The Project area would be located at the contact of two major bedrock units, the Giants Range Batholith (GRB) and the Duluth Complex.

The Duluth Complex is composed of mafic to felsic tholeiitic magmas related to the Midcontinent Rift System and makes up much of the bedrock of northeast Minnesota. It is bounded byafootwall of Paleoproterozoic sedimentary rocks and Archean granite-greenstone terranes andahanging wall largely of rift-related flood basalts and hypabyssal intrusions of the Beaver Bay Complex (Miller et al., 2002).

The targeted mineralization of the Maturi deposit is hosted within the basal portion of the South Kawishiwi Intrusion (SKI), known as the BMZ. The SKI is bordered on the southwest by the Partridge River Intrusion, on the northwest by the GRB and Biwabik Iron Formation, the Anorthositic Series to the northeast, and on the southeast by the Bald Eagle Intrusion. Excluding the transmission corridor, lithologic units within the Project area include Mesoproterozoic rocks of the SKI and the Anorthositic Series of the Duluth Complex, as well as basalt xenoliths of the North Shore Volcanic Group.

Surficial geology in the Project area is dominated by glacial deposits associated with the Rainy Lobe that include areas of peat and lake sediment. In some localities along the shoreline of Birch Lake reservoir, the Rainy Lobe Till has been eroded by water, resulting inaless rugged surface expression andapossible surface lag consisting o concentrated coarse-grained clasts. The lake sediment is predominantly silt, clay, and organic material (Jennings and Reynolds, 2005). The thickness of surficial material in the Rainy Lake Watershed is generally less than (<) 50 ft (15.6 m) and is laterally discontinuous. In the vicinity of the plant site, bedrock crops out in five to 20% of the area (Ericson et al., 1976).

The deposit is composed of anorthositic troctolite to troctolites. The mineralogy consists primarily of plagioclase, olivine, pyroxenes, and oxides which make up more than 85% of the total mineralogy. The alteration minerals (e.g., serpentine, chlorite, etc.) typically comprise 1% to 6% of the mineralogy but are locally found in amounts up to 15%. Sulfide content of the ore-bearing geologic units ranges from 1% to 6%, with very local areas having sulfide contents outside of that range.

The main four sulfides present in the deposit include:
• Chalcopyrite;
• Cubanite;
• Pentlandite; and
• Pyrrhotite.

Other copper and nickel sulfides are present in the deposit but occur in minor amounts (<5% total sulfides).

Rock units and mineralization in the BMZ are planar and sub-parallel to the lower contact with an average strike of approximately 60 degrees (°) and dips of 20° to 52° to the southeast. The vertical thickness of the potentially mineable grades varies in width from 49 to over 591 ft (15 to 180 m), averaging from 197 to 328 ft (60 to 100 m). The depth of the potentially mineable grades ranges between 984 to 3,005 ft (300 to 916 m) amsl. The Maturi deposit has not been significantly deformed, but it has been subjected to minor displacements along reactivated basement faults, as well as cross faults. Mapped structures are mostly sub-vertical north–northeasterly striking faults.

Twin Metals Minnesota (TMM) is focused on designing, permitting, constructing, and operating an underground copper, nickel, cobalt, platinum, palladium, gold, and silver mining project. Located approximately nine miles southeast of the city of Ely, Minnesota, and 11 miles northeast of the city of Babbitt, Minnesota, the Project targets valuable and strategic state, federal, and privat minerals within the Maturi deposit, which isapart of the Duluth Complex geologic formation. The Project consist of an underground mine,aplant site,atailings management site, andanon-contact water diversion area along with an access road, water intake corridor, and transmission corridor.

The Project would develop an underground mine at the Maturi deposit. In the underground mine, the ore would be blasted using explosives. The blasted ore would be transported by load-haul-dump machines and haul trucks to underground crushers. The underground crushers would crush the ore toasmaller size for transportation out of the underground workings by conveyor.

Access
The underground mine would be accessed from portals located within the plant site. Two parallel declines, the conveyor decline (to the west) and the access decline (to the east), would be excavated to provide access to the subsurface orebody and underground workings. Each decline would be approximately 20 ft wide by 20 ft in height (6m by 6m). To limit the distance of overland conveying from the portals, the decline portals would be located close to the coarse ore stockpile the temporary rock storage facility.

The conveyor decline would be the western of the two declines. The length of the conveyor decline from the portal to the initial haulage level tie-in would be approximately 1.6 miles (2.5 km). The conveyor decline would house the decline conveyor which would transfer ore from the mine to the surface and would eventually extend further down the deposit as mine development progresses. After the conveying system is installed, the conveyor decline would provideamain exhaust path for the mine ventilation system and would serve as secondary access to the underground mine.

