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Petrogenesis of Fe-Ti-P mineral deposits associated with Proterozoic anorthosite massifs in the Grenville Province: insights from oxide and apatite trace-element geochemistry at Lac à l’Orignal, Quebec, Canada

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Pedro Miloski
Pedro Miloski
Sarah A. S. Dare at Université du Québec à Chicoutimi
Sarah A. S. Dare
Caroline-Emmanuelle Morisset
Caroline-Emmanuelle Morisset
Caroline-Emmanuelle Morisset
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Joshua Davies at University of Quebec in Montreal
Joshua Davies
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Abstract and Figures

Proterozoic anorthosite massifs can host significant amounts of critical and strategic metals such as Ti, V, and P, associated with magmatic Fe-Ti oxides and apatite. Yet their petrogenesis is much less understood than Fe-Ti-V-P deposits hosted in layered intrusions within large igneous provinces. Several mineralized lenses of Fe-Ti-P outcrop near the border of the 1080 (±2) Ma Vanel and the 1016 (±2) Ma Mattawa Anorthosite Massifs, in the Central Grenville Province, Quebec, Canada. For example, the Lac à l’Orignal Fe-Ti-P deposit, hosted in the Vanel Anorthosite near the northern border of the Mattawa Anorthosite, comprises a lenticular structure of oxide apatite norite (OAN) with thin layers of apatite-bearing anorthosite and minor amounts of nelsonite (massive Fe-Ti oxides and apatite), indicating accumulation by density differences. Oxide settling generated the melanocratic OAN cumulates and nelsonite. Plagioclase flotation generated the leucocratic apatite-bearing anorthosite layers. The mineralization is dominated by hemo-ilmenite, accompanied by apatite and a minor amount of magnetite at the borders, whereas the core is dominated by ilmenite, magnetite, and apatite. In-situ U-Pb dating of magmatic zircon indicates that the Lac à l’Orignal deposit is a multistage intrusion with two different crystallization ages between the younger core (993 ± 13 Ma) and the older upper border (1069 ± 12 Ma) of the intrusion. These ages are similar to those of nearby anorthosite-massifs (Mattawa and Vanel Anorthosites, respectively). In-situ trace element analysis of plagioclase, apatite and oxides, by laser ablation ICP-MS, reveals subtle variations in certain trace elements (e.g., Cr, Ni, V) related to differentiation under relatively high-fO2 conditions (FMQ = +0.9 to +1.7). Calculated melt compositions from apatite indicate a similar parental magma for both the border and core that matches the composition of high-Fe-Ti-P ferrodiorite dykes at Lac à l’Original. This high-Ti-P ferrodiorite magma was probably residual after anorthosite formation. Sub-solidus inter-oxide equilibration modified the original composition of the different cumulates in the intrusion. The absence of extensive massive oxide cumulates and the presence of higher amounts of cumulus magnetite and apatite, supported by mineral chemistry, denotes a more evolved character for the Lac à l’Orignal deposit compared with other Fe-Ti-(P) deposits in the Grenville Province (e.g., Lac Tio Fe-Ti and Grader intrusion Fe-Ti-P deposits in the Havre St. Pierre Anorthosite, eastern Quebec). Petrogenetically, the Lac à l’Orignal Fe-Ti-P deposit corresponds to an evolved part of a low-Ti/Fe system in the Grenville Province in the late stages of differentiation of ferrodiorite/jotunite magmas.
a Location of the Grenville Province in Quebec, Canada. Red square represents the Central Grenville shown in “b”. b Regional geological map of the AMCG suites in the Central Grenville Province, Quebec with the location of the Fe-Ti-(P) deposits and regional deformation zones (DZ). c Close up of the AMCG suites and Fe-Ti-(P) mineral deposits in the Lac à l’Orignal area. Red dotted lines indicate the inferred limit between core (CZ) and border (BZ) of the Mattawa Anorthosite Massif, according to Owens and Dymek (2005), based on geochemical criteria. Geological maps modified from SIGEOM (Quebec System of Geomining Information). d, e Schematic geology sections of the Lac à l’Orignal Fe-Ti-P deposit: d N-S section showing the oxide-apatite mineralized zone (average P2O5 around 5 wt.%) hosted by anorthosite and leuconorite. Cut-off grade is 3 wt.%. (Laverdière 2013; 2016). e Schematic W-E section showing the approximate lens-shape of the mineralized zone, dipping around 30° to the north. The large thickness of the LO-14-21 drillcore was chosen for this study
