This mining district is dominated on the skyline by the granite outcrop of Carn Brea. The district has been a large producer of copper and tin in the Cornubian Orefield. Mining had been continuous from pre-history up to the end of the 20th century and as a consequence has excellent mining landscapes. At one time it had the world's deepest mine at 1000 m deep at Dolcoath in the late 1800s. As a result of this past activity there is a very high density of mine workings in the district.

The geology is dominated by metamorphosed pelitic rocks with minor metabasites, which have been intruded by the Carnmenellis granite. Carn Brea is a small cupola, formed as a topographic high on the underlying granite. On the top of Carn Brea there is evidence of early magmatic mineralization in the form of greisen veins. Stresses related to the granite intrusion into the country rocks and subsequent cooling has resulted in fracture zones (normal and reverse faults), which are now occupied by fissure lodes. The lodes have formed on the flanks of the granite in metasediments and extend into the granite

Lode structure

below. These are a result of later granitic intrusions; others such as the Great Flat Lode follow the granite contact. Fissure lode systems can extend for many kilometres in the district. Copper was usually mined in the upper parts of the mines where supergene enrichment had taken place forming rich copper ores of chalcocite and bornite. Rhyolite dykes, following the same trend as the fissure lodes, have also been emplaced in the district. Wrench faults with a N-S orientation, activated in the Permo-Trias, crosscut the district producing in some cases a 100 m displacement of fissure lode systems.

After Dines, 1956.

South Crofty Mine ceased working in 1998. Parts of the mine had been in operation as early as the 1700s as it had embraced many old workings during the lifetime of the mine.

The mine geology is one of metasediments and metabasites in the upper part of the mine to granite in depth. In the mining sett (mining boundary) there are a multiplicity of fissure lodes. These lodes strike ENE-WSW and are up to 2 km long and have a dip length of 600m from surface.

In the upper part of the mine the lodes were sulphidic (sulphur rich) and worked for copper, zinc and minor lead; in depth this changes to cassiterite and wolfram. However tin is present in the upper part of the sulphide rich lode systems as the sulphide mineralization post-dates that of the tin due to a collapsing hydrothermal convection cell. Tin grades in recent years ranged from 1 to 1.5% Sn, but locally could occur up to several tens of percent.