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United States
NorthMet Project

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 Location:
17 km NE from Hoyt Lakes, Minnesota, United States

  Project Contacts:
PO Box 475, 6500 County Road 666
Hoyt Lakes
Minnesota, United States
55750
Phone218-471-2150
WebsiteWeb
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Overview

StagePermitting
Mine TypeOpen Pit
Commodities
  • Copper
  • Nickel
  • Cobalt
  • Palladium
  • Platinum
  • Gold
  • Silver
Mining Method
  • Truck & Shovel / Loader
Processing
  • Dewatering
  • Hydrometallurgical plant / circuit
  • Filter press plant
  • Flotation
Mine Life20 years (as of Jan 1, 2020)
Latest NewsCourt of Appeals Rules Favorably on PolyMet Water Permit     January 24, 2022


Owners

Source: p. 5
CompanyInterestOwnership
PolyMet Mining, Corp. 100 % Indirect
PolyMet Mining, Corp. through its 100%-owned subsidiary, Poly Met Mining, Inc. the Company is engaged in the exploration and development of natural resource properties.

Deposit Type

  • Magmatic

Source: Source p.20, 53-55

Summary:

The NorthMet Deposit is a large-tonnage, disseminated accumulation of sulphide in mafic rocks, with rare massive sulphides. Copper to nickel ratios generally range from 3:1 to 4:1. Primary mineralization is probably magmatic, though the possibility of structurally controlled re-mobilization of the mineralization (especially PGEs) has not been excluded. Sulphur source is both local and magmatic (Theriault et al., 2000). Extensive detailed logging has shown no definitive relation between specific rock type and the quantity or grade quality of sulphide mineralization in the Unit 1 mineralized zone or in other units, though the localized noritic to gabbronoritic rocks (related to footwall assimilation) tend to be of poorer PGE grade and higher in sulphur.

The NorthMet Deposit is part of the Duluth Complex in northeastern Minnesota, which is a large, composite, grossly layered, tholeiitic mafic intrusion that was emplaced into comagmatic flood basalts along a portion of the Mesoproterozoic Mid-continent Rift System. NorthMet is one of eleven known copper-nickel deposits that occur along the western edge of the Duluth Complex and within the Partridge River (PRI) and South Kawishiwi (SKI) intrusions. The NorthMet Deposit is hosted within the PRI, which consists of varied troctolitic and (minor) gabbroic rock types that have been subdivided into seven igneous stratigraphic units based on drill core logging.

The metals of interest at NorthMet are copper, nickel, cobalt, platinum, palladium and gold. Minor amounts of rhodium and ruthenium are also present though these are considered to have no economic significance. In general, with the exception of cobalt, the metals have strong positive correlations with copper mineralization. Cobalt is well correlated with nickel and reasonably correlated with copper.

Mineralization occurs in four broadly defined horizons or zones throughout the NorthMet property. Three of these horizons are within basal Unit 1, though they likely will not be discriminated in mining. The upper horizon locally extends upward into the base of Unit 2. The thickness of each of the three Unit 1 enriched horizons varies from 5 ft to more than 200 ft. Unit 1 mineralization is found throughout the base of the NorthMet Deposit. A less extensive (the copper-rich, sulphur-poor Magenta Zone) mineralized zone is found in Units 4, 5 and 6, in the western part of the NorthMet Deposit.

Mineralization occurs in two broad forms. Firstly, sulphides may be disseminated in heterogeneous troctolitic rocks (mainly Unit 1) in which the grain sizes of both silicates and sulphides widely vary. The occurrence and amount of this mineralization within drill holes can be unpredictable over the scale of 20 to 30 ft though mineralization is relatively constant in some horizons (i.e., top of Unit 1). Secondly, economic concentrations of sulphides in the upper units tend to be coarser grained and copper-rich (Units 2 to 7, particularly the Magenta Zone).

Sulphide mineralization consists of chalcopyrite and cubanite, pyrrhotite and pentlandite, with minor bornite, violarite, pyrite, sphalerite, galena, talnakhite, mackinawite and valerite. Sulphide minerals occur mainly as blebs interstitial to plagioclase, olivine and augite grains, but also may occur within plagioclase and augite grains, as intergrowths with silicates, or as fine veinlets. Small globular aggregates of sulphides (less than two centimetres) have been observed in core and in the small test pit on the site. The percentage of sulphide varies from trace to about 5%, but is rarely greater than 3%. Local massive sulphide is present, but rare. Platinum, palladium, and gold are associated with the sulphides as well as in tellurides and bismuthides.


