Summary
The Whin Sill is a dolerite intrusion with extensive outcrops in North East England. Quarries in the sill, provide the bulk of the crushed rock aggregates in the region suitable for roadstone. The dolerite is generally of high strength and little affected by weathering and thus yields high quality aggregates. At some quarries, however, dolerite of poor quality, locally known as “Woodhead”, is found. The “Woodhead” material differs from the normal dolerite is having a distinctive colour, lower strength and higher porosity. It can be shown that the material is produced by hydrothermal alterations related to calcite veining. Inclusion of Woodhead material in aggregates from one quarry lead to their rejection by a Local Authority and, as it proved impossible to separate the poorer material, the quarry closed.
Quality variations have been determined by a range of standard tests. Test results can be related to petrographic indices determined by quantitative thin-section analyses.
Résumé
Le sill de Whin correspond à une intrusion doléritique, affleurant largement dans le Nord-Est de l'Angleterre. Les carrières dans ce sill fournissent la plupart des granulats pour les chaussées de la région. La dolérite, généralement peu altérée et de résistance élevée, donne des granulats de bonne qualité. Cependant, dans quelques carrières, une dolérite de mauvaise qualité est connue sous le nom local de “woodhead”; ce matériau diffère de la dolérite saine, par une couleur distincte, une plus faible résistance et une plus grande porosité. Il est montré que ce faciès est dû à une altération hydrothermale, en relation avec des filons de calcite. Une certaine proportion de “woodhead” dans les granulats a entraîné leur refus par les autorités locales et la fermeture de la carrière, car il était impossible de les séparer.
Les variations de qualité de ces matériaux ont été déterminées par des essais, dont les résultats sont corrélés avec des indices pétrographiques quantitatifs mesurés en lames minces.
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Dearman, W.R., Irfan, Y., Money, M.S. et al. Quality variations in whin sill aggregates from Northumberland, England. Bulletin of the International Association of Engineering Geology 29, 355–359 (1984). https://doi.org/10.1007/BF02594435
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DOI: https://doi.org/10.1007/BF02594435