August 24, 2026

Travel Notes & the Copper Deposits of Michigan’s UP

Introduction

Figure 1 – Former Quincy Mine, Michigan Upper Penninsula

We returned from our vacation road trip August 19th. While it’s great to travel, it’s also good to come home again. Full acknowledgement of the hospitality of the Americans we met along the way – a great people!

On August 17th, after visiting the Canadian Bushplane Heritage Centre, we entered the USA at Sault St. Marie. We did some shopping and then drove on to Ontanagon MI for the night. The next day we drove north on the Keweenaw Peninsula up to Copper Harbor, it’s a beautiful drive on its own. We also stopped to visit a few of former copper mines at the former Adventure Mine, Quincy Mine and Delaware Mine. I’ll summarize the geology of the copper deposits of the Michigan Upper Penninsula (UP) below.

After visiting the Keweenaw Peninsula, we drove on to to Duluth MN, through the region called the Iron Range, where the largest producers of iron ore in the USA are found. These deposits are Archean and Proterozoic aged banded iron formations. I discussed the Mesabi Iron Range deposits in a previous blog post, June 6, 2022. Here are links to recent papers, from 2023 and 2025, on the subject.

On the way home on August 19th, we drove through the Boundary Waters (Rainy River) area of Minnesota. Along the way, we heard on the radio that Minnesota Governor Tim Walz issued an executive order moves to block copper mining near the Boundary Waters.

History and Geology of Copper in the Michigan Upper Penninsula

Figure 2 – Native Copper from the Keweenaw Peninsula, MI
Credit: James St. John, Creative Commons Attribution 2.0 Generic license

History

Copper mining in Michigan’s Keweenaw Peninsula has a long history, going back some 6,500 years or so to the Old Copper Culture of America’s first people (if you like videos, check out this one from Ancient Americas - Old Copper Culture: North America's Forgotten Metal Workers). Native copper, natural copper metal, occurs in the Keweenaw Peninsula and the ancient ones dug it up to make spearheads, axes, fishhooks and jewellery. In addition to their utilitarian value, copper goods were also prestige items traded throughout the Great Lakes region. For unknown reasons, the production of copper goods ceased around 1,000 BC.

Figure 3 - Copper Mining in Michigan
Credit: Wikipedia, Copper mining in Michigan
Creative Commons Attribution 4.0 International license

The arrival of European explorers and settlers led to industrial scale mining of the Keweenaw copper deposits beginning around 1844. The original mines focused on extracting native copper from copper-filled fissures and stratiform native copper deposits. These include the Adventure Mine, Calumet Mine, Central Mine, Dana Mine, Nonesuch Mine, Northwestern Mine, Quincy Mine, Winthrop Mine and the White Pine Mine.

All these original mines were closed by 1970. More recent developments, focusing on exploiting volcanogenic metal sulphide deposits include the Back Forty Mine and the Eagle Mine. The Copperwood Mine project is focused on recovering native copper.

Geology

Figure 4 - Midcontinent Rift of North America
Credit: USGS, Communications and Publishing, 2018, public domain

The origin of the copper deposits in the Keweenaw Peninsula lies in the development of a failed tectonic rift, the Midcontinent Rift of North America, approximately 1.15 to 1.0 billion years ago (Ga) during the Mesoproterozoic Era. This structure extends in an arc from near Wichita KS, north through the Keweenaw Peninsula to Nipigon ON, and then south to Sault St. Marie and along the west side of the Michigan Basin to Detroit MI. Most of the structure is buried beneath Phanerozoic deposits but is exposed in Minnesota, Wisconsin, Michigan, and Ontario.

Figure 5 – Geology of the Keweenaw Penninsula
Credit: Figure 2 in Bornhorst & Mathur, 2017, Open Access Information

In the Keweenaw Peninsula, the Midcontinent Rift is filled with more than 25 kilometres (km) of dominantly subaerial basalt lava flows overlain by a succession of clastic sedimentary rocks about 8 km thick. About 5 km of the stratigraphic section in the Keweenaw Peninsula is the Portage Lake Volcanics which hosts the economic native copper deposits.

So how do you get native copper? The most common deposits of copper are associated with volcanic rocks such as those found in volcanogenic metal sulphide deposits. While there are many theories on the formation of native copper, the background to these theories includes the following:

The copper was probably originally deposited in volcanogenic metal sulphide deposits;
Some of the copper sulphides were eroded out into stratiform deposits;
Subsequent metamorphism essentially smelted the copper in place; and
Unless exposed to oxygen, the native copper would remain in place unaltered.

There is a lot more that you can read on the copper deposits of the Keweenaw Peninsula, you can start by following the links above. A few good articles include:

B. S. Butler and W. S. Burbank, 1929, The copper deposits of Michigan, USGS Professional Paper 144, https://doi.org/10.3133/pp144 (the classic paper on the subject)

A. Brown, 2006, Genesis of Native Copper Lodes in the Keweenaw District, Northern Michigan: A Hybrid Evolved Meteoric And Metamophogenic Model, Economic Geology (2006) 101 (7): 1437–1444. https://doi.org/10.2113/gsecongeo.101.7.1437

T. J. Bornhorst and R. Mathur, 2017, Copper Isotope Constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA, Minerals 2017, 7, 185. https://doi.org/10.3390/min7100185 (a more recent discussion on the deposits)

P. Brandes, 2020, Geology of the Keweenaw Peninsula, Michigan, Mindat.org, https://www.mindat.org/article.php/255/Geology+of+the+Keweenaw+Peninsula%2C+Michigan?__cf_chl_tk=MsFt5icKalMTpV.yz_tTzvuTKiLmPkvKy8jM7aX9tf8-1787235378-1.0.1.1-M7k3LsCdofNIocIR6DOgK6mnpM7la8DTg.t.3Pw1MOU (a really good summary)

I’ll wrap it up there.

Standard Caveat

J. Robert Oppenheimer on freedom and scientific inquiry

The purpose of my weblog postings is to spark people's curiosity in geology. Don't entirely believe me until you've done your own research and checked the evidence. If I have sparked your curiosity in the subject of this posting, follow up with some of the links provided here. If you want to, go out into the field and examine some rocks on your own with the help of a good field guide. Follow the evidence and make up your own mind.

In science, the only authority is the evidence.