Offshore Tin in Cornwall: Is Anyone Dredging the Seabed, and What Would It Do?

Is anyone about to dredge tin off Cornwall? The short answer is no, and the register is where you check. St Ives Bay is where the question keeps coming back, so this guide starts there, then explains what the seabed tin is, what dredging does and how to comment on an application. The mining story that put the tin there is in Cornish tin mining history. The offshore tin hub lists the rest of the series.

Is anyone proposing to dredge tin off Cornwall now?

No application has been published for public comment. The Marine Management Organisation keeps a public register of marine licence applications and decisions, held under section 101 of the Marine and Coastal Access Act 2009. On 21 October 2026 its “open for public consultation” tab held 11 applications. They were aggregate dredging at Area 407, pontoons, outfalls, pier works, dredge disposal and a wind farm cable among them, and none was for tin or for a location in St Ives Bay.

That is a snapshot of open cases, not of every case ever filed. Anyone can view applications and decisions, search by area or licence type and download the applications. If you only do one thing, search the register by area before you repeat anyone’s claim about a live proposal. It is free and it takes a minute.

To check a claim yourself, in order:

1. Open the MMO public register of marine licence applications and decisions.
2. Search by area or licence type, and look for tin, St Ives Bay or the stretch of coast in question.
3. Read the application itself, which anyone can download.
4. If a case is open, send a representation: the MMO consults for 42 days and invites comments from the public.

What the seabed tin off Cornwall is

Offshore tin is cassiterite, the tin oxide mineral, sitting in sand and silt under the sea. Cassiterite was the chief tin ore throughout ancient history and remains the most important source of tin today. Because it is heavy and chemically resistant it collects in sediment as a placer deposit, and about 80% of mined tin comes from secondary deposits downstream of the primary lodes.

The tin off Cornwall owes much to people. The silt off the north coast contains cassiterite, most of it dumped into streams by the proprietors of 19th-century tin mines on the mainland. With the technology of the day, they were unable to extract the tin and viewed the silt simply as waste. Tin metal production peaked at about 12,794 tonnes in 1870, and the waste was frequently flushed into local water courses. Cores from coastal sediments show heavy metal concentrations above what normal weathering would produce.

Some tin was followed beneath the waves. Some Tin Coast mines stretched up to a mile under the sea. At Geevor a sub-incline was driven into Levant so that mining under the sea bed was carried out again, after a breach from the seabed into Levant’s upper levels had to be plugged.

The paper trail: a 1912 file and a 1983 plan

The idea of dredging this tin has a long paper trail in St Ives Bay. A file at The National Archives records applications to dredge alluvial tin in St Ives’ Bay, with a note dated 9 October 1912. It sits among the records of the Crown Estate and its predecessors.

A 1983 scheme went much further on paper. The plan was to dredge from the sea, off Cornwall’s northern coast, layers of silt that rivers had carried out over the centuries. Its backers estimated that the mud held about 10,000 tons of tin that could be extracted with modern techniques.

These were targets reported in May 1983, and no source used here records the scheme going ahead. The market it depended on broke in October 1985, the year the first load was due: tin prices fell from $12,389 a ton that month to $5,485 in June 1986.

What dredging does to the seabed

The documented effects come from sand and gravel dredging, the nearest comparable activity with a long scientific record.

Dredging removes sediment, changes the shape of the bottom and throws up a plume of cloudy water. How much that matters depends on the dredger and on the seabed it works. The first effect on seabed life is a drop in the abundance, species diversity and biomass of the benthic community.

Recovery is the argument. A peer-reviewed study at the Hastings Shingle Bank found the disturbed seabed capable of full recovery given enough time. That is not always the case and it depends on the dredging protocol used, for example sediment screening. Where a site is dredged repeatedly at high intensity, recovery can take more than seven years. In the end the biological impact of an extraction operation depends on the physical impacts and on the local seabed communities.

Cornish silt adds a question the aggregate studies do not cover: this sediment already holds heavy metals from mine waste, which is the kind of detail an environmental impact assessment has to examine.

What a tin-dredging application would have to show

The MMO regards extracting minerals by dredging as a project likely to have significant effects, which is the trigger for an environmental impact assessment. The aims of that assessment are to protect the environment and allow the public to play a part in making decisions. Some parts of the marine area are protected in law, including Marine Conservation Zones, European protected sites and protected species’ habitats. Near a Marine Conservation Zone an applicant has to show how it would reduce negative effects.

The public has a defined part. During the review the MMO consults for 42 days and invites representations from the public. The decision goes on the public register and to everyone who made a representation. To comment, find the case on the register.

What the licensing rules say

Taking tin from the seabed around England is a licensable activity. Section 66 of the Marine and Coastal Access Act lists removing any substance from the sea bed with a vessel as a licensable marine activity. It lists dredging too, and the Act defines dredging to include using any device to move material from one part of the sea or sea bed to another. No person may carry on a licensable marine activity except in accordance with a marine licence granted by the appropriate licensing authority.

A seabed survey licence lasts up to 12 months. The standard application fee is £500, and issuing one can take the Crown Estate around 6 weeks. The MMO’s public register carries marine minerals extraction documents alongside renewable energy ones. In Cornwall the foreshore and estuary beds are partly Duchy of Cornwall land rather than Crown Estate land, as the Crown Estate seabed rights guide explains. For the full process, fees and appeal routes, read the UK marine licence guide.

A short history and the mineral statistics: why the tin reached the sea

Mining has gone on in Cornwall since the Bronze Age. The waste that now lies in the bay is mostly nineteenth-century: the industry ended in stages after the tin crisis of October 1985. Geevor and South Crofty each have their own timeline in the mining history guide, which also covers arsenic, china clay and slate.

Tin from the sea floor today: Bangka

Seabed tin is dredged for real in Indonesia. Treat it as a comparison, not a Cornish prospect. Miners on Bangka head out to scores of crudely built wooden pontoons equipped to dredge the seabed for tin ore. Pontoon pipes can be over 20 metres long to suck up sand from the seabed. Land deposits in Bangka-Belitung have been heavily exploited, leaving vast craters and highly acidic, turquoise lakes.

Not everyone there is happy about it. Fishermen say their catches have collapsed due to steady encroachment on their fishing grounds since 2014. Indonesia mined an estimated 55,000 tonnes of tin in 2024 and 61,000 tonnes in 2025, against China’s 71,000 tonnes in both years. For tin at the far deeper end of the scale, see what deep-sea mining is.