The North Caribou Greenstone Belt (NCGB), located within the North Caribou Terrane of the Archean Superior Province, is host to multiple ~3.0 Ga metavolcanic and metasedimentary assemblages. The assemblages have been metamorphosed from greenschist to upper-amphibolite grade and are bounded by ~2.7-3.0 Ga granitoids and gneisses. The study area is located approximately 5km south of Musselwhite Mine within what was previously thought to be the Opapimiskan-Markop metavolcanic assemblage. Three lithologies were identified within the study area (basaltic, komatiitic, and felsic volcanic flows) which have been subdivided into four separate volcanic suites: Volcanic Suite A, Volcanic Suite B, Volcanic Suite C, and the Felsic Volcanic Suite.
Volcanic Suite A is comprised of a succession of massive and pillowed basaltic flows that have been metamorphosed to amphibolites. These flows exhibit a mineral assemblage of amphibole, chlorite, and plagioclase with minor quartz, muscovite, titanite and epidote. Major element geochemistry reveals that this suite is compositionally similar to that of a high-Mg tholeiitic basalt. Primitive mantle normalized plots for this volcanic suite are characterized by a flat rare earth element (REE) pattern comparable to tholeiites from the South Rim Unit (SRU), which have been interpreted to represent ocean plateau basalts formed from a mantle plume. Volcanic Suite B is comprised of pillowed and massive basaltic flows that have been metamorphosed to amphibolites. The main mineral assemblage observed in this suite was amphibole and chlorite with minor plagioclase, clinozoisite, quartz, titanite and dolomite. Major element geochemistry indicates that this suite is comprised of high-Mg tholeiitic basalts, komatiitic basalts, and a komatiite. Primitive mantle normalized plots display a relatively flat REE pattern but with a negative Nb anomaly. The similar trace element geochemistry of Volcanic Suites A and B suggests that they are both derived from a plume source, however, the negative Nb anomaly in Volcanic Suite B indicates that it has undergone crustal contamination during emplacement. Volcanic Suite C is also comprised of massive and pillowed basaltic flows with a main mineral assemblage of amphibole and chlorite. A single sample was taken from this suite and it was determined to be a high-Fe tholeiitic basalt based on major element geochemistry. Primitive mantle plots of this suite are light rare earth element (LREE) enriched with a negative Nb anomaly and positive Zr and Hf anomalies. A similar REE pattern was observed in the tholeiitic basalts from the Opapimiskan-Markop Unit (OMU). The Felsic Volcanic Suite overlies the mafic volcanic suites and is comprised of rhyolitic flows. This suite is LREE enriched with a relatively flat heavy rare earth element (HREE) pattern and negative Nb and Ti anomalies in conjunction with positive Zr and Hf anomalies. Similar REE patterns were observed in the SRU and were interpreted to be derived from a subduction tectonic setting.
The results of this study are consistent with previous work in the region and suggest that the early history of the area preserved the interaction of a mantle plume with pre-existing continental crust. In addition this study has refined the boundaries of the various assemblages within the NCGB.