Drilling underground at Venetia
Drilling underground at Venetia

Venetia’s underground lifespan extension project, due to start producing diamonds in 2021, is well underway and can already be described as a successful venture.

Global diamond company De Beers’ US$2 billion cash injection to transition Venetia from a surface operation to an underground mine is the company’s largest investment ever made in South Africa and a massive development undertaking which effectively secures its lifespan for another 20+ years. The project also celebrates world-class shaft sinking innovation – with an internationally tried-and-tested methodology which guarantees significant safety improvements that could forever change the way mine shaft s are sunk in South Africa, writes Laura Cornish.

While the Venetia Underground Project (VUP) officially moved into execution in July 2013, the preparation work to ensure its optimal development timeline and production start-up started a decade before. “The concept studies for the project commenced in 2003, signifying the level of importance De Beers places on Venetia’s diamond contribution. 10 years’ worth of upfront investment in studies alone clearly signals this,” starts Christoff Kuhn, VUP head. Venetia is South Africa’s largest diamond producer and will now remain so well into the future.

The project feasibility study was approved by De Beers and 85% shareholder Anglo American in July 2012 and ‘kicked off ’ a year later.

The project’s sole purpose is to extend the Limpopo-based mine’s lifespan – by 2021 the diamond-bearing ore at its 4.5 Mtpa open pit K01 and K02 ore bodies will be depleted. But as an underground mine, based on current reserves and resources, Venetia will continues to operate comfortably until 2043. It is expected to produce roughly 96 million carats from 130 Mt of mined kimberlite material over its 22 year lifespan.

The K01 ore body will be mined by means of a sub-level caving mining method, with K01 producing 4 Mtpa (average of 3.5 million carats per annum). The K02 ore body will be mined by means of a modified sub-level caving mining method producing 1.9 Mtpa (average of 0.9 million carats per annum). This equates to 5.9 Mtpa, which matches the throughput capability of the existing main treatment plant.

“The handover year in 2022 from open pit to underground must be executed seamlessly as there is limited opportunity for overlap between surface and underground. From the very first underground blast we will extract the main truck ramp in the open pit,” Kuhn explains.

Project progress to date

With minimal upgrades required for the process plant, which will continue processing about 5.9 Mtpa of kimberlite 1992 The year Venetia was established and started operating from underground, all focus is on developing the underground mine. This entails sinking, equipping and commissioning a decline as well as two vertical shafts; horizontal tunnel development to provide access to and the establishment of loading levels; as well as associated ventilation, ground and water handling infrastructure. Local shaft sinking and mine development specialist Murray & Roberts Cementation was awarded the contract in 2013 and is underway with development across all three shafts.

The decline tunnel development commenced early in 2014 and to date is just over 1 km in length. “It will extend to the bottom of the ore body and total 7 km in distance,” says Kuhn.

With both headgears erected, pre-sink activities on both the production and services headgears started at the end of 2014 and both stretch to a depth of about 60 m. “Preparation is underway to move into full steady-state shaft sinking which we aim to achieve by the end of the fi rst quarter in 2016,” Kuhn continues. Both 7 m diameter vertical shaft bottoms will stretch 1 080 m although the ore body will be exploited to about 900 m. Although the ore body extends beyond 1 000 m, this was determined the optimal depth, particularly with regard to development completion timeframes.

While the shift from surface to underground is a few years way, the changeover process has already started, Kuhn notes. “Some of the underground equipment is already operating as part of the development phase (drill rigs and loaders).”

“Shaft sinking is scheduled to be largely completed towards the end 2017/start of 2018 after which lateral development starts and transition begins. At this point the level of work will increase two or three fold and will see us enter our busiest time on site,” Kuhn continues.

Pioneering shaft sinking methodology

One of the most unique project attributes is the shaft sinking methodology Murray & Roberts Cementation is applying to the vertical shaft developments, and which has never been done in South Africa before. It is designed to deliver optimal safe working conditions in what is traditionally recognised as one of the least safe mining development processes.

“The shaft sinking procedure may be new in South Africa but is internationally common practice. We have adopted the methodology from our sister company in Canada,” Graham Chamberlain, Murray & Roberts Cementation project executive, states. In essence, it entails harnessing sling-down Jumbo drill rigs that nest in the sinking stage. These jumbo drill rigs need only one driller per boom to be on the shaft fl oor to operate the rig and to change drill rods.

“We also make use of vertical shaft muckers (VSMs), housed in the stage to clear the broken rock – as opposed to cactus grabs. This allows for a faster cleaning time, with only one person needed at the bottom of the shaft during the mucking cycle,” Chamberlain explains. Because the muckers are capable of manoeuvring the kibbles into position quickly and accurately, the need for the human element in this dangerous task is eliminated. Cactus grab cleaning by comparison requires the kibbles to be manhandled by those on the shaft bottom to move it into position.

All activities throughout the sinking cycle will be handled sequentially, meaning no two jobs will take place simultaneously. With fewer people working in the shaft and exposed to the contact area, safety risks are automatically reduced – significantly. And, contrary to the assumption that this will slow down the entire cycle, with the full combination of changes, this approach will actually improve productivities.

The drill rigs can drill a burn cut round, which improves the advance and reduces the fl y rock that typically causes damage in the conventional method. They also have greater drilling precision which reduces overbreak and conversely eliminates the need for any secondary breaking.

With the blasting of a smoother shaft barrel, concrete usage is also substantially reduced. The use of emulsion will provide a better blasting break, which will in turn make the task of the cleaning crew easier. While this shaft sinking process is not new to Canada, it has never been done in South Africa before, Chamberlain repeats. “We want to be the frontrunners in changing the face of sinking shafts in South Africa (and Africa) and have invested considerably to achieve this successfully. Prior to starting on site, Murray & Roberts Cementation invested in the construction of entire mock-up shafts at its Bentley Park training facility in Carletonville. This was performed in conjunction with intense drilling/VMS operator upskilling and training with hands-on input from Murray & Roberts Cementation Canadian expatriates.” With highly qualified personnel on site at Venetia, the crew required to deliver the project has been halved. The end result of such a process will give rise to a new mindset and a new breed of empowered, intelligent and highly skilled employee.

A project of this magnitude and value is not only a major achievement for De Beers but also for South Africa as a country. It secures hundreds of jobs for people in the region and retains the country’s position as owner of one of the world’s largest diamond mines. MRA