Stellar Diamonds (LON:STEL) advanced over 7% in early deals after revealing that bulk sampling grades from the Tongo kimberlite now exceeds 150 carats per hundred tonnes (cpht), after tailings were reprocessed.
It means a 29% increase in the diamond grade to 155cpht from 120 cpht.
A total of 843 carats have now been recovered through processing material from the bulk sampling programme. Stellar says the diamonds are high quality, with a modelled value of US$248 per carat, or US$384 per tonne on in-situ ore.
The company says it is anticipated the project’s resource size, currently estimated at 1.1mln carats, will be increased.
Final bulk sampling results are expected next month.
"Tongo continues to yield excellent results underpinning the project's significant potential,” said chief executive Karl Smithson.
“This grade compares very favourably with the previously calculated resource grade of 120cpht and should impact positively on project economics as well as the resource size, which is currently independently estimated at 1.1 million carats (JORC compliant).
“The final bulk sample to complete the 1,000 carat parcel is currently being extracted and processed and we expect the final grade and value data to be available in August."
On AIM, Stellar shares were up 0.1p, 7.55%, trading at 1.42p each.