The first deep-sea mining machines - for extracting gold, silver and copper deposited near volcanic fissures on the ocean floor - are being built by a British engineering company. The pioneering designs, which will resemble giant, abrasive vacuum cleaners, are at the forefront of an emerging underwater mineral extraction industry that is sounding alarm bells among marine biologists and environmental scientists.

A £33m contract for two seafloor mining tools, capable of working at depths of more than a mile (1,700 metres), was awarded last December to the Newcastle upon Tyne firm, Soil Machine Dynamics. If delivered according to schedule, the machines could begin excavation work by 2010 in the Pacific and inaugurate a new era in sub-sea exploration and mining.

The operation to recover these "poly-metallic" minerals, which are found in far higher concentrations than land-based ores, will generate a rich revenue source at a time when commodity prices are hitting record levels.

Big change

"We are leading the mining industry into the deep oceans," says Scott Trebilcock, vice-president of business development at Nautilus Minerals Inc, the Canadian prospecting company that has ordered the machines. "This is as big a change as it was for the oil and gas industry when it went offshore in the 1960s and 70s. Billions of dollars have been spent over decades developing [underwater] pumps, hydraulics and trench-digging machinery. We can use their technology for new targets: the poly-metallic deposits that contain gold, silver, zinc and copper."

Nautilus's first project, the Solwara 1 field, is within Papua New Guinea's territorial waters, but the firm, whose operational management is based in Brisbane, Australia, has also taken up licence options on sites near Tonga, Fiji and New Zealand. Those locations have been chosen because of proximity to volcanic activity at the margins of the Earth's tectonic plates.

"Deposits are formed from heated sea-water," Trebilcock explains. "As it filters deeper into cracks, it absorbs sulphur and becomes acidic. It can reach 300C and dissolves minerals until it bubbles up and hits water on the ocean floor, which is at approximately 2C."

The metals precipitate out of solution and are deposited on the seabed. These so-called SMS - seafloor massive sulphides - resemble giant "elephant turds", according to one oceanographer.

Nautilus will work on underwater old vents that have cooled, some way back from the super-heated, active plate edges. "Our material is 8%-10% copper," Trebilcock says. "In land mines, the average is 0.59%. So for every tonne of copper produced, we move 40 times less material."

Similar SMS deposits lie on the ocean floors around the world, particularly in the Arctic and along the Mid-Atlantic Ridge. Those areas, however, are at far greater depths and are subject to worse sea conditions.

Soil Machine Dynamics is designing and assembling a tool that has a rotating, cutting head - like the machines used to hew coal out of underground seams - surrounded by a giant suction pipe. The company describes the equipment as "a novel design for recovering ore which is found in massive sulphide deposits in rugged terrain. It draws on technology ... developed in recent projects for trenching systems." The two seafloor mining systems will suck up 1.5m tonnes of ore annually.

Trebilcock believes the operation will cause far less environmental damage than a similar-sized onshore mine. He says: "There's no disturbance to the site around the mine. We'll have no waste rock. Everything we take up will be smelted.

"We have carried out an environmental impact study, which will be published this year. We will have to show that we don't have any long-term impact on any species or ecosystems. We have spoken to NGOs and the Papua New Guinea government about this.

"Oil and gas [companies] disturb a far larger area when they open up a new field. The dredging industry takes millions of tonnes off the ocean floor. We have significant [environmental] advantages over land-based companies."

However, some environmental groups, including WWF, are concerned that underwater mining will lead to despoilation of vast tracts of the seabed before they can be explored. "These sites have limited physical integrity and great biodiversity," Simon Cripps, director of WWF's global marine programme, recently told Chemistry World magazine. "We would like to see a thorough, independent impact assessment before any mining work begins."

Catherine Coumans, a coordinator at Mining Watch Canada, has been to Papua New Guinea to examine the impact of mining. "I have studied mines . . . where the tailings [wastes] are flushed out to sea or simply dumped in rivers," she says. "[Papua New Guinea] has, tragically, some of the worst forms of mining and disposal. Now it is going to have experimental undersea mining.

New frontier

"There are concerns about disturbance of the sea bottom. Very little is known about it. This is a new frontier that has yet to be explored with a fragile, marine ecosystem. There's no significant independent work that has been done on the impact of mining. I would challenge the company to provide an independent scientific study."

Nautilus will not be the first underwater mining operation in the world. De Beers has been stripping diamonds from the seabed off Namibia for several years, but at far shallower depths - generally around 150 metres.

Metal detecting

US scientists first began probing the Pacific seabed for manganese nodules in the 1970s. The price of the metal plunged shortly after and exploration was suspended. Nautilus is not alone in prospecting for concentrated ores on the deep-sea floor.

Neptune Minerals, a UK registered company, is also working on deposits left around extinct "black-smoker" vents. The firm, which has headquarters in Australia, has identified SMS deposits in several locations.

Exploration licences have been applied for by Neptune in territorial waters off Papua New Guinea, Japan, New Zealand, Palau, the Federated States of Micronesia, the Northern Mariana Islands, Vanuatu and Italy. An estimated 350 vent fields have been found worldwide.

Both firms cite gold, silver, copper and zinc as main targets. Nautilus says its operation will be profitable as long as the price of copper stays above $1.50 a pound; it is now $3.80. The cost of metals has been boosted by the expansion of China and India's economies, likely to sustain prices for some time.

Nautilus plans to extract 6,000 tonnes daily - some 1.8m tonnes a year - from a field in the Bismarck Sea. It says it should eventually recover up to 500,000 ounces of gold and 160,000 tonnes of copper a year.