Impala Archives - International Mining

As open-pit mines reach their economic end of life, mine owners are considering the viability of transitioning their open-pit operations to underground.

Drawing on its deep level mining expertise in South Africa, Worley helps mine owners around the world to explore the feasibility of underground life of mine extensions and identify the most efficient and safe underground mining methods.

Among the driving factors in the transition to underground mining are declining ore grades, deeper ore deposits, and an increase in demand for minerals required for the global energy transition, such as copper, lithium, manganese and nickel, Worley says.

“Worley’s centre of excellence for copper in Chile has been supporting open-pit copper mine customers for nearly three decades,” the company said. “The company is gearing up its underground capability as these mines shift their operations to below surface to access deeper ore reserves.”

Going deep in South Africa

Worley’s South Africa operations is one of the company’s mining centres of excellence with niche experience in deep level mining.

Mining has been the mainstay of South Africa’s economy for well over a century, and a major source of employment as well as foreign investment. Consequently, Worley has grown its South Africa mining team in one of the best mining environments in the world, with a collective experience of over 120 years in deep level mining and process expertise.

Robert Hull, Vice President for Mining, Minerals & Metals in Africa, says Worley’s South African operation is recognised for its deep level shaft experience, and the company also has experience across most commodities including base metals, coal, platinum, gold, diamonds and ferrous metals.

Hull says Worley has a strong global workshare philosophy and culture of collaboration. The specialist skills in South Africa gained from working on some of the biggest underground projects in the world are an integral part of Worley’s mining, minerals and metals global project delivery offering.

Deep level mine skills

Some of South Africa’s specialist deep underground skills include shaft design, ventilation and refrigeration shafts, high pressure pumping, and deep level hoisting.

Worley says it is one of the few companies in the world that has the expertise to design hoisting systems for mass hoisting, such as at the Venetia Underground Project, which will hoist approximately 6 Mt/y of rock.

The De Beers Venetia Mine in South Africa is the biggest source of rough diamonds in the country, according to Worley. The mine is in the process of transitioning from open pit to underground, to extend its life by some 25 years.

As engineering procurement and construction management contractor for South Africa’s largest mining execution project, Worley is using 3D designs for the project infrastructure to provide 3D models for the entire project’s surface and underground infrastructure, it said.

Intelligent mines

Hull says Worley is leading the way in developing digital solutions for the planning, design and execution of mining projects, with the South Africa office having played a key role in the design and development of much of the group’s digital technology in mining and minerals processing.

Hull (pictured) cites the Wafi-Golpu (owned by Harmony Gold Mining and Newcrest Mining) feasibility study update, in Papua New Guinea, where the South Africa team drew on SmartPlant design technology, which uses rapid prototyping and Building Information Modelling. The technology allowed the entire project team to visualise project objectives as never before, greatly improving operational efficiency in a dynamic time and cost-saving environment, according to Worley.

The Wafi-Golpu project is ranked as a world-class deposit in terms of its size and the grade of gold and copper within it. If developed, it will be the largest, deepest and most complex underground mine in Papua New Guinea, with a mine life of 28 years, Worley says.

Integrated project delivery teams

Worley’s South Africa team is also supporting its Australia counterparts to project manage the delivery of the deepening and expansion of an underground gold mine. This includes construction of a 1,460 m shaft, additional capacity in the processing plant, and supporting infrastructure to enable profitable recovery of ore at depth to 2 140m below surface. IM understands the project in question is the Newmont-owned Tanami Expansion 2 project, in the Northern Territory of Australia.

Mega machines for mega mines

Hull says every underground project Worley has executed has drawn on the company’s large material handling capabilities.

“In South Africa, we have a dedicated materials handling department that has the latest tools including discrete element modelling and finite element analysis, and advanced simulation tools for conveyer design,” he said.

Coenie Mynhardt, Winder Engineering at Worley, adds that mine payloads have increased dramatically in the last two decades in pursuit of higher productivity rates. Mines such as Impala and Phalaborwa, in South Africa, with an approximate 12-t per skipload, were considered ‘mega mines’ in their day. The mines of the future are more than double that size.

