Ann: 204 Carat Diamond Recovered at Mothae Mine, page-34

That single stone is likely worth more than US$1million as it is, depending how it cleans up and the % gain from the polishing agreement with Safdico.
Mothae is one of the few mines that produce such stones and they have the potential for significantly higher prices if better quality.
The former owners Lucara, decided to focus on Karowe, which happened to be a deposit previously held by DeBeers who didn't think it was economic!
Merlin was mined for 3-4 years by Rio, it was never of the scale that Rio wanted so they discontinued even though it produced 500,000cts.
That was back in 2002, diamond prices are significantly higher now and likely to continue to climb. The previous owner JG was never capable of bringing it back to mining.