In the 1820 s, the parish of Gwennap alone produced one third of the entire world supply of copper. Around 1860 large easily mined deposits of copper were found in the USA, South America and Australia, and steam ships were becoming available as bulk carriers. Very quickly it became cheaper to ship foreign ore back to South Wales for smelting, or to smelt it on site, than to persist with the now inefficient workings of the progressively exhausting Cornish and Devon mines, and the Great West-Country Copper boom collapsed. The copper boom had presented great employment opportunities, and there had been a general migration to Cornwall, particularly from Devon and South Wales. The population of Cornwall nearly doubled between 1700 and 1801, and nearly doubled again between 1801 and 1860.
Miners have to be mobile so that when one pit closes they can move on to newer ones.
This occurred towards the end of the boom, when the Devon Great Consols mine, the largest and richest of all the West Country mines, opened near Tavistock in Devon. Cornish miners migrated back to Devon to work it, but its life was short, and the sudden collapse of the boom in the 1860 s left thousands of hard-rock miners in both Cornwall and Devon without a living. The miners who had flocked to Cornwall in the early part of the boom, some of whom had migrated back to Devon at the end, were now forced to migrate overseas. Experienced hard-rock miners were in demand all over the world where new deposits of all sorts of metals were being discovered, and they went to places like Nevada, Arizona and the Great Lakes area of the USA, Chile, Argentina, Peru and the other countries bordering on the Andes in South America, South Africa and Burra in South Australia, many of which were producing the cheap copper which forced the collapse of the industry in England. As the copper mining industry of Cornwall developed, so the name Gribble started to appear in the mining region of Cornwall particularly around Redruth.