New tailings storage facility at Cerro Corona: A major feat of innovative engineering

In 2012, Gold Fields continued work on one of its most ambitious engineering projects to date: the new ‘centre-line rock-fill’ tailings storage facility (TSF) at its Cerro Corona mine in Peru. So far, Gold Fields has invested US$300 million in this major engineering project, which has been under construction since December 2006 and is scheduled for completion in 2023. Upon completion, it will measure about 2km in length and 190 meters in height, and have a storage capacity of about 130 million tonnes. The TSF is being constructed in stages to ensure the safe, cost-effective and environmentally responsible storage of tailings for the remaining life of the Cerro Corona mine.

Gold Fields and its engineering partners – including MWH Design and CQA, San Martin & GFLC Constructors, and GeoAndina CQC – faced significant challenges in designing and constructing the TSF due to a range of logistical, topographic and climatic considerations. These included, for example:

  • The relatively small scale of the Cerro Corona mine site
  • High levels of local seismicity
  • The remote, inaccessible location of Cerro Corona, which sits at between 3,600 and 4,000 meters above sea-level
  • High annual rainfall of about 1,400mm (80% of which occurs during the October to April wet season)

The engineers overcame these challenges through the adoption of a design concept that includes a centre-line rock-fill dam. This incorporates a low permeability core zone to minimise the risk of seepage and facilitate enhanced, cost-effective water contamination control. The core of the TSF has been constructed by joining two separate starter dams. The TSF is then gradually elevated (by an average of six meters per year) through the addition of a series of vertical raises. This allows for the TSF to be expanded vertically from the same location as opposed to being expanded either upstream or downstream (hence the term ‘centre-line’). Under this concept, rock-fill is used to create robust embankments (as opposed to the conventional method of using dried tailings).

This concept offers a range of advantages over competing designs (e.g. upstream or downstream TSF concepts) including, for example:

  • Higher (but safe and stable) walls and a reduced footprint: The use of rock-fill embankments allows for a high storage capacity within a relatively small area. This was a significant issue, as the location of the Tingo River significantly limits the dam construction footprint
  • Enhanced seismic resistance: The rock-fill used at the Cerro Corona TSF is significantly more effective than dried tailings at maintaining its integrity during seismic events
  • Cost-effective construction: The TSF incorporates locally available construction materials including rock-fill, which was quarried and processed onsite, and locally sourced clays. Furthermore, the relatively small footprint of the TSF means it requires less construction material than competing designs – resulting in additional cost savings
  • Suitability for high precipitation rates: The staged construction methodology allowed for the majority of construction activities to take place outside the wet season. In addition, the design incorporates an impervious collection system, known as a Low Volume Underflow (LVU), which reduces the risk of seepage from the facility – mitigating any risks posed to local water sources
  • Reduced dust generation: The use of rock-fill in construction generates significantly less dust than the use of dried tailings

The TSF is being constructed in line with relevant standards set by the Peruvian Ministry of Energy and Mines, the Mining Association of Canada, the Canadian Dam Association, and the International Commission on Large Dams. In addition, the engineers have applied an innovative ‘observational engineering approach’, based on the continuous observation and evaluation of the dam’s performance during the staged construction process. Results are fed back into the dam design (in parallel with ongoing construction activities) to continuously enhance the TSF’s capabilities. The dam design was also subject to a high level of independent review – and integrated feedback from internationally recognised engineering experts.