Mining Methods

  • Truck & Shovel / Loader

Source: p.134, 138

Summary:

The NorthMet Project contains mineralization at or near the surface that is ideal for open pit mining methods.

Mining is planned on a 7 day per week schedule, with two 12-hour shifts per day. Other mining schedules may prove to be more effective, but are not expected to significantly change Project economics. The mine plan includes 225 million tons of ore at an overall strip ratio of 1.6:1. Mining is planned in three pits: The East Pit, the Central Pit, and the West Pit. As mining of the Central Pit commences, it will extend into the East Pit, thereby joining the pits. The combined pit will be referred to as the East Pit.

The method of material transport evaluated for this study is open pit mining using two 36.6-yd3 hydraulic front shovels as the main loading units with a 22.5-yd3 front end loader as a backup loading unit. The material will be loaded into 240-ton haul trucks and the ore will be hauled to the rail transfer hopper for rail haulage to the mill or ore surge pile (OSP) areas, and the waste rock to waste stockpiles or pit backfills.

During the first half of the operation, the more reactive waste rock mined will be placed in two temporary stockpiles (one west of the East Pit referred to as the Category 4 Stockpile, and one south of the East Pit referred to as the Category 2/3 Stockpile), and the least reactive waste rock will be placed in a permanent stockpile north of the West Pit (referred to as the Category 1 Stockpile). Once mining is completed in the East Pit, the more reactive waste rock mined will be placed directly in the East Pit as backfill. The more reactive waste rock in the Category 4 stockpile (in the location of the future Central Pit) will then be relocated as backfill into the East Pit, thus clearing the area for mining of the Central Pit. the Category 2/3 Stockpile will then be moved into the East Pit as backfill. Once mining is completed in the Central Pit, waste rock will be backfilled into that pit, too. By the end of the mine life, all of the more reactive waste rock will be placed as backfill in the pits. As the least reactive waste rock is mined, it will be placed in the permanent Category 1 Stockpile or in the East and Central Pits as backfill. The three mine pits will flood with water after mining and backfilling are completed, which results in the more reactive waste rock being permanently disposed of subaqueously.

Haul roads were designed at a width of 122 ft, which provides a safe truck width (27’3” canopy width) to running surface width ratio of 1:3.5, including a 26.5-ft width for a bench on the edge of the road. Maximum grade of the haul roads is 10%.


Crushing and Grinding
Flow Sheet: Source
Source: Source p.165-179
Crusher / Mill TypeModelSizePowerQuantity
Gyratory crusher 36" x 72" 4
Gyratory crusher 60" x 113" 1
Pebble crusher Metso Nordberg MP800 36" x 72" 1
SAG mill 40' x 22.5' 28 MW 1
Ball mill 24' x 37' 14 MW 1

Summary:

Crushing and Material Handling
The Coarse Crushing building and equipment would be used for primary and secondary crushing of the plant ore feed. A new 60” primary crusher would be installed in the South Coarse Crushing facility. All crusher auxiliaries including the lubrication unit, drive, counter shaft assembly and hydraulic pack would be replaced with new units and control systems. The four existing 36” secondary crushers associated with the primary crushing system would require complete refurbishment.

Milling
The milling section consists of a SAG mill operating in open circuit and a ball mill operating in closed circuit with two clusters of classifying hydro cyclone clusters to give a product of 80% passing 120 µm. A pebble crushing circuit is incorporated to handle the SAG mill scats.

Ore is transferred from the crushed ore storage bin to the SABC circuit, which consists of a SAG mill, ball mill and pebble crusher. The ball mill is fed by cyclone clusters. The overflow from the cyclones will discharge into a flotation feed tank that feeds the flotation circuit.

Crushed ore is withdrawn from the crushed ore storage bin using 62 variable speed driven vibrating pan feeders. The pan feeders discharge through chute arrangements onto two reclaim conveyors. Between four and eight pan feeders per conveyor will operate at any one time.

Both reclaim conveyors discharge onto the transfer conveyor which in turn delivers ore to the SAG mill feed conveyor. The SAG mill feed is measured and recorded using a weightometer installed on the SAG mill feed conveyor. The 40’ diameter × 22.5’ EGL SAG mill has a grate discharge and is fitted with a 28 MW motor.

