Frequently Asked Questions

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In developing its mine plan, Twin Metals has pulled together a combination of best-in-class technologies in order to put forth the best possible project. Eagle Mine in Michigan is a nearby example of an active modern underground copper and nickel mining operation.

Some examples of North American mines operating or permitted utilizing dry stack tailings include:

  • Currently Operational:
    • Eleonore (located in Quebec)
    • Greens Creek (located in Alaska)
    • Pogo (located in Alaska)
    • Raglan (located in Quebec)
    • Pumpkin Hollow (located in Nevada)

The underground mine will be divided into five zones, mined sequentially (though some might be simultaneous). The mining will happen in areas called stopes that are opened through drilling and blasting. Mineralized ore will be separated – underground – from waste rock and conveyed to the surface on a conveyor belt. When the stope is finished it will be backfilled with waste rock and engineered backfill – tailings mixed into a cement-like paste — and sealed. The same two declines will be used to reach all stopes with trucks and other equipment, and to hold the conveyor belt. One analogy for the underground mine might be riding an escalator down to successive basement floors in a department store, stopping off to remove the items from each floor, then sealing off the floors in turn.

TMM’s processing site will include the entrances to two 1.25-mile declines, or downward-sloped tunnels. One will transport workers underground in trucks and the other will hold a conveyor belt to move crushed ore to the surface, where target minerals will be extracted through a concentration process. Tailings will be either returned underground or trucked to an adjacent 429-acre tailings management site where tailings are dewatered and stacked in lined, sandy mounds.

The site will also include a concentrator building and a tailings filtering facility.

TMM plans to use the environmentally friendly dry stack method to store the leftover rock from its proposed underground copper-nickel mine to be located nine miles southeast of Ely, Minnesota. The dry stack method eliminates the storage pond and dam associated with conventional tailings facilities. It has been successfully used in four mines in the northern United States and Canada with similar climates to Minnesota and has been permitted at two mines in the western United States. Tailings from a mine are the crushed rock left over after target minerals are removed. Using the dry stack method, remaining tailings will be compressed into low-moisture, sand-like deposits and stored on a lined ground facility near the plant site. Reclamation of the tailings site can occur in stages and can be capped or covered with natural vegetation. Learn more about dry stack tailings storage.

After the concentrates are sold, they would be shipped out for final processing to separate the elemental minerals from the concentrates. TMM is not involved in that part of the process.

TMM will sell copper concentrate, nickel-cobalt concentrate, and platinum group metals concentrate.

TMM is committed to operating a safe, 21st-century underground mine, meaning it is safe for both workers and the environment. When we say 21st-century mine, we mean: a mine that is designed, built, operated and eventually reclaimed in a way that prioritizes environmental protection and stewardship, worker safety and community engagement. The mine will use the environmentally friendly dry stack method to manage tailings, and it will have the advantage of technological developments that have significantly reduced the potential impacts on land, water and air. Features of this mine will include:

  • Minimal surface footprint: Most of mining will take place underground, between 400 and 4,500 feet below the surface where noise, dust and lighting will be contained. About 80 percent of mining will occur below 1,500 feet, and about 40 percent of mining will occur below 2,700 feet. The TMM Project will have a surface footprint that is 80 to 85 percent smaller than an open pit mine with similar production. It minimizes the environmental exposure of the mining operation.
  • Precision targeting of minerals: Ten years of study of the deposit have clearly mapped the location of the minerals to be mined. Three-dimensional modeling allows for accessing and extracting only the ore that contains the valuable minerals. Waste rock will be left underground.
  • Safety: Two tunnels (or declines) will provide mine access, along with the means for transporting minerals, with openings at the mine site. Vehicles will transport workers to a mining site via a tunnel. This is an improvement over the outdated method of lowering miners down a shaft in an elevator to access an underground mine. The project will operate under National Mining Association Core Safety Program standards, a systematic approach to developing a safety culture.
  • Water management: The project would not discharge process water and is designed not to require discharge of contact water. Water used in the mineral concentration process would be reused on site.
  • No acid rock drainage: Modern exploration methods have allowed TMM to develop a deep understanding of the unique features of the Maturi Deposit in the Duluth Complex. The geology of the Maturi Deposit, and the mining method proposed by TMM, means tailings that remain after the concentration process will be a dry, non-acid-generating, sandy rock residue. The concentration process will remove almost all sulfide, bound to our target minerals, which will be extracted and shipped to customers. Extensive testing has shown that trace amounts of residual sulfides in these dry stack tailings (0.12-0.15 percent) will be non-acid-generating, and independent research confirms these findings.
  • Tailings management: TMM will manage tailings using the most environmentally friendly technology available. Up to 50 percent of tailings will be permanently returned underground as cemented engineered backfill. The remaining tailings will be filtered and stored within the mine site in a lined, sandy “dry stack” mound topped with native vegetation. This tailings management technology means there will be no permanent tailings pond or dam on-site, eliminating any risk of a dam failure.
  • Reclamation: Most of the infrastructure at the mine site is designed to be removed at the end of the life of the mine, and the land will be reclaimed. The land will be replanted with native vegetation and the remaining underground facilities will be permanently sealed.

