|Author:||Goutier et al., in preparation|
|Type area:||The southeast portion of NTS sheet 33F01, approximately 10 km east of Lablois Lake. The most differentiated facies outcrops in the suite are located 3 km west of Pelletan Lake (sheet 33H04, Pelletan Ultramafic Intrusion, Goutier et al., in preparation) and 21 km northeast of the Éléonore Mine facility (sheet 33B13, Giard Ultramafic Intrusion, Bandyayera et al., 2010). The sample taken for U-Pb isotopic dating in a felsic dyke cutting the Giard Ultramafic Intrusion (2008-PR-6037) gives the minimum age of the Lablois Suite.|
|Geological province:||Superior Province|
|Geological subdivision:||La Grande and Opinaca subprovinces|
|Lithology:||Olivine metawebsterite and metawebsterite|
Table des matières
Ultramafic intrusions in the La Grande and Opinaca subprovinces have been observed since the early mapping of this area (e.g., Eade Unit 9, 1966; Ub on Sharma Map 1878, 1977). During the 2012 geological mapping, several orthopyroxene porphyroblast or anthophyllite-rich ultramafic intrusions were mapped in several portions of sheet 33H (Chartier-Montreuil, 2013; Hammouche et al., 2016; Goutier et al., in preparation). In 2013, an honours thesis was undertaken to characterize these intrusions and divide them into several groups (Grezla, 2014). As a result, the Lablois Suite was defined based on the results of Chartier-Montreuil (2013), Grezla (2014), the geological mapping work of 2015 (sheets 33F01 and 33F02, Goutier et al., in preparation) and the visit of the Giard Ultramafic Intrusion outcrops by Goutier in 2015. Hammouche and Burniaux (in preparation) divided this suite into two units, depending on the abundance of micas in the rock; unit nAslb1 combines intrusions rich in phlogopite and biotite, while unit nAslb2 is composed of intrusions lacking or very poor in micas.
Unit nAslb of Lablois Suite consists of an olivine metawebsterite, with or without phlogopite, commonly orthopyroxene and anthophyllite porphyroblastic. These intrusions are generally small (<2 km²). They are characterized by a high magnetic susceptibility that allows for easy identification on the magnetic gradient map. Unit nAslb corresponds to ultramafic intrusions without distinction of the presence of phlogopite.
At the scale of the outcrop, the rocks form rounded hills a few metres high. The rock patina is brown to greenish and the fresh surface is dark green to black. Olivine metawebsterites of the Lablois Suite usually contain phlogopite. Rock typically has a porphyroblastic texture due to orthopyroxene recrystallization. This corresponds to a “ball” facies with porphyroblasts ranging in diameter from 0.5 to 10 cm. These rocks may show weak foliation or even banding. The typical mineralogical assemblage consists of orthopyroxene, partially serpentinized olivine, tremolite, phlogopite, magnetite and traces of spinel.
These rocks are also characterized by weak preservation of primary orthopyroxene and olivine, which are replaced by tremolite/cummingtonite, orthopyroxene and anthophyllite porphyroblasts. The “needle” facies is associated with anthophyllite-rich rock (>15%) with crystals up to 7 cm long. Carbonate, talc and chlorite alterations are also observed. A number of these are located near shear corridors. Locally, they contain anomalous levels of gold (> 300 ppb Au, 1906020351), platinum group elements or chromium (2013056557).
Unit nAslb1 in the Lablois Suite meets the same criteria as those in the undifferentiated Lablois Suite (nAslb), except for a high percentage of phlogopite (≥5%).
Unit nAslb2 meets the same criteria as the undifferentiated Lablois Suite (nAslb), except for the absence or very low amounts of phlogopite in the rock (<5%).
The intrusions belonging to the Lablois Suite are small (area less than 2 km² with an average of 0.32 km², Duvernois, 2017). Altogether, the 80 bodies surveyed cover a total area of 22 km². They are primarily located in the Opinaca Subprovince, or at the interface between the La Grande and Opinaca subprovinces (sheets 33H01, 33H02 and 33H03). In many cases, they follow or are adjacent to shear zones, which can be mapped or locally present as boudinaged metric dykes. Some of these dykes are adjacent to gold-bearing zones (e.g., Quentin Index, 2012-QD-2133, sheet 33H04).
The age of 2619.6 +1.9/-1.4 Ma was obtained from a felsic dyke cutting the Giard Ultramafic Intrusion which is related to the Lablois Suite (outcrop 2008-PR-6037). It is therefore a minimum age.
|Isotopic System||Mineral||Crystallization Age (Ma)||(+)||(-)||Reference(s)|
|U-Pb||Zircon||2619.6||1.9||1.4||David et al., 2011|
Ultramafic intrusions cut almost every unit in the Opinaca Subprovince. They are intrusive into the rocks of the Trieste and Rivière Solomon formations. These rocks are less deformed than those of the Laguiche Complex, but have undergone significant metamorphism which resulted in the recrystallization of orthopyroxene and olivine. They are cut by dykes from the Vieux Comptoir Granitic Suite, as well as diabases of the Lac Esprit Dykes.
Does not apply.