Copper was identified around Kapunda and Burra in 1841, but it was Burra's strike that became legend. Worked from 1845, the Burra deposit was so vast that locals simply called it the Monster Mine, and for the first decade of its life it was the largest mine in Australia. The numbers still impress: between 1850 and 1860 it produced roughly five per cent of the entire world's copper, and by 1850 the colony as a whole had become the third-largest copper producer on the planet. A struggling young settlement suddenly had an export that mattered globally. Capital, machinery and people flowed in, and a string of company and squatter towns grew up around the open workings, their character shaped less by Adelaide than by the granite villages of the Cornish coast.

The migration was not romance but necessity. In the 1840s the potato blight that devastated Ireland also struck Cornwall, and through the following decades the Cornish economy, dangerously dependent on tin and copper, began to collapse as its own ore ran out and prices fell. When fresh copper was discovered on the Yorke Peninsula in 1859 and mines sprang up almost overnight at Moonta, Kadina and Wallaroo, unemployed Cornish miners had somewhere to go. They carried with them an edge no one else in the colony possessed. The Cornish steam engine, used to pump water and lift ore, let miners reach depths that had been impossible before, and generations of inherited skill suited the conditions perfectly. By 1865 it was reckoned that Cornish settlers made up more than forty per cent of South Australia's immigrant population.

Around the three towns of the Yorke Peninsula, the Cornish presence grew so dominant that the area earned a nickname it still carries: the Copper Triangle, or Little Cornwall. Moonta itself became extraordinary. In its first year the mine produced nearly 5,000 tons of ore worth more than 67,000 pounds, and by 1875 it had overtaken Cornwall to become the largest copper-producing region in the British Empire. It was the first mine in Australia to pay a million pounds in dividends. The Copper Triangle mines would yield around 350,000 tonnes of copper, an amount approaching half of all South Australia's mineral output up to 1924. Beneath the production figures lay an entire transplanted culture of Methodist chapels, brass bands and Cornish wrestling that endures in the towns today.

The boom exacted a heavy human price. In 1874 a measles epidemic tore through the Moonta district; by December an estimated 2,400 cases had been reported, with five or six deaths a day, most of them infants and children. Death certificates show the toll was compounded by dysentery and diarrhoea in a community plagued by unsanitary conditions and impure water, grim enough that the Central Board of Health took control of the mineral leases to intervene. The miners were not passive. As early as September 1848, Burra's workers struck against the powerful South Australian Mining Association and the formidable Henry Ayers, first over disputed ore assays and then in solidarity with the surface labourers, the so-called grass workers, when their wages were cut. The first strike favoured the miners; the second was broken. It was, in its way, a very Cornish kind of defiance, carried across the world along with the picks and the pumps.