a Location of the Grenville Province in Quebec, Canada. Red square represents the Central Grenville shown in “b”. b Regional geological map of the AMCG suites in the Central Grenville Province, Quebec with the location of the Fe-Ti-(P) deposits and regional deformation zones (DZ). c Close up of the AMCG suites and Fe-Ti-(P) mineral deposits in the Lac à l’Orignal area. Red dotted lines indicate the inferred limit between core (CZ) and border (BZ) of the Mattawa Anorthosite Massif, according to Owens and Dymek (2005), based on geochemical criteria. Geological maps modified from SIGEOM (Quebec System of Geomining Information). d, e Schematic geology sections of the Lac à l’Orignal Fe-Ti-P deposit: d N-S section showing the oxide-apatite mineralized zone (average P2O5 around 5 wt.%) hosted by anorthosite and leuconorite. Cut-off grade is 3 wt.%. (Laverdière 2013; 2016). e Schematic W-E section showing the approximate lens-shape of the mineralized zone, dipping around 30° to the north. The large thickness of the LO-14-21 drillcore was chosen for this study
… 
Photographs of representative lithologies of the Lac à l’Orignal Fe-Ti-P deposit from surface and drillcore. a Coarse-grained oxide-apatite-norite (OAN) (sample 20PM02). b Oxide-apatite-norite (LO-24, 28 m). c Pegmatitic OAN (LO-41, 71 m). d Layering of OAN with plagioclase-rich (anorthosite) layers. e Massive apatite layer within pink-anorthosite layers (LO-03, 5 m). f Massive oxides (ilmenite + magnetite) containing blocks of the host-anorthosite (sample 20PM03). Mineral abbreviations: pl, plagioclase; opx, orthopyroxene; ox, oxides; ilm, ilmenite; ap, apatite
Photographs of representative lithologies of the Lac à l’Orignal Fe-Ti-P deposit from surface and drillcore. a Coarse-grained oxide-apatite-norite (OAN) (sample 20PM02). b Oxide-apatite-norite (LO-24, 28 m). c Pegmatitic OAN (LO-41, 71 m). d Layering of OAN with plagioclase-rich (anorthosite) layers. e Massive apatite layer within pink-anorthosite layers (LO-03, 5 m). f Massive oxides (ilmenite + magnetite) containing blocks of the host-anorthosite (sample 20PM03). Mineral abbreviations: pl, plagioclase; opx, orthopyroxene; ox, oxides; ilm, ilmenite; ap, apatite
… 
Stratigraphic subdivision of the Lac à l’Orignal intrusion based on the distribution of different cumulus phases from the borders to the core. Modal proportion of oxides and apatite (left). Cryptic variation in plagioclase of anorthite (An) content (An=100 [Ca/(Ca+Na)]) and TiO2 and P2O5 values of whole-rock analysis are shown. Cumulus (-C) assemblages follow the nomenclature of Irvine (1982). Mineral abbreviations: p, plagioclase (pl); i, ilmenite (ilm); a, apatite (ap); h, orthopyroxene (opx); m, magnetite (mt); hm-ilm, hemo-ilmenite. Error bars = 1 standard deviation of the average value and represents the natural variation within the thin section
Stratigraphic subdivision of the Lac à l’Orignal intrusion based on the distribution of different cumulus phases from the borders to the core. Modal proportion of oxides and apatite (left). Cryptic variation in plagioclase of anorthite (An) content (An=100 [Ca/(Ca+Na)]) and TiO2 and P2O5 values of whole-rock analysis are shown. Cumulus (-C) assemblages follow the nomenclature of Irvine (1982). Mineral abbreviations: p, plagioclase (pl); i, ilmenite (ilm); a, apatite (ap); h, orthopyroxene (opx); m, magnetite (mt); hm-ilm, hemo-ilmenite. Error bars = 1 standard deviation of the average value and represents the natural variation within the thin section
… 
Photomicrographs of the main lithologies of the Lac à l’Orignal Fe-Ti-P mineralized zone. a Medium-grained oxide-apatite-norite (OAN) (LO-24, 28 m). b Pegmatitic coarse-grained OAN. Note the appearance of centimetric-scale orthopyroxene (LO-41, 71 m). c Orthopyroxene megacrystal with rutile exsolution lamellae (LO-41, 71 m). d Contact between medium-grained OAN and massive nelsonitic layer (LO-21, 20.8 m). e, f Accumulation of apatite crystals within anorthosite layer (apatite-bearing anorthosite, LO-38, 62 m) containing plagioclase with exsolutions of K-rich phase. (LO-38, 62 m). g Massive apatite layer (LO-02, 4.7 m). h Fine-grained OAN dyke (LO-06, 6.7 m). i Coarse-grained host-anorthosite lacking apatite and exsolutions in plagioclase (LO-58, 105.3 m). Mineral abbreviations: pl, plagioclase; opx, orthopyroxene; bt, biotite; hm-ilm, hemo-ilmenite; ilm, ilmenite; mt, magnetite; rt, rutile; ap, apatite; spl, Al-spinel; sulph, sulfides
Photomicrographs of the main lithologies of the Lac à l’Orignal Fe-Ti-P mineralized zone. a Medium-grained oxide-apatite-norite (OAN) (LO-24, 28 m). b Pegmatitic coarse-grained OAN. Note the appearance of centimetric-scale orthopyroxene (LO-41, 71 m). c Orthopyroxene megacrystal with rutile exsolution lamellae (LO-41, 71 m). d Contact between medium-grained OAN and massive nelsonitic layer (LO-21, 20.8 m). e, f Accumulation of apatite crystals within anorthosite layer (apatite-bearing anorthosite, LO-38, 62 m) containing plagioclase with exsolutions of K-rich phase. (LO-38, 62 m). g Massive apatite layer (LO-02, 4.7 m). h Fine-grained OAN dyke (LO-06, 6.7 m). i Coarse-grained host-anorthosite lacking apatite and exsolutions in plagioclase (LO-58, 105.3 m). Mineral abbreviations: pl, plagioclase; opx, orthopyroxene; bt, biotite; hm-ilm, hemo-ilmenite; ilm, ilmenite; mt, magnetite; rt, rutile; ap, apatite; spl, Al-spinel; sulph, sulfides
… 
