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 Intrusive Suite, including plagioclase granite, but did not differentiate them on the map. In 1970, Duquette described the Lapparent Pluton, a massif to which is associated the Est Tonalite, as a tonalite-diorite mass. Racicot et al. (1984), Tait and Chown (1987) and Tait et al. (1990) developed the first subdivisions of the Lapparent Intrusive Suite, but did not distinguish the Est Tonalite, which was finally defined by. Midra et al. (1992a, b).

 

Est Tonalite, Undivided (nAtoe): Biotite Tonalite

According to Midra et al. (1992a):

“[The Est Tonalite] is medium grained and contains plagioclase phenocrystals in some areas of the northern part. On the south shore of Dickson Lake, the rock displays subhorizontal magmatic foliation (plagioclase alignment). A second E-W foliation is also present and is marked by the orientation of ferromagnesian minerals and stretching of quartz grains.

[The NW area] is characterized by the predominance of greyish biotite, and is black grey spotted in fresh exposure. In the southern area, however, chlorite tonalite predominates and is green-spotted greyish in fresh exposure. In both cases, the alteration patina varies from light grey to orange grey. [… ] Texture in tonalitic phases is generally subhedral. Biotite tonalite is slightly more foliated than chlorite tonalite.

Tonalite has a mafic index ranging from 5 to 10%.The main minerals encountered are plagioclase, quartz, biotite and epidote. Accessory minerals are hornblende, apatite, opaque minerals, allanite, zircon and sphene. Plagioclase crystals are millimetric, locally porphyritic, and subhedral. They exhibit slight sericitization and twisted twinning. Anhedral quartz is interstitial and commonly polygonized. Biotite occurs as millimetric subhedral laths and defines a light foliation in the rock. Epidote occurs as irregular clusters, and also rimming allanite. Accessory minerals are generally associated with biotite.”

In 1956, Remick recognized a slight alteration along the SW arm of Dickson Lake. This alteration is characterized by “the presence of small amounts of magnetite, fluorite and pyrite” and “an abundance of cracks filled with pink feldspar or epidote. South of the arm, he notes fractures filled with specularite, calcite or euhedral quartz.

 

According to Midra et al. (1992a, page 36): “Around Mann Lake, the rock becomes granodioritic and has a slight NE foliation.”

 

Thickness and distribution

The Est Tonalite forms a more or less hexagonal mass ~20 km long E-W by 15 km wide N-S around Dickson, Poingdextre and Mann lakes. The Est Tonalite corresponds to the NW part of the Est Tonalite described by Midra et al. (1992a, b). Indeed, Simard (1996) incorporated the SE part of the tonalite as described by Midra et al. (1992a) into the Eau Jaune Complex. According to Midra et al. (1992a, pages 36-38): “The Est Tonalite is bounded to the north and west by tonalitic gneiss and to the SW by the Rachel Pluton.”

 

Dating

None.