Finding tin on the seafloor

13 March 2018 (Last Updated March 12th, 2018 17:02)

For thousands of years mining waste has been washed into the sea off the coast of Cornwall thought to be lost forever. Now, Marine Minerals is preparing to recover the tin that went down with it.

Finding tin on the seafloor
The VAMOS project aims to develop underwater mining vehicles, including seabed crawlers which will be used in Marine Minerals’ work off the northern coast of Cornwall. Credit: Courtesy of Marine Minerals

For more than 4,000 years tin has been mined in Cornwall, by the 1800s the region was a world leader in tin production boasting 2,000 mines. Throughout this period of activity, waste was discharged into rivers and carried out into the sea, including amounts of tin that were historically too difficult or uneconomic to process.

Over the years, this tin has built up as a layer beyond the breakwater and now amounts to an estimated 22 million tonnes.

Marine Minerals, a mining exploration company based in Falmouth, Cornwall is currently working to obtain a license to take advantage of this forgotten resource. With technological developments bringing hope for recovery and a bolstered tin market, is it time for tin mining to return to Cornwall?

80s efforts in tin mining

Marine Minerals CEO Mike Proudfoot worked on a project to explore the possibility of mining tin from the seafloor off the coast of Cornwall more than thirty years ago. Feasibility studies were undertaken and the project briefly managed to produce and sell tin. “I ran this project from 1980 to 1985, at that stage there was a collapse in the global tin market, which eventually caused all the tin mines in Cornwall to close,” says Proudfoot. “Like the others, the offshore project then came to an end.”

The collapse of tin in the latter half of the 20th Century devastated Cornwall. In 1998, the last tin mine in Europe, South Crofty in Cornwall, closed marking the end of the industry that had shaped the region. The loss of jobs provided by mining has contributed to Cornwall becoming the poorest county in England.

But the global market for tin has changed, with increasing demand and supply constraints boosting prices. Tin is predominantly used as solder in electronics to connect circuit boards and transistors. For instance, the average smartphone contains 7gams of tin and it’s also used in lithium-ion batteries, a market that is quickly expanding.

In 2016, the global demand for tin was 348,900t, a growth of 2% from 2015. The London Metal Exchange, however, registered a 7% drop in inventory levels of tin in 2016, and a drop of 31% the previous year. As such, tin prices have been boosted to around $20,000 per metric tonne (mt).

With demand for tin strong, Proudfoot believes now is the time to once again look search the seafloor for tin. “We’ve been watching the tin price and its recovery and we’ve seen the projections by various experts. We believe that the price now is economic for the project and the price will continue to escalate from here.”

Mining waste from the seabed

Marine Minerals is a member of Euro 2020 grant research group Viable Alternative Mine Operating System. The project aims to develop underwater mining vehicles, including seabed crawlers which will be used in Marine Minerals’ work off the northern coast of Cornwall.

These technologies will allow the company to move away from traditional techniques such as dredging, which are used elsewhere in the world for the extraction of tin. In Indonesia, the second biggest tin exporter in the world, the seabed is dredged for ore around Bangka, causing significant environmental damage and decimating the local fishing industry.

“The tin sand, because of its fineness, lies out to sea way beyond the breaker line,” says Proudfoot. “Because of the waste tin sand’s fineness, the sea has sorted and graded and moved it so that it lies at water depths of between 10m-20m. The tin sand is in a layer of about 1.5m thickness. We will sieve out the tin and return the 95% cleaned sand back to where we lifted it from.”

A combination of sieving and cleaning spirals will be used onboard the specially modified ship to extract the ore. In total, a layer just 3in thick will be removed from the seabed following this process.

“The sand landed has been upgraded to the equivalent of a rich underground tin mine’s ore,” says Proudfoot. “A vessel will transport the tin sand to and discharge it at the Port of Fowey. The company will have a processing plant in the St Austell China Clay district. Once all the tin has been extracted, the remaining sand will be used environmentally to revegetate old clay dumps and refill and reinstate a big mining pit, creating further environmental benefit.”

Is it environmentally sound?

Despite technological advancements, environmental concerns remain the core challenge Marine Minerals faces. “We need to get a licence from the Marine Management Organisation (MMO), which is a government organisation,” says Proudfoot. “For that, we need to do a range of environmental assessments. This includes physical and mathematical test work, to show what erosion, if any, the work would do to the coast and if there’ll be any other significant negative impacts, that sort of thing.”

Marine Minerals estimates that 8,000t of tin-bearing sand a month would be brought to shore, a fraction of the billion tonnes estimated within its licensed area. Furthermore, the sand in which the tin is found is ‘dynamic’, loose sand which moves with the current, tides and storms. Being such an unstable ecosystem, it’s thought the removal of sand will have little effect on the ecology of the immediate area.

“The major question that has to be answered is ‘will the operation do damage to the coastline?’” says Proudfoot. “The study is called a Coastal Impact Assessment and we will have the best experts conducting the assessment, this includes the world leading consultancy Hydraulics Research Wallingford. They are located fairly close to Oxford and are the world’s leaders in the studies they will undertake. Their research will include conducting physical, tank and mathematical tests looking at the various aspects required, to satisfy the report that goes to the MMO, who will decide whether it’s appropriate to grant us a licence or not.”

It’s hoped that by recycling what was seafloor mining waste using precise underwater vehicles, Marine Minerals will be able to take advantage of a valuable mineral without causing environmental damage. The project would bring significant benefits to the local area as well.

“There are a number of significant benefits this recycling project will bring, this will include the 110 high-paid year-round jobs that will be generated for Cornwall,” says Proudfoot. “A local newspaper conducted a survey to determine the level for support for dredging in Cornwall and found that because of the associated job creation aspects, more than two thirds supported it.”

As resources become more constrained, recycling mining waste to capitalise on technological advancements becomes increasingly appealing. Marine Minerals could contribute significantly to the tin industry and the local community in Cornwall, provided it can guarantee the safety of the coast.