Process water is added to the SAG mill to achieve a slurry solids content of 75% by mass within the mill. Mill cooling water is provided by the mill cooling water pumps operating on a duty/standby configuration. The SAG mill discharge flows over a vibrating screen and the screen oversize is either conveyed to the pebble crushing circuit or to the scats bunker, via a diverter chute.

The pebbles that are diverted to the pebble crusher feed conveyor are conveyed to the pebble crusher surge bin. A weightometer installed on the pebble crusher feed conveyor measures and records pebble crusher feed tonnage. A belt magnet removes ball scats prior to the pebble crusher and discharges the scats onto the scats removal conveyor. Pebbles are withdrawn from the pebble crusher surge bin using a variable speed driven pan feeder, fed through the crusher, and discharged onto the pebble crusher discharge conveyor. The crushed pebble transfer conveyor receives material from the crusher discharge conveyor and returns crushed pebbles to the SAG mill feed conveyor.

Undersize from the SAG mill discharge screen discharges into the SAG mill discharge sump from where it is transferred to the cyclone cluster feed sump. Process water is added to both the SAG mill discharge sump and the cyclone feed sump at a controlled rate to achieve the required slurry solids content at the respective discharge points.

Diluted slurry is pumped to the hydro cyclone clusters using hydro cyclone feed pumps. Overflow slurry from the cyclone clusters (33.2% solids by mass) gravitates to the flotation feed surge tank. Cyclone cluster underflow slurry (75% solids by mass) feeds the ball mill.

The 24’ diameter × 37’ EGL ball mill has an overflow discharge and is fitted with a 14 MW motor and operates in closed circuit with the cyclone clusters. The discharge from the ball mill flows through a trommel screen and discharges into the cyclone cluster feed sump. Trommel screen oversize will be transferred by conveyor to the milling scats bunker.

Spillage within the milling area is contained in a containment area and washed down to the spillage sump, from where it is pumped back into the cyclone cluster feed sump.


Processing

  • Dewatering
  • Hydrometallurgical plant / circuit
  • Filter press plant
  • Flotation

Flow Sheet: Source p.168, 180
Source: Source

Summary:

The NorthMet process plant will consist of an initial beneficiation plant in Phase I, and a hydrometallurgical plant in Phase II. The specific processing steps that will be involved in the hydrometallurgical plant include pressure treatment of concentrates and precipitation of gold and PGMs in separate processes. Additional facilities also include a hydrometallurgical residue facility.

Phase I: The Beneficiation Plant consisting of crushing, grinding, flotation, concentrate thickening and concentrate filtration. The Beneficiation Plant will produce and market concentrates containing copper, nickel, cobalt and precious metals.

Flotation
The overflow from the milling cyclone is pumped to the flotation feed tank. The flotation circuit consists of three separate flotation stages each with a regrind step:

- Bulk Cu-Ni circuit
- Cu-Ni concentrate separation circuit
- Pyrrhotite (Po) circuit.

Concentrate Thickening and Filtration
The three flotation concentrate products are dewatered via 2 stages, thickening followed by filtration. The recovered water from the dewatering stages is returned to the process water tanks for redistribution into the process plant.

The thickened concentrate is then filtered using a filter press to achieve a cake moisture of less than 12.1%.

Concentrate Storage
Front-end loaders transfer the selected filtered concentrate from the product stockpile onto the product transfer conveyors. The concentrate is then discharged into the rail cars via a bin and reversible shuttle conveyor. The transfer of concentrate to the rail cars is done separately so as not to contaminate the individual products.

HYDROMETALLURGICAL PROCESSING
Phase II: In mine year 2, a hydrometallurgical plant is expected to be commissioned to process nickel sulfide and pyrrhotite concentrates, with processing starting in mine year 3. This concentrate stream will be processed through a single autoclave to recover high-grade copper concentrate, and recover the nickel-cobalt hydroxide and precious metals precipitates as by- products.

Hydrometallurgical processing will be used for downstream treatment and enrichment of concentrates. The process involves high pressure and temperature autoclave leaching, followed by solution purification steps to extract and isolate PGMs, precious metals and base metals. All equipment used in the hydrometallurgical process would be located in a dedicated Hydrometallurgical Plant Building.

Once the hydrometallurgical plant becomes operational some of the concentrates produced in the beneficiation plant will be feedstock to the hydrometallurgical process. The feedstock would be a combination of the separate nickel and pyrrhotite concentrates produced by the beneficiation plant. The decision to ship or process concentrates will be based on equipment maintenance schedules, customer requirements and overall project economics.

