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What Are Tailings?

Newmont's tailings management approach has a goal of zero harm to people and the environment while adhering to best available practices, adopting best available technologies, strengthening and integrating socioeconomic awareness and stakeholder engagement, and environmental considerations throughout the lifecycle.

Tailings pit Tailings pit

Tailings are created as mined ore is processed through crushing, grinding and milling.

1.

Mined ore is moved to the milling circuit where the rock is reduced into sand-, silt- and clay-sized particles and then mixed with water and moved as slurry through the mineral recovery process.

2.

The valuable minerals are separated from the rest of the milled rock particles either through physical or chemical recovery processes.

3.

After removal of the valuable minerals, the remaining milled rock slurry, now referred to as tailings, is pumped, flows by gravity, or is dewatered and transported by truck or conveyor to a surface engineered facility or placed underground or in-pit as mine backfill.

Surface engineered tailings facilities are carefully designed, constructed and operated to safely contain the tailings and water, even during extreme climatic or seismic events. Depending on the chemical characteristics of the tailings and the surrounding environment, Newmont typically lines the engineered tailings facilities with a composite liner system consisting of a low permeability soil liner overlain by a geosynthetic liner such as high-density polyethylene (HDPE) to prevent impacts to surface and groundwater systems.

Where tailings slurry is deposited in the facility, water separates from the heavier tailings particles and collects to form a decant/reclaim pond on the surface. The pond water is then recycled back into the milling process for reuse or treated for return to the environment. The tailings are contained within the facility and once it reaches capacity, the facility is typically closed and reclaimed with a designed cover system used to minimize erosion and infiltration, while maintaining containment of the materials, protecting the environment and achieving post-mining designated land use.

TSF embankments are typically progressively raised using one of three construction methods - downstream, upstream or centerline - which designates the direction in which the embankment crest moves in relation to the starter dam (or dike). Each of these construction methods is discussed below:

Upstream

Figure 1: Upstream construction method

Construction of an upstream embankment begins with development of a starter dam. The tailings are then discharged from the dam crest and form the foundation for future raises, as shown above.

Downstream

Figure 2: Downstream construction method

Downstream methods commence with a starter dam, which often comprises an internal drainage system, as shown above. The tailings are first deposited behind the dam and the embankment is raised progressively in a downstream manner as additional storage capacity is required.

Centerline

Figure 3: Centerline construction method

With the centerline method, the embankment is raised vertically, maintaining the embankment centerline as shown on above. This design method often also incorporates internal drainage and/or construction of a free-draining shell. Modified centerline is a combination of upstream and centerline methods and is done to reduce downstream impacts as well as reduce the volume of construction material that is required to be placed within the embankments.

Tailings are generally described by water and solids content using a scheme referred to as the dewatering continuum, illustrated in the figure below.

Figure 1: Dewatering continuum

Tailings are typically dewatered to a certain degree, or modified in other ways prior to deposition, including:

  • Thickened tailings (which involves a process of dewatering to form a slurry);
  • Paste tailings (which includes dewatering until the tailings do not segregate as they are deposited and have minimal excess water);
  • Filtered tailings (includes dewatering to a filtered wet or dry cake that is transported via trucks or conveyors); and
  • Co-deposition includes mixing mine waste with tailings (other terminology includes co-mingling, or co-placement whereby each has slightly different methods of mixing material and degrees of tailings dewatering).