The Nichicun Pluton was introduced by Hammouche and Burniaux (2018) following 1:50 000 geological mapping work in the Joubert Lake area (sheets 33H01, 23E03 and 23E04), carried out during the summer of 2015. The pluton was initially assigned to the Lataignant Suite by Lamothe et al. (2000), during the 1:250 000 survey in the Nitchéquon Lake area. They relied on the composition a priori similar to the Dusterlo and Delmothe batholiths which are part of the Lataignant Suite. However, U-Pb dating of the Nichicun Pluton (David, 2018) indicates that it is much younger than the Lataignant Suite. On the other hand, the Artigny Pluton (Talla Takam et al., in preparation) has a crystallization age close to that of the Nichicun Pluton.

The Nichicun Pluton consists of a megaporphyritic granite that contains up to 25% K-feldspar phenocrystals 1 to 7 cm long. The rock is massive (not foliated), homogeneous, pinkish in exposed surface and fresh exposure. Locally, there is an alignment of phenocrystals of magmatic origin. The rock consistently contains biotite (3-15%), hornblende (1-10%, locally up to 15%) and magnetite (2-4%). In places, isolated submillimetric garnet grains (1-2%) and trace sphene are observed.

The pluton contains numerous enclaves of paragneiss, metatexite and diatexite from the Rivière Salomon Formation. It is cut locally by pegmatitic granite.

Thickness and distribution

The Nichicun Pluton forms a mass ~180 km² in the NE quarter of sheet 23E03. It extends 12 km N-S by 18 km E-W. No data are available to define its parameters in depth. The pluton is located NW of Nichicun Lake. In this area, two small intrusions with the same characteristics as the main intrusion were therefore assigned to this pluton.

Dating

Lamothe et al. (2000) attributed this intrusion to the Lataignant Suite aged between 2638 and 2642 Ma (David and Parent, 1997; Parent, 1998). Recent dating of the Nichicun Pluton indicates a crystallization age of 2592 ±5.2 Ma (David, 2018), much younger than intrusions of the Lataignant Suite. This age is comparable to that of the Artigny Pluton (2589 ±4 Ma; Davis and Sutcliffe, 2018).