If you do some digging there is some old bulk sample data, might...

If you do some digging there is some old bulk sample data, might have been BHP? That would be a starting point.
Grade/carats per ton is the first marker, usually in the tens of carat per hundred ton.
Size of deposit, depth and overburden.
Size distribution of diamonds.
Value of the diamonds.

My understanding is that some of these parameters are well known but they want to fully explore the size distribution and value particularly of the Fancy Yellow/Orange diamonds. There is a perception that these diamonds were not fully represented in the original small bulk sample taken. Potentially these diamonds can have a significant impact to the price per carat that can make the mining viable.
The likely outcome is that a further larger bulk sample will be required.