a-d μXRF-maps, combining P (white), Ti (blue) and Fe (green), showing the different proportions of oxides and apatite from the Lac à l’Orignal Fe-Ti-P mineralized zone. Ilmenite is blue, whereas hematite-rich part of ilmenite is cyan. Magnetite is bright green. Orthopyroxene/biotite is dark green. a Medium grained-OAN dominated by hemo-ilmenite containing coarse exsolution lamellae of hematite, and minor magnetite (top border zone, LO-01, 3.7 m). b Coarse grained-OAN dominated by hemo-ilmenite containing thin exsolution lamellae of hematite, and magnetite (transition zone, LO-22, 21.5 m). c Medium grained-OAN dominated by magnetite and ilmenite (Hemo-ilmenite is absent) from core zone (LO-43, 75.7 m). d Medium grained-OAN dominated by hemo-ilmenite, containing coarse exsolution lamellae of hematite, and minor magnetite, from the bottom border zone (LO-57, 102.1 m). Note the higher presence of apatite near the oxide crystals. e-h Photomicrographs (reflected light) of the oxide assemblages. e Medium grained oxide-apatite norite (OAN) dominated by hemo-ilmenite containing coarse exsolution lamellae of hematite (pale) and ilmenite (dark) and minor magnetite (border zone, LO-10, 10.5 m). f Medium grained-OAN dominated by hemo-ilmenite, with fine exsolutions of hematite, and ilmenite (exsolution-free) close to magnetite (transition zone, sample LO-24, 28 m). g Medium grained-OAN dominated by magnetite, ilmenite and Al-spinel exsolutions. Hemo-ilmenite is absent (core zone, LO-32, 48.5 m). h Evidence of sub-solidus re-equilibration between magnetite and ilmenite, with depletion of hematite exsolutions in ilmenite towards the border with magnetite. Note the higher presence of Al-spinel exsolutions at the contact between magnetite and ilmenite grains (LO-29, 42m). Mineral abbreviations: pl, plagioclase; opx, orthopyroxene; hm-ilm, hemo-ilmenite; ilm, ilmenite; mt, magnetite; ap, apatite; spl, Al-spinel; sulph, sulfides; bt, biotite
+10
a-d μXRF-maps, combining P (white), Ti (blue) and Fe (green), showing the different proportions of oxides and apatite from the Lac à l’Orignal Fe-Ti-P mineralized zone. Ilmenite is blue, whereas hematite-rich part of ilmenite is cyan. Magnetite is bright green. Orthopyroxene/biotite is dark green. a Medium grained-OAN dominated by hemo-ilmenite containing coarse exsolution lamellae of hematite, and minor magnetite (top border zone, LO-01, 3.7 m). b Coarse grained-OAN dominated by hemo-ilmenite containing thin exsolution lamellae of hematite, and magnetite (transition zone, LO-22, 21.5 m). c Medium grained-OAN dominated by magnetite and ilmenite (Hemo-ilmenite is absent) from core zone (LO-43, 75.7 m). d Medium grained-OAN dominated by hemo-ilmenite, containing coarse exsolution lamellae of hematite, and minor magnetite, from the bottom border zone (LO-57, 102.1 m). Note the higher presence of apatite near the oxide crystals. e-h Photomicrographs (reflected light) of the oxide assemblages. e Medium grained oxide-apatite norite (OAN) dominated by hemo-ilmenite containing coarse exsolution lamellae of hematite (pale) and ilmenite (dark) and minor magnetite (border zone, LO-10, 10.5 m). f Medium grained-OAN dominated by hemo-ilmenite, with fine exsolutions of hematite, and ilmenite (exsolution-free) close to magnetite (transition zone, sample LO-24, 28 m). g Medium grained-OAN dominated by magnetite, ilmenite and Al-spinel exsolutions. Hemo-ilmenite is absent (core zone, LO-32, 48.5 m). h Evidence of sub-solidus re-equilibration between magnetite and ilmenite, with depletion of hematite exsolutions in ilmenite towards the border with magnetite. Note the higher presence of Al-spinel exsolutions at the contact between magnetite and ilmenite grains (LO-29, 42m). Mineral abbreviations: pl, plagioclase; opx, orthopyroxene; hm-ilm, hemo-ilmenite; ilm, ilmenite; mt, magnetite; ap, apatite; spl, Al-spinel; sulph, sulfides; bt, biotite
… 
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Vol.:(0123456789)
1 3
Mineralium Deposita (2024) 59:519–556
https://doi.org/10.1007/s00126-023-01216-5
ARTICLE
Petrogenesis ofFe‑Ti‑P mineral deposits associated withProterozoic
anorthosite massifs intheGrenville Province: insights fromoxide
andapatite trace‑element geochemistry atLac à l’Orignal, Quebec,
Canada
PedroMiloski1 · SarahDare1· Caroline‑EmmanuelleMorisset2· JoshuaH.F.L.Davies3· MorgannG.Perrot3·
DanySavard1
Received: 31 May 2023 / Accepted: 14 September 2023 / Published online: 20 October 2023
© The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023, corrected publication 2023
Abstract
Proterozoic anorthosite massifs can host significant amounts of critical and strategic metals such as Ti, V, and P, associated
with magmatic Fe-Ti oxides and apatite. Yet their petrogenesis is much less understood than Fe-Ti-V-P deposits hosted in
layered intrusions within large igneous provinces. Several mineralized lenses of Fe-Ti-P outcrop near the border of the 1080
(±2) Ma Vanel and the 1016 (±2) Ma Mattawa Anorthosite Massifs, in the Central Grenville Province, Quebec, Canada.
