Gold cyanidation, a process where gold is temporarily converted into a water soluble form, is the most widely accepted method for efficient and environmentally sound gold extraction. Donlin Gold plans to use this widely accepted practice to extract the gold from the ore, and will follow guidelines provided by the International Cyanide Management Code on how to handle cyanide from its manufacturer, to its transport, storage, use, and disposal. Dry sodium-cyanide briquettes will be shipped to the mine site in sealed steel ISO (International Standard Organization) tanks. The cyanide will be dissolved into a weak, pH-controlled solution for use in gold extraction. After the ore is crushed into smaller sized grains, it will be transported to an on-site leaching plant where the ore will be mixed with cyanide. The cyanide will dissolve the gold into a solution, and then the gold will be precipitated out of the solution. The cyanide solution will go through a destruction process that reduces its concentration. This industry leading detoxification process has been adopted in the last 25 years by major gold mining companies worldwide. The trace amounts of cyanide remaining in the tailings storage facility will disintegrate further under the influence of sunlight and air.
Operating and powering the mine will require fuel and other supplies to be transported to the site. Many of these materials will be transported to the project by barges that will travel up the Kuskokwim River during the shipping season between June and October. The introduction of the natural gas pipeline to supply power to the project reduced the amount of diesel needed to be barged on the river by approximately 80 million gallons. This also reduced the amount of barges needed to approximately one fuel barge and one supply barge leaving the port each day.
With the unlikely potential of a spill to occur, the Donlin Gold project will have an emergency Spill Response Plan ready to implement. The plan will include staged response equipment and trained response crews.
After extracting the gold, wet tailings resembling silt will be a byproduct of the milling process. A containment dam, engineered to withstand environmental events and changes in Alaska, will be built to house the tailings. It will have a synthetic liner similar to those used in city landfills. Donlin Gold will use this industry recommended liner for tailings storage. The ultimate size of the tailings storage facility will be approximately 1.75-miles-long by 1-mile-wide. When the mine is no longer in operation, the tailings storage facility will be covered with rock, gravel, and soil and planted with vegetation. The tailings dam will be re-contoured to blend in with the surrounding terrain.
The rock at Donlin Gold has naturally occurring mercury, as do many areas associated with volcanic activity, high heat flows, and plate tectonic boundaries. This mercury is released into the atmosphere through natural processes such as weathering of rock, vaporization from soil, wildfires, and off-gassing of the world’s oceans. According to the U.S. Environmental Protection Agency (EPA) and other scientific sources, about one-half of the mercury emitted into the air each year is from these natural processes.
The primary source of human-generated mercury air emissions is combustion of coal, whereas mining is a relatively minor source of mercury air emissions both nationally and globally. Once released into the atmosphere, mercury may be transported great distances from its original source. For example, according to the EPA, half of the human-generated mercury that is deposited in the western U.S. comes from industrial sources in Asia.
In 2010, the EPA finalized national emissions standards for mercury based on maximum achievable control technology (MACT). These new limits are based on the nation’s best-performing gold processing facilities, which are well controlled for mercury. To adhere to these new EPA regulations, Donlin Gold is committed to installing and operating state-of-the-art mercury emissions controls to meet or exceed these standards.
Aquatic biologists have conducted aerial salmon count surveys during the chinook, chum, and coho runs on Crooked Creek and its tributaries since 2004. A fish weir was installed in 2008 to get more reliable counts. The resistance board fish weir includes a digital video recorder (DVR) to accurately record and count the fish. This video counting method means there is no live trap collection of the fish; they simply pass through the guidance structure and continue upstream. Resistance board weir and DVR technology has been proven by both the Alaska Department of Fish and Game and the U.S. Fish and Wildlife Service to be effective in streams that experience turbidity issues similar to those of Crooked Creek.
Aquatic biologists have identified different juvenile fish species in the Crooked Creek drainage including sculpin, round whitefish, dolly varden, arctic grayling, and salmon. In addition to sampling fish populations, aquatic biologists have also collected fish tissue samples and tested basic water quality.
The YK region has an abundant supply of fresh surface water, with about 20 inches of annual precipitation at the Donlin site. Donlin Gold is committed to protecting local water sources from pollution and has been conducting surface water quality monitoring and groundwater quality monitoring as part of the baseline studies for the project.
Any water that comes in contact with the mine, such as rainwater or snowmelt would be diverted into a contact water pond. The pond would be used to supply water for the mill. A fresh water reservoir could also provide an additional supply of water for processing, as well as other emergencies and unexpected situations like fires. Before any water is discharged into the environment, it will be treated to meet strict water quality standards. Donlin Gold is also looking at different methods of recycling water to help reduce water use.
- Fishing activity and river use surveys from Georgetown to Kuskokwim Bay
- Erosion studies
- Barge wake impact studies
- Sediment and water sampling
- Noise observations
- Wildlife observations
- Surface water quality monitoring
- Groundwater quality monitoring
- Air quality monitoring
- Cultural studies (socioeconomic and archaeological surveys)
- Mercury baseline studies
- Aquatic/fish studies
- Wildlife surveys
- Habitat mapping
- Subsistence resources
- Wetlands mapping
Sustaining the environment in the Yukon Kuskokwim (YK) region is one of the top priorities of the Donlin Gold project. For the past 16 years, Donlin Gold has been conducting numerous environmental studies to evaluate the possible impacts of the activity required to construct and operate the mine. Data from these studies will be used in the design process so the mine can meet or exceed environmental standards, in addition to the protection of the natural and subsistence resources in the YK region. The data will also provide information about the environment before, during, and after mine operations to ensure the land is continuously protected. These studies will be submitted to regulatory agencies during the permitting process.