Tailings are the resulting material from finely-ground processed ores that have been through a number of sizing, grinding, and processing steps.
Tailings are generally discharged as dense slurry into containment areas, a tailings storage facility (TSF) or through deep sea tailings placement (DSTP) in suitable deep-ocean locations. Modern gold and copper processes seek to maximise the extraction of chemicals and reagents before the tailings are deposited.
Tailings Storage Design
Every location of our mines is unique and, as such, our tailings facilities are designed to take into account a range of factors including the local topography and climate, the geotechnical, geological and seismic activity, its proximity to people and infrastructure, land rehabilitation, and future land use considerations.
There are three main tailings construction methods:
- Downstream design continues the construction of the embankment wall on the external side of the compound with the batter extending on to what we call natural surface (or land that previously has not been disturbed), by depositing more support rock and bunding against the previously built tailings wall, thereby expanding the footprint, width and height of the initial embankment wall.
- Centreline design involves the continuation of the embankment construction on the external side of the compound however, does rely on the deposited tailings adjacent to the top of the initial embankment wall to support the raises.
- Upstream design allows the embankment wall to be constructed on the inner side of the compound and relies on the strength of the deposited tailings to support the structural material for each lift of the embankment. This method allows for smaller quantities of earth and rock fill to be built on top of the tailings and therefore does not expand the footprint of the facility.
Over a number of years each new tailings wall moves upwards creating a layered or contoured hill for all methods. The tailings wall needs to lift to allow the facility to contain the design capacity of tailings being generated by the operation, and to reduce the overall land disturbance of tailings placement.
Newcrest Tailings Facilities
As of March 2019, Newcrest had 13 terrestrial tailings storage facilities of which three were in active use. Newcrest tailings disposal activities are summarised below:
- Gosowong, in Indonesia, has two facilities with one in operation, which is based on downstream design.
- Telfer, in Australia, has one facility in operation with six small facilities no longer in use. The operating TSF commenced as downstream design and has had lifts added in an upstream configuration.
- Lihir, in Papua New Guinea, uses the deep-sea tailings disposal (DSTP) method given proximity to suitable deep-ocean deposition, its volcanic setting, high rainfall, and the lack of available land.
Cadia, in Australia, has three facilities. The Cadia Hill open pit is being utilised as a tailings facility. The Northern Tailings Storage Facility (NTSF) and Southern Tailings Storage Facility (STSF), which both commenced as downstream design, have had lifts added in upstream configurations. At Blayney, near Cadia, there is a historic copper mine and an associated small remnant tailings facility that is currently under care and maintenance. In Ecuador, Newcrest has an equity interest in Lundin Gold which is building the Fruta Del Norte gold project with an associated downstream TSF.
Newcrest’s Sustainability Report covers many aspects of our operations’ energy, water and land use, including ore extraction rates and the tonnage of waste rock and tailings generated at each site.
Tailings Management System
Tailings are managed within engineered tailing storages. Risk is managed through completion of engineering designs in accordance with leading practice guidelines (e.g., ANCOLD 2012), safety assurance through independent review, and following Newcrest’s internal risk and change management procedures.
In addition, a Tailings Management Framework is being implemented in accordance with the ICMM guidelines and in the detail as described by the Mining Association of Canada.
Tailings and Safety Response
Reviews and Inspection
Newcrest’s tailings storage facilities are audited against criteria that aligns with industry guidelines and specifically against the Australian National Committee on Large Dams (ANCOLD) guidelines.
All of Newcrest’s operations have a program of annual external audits. Like most major mining companies, Newcrest commissioned a series of independent audits of its tailings storage facilities following the Samarco event in 2015.
In response to Cadia’s Northern Tailings Slump in 2018 Newcrest is conducting even more extensive reviews on all its tailings storage facilities.
The findings of the independent review into the technical root cause of the slump.
At Cadia we are continuing investigative drilling near tailings storage facility walls with a significant number of samples tested and analysed. There has been a detailed review of the geological mapping. Engineering work conducted over life of tailings wall has also been reviewed.
In 2018 Newcrest commenced construction of buttresses in two areas of the Southern Tailings Facility, which have now been completed. In designing this buttressing, Newcrest and its external engineers have assumed the potential presence of weak material analogous to that in the area of the Northern Tailings Facility slump and adopted conservative strength parameters.
Investigations to reconfirm the TSF design at Telfer began in May 2018, under the supervision of acknowledged industry experts. As part of this investigation, cone penetrometer tests have been conducted on the TSF to validate design assumptions. Work is ongoing in relation to ensuring the stability of the Telfer TSF.
Likewise, at Gosowong, a stream of work is underway to reconfirm the dam design assumptions. Preliminary analysis indicates they remain sound.
Tailings storages with upstream construction have been subject to analyses to confirm the engineering characteristics of the tailings and with a view to confirming tailings saturation. Several dams have been reinforced with buttresses or are now subject to panel review where such has been recommended.
Our strong commitment to the safety of people and care for the environment underpins our approach to managing our tailings facilities. There is nothing more important to Newcrest than everyone going home safe every day, the safety of our local communities and the environment.
Newcrest is a member of the International Council on Mining and Metals (ICMM) which is taking an industry leadership role on tailings management.
In February 2019 the ICMM announced, with the full support of member company Chief Executive Officers, the establishment of an independent panel of experts to develop an international standard for tailings facilities, for its member companies, and for review and use in the broader mining industry.
The standard will be developed by a review of current global best practice in the design, management and operation of tailings storage facilities in the mining industry.