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

摘要

New high-precision U-Pb ages from the host succession of the Musselwhite banded iron formation (BIF)hosted epigenetic gold deposit (5.7 Moz 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 fades 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 2909 Ma. A felsic tuff from the South Rim volcanic assemblage structurally overlies the ore-bearing Northern BIF, but yields an older age of 2979 Ma. 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 <2850 Ma and <2846 Ma, respectively and provide a maximum age for D2 deformation. The similar to 60-120 Ma 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. Crown Copyright (C) 2015 Published by Elsevier B.V. All rights reserved.