The world-class Musselwhite BIF-hosted gold deposit, Superior Province, Canada: New high-precision U–Pb geochronology and implications for the geological setting of the deposit and gold exploration

Abstract

New high-precision U–Pb ages from the host succession of the Musselwhite banded iron formation (BIF)-hosted epigenetic gold deposit (5.7Moz Au) in the North Caribou greenstone belt of the Superior Province provide timing constraints on the setting of the deposit, with implications for geological and exploration models. The deposit is mainly hosted by a folded garnet-grunerite-chert silicate facies of the Northern BIF, part of the Opapimiskan-Markop assemblage. Dating of a volcaniclastic sedimentary rock, a garnet–biotite±staurolite schist, and a cross-cutting foliated felsic dike indicate that the age of the Northern BIF is between 2967 and 2909Ma. A felsic tuff from the South Rim volcanic assemblage structurally overlies the ore-bearing Northern BIF, but yields an older age of 2979Ma. Reappraisal of stratigraphic and polyphase structural relationships, in conjunction with the U–Pb ages, indicate that the mine stratigraphy is inverted as it is located on the overturned limb of a kilometre-scale refolded F1 syncline, greatly influencing the distribution and geometry of the BIF units hosting the bulk of the gold. Felsic ash tuff and a fine-grained siliciclastic sedimentary rock from the “Lower Sediments” unit (Zeemel/Eyapamikama assemblage) have much younger ages of <2850Ma and <2846Ma, respectively and provide a maximum age for D2 deformation. The ∼60–120Ma time gap between the Zeemel/Eyapamikama assemblage and the structurally overlying Opapimiskan-Markop assemblage is coincident with the location of a high-strain zone within iron-carbonatized mafic–ultramafic rocks. This unconformity/thrust boundary and a polymictic conglomerate in the upper stratigraphic sequence may indicate the presence of a major structure and an important first-order gold exploration target.