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Success of tailings retreatment stands out in lacklustre gold sector

NIEL PRETORIUS The capital cost of establishing an underground mine and other surface infrastructure is likely to substantially exceed the cost of establishing the plant, tailings deposition site and other infrastructure at a typical surface retreatment operation

Photo by Creamer Media's Dylan Slater

LOW RISK, GREAT REWARD With surface retreatment there are no risks related to depth of operations, there are generally less costs and production is fairly consistent

Photo by Creamer Media's Nadine James

COBUS LOOTS The gold market in general has improved over the last few months and that ever-increasing geopolitical risk could further endorse gold’s fundamentals

Photo by Creamer Media's Dylan Slater

ADRIAAN MEINTJIES Retreatment also contributes to environ­mental sustainability by reducing associated risks with contamination from old tailings storage facilities

22nd March 2019

By: Nadine James

Features Deputy Editor

     

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In a sector bedevilled by protracted industrial action, a lack of new discoveries and investment, as well as deeper and declining orebodies, gold tailings retreatment operations have demonstrated better resilience and attracted more investor interest than traditional operations, 71% of which were either marginal or lossmaking in 2018, according to Minerals Council South Africa.

In addition to the council’s concern about the new tariffs exacerbating the sector’s ballooning administered costs, it also points out that, since 2007, jobs in the gold sector have declined by nearly 40%.

Further, there have been no new deep-level gold mines built since 2003, and South Africa’s gold production has consistently declined over the past decade.

Pan African Resources CEO Cobus Loots notes that the gold market, in general, has improved over the past few months and that ever-increasing geopolitical risk could further endorse gold’s fundamentals.

Additionally, with rand weakness expected to persist alongside a somewhat favourable gold price, 2019 should theoretically be a good year for South African gold producers.

However, Loots also notes the poor state of the local economy, and the challenges it imposes on miners cannot be understated.

Similarly, while tailings retreatment is far from a silver bullet for the gold industry, the significant gains realised by retreating existing tailings dams cannot be understated.

A Brief History of Tailings

Tailings retreatment in South Africa began in the 1970s, recalls SRK principal geotechnical engineer and partner Adriaan Meintjes.

Prior to that – largely as a result of a 1953 study by the then Chamber of Mines and the Council for Scientific and Industrial Research – the standard procedure to limit tailings-dam-related air and water pollution was to plant vegetation on the tailings dams.

Meintjes explains that, historically, when grades were very high, gold processing was limited by the technology of the day. As a result, a lot of the older dumps have some of the richest material.

Anglo American started remining dumps in what would become DRDGold’s Ergo Operation in 1977. Concurrent process plants were established in Crown Mines and City Deep to reclaim the dumps south of the Johannesburg central business district.

Meintjes notes that extraction technologies have improved over the past 30 years, and that optimisation of and improvement in technology had been realised in 1980, when the gold mining tailings grind was “already” finer than 80%, passing 80 μm

Loots adds that current innovative technologies and processing techniques have increased the extraction potential significantly, and these tailings dumps can now be effectively mined and processed.

Some of these new technologies include preconcentration steps, ore sorting, gravity concentration and fine grinding to liberate more metal. Mintek demonstrated this evolution when it showcased its retreatment flowsheet for gold and uranium tailings at Gold Fields’ South Deep mine in 2016

Meintjes notes that the optimisation of tailings processes is ongoing and that tailings solutions are still being refined, including the use of microorganisms in tailings facilities to “mine” mineral waste as a partial solution aimed at reducing water consumption in water-scarce countries.

Value Proposition

DRDGold CEO Niël Pretorius says that the company played “a pioneering role” in tailings retreatment; after weighing the growing risks and costs associated with mining at depth with those associated with surface retreatment, as well as the deep-level mining’s operating and financial records, exiting deep-level mining in 2012 was inevitable.

Pretorius notes that, in a “very general sense”, if asked to choose between an ore reserve and a tailings reserve of similar quantity and grade, he would choose the tailings reserve.

He warns that several other factors could affect the economics and viability of any project, but maintains that the “capital cost of establishing an underground mine, a gold plant, a tailings deposition facility and other surface infrastructure is likely to substantially exceed the cost of establishing the gold plant, the tailings deposition site, pipelines, and other infrastructure required of a typical surface retreatment operation”.

Additionally, a surface retreatment operation’s consumption of power, water and other consumables is likely to be lower, and labour costs would be reduced, as it is substantially more mechanised, says Pretorius.

Meintjes agrees, adding that surface retreatment is a relatively simple process, with very few of the safety risks associated with underground mining, such as rock bursts, seismicity, or other challenges related to working at depth.

