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Open AccessArticle

An Integrated Model for Ilmenite, Al-Spinel, and Corundum Exsolutions in Titanomagnetite from Oxide-Rich Layers of the Lac Doré Complex (Québec, Canada)

1
Sciences de la Terre, Université du Québec à Chicoutimi, Chicoutimi, QC G7H 2B1, Canada
2
IOS Services Géoscientifiques, Chicoutimi, QC G7J 3Y2, Canada
*
Author to whom correspondence should be addressed.
Minerals 2018, 8(11), 476; https://doi.org/10.3390/min8110476
Received: 28 September 2018 / Revised: 16 October 2018 / Accepted: 17 October 2018 / Published: 24 October 2018
(This article belongs to the Special Issue Spinel Group Minerals)
The titanomagnetite of the Lac Doré Complex, an Archean layered intrusion that is located in the Abitibi greenstone belt in Québec (Canada), contains a wide variety of exsolution textures, which are the remnants of a complex cooling history. In the present study, we reconstitute the decomposition stages of the original solid solution in order to explain the formation of ilmenite, Al-spinel (hercynite and gahnite), and corundum exsolutions in magnetite. This was conducted through a detailed mineralogical and textural examination and in situ determination of mineral chemistry. Our investigation reveals two discrete types of ilmenite exsolutions, which are ascribed, respectively, to the oxidation of ulvöspinel at temperatures above and below the magnetite-ulvöspinel solvus. Exsolutions of Al-spinel result from either a decrease in the solubility of the (FeZn)Al2O4 components upon cooling, or local excesses of Al and Zn due to the removal of ulvöspinel during the early oxidation. The origin of corundum is ascribed to the oxidation of pre-existing hercynite exsolutions. The trace element composition of the titanomagnetite indicates stratigraphic reversals in Cr, Mg, Co, Ti, and Si and important changes in redox conditions. We interpret this as a direct consequence of a major event of magma chamber replenishment, which strongly influenced the distribution of exsolutions. View Full-Text
Keywords: exsolution; gahnite; ilmenite; spinel; titanomagnetite; ulvöspinel; Lac Doré Complex exsolution; gahnite; ilmenite; spinel; titanomagnetite; ulvöspinel; Lac Doré Complex
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Arguin, J.-P.; Pagé, P.; Barnes, S.-J.; Girard, R.; Duran, C. An Integrated Model for Ilmenite, Al-Spinel, and Corundum Exsolutions in Titanomagnetite from Oxide-Rich Layers of the Lac Doré Complex (Québec, Canada). Minerals 2018, 8, 476.

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