Because of its close association with tin in the mines, copper must almost certainly have been found in Cornwall at the same date, but how far it was exported, if at all, is uncertain. The Romans, for instance, could have had little need of it, since they possessed the abundant and more easily available supplies from Cyprus and Spain; while the Irish were exploiting, apparently long before the Christian Era, their own copper deposits at Avoca, in the Wicklow Mountains. No contemporary records exist and much of the data have been derived only by inference, but nevertheless it is quite certain that the Celtic peoples of Britain had a good although no doubt elementary metallurgical knowledge of both metals, and most of their old workings pre-date the Roman invasion. The chief British copper mines were at Alderley Edge in Cheshire, where the easily worked malachite was abundant. There were others at Amlwch, in Anglesey, also in North Wales, Shropshire, Coniston and southwest Scotland. According to "Bromehead," these were all surface workings, mere open-cast trenches and circular pits, some having once been rich in copper silicate (chrysocolla). No attempt was made to drive galleries. Probably the natives continued to work the deposits under the watchful eyes of Roman overseers; for the invaders were more interested in lead, the mining of which was an imperial preserve.
There were some small Roman copper mines at Llandudno, where an open-cast on Great Orme's Head yielded a coin of Aurelian (A.D. 270) and many more recent ones have been found in the spoil-heaps. This ore was copper carbonate. There was a large Roman mine at Llanymynech and another at Machynlleth, the former comprising a large number of cone-shaped pits and a great open-cast trench with a series of galleries opening into chambers. This place yielded coins of Antoninus and Faustina (A.D. 138). From the Scottish source comes a cake similar to those found in Wales (see below). At Marazion, Cornwall, where the causeway runs out to St. Michael's Mount, a vessel of pure copper was found buried in the marsh in 1825; it contained some thousands of brass coins of about A.D. 260.