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Minerals 2019, 9(1), 21; https://doi.org/10.3390/min9010021

PGE-Enrichment in Magnetite-Bearing Olivine Gabbro: New Observations from the Midcontinent Rift-Related Echo Lake Intrusion in Northern Michigan, USA

Department of Geological and Environmental Sciences, Western Michigan University, 1903 W Michigan Ave, Kalamazoo, MI 49008, USA
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Received: 25 November 2018 / Revised: 13 December 2018 / Accepted: 24 December 2018 / Published: 29 December 2018
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Abstract

The Echo Lake intrusion in the Upper Peninsula (UP) of Michigan, USA, was formed during the 1.1 Ga Midcontinent Rift event in North America. Troctolite is the predominant rock unit in the intrusion, with interlayered bands of peridotite, mafic pegmatitic rock, olivine gabbro, magnetite-bearing gabbro, and anorthosite. Exploratory drilling has revealed a platinum group element (PGE)-enriched zone within a 45 m thick magnetite-ilmenite-bearing olivine gabbro unit with grades up to 1.2 g/t Pt + Pd and 0.3 wt. % Cu. Fine, disseminated grains of sulfide minerals such as pyrrhotite and chalcopyrite occur in the mineralized interval. Formation of Cu-PGE-rich sulfide minerals might have been caused by sulfide melt saturation in a crystallizing magma, which was triggered by a sudden decrease in fO2 upon the crystallization and separation of titaniferous magnetite. This PGE-enriched zone is comparable to other well-known reef-like PGE deposits, such as the Sonju Lake deposit in northern Minnesota. View Full-Text
Keywords: Echo Lake; Midcontinent; palladium; platinum; magnetite; gabbro Echo Lake; Midcontinent; palladium; platinum; magnetite; gabbro
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Koerber, A.J.; Thakurta, J. PGE-Enrichment in Magnetite-Bearing Olivine Gabbro: New Observations from the Midcontinent Rift-Related Echo Lake Intrusion in Northern Michigan, USA. Minerals 2019, 9, 21.

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