Copper mineralisation near Middleton Tyas, North Yorkshire

Historical accounts of copper mining near Middleton Tyas in the 18th century show that small tonnages of very rich ore were dug from veins, flats or irregular cavities in the Underset Limestone. The mineralisation probably originated from metalliferous brines migrating from the Stainmore Trough or a similar Lower Carboniferous sedimentary basin to the east. The possibility that the mineralisation was syngenetic has been investigated but is now discounted; similarly, boreholes through the local Permian succession to test whether a Kupferschiefer facies of the Marl Slate is present locally, gave negative results. The primary copper sulphides were subsequently enhanced in grade by supergene enrichment under arid conditions during early Permian times. Much of the outcrop of the Main and Underset limestones within the Middleton Tyas anticline is heavily drift-covered. Anomalous copper values in soils have been found over about 6 sq km, but it is not known whether these are due to ice dispersion or whether they mark hidden copper deposits. An IP survey in the area was hampered by the presence of strong artificial conductors.