Recoveries & Grades:

CommodityParameterAvg. LOM
Copper Recovery Rate, % 91.8
Copper Head Grade, % 0.3
Nickel Recovery Rate, % 63.5
Nickel Head Grade, % 0.08
Cobalt Recovery Rate, % 35.9
Cobalt Head Grade, ppm 75
Palladium Recovery Rate, % 78.1
Palladium Head Grade, ppm 0.27
Platinum Recovery Rate, % 73.4
Platinum Head Grade, ppm 0.08
Gold Recovery Rate, % 58.9
Gold Head Grade, ppm 0.04

Projected Production:

CommodityProductUnitsAvg. AnnualLOM
Copper Metal in concentrate M lbs 581,155
Nickel Metal in conc./ doré kt 79
Cobalt Metal in concentrate kt 0.12.8
Palladium Metal in concentrate koz 591,189
Platinum Metal in concentrate koz 14286
Gold Metal in concentrate koz 486
Silver Metal in concentrate koz 48958
Copper Equivalent Metal in concentrate k lbs 2,128,112
Nickel Metal in concentrate kt 4

Operational Metrics:

Metrics
Stripping / waste ratio 1.6 *
Daily ore mining rate 32,000 tons *
Waste tonnes, LOM 348,823 k tons *
Ore tonnes mined, LOM 225,000 k tons *
Total tonnes mined, LOM 573,823 k tons *
Daily processing rate 32,000 tons *
Tonnes processed, LOM 225 M tons *
Annual mining rate 11,600 k tons of ore *
* According to 2018 study.

Reserves at September 1, 2019:

CategoryTonnage CommodityGradeContained Metal
Proven 173,495 k tons Copper 0.288 %
Proven 173,495 k tons Nickel 0.083 %
Proven 173,495 k tons Cobalt 74.21 ppm
Proven 173,495 k tons Palladium 0.27 ppm
Proven 173,495 k tons Platinum 0.075 ppm
Proven 173,495 k tons Gold 0.039 ppm
Proven 173,495 k tons Silver 1.05 ppm
Probable 116,904 k tons Copper 0.288 %
Probable 116,904 k tons Nickel 0.081 %
Probable 116,904 k tons Cobalt 73.56 ppm
Probable 116,904 k tons Palladium 0.256 ppm
Probable 116,904 k tons Platinum 0.076 ppm
Probable 116,904 k tons Gold 0.037 ppm
Probable 116,904 k tons Silver 1.08 ppm
Proven & Probable 290,399 k tons Copper 0.288 % 1.674 B lbs
Proven & Probable 290,399 k tons Nickel 0.083 % 480 M lbs
Proven & Probable 290,399 k tons Cobalt 73.95 ppm 42.9 M lbs
Proven & Probable 290,399 k tons Palladium 0.264 ppm 2.24 M oz
Proven & Probable 290,399 k tons Platinum 0.075 ppm 0.64 M oz
Proven & Probable 290,399 k tons Gold 0.039 ppm 0.33 M oz
Proven & Probable 290,399 k tons Silver 1.06 ppm 8.96 M oz
Measured 351,500 k tons Copper 0.24 %
Measured 351,500 k tons Nickel 0.073 %
Measured 351,500 k tons Cobalt 71 ppm
Measured 351,500 k tons Palladium 0.222 ppm
Measured 351,500 k tons Platinum 0.064 ppm
Measured 351,500 k tons Gold 0.033 ppm
Measured 351,500 k tons Silver 0.88 ppm
Indicated 443,700 k tons Copper 0.23 %
Indicated 443,700 k tons Nickel 0.069 %
Indicated 443,700 k tons Cobalt 68 ppm
Indicated 443,700 k tons Palladium 0.207 ppm
Indicated 443,700 k tons Platinum 0.061 ppm
Indicated 443,700 k tons Gold 0.03 ppm
Indicated 443,700 k tons Silver 0.87 ppm
Measured & Indicated 795,200 k tons Copper 0.234 %
Measured & Indicated 795,200 k tons Nickel 0.071 %
Measured & Indicated 795,200 k tons Cobalt 69 ppm
Measured & Indicated 795,200 k tons Palladium 0.214 ppm
Measured & Indicated 795,200 k tons Platinum 0.062 ppm
Measured & Indicated 795,200 k tons Gold 0.031 ppm
Measured & Indicated 795,200 k tons Silver 0.87 ppm
Inferred 457,700 k tons Copper 0.236 %
Inferred 457,700 k tons Nickel 0.067 %
Inferred 457,700 k tons Cobalt 56 ppm
Inferred 457,700 k tons Palladium 0.225 ppm
Inferred 457,700 k tons Platinum 0.063 ppm
Inferred 457,700 k tons Gold 0.032 ppm
Inferred 457,700 k tons Silver 0.87 ppm

