How are diamonds mined?

The Yakutia area of Siberia is one of the coldest and most inhospitable places on Earth. Temperatures of -20 degrees Celsius (-4 degrees Fahrenheit) are common during the winter months and night-time temperatures can plummet so low that oil freezes and steel becomes brittle. Hardly ideal living conditions but it’s here, just outside the Arctic Circle, that the town of Mirny sprung up after the discovery of a large kimberlite field in 1955. Why is this worthless igneous rock so important? It’s because kimberlite is known to sometimes contain diamond ‘pipes’.

 
The Mirny mine in particular was significant because, up until then, the USSR essentially had no diamond industry. Within a few years this single mine proved such a rich source of diamonds that during the Sixties it was accounting for 10 million carats of the world’s diamond industry, which in everyday weight equates to roughly 2,000 kilograms (4,409 pounds) of these precious gems.

Mirny was an open-pit mine up until its last decade of operation. This type of open-cast mining is used when valuable deposits are found close to the surface where tunnelling would be unsafe due to the soft overburden (ie the material above). The mine starts by scraping the topsoil and overburden away to expose the valuable deposits.

Mirny was systematically excavated to a depth of over half a kilometre (0.3 miles) in ever-decreasing concentric circles, with the richest diamond- bearing seams found in the upper layers down to around 340 metres (1,115 feet). The open-cast mining method was dispensed with in 2001 and tunnels were dug to retrieve the remaining gems still cost-effective using this method. The Mirny mine was closed in 2011 and the bottom filled with 45 metres (150 feet) of rubble to prevent the pit from collapsing.