For example, the Lac à l’Orignal Fe-Ti-P deposit, hosted in the Vanel Anorthosite near the northern border of the Mattawa
Anorthosite, comprises a lenticular structure of oxide apatite norite (OAN) with thin layers of apatite-bearing anorthosite
and minor amounts of nelsonite (massive Fe-Ti oxides and apatite), indicating accumulation by density differences. Oxide
settling generated the melanocratic OAN cumulates and nelsonite. Plagioclase flotation generated the leucocratic apatite-
bearing anorthosite layers. The mineralization is dominated by hemo-ilmenite, accompanied by apatite and a minor amount of
magnetite at the borders, whereas the core is dominated by ilmenite, magnetite, and apatite. In-situ U-Pb dating of magmatic
zircon indicates that the Lac à l’Orignal deposit is a multistage intrusion with two different crystallization ages between the
younger core (993 ± 13 Ma) and the older upper border (1069 ± 12 Ma) of the intrusion. These ages are similar to those of
nearby anorthosite-massifs (Mattawa and Vanel Anorthosites, respectively). In-situ trace element analysis of plagioclase,
apatite and oxides, by laser ablation ICP-MS, reveals subtle variations in certain trace elements (e.g., Cr, Ni, V) related
to differentiation under relatively high-fO2 conditions (FMQ = +0.9 to +1.7). Calculated melt compositions from apatite
indicate a similar parental magma for both the border and core that matches the composition of high-Fe-Ti-P ferrodiorite
dykes at Lac à l’Original. This high-Ti-P ferrodiorite magma was probably residual after anorthosite formation. Sub-solidus
inter-oxide equilibration modified the original composition of the different cumulates in the intrusion. The absence of
extensive massive oxide cumulates and the presence of higher amounts of cumulus magnetite and apatite, supported by
mineral chemistry, denotes a more evolved character for the Lac à l’Orignal deposit compared with other Fe-Ti-(P) deposits
in the Grenville Province (e.g., Lac Tio Fe-Ti and Grader intrusion Fe-Ti-P deposits in the Havre St. Pierre Anorthosite,
eastern Quebec). Petrogenetically, the Lac à l’Orignal Fe-Ti-P deposit corresponds to an evolved part of a low-Ti/Fe system
in the Grenville Province in the late stages of differentiation of ferrodiorite/jotunite magmas.
Keywords Fe-Ti-P deposit· Massif-type anorthosites· Grenville Province· Oxide-apatite geochemistry
Introduction
Magmatic oxide-apatite (Fe-Ti-V-P) mineralization/deposits
are spatially and temporally associated with Proterozoic
AMCG (Anorthosite–Mangerite–Charnockite–Granite)
suites (Ashwal 1993; Charlier etal. 2015). They provide
important resources for several critical and strategic
Editorial handling: F. Melcher
* Pedro Miloski
miloski.geo@gmail.com
Extended author information available on the last page of the article
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
... The Grenville Province also contains several layered maficultramafic intrusions (either troctolitic or noritic) that are spatially and temporally associated with the anorthositic suites (Corriveau et al. 2007;Francis et al. 2000) (Fig. 1). The Grenville AMCG complexes in Quebec range in age from ca. 1.3 to 0.9 Ga and host numerous oxide (Fe-Ti and Fe-Ti-V) and oxide-apatite (Fe-Ti-P) deposits and occurrences (Corriveau et al. 2007;Grant 2020;Miloski et al. 2023Miloski et al. , 2024 (Fig. 1), including the world's largest ilmenite deposit (Lac Tio: Charlier et al. 2010). The V mineralisation typically forms lenses and pods of massive to semimassive oxides (dominated by magnetite) and is generally hosted in labradorite-type anorthosite and/or (gabbro) norite. ...
