JOHANNESBURG (miningweekly.com) – Diamond asset developer Rockwell Diamonds has lifted the volumes of gravel processed from its operations during the quarter ended August 31, by 57% to 1.4-million cubic metres, driving a 37% increase in overall carat production to 9 581 ct.

Sales from these operations grew 58% to 8 864 ct at an average of $1 489/ct, bolstered by the recovery of a 104 ct cape yellow diamond and a 117 ct commercial yellow stone.

CEO James Campbell said on Monday that the second-quarter production results reflected continued benefits flowing from the group’s focus on its Middle Orange River (MOR) region.

“This is a clear demonstration that our three producing MOR mines have gained critical mass and that the implementation of our managed mining strategy, including the earthmoving vehicle (EMV) renewal plan, is delivering significantly higher EMV availabilities,” he commented.

Campbell added that the increase in volumes of gravel processed over the quarter was evidence that Rockwell’s processing plants had “risen to the challenge” of the higher mining volumes.

“Accordingly, we are well placed to show a sustainable reduction in unit costs,” he noted in a statement.

As volumes had increased, Campbell said the operations had benefitted from a higher average stone size, which was in excess of 4.5 ct in the second quarter.

“We produced two gem-quality 100 ct-plus diamonds in the second quarter, which brings the total to eight over-100 ct stones recovered from our operations in the last 12 months – another tangible indicator of the success of our focused MOR strategy,” he outlined.

Rockwell’s five royalty mining contractors at Tirisano, meanwhile, continued to deliver positive returns for the group, with production and sales from these partners increasing 66% and 70% respectively.

Diamond values showed a 30% increase, resulting in the value of sales from contractors rising 121% to $4.2-million.

Rockwell’s inventory of 5 954 ct, including royalty contract miners' inventory of 3 034 ct, would be carried over into the third quarter of fiscal 2015.