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 (Goutier, 2012; Gigon et al., 2013 a et b; Chartier-Montreuil, 2013; Hammouche et al., 2016; Goutier et al., 2021). 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, 33F02, 33F07, 33G04 and 33G05; Goutier et Gigon, 2015; Goutier and Gigon, 2016a and b; Gigon and Goutier, 2017; Goutier, 2018; Gigon et al., 2020) and the visit of the Giard Ultramafic Intrusion (Bandyayera et al., 2010) outcrops by J. Goutier in 2015. Its name is associated with the Lablois Lake, in the south of the sheet 33F01, on the west side of which an intrusion outcrops. 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. The undivided 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 usually contains 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.