Petra Diamonds Limited announced in follow up to its announcement of 10 November 2022, the company provides a further update regarding the TSF wall breach at the Williamson mine on 7 November 2022. Impact on the environment and local community: The assessment team has concluded there is a low risk of further breaches of the TSF or a breach of the New Alamasi water dam. Williamson Diamonds Limited (WDL) has constructed an initial 6m high wall to close the breached wall area.
As a precautionary measure, WDL has also constructed containment walls upstream and downstream of the New Alamasi water dam, while buttressing of the New Alamasi water dam wall is underway. Various diversion trenches are also being constructed to prevent any build-up of water and to enable rainwater to flow into the surrounding rivers and streams. A total of 12.8 million cubic metres of water and tailings material were released from the TSF as a result of the breach. A total area of 3.57km2 is covered with this material on Williamson's mine lease area with 1.52km2 outside the mine lease area.
Environmental work to date confirms the tailings material which flowed out of the TSF is inert. Water and tailings material samples were taken by the Tanzanian Government Chemist Laboratory Authority, which confirmed that no dangerous chemicals were found and that all chemicals were within normal parameters. This was confirmed by separate, private, laboratory tests.
Analysis is underway with the assistance of independent experts to ascertain appropriate measures for the clean-up or remediation of affected areas. The company reconfirms that no fatalities or serious injuries occurred as a result of the incident. A temporary rehousing scheme is being planned for the families affected by the breach.
Interim accommodation and humanitarian relief, including psycho-social assistance, continues to be provided to those affected. Valuation, land and socio-economic surveys are being implemented with all the necessary approvals from the Government. A socio-economic study, supported by an external social impact specialist, is well advanced to determine socio-economic impacts.
WDL, along with local, Regional and National authorities, continues its extensive engagements with local communities to ensure that key stakeholders are kept informed of WDL's response, including planned remediation activities. WDL and Petra remain appreciative of the continued cooperation and assistance provided by Government, community leadership and affected parties. Technical and Production: Following the visit of a technical team that included independent external specialists, the preliminary assessment concluded that the failure mechanism was subsidence of a portion of the East wall of the TSF by around 1.5m that enabled the water to crest the wall, initiating the breach.
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. Cost and timing of the investigation will be available after a detailed scoping process is completed, but initial indications are that this exercise will take between 6 and 12 months.
In light of the failure of the existing facility, the design of the new TSF is currently under review. This is only expected to be finalised in February 2023, which will determine the additional construction work required to make the facility operational. 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 the geotechnical investigation. Updates on the progress of these potential long-term solutions will be provided in due course. As a result of the additional work required to progress these long-term solutions, interim deposition options are being developed that may enable the Williamson mine to resume production around the middle of 2023.
These interim options may include utilising a portion of the existing or new TSF. The Williamson mine will not resume any deposition under these interim options until it has been confirmed that it is safe to do so and any necessary regulatory approvals have been obtained. Further work is being conducted between WDL, Petra's technical team and external specialists to determine the best possible options to recommence production safely and as soon as possible.
As previously stated, accelerated waste stripping and planned maintenance activities will continue in order to minimise the impact of lost production. This interim plan will be adjusted as the company progress the interim options referred to above. WDL is considering additional financing options to provide support during this period and is engaging with the Government of Tanzania regarding the sale of the previously blocked and confiscated diamond parcel, the proceeds of which the Government of Tanzania has agreed to allocate to WDL under the Framework Agreement entered into in December 2021.