Commodity Production Costs:

CommodityUnitsAverage
Cash costs Copper Equivalent USD 1.79 / lb *
Cash costs Copper USD 0.59 / lb *†
Assumed price Palladium USD 973 / oz *
Assumed price Platinum USD 1,128 / oz *
Assumed price Cobalt USD 20.7 / lb *
Assumed price Nickel USD 7.95 / lb *
Assumed price Copper USD 3.22 / lb *
Assumed price Silver USD 18.9 / oz *
Assumed price Gold USD 1,308 / oz *
* According to 2018 study / presentation.
† Net of By-Product.

Operating Costs:

Units2018
OP mining costs ($/ton milled) USD 4.02 *
Processing costs ($/ton milled) USD 8.66 *
G&A ($/ton milled) USD 0.48 *
Total operating costs ($/ton milled) USD 13.2 *
* According to 2018 study.

2018 Study Costs and Valuation Metrics :

MetricsUnitsLOM Total
Initial CapEx $M USD 1,204
Sustaining CapEx $M USD 220.6
OP OpEx $M USD 806.2
Processing OpEx $M USD 1,948
Total Taxes $M USD 108.3
Gross revenue (LOM) $M USD 6,853
Net revenue (LOM) $M USD 6,339
Pre-tax Cash Flow (LOM) $M USD 1,682
After-tax Cash Flow (LOM) $M USD 1,574
Pre-tax NPV @ 7% $M USD 322
After-tax NPV @ 7% $M USD 0
Pre-tax IRR, % 10.9
After-tax IRR, % 10.3
After-tax payback period, years 7.5

Proposed Heavy Mobile Equipment as of March 26, 2018:
Source: Source p.149
HME TypeModelSizeQuantity
Dozer (crawler) Caterpillar D10 1
Dozer (crawler) Caterpillar D8 1
Dozer (crawler) Caterpillar D9 1
Dozer (rubber tire) 562 HP 2
Drill 2.25 inch 2
Excavator 396 HP 1
Grader Caterpillar 16M 1
Grader Caterpillar 14M 1
Loader Caterpillar 992K 1
Loader (FEL) 22.5 cu. yd 1
Shovel (hydraulic) 36.6 cu. yd 2
Truck (haul) 240 tons 9
Truck (haul) Caterpillar 777G 1
Truck (water) 30000 gallons 1

Mine Management:

Job TitleNameEmailProfileRef. Date
Mine Manager James Tieberg jtieberg@polymetmining.com LinkedIn Feb 22, 2022


Corporate Filings & Presentations:

DocumentYear
Annual Information Form 2020
Press Release 2019
Feasibility Study Report 2018
Technical Report 2013

News:

NewsDate
Court of Appeals Rules Favorably on PolyMet Water Permit January 24, 2022
PolyMet Mining Reports Results for Period Ended September 30, 2021 November 4, 2021
PolyMet Statement on Today's Minnesota Court of Appeals Decision July 19, 2021
EPA decision sets up potential review of PolyMet wetlands permit June 4, 2021
State Supreme Court rules in favor of PolyMet Permit to Mine and dam safety permits April 28, 2021
PolyMet Issues Statement Addressing EPA's Filing on Section 401 Determination March 4, 2021
U.S. District Court Ends Federal Challenge to PolyMet's Water Quality Permit February 16, 2021
PolyMet drilling program results in additions to NorthMet Mineral Resources and Reserves November 19, 2019
Department of Natural Resources declines environmental groups' request to reconsider PolyMet Permit to Mine and dam safety permit August 7, 2019
Minnesota Court of Appeals Upholds Nonferrous Mining Rules for PolyMet NorthMet Project August 5, 2019
Minnesota Issues Last of Its Major Permits For PolyMet Copper-nickel Mine December 20, 2018
Minnesota Issues Permit to Mine for PolyMet Copper-Nickel Mine November 2, 2018

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