|Type area:||North end of Kuuvvaluk River, which connects the Povungnituk River to Péloquin Lake (NTS sheet 35G04). Kuuvvaluk units at the eastern end of the Southern Domain (sheet 35H07) represent metamorphosed equivalents of the type area facies|
|Geological province:||Churchill Province|
|Geological subdivision:||Ungava Orogen / Ungava Trough / Southern Domain|
Table des matières
Beall (1960) was the first to mention the existence of ferriferous deposits at the base of the Povungnituk Group. These units were subsequently described and subdivided by Schimann (1978) and Taylor (1982). Moorhead (1989) detailed the stratigraphy and composition of the Kuuvvaluk Formation in the central section of the Southern Domain. St-Onge and Lucas (1990a-f, 1993) mapped at 1:50 000 scale the extension of the formation in the eastern part of Southern Domain.
The Kuuvvaluk Formation is an allochthonous sedimentary unit located in the basal section of the Southern Domain stratigraphic pile. The Kuuvvaluk Formation typically has a metre to decametre-thick magnetite quartzite bed (unit pPku1) at its base. This unit forms centimetric to metric beds locally interstratified with grunerite-magnetite schist beds (pPku2), the proportion of which gradually increases towards the top to form beds 1 m to 20 m-thick beds (Moorhead, 1989). Schist changes laterally to iron formation beds (pPku3). The latter may form decametric layers consisting mainly of crossbeds rich in stilpnomelane, grunerite and quartz, and locally siderite beds, all interstratified with centimetric chert beds (Moorhead, 1989). Lateral interstratifications with alkaline volcanic rocks of the Lac Leclair Formation (Moorhead, 1989) indicate that the Kuuvvaluk Formation deposition is synchronous with this volcanism. At the eastern end of the Southern Domain, the thickness of the Kuuvvaluk Formation ranges between 50 m and 650 m (St-Onge and Lucas, 1993).
The magnetite quartzite unit was observed and described in the Chukotat Lake area by Moorhead (1989). This unit is usually close to the contact with Archean bedrock. It is also interstratified with iron formation (pPku3) and grunerite-magnetite schist (pPku2) beds. The bed’s thickness varies from a few centimetres to 2 m, for a total thickness between 5 m and 10 m. This dark grey rock is almost exclusively composed of microgranoblastic quartz and, in smaller amounts, magnetite as disseminated euhedral crystals giving it a magnetic character. Calcite and grunerite are locally present in varying amounts. In thin section, quartz is completely recrystallized and no original detrital grains were observed (Moorhead, 1989).
The grunerite-magnetite schist unit forms 1 to 20 m-thick beds. The rock is grey-green to grey-yellow in altered surface and grey-yellow in fresh exposure. It consists of massive schist containing 3 mm to 12 mm-long grunerite flakes or rosettes pointing in all directions in a matrix composed of recrystallized quartz. Magnetite occurs as euhedral crystals 1 mm to 3 mm or, more sparsely, as 1 mm to 5 mm-thick laminations. Iron oxide and carbonate platings 5 to 15 mm-thick have been observed in a few places where quartz-rich beds outcrop (Moorhead, 1989).
The iron formation unit consists of a banded rock exhibiting 5 cm to 30 cm-thick bands rich in stilpnomelane, grunerite, quartz, ferruginous chlorite, calcite and iron oxides. These bands, dark red to rusty brown, alternate with whitish bands composed almost exclusively of quartz (recrystallized chert). These whitish bands commonly contain concretions (1 cm in diameter) composed of carbonates and iron oxides with minor amounts of stilpnomelane, grunerite and calcite. This facies is generally interstratified with the grunerite-magnetite schist facies (pPku2). Sedimentary structures, such as crossbeds, have been observed locally on this facies. This could indicate that these ferruginous sediments have deposited in a relatively shallow environment. The Kuuvvaluk Formation’s ferruginous sedimentary sequence becomes thinner and disappears a few kilometres east and west of Allemand Lake. In addition, this unit does not outcrop in areas immediately east and west of Chukotat Lake (Moorhead, 1989).
This unit recognized and described in the Chukotat Lake area is interstratified with the grunerite-magnetite schist (pPku2) and iron formation (pPku3) units in the eastern part of the Southern Domain. The thickness of this facies ranges from 20 m to 50 m. These dark green to grey-green rocks occur in beds 1 m to 3 m-thick, containing subrounded fragments (0.1-1 mm in diameter) of limestone, plagioclase, quartz and granodiorite. The matrix is composed of quartz, actinolite, calcite, biotite, chlorite, siderite and magnetite. Magnetite is very abundant locally, giving the rock a magnetic character. Actinolite forms porphyroblasts 0.1 mm to 1 mm in diameter. Siderite forms euhedral crystals (1-3 mm) that can make up 20% of the rock locally. In places, schist is cut by carbonate veins 1 mm to 3 mm wide. In addition, it should be noted that volcanic fragments are sparse. These schists probably represent a distal facies of epiclastic nature of the Lac Leclair Formation block tuff (Moorhead, 1989).
Refer to the “Description” section for this information.
In general, the Kuuvvaluk Formation is in structural contact with Archean bedrock through a decollement plane. However, west of Leclair Lake (sheet 35C14) and in Burgoyne Bay erosion klippes, the unit conformably overlies the Korak Formation, which itself unconformably (erosional discordance) lies on bedrock (St-Onge and Lucas, 1993; Moorhead, 1996b). Note that the formation is too thin in Burgoyne Bay klippes to be visible on the compilation map.
No fossils reported.