Ashton Mining Ltd's extraordinary success in creating a whole new market for affordable, polished diamonds since quitting the De Beers-controlled Central Selling Organisation five years ago is the key to the South African group's $522 million takeover bid.

As foreshadowed in yesterday's AFR, De Beers 38 per cent owned by Anglo American has offered $1.62 a share for all of Ashton's shares, valuing the target at $522 million, based around the acquisition of a 19.9 per cent stake from Malaysian Mining Corp.