Deep-sea mining opens mineral opportunities on the seabeds

Materials World magazine
10 May 2019

Better harvesting methods would help unlock the opportunities seabed minerals can offer.

Maritime exploration programmes around 150 years ago identified the existence of minerals on the seabed. Since then, one could say the arguments for and against mining seabed minerals have ebbed and flowed. Seafloor massive sulphides (SMS) and cobalt-rich crusts have garnered economic interest in deep-ocean mineral deposits. But the debate is sometimes clouded by the term manganese nodules being applied to deposits comprising several minerals, for instance, nickel and copper. In fact, manganese has a much higher concentration than nickel plus copper. Another, more appropriate term, is polymetallic nodules.

By the mid-1970s, consortia had formed to exploit nodules in the north-eastern Pacific Ocean between the Clarion and Clipperton Fracture Zones (CCFZ). However, the intended commencement of mining never happened as metals prices dropped worldwide. In the years since, 16 exploration contracts in the CCFZ have been agreed or are pending with the International Seabed Authority.

To some extent, this increased interest in seabed minerals follows the increased demand for minerals as a whole, with existing mineral resources facing the dual challenges of decreasing resources because of current extraction rates and a lower mineral quality.

US Geological Survey Pacific Coastal & Marine Science Center’s Research Geologist, Dr James R Hein, commented on the quality of land-based minerals to Materials World. ‘The deposits that can be mined at a profit on land have to be large deposits and may not be of the highest grade because the amount of infrastructure and investment required at a mine site prohibits mining small, high-grade deposits’, he said.

‘So, the new generation of land-based mines will be deeper, open-pit mines will become much larger due to lower metal grades, and underground mines will be deeper and also huge in size. Small, high-grade ores on land do exist, but may not be mined, except perhaps by artisanal mining in places.’

So why seabed mining?

The case for seabed extraction is sometimes deemed acceptable because it does not have other disadvantages of on-land mining – there are no people at the mine site to experience the disruption to their health, the breakup of their community or the need to move entire villages.

In the case of SMS against nodules and crusts, seabed minerals generate a smaller footprint in terms of size of operation, but in all cases there are lower emissions from mining machinery, little over-burden and no need for surface roads, ore transport systems and substantial construction costs.

Mining techniques, too, are straightforward even if this form of mining is in its infancy. Extraction has been delayed because the development of highly specialised and hitherto unknown technology has held up advancement. Exploration offers its own challenges, as marine-oriented scientific sampling, photography and research must be factored in.

In short, actual mining of deep-ocean seabed mineral resources is still some years away. However, for decades now, seabed mining has been happening in coastal waters in depths of up to 150m.

If sea mining is allowed

‘Different methods are required for the different SMS, nodules and crusts,’ Hein said. ‘Four or five methods have been developed
for mining SMS, but none is favoured because mining has not yet started and testing has not been completed. For nodules, several methods have been developed, with none favoured for the same reason. For crusts, methods as far as I know have not been developed although much of that work has been kept proprietary and may exist.’

Various potential methods for mining the seabed have been put forward. They include the use of remotely operated vehicles (ROVs) which would operate on the seabed itself, and would scoop up the nodules. The latter would be conveyed from the ROVs via a pipeline or a continuous-bucket dredging system, both ending with a platform or ship on the surface.

At this point the platform or vessel would separate the water from the nodules, which would be released back into the sea, with the nodules taken onshore for processing and sale.

The right quality

Considerable time has been devoted to discussing whether minerals on the seabed are of the quality demanded by the organisations likely to purchase them. Hein suggested that the grades in question were excellent, and there are good tonnages available in terms of crusts and nodules. When it comes to the SMS, small deposits with very high grades can be mined because the mining ship – the infrastructure – can be moved from one small deposit to another.

