Tailings residue deposit management

Petra’s Commitment

• Petra is committed to safe tailings facility management, through the implementation of appropriate tailings governance structures, organisation-wide policies, procedures and standards.
• This is done through all phases of a facility’s life cycle including the design, construction, operation and closure phases.

Our Aim

Petra aims to improve execution and governance of operational and engineering practices to prevent potential breach of the tailings storage facilities to achieve the ultimate goal of zero harm to people and the environment.

Our Journey

• Petra started its journey towards adopting and implementing compliance with the Global International Standard for Tailings Management (GISTM) in 2022, with Petra’s Board approving its Tailings Management Policy and Procedure (the Policy) in July 2022. The Policy is aligned to the requirements of the GISTM.
• For a copy of the Policy, please click here.
• Following adoption of the Policy, Petra has taken steps to:
  i.

  establish governance structures, including the appointment of individuals with clear accountabilities and responsibilities such as the Accountable Executive, Responsible Tailings Facility Engineers, Engineers of Record and an external Independent Review Board (in compliance with GISTM).
  ii.

  deploy a combination of internal and external experts across various disciplines to perform gap analysis at all facilities.
  iii.

  develop action plans to address gaps identified to improve levels of compliance, e.g. development of a document management system to demonstrate compliance.
• An external Independent Review Board was engaged to conduct compliance verification audits, with these audits being concluded in 2023. Although these audits revealed good overall progress towards compliance with GISTM, it also highlighted some areas of improvement:
  iv.

  a key area involves improving the quality of the original design information, in particular, geotechnical and construction information in the early phases of the facility life cycles; and
  v.

  to address this (and other improvement areas), the Engineers of Record were commissioned to prepare a gap closure plan which will form part of the GISTM implementation plan at each operation. The Independent Review Board will be conducting its annual audit towards the end of FY2023 and as part of this audit progress will be reviewed and plans will be validated to address the areas of improvement.

Our tailings storage facilities

• For a table summarising key features of each our tailings storage facilities, please click here.
• For tailings facilities with “Very High” or “Extreme” GISTM consequence classifications, we have published a detailed disclosure which complies with Principle 15 of the GISTM. These disclosures provide information on the implementation status and summaries of our tailings management processes.
• For the Tailings Facility Disclosures in relation to:
  i.

  the No. 7 Dam at the Cullinan Mine (Extreme), please click here; and
  ii.

  the No. 1 FRD at the Finsch Mine (Very High), please click here.
• For our remaining tailings facilities (those with a “Low”, “Significant” or “High” consequence classification), we intend publishing similar disclosures following the independent review which will be completed towards the end of FY 2024.

Our approach to governance and risk management

For further information on how Petra’s governance structures and risk management processes address the risk associated with our tailings facilities, please click here.

Applicable legislation

• In South Africa, risk-based mandatory Codes of Practices (COP) are available for all residue deposits at our mines as required by, and according to set guidelines from the Department of Mineral Resources (DMR), Mine Health and Safety Inspectorate. All COP documents are signed off by the DMR and the respective third party appointed Professional Engineers.
• The relevant COP includes and refers to the design, managerial instructions, recommended standards and procedures required to manage and monitor the operation of facilities
• The Williamson diamond mine in Tanzania does not require a COP by law but, since 2016, in line with best practice Petra developed and implemented operating practices, set out in an operating manual, similar to a COP for the mine’s tailings deposits.

Technical information

• Petra differentiates between a Coarse Residue Deposit (CRD) and a Fine Residue Deposit (FRD). All operations make use of CRDs and FRDs. Coarse tailings (particles > ca. 0.5mm) are normally deposited on a CRD whilst fine tailings (particles < ca. 0.5mm) are deposited on a FRD. Petra employs a dry conveying and stacking method for the CRD whilst the fine tailings are normally pumped to a FRD.
• Generally, CRDs are relatively stable structures that do not impound water and therefore do not pose a risk of wall breach and flooding. At some operations, older CRDs are being re-treated to extract residual diamonds lost in the diamond winning process during earlier years when diamond winning technology was less efficient.
• All FRD facilities are constructed using the upstream deposition method. The outer walls are constructed with the coarser fraction of the fines residue whilst the finer fraction will settle in the dam basin, maintaining the pool away from the embankment walls. Supernatant and storm water are pumped off the deposits on a continuous basis to reuse in the diamond winning process.
• The tailings management facilities at each of our mines are as follows:
  i.

  at the Finsch Diamond Mine, there are five FRDs: four of the facilities are located on the eastern side of the mining area with three being active and one decommissioned as current deposition rates do not require it to be used. A further facility is located on the western side of the mining area and is also active;
  ii.

  at Koffiefontein there are three FRDs and with the mine under Care and Maintenance, small amounts of water are pumped into two of these FRDs as part of underground dewatering
  iii.

  at the Cullinan Mine, there is only one FRD, referred to as the No.7 dam; and
  iv.

  at the Williamson mine in Tanzania is one active, newly constructed FRD. In addition to this, there is also the facility which was breached in November 2022, and which is not in use.
• In addition to internal compliance, assurance and performance audits, third party Professional Engineers together with qualified mine personnel are appointed by Petra to oversee and provide assurance on the design and operational standards of the tailings facilities through quarterly inspections.
• Further to third party assurance, annual external audits are conducted in line with OHSAS18001:2007 and ISO 14001:2015 management standards and ad hoc inspections are carried out by the regulator.
• Important parameters that are being recorded, documented and managed include the overall condition of side slopes, benches and basin, drain flow records, deposition rates and corresponding rate of rise, freeboard, the phreatic surface level, structural integrity of the penstocks, pool size and location, impact on surrounding environment and potential zone of influence.