RING OF FIRE GEOLOGY
The Ring of Fire, also known as the McFaulds Lake greenstone belt, is a 180km long Neo- to Mesoarchean arcuate greenstone belt located largely under the cover of the James Bay Lowlands in Northern Ontario (figure 1). In 2002, diamond explorers encountered copper-zinc rich VMS mineralization at McFaulds Lake which spurred one of the largest staking rushes in recent history in Canada. Since then, exploration companies have discovered eight deposits with calculated resources and/or reserves of chromite, magmatic nickel-copper-platinum group metals (Ni-Cu-PGE), and copper-zinc (Cu-ZN) VMS, as well as over 70 occurrences of multiple commodities.
Geological work by the OGS and GSC since 2010 has defined six distinct lithotectonic assemblages within the Ring of Fire (Metsaranta et al., 2015). Of these, the Muketei assemblage (figure 2), is by far the most prospective as it hosts all known chromite and Ni-Cu-PGE deposits, and a large proportion of the known Cu-Zn rich VMS occurrences.
The Muketei assemblage is a magmatic-volcanic succession interpreted to have been deposited and emplaced during ca. 2,735 Ma rifting of older crust underplated by a mantle plume from which were derived komatiitic melts. Mafic-ultramafic intrusions of the Muketei Assemblage are divided into two subsuites: i) the Koper Lake ultramafic subsuite, host to all chromite and Ni-Cu-PGE mineralization, and ii) the Ekwan River mafic subsuite, host to all Fe-Ti-V mineralization.
In the southeastern Ring of Fire where most exploration has taken place, komatiitic melts of the Koper Lake subsuite were emplaced as tabular sill-like ultramafic bodies at or near the contact between basement felsic plutonic rocks and overlying volcanic units (figure 3). Feeder systems to these ultramafic sills are locally well defined and have the potential to host significant high-grade Ni-Cu-PGE sulfide mineralization as at Eagle’s Nest. World class chromite resources occur stratigraphically above basal Ni-Cu-PGE mineralization as thick accumulations of semi-continuous strata within two main sill complexes, The Black Thor Intrusive Complex (BTIC) and Double Eagle Intrusive Complex (DEIC). Mafic magmas associated with the Ekwan River subsuite form regionally extensive ferrogabbro sills and large layered intrusions higher up in the stratigraphy and are known to host Fe-Ti-V-P mineralization in cumulate layers. Stratigraphically above the ferrogabbro sills lies the Muketei volcanic sequence, a folded bi-modal volcanic succession up to 10km in mapped thickness which hosts the Nikka VMS deposit in the McFaulds basin in the south, the 5.01 Zn-Cu VMS occurrence in the north, and the Butler VMS occurrences in the west, though geochronology has yet to confirm the later. Age dating of the Muketei volcanic assemblage indicates that it is broadly contemporaneous with mafic-ultramafic magmatism at depth, suggesting the heat source for the VMS hydrothermal systems may have been linked to emplacement of the Koper Lake and Ekwan River intrusive subsuites.
Subsequent to deposition of the Muketei Assemblage, a series of late structural events strongly deformed portions of the McFaulds Lake greenstone belt along the South Kenyan Fault Zone in the north, and the Webequie Shear Zone in the south. Both regional structures display numerous second and third order structures, some of which contain mesothermal gold mineralization (Triple-J gold zone). While the base metal endowment of the Ring of Fire is well established, Noront believes the Ring of Fire also has excellent potential for discovery of a significant gold deposit.