The granitoid mass of the Lapparent Intrusive Suite first appeared on the map of Retty and Norman (1938). Remick (1956, 1957) recognized different phases of the Lapparent Suite but did not differentiate them on the map. In 1970, Duquette described the Lapparent Pluton, to which the MacIntosh Pluton is associated, as a tonalite-diorite mass. Granodiorite of the MacIntosh Pluton was first identified on the map of Racicot et al. (1984). Nantel (1985) identified the pluton’s potential for dressed stone. The current pluton boundaries were defined by Midra et al. (1992a), who provided a more detailed description.

According to Midra et al. (1992a):

“[The MacIntosh Pluton] is whitish to reddish pink in altered surface and light pink to orange in fresh exposure. The rock is medium grained on the edge and very coarse in the core. Centimetric microcline and quartz phenocrystals give granodiorite a porphyritic appearance. Foliation in the rock is marked by the flattening of quartz grains, which are locally crenulated at the scale of the outcrop. In places, the pluton is cut by high deformation zones with a thickness of no more than one metre; the rock in this case is mylonitized. These observations suggest a late-tectonic age for the MacIntosh Pluton.

The pluton is cut in two parts by the Gwillim Fault. Only the eastern part outcrops. Hematitization that accompanies late and brittle N-E oriented faults is responsible for the reddish colour in some parts of the intrusion.

The texture is granular at the edge and quickly changes to porphyritic in the core. In high deformation zones that cut the pluton, mylonitic textures develop.

Microcline phenocrystals are centimetric and euhedral. Ovoid quartz (1.5-3 cm) is recrystallized into polycrystalline aggregates with edges of millimetric crystals being sutured. Microcline and quartz phenocrystals are embedded in a matrix composed mainly of plagioclase, microcline, quartz and epidote. Subhedral plagioclase (< 2 mm) displays twisted twinning and locally contains inclusions of epidote crystals. Microcline is millimetric and forms subhedral to euhedral crystals. Quartz, present in minor amounts, is interstitial. Epidote (clinozoisite) usually occurs as polycrystalline aggregates (2 mm) at the edges of plagioclase and in voids. Secondary minerals are chlorite, muscovite, sphene and opaque minerals.”

The MacIntosh Pluton has a uniform red colour that is particularly interesting for dressed stone (Nantel, 1985).

Thickness and distribution

Midra et al. (1992a) defined the MacIntosh Pluton around the lake of the same name, the eastern part of which represents the type area. The MacIntosh Pluton has an oval shape dissected by faults. It extends for 5 km towards the ENE along the Gwillim Fault, and is ~2 km wide.

Dating

None.