Geologic tour of Lake Superior

Map of my route from Ann Arbor to Terrace Bay area

After classes ended on April 29th I embarked on an amazing trip around Lake Superior that took me on two mine visits, two field trips, and a geology conference in 9 days. I met some pretty great people, saw awesome rocks, and learned from many geologists who are experts in their industry. Here’s the breakdown of the trip:

Eagle Mine – Marquette, MI

I left Ann Arbor on Thursday, May 3rd, and drove north to the Upper Peninsula to Marquette, MI. My adviser, Adam, had connected me with the Wiitala’s who live just outside Marquette on Lake Superior and they warmly welcomed me to stay with them. The next morning I met Bob Mahin, the Exploration Manager at Eagle Mine, bright and early at 6:30am to get started with my tour of the mine. I had met Bob at PDAC in March, and he is also our U-Michigan Society of Economic Geology chapter’s industry sponsor. Eagle is located less than an hour northwest of Marquette and is an underground high-grade copper and nickel mine – currently the only operating nickel mine in the US! Production began at Eagle in 2014 and is expected to continue until 2023.

Bob and I underground at Eagle Mine

After going through the safety training, Bob told me all about the geology of the region and the history of the mine. As an underground operation, the surface footprint of Eagle is not big. I learned about how Eagle complies with the strict environmental regulations by keeping dust levels low, washing every semi before leaving the facility, and treating every drop of water that is sprayed (or falls) inside the fence. Then we suited up and joined one of the geologists for a trip underground. We drove down into the rock through “the portal” and after a series of switch-backs in the steep tunnel we parked in one of the off-shoots from the main road to go examine the rocks. The mineralization consists of massive, semi-massive, and disseminated copper-nickel sulfides. The massive sulfide portion of the deposit is almost entirely composed of the ore minerals – pentlandite and chalcopyrite – and is exactly what you want to find as an exploration geologist because of the high proportion of ore minerals to regular rock. It was easy to spot the massive sulfide contact with the regular country rock, with the deposit grading from massive – semi-massive – disseminated sulfides at the contact. After being blasted apart, the ore is loaded on to heavy-duty trucks and hauled up to the surface where it is stored before being loaded on to semi trucks to be transported to the processing plant just outside Marquette. There the rock is crushed into fine pieces and the copper and nickel minerals separated into two piles using a process called floatation, which essentially uses different chemicals to physically separate the minerals based on density and wetting properties. Eagle then sells these fine mineral powders to companies who further extract the elemental copper and nickel for industrial or technological purposes. It was so cool to be underground, see the ore, and learn about the mining process.

After returning to the surface Bob took me to the offices where he and the other geologists work in Marquette. I met the people who log the core coming out the ground to explore for more mineralized zones, model the geochemistry of the deposit from the assays, and come up with new ways to find more copper and nickel ore. It was a really great day at Eagle and I can’t wait to go back!

PolyMet Mine – Hoyt Lakes, MN

Looking at drill core from the NorthMet Deposit

My next stop was the PolyMet Mine in northeast Minnesota, where I met with chief geologist Andrew Ware to learn about the NorthMet Deposit. I also met Andrew at PDAC, although I had met him previously on my very first geology field trip in 2013 when we toured PolyMet as part of our North Shore geology field trip at NDSU. PolyMet is not in operation yet but received all the necessary permits to mine this past spring and are hoping to start mining next year. Like Eagle Mine, PolyMet is a copper-nickel deposit but will be an open pit instead of underground. It will use facilities already in place from iron mining in the same area, which shut down in 2001. The deposit itself is much bigger than Eagle, but the mineralization is all disseminated so it’s not as high-grade as Eagle.

I talked with Andrew about the geology of the Duluth Complex, which are the rocks that host the copper-nickel mineralization. I then got to examine over 500 feet of core from the deposit and really see what the rocks and minerals look like that host the ore. After only reading about those things it was great to actually lay eyes on everything! Then we drove out to the small outcrop of rocks that will be start of mining. As an open pit, rock will be blasted and loaded onto semi’s and railroad cars to be transported to the processing facility that is on site, where they will be crushed and separated in the same process as at Eagle. The pit will extend to about 700 feet below the current surface with a mine life of around 20 years.

Institute on Lake Superior Geology conference – Terrace Bay, Ontario

Examining a road cut of exposed rocks on one of the ILSG geology field trips.

The final stop on my Lake Superior geology tour was on the Canadian shore in Terrace Bay, ON. The Institute on Lake Superior Geology (ILSG) is an annual conference that brings researchers, students, professors, government, and industry geologists together who are working on anything related to the geology surrounding Lake Superior. The meeting location changes every year but is always somewhere near the lake in Ontario, Minnesota, Wisconsin, or Michigan. This year about 150 geologists converged for two days of conference – May 8-9 with speakers giving presentations – and two days of geology field trips in the area bracketing the conference. My goal in attending was to meet as many people as I could and learn about the geology of the Duluth Complex in northeast Minnesota from people who have studied it for their entire careers because I would like to start a project working on rocks in the area in the next couple years.

My friend, Cheyanne, and I in front of my poster at the ILSG poster session

I arrived the evening of May 6th and went on the Nipigon area field trip the next day. We saw leuco-granites, 1.4 billion year old sedimentary rocks, migmatite – partially melted rock – , pegmatites – rocks that have really big mineral crystals – , and the unconformable contact between the sedimentary rocks and the underlying granite. The next two days were filled with many talks from a variety of geologists on lots of topics. It’s always great to go to small, intimate conferences because you really get to know most of the people there. I also presented my research at the poster session where I talked about my current project. The last day – May 10 – was the last field trip to the Coldwell Alkalic Complex near Marathon, ON. Seeing those rocks was super cool as the complex is the largest alkaline complex in North America. We saw really cool igneous textures, evidence for magma mixing, mafic intrusions with layers, and more pegmatites with huge crystals. I’m definitely inspired to work on Duluth Complex rocks after hearing about how cool they are and have a couple of ideas for projects to think about.

Overall I had a wonderful tour around Lake Superior and met so many nice, awesome people along the way. It was such a great time and worth every one of the 1,900 miles!

Standing in front of a sill that intruded 1.4 billion year old sedimentary rocks near Nipigon, Ontario