The Twin Metals Minnesota (TMM) Project is focused on designing, constructing and operating an underground copper, nickel, cobalt and platinum group metals mine, and is committed to doing so in an environmentally responsible way. Located approximately nine miles southeast of the city of Ely, Minnesota, and 11 miles northeast of the city of Babbitt, Minnesota, the TMM Project targets the valuable minerals within the Maturi deposit, part of the Duluth Complex geologic formation.

The TMM Project is located in northeast Minnesota. The mine would be located within the Maturi deposit, which is located outside the Boundary Waters Canoe Area Wilderness and approximately nine miles southeast of the city of Ely, Minnesota, and 11 miles northeast of the city of Babbitt, Minnesota.

Minnesota is home to the Duluth Complex in northeast Minnesota. In 1977, the Minnesota Department of Natural Resources estimated that the Duluth Complex contained 4.4 billion tons of ore containing copper, nickel and PGM resources. Information from Twin Metals, PolyMet Mining and other companies exploring in the area suggests that mineral resources in the Duluth Complex are much greater. Domestic and international demand for these strategic and critical minerals is projected to grow steadily over the long term, positioning Minnesota to be a world leader in supplying these metals. According to the U.S. Geological Survey (USGS) 2017 report on critical minerals, there is a growing dependence on foreign sources of critical platinum group metals. The report called out Minnesota’s Duluth Complex as a potential source of domestically produced critical platinum group metals.

Copper, nickel, platinum group metals and cobalt are critical aspects of a sustainable future across industries including construction, communications, power distribution, national defense, medicine and renewable green energy. The TMM Project would contribute to establishing Minnesota as a world leader in the production of green energy metals used in wind turbines, hybrid and electric vehicles, batteries, and solar energy panels. Visit our Creating Local Jobs page to learn more.

The TMM Project represents an extraordinary opportunity for economic growth and job creation regionally and statewide. Construction will generate several million labor hours, on par with the number of construction and related professional jobs created by projects such as U.S. Bank Stadium and Target Field in the Twin CitiesOnce operational, TMM expects to directly employ more than 700 people long term in northeastern Minnesota and to create an estimated 1,400 spinoff jobs in other industries. Learn more on our Creating Local Jobs page.

Yes. Under a Project Labor Agreement signed in August 2019 with the Iron Range Building and Construction Trades Council, union workers will complete construction of the entire TMM underground mine. We are grateful for the public support many unions have expressed for our project and our industry.

The status of unionization of the TMM Project labor force would be determined by the workforce itself later in the project development effort. TMM respects the strong union history in northern Minnesota. We are grateful for the public support many unions have expressed for our project and our industry.

TMM has submitted a 25-year mine plan of operations as part of the formal proposal to state and federal regulatory agencies for permitting review. The Duluth Complex contains mineralization, which can—through future exploration, permitting and operations—support jobs for generations.

Currently, TMM is at the beginning of the state and federal regulatory processes that will determine if the project can be developed. TMM formally submitted its mine plan of operations to the U.S. Bureau of Land Management and a scoping environmental assessment worksheet data submittal to the Minnesota Department of Natural Resources in late 2019. Those submissions initiated both the state and federal extensive Environmental Impact Statement process. The proposals outline more than 10 years of site-specific studies TMM has completed, along with the design for a compact and efficient underground mine project. For more information, visit the Regulatory Process page.

Yes. Both the state and federal environmental review processes will take several years, and there will be numerous opportunities for public input on what potential impacts the agencies should study throughout the Environmental Impact Statement processes. For more information, visit the Regulatory Process page.

Yes. Today’s environmental regulations tightly control how mines are designed, operated and eventually closed. The Minnesota Department of Natural Resources, Minnesota Pollution Control Agency, U.S. Environmental Protection Agency, U.S. Army Corps of Engineers and other state and federal agencies will enforce regulations protecting water, soil, animals and air. Twin Metals Minnesota recognizes environmental conservation as a core value and is committed to protecting Minnesota’s wilderness, natural environment and recreational resources. For more information, visit the Responsible Mining page.

State and federal environmental laws, standards and regulations under which TMM would operate are some of the most stringent and comprehensive in the world. These rigorous standards not only guide the design and permitting of mining projects, but also hold companies accountable during operations and through closure of a mine. TMM is dedicated to building and operating a mine project that utilizes industry best practices and meets all state and federal environmental standards. In addition, the Minnesota Department of Natural Resources, Minnesota Pollution Control Agency, U.S. Environmental Protection Agency, U.S. Army Corps of Engineers and other state and federal agencies will enforce regulations protecting water, soil, animals, air, and other natural resources.

