Gélinas (1959) used the term « Stewart Dome » to describe a unit of quartzofeldspathic gneiss sourrounded by biotite-rich and locally garnet-rich gneiss. Perreault and Hynes (1990) later used the term “Kuujjuaq Batholith” to describe this unit. Reinterpretation of this area by Simard et al. (2013) using field descriptions by Serge Perreault (unpublished data) has linked rocks assigned to the Kuujjuaq Batholith to a single intrusion corresponding to a geophysical anomaly of very clear oval shape. Consequently, the name « Kuujjuaq Batholith » was replaced by the more appropriate name « Kuujjuaq Pluton ». To the east of the Pingiajjulik Fault, banded gneissic rocks originally assigned to the Kuujjuaq Batholith were reassigned to the Ungava Complex. Intrusive rocks on the west side of this fault were associated with the Kaslac Complex or Tasialuk Suite, depending on their composition.

Orthogneiss of the Kuujjuaq Pluton varies in composition from tonalitic to granodioritic, with locally dioritic and granitic phases. They are also strongly injected by pegmatites. Orthogneiss are whitish grey or pink. Gélinas (1959) mentions that gneiss in the Stewart Lake area is rarely banded, but it is well foliated. Thus, they appear to be deformed intrusive rocks with a gneissic appearance rather than ancient gneiss. Kuujjuaq Pluton rocks contain 40-70% quartz and 20-40% feldspatr, with oligoclase more abundant than microcline. Ferromagnesian minerals are sparse (5%) and include biotite and locally hornblende. Accessory minerals are sphene, allanite, zircon, apatite and magnetite.

Thickness and distribution

The Kuujjuaq Pluton forms an elliptical intrusion oriented NW-SE, 11 km long by 6 km wide, in the NW portion of the Baleine Lithotectonic Domain. It covers an area of ~53 km² and is located just east of the Pingiajjulik Fault.

Dating

U-Pb dating on zircons of the Kuujjuaq Pluton has given crystallisation ages between 1869 Ma and 1833 Ma, and metamorphic ages around 1830 Ma. This confirms the hypothesis of Gélinas (1959) which proposed that this unit consist of deformed intrusive rocks rather than ancient gneiss. The sample from Perreault and Hynes (1990) was taken in the SE portion of the pluton, while that of Corrigan (personal communication, 2018) was sampled in the central portion. These ages are contemporaneous to the emplacement of other intrusive units within the Baleine Domain, namely the Champdoré Suite (1859-1837 Ma), Kaslac Complex (1835-1828 Ma), De Pas Supersuite (1862-1805 Ma), Lhande Suite (1834 Ma), as well as crystallization of diatexites of the Winnie Suite (1839-1838 Ma).