North Star Manganese Inc. (NSM), a wholly owned subsidiary of Electric Metals (USA) Ltd., has a 100% interest in the North Star Manganese Project.
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Summary:
The Emily Manganese Project is situated within a region of Precambrian bedrock referred to as the Cuyuna Iron Range. The region includes an early Proterozoic sequence of a lower quartz arenite (Pokegama Quartzite), an intermediate iron-formation with intervening black shale (Biwabik Iron Formation) and an upper feldspar-rich greywacke-shale (Virginia Formation).
The Emily District of the Cuyuna Iron Range is part of the Superior-type banded iron formations of the Lake Superior region, which also include the Marquette, Gogebic, Mesabi, and Gunflint Iron Ranges.
The Emily deposit is hosted by rocks of the Paleoproterozoic Animikie Basin (the Emily Iron Formation).
The depositional sequence at the Emily deposit records two periods of transgression and regression within the chemical sediments of the Emily Iron Formation and overlying Virginia Formation, bracketed by periods of clastic deposition. The Emily Iron Formation comprises a sequence of fine- and coarse-grained iron formation subunits that correspond to the rise and fall of sea level during deposition. Manganese precipitation is also associated with the rise and fall of the sea level and subsequent mineral deposition.
The iron-formations and associated rocks of the Emily District have been pervasively oxidized and leached. Oxidation and leaching are variable, with more oxidation associated with fracture zones along fold hinges (Morey et al., 1991).
The Project area is located in what Morey et al. (1991) describes as the “Ruth Lake Area”. In this area, the iron-formation strikes to the east and dips 15° to 40° to the north. Morey et al. (1991) interprets the site to lie along the north limb of an east-northeast plunging anticline that flattens to the north. The iron-formation is broken by a conjugate set of north-northeast and west-northwest-striking faults with displacements on the order of meters to tens of meters.
Manganese at the Project occurs within zones of massive manganese-oxide replacement in an early Proterozoic sequence of quartz arenite, an intermediate iron-formation (containing lenses of massive manganese) with intervening black shale and a feldspar-rich greywacke-shale. The manganese rich rock is generally more granular than low-grade manganese rock and contains abundant ovoid-shaped structures. The richest manganese layers are composed of massive, black, metallic manganite (manganese oxidehydroxide (MnO(OH) containing up to 87% Mn).
The Emily Manganese Deposit is dominated by manganese oxides (mostly the mineral manganite) and iron oxides (mostly hematite) with silica. Analyses of manganese-rich drill core samples tested seldom contain more than 0.05% sulphur showing that the mineralization is sulphide-free.
Mineralization
Unit A iron-formation of the Ruth Lake Area in the Emily District is a sequence of chemically derived sediments that consist of three main units: an upper hematitic chert, a manganiferous iron-formation, and a basal manganiferous, jaspery, oolitic to sandy chert.
Upper Unit A
Analysis by Dahl et al. (1994) describes the upper 116 feet as finely laminated chert, grading downward to massive, oolitic to granular chert. Minor interbeds of hematite (Fe2O3)-chert iron-formation are also present. The lower part of this unit averages 42.6% Fe2O3; 53.05% SiO2, and 0.32% MnO.
Middle Unit A
Dahl et al., (1994) describes the middle 297 feet of Unit A as a fine-grained and well-bedded manganiferous iron-formation. Laminated beds consist of fine laths of specular hematite in a chert matrix. More granular layers contain variable amounts of disseminated octahedral hematite, rounded quartz grains, and oolites in a chert matrix. The oolitic structures are composed of alternating rims of chert and hematite in a chert matrix. More granular layers contain variable amounts of disseminated octahedral hematite, rounded quartz grains, and oolites in a chert matrix. The oolitic structures are composed of alternating rims of chert, hematite, and manganese-oxides coating quartz sand or chert. Jaspery, oolitic chert beds 2 to 6 cm thick are interbedded throughout this middle unit. The primary mineralogy and structure of the iron-formation is overprinted by partial to total replacement by hematite, goethite, and manganese-oxides. Manganese enrichment ranges from 0.3% to as high as 45.3% Mn in zones of massive manganese-oxide replacement. The manganese-rich rock (>20% Mn) is more granular than lower grade rocks and contain abundant ovoid-shaped manganese-rich oolites structures. The highest-grade manganese layers are composed of massive, black, metallic manganite.
Lower Unit A
Dahl et al., (1994) describes the lower 27 feet of Unit A iron-formation as manganiferous, jaspery, oolitic to sandy chert. The chert consists of terrigenous quartz sand grains, hematite granules, and a variety of oolite types (some of which have manganese-oxide rims). The granular components are cemented by a chert matrix. This unit averages about 10% manganese.