JOHANNESBURG (miningweekly.com) – The sale of the first parcel of diamonds from the TSX- and JSE-listed Rockwell Diamonds' recommissioned Tirisano mine in North West province has met with strong bridal-market demand. 

“We’re probably sitting on an all-time high on bridal stones, and I see no better time to have actually brought the Tirisano mine into production,” Rockwell CEO James Campbell tells Mining Weekly Online.

Production from the 18-year-life Tirisano in Ventersdorp averaged $606/ct in the second quarter of Rockwell’s 2012 fiscal year for generally 3 ct to 4 ct diamonds.

Interestingly, Rockwell is also recovering large 10 ct and 20 ct stones at the recommissioned Tirisano.

“We all had a belief that the larger diamonds were there and from what we have seen after only a few weeks of production at Tirisano, our belief is going to be endorsed,” Campbell reports.

The exceptional quality 10 ct-plus stones from Rockwell’s Middle Orange River operations in the Northern Cape are still holding their value, if not increasing, and the high-quality 10 ct-plus diamonds are on par, but the prices of diamonds that are poor in quality have decreased.

While smaller, lesser quality diamonds have dropped in price by between 20% and 40%, that has negligible impact on Rockwell, the Saxendrift operation of which is yielding $3 000/ct. In the latest quarter, 11 Saxendrift diamonds exceeded 20 ct.

Eighty percent of Rockwell’s diamonds are beneficiated in South Africa as part of the company’s joint venture agreement with the Steinmetz group, which has its factory in downtown Johannesburg.

Flawless Diamonds markets and sells the diamonds on Rockwell’s behalf for a 1% commission, which is below the more general 3% to 5% commission and well below De Beers’ 10% commission.

While some see alluvial mining as a hit-and-miss, up-and-down business on which grade prediction is elusive if not impossible, Rockwell reports that it has developed a tool that allows it to predict grades by modelling four geological metrics on each of the mining faces.

Use of the tool has enabled Saxendrift to exceed its carat target for the last three months.

The 150 t/h, $1.5-million Bourevestnik bulk X-ray sorting machine that Rockwell has ordered from Russia for Saxendrift will be commissioned by the end of March.

Traditional pan plants, which are difficult to control and only 60% to 70% efficient, will be replaced by the new high-throughput single-particle sorter, which is 95% efficient and uses less power, water and labour.

The unit will be used as a proof-of-concept for the design of future mines on the Middle Orange River.

The plan is also to fine-tune the Tirisano operation, which is achieving a production capability of 90 000 m³/m, which will be more challenging when wetness sets in.

“We would like eventually to go towards a wet front-end because once rain falls in the Ventersdorp area, the material becomes difficult to treat,” Campbell adds.

Klipdam, which has broken into operating profit at $1 200/ct, has life extension potential under a new mine manager.

Rockwell may contemplate selling Klipdam and investing the proceeds in Saxendrift and Tirisano, which are both more value accretive.
 

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