Updates on surficial geology and glacial history of the Birch Lake area, in the Dessert Lake drumlin field, Northwest TerritoriesOnline pre-recorded
Surficial geology mapping and glacial history reconstruction are essential to drift prospecting, infrastructure development, terrain sensitivity characterization, and baseline geochemical data interpretation. A multi-year initiative is being led by the Northwest Territories Geological Survey to better understand glacial sediment erosion, transport, and deposition history, as well as glacial and post-glacial processes responsible for the heterogeneity and variability of surficial materials in the poorly understood 85K map sheet area.
The focus of the 2020 campaign was to evaluate dispersal patterns potentially associated with aeromagnetic anomalies, as well as to provide a preliminary evaluation of the industrial mineral potential of the area. The 2021 field campaign focused on the till transport history, incorporated a study of drumlin sections, and included regional till sampling to complete the 2020 program. The final collection of 130 till samples includes 30 samples taken to test geophysical anomalies, 24 samples from four distinct vertical stratigraphic sections through drumlins, and 76 samples collected for regional coverage. Till samples are being picked for indicator minerals and analyzed geochemically. Two days were spent on bedrock and striation work up-ice from the main field area to facilitate provenance studies. Several clast fabric measurements were made in the drumlin till sections to further constrain sediment transport history.
Preliminary interpretations of the laboratory results from the 2020 dataset show possible correlations between the till indicator mineral counts and aeromagnetic anomalies. Minerals potentially associated with anomalies include chalcopyrite, sphalerite, scheelite, arsenopyrite, and monazite. Early results suggest long, ribbon-shaped dispersal trains; however, further work, and the incorporation of the 2021 dataset, will be necessary to rule out the possibility of indicator mineral transport from the Slave geological province. Preliminary field observations also confirmed the presence of gypsum as well as abundant angular shale fragments which are key raw materials for cement production.
Field access by helicopter during 2021 was facilitated by lower lake water levels than in 2020, allowing for greater availability of suitable landing sites. New ground observations revealed multiple occurrences of thin, clast-rich, locally derived surficial material and exposed bedrock in a wide swath of land formerly thought to be covered by thick till, crossing the 85K map sheet southeast to northwest. Nonetheless, thick till is actually present in some areas including northwestern 85K, where a major glaciofluvial system cut through thick, continuous till cover. This till, and glaciofluvial system, represents the northern limit of the drumlin field, though high-amplitude ‘pristine’ drumlins, less affected by postglacial processes, occur only 60 km to the southwest.
Future work will focus on the analysis of transport history and glacial processes in the drumlin field, and the evaluation of the indicator mineral results as they pertain to till composition and post-glacial processes. These projects are the main focus of a newly started master’s thesis and an undergraduate thesis, respectively. Both of these projects are taking place at the University of Waterloo.