Background

Description

Champion Complex 1 (Achp1): Tonalitic Gneiss Locally Granitic

Champion Complex 2 (Achp2): Tonalite, Pyroxene-Hornblende Granodiorite

Unit Achp2 consists of tonalite and granodiorite in lesser proportions. Tonalite contains biotite (10%), hornblende (5%), magnetite (3%), and, in smaller proportions, epidote, sphene and apatite. The rock is medium-grained and locally hematitized. It is homogeneous or weakly foliated in appearance and has a granoblastic and equigranular texture. It is pale grey or pinkish white in altered surface and beige in fresh exposure. Unit Achp2 also contains bands of granodiorite that are difficult to distinguish from tonalite in outcrop. The latter also contains up to 10% medium-grained and granoblastic diorite enclaves characterized by a dark-grey alteration patina. Enclaves are flattened and elongated parallel to foliation planes.

Champion Complex 3 (Achp3): Diorite and Quartz Diorite

Unit Achp3 is best exposed NE of the Lake Boisrobert area (sheet 32N11), close to the contact between the Champion Complex and the Anatacau-Pivert Formation. It consists of biotite-rich intermediate rocks that vary in composition from diorite to quartz diorite. These diorites are medium grained and homogeneous, weakly to strongly foliated and granoblastic. They are light grey in altered surface and beige in fresh exposure. The rock typically contains 40-60% of mafic minerals (hornblende and biotite) and 2% of magnetite. From a geochemical perspective, diorites and quartz diorites of unit Achp3 are metaluminous, of calc-alkaline affinity and characterized by the absence of europium anomaly.

Champion Complex 3a (Achp3a): Monzodiorite and Quartz Monzodiorite

Subunit Achp3a is better exposed NE of Amikap Lake (sheet 32N11), following unit Achp3. It was created to describe a group of monzodiorite and quartz monzonite, generally foliated, locally massive, homogeneous and medium to coarse grained. These intermediate rocks are characterized by the presence of 20% disseminated euhedral to subhedral phenocrystals of plagioclase or K-feldspar, 0.5 to 1 cm (longest axis). The rock is white to slightly pinkish in altered surface and beige to pinkish grey in fresh exposure. The pinkish colour is due to hematization. The rock is weakly to strongly hematitized and contains chloritized hornblende (10-30%), biotite (5-15%), chlorite (1-10%), epidote disseminated or in veinlets (10%), and accessory apatite and allanite. Monzodiorite of subunit Achp3a also centimetric to metric enclaves of unit Achp3 fine-grained diorite, rich in mafic minerals (>55%), stretched parallel to foliation planes and partially assimilated.

Champion Complex 4 (Achp4): Granodiorite

Unit Achp4 outcrops on the southern edge of the Champion Complex, between Nemiscau Lake and the Jolliet River (sheets 32N06 and 32N07). It is also observed in the Champion Lake area (32N09), north of the Nemiscau and Caumont lakes. Unit Achp4 is separated from the Lac des Montagnes Group by the RRSZ. On aeromagnetic maps, it is distinguished from the surrounding rocks by low magnetic susceptibility. This unit consists of medium-grained, homogeneous, weakly to strongly foliated granodiorite. Petrographic and geochemical analyses show that locally, unit Achp4 consists of tonalite. However, to the naked eye, these two rocks are very similar. The rock is light grey in altered surface, locally pinkish, and light grey in fresh exposure. It generally contains 10% biotite, 2-10% hornblende and 1-2% magnetite. The foliated rocks are also the richest in mafic minerals (hornblende and biotite) with contents of up to 20%. Unit Achp4 contains up to 10% centimetric to metric amphibolite and quartz diorite enclaves that contain up to 50% of hornblende. Geochemical analyses show that these rocks are the type I, bordering metaluminous and pareluminous, of calc-alkaline affinity and depleted to moderately enriched in potassium.

