Over 6 billion carats of diamonds have been extracted from the Earth since antiquity, whereas only 1.2 billion carats of mineable diamonds are estimated to remain in the Earth today according to the public filings of the De Beers and the other large diamond mining companies.
Unfortunately, each marginal carat mined is more difficult to extract and more energy intensive than the last. Quite simply, all the easy to get diamonds have already been extracted.