|Author:||Leclerc et al., 2017|
|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|
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.
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)|
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.