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Petrogenesis of the 1149 Ma Etoile Suite Mafic Intrusion, Quebec: implications for vanadium mineralisation in Proterozoic anorthosite-bearing terranes

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Iron-titanium-vanadium (Fe-Ti-V) oxide mineralisation is commonly associated with Proterozoic massif-type anorthosites, but the conditions required for their formation remain poorly understood. The Etoile Suite Mafic Intrusion (1149 ± 11 Ma), in the Grenville Province, Quebec (Canada), comprises a layered mafic intrusion that is coeval with nearby massif-type anorthosites. The mafic intrusion consists of troctolite and olivine gabbro cumulates, where magnetite and ilmenite are intercumulus at the base (Zone A) and top (Zone C) but cumulus (<30 modal %) in the centre (Zone B). Towards the base of Zone B, vanadium mineralisation occurs in a 1-km-thick oxide-rich wehrlite horizon, where V-rich titanomagnetite (<1.85 wt% V2O5) and ilmenite form semi-massive oxide layers. From the base to the top of Zone B there is an overall progressive decrease in Anpl, Fool, and Mg#cpx, and in Cr and Ni concentrations of magnetite, albeit with several reversals to more primitive compositions, including one near the base of Zone C. This indicates fractional crystallisation in an open magma chamber. The intrusion crystallised at moderate fO2 (~FMQ 1.1 ± 0.3), resulting in the late crystallisation of V-rich magnetite from a relatively evolved magma. The parental magma was likely a high-Al basalt derived from a depleted mantle source, recording minimal crustal contamination, in contrast to coeval massif-type anorthosites that commonly contain orthopyroxene reflecting higher degrees of crustal contamination. As a result, V mineralisation in noritic anorthosites formed at higher fO2, with early crystallisation of relatively V-poor magnetite, whereas magnetite in troctolitic-olivine gabbroic intrusions crystallised later with higher V contents, due to lower fO2.
Back-scattered electron images (A–D), highlighting the three types of hercynite exsolution textures (see text for description) in Fe-Ti oxides from Zone B of the intrusion. a Example of type 1 hercynite, characterised by a large (~500 μm) grain of granular hercynite in magnetite. Type 2 hercynite lamellae in sandwich-type ilmenite lamellae are also visible (mela-olivine gabbro; RM17; Zone B; 1585 m). b Type 2 hercynite (granular/lamellar hercynite in ilmenite at/near the magnetite contact) (mela-olivine gabbro; RM17; Zone B; 1585 m). c Coarse granular ilmenite interpreted to be of primary origin in contact with magnetite. Contact is marked by a chain of fine granular hercynite exsolutions. A second chain of coarse-grained hercynite within ilmenite may mark the former border between the ilmenite and magnetite. The two chains represent type 2 hercynite. Type 3 hercynite (hercynite intergrowths) is also visible within the magnetite (gabbro; RM24; Zone B; 2813 m). d Multiple generations of type 2 hercynite at/near the border of a secondary ilmenite granule. The ilmenite granule forms extensions into the host magnetite. Type 3 hercynite (hercynite intergrowths) is also visible within the magnetite (leucogabbro; RM32; Zone B; 2752 m). e Enlarged element map of RM6 reveals small-scale exsolution features in magnetite not visible in the large-scale element map. Two types of hercynite (type 2 and type 3; described in the main text) are visible. The concentration of ulvöspinel intergrowths is relatively high in this sample, and the distribution of ulvöspinel is not homogenous: progressively less ulvöspinel is present towards the contact with ilmenite, and there is a ~10-µm-wide domain around the disc-shaped hercynite intergrowths that is relatively free of ulvöspinel. f High-resolution element map of part of RM13, displaying several exsolution features in detail. For example: (1) the near absence of cloth-textured ulvöspinel compared to the oxide-rich wehrlite; (2) the reduced amount of type 3 hercynite (hercynite intergrowths) in the vicinity of type 1 hercynite (granular hercynite in magnetite), as well as in the vicinity of the sandwich-type ilmenite lamella; (3) the somewhat different appearance of type 3 hercynite (hercynite intergrowths), which, in this sample, is characterised by hercynite lamellae in two planes of the magnetite crystal lattice rather than only one plane. Abbreviations: mt, magnetite; ilm, ilmenite; hc, hercynite
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Vol.:(0123456789)
Mineralium Deposita (2025) 60:323–349
https://doi.org/10.1007/s00126-024-01298-9
ARTICLE
Petrogenesis ofthe1149Ma Etoile Suite Mafic Intrusion,
Quebec: implications forvanadium mineralisation inProterozoic
anorthosite‑bearing terranes
RandolphP.Maier1 · SarahA.S.Dare1· WilliamD.Smith2,3
Received: 2 January 2024 / Accepted: 9 July 2024 / Published online: 10 August 2024
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024
Abstract
Iron-titanium-vanadium (Fe-Ti-V) oxide mineralisation is commonly associated with Proterozoic massif-type anorthosites,
but the conditions required for their formation remain poorly understood. The Etoile Suite Mafic Intrusion (1149 ± 11Ma),
in the Grenville Province, Quebec (Canada), comprises a layered mafic intrusion that is coeval with nearby massif-type
anorthosites. The mafic intrusion consists of troctolite and olivine gabbro cumulates, where magnetite and ilmenite are
intercumulus at the base (Zone A) and top (Zone C) but cumulus (<30 modal %) in the centre (Zone B). Towards the base of
Zone B, vanadium mineralisation occurs in a 1-km-thick oxide-rich wehrlite horizon, where V-rich titanomagnetite (<1.85
wt% V2O5) and ilmenite form semi-massive oxide layers. From the base to the top of Zone B there is an overall progressive
decrease in Anpl, Fool, and Mg#cpx, and in Cr and Ni concentrations of magnetite, albeit with several reversals to more primi-
tive compositions, including one near the base of Zone C. This indicates fractional crystallisation in an open magma chamber.