... Ga: Hébert et al. 2009;Grant 2020;Valvasori et al. 2020) whereas Fe-Ti mineralisation (dominated by hemo-ilmenite) is exclusively associated with the younger anorthositic suites (1.08-0.9 Ga: Hébert et al. 2009;Morisset et al. 2009;Charlier et al. 2010;Miloski et al. 2023Miloski et al. , 2024. Furthermore, troctolitic intrusions and olivine-bearing anorthosites are also only associated with the older anorthositic suites (Higgins and van Breemen 1996;Hébert et al. 2009). ...
... In contrast, the younger anorthositic suites in the central Grenville Province (e.g., the 1080-1069 Ma Pipmuacan Suite and 1020-1008 Ma Valin Anorthositic Suite) exclusively contain andesine-type plagioclase and orthopyroxenebearing lithologies (Hébert et al. 2005). The Fe-Ti-P deposits, dominated by (hemo)-ilmenite, apatite and minor magnetite, are restricted to the orthopyroxenebearing younger anorthosite suites (e.g., Lac à l'Orignal and Lac Mirepoix: Miloski et al. 2023Miloski et al. , 2024. However, Fe-Ti-P deposits (dominated by magnetite and ilmenite) containing olivine may also be hosted in the andesinerich parts of the older LSJ Anorthositic Suite (e.g., St. Charles de Bourget and Lac à Paul: Grant 2020). ...
Petrogenesis of the 1149 Ma Etoile Suite Mafic Intrusion, Quebec: implications for vanadium mineralisation in Proterozoic anorthosite-bearing terranes
Article
Full-text available
  • Aug 2024
  • MINER DEPOSITA
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.
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Apatite Chemistry as a Petrogenetic Indicator for Mafic Layered Intrusions
Article
  • Feb 2024
  • J PETROL
Mafic layered intrusions constitute a natural laboratory to investigate petrogenetic processes using trace element variations in apatite chemistry. Although these intrusions are related to large igneous provinces, there is a wide range of parameters that can affect the chemistry of the primary melt (i.e. composition of the source, pressure, temperature, oxygen fugacity), followed by possible crustal contamination. In this study, we use a comprehensive dataset of analyses of cumulus and intercumulus apatite from a variety of mafic layered intrusions to demonstrate the use of apatite as a powerful petrogenetic indicator. The dataset (determined in this study and compiled from the literature) comprises electron microprobe and LA-ICP-MS analyses, as well as in-situ LA-MC-ICP-MS analyses of Sr isotopes in apatite from well documented layered intrusions (Sept-Iles, Skaergaard, Bushveld, Panzhihua) and the Sudbury Igneous Complex. For the first time, we show that high values of (La/Nd) N , Th, U, Pb, and As in apatite correlate with high (87 Sr/ 86 Sr) initial and are related to contamination with continental crust. An elevated (Gd/Yb) N ratio might indicate melting of a mantle source deep enough to retain Yb in garnet. We also confirm that increasingly negative Eu anomaly and decreasing Sr/Y ratio in apatite are indicators of fractional crystallisation of plagioclase, and that high Sr/Y is indicative of early saturation of apatite and/or delayed crystallisation of plagioclase. The reversal to more primitive compositions caused by magma mixing is expressed by higher Sr, V, Mg and Sr/Y ratio, and lower REE + Y, As and Na concentrations in apatite following magma replenishment. Lastly, we show that apatite signature can efficiently distinguish a mafic from a felsic intrusion using its REE and Sr content coupled to its Eu anomaly. It is also possible to further identify the more primitive from the more evolved parts of a mafic layered intrusion, using the Lu, Th, V and volatile (F/Cl) content to distinguish intercumulus from cumulus apatite, respectively. Finally, identifying a mafic magmatic system using detrital apatite in till will prove useful for provenance and mineral exploration studies.
