Southern African diamond development and exploration company DiamondCorp last week said it had completed the required modifications to the 1.2-million-ton-a-year processing plant at its Lace mine, in the Free State, to allow for the seamless transition from treatment of the tailings to the treatment of underground kimberlite.

The modifications, which were completed on schedule and within budget, were related to the 47-level block cave development at the mine, with plant commissioning under way and tailings retreatment to start this month.

DiamondCorp noted that tailings retreatment would initially operate on a single shift until the market price for the Lace tailings diamonds was established with the first sale likely to be held in September.

“If prices achieved result in sufficiently attractive operating margins, the company will look to increase to two-shift and potentially three-shift operations before year-end, as approximately 3.5-million tonnes of tailings remain on site and available for processing. Tailings retreatment economics should be assisted by the recent weakness in the South African rand and the reported improvement in diamond prices,” the firm said in a statement.

From April to June, trackless mining crews focused their blasting activities on upper level conveyor belt declines and the loading loop on the 200 m level. A hand-held drill crew advanced the 165 m level vent raise, which would allow temporary ventilation for continuous blasting conditions to the 470 m level.

Crews achieved the scheduled development metres during the period with cumulative cost a metre to the end of May being about 15% under budget, owing to tight cost control and the operational efficiency of the company’s owner-operated mining fleet.

Further, excavation of a new 66 000 bank cubic metre (bcm) boxcut, which would serve as the surface entrance to the twin conveyor belt and services declines for the life of the mine, was 75% complete. The boxcut was three weeks behind schedule, as more competent ground was encountered earlier than expected, slowing down the mining rate.

However, DiamondCorp indicated that the delay would have no impact on the overall development schedule, as the activity was not on the critical path and the more competent ground was a positive with respect to mine portal stability.

As a result of owner-operated fleet efficiencies, the boxcut development was 40% under budget on a bcm basis.

Meanwhile, the company’s decision to develop a core competence in rebuilding its heavy equipment mining fleet in-house was yielding results in terms of operating efficiencies. The first fleet of rebuilt underground trucks and loaders were providing in excess of 90% availability and operating significantly under budget with respect to diesel consumption.

The company’s heavy equipment workshop was rebuilding machinery for between 25% and 50% of the price of new machines.

During the past quarter, the engineering, procurement and construction management contract for the company’s underground conveyor belt design, fabrication and installation was awarded. The design work was complete and detailed drawings were being generated and verified. Orders have been placed for the major imported belt and drive components, thereby fixing exchange rates.

DiamondCorp had also taken delivery of a new Boart Longyear LM30 underground diamond drill rig and a programme of 2 000 m of underground core drilling was planned for completion before the end of the year.

Drilling would be undertaken from inside the kimberlite to better define the margins of the bulge, as well as the 47-level block-cave area.