Tsodilo Resources Limited announcing the results of a second independent Size Frequency Distribution (SFD) modelled grade and diamond value for the BK16 Large Diameter Drilling (LDD) said yesterday that the study had posited a model price between US$ 281 to US$ 792 per carat and a model grade of four to eight cpht. The study was based on an aggregate 77.94 carat parcel of 502 commercial size (+1mm) diamonds initially reported on November 7, 2018.

The second study was undertaken to correct any potential overstatement of the first study. Stephen Coward of Interlaced was appointed “to review and develop new model grade and valuation figures based on the same raw BK16 data”, the Company reported. Coward has over 30 years of experience in the diamond industry – including over 20 years with De Beers – during which time he has built his expertise in project estimation, evaluation and value chain modelling across several commodities.

“Using a combination of simulation and extrapolation, the SDF grade (cpht) and value (US$ per carat $/ct) have been re-modelled to give the following likely in-situ or “run of mine” grade and value (#1 DTC bottom-cut off size): The diamond value ranges from $/ct 281 to $/ct 792; The grade ranges from 4 cpht to 8 cpht (carats per hundred tonne),” the Company announced.

Further, based on the report, Tsodilo said: “The Size Frequency Distribution (SFD) study demonstrates the potential presence of large stones, indicating that ~2% to 5 % of the total carats may be greater than 10.8 carats (specials). This compares favourably to Lucara’s Karowe Mine on AK06 of which some ~5 % of the total carats produced are greater than 10.8 carats.”

It also revealed that BK16 contains high quality diamonds “dominated by highly marketable shapes (makeable and sawable)”, and that no boart has been recovered to date.

Of the stones tested, 3.8% were identified as high-quality Type IIa diamonds consisting predominantly of D colour stones.

“Due to the small size of the LDD sample, stones above 2 carats have not yet been recovered but can be expected based on the SFD analysis,” the Company said.

Coward stated: “Based on my analysis of the SFD of the diamonds recovered from the LDD samples, it appears that the size distribution of BK16 could be coarser than several producers in southern Africa. There are indications that BK16 could have a broadly similarly coarse shaped size distribution to that of the Lucara’s Karowe Mine (Botswana), Petra Diamonds’ Premier Mine (South Africa), and Lucapa Diamond’s Mothae Mine (Lesotho). However, there is a clear under sampling of coarse stones thus far at BK16 which adds significant uncertainty to the grade and value modelled. This uncertainty is explained by the fact that the current 2,077 dry metric tonne LDD sample represents a distinct under sampling of the true SFD of the BK16 kimberlite (~0.01% of the total kimberlite body). This under sampling explains why the sample grade and diamond value are well below the modelled grade and value, and thus why the value and grade modelling reported by this study are so important and should be considered a more accurate reflection of a likely BK16 run of mine production.”

Tsodilo is contemplating a second phase of bulk sampling to increase the sample caratage from BK16. “This is necessary to improve the confidence limit of the US$ per carat modeled values for feasibility purposes,” the Company stated. “Several different scenarios are being investigated to recover a minimum of 500 carats either by extending the existing shaft and tunnels or using 24-inch LDD work either as cluster holes or individual holes on a grid system.”