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Petrogenesis of oxide-apatite mineralization associated with Proterozoic anorthosite massifs at Lac Mirepoix, Quebec, Canada: a multi-intrusion model for Fe-Ti-P mineralization in the Central Grenville Province
Article
Full-text available
  • Oct 2023
  • ORE GEOL REV
The Lac Mirepoix Fe-Ti-P mineralization presents several mineralized lenses that outcrop near the border of the 1080 (±2) Ma Vanel and the 1016 (±2) Ma Mattawa Anorthosite massifs, in the Central Grenville Province, Quebec, Canada. The mineralization is (hemo)-ilmenite-dominated, accompanied by magnetite and apatite. It is subdivided in three different zones due to the appearance of different cumulate phases: zone I comprises mainly massive oxide (>70 % hemo-ilmenite ± magnetite) layers hosted in anorthosite. Towards the center of the mineralization (zone II), massive oxide layers are less common whereas apatite-bearing cumulates appear, forming massive nelsonite (50–70 % magnetite ± ilmenite and 25–30 % apatite) and oxide apatite norite (OAN, 15–25 % hemo-ilmenite ± magnetite and 8–20 % apatite). Finally, zone III is marked by the alternance of OAN layers (10–25 m), richer in magnetite, in addition to (hemo)-ilmenite and apatite, and an absence of massive oxide and nelsonite. In-situ trace element analysis of plagioclase, apatite and oxides by laser ablation ICP-MS, reveals cryptic variations related to magma differentiation and multiple injections of ferrodiorite parental magmas of similar composition. In-situ U-Pb dating of zircon from the OAN mineralization itself indicates two different crystallization ages between zone III (1048 ± 8 Ma) and zone I (964 ± 9 Ma), favouring a model of multiple injections of similar Fe-Ti-P-rich melts of similar composition over a period of 80 Mys rather than in-situ crystallization of a single intrusion, which is supported by trace-element geochemistry. The Lac Mirepoix mineralization records the following fractional crystallization sequence of a high-Ti-P magma, residual after the anorthosite formation: first, massive oxides of hemo-ilmenite crystallized (high Ti/Fe) by oxide settling, with primitive compositions, similar to the world-class Lac Tio deposit. The oxide-apatite mineralization (nelsonite and OAN) crystallized from the residual liquid (lower Ti/Fe, evolved compositions) in which magnetite and apatite were more abundant, similar to nearby mineralization in the area (e.g. Lac à l’Orignal Fe-Ti-P deposit). The observed decrease in Ti content of the evolving melt is supported by the liquid line of descent of several ferrodiorite dykes within the host-rocks and mineralization. Finally, we propose a model of multiple injections of residual Fe-Ti-P-rich liquids drained from or filter-pressed within diapirs of plagioclase-rich mushes that were emplaced over 80 Mys apart along the same crustal detachment zone.
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Anorthosite formation and emplacement coupled with differential tectonic exhumation of ultrahigh-temperature rocks in a Sveconorwegian continental back-arc setting
Article
Full-text available
  • May 2022
  • PRECAMBRIAN RES
The tectonic setting and mechanisms and duration of emplacement of Proterozoic massif-type anorthosites and the significance of typically associated ultrahigh-temperature (UHT) host rocks have been debated for decades. This is particularly true of the Rogaland Anorthosite Province (RAP) in the SW Sveconorwegian Orogen. Earlier studies suggest that the RAP was emplaced over 1–3 Myr around 930 Ma towards the end of orogenesis, resulting in an up to 15–20 km-wide contact metamorphic aureole. However, our structural observations show that the RAP is located in the footwall of a 15 km-wide extensional detachment (Rogaland Extensional Detachment, RED), separating the intrusions and their UHT host rocks from weakly metamorphosed rocks in the hanging wall. U–Pb zircon dating of leucosome in extensional pull-aparts associated with the RED yields ages of 950–935 Ma, consistent with Re–Os molybdenite ages from brittle extensional structures in the hanging-wall block that range between 980 and 930 Ma. A metapelite in the immediate vicinity of the RAP yields a 950 Ma U–Pb age of matrix-hosted monazite, and part of the RAP was intruded by the Storgangen norite dike at ca. 950 Ma, providing a minimum age of emplacement. These ages are consistent with Ar–Ar hornblende and biotite ages that show rapid cooling of the footwall before 930 Ma, but slow cooling of the hanging wall. Field and geochronologic data suggest that the RAP formed and was emplaced over a long period of time, up to 100 Myr, with different emplacement mechanisms reflecting an evolving regional stress regime. The distribution of UHT rocks around the RAP reflects differential extensional exhumation between 980 and 930 Ma, not contact metamorphism. The duration and style of orogenic activity and externally (as opposed to gravitationally) driven extension suggest that the RAP formed in a continental back-arc setting.