The access decline would accommodate access and egress of miners, equipment, and materials to operate the underground mine. Traffic would be two-way, with crosscuts to serve as access to the conveyor decline for emergency egress.

Mining
To achieve efficient recovery of the resource, underground mining at the Project would utilize the longitudinal longhole retreat (LLR) mining method with backfill. For this mining method, primary and secondary stopes (excavations in the underground mine) would be separated by sill pillars and rib pillars. The use of sill and rib pillars, as well as the backfilling of mined stopes with waste rock and engineered tailings backfill would provide confinement to the pillars between the stopes and ensure long term stability of the underground mine. Additionally, to prevent subsidence, the Project would operate with an appropriate crown pillar depth. Approximately 40% to 60% of the mineral resource within the designed underground mine would be left in sill and rib pillars for geotechnical stability purposes. These resources would be rendered un-minable by the LLR mining method at the cessation of mining operations. The recovery rates identified arearesult of the economic feasibility of using the LLR mining method. The use of the LLR mining method was chosen as it allows for the long-term stability necessary for safe operations and the appropriate crown pillar depth to prevent subsidence.

Once drilled and blasted, load-haul-dump (LHD) equipment, either remotely or manually operated, would extract ore from the trough drift, through the drawpoint, and haul it to an orepass located in the extraction level.

The orepass would transfer ore from the extraction level to the haulage level where it would be rehandled by another LHD directly intoacrusher or toa40-ton truck that would haul the material to the closest crusher. Semi-portable jaw crushers would be located at crushing stations near the highest production orepasses. At the crushing stations, ore would be crushed to an approximate passing diameter of six inches . The crushed material would then be conveyed to the decline conveyor viaatransfer conveyor. The decline conveyor would transport ore to the coarse ore stockpile via the conveyor decline.

Primary mining equipment would include the mobile equipment directly involved in the mining cycle including underground development and the haulage of muck and ore.

Secondary mining equipment would include equipment necessary for the safe and efficient continuation of the mining cycle but not directly involved in the mining cycle. Estimated secondary mining equipment would include:
• Cable bolters, shotcrete transmixers, and sprayers for ground support;
• Grader and water truck for roadway maintenance and dust suppression;
• Scissor lifts, boom trucks, and transmixers for underground construction;
• Mobile fuel and lubricant trucks to service mobile equipment; and
• Personnel carriers and light vehicles for transportation of workers, supervisors, and technical personnel.

The blasted ore would be transported by load-haul-dump machines and haul trucks to underground crushers.

The SAG mill feed conveyor would convey ore from the coarse ore stockpile to the SAG mill to be processed. Ore from the coarse ore stockpile along with recirculated oversize material would feed the SAG mill. The SAG mill discharge would be screened and oversize pebbles would be conveyed and reintroduced to the SAG mill feed on the SAG mill feed conveyor. Recirculation conveyors for oversize material would be contained within the building to keep the wet ore on the conveyor belt inside the building to prevent potential freezing during winter. SAG mill discharge material which passes through the screen would have achieved the target grind size from the SAG mill circuit and would be directed to the ball mill circuit.

The ball mill circuit would grind ore toaP80 of 135 microns before the ore is pumped to the flotation circuit. The ball mill would be operated inaclosed-circuit configuration to achieveatight particle size distribution. The ball mill circuit would be fed from the product of the SAG mill circuit (the screened undersized material from the SAG mill discharge) combined with material being recirculated to the ball mill (the ball mill recirculating load). This stream would then be classified throughacyclone with the cyclone overflow as the product of the circuit being pumped to the flotation circuit. The cyclone underflow would be recirculated to the ball mill to be ground and further reduced in size.

Aportion of the ball mill recirculating load would be split equally to feed multiple gravity concentration units operating in parallel. The gravity concentration units would operate in batch to recover gold, platinum, and palladium based on the higher specific gravity of the minerals to the gravity concentrate. The gravity concentrate would be dewatered while the gravity tailings would be returned to the ball mill recirculating load.

The gravity concentrate would flow in batches toagravity concentrate holding tank. The gravity concentrate would be dewatered and transferred to concentrate bags or other containers. The concentrate bags or containers could be stored or loaded onto trucks for transport.

The flotation circuit would produce two concentrates: the copper concentrate and the nickel concentrate. Through the copper flotation circuit, copper, gold, silver, platinum, and palladium would be recovered while minimizing the amount of nickel and cobalt recovered. T ........