Mineral deposits are commonly associated with geological structures. When mineral-rich fluids circulate deep underground, their dissolved minerals may crystallize within faults, fractures and joints, forming mineral veins. In Swaledale the mineralisation was focused along fractures and faults (e.g. Stockdale Fault) cutting the Carboniferous strata, with mineralisation particularly focused within the limestone beds of the Yoredale Group and lower Millstone Grit Group. It is these mineral deposits that were exploited by miners in Swaledale. The Swaledale mineralisation is related to the North Pennines Orefield centred on the Alston Block found further to the north of the region.
The occurrence of mineralisation has been identified to be synchronous with renewed faulting and the intrusion of the igneous Whin Sill in earliest Permian times (c. 297-294 million years ago). The Whin Sill is not present in Swaledale, but is associated with the same age rocks as seen in Teesdale (e.g. High and Low Force) and along Hadrian’s Wall.
Lead has typically dominated the mining in the Dales, with rich veins mined to the north of Swaledale and on Grassington Moor. The mining remains around Gunnerside Gill, near Surrender Bridge and in Arkengarthdale are particularly interesting to visit, because of the scale of the ruins, the stunning settings and because they can be incorporated into some really fine walks!