The Archean Winter Lake greenstone belt (WGB) is located in the western part of the Slave craton ~250 km north-northeast of Yellowknife. Archean volcanic sequences of the Slave craton in the Northwest Territories are highly prospective for base metal mineralization, as several are known to host volcanogenic massive sulfide (VMS) deposits. Despite this, advanced exploration activity is currently focused in Nunavut (e.g., High Lake, Hackett River, IZOK Lake), and therefore prospective volcanic belts in NWT remain under-evaluated for their VMS potential. Part of the challenge in exploring for these deposits is a lack of knowledge regarding their geological setting. This research will aid in understanding the hydrothermal, depositional, and tectonic history of volcanic rocks, which host massive sulfide mineralization in the WGB. A comprehensive study of these massive sulfide mineralization occurrences is timely, since the WGB is adjacent to the proposed Contwoyto all-season road corridor, which could facilitate future exploration efforts.
Previous studies of the mafic volcanic rocks of the WGB resulted in the subdivision into two distinct formations based largely on age; the 3.3-3.1 Ga felsic to intermediate Newbigging Formation and the 2.7-2.6 Ga Snare Formation composed of calc-alkaline and tholeiitic basalts with lesser komatiitic flows. Both formations are extensively intruded by mafic to ultramafic intrusive rocks. Structural interpretations of the WGB have suggested a broadly synclinal architecture but have reached limited conclusions on the relationships between the distinct mafic units or their relationship with adjacent supracrustal formations. The Snare Formation is assumed to be equivalent to tholeiitic mafic volcanic rocks of the 2.7 Ga Kam Group of the Yellowknife greenstone belt, but evidence for this is limited to poorly exposed contacts and a bias towards Yellowknife-centric models in the Slave craton.
Work completed this past summer included detailed mapping (1:2000) of the mafic volcanic rocks of the WGB in three different locations: 1) the south end of Newbigging Lake, 2) the south end of Big Bear Lake, and 3) at a massive sulfide showing roughly half-way between the first two locations. Lithofacies observed at Newbigging Lake included felsic and mafic volcaniclastics with the area being volumetrically dominated by later mafic intrusions. The later two transects at Big Bear Lake and the showing were predominantly composed of pillow basalts with mafic volcaniclastics on the western margins. The upper contact with the younger sedimentary rocks is faulted and the lower contact with the Newbigging Formation is interpreted to be conformable. A rhyolite and a syn-volcanic quartz-bearing gabbro from the Newbigging Lake map area were selected for U-Pb geochronology, while basalts were sampled extensively for whole rock geochemistry and Sm-Nd isotopes to better understand their petrogenesis. Future work includes detailed lithofacies descriptions of the host rocks and alteration assemblages of the massive sulfide showings to reconstruct the volcanic environment and better constrain volcanic and ore-forming processes.