Summary:
Deposit Types
Magnetite mineralization at the Mont Sorcier Project shows several similarities to other vanadiferous titanomagnetite (“VTM”) deposits or ilmenite deposits associated with layered mafic intrusive complexes, such as the Bushveld Complex (South Africa) or the Skaergard Intrusion (Greenland).
North Zone
Following the 2021 drilling campaign, the west and central part of the North Zone has been divided into two main zones (Arguin, 2022): Lower (“LZ”) and Upper (“UZ”). The stratigraphic limit between the LZ and the UZ was established by the substantial chemical break between two distinct mineralogical domains (units 3 and 4). Both the LZ and the UZ are composed of distinct magnetite-bearing ultramafic units (or mineralogical domains). The LZ consists of units 1, 2 and 3, whereas the UZ is composed of units 4 and 5.
The east part of the North zone is quite different from the west and central part as the subdivision into five units is not observed. It is essentially composed of ferro-pyroxenite, which is bordered by a “minor envelope” that consists of an inner horizon of talc-peridotite (metadunite) and an outer horizon of gabbroic rocks. No massive sulfides were reported in the east part of the North zone (Arguin, 2022).
Unit 1
Unit 1 is located at the base of the LZ, generally in contact with anorthosite. The silicate matrix consists of a greenish-grey to bottle-green mixture of very fine grains. The grain size makes the matrix minerals difficult to identify with the naked eye. Serpentine is most likely the dominant phase and appears to be accompanied by various amounts of chlorite and accessory talc.
The magnetite is mostly in the form of fine to medium grains, disseminated or sometimes clustered. Magnetite veins (or fracture fillings) are common but not dominant. They are secondary in origin and result from an excess of iron during the serpentinization of olivine and orthopyroxene.
Unit 2
The Unit 2 represents the smallest volume of the North Zone units (~7%). It is characterized by 10-40 vol.% of centimetric, subrounded to euhedral-prismatic phenocrysts. The crystals are pseudomorphosed, either completely replaced by chlorite or displaying mineral zoning composed of (from rim to core) chlorite, green amphibole and possibly altered pyroxene.
The magnetite grains are finely disseminated throughout the matrix, of which the silicate minerals are mainly serpentine and chlorite
Unit 3
Unit 3 is generally located at the top of the LZ. The rock is medium to coarse grained and shows hypidiomorphic granular to intergranular textures. It contains up to 60-70 vol.% of chlorite pseudomorphs, possibly after pyroxene, as well as magnetite and white-colored silicates. Phenocryst pseudomorphs were found as accessory phases in Unit 3. These are white to pale grey in color and shows a well-developed network of fractures filled with magnetite.
The magnetite content of Unit 3 is generally lower than that of other North Zone units. Magnetite is fractured, either interstitial to chlorite (anhedral) or in the form of subhedral to euhedral (cubic) crystals. The grains are usually 0.3-1.0 cm in size but can reach up to a few centimetres. Magnetite is commonly accompanied by accessory disseminated ilmenite.
Unit 4
Unit 4 is located at the base of the UZ. The rock is usually characterized by a well-developed foliation with shear band-like features. The foliation is marked by parallel arrangement of magnetite grains hosted in a fine-grained matrix of platy talc and chlorite. More massive textures are also present sporadically in Unit 4.
Magnetite is generally medium-grained and stretched along the foliation planes. It is commonly accompanied by pyrrhotite, which is likely formed at the expense of magnetite as evidenced by replacement textures.
Unit 5
Unit 5 is located at the top of the NZW, in contact with massive to semi-massive pyrrhotite or sulphide-rich basaltic rocks. The rock is brecciated (or rarely massive) and is typically characterized by chlorite-rich, sub-angular to angular fragments of various sizes (up to a few centimetres) enclosed in a chaotic network of interstitial magnetite.
The magnetite content of Unit 5 is relatively high. Magnetite is in the form of interstitial fillings between breccia fragments and finely disseminated grains. It is commonly associated with substantial amounts of pyrrhotite as veinlets or magnetite replacements. Trace amounts of chalcopyrite often accompany pyrrhotite.
Mineralization on the Property
Two significant mineralized zones are found on the Property, the North Zone and the South Zone.
The North Zone is identifiable in the field and through airborne magnetics over a strike length of approximately 4 km. It appears to be between 100 m and 300 m thick, forming a roughly tabular subvertical body that strikes east-west and extends to depths of at least 500 m based on drilling. The North Zone has been drilled over approximately 4.0 km of its strike length. Possible extensions of the North Zone could be found to the east, as well as down-dip.
The South Zone, identifiable over approximately 3 km, strikes east-northeast to west-southwest. It has been mapped in detail and drilled over its entire strike length. It is thought to form a tight synclinal structure, with a shallow plunge to the west-southwest. It is 100–200 m thick and extends to a depth of at least ~300 m in the western part of the zone, shallowing towards the east. Although the total depth of mineralization has not been fully tested, it is not expected to continue to depths significantly deeper than currently defined. The South Zone has been cut by several small northeast-trending faults, a larger northeast-trending fault with a dextral displacement of ~150 m, and a north-northeast trending dyke ~150 m thick.
The North Zone and South Zone had been interpreted by Dorr (1966) as representing the same stratigraphic unit that has been folded into kilometre-scale parasitic folds by the upright folding that affects the region, with the North Zone representing the north-dipping limb of an anticlinal fold structure, and the South Zone representing the hinge zone of a syncline.
The North and South zones are interpreted to have formed from the crystallization of vanadiferous titanomagnetite (“VTM”) that was triggered when mafic magmas of the LDC assimilated a carbonate-facies iron formation (the Lac Sauvage iron formation) . In both zones, magnetite is disseminated within ultramafic rocks (dunite, peridotite pyroxenite), and the ultramafic VTM-bearing lithologies are surrounded by mafic units (gabbro and anorthosite).