Champion Complex 5 (Achp5): Porphyritic Granodiorite

Unit Achp5 is located in the heart of the Champion Complex. It consists of granodiorite characterized by a porphyraceous texture linked to the presence of 1-2 cm long euhedral to subrounded K-feldspar phenocrystals. The proportion of phenocrystals varies from 2 to 20%, but is on average around 10%. In places, K-feldspar (orthose) phenocrystals have whitish plagioclase rims, giving the rock a rapakivi texture. Massive to weakly-foliated granodiorite is homogeneous, medium grained and usually magnetic. It is pinkish grey in fresh exposure and altered surface. Locally, a weak foliation is highlighted by the alignment of K-feldspar phenocrystals; it likely represents magmatic foliation associated with intrusion of the granodiorite. The rock contains less than 15% mafic minerals including partially chloritized biotite (10-15%) and hornblende (1-10%). Sphene, allanite and magnetite are the most common accessory minerals.

In places, outcrops assigned to unit Achp5 contain up to 30% of granite in diffuse or transitional contact with granodiorite. Unit Achp5 also contains metric to decametric enclaves of tonalite, amphibolite or diorite.

Champion Complex 6 (Achp6): Granodiorite and Granite Containing Migmatite and Tonalitic or Granodioritic Gneiss Enclaves

Unit Achp6 outcrops northeast of the Lake Boisrobert region (sheet 32N11), in contact with the Northern Anatacau-Pivert Formation and the Rupert Complex in the west and south. It consists of a package of granodiorite and granite characterized by a significant amount of migmatite and tonalitic or granodioritic gneiss enclaves. These enclaves generally show a very high degree of assimilation and form ribbons that resemble schlierens.

Granodiorite and granite are very heterogeneous lithologies, with a heterogranular and foliated texture, locally gneissic. These magnetic and hematitized rocks are brownish beige in altered surface and light grey in fresh exposure. They contain strongly chloritized biotite schlierens, hornblende and magnetite. Migmatite enclaves, consisting of migmatized paragneiss, metatexite and diatexite, are folded and stretched in foliation planes. The northern part of this unit, located in contact with the Anatacau-pivert Formation, is composed mainly of a homogeneous, massive to weakly foliated, pink granodiorite. Finally, this area is an area of high magnetic susceptibility. 

Thickness and Distribution

The Champion Complex is the southern extension of the La Grande Subprovince. New geophysical and geological data show that this unit extends NE over a distance of 200 km and a width of 65 km. In the west end of the Rupert River, granitic and granodioritic rocks account for 80% of the Champion Complex. The oldest rocks in the Champion Complex are tonalitic gneiss, which are ~8 km wide and 20 km long. 

Dating

During the work of Bandyayera and Daoudene (2018a) in the Nemiscau Lake area, a sample of gneiss belonging to the Champion Complex (Achp1) was taken from outcrop 2016-CS-4003, 8 km to the NW of Mézière Lake. This sample of tonalitic gneiss gave an age of 2815,8 ±3 Ma (David, 2020). Another sample also belonging to unit Achp1 was dated by Bynoe (2014). This granitic gneiss is located 1 km to the NE of the Spodumène Lake; it returned an age of 2889 ±14 Ma. These Mesoarchean ages are consistent with the hypothesis that Champion Complex gneiss are bedrocks and among the oldest in the region.  

Stratigraphic Relationship(s)

The Champion Complex is one of the oldest units in the Rupert River area. It forms the host unit of the majority of intrusive units in the region and is located in enclaves in these same units. In the south, the Champion Complex is separated from the Rupert Complex by the Rivière Rupert Shear Zone (ZCrup), and from the Lac des Montagnes Group by the Nisk Shear Zone (ZCnsk). The various units of the Champion Complex are cut by pink granite and granitic pegmatite intrusions assigned to the Kaupanaukau Suite. 

Paleontology

Does not apply.

References

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