“The mega mines of the future need mega machines to be able to handle such big payloads,” Mynhardt says. “Materials handling technology for such deep, high tonnage operations will test current technology for capacity and reliability to bring the ore from the production levels to surface. We have the skills and expertise to find the solutions to these challenges.”

Global project delivery

“Countries such as Chile have immense potential for transitioning from open pit to underground if the geology supports it,” commented Hull. “With the wealth of experience across locations and over 4,000 staff in our mining, minerals and metals business line, we can safely and successfully deliver our customers’ underground mine assets through collaborative development of the mine and associated infrastructure anywhere in the world.”

Safer tailings storage facilities (TSFs) – or tailings dams – can be achieved when mine owners, contractors and engineering consultants work closely together, says SRK Consulting’s Linda Spies.

Speaking after a recent Southern African Institute of Mining and Metallurgy (SAIMM) conference focusing on tailings dams, Spies, Senior Geotechnical Engineer at SRK Consulting, said that mining executives today required more assurance that their tailings dams are safe, with controls becoming much stricter. Greater transparency was also being demanded by other stakeholders such as investors and communities, she added.

“After several hundred lives were lost in two well-publicised tailings dam failures in Brazil, in 2015 and 2019, awareness of tailings dam risks has been raised within the mining industry and in the public eye globally,” she said. “These latest failures were especially significant insofar as senior management at the mining companies were for the first time being implicated directly with charges of manslaughter and environmental damage.”

She noted that while conferences on this topic usually involved mainly tailings dam practitioners and academics, this event had strong representation from owners; contractors, who are responsible for tailings dam construction; and consultants, who design TSFs and monitor their construction.

“This meant that the discussion was more holistic and valuable, enriched with insights from these various perspectives,” she said. “This is vital in promoting innovation, safety and environmental and social responsibility in the design, operation and closure of tailings dams.”

While the tone of the event was serious considering recent failures, there was also an optimism flowing from a showcasing of best practice in the field and how this was being successfully applied. In her own case study presentation on a lined tailings dam at a South African platinum mine (Impala’s Marula dam), Spies highlighted the complexities introduced by the liner requirement – and how good drainage design and quality assurance were an important part of the solution. (see Getting lined tailings storage facilities right below)

Among the key issues discussed at the conference was whether upstream tailings dams should be allowed – as this was one of the commonalities in the recent Brazil failures. High-level input was given in a panel discussion by senior leaders from a mining company, a law firm and an insurance firm, including technical opinions from tailings industry expert and specialist geotechnical engineer Adriaan Meintjes, a Partner and Corporate Consultant from SRK.

According to SRK Principal Hydrogeologist and Numerical Modeller, Sheila Imrie, who also presented at the event, tailings is rightly receiving considerable attention from a combined engineering and scientific perspective and will continue to do so in the future.

“The continued application of the latest technologies by the industry’s top experts is critical,” Imrie said. “Industry must also ensure that sufficiently detailed research, monitoring and numerical modelling informs the future design and current management of tailings dams.”

She presented a paper on ‘3D Seepage Modelling in Tailings Storage Facility Analysis and Design for Low Permeability Lined Basins’ with SRK Civil Engineer, Wesley Rouncivell. A key aspect of the safe operation of tailings dams into the future involves comprehensive and rigorous monitoring of these facilities on a regular and real-time basis, they said.

In another SRK presentation, GIS Specialist, Ansu Louw, and Civil Engineer, Riaan van der Colf, gave their insights on a ‘GIS-enabled, Web-based TSF Monitoring Solution’ by SRK to enhance monitoring of tailings facilities.

Getting lined tailings storage facilities right

The inclusion of a liner in a tailings dam brings many environmental benefits, but also increased complexity in design, construction and operation, Spies says.

In her presentation – ‘Design of an HDPE-lined platinum tailings facility in South Africa’ – at the SAIMM Tailings Storage Conference, in Gauteng, recently, Spies highlighted the importance of well-designed drainage systems. These are vital to drawing down the phreatic surface, reducing the seepage gradient and minimising the liquefaction potential of tailings, she said.

She also emphasised high construction standards to ensure tailings dams successfully limit seepage, and outlined a series of quality control and assurance measures.

Worley out to help miners on their open pit to underground mining transition