The Grondin Plutonic Suite (mPgro) is a polyphase suite consisting of alkali feldspar granite, syenogranite, quartz monzodiorite, monzodiorite, charnockite and gabbronorite. The different phases of this suite are magnetic and the intrusion is easily identified on aeromagnetic maps (Intissar and Benahmed, 2015). 

Alkali feldspar granite is pink in alteration patina and fresh surface. The rock is fine to coarse grained. Although the structure is generally massive, it is locally deformed and more finely grained (e.g., outcrops 2021-FS-4130 and 2021-FT-3009). The granite consists of quartz, potassium feldspar, plagioclase, biotite and magnetite. Under the microscope, the quartz is in a small patch with undulatory extinction and associated with grains of myrmekite, the potassium feldspar is of the microcline type with a Scottish kilt twin, and the plagioclase has polysynthetic twins subparallel among themselves and contains biotite inclusions. Accessory minerals include apatite and zircon. Alkali feldspar granite contains enclaves and boudins of gabbronorite 5 cm to 2 m thick with amphibole, biotite and pyroxenes (orthopyroxene and clinopyroxene). It is also cut by dykes of pinkish granitic composition 2 cm to 1 m thick.

Syenogranite is pink-brown in alteration patina and pink in fresh surface, medium to coarse grained, heterogeneous and foliated (e.g., outcrop 2021-FT-3074). It consists of quartz, potassium feldspar, magnetite, biotite and amphibole. The proportion of orthopyroxene varies from one outcrop to another, reaching 8% of the rock, which is then known as charnockite (hypersthene granite; e.g., outcrop 2021-FS-4074). Charnockite is rust-white in alteration patina and grey-green in fresh surface. Microscopically, it consists of quartz in a large patch with undulatory extinction, locally perthitic potassium feldspar, plagioclase with polysynthetic twins, biotite, orthopyroxene, magnetite and amphibole. Accessory minerals include allanite, apatite and zircon.

Quartz monzodiorite and monzodiorite are associated with the alkali feldspar granite of this suite. Quartz monzodiorite is grey-brown in alteration patina, grey-white in fresh surface, fine to medium grained, granoblastic and gneissic to banded when deformed (e.g., outcrops 2021-GS-2149 and 2021-FT-3072). It consists of quartz, plagioclase, biotite, hornblende, magnetite, and traces of potassium feldspar. It is injected with veins and veinlets of granitic composition and contains veins of whitish quartz of 1 cm to 3 cm in thickness. The monzodiorite is grey-brown in alteration patina, grey-white in fresh surface, fine to medium grained and gneissic (e.g., outcrop 2021-FT-3071). It is composed of plagioclase, biotite, amphibole, clinopyroxene and magnetite.

Gabbronorite is grey-green in alteration patina, grey-black in fresh surface, medium to coarse grained, subophitic and locally foliated (e.g., outcrop 2021-FT-3010). It consists of hornblende, sericitized plagioclase, fully to partially uralitized orthopyroxene, clinopyroxene, magnetite, and traces of biotite and apatite. Hornblende is more dominant than orthopyroxene and associated with biotite. Locally, the gabbronorite is migmatitic and contains stromatic leucosomes of tonalitic composition measuring 0.5 cm to 5 cm in thickness. It is also cut by injections and dykes of alkali feldspar granite and granite (e.g., outcrop 2021-FT-3013).