The Popigai crater is the world's fourth-largest asteroid impact crater known so far, after the Chicxulub, Sudbury and Vredefort craters.
The Soviet government reportedly discovered the deposits in the 1970s on a scientific expedition, but decided to keep the information secret so as not to disturb world markets and lower the value of their already-profitable Mirny mine further east, which at its height was producing ten million carats of diamonds per year.
The mine, now closed due to falling yields, is currently the second-largest excavated hole in the world, and helicopters are forbidden from flying over it in case downward air flow sucks them in. 
The Soviet Union had also invested large sums in manufacturing high-quality diamonds, and wanted to see a return on their research.
For over a century since the discovery of diamonds in the British colonies of southern Africa, the de Beers corporation had sustained an effective monopoly over world diamond prices by controlling roughly 80 percent of the world's supply. That monopoly broke down in 2000 as countries like Russia and Australia began discovering and producing their own vast reserves, leading to de Beers' share dropping to around 45 percent. If the Russian source under Popigai is as big as reported, then the world diamond industry will be in for further changes -- especially if their quality is as high as is claimed.