Cobalt was first noted in Cornwall in 1754 (only 15 years
after being first identified as an element) in the form of
erythrite. At Pengreep, Gwennap, a 3ft wide N-S ‘cobalt lode’
was found in an adit being driven through greenstone
(dolerite). At the time, the lode was dubbed “the richest cobalt
found in England” and the landowner, Mr Beauchamp, was
awarded a £30 prize for the discovery by the Society for
Encouraging Useful Arts. Shortly afterwards the adit was
abandoned due to water influx (Borlase, 1758; Pryce 1778). In
1958, A. K. Hamilton Jenkin inspected the adit and found no
trace of any mineralisation (Hamilton Jenkin, 1963b).

Rollinson, G., Le Boutillier, N. and Selley, R., 2018. Cobalt mineralisation in Cornwall—A new discovery at Porthtowan. Geoscience in South-West England, 14, pp.176-187.