Mineral Deposits in the WHS
The location, structure and orientation of the lodes (deposits or veins of metallic ore in the rock) within the Cornish Mining World Heritage Site determined the different characteristics and developments of mining in each Area.
The Great Flat Lode
The area to the south of Carn Brea is known to have been extensively mined for its shallow copper deposits during the 18th century, but by 1720 tin was also being produced in significant quantities. It is recorded that in around 1870, working at depth at West Wheal Basset led to the discovery of a lode that was to become one of the most extensive bodies of high-grade tin to be mined in Cornwall. ‘The Great Flat Lode’ produced almost exclusively tin and sustained numerous mines along its approximate 6 kilometre (3.75 mile) extent for the following half century. It is called ‘flat’ because it extends underground at a shallower angle than most lodes in Cornwall, at an average of around 35 degrees from the horizontal.
The lodes in the St Agnes area were formed by the contact between the granite underlying St Agnes Beacon – an outlier of the Carn Brea boss – and the complex metamorphosed country rock that surrounds and overlies it.
To the west and close to the granite contact, tin is prominent –stretching from the dramatic openwork of Wheal Luna overlooking Trevaunance Cove through Seal Hole and Polberro towards St Agnes Head. To the south-west lies Wheal Coates, one of the best known Cornish mine sites, and the important copper mines of Wheal Charlotte and the Porthtowan mines. Modern developments have left little of the once important workings on the Perran Iron Lode and the Penhale mines.
Before 1836, much of the land here was regarded as little more than poor, exposed, upland sheep country. This all changed when a small group of prospectors located a major east-west copper lode traversing the Seaton Valley on the southern slopes of Caradon Hill. Within four years, mines were being established all over the district
Before 1836, much of the land in Caradon was regarded as just poor, upland sheep country.
in an attempt to either find extensions of the South Caradon lode to the east or west, or others parallel to it. To the north, the old Clanacombe and Stowes mines were reopened as Phoenix United. Here, too, substantial resources of copper ore were found – with the added bonus of rich tin alongside.
Devon Great Consols
The spot where workings began in 1844 – known then as North Bedford Mines or Wheal Maria – had been suspected of containing a rich copper lode in the early 19th century. However, development had been delayed by the then Duke of Bedford, who did not want Blanchdown Plantation to be despoiled by mining.
What was discovered in 1844 was the largest unbroken sulphide copper lode in south-west England. The richness of the ore caused a sensation. It was so abundant that it was difficult to find sufficient space to store it.
A small waterwheel was erected and the lode was exploited for 16 fathoms eastwards until it was suddenly lost – intersected by the Great Cross Course which heaved it 75 fathoms to the south. A minor panic ensued until the lode was found again to the south-east of Wheal Maria, initiating another working named Wheal Fanny. There followed a series of mines along its course, including Wheal Anna Maria, Wheal Josiah and Wheal Emma, the last opened in 1848.