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Evidence for Silicate–Liquid Immiscibility in Monzonites and Petrogenesis of Associated Fe–Ti–P-rich rocks: Example from the Raftsund Intrusion, Lofoten, Northern Norway
Article
Full-text available
  • Mar 2020
The 1800 Ma monzonitic to syenitic Raftsund intrusion is the largest intrusive body of the Lofoten-Vesterålen AMCG (anorthosite-mangerite-charnockite-granite) suite. It is composed of three units that can be differentiated based on their textures. This study focuses on the most voluminous, predominately equigranular, unit consisting of a pigeonite-augite syenite and a fayalite-augite monzonite. The pigeonite-augite syenite is associated with cm-scale to hundred-meter scale occurrences of Fe-Ti-P-rich rocks which display sharp to gradational contacts with the surrounding syenite. Iron-Ti-P-rich rocks consist of augite, Fe-rich olivine ± partly inverted pigeonite, apatite, ilmenite, titanomagnetite and sparse pyrrhotite, hornblende and biotite. Partly resorbed ternary feldspar crystals are common toward the contact with the syenite. Microtextures, such as symplectites, encountered at the contact between the syenite and the Fe-Ti-P-rich rocks, indicate local disequilibrium between the two rock types. The Fe-Ti-P-rich rocks show large compositional variations but overall are enriched in Ca, Zn, Sc and REE in addition to Fe, Ti and P compared to the host syenite. Field evidence, whole-rock compositions and textural relationships, all suggest that that silicate-liquid immiscibility was involved in the genesis of the Fe-Ti-P-rich rocks. These are interpreted to represent Fe-rich unmixed melts, whereas the syenite is inferred to originate from the crystallization of conjugate Si-rich immiscible melt. The existence of an Fe-rich melt is further supported by the high trace element content of augite from the Fe-Ti-P-rich rocks, showing that they grew from a melt enriched in elements such as Sc and Ti. The fayalite-augite monzonite also displays textural and chemical evidence of silicate liquid immiscibility resulting in unusually variable Zr contents (few hundred ppm to more than 3000 ppm) and the presence of abundant zircon and allanite restricted to mm- to cm-scale Fe-rich mineral clusters. The most Fe-rich and Si-poor rocks are interpreted to represent larger proportion of the Fe-rich melt. Liquid immiscibility can be identified at various scales in the pigeonite-augite syenite, from mm-size clusters to large-scale bodies, up to hundreds of meters in size, indicating various degrees of separation and coalescence of the Fe-rich melt in the intrusion. The immiscible liquids in the fayalite-augite monzonite consist of an emulsion, with small mm- to cm-scale droplets of Fe-rich melt, whereas in the pigeonite-augite syenite, Fe-rich melt pockets were able to coalesce and form larger pods. The difference between the two units results from either earlier onset of immiscibility in the pigeonite-augite syenite or reflects a difference in the degree of polymerization of the melt at the time of unmixing. This study emphasises the importance of silicate-liquid immiscibility in the evolution of intermediate to felsic alkalic ferroan systems and provides a series of arguments which can be used to identify the process in such systems.
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An Integrated Model for Ilmenite, Al-Spinel, and Corundum Exsolutions in Titanomagnetite from Oxide-Rich Layers of the Lac Doré Complex (Québec, Canada)
Article
Full-text available
  • Oct 2018
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.
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Immiscible hydrous Fe-Ca-P melt and the origin of iron oxide-apatite ore deposits
Article
Full-text available
  • Apr 2018
The origin of iron oxide-apatite deposits is controversial. Silicate liquid immiscibility and separation of an iron-rich melt has been invoked, but Fe-Ca-P-rich and Si-poor melts similar in composition to the ore have never been observed in natural or synthetic magmatic systems. Here we report experiments on intermediate magmas that develop liquid immiscibility at 100 MPa, 1000-1040 °C, and oxygen fugacity conditions (fO2) of ∆FMQ = 0.5-3.3 (FMQ = fayalite-magnetite-quartz equilibrium). Some of the immiscible melts are highly enriched in iron and phosphorous ± calcium, and strongly depleted in silicon (<5 wt.% SiO2). These Si-poor melts are in equilibrium with a rhyolitic conjugate and are produced under oxidized conditions (~FMQ + 3.3), high water activity (aH2O ≥ 0.7), and in fluorine-bearing systems (1 wt.%). Our results show that increasing aH2O and fO2 enlarges the two-liquid field thus allowing the Fe-Ca-P melt to separate easily from host silicic magma and produce iron oxide-apatite ores.
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Detrital zircon U-Pb geochronology of the Magog Group, southern Quebec - Stratigraphic and tectonic implications for the Quebec Appalachians
Article
Full-text available
  • Dec 2017
ABSTRACT. In the Quebec Appalachians, the Laurentian continental margin (Humber Zone) and adjacent oceanic domain (Dunnage Zone) were amalgamated during the Ordovician Taconian orogeny. The Dunnage Zone includes ophiolites and overlying synorogenic deposits of both the Saint-Daniel Mélange and Magog Group. The latter consists of a ~3 km-thick pile of sandstone, felsic volcaniclastic rocks and graphitic slate at the base (Frontière, Etchemin and Beauceville formations) overlain by a ~7 km-thick turbiditic flysch sequence, constituting the Saint-Victor Formation. The maximum upper age limit of the Magog Group was considered to be Darriwilian based on graptolite fauna. This was proven consistent with a 462 +5/-4 Ma (U-Pb ID-TIMS) from a felsic tuff of the Beauceville Formation, but contradicts a detrital zircon U-Pb age of 424  6 Ma recently measured in the Saint-Victor Formation. A new detrital zircon U-Pb geochronology study (HR-LA-ICP-MS and ID-TIMS), focused on the Saint-Victor Formation, yields young detrital populations that suggest that the Saint-Victor Formation is not exclusively Ordovician and extends into the Silurian, as indicated by a maximum age of sedimentation around 430 Ma. Detrital zircon U-Pb geochronology associated with fossil age constraints and stratigraphic correlations in adjacent areas attest that the Saint-Victor Formation should be considered as an upper Magog Group sequence that is separated from lower units (the Frontière-Etchemin-Beauceville formations) by an unconformity corresponding to a sedimentary hiatus of  10 m.y. Regional tectonic considerations imply that the Magog Group evolved from a syn-Taconian forearc basin in Middle-Late Ordovician time to a syn-Salinic peri-continental basin in early Silurian time. Several NW and SE erosional sources are invoked for the sedimentation of the Magog Group, evolving from the erosion of both the southern Quebec ophiolites and adjacent sedimentary rocks of the Laurentia margin to the NW, and volcanic arc rocks of the Ascot Complex, Shelbourne Falls and Bronson Hill massifs to the SE. Potential sources for ca. 430 Ma zircons found towards the top of the Saint-Victor sequence are the Silurian Frontenac Formation and the East Inlet granitic pluton, both located in the vicinity of the Quebec-Maine border.
