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Project Review: PolyMet’s NorthMet Copper-Nickel-PGM Deposit in Minnesota, USA

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 has significantly advanced the project and has been working it continuously since that time. The proposed mine at the NorthMet project has been under environmental review for nearly 7 years.

The latest mineral reserve estimate (dated 2007) for the NorthMet deposit is as follows:

The most recent (2007) mineral reserve estimate of the NorthMet deposit

Based on current commodity prices and assuming 100% recovery, the copper equivalent for the total resource is roughly 0.66% CuEq. Note that the units are in Mst (million short ton).

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.


Local deposits within the Duluth Complex
Local deposits within the Duluth 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.


A stratigraphic (vertical slice) of the Polymet deposit
A stratigraphic cross-section (vertical slice) of the NorthMet deposit


Polymet’s NorthMet deposit has been stuck in the environmental permitting process for several years. 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. The company is hoping to have some of the major permits required to begin construction by the end of the year.

PolyMet has spent decades on this project and 7 years on the environmental assessment alone. While they’ve made significant progress, it’s been a long and winding road. They’re not alone. According to the Behre Dolbear Group’s most recent report on state of the mining industry, US miners (outside of Nevada, Arizona and a few other mining friendly states) should expect to wait 7-10 years for project approval – the longest in the world. Compare that to Australia or Canada where the process can take 1 or 2 years.

So what makes for a mining friendly state? Or country? Perhaps the term “mining friendly” should be changed to “mining reliant”. Jurisdictions that rely on mining for a significant contribution to their GDP are more likely to give miners an easier time getting started. In Nevada, mining is second (behind tourism) as the most important industry. In Arizona, mining supports more than 50,000 jobs and almost $5 billion in worker income. Fifteen percent of Canada’s exports are minerals and metals (mostly to the US) and in Australia the mining sector contributes 19% to the total GDP. Mining friendly? Damn right.

Further Reading

Layered Mafic Intrusions: Our largest Source of Platinum and Palladium

Commodity Overviews: Platinum Group Metals, Nickel, Copper

Copper Equivalent Calculator

2014 Ranking of Countries for Mining Investment (Behre Dolbear Group)

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3 thoughts on “Project Review: PolyMet’s NorthMet Copper-Nickel-PGM Deposit in Minnesota, USA”

  1. Pingback: NioCorp Upgrades Niobium Resource at Elk Creek | Geology for Investors

  2. 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.

  3. 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.

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