The Archean Winter Lake greenstone belt (WGB) in the Slave craton, Northwest Territories, has been relatively underexplored compared to other supracrustal belts in the Slave craton, but shows potential for base-metal mineralization. It is situated ~250 km northeast of Yellowknife and consists of lower greenschist to upper amphibolite grade mafic to felsic volcanic rocks and sedimentary rocks that are surrounded by ca. 3.3 to 2.9 Ga granitoids of the Central Slave Basement Complex (CSBC).
The overall objective of this study is to increase our understanding of the origin and geodynamic evolution of the WGB and to evaluate its economic potential. The project aims to increase knowledge of the tectonic setting of volcanic and sedimentary rocks of the WGB and their relationships to the CSBC granitoids. In 2019, as part of a larger Northwest Territories Geological Survey mapping initiative, three weeks were spent bedrock mapping near Newbigging Lake and one week near Big Bear Lake (at 1:5,000 and 1:10,000 scales, respectively). At these locations, detailed mapping (1:2,000) of the mafic volcanic sequence was also completed to generate a lithostratigraphy for the southern WGB. This program enabled us to evaluate the nature of contacts, previously interpreted as unconformities, between the CSBC, the ca. 2734-2924 Ma Central Slave Cover Group (CSCG) volcanic and sedimentary rocks, and post-volcanic sedimentary and granitoid rocks. Mapping near Big Bear Lake also allowed the examination of a previously mapped ~ 1.3-1.7 km wide rhyolite interpreted to be part of the ca. 3.3 Ga Newbigging Formation. Based on field observations, the formation does not include a rhyolite sensu stricto but rather a succession of weathered mafic to intermediate volcanic and intrusive rocks. This field season, the first of three, also led to the discovery of several semi-massive to massive sulfide showings within the mafic volcanic sequence, and the identification of sulfides (interpreted as remobilised) and multiple younging indicators within the younger conglomerate unit that are necessary for our lithostratigraphy study.
Future geochronological analysis of U-Pb detrital zircon ages and Sm-Nd isotope geochemistry of the polymictic metaconglomerates and the CSCG quartzite will enable us to determine their sources and age. Together with absolute timing of thermotectonic events, an Archean oceanic and continental crust geodynamic evolution model will be produced. The variability of crustal contamination determined through trace element and and Sm-Nd isotope geochemistry of the mafic volcanic sequence will be investigated to understand their genesis and associated tectonic settings. A petrogenetic study of the mafic volcanic sequence that hosts the sulfide mineralization combined with detailed mapping of volcanic and sedimentary lithofacies will define facies distribution and the volcanic and sedimentary architecture across the WGB. It will also determine depositional environment for the volcanogenic massive sulfide (VMS) -type mineralization, present a new criterion for VMS deposit exploration for this specific belt, create the basis of a WGB VMS genetic model, and aid in our understanding of VMS formation in the Slave craton.