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Microstructure and compositional changes across biotite-rich reaction selvedges around mafic schollen in a semipelitic diatexite migmatite
Article
  • Feb 2019
Biotite‐rich selvedges developed between mafic schollen and semipelitic diatexite in migmatites at Lac Kénogami in the Grenville Province of Quebec. Mineral equilibria modelling indicates that partial melting occurred in the mid‐crust (4.8 to 5.8 kbars) in the range 820 to 850°C. The field relations, petrography, mineral chemistry and whole rock composition of selvedges along with their adjacent mafic schollen and host migmatites are documented for the first time. The selvedges measured in the field are relatively uniform width (~1 cm wide) irrespective of the shape or size of their mafic scholle. In thin section, the petrographic boundary between mafic scholle and selvedge is defined by the appearance of biotite and the boundary between selvedge and diatexite by the change in microstructure for biotite, garnet, plagioclase and quartz. Three subtypes of selvedges are identified according to mineral assemblage and microstructure. Subtype I have orthopyroxene but of different microstructure and Mg# to orthopyroxene in the mafic scholle; subtype II contain garnet with many mineral inclusions, especially of ilmenite, in contrast to garnet in the diatexite host which has few inclusions; subtype III lack orthopyroxene or garnet, but has abundant apatite. Profiles showing the change in plagioclase composition from the mafic schollen across the selvedge and into the diatexite show that each subtype of selvedge has a characteristic pattern. Four types of biotite are identified in the selvedges and host diatexite based on their microstructural characteristics. 1) Residual biotite forms small rounded red‐brown grains, mostly as inclusions in peritectic cordierite and garnet in diatexite; 2) selvedge biotites are tabular subhedral grains with high respect ratio; 3) diatexite biotite forms tabular subhedral grains common in the matrix of the diatexite, and 4) retrograde biotite that partially replaces peritectic cordierite and garnet in the diatexite. The four groups of biotite are also discriminated by their major element (EMPA) and trace elements (LA‐Q‐ICP‐MS) compositions. Residual biotite is high in TiO2 and low in Sc and S, whereas retrograde biotite has high Al2O3, but low Sc and Cr. Selvedge and diatexite biotite are generally very similar, but selvedge biotite has higher Sc and S contents. Whole rock compositional profiles across the selvedges constructed from micro‐XRF and LA‐Q‐ICP‐MS analyses show; 1) Al2O3, FeO, MgO and CaO all decrease from mafic scholle across the selvedge and into the diatexite; 2) Na2O is lowest in the mafic scholle, rises through the selvedge and reaches its maximum about 20 to 30 mm into the diatexite host; 3) K2O is lowest in the mafic scholle and reaches its highest value in the first half of the selvedge, then declines before reaching a higher, but intermediate value, about 20 mm into the diatexite. Of the trace elements Cs and Rb show distributions very similar to K2O. This article is protected by copyright. All rights reserved.
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Minerals and Rocks
Article
  • Jan 1993
The idea for a book on anorthosites came to me in January of 1986 while returning to Houston after holiday festivities in Dallas. The original idea was a review paper on anorthosites, but by the time I reached Houston, the subject material I contemplated induding was obviously too extensive for a single paper. The Director of the Lunar and Planetary Institute, Kevin Burke, was receptive to the idea of a book, and suggested that I contact Peter Wyllie, who serves as Editor of the Springer-Verlag series Minerals and Rocks. This effort, which I originally expected would take about a year, has taken nearly 6. I have many excuses- indolence, moving to another continent, other commitments, etc.-but the basic truth is that writing a book is much larger an undertaking than can be anticipated. Many people are aware of this, and I was duly forewarned. . But why write a book on anorthosites? This is a very good question, which I have considered from many angles. One rationale can be expressed in terms of a comparison between anorthosite and basalt. A first-order understanding of basalt genesis has been extant for many years. By contrast, there is little agreement about the origin of anorthosite. There are good reasons for studying and writing about basalt: it is the most abundant rock type on the Earth's surface, and is also plentiful on the surfaces of the other terrestrial planets.
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