Tin streaming is a process for extracting tin from the mineral cassiterite (SnO2), which could be obtained from river valleys where the mineral was abundant in alluvial deposits, dug out from the river bed and washed through running water to leave the heavy tin deposits behind. It is a very basic method that has been used for thousands of years. Tin streaming was important to the economy of Cornwall from pre-historic times, and was carried out in many river valleys including the Red River at Godrevy, in the Carnon Valley and on Dartmoor.
Over thousands of years, the tin ore was washed from outcrops where the mineral lodes were present at the surface. Rivers draining the tin ore-rich areas carried particles of cassiterite, black tin, in the sediments as they flowed through their valleys. Particles of ore which are denser than particles of quartz or silica, sank to the valley floor where, over time they became concentrated as an alluvial deposit. The particles of ore or black tin varied in size from grains of sand to larger nuggets the size of eggs.
Tailings streaming grew in importance during the mid-15th century as lode mining grew. Lode ore was broken up, stampedLarge machines for crushing tin and copper ore. and buddled before the tailings were released into adjacent streams. Works to retrieve the lost tin from the tailings were set up, and by the mid-18th century had grown to be as important as alluvial streaming.