Recoverable diamond grades are generally low (0.30 to 0.80 cpht), but the stones recovered are of exceptionally high quality. Average selling prices are in the order of US$1 500 to 2000 per carat.
Rockwell Diamonds has achieved average diamonds prices in excess of US$2,000/ct during 2006 and 2007, with monthly average sale prices as high as US$2,900/ct (SRK 2007).
During 2010, a total of 5 500ct of diamonds were sold from the opposite Saxendrift mine for an average price of US$2,029/ct.
In current market conditions ROM diamond parcels for the Middle Orange River deposits are >US$1,500 per carat (12-month average). The majority (70%) of diamonds recovered from the Wouterspan deposit is +2 carats in size, and 1-2% of stones from this deposit are larger than 100 carats in size.
These figures thus predict a high average diamond value and indicate that the deposit will yield stones of over 100 carats on a regular case as has been shown by recent and historical mining.
A sampling programme conducted from March 2005 to October 2007 at Wouterspan, recovered a total of 8,767 stones with an average stone size of 2.13 ct/stone with 14 out of the total of 8,767 stones being over 50cts in size. The top and bottom diamond cut-off for the sampling programme was 30mm and 2mm respectively. A total of 13,116.5 carats were sold by Rockwell from Wouterspan during March 2007 to October 2007 for US$29.45 million at an average price of US$2,245.31/ct (Rockwell Diamonds, Wouterspan project, 2013).
During March – October 2008, over 2,000cts were sold from Wouterspan for an average of only US$1,511/ct. During this period, there was a decrease in average diamond value of some 33% from the previous year –reflecting a drop in the average size of the diamonds recovered from the Wouterspan operation, combined with general decreases in international diamond prices towards the end of 2008.
No bulk-sampling or any trial mining was completed for the Lanyon Vale project.
Diamond grades and value estimates for the Lanyon Vale resource are based on the basis of extrapolation beyond the nominal sampling spacing and taking into account the style of the mineralisation, extrapolated from the nearby Wouterspan and Saxendrift complex deposits, respectively 500m adjacent and 1.0km opposite the Lanyon Vale deposit.
Taking into account the style of the mineralisation and insufficient exploration data available at Lanyon Vale, a conservative value of US$2,000/ct is estimated for the resource.