Africa |
Failing African tailings
Two more tailings dam failures have occurred at mines in Tanzania and South Africa. Mining companies everywhere are being urged to immediately embrace the Global Industry Standard on Tailings Management as a top priority
Above: Panorama of the Jagersfontein diamond mine in South Africa taken in 2016. A tailings dam failed here in September 2022 Credit: Grobler du Preez /
Shutterstock.com
ON 7 NOVEMBER 2022 the eastern wall of the tailings storage facility (TSF) at Petra Diamonds’ Williamson mine in Tanzania was breached. A total of 12.8Mm3 of water and tailings materials covered an area of 4.57km2
inside, and 1.5km2 outside, of the mine lease
area. The main portion of the tailings were contained by the New Alamasi water dam – which sits within the mine lease area. Testing confirmed that no dangerous chemicals were found within the water and tailings. No major injuries or fatalities were reported but 286 individuals from 50 houses had to be relocated. All affected households have been provided with accommodation and humanitarian relief within the village they were displaced from. Investigations into the cause of the breach and assessments on the environmental, social and economic impact are ongoing. Production was temporarily suspended whilst the company investigates the root cause of the failure mechanism and explores options to recommence operations safely and as soon as possible. Preliminary assessment concluded that the breach was initiated by subsidence of a portion of the east wall of the TSF that enabled water to crest the wall. The root cause of the subsidence has not been determined and will require a forensic geotechnical investigation to be completed. This work will be undertaken by an independent company specialising in tailings dam design and management and will take between 6 and 12 months. Precautionary measures to contain the tailings
material and strengthen the New Alamasi water dam were completed in early January 2023. The creation of a safety bund, mitigating risk in the affected areas, has also been completed. In light of the failure of the existing facility, the design of a new TSF which was already under construction at the time of the incident, is currently under review. It is now expected that this new TSF will take longer than initially anticipated to become operable. In parallel, a further potential option of repairing and using the existing TSF is also being explored as a long-term solution, but this is subject to the outcome of geotechnical investigations.
24 | March 2023 |
www.waterpowermagazine.com
Environmental assessments, with the assistance of independent experts, continue to be carried out to determine how best to clean-up or remediate affected areas. Trials are also in place to identify the best land use options post remediation of affected areas. To date, these studies indicate that areas lying within the mining lease area are best suited to be returned to wilderness, either as forest or wetlands, through amelioration of the soil and revegetation. Areas outside of this will be treated according to the depth of tailings material. Thinner layers of tailings can be mixed into the surrounding soil and thicker layers can be used for agricultural purposes following trials which demonstrate that enrichment with compost will enable cash crops to be farmed on a viable basis. In addition, Petra says the vulnerability of affected people is an important consideration and a key component of this work. Psychosocial support is being provided and once any issues are identified, a mitigation process will be implemented. Alternative agricultural land is being identified to enable farming activities for those affected to recommence as soon as possible. A comprehensive risk assessment is underway at all of the mine’s tailings facilities. Work to identify the best interim tailings storage facility is continuing with external experts from Tanzania and South Africa. Once competed a detailed report will be forwarded to the Government of Tanzania for approval. This will allow startup of production to commence while work is being conducted on the longer-term tailings storage solution. It is anticipated that production will resume at the beginning of FY 2024. Previously, Petra Diamonds Limited has said that it is committed to implementing the Global Industry Standard on Tailings Management (GITSM) and has made good progress, aiming to fully comply by 5 August 2023. On 28 June 2022, its Board of Directors approved and adopted a tailings management policy which commits Petra to implementing a tailings management system for all its active and dormant tailings facilities, based on international best practice and aligned with the GISTM, relevant technical guidelines and applicable legislation.
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