REFINED ICE-FLOW DIRECTIONS OF THE CORDILLERAN ICE SHEET AND IMPLICATIONS FOR MINERAL EXPLORATION

In the past 15 years, advancements in our understanding of changing flow directions within the Cordilleran Ice Sheet (CIS) during the last glaciation have followed numerous field-based geological survey surficial mapping campaigns. Reconstructed ice-flow histories have formed the basis for the interpretation of till composition studies which have direct application to mineral exploration. At the onset of the last glaciation in the southern CIS, ice from the Cariboo and Coast mountains advanced into the Interior Plateau, with Cariboo ice reaching the Fraser River. At the glacial maximum, an east-west oriented ice divide formed around 52° north latitude from which ice flowed north and south. The different phases of ice flow in this region produced palimpsest dispersal patterns in subglacial tills. In central CIS, outcrop-scale erosional landforms reveal that at the glacial maximum ice flowed outward across both the Coast and Rocky mountains. In the Houston area, for example, an ice divide originally located over the Coast Mountains at the onset of the last glaciation, migrated into the Interior Plateau at glacial maximum reversing flow to the west over the Coast Mountains. During deglaciation, this ice divide re-established over the Coast Mountains. The resulting ice flow reversals greatly impacted glacial transport as identified at Huckleberry Mine where till geochemistry in stratigraphic sections is interpreted in the context of the shifting ice divide. In the northern CIS in Yukon, the interior mountain ranges that hosted alpine glaciers during the onset of the last glaciation were subsequently overridden by the CIS at glacial maximum. This caused a reversal of ice flow in valleys such as those on the south side of the Pelly Mountains (e.g. Seagull Creek) where mineralized float was transported up-valley. Reconstruction of ice-flow histories not only allows for an understanding of the behaviour of past ice sheets but provides the transport vectors essential for tracing mineralized debris in glacial sediments to their bedrock sources. This is increasingly important in Canada as discoveries of surface-exposed mineralization are less common and vast areas with high mineral potential are covered by glacial sediments.