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Venetia Underground Project forecasting to deliver first ore in H2 2022
Monday, 7 September 2020
Having commenced with excavation work for the underground expansion of the Venetia mine in 2013, Allan Rodel, Venetia Underground Project Director, tells Modern Mining that the overall project is 38% complete.
In its sixth year of development, the US$2.1-billion underground mine development project remains the single biggest investment in South Africa’s diamond industry in decades. Over the course of its life, it will treat about 132-million tonnes (Mt) of material containing an estimated 100-million carats.
The two orebodies at Venetia – K01 and K02 – extend well below surface to depths of up to approximately 1000 m. Having operated Venetia successfully as an opencast mine since 1992, De Beers Group took a decision to develop an underground mining operation to economically extract the kimberlites that extend well below the depth limit of open-pit operations.
“We always knew that at some point we would have to transition to an underground operation,” says Rodel. “Of consideration was to find the best time and position to transition to underground. From an economics perspective, it made sense to transition the mine at the end of the current cut (Cut 4). Taking into account the capital spend and the long timeframe to construct an underground mine versus the increased stripping ratios and associated costs as you go deeper in an open-pit mine, it made sense to go the underground route.”
The underground mine will extend the life of Venetia mine up to 2046. De Beers Group selected Murray & Roberts Cementation (MRC) as the favoured contractor for portions of the development project. The scope of work for MRC basically entails the sinking, lining and equipping of two shafts – the production and service shafts.
The two vertical shafts, explains Mike da Costa, Murray & Roberts CEO Underground Mining Platform, have been sunk to their maximum depth of 1 080 m. The scope also entails the development of a decline tunnel and the development of associated surface and underground infrastructure, access development from the ramp to the orebody, as well as raiseboring work to establish ventilation infrastructure on the project.
[Subhead] Forecasting for first ore in H2 2022
One of the key challenges in recent months has been the forced stoppages due to the COVID-19 influenced lockdown. On 23 March, a national lockdown was announced in South Africa, starting on 26 March 2020, which necessitated stoppages at the project. “We had a short stoppage during Alert level 5 of the lockdown. However, in early May in accordance with the relevant Disaster Management Regulations and Directives, we started remobilising on site after putting in place the necessary mitigation measures in line with the directives from the Department of Mineral Resources and Energy, as well as the Disaster Management Act guidelines. The top of mine people returned at the start of May, while the underground development team remobilised in late May,” explains da Costa.
Rodel says the health and safety of people was paramount and changes to the schedule were thus necessary. “We had stoppages to mitigate against the spread of the coronavirus. It is, however, difficult at this stage to pre-empt the full impact of the stoppages on the schedule. At the moment we remain on target in terms of the forecast to produce the first ore from the underground mine by early H2 2022,” he says.
Rodel adds that De Beers Group, together with its business partners, including MRC, have worked closely to minimise the impact of COVID-19 on the project. “It has been a challenge, but we are actively managing the progress. A lot of work has been done between us and MRC as well as several other business partners on site to try and minimise the impact of COVID-19. Safety of all employees remains paramount,” he says.
Both shafts are largely sunk. The development of infrastructure has commenced and is progressing well.
“Both shafts have reached their final depth of 1 080 m. Equipping of the production shaft has started. The production ramp has reached the top level access. We are now starting to develop the second surface decline access, which is important to the overall project,” explains da Costa.
Da Costa adds that, having been on the project for six years, one of the major milestones achieved to date is the intact safety record. “We are proud of the safety record on site and we plan to continue in that vein until the completion of the project,” he says.
[Subhead] Competitive edge
Da Costa is really proud to be associated with a project of this magnitude and feels that it is an honour for MRC to be part of a team that is enabling this huge investment into the South African mining industry.
Commenting on MRC’s competitive edge, da Costa says the company’s successful track record in sub-Saharan Africa in terms of executing this type of project was one of the factors taken into account in the award of the Venetia Underground Project. MRC, he says, is also part of the bigger global mining engineering and construction group, Murray & Roberts Mining Group, which provides access to global initiatives, developments and critical skills that can be sourced from other parts of the world.
Rodel says that there are many factors to take into consideration when selecting a contractor for such a huge and challenging project. “A large component is to do with the safety performance, shaft and underground development expertise, as well as access to technology,” he said.
MRC continues to develop innovative technologies aimed at enhancing safety and increasing efficiencies and productivity. By taking best practice components of methodologies used in other industry sectors such as civil engineering and tunnelling and adapting them, the company has produced new best practice technology for the mining sector.
A case in point is the pre-sink gantry system which it used at VUP. The innovation was initially designed by MRC for the sinking of a number of ventilation shafts at the Gautrain. The shaft sinking method is engineered to deliver optimal safe working conditions and comprises a single rail-mounted gantry which combines the stage and kibble hoists as well as the blast barricade. The stage is suspended from the gantry on steel wire ropes attached to two 8-tonne stage winders on purpose-built platforms to the sides of the main girders.
