Our University of Michigan Society of Economic Geologists Student Chapter (U-M SEG) went on a field trip to tour the geology around Marquette, MI, in the Upper Peninsula November 7-9th, 2019. Our main motivation was to tour the Eagle Cu-Ni Mine with our SEG industry sponsor, Bob Mahin, but we also had a great time exploring other great stops to check out the rocks in the area. Four U-M grad students attended: Maria, Justin, Chrissie, and I.
We departed Ann Arbor in the early afternoon on Thursday, November 7th and arrived at our hotel in Marquette later that evening. Early the next morning we drove to the mine site and met Cody Suits, a member of the Eagle exploration team for more than a decade, to gear up for the underground tour at the mine site. Andrew Vaughn, Jonathan Dale, and Cody took us underground to show us how mining in the subsurface works and give us perspective on the mineralization styles and ore minerals. We saw the contact between the massive, semi-massive, and disseminated sulfide mineralization and the host rock contact with the ore body,. We had the opportunity to collect small samples and tour an underground emergency O2 refuge safety chamber. We learned about the actual steps involved in mining out a stope and back-filling with a combination/mixture of cement and gangue rock. After the underground tour Jonathan Dale showed us his ore control workflow and model development for some insight into the daily responsibilities of a senior ore control geologist at Eagle. We then visited the core shack to view the Eagle ore mineralization at various depth increments from the drill hole perspective.
After leaving the mine site of Eagle, we drove back to Marquette and met with Dan Wiitala, co-founder of the North Jackson Environmental Science and Engineering Company. The North Jackson Company has been conducting environmental and hydrological monitoring of the Eagle Mine site since 2002 and has collected an extensive hydrogeological/geochemical database of local water levels of the Salmon River that runs adjacent to the mine site. Dan and another hydrologist at North Jackson Company, Forrest Gilfoy, gave a short presentation on how they monitor the environmental impacts of the mine and also provided career advice from the environmental consulting side of economic geology. That same evening we attended the meeting of the Society for Secondary Enrichment, led by Eagle Mine’s Exploration Manager and our U-M SEG chapter industry sponsor Robert Mahin. This monthly meeting brings together geologists from across the Upper Peninsula and was a fantastic networking opportunity for U-M students. We talked with employees of the Humboldt Mill, including the current Mill Manager, where the and learned about how they process the ore from Eagle Mine. We also met an exploration geologist with experience in Nevada Au mines and other projects in the Upper Peninsula and Wisconsin.
On Saturday, November 9th, we embarked on a geology tour with Bob Mahin to explore the amazing outcrops in the Marquette area. We first visited an outcrop of 2.7 Ga pillow basalts exposed right on the lake shore, some of which were polished smooth by glaciers. Then we headed to the Black Rocks area on Presque Isle, which is an ultramafic intrusion in Jacobsville Sandstone deposited during the Mid-Continent Rift around 1.1 Ga. Our favorite stop was the phenomenal outcrop of 1.8 Ga banded iron formation of the Nagaunee Formation on Jasper Knob in Ishpeming, MI. The folded, contorted alternating layers of magnetite and jasper were a highlight of the trip, and we lingered at the outcrop despite freezing temperatures! We drove back Sunday and are now looking forward to planning another geology field trip to the UP to tour the copper mineralization on the Keweenaw Pensinula!