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More about mine exploration

Technical elements, such as asset management, geology and resource modeling, project engineering and metallurgical process planning, are evaluated in order to determine the mining and process requirements of a prospective site – all of which is done with full consideration of the international, national, regional and local laws and regulations, as well as Newmont’s own standards and voluntary commitments. A full review of business elements such as human resources, insurance, legal, security, and health and safety is also included in the work activity required to evaluate a project’s feasibility.

Typical project development can take up to 10 years from when the exploration group discovers the gold deposit, with the time expanding depending on economic conditions, legal requirements, technical difficulty and other factors.

Sustainability and Stakeholder Engagement

While we are busy designing the mine, we must simultaneously partner with local stakeholders to design a sustainable path forward that takes into account a vision for the mine site after mining operations close. This means listening to their input and prioritizing development objectives together – while managing our current impacts at the same time.

Newmont engages during this phase in various ways, which can include public consultation activities driven by the social and environmental impact analysis process (social and environmental impact assessments). The decision to progress to mine construction does not sit solely with Newmont; the decision involves the local communities and government. Without their consent, the project cannot proceed. We value the feedback that stakeholders provide, and seek to design our projects in ways that create long-term mutual value.

More about construction

Mine construction

There are two types of mines in operation at Newmont: surface and underground. Which one do you want to learn more about?

Surface Mine

Constructing a Surface Mine

As we dig farther down, it may be necessary to dewater the mine to ensure that the water level remains below the pit floor. We may need to pump significant volumes of water from the pit each day. Much of it is reused on site (for dust control, processing, etc.). Whenever possible, excess water is treated, tested and safely discharged back into nearby underground aquafers, rivers or lakes.

A significant amount of monitoring takes place in and around the open pit, to keep a watchful eye on:

  • Slope stability and dewatering-induced settlement
  • Noise, dust and vibration
  • Water levels and water quality, including pit wall run-off
  • Social impacts
Underground Mine

Constructing an Underground Mine

Underground mines are used to recover minerals or metals from deep in the Earth. When building an underground mine, first we dig a tunnel to get to the minerals contained in the ore body. This can be a straight vertical tunnel, called a shaft, or a tunnel called a decline, which will use a spiral pattern at any point underground to navigate into the Earth. To access the ore from the shaft or decline, we dig other tunnels (in mining, called drifts). We also develop other shafts for drifts specifically to provide proper ventilation and emergency exits.

We excavate the tunnels and the ore body by drilling and blasting. The ore is mined from designed “rooms,” called stopes, which are of varying sizes and shapes to ensure we maximize the extraction of ore. The broken-up ore is then transported to the surface for processing. Barren rock known as waste may also be transported to the surface or left in the mine and used to fill mined-out stopes.


Ore Processing

Haul trucks transport the ore from open pits or underground to processing operations. Some ore may be stockpiled for later processing. Rock that is not economical to process is stored in overburden rock storage areas.

Newmont uses two ore processing techniques to extract gold: mill processing and heap leaching. The grade and type of ore determine the processing method used. Additionally, the geochemical makeup of the ore, including its hardness, sulfur content, carbon content and other minerals found within it, impacts the cost and methods used to extract gold.

Heap leaching is used when the ore contains a lower grade of mineral content. The basic process is as follows:

  1. Low grade ore can be dumped directly on a leach pad (this method is called run of mine) or can be crushed and stacked on top of slightly sloped ground that has been lined with an impermeable plastic.
  2. A leaching solvent, commonly a weak cyanide solution, is then applied to the surface of the ore heap using drip irrigation.
  3. As the solvent percolates through the ore heap, the precious metals dissolve into the solution and travel to storage ponds at the base of the leach pad – a process that can take upwards of two months.
  4. Once collected, this gold-bearing solution is pumped to process facilities where the gold is extracted using a process known as carbon stripping or collection on carbon.
  5. Cyanide levels are readjusted in the leftover or barren solution so it can be recycled back into the leach cycle.

Mill processing is used when the ore contains a higher grade of mineral content. The basic process is as follows:

  1. We feed ore into a series of crushers and grinding mills to reduce the size of the ore particles and expose the mineral. Water is also added, which turns the ore into a slurry.
  2. We send this slurry to leaching tanks, where we add a weak cyanide solution to the slurry, which leaches gold and silver into the solution. This process recovers up to 93 percent of the gold and 70 percent of the silver from the ore. Carbon granules are then added to the solution. The gold attaches to the carbon and is pulled from the solution.
  3. We then “strip” the gold from the carbon by washing it with a caustic cyanide solution. The carbon is later recycled.
  4. Next, we pump the gold-bearing solution through electrowinning cells, in a process that uses an electric current to recover metals from the solution.
  5. After the ore has been processed and gold extracted, the leftover waste material, called tailings, contains small amounts of cyanide and other chemicals, so must be disposed of in an environmentally safe way. The tailings are stored in tailings dams, which are lined with impermeable layers. Although the cyanide levels in the dams are safe, steps are taken to keep wildlife away from the dams. Over time, the chemicals break down, the solids settle to the bottom and the water can be returned to the plant to be reused in processing.
  6. We then smelt the gold, melting it in a furnace at about 1,200 degrees Fahrenheit.
  7. From there, the liquid gold is poured into molds, creating doré bars. Doré bars are unrefined gold bullion bars containing anywhere from 60 to 95 percent gold.
  8. Finally, we send the bars to a refinery for further processing into pure gold.

The purpose of this post-closure period is to ensure that all reclaimed mine lands, water management structures and revegetation are working as intended. Additionally, reclamation and long-term stabilization often occur incrementally, requiring a phased approach as well as ongoing performance monitoring. There are maintenance activities to be conducted to address erosion, and monitoring to ensure that post-closure performance criteria are being met and intended land uses are being achieved. Normally, there are financial surety instruments in place, which require that Newmont demonstrate successful closure in order to be released from financial liability. In many cases, long-term water management obligations require active water treatment and monitoring that could last for decades. In such cases, financial trusts are often established in cooperation with regulatory agencies to ensure adequate funding for personnel, supplies and equipment to fulfill these ongoing obligations.

During this stage, engagement activities with the local communities continue, and emphasize monitoring, land use and information about on-site activities. Communities are obviously still interested in site activities and often participate in reviewing technical issues and decision making. In some cases, a small number of people remain employed, depending on on-site activities, which often translates into local purchases of goods and services and payment of fees and property taxes.

With sound planning and a focus on sustainability, the mine and the community will have collaboratively set the foundation for life after the mine’s closure.