Wheal Busy, originally Chacewater Mine, was probably being worked for copper since the 16th century, but it began producing on an industrial scale only in the 1720s. The principal landowner was the Boscawen family, later Viscounts Falmouth, and the country rock here is killas crossed by elvan dykes, narrow bands of porphyritic rock fifteen to forty feet across that in places became spectacularly mineralized. The mine's chief problem from the beginning was water. To pump out the workings, Joseph Hornblower installed one of the very first Newcomen atmospheric engines in Cornwall in 1727, only fifteen years after Thomas Newcomen built his first working engine at Dudley Castle. In 1775 the Newcomen was replaced by a 72-inch engine designed by John Smeaton, the great civil engineer who built the Eddystone Lighthouse. Smeaton's engine proved ineffective. In 1778 James Watt rebuilt it, making the Wheal Busy machine one of the first Watt steam engines anywhere in Cornwall.

The Gwennap-Chacewater mining district was, by the late 18th century, the densest concentration of copper production in the world. Wheal Busy was at its centre. Over its working life it produced more than 100,000 tons of copper ore and 27,000 tons of arsenic. In 1836 the mine employed 34 men working underground, 50 women at the surface, and 28 children, a total of 112 people. The men hauled and broke the ore at depth. The women and children, working long hours for low wages, broke down the larger ore on the dressing floors above ground, sorting it into the grades that the smelters would buy. Smaller children carried water and tools. The mine connected to the Great County Adit in 1778, an enormous drainage tunnel system that linked dozens of Gwennap mines and ran water out to the Carnon Valley. Even so, in any given year, six of Wheal Busy's twenty-four boilers had to be renewed because the corrosive mine water was eating them from the inside out.

For all its tonnage, Wheal Busy was never quite a financial success. In the 1770s and 1780s the adventurers, the investors who bankrolled the mine, lost more than £150,000 across a decade despite massive output. The mine adopted the name Wheal Busy in 1823, the Cornish wheal meaning simply "working" or "mine." The 1866 sabotage closed it down for years. In 1873, in the depths of a copper-price collapse, it reopened, a brand-new ninety-inch pumping engine ordered from Perran Foundry, ignoring all the cheaper second-hand engines on the market. The engine ran for seven months. The mine never produced any ore. The engine itself went up for sale. Around 1910 the operators installed an 85-inch second-hand pumping engine and reopened the workings briefly to chase arsenic, but the great age of Wheal Busy was already half a century gone.

Walk the site now and you see the Brunton calciner, named for William Brunton, the engineer who invented the rotating-hearth roasting furnace. Arsenic was the product here in the later years. A scheduled monument since March 1974, Wheal Busy sits inside area A6i of the Cornwall and West Devon Mining Landscape, made a UNESCO World Heritage Site in 2006. The engine house and arsenic calciner have been Grade II listed since 1985, the small Methodist chapel that served the miners' families since 1999, the smithy building since 2004. In 2014, Natural England's Higher Level Stewardship funded restoration of the engine house and associated buildings, although they could not at the time stretch to the smithy. The wheel-marked stones in the dressing yards, the slag-blackened patches of ground, the granite shells of the engine houses with their tall single-flue chimneys, are as close as Cornwall comes to its own Pompeii.