Date of Award

4-2018

Degree Name

Master of Science

Department

Geological and Environmental Sciences

First Advisor

Dr. Joyashish Thakurta

Second Advisor

R.V. Krishnamurthy, Ph.D.

Third Advisor

Robb Gillespie, Ph.D.

Fourth Advisor

Peter Voice, Ph.D.

Keywords

Sulfide, Michigan, intrusion, Ni-Cu-PGE, geology

Access Setting

Masters Thesis-Open Access

Abstract

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.

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