The intrusion crystallised at moderate fO2 (~FMQ 1.1 ± 0.3), resulting inthelate crystallisation of V-rich magnetite from a
relatively evolved magma. The parental magma was likely a high-Al basalt derived from a depleted mantle source, recording
minimal crustal contamination, in contrast to coeval massif-type anorthosites that commonly contain orthopyroxene reflect-
ing higher degrees of crustal contamination. As a result, V mineralisation in noritic anorthosites formed at higher fO2, with
early crystallisation of relatively V-poor magnetite, whereas magnetite in troctolitic-olivine gabbroic intrusions crystallised
later with higher V contents, due to lower fO2.
Keywords Fe-Ti-V oxide mineralisation· Layered intrusion· Magnetite· Oxygen fugacity· Proterozoic massif-type
anorthosite· Trace elements
Introduction
Magmatic iron-titanium-vanadium (Fe-Ti-V) oxide deposits
are the most important source of Ti and V globally (Kelley
etal. 2017; Woodruff etal. 2017), but the processes required
to accumulate oxides into massive layers/lenses remains a
debate (Cameron 1980; Wilson etal. 1996; Robinson etal.
2003; Charlier and Grove2012; Charlier etal. 2015; Maier
etal. 2013; Zhou etal. 2013; Howarth and Prevec 2013). Fe-
Ti-V deposits can be subdivided into two types, namely those
hosted in layered mafic-ultramafic intrusions (e.g., Bush-
veld Complex, South Africa: Klemm etal. 1985; Panzhihua,
China: Pang etal. 2008), and those hosted in Proterozoic
massif-type anorthosites (e.g., Lac-Saint-Jean: Grant 2020;
Northwest River: Valvasori etal. 2020; Suwalki: Charlier
etal. 2009). Layered mafic-ultramafic intrusions are typically
associated with large igneous provinces (Ernst etal. 2019;
Smith and Maier 2021; Latypov etal. 2023) which, in turn,
tend to be associated with mantle plumes and intraplate tec-
tonic settings (Bryan and Ernst 2008). As a result of differen-
tiation, the intrusions display a wide range of rock types, rang-
ing from ultramafic (peridotite, pyroxenite), to mafic (norite,
gabbronorite, troctolite, anorthosite), and to more evolved
Editorial handling: E. Mansur
* Randolph P. Maier
randolph.maier@gmail.com
1 Département des Sciences Appliquées, Université du Québec
à Chicoutimi (UQAC), Saguenay, QuébecG7H2B1, Canada
2 Department ofEarth Sciences, Herzberg Laboratories,
Carleton University, Ottawa, OntarioK1S5B6, Canada
3 School ofEarth & Environmental Sciences, Cardiff
University, CardiffCF103AT, UK
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... The PGE budget inherited from the accretion of the Earth is thought to have been largely stripped from the silicate mantle and crust during the formation of the metallic core (Holzheid et al. 2000). Hence, most of the PGE now concentrated in layered intrusions were originally introduced to their mantle sources by a late veneer following the core formation (Maier et al. 2009). This extraterrestrial input was spatially erratic and imposed a first-order control on the PGE contents of magmas prior to the mantle-wide homogenization of this newly inherited material, which was possibly complete by 2.9 Ga (Maier et al. 2009). ...
... Hence, most of the PGE now concentrated in layered intrusions were originally introduced to their mantle sources by a late veneer following the core formation (Maier et al. 2009). This extraterrestrial input was spatially erratic and imposed a first-order control on the PGE contents of magmas prior to the mantle-wide homogenization of this newly inherited material, which was possibly complete by 2.9 Ga (Maier et al. 2009). Therefore, it is possible that the oldest layered intrusions in the geological record could have originated from mantle sources that were either strongly depleted or enriched in the PGE compared to the mantle that existed from the Neoarchean onward. ...
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