| JOURNAL 2015 |
| North Craven Heritage Trust |
On a dry warm afternoon a large group assembled at the quarry entrance. There were many non-members present taking advantage of the chance to visit the quarry. An explanation of the site and its products was given to us in the visitor centre.
Dry Rigg, near Helwith Bridge, is owned and operated by the Lafarge Group, a world leader in the supply of rock, sand, gravel, asphalt, cement and gypsum. Dry Rigg is a gritstone quarry - more specifically a greywacke, a very hard mudstone. The stone is exceptional in the UK because of its very good wearing and skid-resistant nature. Its Polished Stone Value (PSV) of 65 or more makes it invaluable for road surfacing where a good braking surface is needed, such as on motorway exit roads. The stone wears by losing tiny particles from its surface so that surface roughness is maintained.
The quarried stone was laid down about 420 million years ago and was exposed when the North Craven fault developed about 300 million years ago. Quarrying began on a very small scale in the 1780s. After making drill holes for explosives, blasting is carried out every few weeks to produce 20,000 tonnes of broken rock, care being taken to utilize the natural fault lines to minimize lump size. Dumper trucks carry the rock to a three-stage crusher system - a jaw crusher, followed by cone crushers and screens to produce various sizes from 20mm to 3mm. The coarser stone can be used with asphalt as the underlayer for a road and the finer material in asphalt on the surface.
Our guide, Mr Mick Cardus, showed us first the pond which has successfully attracted nesting birds (over 25 species). Water from the main quarry is pumped through the pond without treatment, indicating that pollution problems are non-existent. Swarth Moor (an SSSI) lies on the northern edge of the quarry, separated by the bund wall of waste rock. The company undertake to monitor the bog and its wildlife, including rare Great Crested Newts. We continued to the high look-out point to view the old working face. Current excavation is concerned with deepening the hole rather than extending the quarry boundary. In due course, by 2021, the quarry will close, water level will rise substantially and overflow into the pond. The north bund wall will be pushed back into the hole.
We walked back down into the quarry to view the crusher buildings and conveyors and the control centre before thanking our guide for a most interesting and informative visit.
