Northwest Territories Geological Survey

Surficial geology maps at 1:50,000 scale covering 84 NTS sheets in the southern Slave Geological Province (SGP) and interpretation of the area’s deglaciation was recently received and published by the Northwest Territories Geological Survey (NTGS). The mapping and interpretations were completed by the first author and owned by GGL Resources Corp. (GGL) who have now donated the compilation to the public. The compilation of the database, editing, formatting, and publication was facilitated through a collaboration between John Knight, GGL, Aurora Geosciences, and the NTGS. This presentation describes the publicly available digital database and outlines the publication’s main scientific results.

The mapping of surficial materials was completed from the air between 1995 and 2012 using ground truthing. It emphasized the reworking of surficial materials by meltwater. The 1:50,000 maps were compiled into five overview maps at 1:200,000, each of which covered a region containing distinctive mixes of deglaciation features. Overview map A (south-west), centered over Gordon Lake, displays extensive areas of fluvially washed bedrock, an extensive boulder field and small yet widespread areas of reworked till and glaciofluvial sediments. Overview map B (north), from Mackay Lake to Point Lake, displays continuous till cover broken by well-ordered esker complexes within well-defined melt-water erosion corridors hosted by till. Overview map C (center), centered over Mackay Lake, display less ordered esker complexes hosted by a mix of till and moderately reworked till. Overview map D (south-east), from Courageous Lake to Walmsley Lake, displays a mix of all of these features. Overview map E, that covers the Desert Lake area to the south-west of Yellowknife, displays a large drumlin field.

The interpretation of maps A to D indicates that the area can be divided into three distinct elevation zones representing different deglaciation processes. A washed bedrock zone below approximately 380 meters above sea level (a.s.l.) includes vestiges of both esker complexes and till. A transition zone between approximately 380 meters a.s.l. and 420 meters a.s.l. includes disrupted esker complexes that are mostly hosted by moderately reworked till. An esker complex zone, present above approximately 420 meters a.s.l., includes esker complexes displaying varying degrees of order and fluvial reworking.
The differences between the surficial features in the three elevation zones are thought to be related to the coherence of the seal between ice and bedrock, ice and bedrock topography and the presence of glacial lake McConnell. In the washed bedrock zone, disorganized bedrock-controlled wasting of the ice sheet, from west to east, took place under the influence of glacial lake McConnell. In the esker complex zone, self-organized channeled wasting of the stagnant ice sheet took place. The degree of ordering and the active length of the complexes are strongly influenced by ice and bedrock topography. The transition zone joins the two.

This compilation offers the first publicly documented large-scale evaluation of till preservation state over the Slave Geological Province. It is a valuable new tool to assess till sampling suitability for the design of drift exploration programs.