The Saint John d'El Rey Mining Company was formed in London in April 1830 as a joint-stock enterprise. Its first chairman, John Diston Powles, saw an opportunity in the newly independent Brazilian empire, which was opening its mineral resources to foreign capital. The company leased the São João del-Rei mines in Minas Gerais from a consortium of three British merchants and a German physician. In June and July 1830, a group of Cornish miners sailed from Falmouth bound for Brazil. Cornwall had mined tin and copper for two thousand years, and by the 1830s its industry was in decline, sending skilled men overseas by the thousands. The São João del-Rei venture failed within two years, undone by poor ore and legal disputes, but the company kept searching. In 1834 it bought a different mine called Morro Velho, near Nova Lima, and the real story began.

Morro Velho was an old working by the time the company took it - perhaps fifty years of previous mining, mostly open pit. Under British investment, it transformed. Tunnels drove deeper. Shafts descended. The first dividends were paid in 1842. By the 1860s, roughly 350 Cornish miners worked at Morro Velho, forming the majority of the British workforce. They brought their mining culture with them: Methodist chapels in the hills, Cornish pasties adapted to Brazilian ingredients, the particular chants sung when a shift came up from underground. They also brought disasters. In 1867, a fire collapsed the mine, and it took seven years to bring back into operation. In the 1870s, the superintendent was caught in fraud and fired. A rock fall in 1886 collapsed it again, and the company briefly went into liquidation. Reopened in the 1890s, Morro Velho eventually reached 2,545 meters below its entrance adit - for a time, the deepest mine in the world.

In 1845, the Saint John company signed an agreement with the Cata Branca company to rent 385 enslaved people for fourteen years. The contract stated, unambiguously: "all of the said Negroes... shall at the end of such term of fourteen years be and become absolutely free and emancipated." Fourteen years passed. The term ended in 1859. The clause was ignored. Two hundred of those people - whose names were not recorded in the company's public documents but who had lives, families, and memories of the day their emancipation was promised - remained enslaved for another twenty years inside a British-owned mine. The 1879 report that finally exposed the scandal made its outrage plain. Brazilian authorities intervened. The workers were freed. Nine years later, slavery was abolished across Brazil. The Saint John company continued operating, and its archives rarely mentioned what had happened.

Beyond Morro Velho, the company built a working portfolio across the Nova Lima and Rio Acima quadrangles. The Raposos mines, east of Morro Velho, produced 8,388 ounces of gold from 23,404 tons of ore between 1910 and 1928. By 1955 the Raposos group held reserves of 1,694,080 tons at 9.5 grams of gold per ton. The Bella Fama mine lay southeast of Nova Lima. The Bicalho mine worked at Honório Bicalho. The Gaia, Faria, and Gabirobas mines sat to the southwest, connected by a tunnel driven in 1934 from the west bank of the Rio das Velhas. Some mines were pumped dry, explored, and abandoned when gold prices dropped. Others operated for decades. The Faria mine milled 176,286 tons between 1940 and 1947. Every operation ran on a mix of British management, immigrant miners, formerly enslaved Brazilian labor, and the brute geology of the Minas Gerais hills.

By 1957, two mines remained active - Morro Velho at Nova Lima and the Raposos group. That year a group of investors bought a controlling interest in the Saint John d'El Rey Mining Company and sold its iron properties to the Hanna Mining Company of Cleveland, Ohio. The gold operations continued under changing management. The company was formally dissolved in 1985, 155 years after its founding. What remains in the Minas Gerais hills is a landscape of adit entrances, tailings piles, Cornish gravestones, and the town of Nova Lima, which grew up around the mine and still bears its marks. The descendants of the Cornish miners are Mineiros now. The descendants of the people whose freedom was deferred for twenty years are also Mineiros - and the ground they walk on was dug by their ancestors.