Mountains graphic with white diamonds on itGeoscience and Exploration

Evaluation of the metasedimentary rocks within the Archean Winter Lake greenstone belt, Slave craton, Northwest Territories, Canada

Online pre-recorded
(Student abstract)


E.J. MacMillan (Presenting)
University of Saskatchewan
Y.M. DeWolfe
Mount Royal University
C.A. Partin
University of Saskatchewan
B. Knox
Northwest Territories Geological Survey
S.R. Cairns
Northwest Territories Geological Survey

The Archean Winter Lake greenstone belt (WLB) in the Slave craton, located ~250 km north-northeast of Yellowknife, is one of several greenstone belts preserved along the proposed eastern edge of the Central Slave Basement Complex and has an enigmatic relationship with the Beniah fault zone. The WLB contains poly-deformed metavolcanic and metasedimentary rocks that span ca. 3.3 Ga to 2.6 Ga. This project aims to understand the depositional and tectonic settings of the metasedimentary units referred to as the Itchen Formation (turbidite-like) and the Sherpa Formation (Timiskaming-like) and assess their compatibility for structurally-hosted lode gold mineralization, ultimately attempting to understand how these rocks fit into the overall geological architecture and evolution of the Slave craton as a whole.

Fieldwork completed during the summer of 2021 around the Shallow Lake/Left Lake area consisted of 1:2000 scale mapping to compile information regarding facies, stratigraphy, and contact relationships, as well as the collection of a variety of samples for future analysis. Preliminary findings based on the 2021 field season indicate: 1) the depositional environment for the Sherpa Formation is consistent with alluvial/fluvial high-energy environments, and the Itchen Formation is consistent with marine low-energy environments; 2)  the dominant sediment source for the Sherpa Formation consists mainly of granitic material with subordinate mafic clasts (volcanic and intrusive), mudstone clasts, sandstone clasts, and ultramafic clasts – likely generated along local fault scarps, whereas the provenance of the Itchen Formation requires further isotopic analysis and thin section work to be understood, given its fine-grained nature; and 3) contact relationships, metamorphic mineral assemblages, and deformation recorded in both sedimentary units suggest a short-lived hiatus between the two formations; however, a possible paleosol preserved between the Sherpa Formation and underlying basalt, paired with the environments of depositions, metamorphic grade, and structural history, suggests a major unconformity.

Future work includes: 1) detrital zircon U-Pb geochronology and Lu-Hf isotope data for provenance analysis and evolutionary fingerprinting; 2) whole-rock major and trace element geochemistry to investigate the evolution of fine-grained siliciclastic rocks, as well as to evaluate the degree of chemical alteration; 3) microprobe analysis on Grt-Bt (geothermometer system) and Grt-Al2SO5-Qtz-Plg (geobarometer system) to assess the P-T-t path, specifically in the Itchen Formation as it contains a robust metamorphic mineral assemblage that varies across the preserved sedimentary basin; 4) assay analysis of mineralized samples within quartz veins and shear zones to assess gold potential; 5) refining detailed maps and stratigraphic sections through the Sherpa and Itchen formations; and 6) detailed petrology to determine compositions, metamorphic mineral assemblages, provenance, and ore potential.

The results of this study will provide a robust sedimentological and thermotectonic understanding of the WLB and aid our comprehension of other supracrustal sedimentary sequences and the overall evolution of the Slave craton.