Mining under the sea

Materials World magazine
,
1 Sep 2008
The device used by Nautilus to explore the seafloor

The newest frontier for mining is underwater. Meagan Ellis looks at the technology involved and the environmental concerns that remain with this untested excavation technique.

Rising up from the floors of the world’s oceans like miniature mountains, hot springs (called ‘black smokers’) emit heated brines which cool to become rich deposits of zinc, copper, silver and gold, so called seafloor massive sulfides. For about 10 years companies operating off the coasts of Papua New Guinea (PNG), New Zealand, Tonga and Fiji have explored these massive sulphide deposits and dreamt about finding an economical method of tapping these vast but hard-to-reach resources.

Now, with demand for minerals growing day by day, and new technological advances in cable laying, diamond trenching, and deep water oil and gas excavation, the obstacles to undersea mining have become less daunting. Two of the world’s first seafloor massive sulphide mines will begin operations in 2010, run by the UK’s Neptune Minerals in New Zealand, and Canada’s Nautilus Minerals in PNG.

Scott Trebilcock, Vice-President of Business Development at Nautilus, headquartered in Toronto, says his company operates ‘on the same principles as the oil and gas industry, which lays thousands of kilometres of pipeline on the seafloor by digging trenches. We also operate on similar regimes to the dredging industry, which extracts billions of tonnes of gravel and sand from the seafloor. So the precedent is out there’.

Setting standards

But as companies prepare for a new age of minerals excavation, the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) has released a report on the potential social impact such mining could have on the Australian coast. Its results, while highlighting the possible economic benefits, have revealed concerns as so little is known about underwater mining of this kind.

‘A key concern of the community is the perceived environmental impact of such an expansion, and the lack of scientific knowledge to measure or monitor this impact,’ explains Dr Joanna Parr of the CSIRO, who helped write the report.

Exploring the Social Dimensions of an Expansion to the Seafloor Exploration and Mining Industry in Australia, published on 13 June, notes, ‘No major comprehensive review on seafloor exploration and mining, or deep seabed mining, issues has been produced for at least the last five years’. It says
there have been no synthesising studies on international seafloor mining developments in countries such as Canada, Russia, Korea, Chile and Finland, and there are no codes of practice for companies to draw on.

But being the first in the water can have its benefits, notes Dr Simon McDonald, Chief Executive of Neptune Minerals, based in London. ‘[We] are in the enviable position of starting with a clean slate, without the legacy issues faced by land-based mining,’ he says. ‘We are able to design a mining system from scratch that will comply with environmental best practice.’

Parr agrees that Neptune and Nautilus ‘clearly recognise the danger of losing public support, and are therefore actively involved in research to assess the potential environmental impact of mining in their tenements’.

Treading carefully

Nautilus has been exploring the waters of PNG since 1997. For the last three years it has been conducting environmental baseline studies in and around Solwara 1, an area 1,500-1,600m deep, 1.3km long and 200m wide in the Bismarck Sea. It has an indicated and inferred resource of 2,170kt at 7.2% copper, 6.2g/t gold, 31g/t silver and 0.6% zinc.

Trebilcock says the company has taken steps to keep the PNG Government involved, and to follow recommendations made by it as well as other non-government organisations. The assessment looks at oceanography, animal and plant habitats, sedimentation rate, noise and light, and waste management. The project is expected to have minimal impact on fishing and the seafloor, and will not operate on the reefs. Energy will come from electricity supplied by the ship. The results of the Environmental Inception Report will be published in October2008.

Building blocks

Using designs borrowed from the trenching, oil and gas industries, Nautilus’ proposed mining system will consist of an excavator, a support ship, and a riser and lifting system to pump metal sulphide debris to the surface.

Soil Machine Dynamics (SMD), based in Newcastle, UK, received the £33m contract to design and build Nautilus’ digging tool, which will incorporate the most technically difficult component – the cutting head. ‘Although [SMD] has cutting heads that break up rock, they have never done it on this kind of rock before,’ explains Trebilcock.

‘The material they have to cut is rather soft compared to ores on land,’ adds Dr Steven Scott, Director of the Scotiabank Marine Geology Research Laboratory at the University of Toronto, Canada. ‘There will probably be problems with [the new equipment] – there always are with new ventures – but there is a lot of collective knowledge to overcome these.’

High pressure underwater drilling tests using sulphide samples from Solwara 1 are being carried out at SMD to determine the best design for the cutting head and the pump which will suck the materials to the surface.

Trebilcock calls this type of excavation ‘surgical mining’. ‘As we break up the material, it is sucked up with an enormous amount of seawater to the deck of the ship. The water is then filtered and cleaned in a dewatering system, and the cold seawater is put back down at depth. So unlike in dredging, our discharge water goes back where it came from. There will be no ugly plume of mud coming out of the back of the ship.’

All equipment is scheduled to be delivered at the end of 2009, with mining beginning at the end of 2010. The operation is expected to produce 1.5-1.8Mt of ore a year.

Neptune tests the water

Neptune has plans to begin the pilot phase of its 1,500m underwater mining project in the Rumble 2 West site in the territorial waters of New Zealand in 2010. Its equipment is based on a device trialled by Canadian company Placer Dome in 2006, which successfully recovered 15t of massive sulphides.
The system involves mounting an excavation device on a remote operated vehicle. A clamshell grabber will be used for surface layer recovery, while an ore crusher breaks up pieces to sizes between one to two inches (2.54-5.08cm). These fragments, and the water surrounding them, are sucked up to the ship using an airlift pump.

McDonald believes the environmental benefits of undersea massive sulphide mining are many. ‘It is high-grade and low-tonnage, there is minimal to no overburden, and no mining of waste rock.’ The mine is expected to process two million tonnes a year of massive sulphides in an area that covers just 300x300m.

The company has conducted its own environmental impact assessments, in association with the New Zealand National Insitute of Water and Atmospheric Research, and will continue do so during each stage of its preparation and test mining. After the six-month trial, a final assessment will have to be approved before full-scale mining can begin.

A new era for mining?

Should Neptune and Nautilus’ mining experiments prove successful, it could
usher in a new age of large-scale mining. McDonald says his company expects
to spend between US$145-162/t to extract minerals that could sell for US$50-2,000/t.

Trebilcock agrees with this financial forecast, noting any extra costs of operating offshore are compensated for by the high concentrations of copper and gold found.

Scott is equally optimistic. ‘It is very early days, and no one really knows what the seafloor has to offer. Almost all of our mineral resources come from the 26% of our planet that is land and not covered by ice. If Nautilus [and Neptune] pull it off – and I believe they will – others will surely follow.’

Parr says the CSIRO will follow both projects with interest, and will conduct detailed surveys and models to better inform the Australian Government on how its own offshore mining policies should be directed.

Further information:

Neptune Minerals

Nautilus

Commonwealth Scientific and Industrial Research Organisation