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Where on Earth are the deepest sinkholes

© Форпост Северо-Запад / алмаз

Living on the edge of a hole 240 meters deep and nearly half a kilometer in diameter is a dubious joy, but the residents of the South African town of Kimberley are quite happy. Their "Big Hole" is the world's oldest primary diamond deposit. From 1872 to 1914 it yielded three tons of the hardest and most expensive stone (14.5 million carats).

Today there is a tourist business around the flooded excavation: tramways are laid, and a late 19th-century mining camp has been recreated.

трамвай в Кимберли
© Juanita Swart, / трамвай в Кимберли

At that time the territory belonged to the Free Orange State. It was founded by the Boers, descendants of Dutch, French and German Protestant colonists, 18 years before diamond mining began in Kimberley. The British pushed them out of the convenient sea bay of Capstad (Capetown) into the interior of the continent. They had to develop farming from scratch instead of the "non-dusty" port activity on the sea transit route from Europe to India, Indonesia, and China.

"Our country is young, but we step boldly into the future,

with our eyes fixed on God.

He will not shame those who build in his name

and trust in him as a fortress beyond all storms," sings the national anthem of the Orange State.

The forced migration brought the Boers freedom from storms (literally, because of the remoteness of the new lands from the ocean). But it did not rid the Boers of British hostility and caused many other problems - from crop failures to military clashes with local African tribes.

In the Orange motto, patience came first, then courage. The shepherd who found the first large diamond near Kimberley must have been especially patient. In keeping with Protestant tradition, his piety was confirmed materially. At first, people thought the sign of God only applied to the shepherd's family. However, it soon became clear that there was enough wealth for everyone - a small hill near the town was made of a peculiar diamond-bearing rock of magmatic origin. Subsequently, it was called kimberlite, after the name of the settlement, and the geological body consisting of it was called the kimberlite pipe.

© Форпост Северо-Запад / алмаз

Such magma outcrops are the result of very ancient volcanic explosions. Their shape is more likely not tubular, but cone-shaped with expansion to the earth's surface. From the seismic point of view platform areas of the Earth's crust, where such cones were found, are absolutely stable nowadays.

About 90% of the world's diamond reserves are located precisely in kimberlite pipes. Precious stones embedded in the solidified magma were formed in the Earth's mantle at a depth of 150 to 600 kilometers under the influence of temperatures of 1300 degrees Celsius and a pressure of 50 thousand atmospheres. This took place between 100 million and several billion years ago.

© Форпост Северо-Запад / алмаз

As you know, the length of the Earth's circumference is 40 thousand kilometers. The automobile route between South Africa and Botswana, where the lion's share of Africa's diamonds is mined, and Yakutia's largest diamond deposits are only half as long. Incidentally, the funnel of the Russian Mir open pit is much larger than in South Africa. Its diameter is 1.4 kilometers and its depth is 735 meters.

Kimberlite pipes comparable in potential are found at the other two ends of the world - in the north of Canada (Diavik) and in Australia (Argyle). Ironically, these two points are about the same distance from each other as Yakutia and South Africa. However, you have to get there mostly by sea.

© Форпост Северо-Запад / алмаз

Why did nature place the largest hoards of precious fused carbon in the most distant parts of the Earth's land? Scientists still have no answer to this question. Perhaps it's just a coincidence. Or a hint: the patience and courage of those who were able to reach the edge of the earth will be rewarded.

At the exposition of the Mining Museum in St. Petersburg there are several samples of kimberlites and diamonds, including those from the Mir deposit, where the first commercial production of the precious stone in our country was launched.