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