underwater."

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As seen with fracking, we are experts at pulling things out of the ground and then pumping water back into the holes without incurring horrible consequences. And it's all totally contained. No worries. What are the chances anything could leak out?