The McFaulds Lake greenstone belt, in addition to its world-class chromite endowment, also hosts significant magmatic Ni-Cu-(PGE) mineralization at the Eagle's Nest deposit. Mineralization at Eagle's Nest occurs in a dynamic system that contains multiple generations of sulphide textures, consistent with its interpretation as a magmatic feeder among a network of ultramafic intrusions. Massive sulphides and abundant leopard net-textured, oikocrystic net-textured, and inclusion net-textured sulphide mineralization formed first and were consolidated enough to be cross-cut by late-stage pyroxenite, creating disrupted net-textured sulphide and minor late-segregating massive/semi-massive sulphide melts. Resolving the fundamental characteristics and genesis of mineralization at Eagle's Nest will provide critical information about the evolution of large chromium and Ni-Cu-PGE ore systems associated with Archean komatiitic magmatism within the Superior Province.

One of the dominant geological features in the arcuate, >175 km long, Mesoarchean to Neoarchean McFaulds Lake greenstone belt in northern Ontario is the semi-continuous trend of mafic to ultramafic intrusions belonging to the Ring of Fire intrusive suite, which hosts world-class Cr mineralization, major Ni-Cu-(PGE) mineralization, and potentially significant Fe-Ti-V-(P) mineralization. It appears to have been emplaced over a relatively short time interval of approximately 4 to 4.5 million years. The intrusive suite contains two subsuites: the less widely distributed Koper Lake subsuite, which consists of komatiitic ultramafic- dominated intrusions and typically hosts Cr and Ni-Cu-(PGE) mineralization (e.g. Esker intrusive complex), and the more widely distributed Ekwan River subsuite, which consists of tholeiitic high-Fe-Ti mafic-dominated intrusions and typically hosts Fe-Ti-V-(P) mineralization (e.g. Thunderbird intrusion). The Esker intrusive complex contains the majority of the known Cr and Ni-Cu-(PGE) mineralization in the Ring of Fire intrusive suite. It is a semi-continuous, structurally rotated, subvertical ultramafic-mafic sill-like body that is composed of multiple intrusions with morphologies that vary from bladed dyke morphologies (e.g. Eagle's Nest), transitional dyke/chonolith morphologies (e.g. Double Eagle, AT-3, and AT- 8), to some with transitional chonolith/sill morphologies (e.g. Black Thor). It extends over more than 16 km, youngs to the south-southeast, and is bordered to the north-northwest by several keel-like ultramafic intrusive bodies (e.g. AT-12, C-6, AT-5, AT-1). Clear connections between AT-12 and AT-1 and the overlying Black Thor and Double Eagle intrusions, respectively, and the continuous spectrum of intrusion morphologies suggest that the keels were originally subhorizontal blade-shaped dykes (e.g. Eagle's Nest), the upper parts of which expanded laterally to form transitional dykes/chonoliths (e.g. Double Eagle intrusion) and chonoliths/sills (e.g. Black Thor intrusion), which inflated laterally and coalesced over time to form the silllike Esker intrusive complex. Most of the Ni-Cu-(PGE) mineralization in the Esker intrusive complex appears to have formed by incorporation of sulphur from footwall oxide-silicate-sulphide iron formations, a process that is similar to most other komatiite-associated Ni-Cu-(PGE) deposits worldwide. A fundamental issue in the genesis of all stratiform chromite deposits is how to form thick layers of massive to semi-massive chromite, an issue exacerbated by the vast amounts of chromite in the Esker intrusive complex. A genetic model that resolves the mass balance problem involves partial melting of Fe+/-Ti oxide-rich rocks (oxide-facies iron formation or ferrogabbro) and conversion of fine-grained oxide xenocrysts to chromite by reaction with Cr-rich komatiitic magma in a dynamic magma conduit. This model has been recently challenged based on the capacity of komatiitic magma to dissolve large amounts of magnetite, which would prevent upgrading. However, alternative models cannot explain the presence of composite chromite-silicate-sulphide grains with textures like those in footwall magnetite-silicate-sulphide facies iron formations. More research is required to reconcile the discrepancies. Regardless of their origin, the wide diversity of mineral deposit types in the McFaulds Lake greenstone belt, including world-class Cr, significant Ni-Cu-(PGE), and potential Fe-Ti-V-(P) mineralization related to mafic and ultramafic rocks, make the Ring of Fire region an excellent exploration target to increase the world's supply of critical minerals.

