Building on my last post as the Granite du Vieux Comptoir is invoked in GÉOLOGIE DE LA RÉGION DU LAC CARMOY, BAIE-JAMES (SNRC 33H06, 33H11, 33H14) as the source of the pegs in the area:
"Granite du Vieux Comptoir forms a series of intrusions distributed throughout the volcanic band of the river La Grande and the Opinaca Subprovince. This is the unit the youngest Archaean in the region (2618 +18/-13 Ma, 2618 ±2 Ma, Goutier et al., 1999b and 2000). In the area mapped, it is in the form of small undeformed kilometric intrusions made up of granite coarse to pegmatitic with
biotite,
muscovite and, locally,
tourmaline (figure 2 and inset maps).
These intrusions often form small white hills that stand out clearly in the landscape. Granite is usually light pinkish white with a darker pink patina. The rock commonly exhibits a graphic microstructure.
Biotite (1 to 10%) is the most ferromagnesian mineral commmon. Magnetite (1 to 5%) is also found in millimeter to centimeter crystals,
muscovite (1%),
tourmaline in places and, more rarely, pink garnet and
beryl."
This is very similar to the mineralogy of the Corvette pegmatites as per the PMT prospectus (below) suggesting a potential genetic link:
The highly fractionated S-type Vieux Comptoir granites are the youngest in the region (as is common in other LCT pegmatite provinces), intruding the older units. From Blue's map earlier in the thread, the smaller dark units are definitely Vieux Comptoir granites (VCG) as mapped in the GÉOLOGIE DE LA RÉGION DU LAC CARMOY, the larger central one is likely VCG (VCG?) as its mapped as the same unit on SIGEOM and clearly intrudes earlier granites.
If so, could be a case of fluids (blue arrows) moving outwards along faults from the VCG complex forming the pegs on PMT and C1X ground in structural traps in the amphibolites.
Just spit-balling geology ideas, this is not advice or the absolute truth of the genesis of the regional pegmatites!
