|Author:||Goutier et al., in preparation|
|Type area:||SE 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 NE of the Éléonore Mine facility (sheet 33B13, Giard Ultramafic Intrusion, Bandyayera et al., 2010).|
|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 work results of Chartier-Montreuil (2013) and Grezla (2014), as well as geological mapping work of 2015 and 2016 (sheets 33F01 and 33F02, Goutier and Gigon, 2016; Gigon et Goutier, 2017) and the visit of the Giard Ultramafic Intrusion outcrops by Goutier in 2015. Hammouche and Burniaux (2018) 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.
Undifferentiated unit nAslb of the Lablois Suite consists of an olivine metawebsterite, with or without phlogopite, commonly orthopyroxene and anthophyllite porphyroblastic. Intrusive masses 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 metawebsterite 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.
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 certain number of outcrops are located near shear corridors. Locally, contain anomalous contents in gold (> 300 ppb Au, geochemical anlysis 1906020351), platinum group elements or chromium (geochemical anlysis 2013056557) are observed.
Lablois Suite unit nAslb1 corresponds in all respects to the undifferentiated Lablois Suite (nAslb), except for high phlogopite content (≥5%).
Unit nAslb2 has the same characteristics as the undifferentiated Lablois Suite (nAslb), except for the absence or very low content of phlogopite (<5%).
The intrusions belonging to the Lablois Suite are small (maximum area of 2 km², average of 0.32 km²; Duvernois, 2017). Altogether, the 106 bodies surveyed cover a total area of 24,2 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 are parallel or adjacent to shear zonesand occurring as locally boudinaged metric dykes. Some of these dykes are adjacent to gold-bearing zones (e.g., Quentin Showing, outcrop 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 intrusion age for the Lablois Suite.
|Sample Number||Isotopic System||Mineral||Crystallization Age (Ma)||(+)||(-)||Reference(s)|
|2008-PR-6037||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 of the Vieux Comptoir Granitic Suite, as well as diabases of the Lac Esprit Dykes.
Does not apply.