Beaudette et al. (2020) introduced the Hubert Formation to individualize sedimentary beds unconformably overlying (angular discordance) the Chukotat Group. These beds had already been mentioned by Roy (1989), Moorhead (1989) and Barrette (1990b), without, however, recognizing the angular unconformity observed more recently (Beaudette et al., 2020).

The Hubert Formation consists of coarse silicoclastic beds of pebble conglomerate and sandstone having a brick-red patina and fresh surface. The presence of conglomerate beds and thin (4-40 cm) sandstone beds displaying parallel laminae, as well as the absence of fine deposits, imply a proximal energetic deposition environment probably of fluvial origin. Parallel laminations and several erosion surfaces allow the measurement of primary bedding with normal polarity towards the NW. The Hubert Formation is not magnetic.

Polymictic conglomerate contains joint fragments; the proportion of the sandy matrix is <20% and generally almost non-existent. Fragments are 5 mm to 25 mm in size. They consist mostly of angular reddish aphanitic volcanic rock fragments (20-90%), subangular to subrounded aphanitic or very fine-grained greenish grey rock fragments interpreted as being of volcanic origin (up to 15%) and, in smaller amounts, subrounded milky chert fragments (up to 5%), rounded massive gabbro fragments (up to 5%) and subrounded to rounded massive or foliated intermediate to felsic intrusive rock fragments (0-15%). Clastic sequences display normal sorting towards the NW. They consist of conglomerate covering a thickness of 50 cm to 2 m at the base and overlain by a sandstone bed 5 cm to 40 cm thick. The latter is generally truncated by the erosion surface of the next sequence.

In thin section, arenite is composed of an assemblage of subangular quartz and rarely twinned feldspar grains (50%), chlorite (30%) and interstitial carbonates (5%), as well as disseminated hematite (10%) and epidote (10%), as well as trace amounts of muscovite flakes. Epidote is heterogeneously distributed, either disseminated in the matrix or in clusters.

Conglomerate is characterized by a very low spaced schistosity defined by the local orientation of fragments and muscovite flakes observed in thin section. The difference between primary bedding (245°) and foliation (260°) is 15°.

The unconformity carries native copper mineralization (Dryade mineralized zone).

Thickness and Distribution

The Hubert Formation outcrops as elongated sedimentary basins of modest dimensions with a surface area of ≤1 km². Outcrops are located at the structural and stratigraphic summit of the Chukotat Group, directly south of the boundary between the Northern and Southern domains, in the wall of the Bergeron Fault. The true thickness of the formation observed on outcrop 19-GL-2108 is ~90 m.

Dating

None.