Lac Doré Upper Unit
Stratigraphic label: [narc]cds
Map symbol: nAcds

First published: 1 February 2019
Last modified:













Translation of original French

Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
Author: Leclerc et al., 2017
Age: Neoarchean
Reference section: None
Type area: The Lac Doré Upper Unit is very well exposed to the NW of Clark Lake and north of David Lake (NW portion of NTS sheet 32G16 and SW portion of sheet 32G15)
Geological province: Superior Province
Geological subdivision: Abitibi Subprovince
Lithology: Mafic to ultramafic intrusive rocks
Type: Lithodemic
Rank: Lithodeme
Status: Formal
Use: Active


The large stratiform and differentiated mafic to ultramafic Lac Doré intrusion was originally identified as the Lac Doré Complex (Allard, 1956, 1976). This name, emphasizing the analogy with stratiform layered complexes such as Bushveld or Stillwater, was maintained by Daigneault and Allard (1990) for historical reasons, despite the recommendations of the North American Stratigraphic Code regarding the use of the term “complex” (Articles 37d and 38; MER, 1986). The most recent version of the North American Stratigraphic Code (NASC, 2005) maintains that it is incorrect to use the term “complex” to refer to “various types of rocks belonging to a single class”. For this reason, Leclerc et al. (2017) propose the following changes to the nomenclature of the Lac Doré Complex in accordance with sections 31 to 41 of the North American Stratigraphic Code: a) the Lac Doré Complex is renamed the Lac Doré Intrusive Suite; b) the Lac Doré Lower Series, Layered Series and Upper Series become the Lac Doré Lower Unit, Layered Unit and Upper Unit respectively; and c) the Layered Zone, included in the Layered Series (former nomenclature), is now referred to as the “layered zone” and is considered an informal lithodeme.


The Lac Doré Upper Unit consists of the border zone and the granophyric zone.

Thickness and Distribution

The Lac Doré Upper Unit was recognized on the north side of the Chibougamau Anticline for a distance of >53 km. On the south side of this anticline, the Lac Doré Upper Unit outcrops on a distance of >30 km. The thickness is estimated between 150 m and 900 m (Daigneault and Allard, 1990).


A granophyre sample from the granophyric zone (Lac Doré Upper Unit) yielded an age of 2727 ±1.3 Ma (Mortensen, 1993).

Isotopic System Mineral Crystallization Age (Ma) (+) (-) Reference(s)
U-Pb Zircon 2727 1.3 1.3 Mortensen, 1993

Stratigraphic Relationship(s)

Rocks of the Lac Doré Upper Unit are overlying those of the Lac Doré Layered Unit. They cut volcanic rocks of the Obatogamau and Waconichi formations (Roy Group‘s first volcanic cycle). They are unconformably overlain by sedimentary rocks of the Opemisca Group.


Does not apply.


Author(s) Title Year of Publication Hyperlink (EXAMINE or Other)
ALLARD, G.O. The geology of a portion of McKenzie Township, Chibougamau District, Quebec. John Hopkins University; thèse de doctorat, 168 pages. 1956
ALLARD, G.O. Doré Lake Complex and its importance to Chibougamau geology and metallogeny. Ministère des Richesses naturelles, Québec; 486 pages, 2 plans. 1976 DPV 368
DAIGNEAULT, R. – ALLARD, G.O. Le Complexe du lac Doré et son environnement géologique (région de Chibougamau – Sous-province de l’Abitibi). Ministère de l’Énergie et des Ressources, Québec; 290 pages. 1990 MM 89-03
LECLERC, F. – ROY, P. – HOULE, P. – PILOTE, P. – BÉDARD, J.H. – HARRIS, L.B. – McNICOLL, V.J., VAN BREEMEN, O. – DAVID, J. – GOULET, N. Géologie de la région de Chibougamau. Ministère de l’Énergie et des Ressources naturelles, Québec; 97 pages, 3 plans. 2017 RG 2015-03
MINISTÈRE DE L’ÉNERGIE ET DES RESSOURCES (MER) Code stratigraphique nord-américain. Ministère de l’Énergie et des Ressources, Québec; 76 pages. 1986 DV 86-02
MORTENSEN, J.K. U-Pb geochronology of the eastern Abitibi subprovince. Part 1: Chibougamau – Matagami – Joutel region. Canadian Journal of Earth Sciences; volume 30, pages 11–28. 1993 Source
NORTH AMERICAN STRATIGRAPHIC COMMISSION ON STRATIGRAPHIC NOMENCLATURE (NASC) North American Stratigraphic Code. AAPG Bulletin; volume 29, pages 1547–1591. 2005 Source
16 janvier 2020