Enhanced safety and productivity are achieved with people and material loading being handled on one side of the gantry and waste rock being dumped from the other. This is achieved with the gantry traversing between these two points. The main hoist of the gantry, used for kibble hoisting and slinging, was custom engineered to allow a pre-sink of up to 80 m below the collar elevation. On the VUP, an actual depth of 60 m below collar elevation was sunk.
The hoist is able to raise and lower a kibble with a 10-tonne payload at a conveyance speed of 0,5 m per second. The gantry system incorporates an automatic tipping frame. The kibble is slewed into its docking position where it is automatically positioned and hooked onto the frame. By lowering the hoist, the kibble’s payload is discharged into a truck waiting below.
The height of the gantry structure is matched to the height of the stage and this allows the stage to clear the collar once raised to its upper limit. Once the stage has been raised in this upper position, the long travel wheel drive motors are energised to move the gantry, complete with suspended stage, away from the shaft. The blast barricade is then drawn over the excavation and this effectively prevents fly rock from leaving the shaft barrel during blasting.
After blasting and clearing the shaft of the blast fumes by means of forced ventilation, the gantry rolls back to its position over the shaft, and the fully equipped stage is automatically aligned and positioned using a fully integrated programmable logic controller, and then lowered back into the shaft to the required depth.
An innovation which further facilitates productivity applies to projects where more than one shaft needs to be sunk like the VUP. The pre-sink gantry offers the ability to pull itself along the rails between the first and second shaft positions.
“Being able to move rapidly from the one shaft to the second during the pre-sink phase offers major time saving advantages and further reduces risk,” says da Costa. Traditionally, set up for a pre-sink can take between one to three months but with this innovative technology it is now possible to achieve this over as little as two to three days.
Further improvements on the pre-sink stage include integral mechanised drilling systems. This comprises six vertical drill rigs supported on swivel arms suspended under the stage. Each operator guides the drill and manoeuvres it to match the pattern of holes required for the blast. An inline pneumatic air leg on the rock drill extends to create the necessary thrust between the stage and the floor and for drill retraction after drilling is completed.
This technology has reduced the physical effort involved in the drilling operation and most importantly there are no longer any manual drill operators in the shaft bottom. The shaft lining process has also been simplified. A proprietary shuttering system is now suspended from the sinking stage. The shutter depth is 6m and after each 6m excavation the shutter is positioned 12 to 18 m above the shaft bottom. This means that the shutter can be left in position during drilling and blasting operations.
[Subhead] Not without challenges
Both De Beers Group and MRC note that a project of this stature is bound to come with an array of challenges. From a project management perspective, Rodel notes three key challenges – maintaining stringent safety requirements, complex interface management and the recent COVID-19 impacts on employee’s health and wellness.
“A major challenge on a project of this magnitude is always how to keep people safe,” he says. “You have to keep reinventing yourself in the safety space. The focus on people development, providing leadership, visible engagement and critical control management is thus key. We have and continue to apply technology in the tracking of critical safety controls.”
Rodel adds that the project also has to deal with the complex interface management. This pertains to the need to simultaneously manage surface construction, shaft development and an operational mine, with a series of engagements happening throughout that process. “This requires constant focus on work management and execution,” he says, adding that planning the work entails taking into account all the interface points under restrictive resource requirements. A project of this duration allows for many lessons learnt and constant improvement.
The COVID-19 situation has also brought its fair share of challenges. This has called for a stringent health and safety control regime, with the continuous changing of protocols necessary as the project progresses.
From a project execution perspective, da Costa says when starting out on the project, MRC’s South African crews had to adapt to the new shaft sinking methodology, which was a challenge in the early days of the project. The company brought in a few Canadian experts on the site to manage the process and to assist its SA teams to get familiar with the system. “It took a while,” he says “but once they got the grasp, they saw the benefits.”
Da Costa reasons that a typical challenge in SA’s mining industry is the dearth of critical skills, especially mining operators and supervisors. “That was a challenge for us on the project,” he says. “It continues to be a bit of a challenge but we have brought in a number of our Australian operators from our Australian business to help with skills transfer. We have also made use of our Carletonville training facility to train the skills that we need.”
MRC has also recruited a number of people from the local community and trained them as mechanised operators. “We use the more experienced operators that we have on the job to transfer skills to the local people that we have recruited. While it was initially a challenge, we have been able to develop some really competent, skilled people out of the project,” says da Costa.
Da Costa agrees that the COVID-19 pandemic has also come with its challenges. The disruptions caused by the pandemic have impacted the contractor. He, however, says the MRC and De Beers Group management teams on site have done a stellar job to minimise the impact of the pandemic on the schedule.
In conclusion, Rodel is proud that VUP remains the most significant investment in mining in recent years, not only in South Africa but in Africa. The socio-economic development impact of the project in host communities is massive. The project continues to create around 2 000 jobs during the construction phase and the majority of these people have been sourced from local communities.
“Our business partners have also played an active role in supporting local communities through our CSI programmes. MRC, in particular, has been hugely involved in most of our CSI projects as we try to curb the impact of the COVID-19 pandemic in our host communities,” he says.
“VUP is a very complex project, but we have the right people on the job and are really excited about the future. We are looking forward to extracting our first ore from the project by early H2 2022,” concludes Rodel.