Quaternary geology and till composition north of Wager Bay, Nunavut: results from the GEM Wager Bay Surficial Geology Project

Abstract

This report presents the field database and analytical results from the Geological Survey of Canada's 2010 to 2012 surficial geology mapping and till sampling campaign in the north Wager Bay project area, mainland Nunavut. An overview of the Quaternary geology of this area is provided together with an interpretation of till provenance, as well as a discussion on the implications for mineral exploration. Field observations and surficial geological mapping indicate the region is key for the glacial history reconstruction of the northeastern part of the Keewatin Sector of the Laurentide Ice Sheet. Most of the study area was located within an extensive onset zone of a large ice stream flowing north into Committee Bay during the last glaciation and early deglaciation, from an ice divide located over and/or south of Wager Bay. Major ice-flow reversals into Repulse Bay and Wager Bay, as a result of drawdown into the opening marine waters in Hudson Bay, are indicated for the latest deglaciation phases. Coldbased ice remnant masses over the uplands north of Wager Bay preserved relict, weathered and fresh glacial landscapes at the end of deglaciation. Although there is evidence of multiple ice-flow directions in the study area, the main ice-flow phase, which converges north (NNE to NNW) towards Committee Bay, is the predominant direction of glacial transport and shaped most prominent streamlined landforms. The carbonate clast content and Al2O3 concentrations in surface till indicates relatively long glacial transport distances linked to glacial dispersal by the ice stream. Mg-rich olivine, many having >Fo90 and high NiO contents, are abundant in till in the center of the study area where a frost-shattered ultramafic lamprophyre boulder was found at the surface. Location of the boulder, its distinctive composition, and the olivine in till distribution in conjunction with the glacial transport history, suggest an ultramafic bedrock source other than kimberlite fields known in the region. In the western part of the study area south of Walker Lake, forsteritic olivine and chromite grains in till, locally coincident with ultramafic boulders, form a 35 km-long NNE dispersal train. This dispersal plume points to olivine-rich crustal rocks within undifferentiated Archean supracrustal rocks, and suggests these rocks have potential to host Ni-Cu-PGE mineralization. In addition to known Penhryn Group rocks and extensions of this belt to the southwest, there are suspected but poorly mapped strands of supracrustal rocks between Beach Pt and Wager Bay which show potential for base- and/or preciousmetal mineralization. More detailed till sampling, prospecting and bedrock mapping is required to better assess mineral potential in these areas.