Tailings residue deposit management
Below is information on Petra’s tailings management programme.
- In South Africa risk-based mandatory Codes of Practices (“COP”)1 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 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.
- 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 residue 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.
- At Finsch 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. At Koffiefontein there are three FRDs of which two are currently being used for fines residue deposition. The third dam has been rehabilitated and is no longer utilised. At Cullinan there is only one FRD, referred to as the No.7 dam. At the Williamson mine in Tanzania there are two FRDs of which one is currently active.
- In addition to internal compliance, assurance and performance audits, third party Professional Engineers together with Mine Geotechnical Engineers 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.
- COP includes and refers to the design, managerial instructions, recommended standards and procedures required to manage and monitor the operation of facilities.