Early Mining Methods: Tin streaming
The earliest form of tin removal was by streaming, which was taking tin out of river valleys.
This happened on a huge scale: moors like Bodmin and Dartmoor were worked a great deal from very early times. Most of the river valleys in areas where tin was present were streamed.
Tin ore in streams is called ‘alluvial’ tin. Rocks containing tin are gradually washed away from the bedrock by running water over hundreds of years: this is called erosion. Where the ground had been broken down it would be washed along by the running river water. This water movement helped to concentrate the ore. The rock containing tin ore (cassiterite) is much heavier than other material and small rocks and pebbles containing tin quickly sank.
The tin was eventually covered by sand and later peat, sometimes for several metres. Occasionaly small shafts were sunk to find the tin layer. The covering had to be dug away and moved using shovels and wheelbarrows. In some places the piles of material moved like this can still be seen. Often the tin layer was still below the stream which had to be diverted so that it could be worked. In some places the channels made for this can still be seen.
When the ‘tinners’ had uncovered the layer of tin, they used water to separate the tin from the waste material. A channel was made to bring water to the layer of tin which washed away the lighter sand leaving the heavier tin behind.
Outcrop mining is working the lodes that can be found on the surface.
Tin Streamers started to look for the origin of the streamed minerals in the rivers and this led to open caste mining. Sometimes lodes were visible in the cliffs or Rocky hillsides and continued inland, particularly in coastal areas, like St Just. This provided the miners with the location of lodes that otherwise might not have been found. Outcrops of lodes could be mined using opencast pits and trenches or by tunnels, following the lode.
This method was frequently assisted by using water directed over the desired area to remove the lighter waste, leaving the heavier tin ore behind to be collected.
The early tinners who worked alluvial and outcrop deposits left trenches, pits and ridges on the landscape. Today these have been partly destroyed and are sometimes only visible from the air as bumps and lines on the landscape.