How many old mines are in the UK?

At its peak in 1920, the UK coal industry employed more than a million workers. Tin, lead and copper mining here also helped play a significant part in helping to drive the industrial revolution. The number of people employed in mining, however, began to decline rapidly in the second part of the 20th century as it became cheaper to get these raw materials from Europe and further afield. Mining has continued elsewhere to feed our need for a variety of everyday items like cars, smartphones and jewellery. But what happens when these often vast mines seemingly close for good? And can they ever find a new lease of life? Gavin Mudd from the British Geological Survey…

Gavin - If we look at the UK, we know that about 25% of homes actually sit above a former mine, most of which is coal. But in some areas of course, we're looking at old tin mines, copper or lead mines and so on as well. But certainly we see that same pattern globally.

Chris - And are they well documented? Do we know where they are?

Gavin - In general, we know where they are. Often we don't necessarily have the production records and each individual mine can range from anywhere from tens of tonnes of metal to sometimes tens of thousands of tonnes or more as well. Same as with coal. We can go from thousands of tonnes up to hundreds of millions of tonnes of coal or even billions of tonnes of coal in some cases. So the scale can vary enormously.

Chris - And what sort of condition are these old workings in?

Gavin - Yeah, a condition can vary. We can see mines that nature has basically taken back over. We can see mines where there are still active issues that need to be very carefully managed, such as mine waters that could be acidic and carry trace metals that do provide risks to that local environment. Typically, I suppose that's the big question, is we need to understand what those sorts of risks are and work out how to manage mining and work out what the post mining land use really becomes.

Chris - And I suppose it's not just the hole in the ground, it's the stuff that's come up with the stuff we wanted that got discarded and turned into a spoil heap. That's also a problem sitting there.

Gavin - Mining is pretty simple in some ways we dig the rock out of the ground that contains either the metal or the minerals that we're after. And then to get that rock, we also need to dig out other rock, rather other sediment. Let's just say it's, it's 5% copper contained in the rock that you are processing in mining that would be called ore. But you've got 95% is therefore not copper. And that's basically left behind as a solid waste or what we call tailings. And so that tailings have grown over time and as mines have got bigger and bigger or the grades have declined, so now we're not chasing copper that's five or 10%. We're chasing copper, that's 0.5% and in some parts of the world, even as low as 0.2%. So in order to produce more and more copper, we need to mine more and more material all the time. And this is why modern mines are typically much, much bigger, whereas your older mines, pre 20th century, typically were much smaller. And so that's one of the key distinctions that I think we always need to be mindful of

Chris - Double-edged sword. This in some respects, isn't it? Because I remember talking to a colleague of mine in South Africa. I went to visit one of their gold mines and they showed me their spoil heap there and they had billions of tonnes of material they'd been told to sort out. But they pointed out that the old timers had much less good technology than we do today. So in fact, rather than dig up fresh stuff, you go digging up the tailings because you can get much more out of that with a higher yield with new technology than you could ever get outta the ground these days.

Gavin - Yeah, if you look at the Witwatersrand basin in South Africa, typically mining anywhere from, in the early days it was 30 grams per tonne or an ounce of gold per tonne of rock they processed to get the gold out of. Then an operating mine these days it'd be five grams per tonne there. The tailings would still be 0.5 grams per tonne. Now when you look at many gold mines around the world, the average globally is around about one gram per tonne. So if you don't have to pay the costs of actually digging the rock out of the ground and all you have to do is basically get it from the tailings dam or that mountain of residue into a process plan, you've basically had to pay half the cost. You only have to pay for the processing cost and not the mining cost as well. For South Africa, the other issue is uranium. There's residual uranium in the tailings as well. But sometimes we're also thinking about it and saying, well, the old timers were very efficient in terms of the way they mined and processed with the technology they had, but they didn't think about environmental issues or the longer term environmental risks. And so sometimes going in and reprocessing old tailings, you can actually re-engineer where they're placed, clean up that site and get the environment into a much healthier, more sustainable sort of condition as well. That could be a really important part of the overall reasons to go back and have another go.

Chris - So that's one way that we can give an old mine a new lease of life. We can go and clean up the mess that was made, perhaps even making it pay for itself in the process. What other opportunities are there for some of this legacy mine workings that we have in countries like the UK old world economies? What can we do with and what are people trying to do with those old mine workings?

Gavin - Old mine working can be thought of in all sorts of ways. You can use the workings as a kind of pumped hydro scheme. So using gravity as a way to store energy. Technically challenging, but it can actually work. And there's certainly, I've seen some work at mining regions around the world, but that type of technology has actually been used historically in the old hydraulic days, I guess. The other thing we can do is convert it into things like country parks. So you basically recontour the surface, make everything safe, and then you can reuse that land either for recreation. In some places you might even be able to build houses. Another idea would be, especially with quarries for example, to make those old quarries into lakes. So you've got a big hole in the ground. There's always lots of water here in the UK, so fill that hole with water. And then you've got a lake that could be used for various things as well. There's some of the main ideas or like we've seen with the Eden project, you build basically a large sort of centre in the middle of it, and that way you get a great functional venue that you can use for all sorts of things.

Chris - And are people turning old closed down mines back into mines again? Because I did read somewhere that, for instance, some of the old tin mines in Cornwall where initially they were going for things like copper and tin, there were things like lithium down there as well, but they didn't know they wanted that at the time. Now that's incredibly valuable.

Gavin - One of the things that I think is different these days is we don't just look at the singular metal, the sole mineral that's of interest. We think about everything that's there and what's possible. So with some of the projects in Cornwall for example, we're looking at not only at the elements that are there such as lithium or tin and copper, but also things like the heat, right? If we're going deep into the Earth, we know that there is heat stored there. Can we use that geothermal energy as part of the way to actually power the mine? We're not only providing the minerals that we need for modern technologies like lithium, but also the challenges that we have to face in terms of climate change and reaching net zero emissions already building into that mine and making sure we get the most out of everything that we do. There's a lot of effort down in Cornwall to build those sort of 21st century style mining projects.