The Yellowknife greenstone belt (YGB) consists of a north-south trending, near vertically dipping series of mafic and felsic metavolcanic rocks located in the Archean Slave Province of the Northwest Territories, Canada. The YGB has been intruded by several generations of dikes and regional plutons that have not been extensively studied for their magmatic evolution and connections. These include abundant feldspar-quartz porphyry (FQP), quartz porphyry (QZP), and aplite dikes with proximal regional plutons that include the multi-phase Ryan Lake Pluton (RLP), Defeat Suite granite, and Duckfish granite. To date, these dikes have not been definitively linked to a parental pluton and these dikes show lithogeochemical similarities to the calc-alkaline Townsite Formation and Banting Group volcaniclastic units.
Thirteen samples were collected from these intrusions and were submitted for mineral separation and lithogeochemical analysis. U-Pb geochronology and zircon trace element data were collected concurrently to monitor changes in magmatic chemistry recorded by zircon through time. Five FQP dikes have a range of 207Pb/206Pb ages, with four concordant ages between 2685 ± 7 Ma to 2629 ± 10 Ma (proximal to the RLP and Defeat Suite) and one upper intercept age of 2770 ± 24 Ma (proximal to the Duckfish Granite). The QZP dike was sampled adjacent to the Duckfish granite and has an inferred 207Pb/206Pb age of 2763 Ma, based on interpretation of data. Two aplite dikes have concordant 207Pb/206Pb ages of 2675 ± 13 Ma and 2660 ± 18 Ma. The regional plutons include a tonalite and granodiorite from the RLP, which have concordant 207Pb/206Pb ages of 2651 ± 8 Ma and 2647 ± 7 Ma, respectively. Two samples were taken from the eastern Defeat Suite granite, one with a concordant 207Pb/206Pb age of 2580 ± 27 Ma and the other has an interpreted crystallization age of 2579 Ma. Finally, one sample from the Duckfish granite has a concordant 207Pb/206Pb age of 2576 ± 7 Ma.
The zircon trace element chemistry from these intrusions have distinct rare earth element patterns that show the relationships between dikes and plutons, trends that were also be observed in the lithogeochemical data. When all data sets are compared, the results show that the FQP, older aplite dike, tonalite, and granodiorite are genetically related, while the younger aplite dike and Defeat Suite granite are geochemically linked, and the Duckfish granite is related to an undated series of aplite dikes. A comparison of current to historic whole-rock geochemistry of the Townsite Formation and Banting Group shows the separation of two groups. The whole-rock Zr/Hf ratio distinguishes between the granitic samples of the aplite dikes, Defeat Suite and Duckfish granites, and the intermediate FQP, tonalite, granodiorite, Townsite, and Banting Group volcaniclastic rocks. These two groups suggest that only the FQP dikes are genetically related to the Townsite and Banting units as feeder dikes. The spectrum of ages obtained for the FQP dikes also correlates with this conclusion as the dikes were episodically intruding the mafic metavolcanic rocks and progressively formed the calc-alkaline Townsite Formation and Banting Group volcaniclastic rocks.