For example, during operations TMM will have to collect frequent groundwater and surface water quality samples on a schedule established in permits. The samples will be sent to a state-certified laboratory for water quality testing. Minnesota regulators will review the laboratory results to determine if they meet the stringent surface water and groundwater quality protection standards that will be specified in TMM’s operating permits. Air quality permits will have similarly rigorous monitoring and reporting requirements.

The water quality, air quality, wildlife, and wetlands environmental monitoring systems that will be required in permits will give these regulatory agencies frequent information about the environmental performance of all aspects of the TMM Project. The project environmental monitoring data will function as an early-notification system that will provide TMM and Minnesota regulators with important and timely information about whether the project’s environmental protection systems are functioning as designed and in compliance with operating permits.

If project monitoring data provide an early indication that the facilities may not be performing as designed, TMM will immediately develop a plan to investigate. If this investigation confirms there is a problem, TMM will take appropriate response measures to correct the situation under supervision from these agencies. Minnesota regulators oversee and enforce all of these steps.

Minnesota regulators also have the authority to fine the company, and suspend or even revoke one or more of TMM’s operating permits if the monitoring data reveal non-compliance with the environmental performance standards in our permits. As an extra safeguard, Minnesota regulators could use funds from bankruptcy-proof financial assurance that TMM provides to respond to the problem.

Minnesota’s mines are required by state law to have bankruptcy-proof financial assurance for reclamation and closure performance. Minnesota requires state-managed and annually adjusted financial assurance to cover any possible costs, including post-closure reclamation, before permits can be issued. Minnesota is authorized to deny or revoke a permit if a company does not comply.

TMM will minimize the impact of mining activity by using underground mining operations coupled with storing approximately half of the tailings as permanent cemented backfill in the underground mine. TMM will use the environmentally friendly dry stack method to manage the remaining tailings. Learn more about dry stack tailings storage. Extensive additional testing will be conducted under the supervision of the Minnesota Department of Natural Resources and federal agencies. As the result of the EIS process, the regulatory agencies may impose additional measures to reduce potential impact.

During operations TMM will have to collect frequent groundwater and surface water quality samples on a schedule established in our permits. The samples will be sent to a state-certified laboratory for water quality testing. Minnesota regulators will review the laboratory results to determine if they meet the stringent surface water and groundwater quality protection standards that will be specified in TMM’s operating permits. Air quality permits will have similarly rigorous monitoring and reporting requirements.

The water quality, air quality, wildlife, and wetlands environmental monitoring systems that will be required in permits will give these regulatory agencies frequent information about the environmental performance of all aspects of the TMM Project. The project environmental monitoring data will function as an early-notification system that will provide TMM and Minnesota regulators with important and timely information about whether the project’s environmental protection systems are functioning as designed and in compliance with operating permits.

If project monitoring data provide an early indication that the facilities may not be performing as designed, TMM will immediately develop a plan to investigate. If this investigation confirms there is a problem, TMM will take appropriate response measures to correct the situation under supervision from these agencies. Minnesota regulators oversee and enforce all of these steps.

State and federal environmental requirements, including those protecting the BWCAW, must be met or exceeded, or the TMM Project will not be authorized to move forward. The project is based on an underground mine plan targeting the Maturi deposit, which is located outside the Boundary Waters Canoe Area Wilderness and long-established state and federal protective buffer zones. Additionally, testing shows the tailings would be non-acid generating. Extensive additional testing will be conducted under the supervision of the Minnesota Department of Natural Resources and federal agencies.

Now that the formal proposals have been submitted to federal and state agencies for review, the TMM Project must complete the rigorous Environmental Impact Statement (EIS) processes. The formal proposals detail specific environmental protection measures incorporated in the design and operations plans. The EIS processes use these detailed project plans and site-specific environmental data in its analyses.

TMM must also demonstrate ongoing compliance with standards throughout the life span of the project. For example, during operations, TMM will have to collect frequent groundwater and surface water quality samples on a schedule established in our permits. The samples will be sent to a state-certified laboratory for water quality testing. Minnesota regulators will review the laboratory results to determine if they meet the stringent surface water and groundwater quality protection standards that will be specified in TMM’s operating permits. Air quality permits will have similarly rigorous monitoring and reporting requirements.

The water quality, air quality, wildlife, and wetlands environmental monitoring systems that will be required in permits will give these regulatory agencies frequent information about the environmental performance of all aspects of the TMM project. The project environmental monitoring data will function as an early-notification system that will provide TMM and Minnesota regulators with important and timely information about whether the project’s environmental protection systems are functioning as designed and in compliance with operating permits.

If project monitoring data provide an early indication that the facilities may not be performing as designed, TMM will immediately develop a plan to investigate. If this investigation confirms there is a problem, TMM will take appropriate response measures to correct the situation under supervision from these agencies. Minnesota regulators oversee and enforce all of these steps.

You can read about these terms and more mining definitions on our Mining Terminology page.