The Big Hole Was Dug by Hand in Twenty-Three Years

The hole at Kimberley, Northern Cape, South Africa, is the surface expression of a kimberlite pipe — a carrot-shaped intrusion of ultrabasic igneous rock forced upward from depths exceeding 150 kilometres by volatile-rich magma. Kimberlite is the primary host rock of diamonds worldwide, and the pipe beneath what became known as the Big Hole is one of the best-documented examples on record. When erosion removes the softer cap rock, the kimberlite weathers to a crumbly yellow surface layer called yellow ground, beneath which lies the harder, blue-grey kimberlite proper — the trade called it blue ground — still carrying diamonds in their original matrix.

The rush began in 1871 on a farm then called Vooruitzigt, owned by the De Beer brothers. Within months, what had been a dry hillside was divided into thousands of individually claimed plots, each worked from directly below. The mine's official working life ran from 1871 to 1914: forty-three years in total, though the most intensive hand excavation occupied roughly the first twenty-three. At its peak in the early 1870s, the site held roughly sixteen hundred claims worked by thousands of diggers and the chaos of individual digging had turned the surface into a cratered web of ropes and pulleys ferrying buckets of kimberlite to the rim.

The disorder of individual claims created two problems that the colonial and eventually corporate authorities moved quickly to solve. The first was structural: adjacent claim-holders undermined one another's walls, causing deadly collapses as the pit deepened. The second was economic. Illicit diamond buying — IDB in the shorthand of the trade — flourished whenever thousands of diggers could sell stones outside the licensed market. The Cape Colony passed successive IDB statutes through the 1880s that made possession of rough diamonds without documentary proof of lawful acquisition a criminal offence, a legal framework that deliberately shifted the burden of proof onto the seller.

The corporate solution arrived in 1888–1889. Cecil Rhodes, using the financial backing of the Rothschild bank, assembled the competing diamond interests at Kimberley into a single entity. De Beers Consolidated Mines was registered in 1888, and by 1889 it had absorbed Kimberley Central, its last significant rival in the pipe, for what was at the time one of the largest cheques ever written in the British Empire. Consolidation ended the IDB problem by eliminating the independent market into which stolen stones had flowed.

By the time pumping and underground working finally ceased in 1914, the Big Hole measured approximately 17 hectares at the surface — about the footprint of twenty-five full-sized football pitches — and descended 240 metres from the original surface level to the lowest point reached by open-cast extraction. The total volume of kimberlite removed is estimated at 22.5 million tonnes, yielding roughly three tonnes of diamonds over the mine's working life: a ratio that underlines how geologically dilute even a rich kimberlite pipe is.

After mining ceased, groundwater rose to fill the lower workings, creating the green lake visible today at the centre of the pit. The viewing platform on the western rim gives the most useful sense of scale: the opposite wall is more than 400 metres away, and the lake surface lies some 40 metres below the rim. The Kimberley Mine Museum, operated by the McGregor Museum group, maintains the surface infrastructure around the pit, including reconstructed diggers' camps and the original sorting house.

The Big Hole is not the deepest mine ever worked, nor the largest by volume. It is, however, the largest hole known to have been excavated predominantly by hand — a fact that the platform makes viscerally plain before any caption is read.