However, Hein sounds a note of caution. ‘The profitability will not be known until mining actually takes place,’ he said. ‘There are many unknowns, such as the longevity of the mining equipment working continuously in extreme environments, which will be critical, and of course global metal markets cannot be predicted, although this may be somewhat lessened by the fact that more than one metal will be extracted from the marine mineral deposits. Right now, the many critical factors that must come together for profitable deep-sea mining look promising for the companies. This requires that the operations will take place in the most environmentally sound ways possible.’

Cook Islands case study

Manganese nodules are identified within the Pacific Ocean, with an abundance in territories such as Kiribati and the Cook Islands. An estimate six years ago determined the Cook Islands’ Exclusive Economic Zone (EEZ) hosts 10 billion tonnes (Bt) of manganese nodules – the second largest deposit after the CCFZ’s 27Bt. The CCFZ nodules are lower in cobalt but higher in nickel and copper.

One technical term relevant here is the seabed of the Cook Islands’ – the Cook Islands’ EEZ, ocean floor and subsoil, which extends for 200 nautical miles, as defined by the United Nations Convention on the Law of the Sea (UNCLOS). In reality this means the Cook Islands can explore and exploit a total marine area of 1,830,999km2.

Numerous surveys since the mid-1970s have provided a resource database that enables marine scientists to gain a reasonable indication of the location, size and content of the seabed minerals resources within the Cook Islands’ EEZ. Much more resource definition, as well as environmental studies of the ecology of the seabed where the manganese nodules are identified, need to be carried out before the feasibility of mining the nodules can be determined. This will be done under exploration licences granted to mining companies that can demonstrate that they have inter alia the necessary technical and financial resources.

Mining and the environment

As with any mineral activity, there are always environmental considerations. On 8 November 2018, The Economist article Mining the deep ocean will soon begin asked, ‘what will it mean for existing denizens of the abyss?’.

The article reported that in 2013, Natural History Museum, London, Research Fellow, Dr Diva Amon, recorded seeing a whale skull on an expedition to the CCFZ. It lay on beige silt, 4,000m beneath the surface and was covered in a black coating. This latter meant the skull was millions of years old with a coating The Economist said was ‘made of the same slowly accumulating metallic oxides as the potato-like ore nodules that are drawing miners to the area’.

It continued that would-be seabed miners visualise seabed mining as a multi-billion dollar industry. One additional factor is seabed minerals are not just abundant but are also found in combinations of two or more such minerals – something rare in terrestrial mines. The publication cites Global Sea Mineral Resources General Manager, Kris Van Nijen, as saying the company is interested in exploiting the nodules, ‘for the same amount of effort, you get the same metals as two or three mines on land’.

Amon’s discovery reinforces how little is known of the seabed. The consideration that arises is weighing up the economic gains of mining the seabed against the environmental consequences of mining activity. A further factor is the benefits for countries in the immediate vicinity of the mining operations. If nodules are mined in the Cook Islands’ EEZ, the islands will reap economic benefits. In the case of the CCFZ, some part of the profits will be distributed to countries as per ISA regulations.

Seabed sustainability

The manganese nodules off the Cook Islands are no exception to the rules governing all nodules – they have developed over millions of years and are not a renewable resource. In other words, once the nodules are gone, they are gone for millions of years so successful and careful management is vital, whether the criterion is profitable operations, conservation or the revenue to benefit the local community such as the Cook Islands.

So are there plans for recycling sea-based minerals? ‘Two companies proclaim that they can process manganese nodules with zero waste – if so, there would be nothing to recycle,’ said Hein. ‘Crusts should be able to be processed in those same plants, while SMS will be processed by the same processing plants that process volcanogenic massive sulphides produced from land-based mines. The waste produced will be handled as usual for those plants.

‘Products made from metals mined in the deep ocean will be recycled along with those from land-based mining. Recycling needs much greater education worldwide to help fill demand gaps for metals and, of course, that will depend on the profitability of the recycling, unless it is subsidised.’

It is likely that some seabed mining will be carried out in the near future, as substantial research and evaluation will have taken place. Exactly how one can reconcile the quantities that would need to be mined to make the project viable with the environmental considerations and benefits for local communities will make this a subject of much debate, and argument, for a long time to come.