London-listed diamond mining group Petra Diamonds’ expansion programmes at its flagship Cullinan and Finsch diamond mines, in South Africa, remain on track and within budget, with development progressing well, states Petra Diamonds CEO Johan Dippenaar.

Construction on the modern, fit-for-purpose processing plant at the Gauteng-based Cullinan diamond mine started in the fourth quarter of the 2015 financial year, with commissioning and full operation expected in two years’ time in the fourth quarter of the 2017 financial year, he notes.

The processing plant has a projected value of R1.65-billion and a planned throughput capacity of six-million tonnes a year. “The plant is an important part of Petra’s plans to create a long-term sustainable future for Cullinan and will replace the existing plant, which was originally commissioned in 1947 and has undergone various refurbishments over the years since its initial construction.

“The technologies planned for the new plant – autogenous milling, high-pressure grinding rolls and the enhanced use of X-ray fluorescence to replace conventional dense-media separation plants to treat coarser material larger than 12 mm in dia- meter – will be implemented with the commissioning of the plant,” Dippenaar adds.

Petra Diamonds notes that “operating efficiencies and security improvements will be driven through increased automation, reduced tonnes in circulation and improved energy efficiencies, with an expected improvement in energy efficiency for each ton”.

The new plant will reduce the processing footprint at Cullinan from about 26 ha to about 5 ha, with an associated reduction of engineering infrastructure, such as reducing the number of conveyor belts from 151 (spanning 15 km) to 22 (spanning 3 km).

Dippenaar reiterates that the new plant is expected to improve the recovery of the full spectrum of diamonds, thereby increasing the volume of stones recovered and better protecting large stones from breakage. The new technologies will also improve the efficiency of the material flow, thereby lowering operating costs.

C-Cut Expansion
The C-Cut Phase 1 expansion plan at the Cullinan mine, which will establish a new block cave on the western side of the orebody, in the upper portion of the major C-Cut resource, remains on track and on schedule, affirms Dippenaar.

The expansion programme will increase production from 800 000 ct in the 2014 financial year to 2.2-million carats a year by the 2019 financial year, comprising two-million carats run-of-mine (RoM) and 200 000 ct of tailings, Mining Weekly reported in March.

“Currently, a new production level, being established at 833 m, is on track and the shaft at 930 m is progressing well. The 880 m ore-handling system, which could allow for future ramp-ups to use the full C-Cut footprint, is also under construction, Dippenaar says.

Petra Diamonds previously noted that the shaft deepening and underground development at Cullinan continued to progress in line with expectations, with the C-Cut Phase 1 waste development yielding 2 361 m, raiseboring delivering 389 m and kimberlite development delivering 967 m for the first six months of this year.

Cullinan is known to consistently produce large, high-value diamonds. At the time that the mine was taken over by Petra, in 2008, it had produced around a quarter of all the world’s diamonds greater than 400 ct, according to the company’s website.

Finsch Progress
Development work at the com- pany’s Northern-Cape-based Finsch diamond mine is progressing well, Dippenaar says.

Petra plans to ramp up production from 1.89-million carats a year in 2014 to about two-million carats a year by financial year 2017 by establishing new mining areas in Block 5, underneath the current production level, accessing undiluted ore from the sublevel cave (SLC), Mining Weekly reported in December 2014.

The company will use the SLC mining method over four levels in Block 5, from 700 m to 780 m, and is ramping up the underground operation to achieve steady-state throughput of 3.5-million tonnes a year from the 2018 financial year. The new Block 5 cave will then be installed at 900 m.

“Development of the SLC at Finsch is on track and the dedi-cated conveyor ore-handling infrastructure to transfer ore from the SLC to existing infrastructure at 650 m is progressing well,” says Dippenaar, adding that the adjacent South West Precursor orebody will also be accessed from 630 m to 780 m.

Market Outlook
“Southern Africa is, and is likely to remain, the most important diamond producing region in the world, with about 60% of the world’s diamonds by value coming from Africa,” Dippenaar stresses.

Meanwhile, he notes that the strong dollar currently has a tempering impact on dollar-denominated diamond prices, but the weak rand has a beneficial effect, as about 75% of Petra’s operating costs are rand-based.

While Petra has noted a softer diamond market in the past financial year, the company believes that the medium- to longer-term strong supply-and-demand fundamentals are still firmly in place, Dippenaar argues.

“The market for rough diamonds is expected to remain underpinned by a firmer US market – the world’s major market for polished diamonds – as well as continued growth in demand from emerging markets,” he says, concluding that constrained diamond supply is also expected to support future rough diamond price increases.