Eylesbarrow Cassiterite

Cassiterite (SnO2) was and is the main tin ore on Dartmoor. The history of mining on Dartmoor is long. As far as I am ware there is no evidence that the Phoenicians ever landed in the South West but there is plenty of archaeology demonstrating a thriving trade between Devon and the Mediterranean. The Romans carried out the first organized mineral extraction on the Moor but were mostly interested in lead rather than tin. Tinning on the Moor peaked in the twelfth century, followed by a thousand years of gradual decline. 

The Eylesbarrow mining sett (about 3 by 2 miles) contains many tin-bearing lodes but the mine was based on extraction from just three of these which were were relatively shallow and accessible. Formation of the lodes was accompanied by extensive metasomatism which converted much of the plagioclase feldspar in the surrounding granite into the soft mineral kaolinite, making excavation much easier than it would have been in unaltered granite. The lodes varied in width up to a maximum of around 0.73 metres and were, at least in the early years of the mine's operation, sometimes of very high quality ore. The existence of these high quality ores near the surface led the miners to believe that even better ore existed deeper down, but this is not the case and the mineralisation becomes patchy at depth. And that's the story of Eylesbarrow - crushing disappointment. 

Talking of crushing, what do you do with the ore once you've dug it out? More on that tomorrow.