Mafic-Ultramafic Magmatism in the Bird River/Uchi/Oxford-Stull/La Grande-Eastmain Superdomain: Potential Remnants of Meso- and Neoarchean LIPs in the Northern Superior Province

English Abstract:

The discoveries of world-class Cr deposits, significant Ni-Cu-PGE deposits, and numerous Fe-Ti-V occurrences in the McFaulds Lake (a.k.a. “Ring of Fire”) area of northern Ontario have greatly renewed interest in orthomagmatic mineralization associated with mafic-ultramafic intrusions in the Superior Province. Cr-(PGE) deposits and, to lesser extent, Fe-Ti-V and Ni-Cu-(PGE) deposits/occurrences, occur predominantly in the northern part of the Superior Province within Meso- to Neoarchean supracrustal successions along the margins and within the cores of the Bird River–Uchi–Oxford-Stull–La Grande–Eastmain domains (i.e., BUOGE “superdomain”).

Ultramafic to mafic magmatism of various types (e.g., komatiitic, tholeiitic, alkalic) extended over a period of more than 200 Ma within the BUOGE superdomain, from ~2.88 to 2.66 Ga. However, only two main intervals (ca. 2810 Ma and ca. 2735 Ma) are recognized to have generated major magmatic events across the superdomain. Although limited in size, emplacement of large amounts of ultramafic to mafic magmas over a short period of time, locally combined with komatiite-tholeiite successions, argues in favor that these intrusions could represents remnants of Archean LIPs. The broader Neoarchean magmatic event that includes the intrusive suites of the Bird River in Manitoba (ca. 2743 Ma), the Ring of Fire in Ontario (ca. 2734 Ma), and several but more localized ultramafic intrusions within the La Grande domain in Québec (ca. 2754 Ma), is by far the best candidate to represent an Archean LIP that consist of at least three magmatic pulses over 20 My associated with the emplacement of Cr-PGE, Ni-Cu-PGE deposits, and significant Fe-Ti-V occurrences.

This superdomain defines a major Cr-Ni-Cu-PGE-V metallotect within the Superior Province that appears to be fundamentally different from other parts, such as the Abitibi greenstone belt or the apparently relatively unmineralized North Caribou core, Island Lake, and Goudalie domains. Ongoing work aims at establishing geological settings and characteristics of these orthomagmatic deposits in many of these areas, to help constrain the likelihood of discovering additional mineral resources in the BUOGE superdomain, but also in other frontier areas throughout the Canadian Shield.