Tin Smelting at Geevor

On Sunday 26^th July at Geevor Tin Mine, a friend of mine and fellow geologist, Ryan Hichens, did a fantastic demonstration showing the process of tin smelting.

Ryan is a Camborne School of Mines graduate and is now exploration manager at Cornish Tin & Lithium. In his spare time he likes to collect tin ore from around the region and smelt it! He approached me about a year ago with the suggestion of organising a public demonstration of this process, and I thought that doing it at Geevor would be the perfect match.

Tin does not occur naturally as a native metal (as in, tin by itself) unlike metals like gold or copper that can. Instead, it likes to bond with other chemical elements, like oxygen, to exist as an ore mineral. The most common ore mineral of tin is cassiterite, with the chemical formula SnO₂ (tin oxide). This is what can be found in Cornwall and has been historically mined here for around four and a half thousand years.

The process of separating out tin from the oxygen it is bonded to in its mineral form is called smelting. This is different from just melting the rock (melting is defined as simply turning a solid into a liquid). Smelting involves heating the material up with a reducing agent of some sort to induce a chemical reaction, removing any impurities bonded to metal in its mineral form to leave you with the pure metal.

To smelt the tin out of cassiterite, this requires temperatures of over 1,100°C! The reducing agent used is carbon. When the required temperature is reached the oxygen leaves the cassiterite to bond with the carbon to produce carbon dioxide. This leaves you with your pure tin metal. To give you a further idea on the difference between smelting and melting, the melting temperature of pure tin metal is relatively low at 232°C, just showing how much higher temperature is needed to drive off that oxygen.

Tin smelting technology has been around for about 5,000 years and was instrumental in triggering the start of the Bronze Age – mixing around 10% tin with 90% copper produces bronze. The development of the Bronze Age, including technology, trade, and communication, is long associated with the eastern Mediterranean; however, not only has historical and archaeological evidence shown that this trade network included Cornwall, but also that some of the smelting techniques may have actually originated from our part of the world as well. This is because tin is a relatively rare metal, and whilst lots of copper can be found around the  eastern Med, tin cannot. It had to have been imported from elsewhere, and Cornwall (or the “Cassiterides” as they were known, which translates from Greek as the “Tin Isles”) was one of the few places within reach where tin could be found. Not only that, but the local knowledge of what to do with that ore would have also been traded with it.

Geevor visitors got to learn all about the history of tin smelting in Cornwall from Ryan, and witness the process of turning tin ore into tin metal! Not only that, but Ryan also actually used Cassiterite concentrate recovered from Geevor as well, resulting in a beautiful tin ingot cast with Geevor’s own bespoke logo. This concentrate was recovered from the ore bins at the bottom of the mill after closure, making it some of the last tin that will ever be produced from this famous mine.

Ryan will be returning to do demonstrations again in the future. To find out when sign up to our mailing list at www.geevor.com to get our news and information on future events. You can also follow Ryan on LinkedIn and on his social media channels @cornwall.cassiterites. There you can find some videos from the event.