Area: 3.2 hectares.
This largest opencast working exposes the best example of a stockwork tin ore deposit in Britain. The vein swarm trends generally in a north-north-east direction and the orebody is described as ‘closely sheeted’. Individual veins in the killas are well seen in the sides and floor of the deep working. They vary from minute cassiterite coated cracks up to veins 0.12 m in width. The vein edges are greisenized and tourmaline replaces more argillaceous bands in the killas for about 0.1 m from the vein walls. Cassiterite, arsenopyrite, wolframite and copper minerals are present. The site is complementary to Cligga Head Mine in that it clearly shows the effect of greisenisation on sediments rather than granite. This type of mineralisation cannot be examined closely elsewhere except in the working tin mines. This high temperature mineralisation is representative of the upper part of the tin zone and is of Hercynian age.