The Misasque River massif was identified by Hocq (1985). He defined this unit as a heterogeneous band of intrusive rocks, leucotonalitic to granitic, located between Neptune and Fire lakes up to Léran Lake. The area occupied by the Misasque River massif was approximately 1500 km². Following geological mapping work in the summer of 2016, Talla Takam et al. (in preparation) divided the Misasque River massif into different plutons based on their mineral composition, geochemistry and magnetic signature. The Misasque Pluton thus redefined mostly includes gneiss and intrusions of tonalite, granite and diorite located north of the René Group. Following mapping work in the summer of 2018, the Misasque Pluton became the Misasque Complex due to the varied nature and ages of rocks included in the unit (Beauchamp et al., 2019).

The Misasque Complex is introduced to describe a large, polyphase gneissic and intrusive mass, bounded to the north by the Laguiche Complex and to the south by the Digne Pluton. This unit represents one of the oldest units in the Cadieux Lake and Bohier Island areas. It consists of the Mesoarchean to Neoarchean basement on which the Upper Eastmain Greenstone Belt (UEGB) has been emplaced. The Misasque Complex corresponds to a “TTG”-type (tonalite-trondhjemite-granodiorite) Archean continental crust. On the total magnetic field map, the Misasque Complex is characterized by uniform and moderate magnetic susceptibility. Only NNE-SSW and E-W oriented brittle fractures form straight lines that demagnetize the complex.

At least four (4) lithofacies have been recognized in the Misasque Complex: 1) variously migmatized tonalitic, dioritic and granitic gneiss, 2) homogeneous and foliated tonalite, 3) heterogeneous and foliated granite and granodiorite, and 4) massive to weakly foliated homogeneous granite. Rocks of the Misasque Complex are granoblastic and usually cut by several granitic phases occurring as multiple injections cutting or conformable to gneissosity. These intrusions are an integral part of the complex. Rocks of the Misasque Complex contain decimetric to decametric horizons and enclaves of intrusive rock (diorite, gabbro, amphibolite, quartz diorite, tonalite, very locally paragneiss and pyroxenite) representing 1% to 25% of outcropping surfaces. The most common enclaves are dioritic and gabbroic. They have a black and white spotted alteration patina. Enclaves are amphibolitized, foliated and highly granoblastic. They are characterized by well-developed L-S deformation.

From a geochemical perspective (Beauchamp, 2019), rocks of the Misasque Complex are tonalite and type I metaluminous granite (Frost et al., 2001). Samples analyzed are enriched in light rare earths compared to heavy rare earths. Granite profiles are more evolved than those of tonalite and have an Eu negative anomaly (Palme and O’Neill, 2004). Spider diagrams of tonalite and granite exhibit negative anomalies in Nb-Ta, P, Ti and Sm, and enrichments in La-Ce and Zr-Hf (McDonough and Sun, 1995).

Because of the complexity and inconsistent distribution of lithological units, it was not possible to isolate them on the geological map. Lithofacies presented below are in order of importance.

Variously Migmatized Tonalitic, Dioritic and Granitic Gneiss

This orthogneiss unit consists of alternating millimetric to decimetric bands having composition varying from tonalitic to dioritic to granitic. In thin section, gneissosity occurs as alternating mafic bands (biotite ± hornblende ± magnetite) and whitish quartzofeldspathic layers. Sharp, irregular and very contrasting banding is accentuated by the presence of sub-conformable granitic injections. A large proportion of these rocks have undergone migmatization to varying degrees of partial melting, which is manifested by the presence of 5 to 70% granodioritic to granitic mobilisate. The mobilisate occurs as centimetric to decametric, discontinuous bands parallel or cutting regional foliation. Within the most migmatized rocks, intermediate to mafic enclaves float in the mobilisate. Hornblende porphyroblasts are distributed irregularly near intermediate rock enclaves. Centimetric amphiboles give the rock a speckled texture.

Orthogneiss contain biotite and magnetite, with varying amounts of green hornblende, chlorite and epidote. Ferromagnesian minerals form clusters accounting for 5 to 15% of the rock. Traces of sphene, apatite and rutile can also be observed. Coarse plagioclase crystals are subhedral, twinned and weakly to strongly altered (sericitized and saussuritized). Biotite is partially to completely chloritized and locally epidotitized. In thin section, gneiss have polygonal and interlobed textures. Quartz grains have a sutured rim and an undulatory extinction. Apatite and three types of epidote (allanite, pistachite and clinozoisite) are also observed in places.

Homogeneous and Foliated Tonalite

This facies consists of a foliated, homogeneous light grey tonalite. This unit is fine to medium grained and contains 5 to 15% ferromagnesian minerals (biotite ± magnetite ± hornblende). This unit, unlike the one described above, is not a gneissic. Within the tonalitic facies, there are 5 to 25% bands of white hornblende granite and hololeucocratic whitish to pinkish granite in sharp and/or diffuse contact. Some sharp and continuous bands are interpreted as early transposed injections, while those that are millimetric to centimetric, diffuse and discontinuous are instead interpreted as mobilisate. In thin section, tonalite is usually well recrystallized. Typical ferromagnesian minerals are biotite and hornblende. They are disseminated in the matrix and form, in places, continuous or discontinuous millimetric laminae. Within a single thin section, some bands are richer in biotite and others in hornblende. Plagioclase crystals, on the other hand, are locally saussuritized. Accessory minerals observed are zircon, apatite, allanite and sphene.