One of the most prominent features of the McFaulds Lake greenstone belt (also known as the 'Ring of Fire'; RoF) in northern Ontario is an abundance of 2.7 to 2.8 Ga mafic to ultramafic intrusive rocks that host world-class magmatic chromium, significant magmatic Ni-Cu-PGE and potentially economically significant Fe-Ti-V mineralization. The Neoarchean intrusions in the RoF have been referred to as the Ring of Fire intrusive suite, which is here subdivided into two main magmatic subsuites: the spatially restricted ultramafic-dominated Koper Lake subsuite and the more widespread mafic-dominated Ekwan River subsuite. The Koper Lake subsuite includes the Esker intrusive complex, which comprises the Black Thor and Double Eagle intrusions that host the Black Thor, Black Label, Big Daddy, Black Creek, Black Horse and Blackbird chromite deposits and several Ni-Cu-PGE showings, the Blue Jay funnel, which hosts the Blue Jay Ni-Cu-PGE prospect, and the Eagle's Nest dyke, which hosts the Eagle's Nest Ni-Cu-PGE deposit. The Black Thor and Double Eagle intrusions are interpreted to have initially intruded separately, but to have coalesced over time with magma inflation within a dynamic komatiitic system to form the chromium and Ni-Cu-PGE-bearing Esker intrusive complex, one of the most important members of an increasingly important class of polymetallic magmatic ore systems.

The Archean Superior Province is well known for its metal endowment. Ultramafic and mafic intrusions/flows are ubiquitous in greenstone belts across the Superior Province and are prospective hosts for magmatic Ni-Cu-(PGE), Cr-(PGE), and Fe-Ti-V deposits, although their abundance and endowment vary widely among the terranes/domains. For example, the Abitibi-Wawa terrane contains numerous but generally small Ni-Cu-(PGE) deposits, a few large Fe-Ti-V deposits, and only rare Cr mineralization. The Bird River-Uchi-Oxford-Stull-La Grande Riviere-Eastmain (BUOGE mp;lt;"superdomainmp;gt;") domains are characterized by several moderate to very large chromite deposits, a few moderate to small Ni-Cu-(PGE) deposits, and a few potentially large Fe-Ti-V deposits that are characterized as prospects due to the lack of definition drilling. The other terranes/domains in the Superior Province, including the Au and Cu-Zn-Aurich Abitibi belt, contain some magmatic Ni-Cu-(PGE) and Fe-Ti-V mineralization, but no significant Cr- (PGE) mineralization. Many factors are responsible for the variable metal endowment, but some critical features appear to be particularly important and may define prospective Ni-Cu-(PGE), Cr-(PGE), and/or Fe-Ti- V metallotects. These include the presence of (1) abundant primitive mantle-derived magmas that were generated by large magmatic events over short durations; (2) magma compositions that favoured the generation of Ni-Cu-(PGE) (high-Mg komatiitic), Cr (low-Mg komatiitic), and Cu-Ni-PGE and Fe-Ti-V (basaltic) mineralization; (3) transcrustal discontinuities that focussed magma flow through the lower crust; (4) shallow structures and densities that favoured emplacement of channelized lava/magma conduits at relatively high levels, (5) high magma fluxes to promote thermomechanical erosion of crustal rocks; (6) high-level crustal rocks containing sulphur (e.g. sulphide-facies iron formation) and oxide (e.g. oxide-facies iron formation) reservoirs for generating and upgrading sulphide xenomelts and oxide xenocrysts; and (7) favourable deformation and erosion to preserve and expose prospective units for exploration. Targeting base and precious metals is challenging, even in well endowed but partially exposed greenstone belts. However, understanding these fundamental controls will help in the discover of additional resources in other frontier areas within the Superior Province and throughout the Canadian Shield.

Chromium and Fe-Ti-(V) mineralization in ultramafic-mafic intrusions is known to occur in several areas of the Superior Province, but was considered to be of marginal significance until the discovery of world-class Cr deposits and potentially significant Fe-Ti-(V) mineralization in the McFaulds Lake greenstone belt ("Ring of Fire") of northern Ontario. Cr-(PGE), Ni-Cu-(PGE), and Fe-Ti-(V) deposits/occurrences in the northern part of the Superior Province occur predominantly within Meso to Neoarchean supracrustal successions along the margins and within the interiors of the Bird River-Uchi-Oxford-Stull-La Grande Rivièreastmain domains (i.e. BUOGE domains). These domains define a new metallogenic province within the Superior Province characterized by the presence of major Cr-(PGE) with Ni-Cu-(PGE) and Fe-Ti-(V) metal associations that appear to be fundamentally different from other parts of the Craton, such as the Abitibi greenstone belt or the apparently relatively unmineralized North Caribou core, Island Lake, and Goudalie domains. Despite the fact that only the Cr-(PGE) deposits and Ni-Cu-(PGE) deposits (Eagle's Nest) in the McFaulds Lake greenstone belt appear to be potentially economic, the presence of a significant amount of Cr-(PGE) mineralization across the BUOGE domains highlights the prospectivity of these regions of the Superior Province.