The Great Flat Lode is a large ore-bearing body of rock under the southern slopes of Carn Brea, south of Camborne in Cornwall, England. It was exploited for its tin ore in the 19th century, when more than twenty engine houses were built in an area of just 1.5 square miles (3.9 km2).
The Great Flat Lode is one of the largest mineral-bearing bodies of rock in Cornwall. It is under the southern slopes of Carn Brea, south of Camborne. The lode is so named because the “flat” ore-bearing rock lies at an unusually shallow gradient of about 30 degrees to the horizontal, it is oriented ENE-WSW and dips towards the south. It was formed when molten granite in the earth’s crust cooled and solidified. Pressure from the molten rock below created fractures and cracks in the solidified rock and liquid heavy metals, separated from the granite, were forced into the fissures where they crystalised into metallic ores.
The Great Flat Lode is a large fissure in the granite with deep cracks through which the mineral bearing liquids were forced called “droppers” below the fissure and “leaders” that rise towards the surface. The leaders closest to the surface were of poorer quality tin ore, which was of higher quality at greater depths. Copper was deposited in rocks above the granite.
The area was first mined for copper and as greater depths were attained tin was discovered. Mining was mentioned at Uni-redruth in the 16th century but the area was not seriously exploited until the 19th century. Copper was worked sporadically at Wheal Uny from the 1820s.
Shafts were sunk at South Condurrow (renamed the King Edward Mine and used by the Camborne School of Mines), Wheal Grenville, South Wheal Frances and the Bassett Mines. The mines were started to obtain copper ore but at greater depths tin was discovered.
In an area of 1.5 square miles between Carnkie and Carn Brae to the south of Camborne are the remains of 24 engine houses and their associated tin stamps and smelters.
The Great Flat Lode Trail, a 7.5 mile circular trail around Carn Brea is one of Cornwall’s Mineral Tramway Trails.