Our approach to tailings management
Tailings storage facilities (TSFs) are engineered structures designed and constructed to hold mineral waste (tailings) from the site’s processing facilities. The management of tailings and the structural integrity of our TSFs are critical to community safety and environmental protection.
Our facilities are designed to meet international engineering standards and we adopt rigorous quality control and quality assurance measures throughout the construction phase.
All our operations have tailings facility management plans that are reviewed annually and document the placement of tailings and how each facility will be managed. An overview of our tailing management governance is outlined below.
OceanaGold operates a company-wide Integrated Management System including specific operational standards for risk and tailings storage facility management. These standards are audited at both a site and corporate level on a regular basis and are available on the OceanaGold website.
We undertake annual technical audits of our operations involving both internal and external expertise. The 2017 technical audits included tailings storage facilities.
Our approach to tailings storage facility risk management involves three steps
- Robust design and site management including permitting, operational management, monitoring and reporting
- Regular auditing of conformance with internal standards and permit requirements at a site and corporate level
- Independent reviews by third party independent experts.
In addition, operations must comply with country specific regulatory requirements.
In June 2019 we responded to the Investor Mining and Tailings Safety Initiative from the Church of England Pension Board and Swedish Council on Ethics for the AP Public Pension Fund. We provided this letter of response and supporting information.
The types of tailings storage facilities we have
We utilise four methods of tailings storage
- Downstream construction
- Downstream construction with upstream lift
- Backfill and capping
- Paste backfill underground
Downstream tailings facilities are constructed with a single embankment (wall) constructed with waste rock to form engineered embankments that are progressively raised to provide additional space for tailings storage. We utilise the downstream method at the Waihi Gold Mine, Macraes Operations, Haile Gold Mine, the Didipio Mine and Junctions Reef.
Downstream construction with upstream lift
The foundation of the facility embankment is the downstream construction method. Tailings are then discharged into the dam and harden to form the foundation for the next level of wall. We utilised the downstream construction with upstream lift method at two closed TSFs at the Macraes Operations.
Once an open pit is no longer being used it can be backfilled with tailings (as long as potential seepage and other factors can be managed). Once the pit is filled it is then capped with layers of rock and soil and can be planted. We used the in-pit storage and capping method at the now-closed Souvenir open pit at the Globe Progress Mine at Reefton and at Junctions Reef.
Once processing is complete up to 40% of the mine tailings can be diverted to a paste plant where it is mixed with cement and used as backfill material for underground mine voids, which reduces the volume of tailings delivered to the tailings storage facility. We utilise the paste backfill method at our Didipio Operation.
Details from our operations
Didipio has one tailings storage facility (TSF). The TSF has been designed to exceed compliance standards as stipulated in the guideline issued by the Philippine Department of Environment and Natural Resources and the Australian National Committee on Large Dams’ Guidelines on Tailings Dams.
Quality control and assurance of construction criteria and materials is undertaken by an independent engineering specialist with support from operational personnel.
Quarterly and annual monitoring has been implemented since the start of construction by an independent third-party technical expert. In addition, an external review was conducted by a separate independent third-party technical expert in October 2017.
Haile Gold Mine
The TSF at Haile was constructed and became operational in 2016 following final regulatory approval by the South Carolina Department of Health and Environmental Control (SC-DHEC), which holds jurisdictional authority over the facility through their Dam Safety Division.
We commissioned an independent technical expert to undertake a Final Construction Inspection Report and a Dam Safety and Structural Review Inspection Report. In addition, the SC-DHEC undertook technical reviews prior to granting approval to operate the TSF.
Waihi Gold Mine
Waihi has two TSFs, although only one is operation. Tailings deposits into the closed and rehabilitated second facility ceased in 2005.
Both TSFs were designed by an independent third-party technical expert in accordance with the New Zealand Society of Large Dams. Both TSFs have monitoring plans that are reviewed and approved by the local regulators and undergo extensive internal monitoring. They also have detailed annual regulatory reporting requirements in relation to the stability and performance of pollution controls and environmental effects.
Annual reviews of the construction and operation of the TSFs are undertaken by an independent project engineer. An expert peer review panel has been appointed to review
the annual monitoring program and completion of the facility. The panel comprises independent third-party technical experts appointed by the local regulatory bodies with
expertise in geotechnical engineering, geochemistry, groundwater and rehabilitation.
These annual reviews have been conducted since 1987 and cover the following information:
- design, construction, monitoring, performance and stability reports from embankment construction
- operation, maintenance and surveillance records for the period of review
- other internal and external reports related to operations and closure of TSFs, including reviews of compliance against the New Zealand Society of Large Dams (NZSOLD) New Zealand Dam Safety Guidelines.
Macraes has three TSFs, two are closed and will be rehabilitated and one remains operational. All undergo extensive internal monitoring and have detailed annual regulatory reporting requirements regarding the stability and performance of pollution controls and environmental effects.
The Macraes TSFs were reviewed by an independent third party technical expert, commencing in 2016 and completed during 2017. The review updated a similar assessment performed in 2011, and included design, operation and monitoring processes, and a risk assessment of the safety and stability of the tailings embankments based on their status. It also reviewed compliance against the New Zealand Society of Large Dams’ New Zealand Dam Safety Guidelines.