Tailings Management at Porgera
The Porgera 2009 Annual Environmental Report [PDF 8.5MB], prepared by the Porgera Joint Venture (PJV) for the Papua New Guinea Department of Environment and Conservation. The report is in accordance with PJV’s Environmental Management Plan and was reviewed by the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia’s national science agency.
Under a comprehensive permit issued by the Government of Papua New Guinea (PNG) to Placer Dome in 1989, the Porgera Joint Venture mine follows a stringent government-approved environmental management and monitoring program. The practice of riverine tailings disposal was in place at start-up, before Barrick acquired its interest in the property as a result of the Placer Dome acquisition in 2006.
The PNG government approved the practice of riverine tailings discharge following extensive consultations with local stakeholders, recognizing the very unique operating environment and risks associated with the area. The mine is situated in an area that is subject to seismic activity and extreme tropical rainfall, which cause frequent landslides. The area’s very steep and unstable terrain makes the safe construction and operation of a conventional tailings facility very challenging.
Environmental measures in place include:
- Pre-discharge treatment at the site, which entails cyanide destruction of the carbon-inleach tails, followed by neutralization of the final tailings through the addition of lime in the processing plant’s neutralization circuit.
- Extensive water monitoring using stringent processes developed in conjunction with the Commonwealth Scientific and Industrial Research Organisation (CSIRO), Australia’s national science agency. Monitoring data is reported on a regular basis to the PNG government and to local stakeholders.
- A team of over 20 environmental staff monitor the operation.
- Specific water quality limits for discharges at the downstream compliance point use Australian/ANZECC (Australian & New Zealand Environmental Conservation Council) water quality guidelines. To our knowledge, the mine has never exceeded its compliance permit levels.
Evaluation Study by Barrick
Upon Barrick acquiring its interest in the PJV in 2006, a comprehensive two-year study was conducted to review and evaluate alternatives to improve and reduce the discharge of tailings. This $5 million review examined the feasibility of building a large tailings storage facility (TSF) and other alternatives to mitigate environmental impacts. The evaluation team included an external engineering firm and other experts and took into account a full range of highly complex technical, environmental, social and regulatory factors - many unique to PNG and the Porgera Valley.
The study identified significant risk factors in ensuring a stable foundation for a large tailings storage facility due to the instability that can accompany high rainfall, deep soil cover and very steep terrain – a risk that would exist during construction, operation and following mine closure. In addition, social factors such as the law and order challenges in PNG and, in particular, the presence of illegal miners were identified as significant risk factors. Reviewers recognized that groups of illegal miners would likely dig and pan for gold from tailings captured within the tailings impoundment, leading to erosion of the dam structure.
As a result, riverine tailings disposal will continue at this time, with the following continuing improvements and modifications to improve and reduce tailings discharge:
- A new $42 million paste backfill plant is now operational and will divert a portion (approximately eight per cent) of the tailings that would have been otherwise released to be used as permanent underground backfill.
- Plans to increase ore production from the underground mine, resulting in an opportunity to store more tailings underground in the mine as backfill.
- In 2007, cyanide destruction of carbon-in-pulp was improved to further break down cyanide compound in tailings.
- In November 2009, the mine was officially certified under the International Cyanide Management Code.
- Consistent with Barrick’s Environmental Management Program, the operation is currently pursuing ISO 14001 certification.