Date of Award
Master of Science
Geological and Environmental Sciences
Dr. Joyashish Thakurta
R.V. Krishnamurthy, Ph.D.
Robb Gillespie, Ph.D.
Peter Voice, Ph.D.
Sulfide, Michigan, intrusion, Ni-Cu-PGE, geology
Masters Thesis-Open Access
The Echo Lake Intrusion is located in Houghton and Ontonagon counties in the Upper Peninsula (UP) of Michigan. The intrusion is approximately 200 m below the surface and covers approximately 18 km2 in lateral extent. It is associated with the magmatic activities of a 1.1 Ga geologic event called the Midcontinent Rift. The rift is responsible for the formation of Ni-Cu ± PGE deposits in the Lake Superior Region. Based on its association with the Midcontinent Rift and a Cu and PGE enriched layer, the Echo Lake intrusion is identified as a prospect for an economic magmatic sulfide deposit.
The Echo Lake Intrusion is an ultramafic-mafic intrusion dominated by troctolite, interlayered with peridotite, mafic pegmatoid, olivine gabbro, magnetite gabbro, and anorthosite. Exploratory drilling has identified a platinum group element (PGE) enriched zone within a magnetite gabbro unit with grades up to 1.2 g/t Pt+Pd+Au. The disseminated sulfide minerals observed in this unit might have crystallized from of a sudden change in the oxidation state of of the magma caused by the crystallization of magnetite. Owing to the consequent decrease in fO2 sulfide saturation occurred on a local scale and immiscible sulfide droplets enriched in Pt, Pd, and Cu were separated from the magma. These separated sulfide droplets are found as disseminated sulfide minerals hosted in a magnetite-rich layer.
Koerber, Alexander J., "Geochemical and Petrological Investigation of the Prospective Ni-Cu-Pge Mineralization at the Echo Lake Intrusion in the Upper Peninsula of Michigan, USA" (2018). Masters Theses. 3416.