DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail.
|Type area:||Cadieux Lake area (NTS sheet 33A02), between Sorbier and Mabille lakes|
|Geological province:||Superior Province|
|Geological subdivision:||Opinaca Subprovince|
|Lithology:||Intrusive, volcanic and metamorphic rocks|
Hocq (1985) identified mafic rock klippes (gabbro, hornblendite) and ultramafic horizons in the Mabille and Maville lakes area. At that time, these mafic-ultramafic horizons were part of the Base Gneissic Complex, a much larger unit interpreted as bedrock. The Mabille Complex was introduced following the Ministère’s 2018 mapping work in the Cadieux Lake area (Beauchamp, 2020). Inside the Opinaca metasedimentary basin, the Mabille Complex consists of mostly tonalitic rocks and supracrustal rock klippes.
The Mabille Complex has been divided into five informal units by Beauchamp (2020): 1) a unit of foliated, granoblastic biotite ± magnetite tonalite and quartz diorite (nAmbi1); 2) a unit of foliated biotite-magnetite granite and granodiorite (nAmbi2); 3) a unit of foliated hornblende-magnetite gabbro and diorite (nAmbi3); 4) a unit of foliated peridotite showing a cumulate texture (nAmbi4); and 5) a unit of amphibolitized basalt, garnet amphibolite and tuff (nAmbi5).
White in altered surface and light grey in fresh exposure, tonalite is usually fine to medium grained. Granoblastic, it ranges from moderately to highly foliated. Folding is marked by the alignment of biotite in flattening planes. In thin sections, rocks show polygonal and interlobed textures. Quartz (20-35%) forms sutured polycrystalline zones having undulatory extinction. Fine-grained microcline is usually interstitial and represents <5% of the rock. Fine bands more potassic are aligned in the same direction as foliation. These thin bands contain up to 12% microcline. Plagioclase is moderately to strongly damouritized. Biotite (<10%) is weakly to fully chloritized. Epidote clusters replace biotite. Accessory minerals observed in thin sections are epidote (allanite and pistachite), muscovite, apatite, zircon, monazite, calcite, pyrite (<2%) and hematite.
Geochemical data (Beauchamp, 2020) of the Cadieux Lake project indicate that homogeneous tonalites of the Mabille Complex are magnesian granitoids, generally calcic (Frost et al., 2001) and type I peraluminous (Maniar and Piccoli, 1989). Normalized to CI chondrite (Palme and O’Neill, 2004), these rocks have a pattern enriched in light rare earths. They exhibit negative anomalies in Nb, P, Sm, and Ti, as well as positive anomalies in Ta, La-Ce, Nd, and Zr-Hf compared to the primitive mantle (McDonough and Sun, 1995).
Based on geochemical data (Beauchamp, 2020), the normative composition of peridotite is defined as lherzolite with a MgO content ranging from 62.95% to 71.34%. It shows flat rare earth profiles and a small negative P anomaly on the spider diagram.
Unit nAmbi5 consists mainly of amphibolitized mafic volcanics of basaltic composition. Rocks feature pillowed (outcrops 18-PG-4126 and 18-WM-3071) or massive textures. Remains of saussuritized cores and amphibolitized pillow edges are apparent. Garnet amphibolite bands, which could correspond to silicate facies iron formation, and thin tuff layers are inserted in the basaltic sequence. The alteration affects this unit in a stratiform manner as silicified and sericitized bands or calcosilicate alteration (diopside, clinozoisite and chlorite). In thin section, basalt and amphibolite contain mostly hornblende, highly damouritized plagioclase and traces of epidote, chlorite and muscovite. Garnet, if present, forms rounded poikiloblasts containing quartz and hornblende inclusions. Garnet fractures are chloritized. The triple junction between minerals indicates strong recrystallization (granoblastic texture). Unit nAmbi5 is intruded by massive granite and cut by quartz-diopside-epidote-calcite-pyrite veins and veinlets.
From a geochemical point of view (Beauchamp, 2020), mafic rocks of the Mabille Complex are subalkaline basalt and tholeiitic andesitic basalt (Winchester and Floyd, 1977; Pearce, 1996; Ross and Bédard, 2009) similar to N-MORB. These rocks, thought to have been formed in an island arc-like setting (Pearce and Norry, 1979; Meschede, 1986), are believed to have originated from a source that has undergone minor crustal contamination (Pearce, 2008). Unit nAmbi5 is characterized by flat rare earth profiles and the presence of small negative Ta and P anomalies on spider diagrams.
The Mabille Complex appears as a wide E-W strip that crosses sheet 33A02 over a distance of >40 km in the Mabille and Sorbier lakes area. The maximum width of this complex is 4.5 km in the central portion of the sheet. It gradually wedges out eastward and westward in sheets 33A01 and 33A03, respectively.
The isotopic dating of a homogeneous biotite-magnetite tonalite (outcrop 18-FM-2034) yielded a Neoarchean age (Davis, 2019).
|Unit||Sample Number||Isotopic System||Mineral||Crystallization Age (Ma)||(+)||(-)||Reference(s)|
The Mabille Complex outcrops within metasedimentary rocks of the Laguiche Complex, which has an estimated maximum sedimentation age of 2694 ±10 Ma in the Cadieux Lake area (U-Pb on detrital zircons; Davis, personal communication, 2019). The Mabille Complex tonalite, dated 2705 ±4 Ma (Davis, personal communication, 2019), intrudes into metasedimentary rocks of the Laguiche Complex. As illustrated on the Cadieux Lake geological map and described on some outcrops (18-FM-2033, 18-AH-8066), tonalite contains paragneiss enclaves. The Mabille Complex tonalite dating thus provides a minimum sedimentation age in the Cadieux Lake area. The Mabille Complex is cut by the Lac Esprit Dykes (pPesp; 2069 ±1 Ma, Hamilton et al., 2001) and Mistassini Dyke Swarm (nAmib; 2515 ±3 Ma, Hamilton, 2009; 2503 ±2 Ma, Davis et al., 2018)
Does not apply.
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Ministère de l’Énergie et des Ressources naturelles (MERN). Mabille Complex. Quebec Stratigraphic Lexicon. https://gq.mines.gouv.qc.ca/lexique-stratigraphique/province-du-superieur/complexe-de-mabille_en [accessed on Day Month Year].
Mehdi A. Guemache, P. Geo., Ph.D. (coordination); Prénom Nom, titre (critical review); Simon Auclair, P. Geo., M.Sc. (editing); Prénom Nom (HTML editing); Céline Dupuis, P. Geo., Ph.D. (English version)