Mining Terminology

Following is a list of mining terms that will be included in TMM’s formal underground mine plan proposal, which the company expects to submit to state and federal regulatory agencies within the next 18 months for extensive and rigorous environmental review.

BACKFILL: Backfill is material used to refill an excavated area of the mine. Approximately half of the tailings from the TMM Project will be stored as permanent cemented backfill in the underground mine.

CONCENTRATES: Concentrates are the end product of the Twin Metals project. These concentrates are sold on a global market and contain the minerals that have been separated from rock in the mine.

If a box was filled with mined ore that has not been processed, the grade, or percentage of the rock that is valuable, could be 1 percent. After crushing, grinding and flotation of the ore, if the same box was filled with concentrate, the grade would be around 25 percent. It is physically concentrated, hence the name “concentrate.”

CRUSHING: When rock is removed from underground, the sizes of rocks can be small (like pebbles) or very large (like a car). Crushing of rock is necessary to send a consistently sized material to the processing site.

ENVIRONMENTAL IMPACT STATEMENT: An Environmental Impact Statement (EIS), under United States environmental law, is a document required by the National Environmental Policy Act (NEPA) for certain actions affecting the environment. Minnesota has a similar program, the Minnesota Environmental Policy Act (MEPA). Multiple state and federal agencies develop the EIS during a multiyear process that includes studies of project-specific engineering and site-specific data. The EIS process includes multiple mandated opportunities for public input.

FLOTATION: Flotation is a physical separation using water, air, and a small amount of reagents to concentrate the desired metals.

GRINDING: This process occurs during several stages and eventually ore is ground into a fine sand-like consistency, liberating and exposing the surfaces of the contained mineral particles.

MINING: Mining begins with the mineral-bearing ore (material with positive economic value) removed from the earth. In reaching the ore, developmental rock is also removed and used for barricading areas or to fill voids underground. Mining at the TMM project would occur below the ground surface from hundreds to several thousand feet. The project will process approximately 20,000 tons of mineralized ore per day.

TAILINGS: Tailings are the leftover finely ground (milled) ore after the desired minerals have been physically separated and removed.

WASTE ROCK: Waste rock is rock stored on the surface that does not contain minerals for economic recovery but is not suitable as construction material. The TMM project would generate no waste rock piles.

CLOSURE: Mine closure is the period of time when the ore-removal and processing activities of a mine have stopped and mine reclamation is being completed. Closure can also refer to the act of reclaiming the mine.

RECLAMATION: Mine reclamation is part of the lifecycle of a mine and is the process of converting an active mine into land that can be used for another natural or economic means. Planning for mine reclamation occurs during the design process, prior to permitting or mine operations.