Summary:
All of the PGE-Cu-Ni mineralization documented on the Property is classified as magmatic sulphide mineralization. Conventional magmatic sulphide deposits are defined as disseminated to massive sulphide deposits hosted by ultramafic or mafic rocks that contain economic concentrations of base metals and/or precious metals (PGE, Au, Ag). These deposits can occur in intrusions or lava flows (Naldrett, 2004). Recent advances in the understanding of the relationships between the geology, structure, alteration intensity, metal grades, geochemistry and geophysical characteristics at LDI show that the majority of the known mineral zones can be explained by physical sorting of dense sulphide liquid droplets and high-temperature orthopyroxene crystals from aluminum- and volatilerich residual magma. Increasingly, the importance of pre-magmatic structures in directing the upward flow of magma into the host intrusive complex and in determining the physical location of metal-rich sulphide trap sites is being recognized.
The Lac des Iles property captures the known extents of two discrete intrusive complexes.
These complexes include the South Lac des Iles Intrusive Complex (IC) — comprising the former Mine block, South Lac des Iles and Camp Lake intrusions —and the North Lac des Iles Intrusive Complex (IC). Intrusive contacts between the two complexes suggest that the southern part of the North Lac des Iles IC is younger than the northern margin of the South Lac des Iles IC.
The North Lac des Iles IC consists of layered ultramafic rocks distributed within two types of cyclic units, including an orthopyroxene-bearing cyclic unit and an orthopyroxene-free cyclic unit. Historical surface prospecting, mapping, limited trenching and diamond drilling have identified several areas in the North Lac des Iles IC which host PGE occurrences exceeding 1.0g/t of combined Pd+Pt+Au. These PGM occurrences are interpreted to represent stratiform or reef-type magmatic PGM mineralisation.
The South Lac des Iles IC was emplaced into a predominantly intermediate composition of orthogneiss basement rocks. Four major intrusive sequences (series) are recognised in the complex. Mapping and drilling have shown that the central-east part of the South Lac des Iles IC is an upright, homoclinal sequence (southfacing igneous stratigraphy), with a general north-easterly strike direction and steep southerly dips. In contrast, the major units in the western end of the complex, which hosts most of the palladium mineralisation on the property, display a general northerly strike direction and steep easterly to vertical dips. Both domains are believed to reflect the influence of pre-Lac des Iles structures on magma emplacement. The Shelby Lake structure is visible as a linear, positive magnetic anomaly to the south of the property. It is visible in the Roby pit and underground workings as an intensely recrystallised schistose melanorite unit that hosts the most mined-out and remaining higher- grade palladium Mineral Resources at Lac des Iles.
A second important pre-intrusion feeder structure to the South Lac des Iles IC has been inferred from geological and remote sensing data, drillhole logging, lineament analysis, and metal grade trends. It is referred to as the Roby Central Fault and has an eastnortheast strike, moderate to steep south dip and bisects the northeastern part of the complex. The intersection of these two structures corresponds to the thicker, central parts of the Roby and Offset Zones.
The South Lac des Iles IC is one of several 2.68 billion-year-old mafic-ultramafic intrusions in the region, most of which are covered by mineral claims held by Impala Canada. In contrast to most of the Bushveld Complex PGE deposits, the Lac des Iles orebodies show extreme palladium enrichment over platinum and appear to have formed within or directly adjacent to feeder structures, resulting in near-vertical orientations and true widths locally exceeding 100m.
All past and current mineral resources described on the Property are located in the northwestern part of the South LDI Complex. PGE and Au mineralization in the South LDI Complex is most commonly associated with 1% to 2% of fine- to medium-grained disseminated iron-copper-nickel sulphides within broadly stratabound zones of PGE and gold enrichment. A majority of the known PGE-rich sulphide mineralization consists of approximately 50% pyrrhotite, 25% pentlandite and 25% chalcopyrite. In some mineralized zones, pyrite is the dominant iron sulphide mineral but these areas tend to have low PGE + gold grades (e.g., less than 1 ppm combined). Minor millerite is locally present in the PGE-rich mineral zones. Sulphides occur as polycrystalline aggregates that generally reflect the grain sizes and shapes of adjacent silicate minerals. The coarsest sulphide blebs observed at LDI are up to several centimetres long but typical sulphide aggregate sizes are less than two centimetres. Rare massive sulphide occurrences up to approximately one metre thick are also reported from the Property (Duran et al., 2016). Primary sulphide textures were commonly destroyed during late magmatic hydrous alteration such that the schistose PYXTE unit contains very fine-grained disseminated sulphides that are difficult to observe without the aid of a hand lens.
Nearly all of the known mineralized zones in the South LDI Complex occur at or adjacent to the boundary between breccia and norite series rocks. Most of the past and present mineral resources are contained in the semi-contiguous Roby and Offset zones. These two zones are considered to have been part of a single, vertically-oriented, disseminated magmatic sulphide deposit that was subsequently affected by post-magmatic displacement along the east-northeast striking and north dipping Offset Fault. Displacement on this fault appears to have involved dextral lateral movement and, possibly, normal vertical movement such that the Roby block moved down and to the right of the Offset block. However, there is conflicting evidence of the magnitude and sense of displacement of various geological markers along the Offset Fault including some mineral zones that show no apparent displacement.