During 2019, Rio Tinto completed the drilling of 10 bulk sample holes (trenches) on the Star kimberlite using a trench cutter sampling rig. A significant number of diamonds from the EJF geological units were analyzed, containing a spectrum of diamond sizes from 0.18 carats through all the large stones, up to diamonds of over 15 carats.
The study conducted by Star Diamond confirmed that unusually high proportions of Type IIa diamonds are present in the kimberlite. Of particular note is the exceptionally high proportion of Type IIa diamonds in the larger size fractions of the EJF, of which 53% (8 of the 15) of the largest stones, 4 carats and above, are Type IIa. Nine of the 12 highest-value stones from the EJF trench cutter samples (3 carats and above) are Type IIa. The largest Type IIa diamond identified is a 16.96-carat stone.
“The presence of a significant proportion of Type IIa diamonds recovered in the Star kimberlite by the…
