Dartmoor Tin-mining - Geology

Geology

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.