Summary:
The Rainy Lake property is located on the extreme western margin of the Labrador Trough adjacent to Archean basement gneisses. The Labrador Trough is a sequence of Proterozoic sedimentary rocks, which includes the Sokoman Formation within the Knob Lake Group. The Sokoman Formation is an iron formation consisting of a continuous stratigraphic unit that thickens and thins throughout the Labrador Trough.
The thickness of the Sokoman Formation varies between 120 and 240 meters and is a typical Lake Superior type iron-formation (taconite) consisting of banded sedimentary rock composed principally of layers of iron oxide, magnetite and hematite. Iron-rich bands are intercalated with cherty bands composed of variable amounts of silicate, carbonate, sulphide, ferruginous slaty iron formation, and carbonaceous shale. The Sokoman Formation is subdivided into eight stratigraphic subunits: Lean Chert ("LC"), Jasper Upper Iron Formation ("JUIF"), Green Chert ("GC"), Upper Red Chert ("URC"), Pink Grey Chert ("PGC"), Lower Red Chert ("LRC"), Lower Red Green Cherty ("LRGC"), and Lower Iron Formation ("LIF").
On the Rainy Lake property the Sokoman Formation is thickened by shallow east dipping northwestsoutheast thrust faults and is gently folded resulting in unusual thickness of iron mineralization reaching 400 meters locally. The area investigated by drilling was named the Full Moon iron deposit.
The Sokoman Formation occurring on the Rainy Lake property consists mostly of recrystallized chert and jasper with bands and disseminations of magnetite, hematite and martite, a pseudomorph of hematite after magnetite and specularite. Other observed iron-silicate minerals include minnesotaite, pyrolusite, stilpnomelane, and iron carbonate, mainly siderite. In most of the sampling programs done on the Sunny Lake project, the highest consistent concentration of magnetite occurs within the PGC unit of the Sokoman Formation. The JUIF also contains locally higher concentrations of magnetite, while hematite is most common in the LRC, URC, and JUIF submembers. Magnetite also occurs within the LIF and LRGC units, but their total iron content includes the presence of variable amounts of iron silicate and carbonate. Siderite is also common in the LRC and LIF submembers, where manganese carbonates are also present. Calcite fills some fractures, while goethite and limonite are also common as fracture coatings, and are likely due to groundwater percolating.