1. Summary of issue
On the 14th March 2016, a 90 metre (300ft) deep mine shaft opened destroying the patio and half a garage of a bungalow in Scorrier, near Redruth, Cornwall . Fortunately the £200,000 property was unoccupied and the unrecorded 18th century tin mine shaft opened during a mining survey.
2. What is the cause of the issue?
Given its prolific mining history (tin, copper, lead etc.), Cornwall is littered with mine shafts and mineral workings. Redruth and Camborne (2.5km and 8km Southwest of Scorrier) are renowned for their extensive tin and copper mines, however, mines operated outside of larger towns often went unnoticed and unrecorded other than in local historic mining and land use maps. Commonly upon mine closure, these mine shafts would have been backfilled and/or capped with timber (often railway sleepers). These 18th Century caps have since rotted away leaving these deep mine shafts covered by a thin layer of soil and/or buildings. This is the case here in Scorrier where an previously unrecorded 18th Century mine shaft called “New Shaft” of a local tin mine called Wheal Chance has had its timber cap rot away leaving a 90 metre deep void covered by a patio. The shaft opened once the patio was drilled into for the mining survey.
3. Can data relevant to the site be sourced, provided and used as evidence
Several datasets can be used in conjunction to provide evidence for mining and, by extension, ground stability hazards. These include local geology and analysis of geological, topographical and satellite data, as well as Site investigation, historic mining and land use maps.
4. What is the professional interpretation according to Terrafirma?
This mine shaft which collapsed is not part of the recorded mines database of the BGS and does not appear in most historic maps. As a result it is easy to see how it went unnoticed, however, it is possible to deduce that there may well have been mineral extraction in the area given the local conditions: The prolific mining history in Cornwall is such that nearly all accessible deposits and mineral veins have been exploited to some extent. The bedrock geology is the Porthtowan Formation; mudstones and sandstones that have been disseminated with hydrothermal fluids following granite batholith intrusions to the South and Southwest. These hydrothermal fluids are what carry the valuable metals forming mineral veins. Mineral veins are well recorded in BGS data and those present in Redruth and Camborne have numerous recorded mines associated with them. In Scorrier there are many recorded mineral veins but little to no recorded mines. Given the desirable nature of these veins and the extensive exploitation of them in nearby Redruth it would be logical to infer that these veins will have been mined in Scorrier. Consultation of historic maps shows several old mine shafts in the vicinity, but given these maps are from the 19th to 20th century, 18th century workings can still be missed. Considering the presence of mineral veins and some recorded workings on historic maps, its seems probable that more extensive mining occurred in the area posing a significant hazard to local property.
A link to drone footage of the mine shaft may be found by following this link: