Duluth Metals has reported the resultsof a draft prefeasibility study (PFS) for the proposed Twin Metals Minnesota (TMM) underground copper, nickel and platinum group metals mining project in northeast Minnesota. The PFS is based on a 30-year underground mine plan with an average production rate of 50,000 st/d of ore, generating marketable copper and nickel concentrates.

Life-of-mine production of metal in concentrates is estimated at approximately 5.8 billion lb of copper, 1.2 billion lb of nickel, 1.5 million oz of platinum, 4 million oz of palladium, 1 million oz of gold, and 25.2 million oz of silver. Life-of-mine C1 cash costs are estimated at $0.76/lb of copper net of byproduct credits.

The PFS estimates an initial capital cost for project development of $2.77 billion and a pre-tax payback period of 6.4 years from the start of production.

The TMM project encompasses the underground mine sites, concentrator site, tailings storage facility and utility corridors. Mining is based on the Maturi and Maturi SW deposits, which would be accessed by declines, with the decline portals located near the concentrator site.

The tailings storage facility would be located south of the city of Babbitt and would store tailings not returned to the underground mine as paste backfill. The tailings storage facility also includes a concentrate filtration plant, intermediate pond, electrical substation and rail load-out facility.

The underground mining operation would utilize a combination of post-pillar cut-and-fill and long-hole stoping mining methods. The mine plan estimates life-of-mine production of 527 million st of mineralized material at 0.59% copper and 0.19% nickel. Mine infrastructure would include a wide variety of fixed underground facilities, including primary crushers, conveyors, pumping stations, explosives magazines and electrical substations.

Mining will occur in mining units or panels separated by barrier pillars. Panel areas are a maximum of 1,700 ft along strike by 1,700 ft along dip. Mining recoveries within the panels vary between 75% and 82%, depending on the depth, dip, width and mining method selected.

Mine construction and pre-production development will take three years. The mine achieves peak production of 50,000 st/d in year two, which is sustained through year 26.

The concentrator proposed for the TMM project is based on a single, 50,000-st/d processing line, using SAG and ball milling, sequential copper and nickel flotation, high-rate tailings thickening, and a concentrate receiving system, filter plant, concentrate storage facility, and rail load-out. Flotation tailings will be very low in sulphur, with approximately half of the tailings contained in a conventional lined tailings impoundment and the remainder combined with cement and fly ash and returned to the mine as paste backfill.

The concentrator proposed for the TMM project is based on a single, 50,000-st/d processing line, using SAG and ball milling, sequential copper and nickel flotation, high-rate tailings thickening, and a concentrate receiving system, filter plant, concentrate storage facility, and rail load-out. Flotation tailings will be very low in sulphur, with approximately half of the tailings contained in a conventional lined tailings impoundment and the remainder combined with cement and fly ash and returned to the mine as paste backfill.

"The PFS technical report confirms that the TMM project offers an extraordinary long-term economic opportunity for the state of Minnesota, local communities, and TMM project stakeholders," Duluth Metals Executive Chairman Christopher Dundas stated. "The project enjoys many advantages including excellent infrastructure, a mining friendly jurisdiction, and upsides for future expansion and potential downstream processing."

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