|Author:||Moukhsil and Daoudene, 2019|
|Reference section:||Reference outcrops (e.g., 18-AM-205) are located north of Bonhomme Lake, along the Trenche River|
|Type area:||SW corner of NTS sheet 32A07|
|Geological province:||Grenville Province|
|Lithology:||Felsic to intermediate intrusive rocks|
Table des matières
The Bonhomme Plutonic Suite is a unit introduced by Moukhsil and Daoudene (2019) during mapping of the Commissaires Lake area, SW of Lake Saint-Jean (NTS sheet 32A07).
The Bonhomme Plutonic Suite is polyphase and consists of mangerite, syenite, orthopyroxene syenite, orthopyroxene monzodiorite and syenogranite. These different facies are scattered in the intrusion and cannot be grouped into separate units at the 1:50 000 map scale. The Bonhomme Plutonic Suite is very magnetic and easy to delineate from aeromagnetic maps (Intissar and Benahmed, 2015).
Mangerite is whitish to brownish in altered patina and greenish in fresh exposure. It is porphyritic, locally megacristic, with 1-5 cm long K-feldspar and plagioclase phenocrystals. These phenocrystals, which can represent up to 30% of the rock, have a weak preferential orientation. In addition, the poorly developed preferential alignment of ferromagnesian minerals shows a weak foliation. K-feldspar is generally perthitic and locally rimmed by whitish plagioclase (rapakivi texture). Quartz and feldspar form myrmekites in places. The rock is also composed of altered orthopyroxene, quartz, green hornblende, biotite with apatite inclusions, zircon, epidote and opaque minerals (magnetite and pyrrhotite).
At the outcrop scale, variation in K-feldspar content can usually be observed, reflecting the gradual shift of mangerite to syenite. The latter is brownish to pink in altered surface and pink in fresh exposure, massive and generally K-feldspar porphyritic. It can contain crystals of orthopyroxene, magnetite and, in smaller amounts, biotite.
Orthopyroxene monzodiorite is greyish in fresh exposure, fine to coarse grained and generally foliated to gneissic. In thin section, it displays large millimetric orthopyroxene crystals, usually altered into a white mica-carbonate-chlorite assemblage. Quartz has an undulatory extinction and magnetite occurs either as disseminated crystals in the rock or as inclusions in brown-red biotite. K-feldspar is perthitic, while plagioclase polysynthetic twinning pinches out.
Syenogranite is pink-grey in altered patina, pink in fresh exposure, coarse grained and K-feldspar porphyritic. In thin section, the latter is usually perthitic and associated with large quartz zones with undulatory extinction. These two minerals also form myrmekites. Ferromagnesian minerals do not exceed 3% of the rock and consist of green hornblende and biotite. Epidote, apatite and zircon are the accessory minerals. In general, the rock does not show evidence of deformation to the naked eye, but quartz grains locally show a slight preferential flattening that marks a poorly developed foliation.
The Bonhomme Plutonic Suite forms an 800 km2 batholith, only 150 km2 of which outcrops in the SW corner of sheet 32A07 and NW corner of sheet 32A02, mapped by Moukhsil and Daoudene (2019). The remainder of the suite (~650 km2) outcrops in sheets 32A03 and 32A06, which have not yet been mapped to 1:50 000. Interpretation of regional aeromagnetic maps indicates the extent of this intrusion in these two sheets (Intissar and Benahmed, 2015).
A dating on the sample 2018-AM-0205A was recently carried out.
|Unit||Sample Number||Isotopic System||Mineral||Crystallization Age (Ma)||(+)||(-)||Reference(s)|
Does not apply.
INTISSAR, R., BENAHMED, S. 2015. LEVE MAGNETIQUE AEROPORTE DANS LE SECTEUR OUEST DU LAC-ST-JEAN, PROVINCE DE GRENVILLE. MERN, GOLDAK AIRBORNE SURVEYS. DP 2015-06DP 2015-06, 7 pages and 2 plans.
MOUKHSIL, A., DAOUDENE, Y. 2019. Géologie de la région du lac des Commissaires, Province de Grenville, région du Saguenay–Lac-Saint-Jean, Québec, Canada. MERN. BG 2019-01.
PAPAPAVLOU, K. 2019. U-Pb geochronology report, Grenville 2018-2019. UQAM. MB 2019-11, 21 pages.