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Lace underground tunnel development slower than planned

31st July 2015

By: Megan van Wyngaardt

Creamer Media Contributing Editor Online

  

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JOHANNESBURG (miningweekly.com) – Underground tunnel development at Southern Africa-focused diamond developer DiamondCorp’s Lace diamond mine, in the Free State, is proceeding slower than planned, owing to fractured ground close to old workings; however, the development work in the Upper K4 (UK4) block remains close to schedule and mining operations are on track to start in the coming months.

DiamondCorp added that ground conditions around old workings did not pose problems for future mining, holding the potential to enhance fragmentation, but required extra support during development to ensure long-term hanging wall stability.

The slower-than-planned development rate meant that mine development costs, to date, were averaging R44 193 a metre, against a budget of R37 000 a metre, owing to the impact of fixed labour and electricity costs.

“While the delay is frustrating, management’s prime concern is the strict adherence to safe underground working practices and it is imperative that safety is not compromised. There is limited scope for making up the lost time but management is investigating options for accelerating blasting of the slot drive to keep the tonnage ramp-up closer to schedule,” the miner said in a statement on Friday.

Meanwhile, excavation of the underground loading chamber and the raiseboring of the ore pass to allow UK4 Block kimberlite to be tipped onto the conveyor belt was completed on time and within budget.

The conveyor belt was 99% fabricated, on site, and 75% installed; however, final installation and commissioning had been delayed as a result of instructions from the Department of Mineral Resources to install additional antiroll-back idlers in sections of the conveyor belt over and above systems already in place.

The additional antiroll-back idlers were ordered and scheduled for delivery in the next four weeks. Following installation of the conveyor belt system, load and haul costs were expected to be reduced by more than half.

The dual-listed company further highlighted that processing of K6 kimberlite recovered from the production level drives also continued, while processing of higher-grade K4 kimberlite had started.

“Diamond recoveries from the development K4 kimberlite processed are exceeding expectations with respect to overall quality and [we are] confident that the UK4 operating margins will exceed 70% as previously predicted from microdiamond analysis,” it said.

Diamondcorp’s 220 t/h dense media separation plant operated efficiently on a batch basis during the period, processing 1 000 t of K6 and K4 kimberlite bulk samples extracted from the development tunnels.

Meanwhile, Diamondcorp’s detailed studies, for installing high-volume optical and/or X-ray waste sorting, were expected to be completed before the end of the year and, if positive, the preferred capital investment recommendation put forward to management.

“Waste sorting has the potential to significantly reduce plant water and electricity consumption and could also allow kimberlite to be processed faster than the current planned 220 t/h. If the testwork is successful, a unit could be installed before the mining ramp-up for the first block cave,” it noted.

During the period, the company’s management also studied its options for a tailings retreatment and concluded that tailings reprocessing would only restart when mining of the kimberlite reaches commercial volumes.

“Then, a small amount of tailings, about 1000 t a week, would be blended into the kimberlite run-of-mine, thereby reducing water consumption and the need for changing screen panels. The dilution impact of this small amount of tailings blending will be minimal and the remaining tailings resource will be treated over the 25-year life of the underground mine,” it added.

Edited by Chanel de Bruyn
Creamer Media Senior Deputy Editor Online

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