The NorthMet deposit is located in northeastern Minnesota,USA and was discovered in 1969 by US Steel. The property was acquired by Fleck resources in 1989 who changed their name to the PolyMet mining corporation in 1998. Polymet entered into a 50-50 joint venture with Teck Resources, forming NewRange Copper Nickel LLC. Polymet was aquired by Glencore later that year, leaving NewRange Copper Nickel LLC, and therefore NorthMet, 50% owned by Teck and 50% Glencore.
The latest mineral reserve estimate (dated 2007) for the NorthMet deposit is as follows:
2022 proven and probable reserves stood at 249.2 Mt at 0.284% copper, 0.08% nickel, and 0.38 g/t PGE+gold.
Regional Geology
The Northmet deposit is part of the Duluth Complex, a large layered mafic intrusion and part of the Precambrian Superior province. The complex formed approximately 1.1 to 1.2 billion years ago as the North American craton began to rift (split) apart. As the crust grew thinner, large cracks formed that allowed the underlying magma to rise to the surface. There are 11 known copper-nickel-pgm deposits along the western edge of the complex.
Deposit Geology
The project area consists of ultramafic rocks known as trocolities. These types of rocks formed at very high temperatures and are composed of silicate minerals such as olivine, plagioclase and minor amounts of pyroxene. Polymet geologists have defined several layers of trocolite within the northmet deposit that host metal-bearing sulfide minerals. The primary sulfides located within the deposit include chalcopyrite and cubanite (both copper-iron sulfides), pyrrhotite (iron sulfide) and pentlandite (nickel-iron sulfide). The diagram below shows a simplified cross section of the layered intrusion. Ore minerals are most abundant throughout Unit 1 of the NorthMet deposit. Other zones of mineralization occur in Units 2 through 7 associated with the “ultramafic” and “magenta” zones.
Discussion
The NorthMet deposit has been stuck in the environmental permitting process for decades. The US EPA (Environmental Protection Agency) initially gave the project an EU-3 status declaring it environmentally unacceptable and recommended numerous changes. One of the primary issues was the company’s plan to handle tailings and the potential for acid mine drainage. Acid mine drainage can occur when water and air react with sulfur and metals in the waste rock to create acids.
In 2012, the company appointed Jon Cherry, an experienced environmental engineer, to guide them through the permitting process. In early 2014, following the submission of an updated and considerably improved plan, the project was given an upgraded status of EC-2 “Environmental Concerns” – a giant leap from the previous rating but still not a green light. PolyMet acquired a number of permits in late 2018. In 2023, after 17 years of permitting, the US Army Corps of Engineers revoked part of the project’s water permit. NewRange is reportedly reviewing its approach to permitting.
PolyMet spent decades on this project and 17 years on the environmental assessment alone. While they’ve made significant progress, it’s been a long and winding road. They’re not alone. US and Canadian miners should expect to wait 7-10 years for project approval – if they’re lucky. Despite promises to the contrary, ie the much-hyped “critical minerals” strategy, permitting and legal issues have made building mines, especially large ones, outside of a few mining-friendly jurisdictions somewhere between difficult and impossible. In the meantime strategic rivals (mainly China) have taken the opportunity to monopolize supply chains and control commodity prices; a classic case of ‘you snooze, you lose.’
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Polymet has completed its FEIS and recieved its adequacy decision from the Minnesota regulators. It has began the permitting phase as of 4/18/16.
Production is expected to begin 2018 some time making this project a 12 year from feasibility – FEIS – Permitting to production. Mining friendly everywhere is morphing into environmentally ‘responsible’, (especially cu-ni pgm) none more than Minnesota.