Dartmoor tin-mining

The Dartmoor tin mining industry is thought to have originated in pre-Roman times, and continued right through to the 20th century, the last commercially worked mine (Golden Dagger Mine) closing in November 1930 (though it saw work during the second world war). From the 12th century onwards tin mining was regulated by a Stannary Parliament which had its own laws.

Tin is smelted from cassiterite, a mineral found in hydrothermal veins in granite, and the uplands of Dartmoor, in Devon, England, were a particularly productive area. The techniques used for the extraction of tin from Dartmoor followed a progression from streaming through open cast mining to underground mining. Today, there are extensive archaeological remains of these three phases of the industry, as well as of the several stages of processing that were necessary to convert the ore to tin metal.

Mining became such an important part of life in the region that as early as the 12th century, tin miners developed their own set of laws (stannary laws) and, ultimately, their own parliaments (Stannary Parliaments). These laws applied to anyone involved in the industry.

Stannaries were established in , Ashburton and Chagford by King Edward I in 1305. Plympton followed soon after. The Devon stannary parliament met in an open air forum at Crockern Tor from 1494.

Anyone who broke a stannary law could find himself imprisoned in the gaol at Lydford. The stannary courts were abolished in 1836.

The majority of the tin mines on Dartmoor are located in granite country rock and most of the lodes trend ENE–WSW and are of limited length, though there are exceptions. In the underground workings, the tin ore, cassiterite, was usually found in association with large amounts of tourmaline, and in central Dartmoor with much specular haematite. In the southern part of the moor, the cassiterite was usually found in relatively large grains, but the lodes were of very variable quality. These factors, combined with the fact that none of the underground workings was found to be profitable at depth, are typical of the deepest zone of tin mineralisation. The once very extensive alluvial deposits of tin ore, that were the first deposits to be mined, also point to the vast quantity of ore that once existed in lodes that have been eroded from above the granite since it was emplaced in the Carboniferous period.

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