Caste Formation
Stratigraphic label: [narc]lc
Map symbol: nAlc

First published: 5 June 2018
Last modified: 17 July 2018























Translation of original French



Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
Author: Brett et al., 1976
Age: Neoarchean
Reference section:  
Type area: Various and undifferentiated sedimentary rock units belonging to this formation are found in NTS sheets 32D07, 32D08, 32C05 and 32C04. The most representative outcrops are found on the shores of La Motte Lake and on forest roads of sheet 32D08.
Geological province: Superior Province
Geological subdivision: Abitibi Subprovince
Lithology: Sedimentary rocks
Type: Lithostratigraphic
Rank: Formation
Status: Formal
Use: Active


Related unit(s)
  • Kewagama Group
    • Caste Formation
    • Mont-Brun Formation
    • Rivière Dufresnoy Formation




The name “Lac Caste Group” was originally attributed to these lithologies by Brett et al. (1976). It comes from a small lake in lots 42 to 49 of range IX and X in Cléricy Township, NTS sheet 32D07. James and Mawdsley (1927), Cooke et al. (1931), Norman (1944), Sharpe (1961) and Dawson (1966) had long identified these sedimentary units and their vast expanse. Dimroth et al. (1973) and Dimroth and Rocheleau (1979) also used this name. Goutier (1997) subsequently proposed the name “Caste Formation”, which is part of the Kewagama Group.



Formation de Caste (Alc)Formation de Caste (Alc)

Sedimentary rock units consisting of sandstone, turbiditic and graphitic mudrock, black claystone, polygenetic conglomerate and biotite schist occur as bands or enclaves in intrusive rocks of the La Corne Batholith. The main minerals identified in megascopic samples are quartz and biotite. Feldspars are abundant in places. In these units, around the La Motte and La Corne batholiths, garnet or staurotide porphyroblasts of up to 3 mm in diameter are found in bands dominated by biotite.

Biotite schist is usually well-foliated and is mainly composed of fine-grained equigranular quartz surrounding large flakes of biotite and sodic plagioclase. Grains have an average size of 0.3 mm. Musovite, chlorite, epidote, apatite, sericite, clinozoisite, zircon and pyrite are accessory minerals (Brett et al., 1976). Chlorite commonly replaces biotite. Biotite schist is medium to fine grained. In altered surface, it is usually grey with iron oxide stains; in fresh exposure, different shades of grey are observed. The general alignment of biotite flakes in the quartz-feldspar matrix defines schistosity. Banding is well developed locally, with bands ranging in width from 1 to 10 cm. Some bands contain mainly quartz, accompanied by biotite.

Schist foliation has an approximate but fairly constant E-W direction, but it locally follows the La Motte and La Corne batholith edges in a N-S direction. Locally, schist can be intensively folded and shows well-developed drag folds, thin ptygmatitic quartz veinlets and quartz veins and clusters. Quartz veins are commonly parallel to or cut schistosity at a sharp angle. Several veins are boudinaged and folded in complex ways. Generally E-W-orientated bedding can be seen in a few places in sheet 32D08. This bedding has the same dip as schistosity but is locally more abrupt. Stratification and bedding commonly dip 30 to 60° northward. Summits generally appear to be facing southwest (Brett et al., 1976).

Partial assimilation of sedimentary rocks by batholith masses is commonly observed. Such examples of partial assimilation, manifested by migmatization, were observed in sheet 32D08 and in the northern portion of sheet 32C04. Biotite schist then occurs as elongated fine-grained enclaves composed of biotite, quartz and feldspar phenocrystals with fuzzy edges.

There does not appear to be any significant change in the degree of metamorphism of schists near batholiths. Grade varies from amphibolite to upper greenschist away from batholiths. Considering that none of these sedimentary units are more than 1600 m away from batholith contact, it can be assumed that all have undergone approximately the same degree of metamorphism (Brett et al., 1976). Enclaved biotite schists are similar to schists found outside batholiths. A well-defined chilled margin between biotite monzogranite of the La Motte massif and this formation is not observed, except for the presence in several places of staurotide and garnet in these schists.


Thickness and Distribution

Sandstone, turbiditic and graphitic mudrock, black claystone and polygenetic conglomerate units average 20 to 30 cm in thickness. They can be found in sheets 32D07, 32D08, 32C05 and 32C04.



Feng and Kerrich (1991) obtained a ziron U-Pb minimum age of 2691 ±2 Ma on a site located in sheet 32D08. David (personal communication) obtained an age of 2695 ±2 Ma, also in sheet 32D08.

Isotopic System Mineral Age (Ma) (+) (-) Reference(s)
U-Pb Zircon 2691 2 2 Feng et Kerrich, 1991
U-Pb Zircon 2695 2 2 David, personal communication

Stratigraphic Relationship(s)

This formation is a sedimentary basin bordered by the Manneville Nord Fault, in the north, and the Manneville Sud Fault, in the south. All of La Motte and La Corne batholiths intrude this formation. Volcanic units bordering this formation on the north side (Kinojévis Group, age 2716-2719 Ma) and on the south side (Malartic Group, age 2714-2706 Ma) are 15-25 Ma older than sedimentary rocks, which clearly demonstrates the regional structural importance of border faults. 


Does not apply.


Author(s) Title Year of Publication Hyperlink (EXAMINE or Other)
BRETT, P.R. – JONES, R.E. – LEUNER, W.R. – LATULIPPE, M. Canton de La Motte. Ministère de l’Énergie et des Ressources naturelles, Québec; RG 160, 153 pages. 1976 RG 160
COOKE, H.C. – JAMES, H.F. – MAWDSLEY, J.B. Géologie et gîtes minéraux de la région de Rouyn-Harricanaw, Québec. Commission géologique du Canada; mémoire 166, 333 pages (1 carte). 1931 Source
DAWSON, K.R. A comprehensive study of the Preissac-La Corne Batholith, Abitibi County, Quebec. Commission géologique du Canada; Bulletin 142, 76 pages (3 cartes). 1966 Source
GOUTIER, J. Géologie de la région de Destor (SNRC 32D/07-200-0201). Ministère de l’Énergie et des Ressources naturelles, Québec; RG 96-13, 37 pages. 1997 RG 96-13
IMREH, L. Sillon de La Motte-Vassan et son avant-pays méridional : synthèse volcanologique, lithostratigraphique et gîtologique. Ministère de l’Énergie et des Ressources, Québec; MM 82-04, 72 pages. 1984 MM 82-04
JAMES, W.F. – MAWDSLEY, J.B. Régions de La Motte et de Fournière, comté d’Abitibi, Québec. Commission géologique du Canada; Rapport Sommaire 1925, Partie C. 1927 Source
NORMAN, G.W.H. La Motte map-area, Abitibi County, Quebec. Geological Survey of Canada; Paper 44-9, 13 pages. 1944 Source
13 novembre 2018