Seafloor mining: the DeepGreen method

As resources dwindle, mining companies are increasingly looking to the sea to provide the minerals and metals we need. Environmental concerns hang heavy over deepsea mining, but Canadian company DeepGreen Resources is developing a new method to mine essential resources without any waste.


DeepGreen Resources is an exploration company focused on the possibility of harvesting polymetallic nodules from the seafloor. Unlike deepsea mining of crust or seafloor massive sulphides, nodules sit semi-submerged on the seafloor and, therefore, do not require intensive mining.

“Seafloor Polymetallic nodules are mineral deposits found on the seafloor that can look like fields of potatoes,” says DeepGreen head of environment and social performance Dr Samantha Smith. “Nodules are often rich in metal, and the key here is that they are multi-metal. So they can contain nickel, manganese, cobalt and copper, as well as other metals.”

By collecting these nodules DeepGreen is hoping to provide important metals in a minimally invasive way. But as deepsea mining becomes an increasingly hot topic, what sets this company apart from the growing subsea pack?

The DeepGreen way

DeepGreen was set up in 2011 by David Heydon with the support of now-CEO Gerard Baron. Both had been involved in Nautilus Minerals, another deepsea mining company which is on track to be the first in the world to start commercial operations off the coast of Papua New Guinea in the next couple of years.

But unlike Nautilus, DeepGreen is pursuing a method that would allow essential metals and minerals to be gathered without creating any waste or tailings at all. “I think zero tailings is a phenomenal objective for a mining company to have,” says Smith.

This pursuit is possible due to the nature of the polymetallic nodules, as they sit on the seafloor so can be harvested by ROVs. Once collected, they can be shipped to a processing plant where DeepGreens’ patented hydrometallurgical processing technology can be used to extract the metals.

"DeepGreen now has two exploration licences to begin work in the Clarion Clipperton Zone in the Pacific Ocean, to collect nodules containing nickel, manganese, cobalt and a copper content grade of 7%."

Alongside the valuable metals is a range of by-products that are all marketable. Zinc sulphide concentrate, high-grade silica, iron hydroxide and nitrogen-calcium feed are all found within the nodules and can be used in various applications, such as in cement or as fertiliser.

DeepGreen now has two exploration licences to begin work in the Clarion Clipperton Zone in the Pacific Ocean, to collect nodules containing nickel, manganese, cobalt and a copper content grade of 7%. The area was first explored with mining in mind in the 1970s, before the International Seabed Association (ISA) was set-up. This meant that prospectors could not be commercially licensed at the time, and the area has been left alone since.

Why deepsea mining?

Around the world, high-grade resources are becoming rarer and mines are increasingly yielding only low-grade ore bodies. Continuing to excavate these deposits creates vast amounts of waste and tailings to recover only a small amount of metal.

“What if we could get minerals or metals where we don't have to dig up mountains to get to the ore body, with often around 75% of what is mined ending up as waste,” asks Smith. “What if people didn't need to be relocated for a mining project to proceed,” she says, adding, “What if people didn't need to live next to tailings dams, what if we could mine deposits with grades or with the number of metals much higher than what is found on land? Going to the seafloor for metals meets many, if not all, of these ‘what ifs’ and, given that, doesn’t it make sense to at least consider going to the sea as a viable alternative way of obtaining metal?”

The rising popularity of renewable energies, and their evermore competitive prices, are also contributing to the pressure on the mining industry. As demand for green technologies such as batteries, lightweight turbine blades and solar cells, is growing, deepsea mined metals and minerals will be essential for their construction. “For example, wind power alone requires significantly more metal to produce power than conventional power generation,” Smith says, “So if you think about a single 5MW wind turbine, and depending on the type of generator you use, you're looking at needing 15t of manganese, 5t of copper and 5t of nickel, and incidentally, all of those are found in polymetallic nodules.”

Threatened environments

Despite the potential economic benefits, there is major concern over the ecological damage sea mining could cause. When mining at sea the seafloor is stripped to allow the rock underneath to be ground and extracted; a process which decimates the sea life communities, as fish and plants are killed. Another factor is the effect of plumes on the local environment, as flurries of displaced sand and debris are sent up into the central column of the water. Debate is ongoing over just how detrimental these practices are, with some miners arguing that the effects will be localised and the plumes would settle quickly.

“At the seafloor, there will be material, habitat and animal removal where mining occurs,” Smith confirms. “The thing to note here is that those types of impacts would be the same for any mining operation, be it on land or in the sea. There will also be plume generation from the removal of the minerals from the seafloor and you have potential for light, noise and vibration – related impacts as well.”

By pursuing nodules, the least invasive deposit, DeepGreen hopes to keep disturbance of the underwater environment to a minimum. There are further environmental benefits to be gained on land, as because the practice is not site-specific, the processing plant can be built anywhere, easily avoiding at-risk areas, and the lack of tailings means there’s no need for tailings ponds which hold the risk of toxic leakage.

What’s next?

DeepGreen has now entered into an agreement with Maersk, which will provide a number of vessels for five marine campaigns over the next two years. These trips will allow the company to complete its exploration work and the final studies required by the ISA. An offtake agreement has also been reached with Glencore, which will take 50% of the copper and nickel produced by one of the sites.

"DeepGreen has now entered into an agreement with Maersk, which will provide a number of vessels for five marine campaigns over the next two years."

“The next step for DeepGreen is to commence long-term environmental baseline studies, which is another exciting part of the project for me,” says Smith. “We'll be putting down oceanographic moorings initially and we have a number of offshore campaigns planned over the coming years to complete the studies needed for an environmental impact assessment.”

Once the studies are completed mining can begin, with DeepGreen hoping to play an important part in securing the future of the world’s metals supply in the most responsible way possible. As part of this approach, the company is ensuring scientists and researchers will be involved throughout the whole process to map, study and protect the oceans.

“One of the objectives that we have is to contribute to the global knowledge of deepsea processes and to make sure that the field of science benefits from the work we're doing in the deepsea,” says Smith. “It's not easy to go out into the middle of Pacific and conduct studies in over 4000m water depth, so we want to make the most of our time spent there and have scientists offshore with us and partnering with us to make sure that we are understanding the site together and that together we work out the environmental management measures that will ensure we develop and move this industry forward as responsibly as possible.”