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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
  • Hydrometallurgical plant / circuit
  • Flotation
Mine Life20 years (as of Jan 1, 2018)
NorthMet Project is part of northeastern Minnesota’s Duluth Complex, one of the world’s largest known undeveloped deposits of copper, nickel and precious metals.

August 05, 2019 - PolyMet Mining, Inc. has completed its Definitive Feasibility Study and received all permits necessary to construct and operate the NorthMet Project.
Latest NewsPolyMet drilling program results in additions to NorthMet Mineral Resources and Reserves     November 19, 2019


Owners

Source: p. 35
CompanyInterestOwnership
PolyMet Mining, Corp. 100 % Indirect
PolyMet Mining Corp. owns 100% of PolyMet Mining, Inc. (PolyMet US), a Minnesota corporation. PolyMet US controls 100% of the NorthMet Project.

Deposit Type

  • VMS
  • 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
Source: Source p.165-179


Processing

  • Hydrometallurgical plant / circuit
  • Flotation

Flow Sheet: 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.

Primary and Secondary Crushing
ROM are delivered to the crushing plant for size reduction of the host rock, making it suitable for further liberation and beneficiation of the target economic metals. Two-stage crushing is used to achieve a final crushed product size of 80% passing 4 in, which is fed into the milling circuit for further liberation of the mineral.

The crushing circuit has a primary crusher feed bin, a gyratory primary crusher, a primary crusher product surge bin, and four gyratory secondary crushers.

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.

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 January 1, 2018:

CategoryTonnage CommodityGrade
Proven 121.849 M tons Copper 0.308 %
Proven 121.849 M tons Nickel 0.087 %
Proven 121.849 M tons Cobalt 74.81 ppm
Proven 121.849 M tons Palladium 0.282 ppm
Proven 121.849 M tons Platinum 0.082 ppm
Proven 121.849 M tons Gold 0.041 ppm
Proven 121.849 M tons Silver 1.11 ppm
Proven 121.849 M tons Copper Equivalent 0.612 %
Probable 132.82 M tons Copper 0.281 %
Probable 132.82 M tons Nickel 0.081 %
Probable 132.82 M tons Cobalt 74.06 ppm
Probable 132.82 M tons Palladium 0.256 ppm
Probable 132.82 M tons Platinum 0.078 ppm
Probable 132.82 M tons Gold 0.037 ppm
Probable 132.82 M tons Silver 1.02 ppm
Probable 132.82 M tons Copper Equivalent 0.559 %
Proven & Probable 254.669 M tons Copper 0.294 %
Proven & Probable 254.669 M tons Nickel 0.084 %
Proven & Probable 254.669 M tons Cobalt 74.42 ppm
Proven & Probable 254.669 M tons Palladium 0.268 ppm
Proven & Probable 254.669 M tons Platinum 0.08 ppm
Proven & Probable 254.669 M tons Gold 0.039 ppm
Proven & Probable 254.669 M tons Silver 1.06 ppm
Proven & Probable 254.669 M tons Copper Equivalent 0.584 %
Measured 237.2 M tons Copper 0.27 %
Measured 237.2 M tons Nickel 0.08 %
Measured 237.2 M tons Cobalt 72 ppm
Measured 237.2 M tons Palladium 0.241 ppm
Measured 237.2 M tons Platinum 0.069 ppm
Measured 237.2 M tons Gold 0.035 ppm
Measured 237.2 M tons Silver 0.97 ppm
Measured 237.2 M tons Copper Equivalent 0.541 %
Indicated 412.2 M tons Copper 0.23 %
Indicated 412.2 M tons Nickel 0.07 %
Indicated 412.2 M tons Cobalt 70 ppm
Indicated 412.2 M tons Palladium 0.21 ppm
Indicated 412.2 M tons Platinum 0.063 ppm
Indicated 412.2 M tons Gold 0.032 ppm
Indicated 412.2 M tons Silver 0.87 ppm
Indicated 412.2 M tons Copper Equivalent 0.47 %
Measured & Indicated 649.3 M tons Copper 0.245 %
Measured & Indicated 649.3 M tons Nickel 0.074 %
Measured & Indicated 649.3 M tons Cobalt 71 ppm
Measured & Indicated 649.3 M tons Palladium 0.221 ppm
Measured & Indicated 649.3 M tons Platinum 0.065 ppm
Measured & Indicated 649.3 M tons Gold 0.033 ppm
Measured & Indicated 649.3 M tons Silver 0.91 ppm
Measured & Indicated 649.3 M tons Copper Equivalent 0.496 %
Inferred 508.9 M tons Copper 0.24 %
Inferred 508.9 M tons Nickel 0.07 %
Inferred 508.9 M tons Cobalt 66 ppm
Inferred 508.9 M tons Palladium 0.234 ppm
Inferred 508.9 M tons Platinum 0.072 ppm
Inferred 508.9 M tons Gold 0.037 ppm
Inferred 508.9 M tons Silver 0.93 ppm
Inferred 508.9 M tons Copper Equivalent 0.489 %

Commodity Production Costs:

CommodityUnitsAverage
Cash costs Copper Equivalent USD 1.79 / oz *
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 *
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


Corporate Filings & Presentations:

DocumentYear
Feasibility Study Report 2018
Technical Report 2013

News:

NewsDate
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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