|Author:||Beauchamp and Massei, 2018|
|Type area:||Bohier island area (NTS sheet 33A08)|
|Geological province:||Superior Province|
|Geological subdivision:||Opatica Subprovince|
Table des matières
Hocq (1985) introduced the 485-km2 Lac Cadieux Massif between the Upper Eastmain Greenstone Belt (UEGB) and the Eastmain River to its work. This large felsic package is described as mostly granodioritic. In 1987, Roy clarified the nature of this massif and introduced the Lac Cadieux Granodiorite, which he described as banded and slightly porphyritic. Beauchamp and Massei (2018) refined the nomenclature of this unit and the name Cadieux Pluton. The Cadieux Pluton becomes the Cadieux Suite (Beauchamp and Massei, in preparation).
The Cadieux Suite consists of granodiorite. The unit is very homogeneous and is easily distinguishable from other rocks in the area, particularly its porphyraceous texture from K-feldspar phenocrystals. These phenocrystals are 1 to 3 cm long and may represent 1 to 5% of the rock, with the remainder of the rock being medium-grained. This granodiorite is grey-white in altered surface and grey-pink in fresh exposure. Foliation is visible but light. The main ferromagnesian minerals are biotite (5-10%), amphibole (1-5%) and magnetite. Sphene is commonly observed. The magnetism of the rock moves from weak to moderate, but may be strong locally depending on the amount of magnetite present. The main alterations affecting the rock are mild chloritization and weak hematization. Under the microscope, sphene, epidote and allanite (locally zoned) are present.
From a geochemical perspective, the Cadieux Suite rocks have a very strong calc-alkaline affinity (Ross and Bédard, 2009). They are peraluminous to metaluminous, but remain type I (Maniar and Picolli, 1989). They plot into the field of volcanic arc granites (Pearce et al., 1984). The rare earth profile does not have any particular anomaly and shows light rare earth enrichment relative to heavy rare earths.
There are three occurrences of the Cadieux Suite in NTS sheets 33A08 and 33A07. The first, in the northern portion, has the shape of an oval 8 km in the direction of the small axis and 15 km in the direction of the large axis, around which basalts of the Groupe de René mould themselves. The Lac Hécla Anticlinal crosses the heart of the pluton parallel to the main axis. The second occurrence runs south of the western branch of the UEGB along its entire length, from the south of Bohier Island in the east to sheet 33A07 in the west.
The Cadieux Suite is in contact with rocks of the UEGB (René and Bohier groups), paragneiss of the Laguiche Complex and tonalite of the Misasque Suite. The suite is actually younger and less deformed than all the units it intrudes.
Does not apply.