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Article

The Kilmar Magnesite Deposits: Evaporitic Metasediments in the Grenville Supergroup, Morin Terrane, Quebec

Department of Geology, Colgate University, Hamilton, NY 13346, USA
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Author to whom correspondence should be addressed.
Minerals 2019, 9(9), 554; https://doi.org/10.3390/min9090554
Received: 10 July 2019 / Revised: 5 September 2019 / Accepted: 7 September 2019 / Published: 14 September 2019
(This article belongs to the Special Issue Minerals of the Southern Grenville Province)
Mesoproterozoic magnesite deposits are found associated with dolomitic marble and intercalated with metasedimentary rocks of the Grenville Supergroup in the granulite facies Morin terrane (Grenville Province, Quebec). This study examines one of the remaining ore deposits exposed on the surface (at the Dobbie mine), and presents stable isotope and mineralogical data for a marine evaporitic origin. The magnesite ore zone has δ18O(Mag) = 25.5 ± 0.4‰ (VSMOW) and δ13C(Mag) = 1.7 ± 0.2‰ (VPDB; n = 7), while surrounding dolomitic marble has δ18O(Dol) = 24.2 ± 0.6‰ and δ13C(Dol) = −0.2 ± 0.7‰ (n = 11). These values are at the high end of the range for other Morin terrane marbles, and this and sharp transitions in stable isotope ratios between lithologies argue for preservation of evaporitic enrichment in δ18O and δ13C. Boron isotope ratios (δ11B = 15.5‰ to 22.7‰) are also consistent with a marine evaporite origin. Identifying evaporitic protoliths in metasedimentary rocks is important for determining pre-metamorphic depositional environments, and in this case links the sedimentary setting of the Morin terrane to the Adirondack Lowlands (New York, NY, USA). The identification of the Kilmar magnesite deposits as evaporitic also has implications for the formation of sedimentary exhalative base metal deposits in the Grenville Supergroup. View Full-Text
Keywords: Grenville Province; Grenville Supergroup; Morin terrane; magnesite; oxygen isotopes; carbon isotopes; boron isotopes Grenville Province; Grenville Supergroup; Morin terrane; magnesite; oxygen isotopes; carbon isotopes; boron isotopes
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MDPI and ACS Style

Peck, W.H.; Eppich, G.R. The Kilmar Magnesite Deposits: Evaporitic Metasediments in the Grenville Supergroup, Morin Terrane, Quebec. Minerals 2019, 9, 554. https://doi.org/10.3390/min9090554

AMA Style

Peck WH, Eppich GR. The Kilmar Magnesite Deposits: Evaporitic Metasediments in the Grenville Supergroup, Morin Terrane, Quebec. Minerals. 2019; 9(9):554. https://doi.org/10.3390/min9090554

Chicago/Turabian Style

Peck, William H., and Gary R. Eppich 2019. "The Kilmar Magnesite Deposits: Evaporitic Metasediments in the Grenville Supergroup, Morin Terrane, Quebec" Minerals 9, no. 9: 554. https://doi.org/10.3390/min9090554

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