“It would be wrong to say there are no risks involved in surface retreatment, but the risks differ enormously in quantum – because much fewer people are involved – and in nature – because people are not exposed to the potential risks of working at depth, such heat and noise,” comments Pretorius.

In pursuing their core business, surface retreatment companies clear away dumps that have become problematic over time. These problems generally arise because the dumps, which were neither designed to today’s standards nor optimally located when established, have been encroached upon by human habitation or have been abandoned and are no longer maintained, adds Pretorius.

Loots says tailings retreatment operations also create economic opportunities and employment, as they have “the potential to free up land for agriculture and other activities”.

Meintjies notes that the process also contributes to environmental sustainability by reducing the associated risks of contamination from old tailings storage facilities (TSFs), as retreatment operations typically result in the deposition of tailings at a new site in a modern TSF.

These sites also tend to be much further away from communities, compared with existing TSFs, thereby ameliorating the health and safety risks they pose.

Abandoned and Derelict Dumps

In his 2018/19 Budget speech, Mineral Resources Minister Gwede Mantashe referred to a “focus on gold tailings retreatment” and, while he attended the gold pour at Elikhulu and announced the awarding of two mining permits, including a tailings mining resource owned by Ekapa Mining, to artisanal miners in Kimberley, in the Northern Cape, there has been little else worth mentioning.

While the Department of Mineral Resources has primarily focused on reducing the environmental and health liabilities pertaining to abandoned and derelict coal and asbestos mines, very little has been publicised on the department’s plan to address abandoned gold tailings.

Mining companies, including DRDGold , hold the rights to several gold tailings dams; however, many more are ownerless and have thus become a liability.

Loots, Meintjies and Pretorius note that setting up small surface operators with their own plants and supporting infrastructure would probably be unviable, given the cost and technical complexity involved.

Loots notes that the successful retreatment of low-grade gold tailings requires “very substantial scale, with large capital requirements”.

Pretorius adds that the requisite skills and management of the environmental impact are other significant considerations. Meintjies notes that, while small-scale operations would be more feasible if the tailings contained free gold, those tailings have already been processed and treatment of the remaining tailings requires some metallurgical experience and technology.

Pretorius is slightly more positive about the feasibility of such a venture: “If there are . . . parties with sufficient will and resources to apply their minds, who knows what might be possible?”

Examples of Success

DRDGold recovers gold from the retreatment of surface tailings on the East Rand and the West Rand, employing 2 450 people, of whom 1 020 are on a permanent basis.

In its 2018 financial year, DRDGold produced 150 423 oz, generated R2.4-billion in revenue and cleared 191 ha of rehabilitated land for redevelopment.

The company’s Ergo operation comprises a 3.3-million-ounce reserve, with the Ergo plant capable of a throughput of 1.8-million tonnes a month, while its satellite plant at Knights, in Germiston, treats material from the Cason dump and deposits waste at the Brakpan/Withok tailings deposition facility.

In 2018, the Crown Mines and City Deep metallurgical plants were re-engineered as milling and pumpstations to support the Ergo plant.

Additionally, DRDGold concluded an acquisition for gold assets associated with Sibanye-Stillwater’s West Rand Tailings Retreatment Project. The assets, comprising a 2.7-million-ounce reserve and acquired on August 1, 2018, are now known as Far West Gold Recoveries (FWGR).

The acquisition increases DRDGold’s reserves by about 82%, with both projects boasting a mineral reserve totalling six-million ounces of gold.

The company also secured a R300-million credit facility from a local financial institution, which enabled it to start the first phase of development of its new tailings recovery project.

FWGR’s Driefontein 5 reclamation site has been commissioned, the Driefontein 2 plant has been completed and the upgrading of the Driefontein 4 tailings dam is on track for completion by the end of this month. Consequently, Phase 1 will be fully commissioned before June, when first gold is expected. This phase will have a throughput of 500 000 t/m.

Meanwhile, Pan African Resources achieved a 52.8% year-on-year increase in revenue to R1.3-billion for the six months to December 31, 2018.

The group increased its gold production by 54.2% to 81 014 oz on the back of robust performances from the Barberton Mines’ underground operations, the Barberton tailings retreatment plant and the newly commissioned Elikhulu tailings retreatment plant (ETRP).

The Barberton tailings retreatment facility improved production on the back of the successful commissioning of a regrind mill in May 2018, while the ETRP contributed 15 292 oz in its first four months of operation and reached its nameplate capacity of one-million tonnes in October 2018.

While Pan African remains active in deep-level mining, its production mix is set to change from being predominantly underground based to being marginally surface based in light of the commissioning and operation of the ETRP.

While both producers have had teething issues, their operations have been largely successful, demonstrating the viability of a sizeable tailings operation in challenging economic environments.

Edited by Martin Zhuwakinyu
Creamer Media Senior Deputy Editor

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