New Millenium: Charts & Fundamentals

I believe the key is this para:

"Grid pattern "grab pit" sample extractions of sector 1/5 have so far proven to
be viable in content of diamondiferous gravels, yielding continuous diamond
finds of various carats throughout the target area. Exploration of this area is
nearing completion."

So the first sector they have explored is proving to be viable for bulk extraction. It seems possible that if sufficient carats have been discovered to confirm viability, bulk extraction might be able to commence in one area before all five areas have been sampled.

I don't think it's sensible to extrapolate total carats found from a couple of large stones - the "nugget effect" in alluvial diamonds is as extreme as it gets. Two pits might yield very little, whilst the next one could yield masses. (And the unsampled ground between the two pits could contain even more!) This is partly because of the way in which the diamonds are deposited in the first place - it can't be described as random, because it's governed by the configuration of the river at the time of deposition, but it can be highly irregular. The systematic sampling on a grid is NOT irregular, and results can therefore be very patchy. A diamond geo once said that the only time you will really have much idea of how many carats are contained in a given tonnage of gravel is when you have processed the lot!