Abstract

Lodgment till exposures in the Myra and Buttle valleys of central Vancouver Island reveal a short (approximately 20 km) glacial dispersal train of Westmin massive sulphide ore in the clay fraction only (Cu, Zn, Pb). Ore dispersal was eastward down the tributary Myra valley, then northward along the west side of the trunk Buttle valley. This study suggests that in alpine drift-prospecting projects, anomalies should be traced upvalley into tributary valleys along the same valley side, using the geochemistry of the −0.002 mm fraction of the basal till matrix.Fraser glaciation in the valleys eroded and deformed underlying sediments and bedrock while removing evidence of previous glacial events. Glaciolacustrine silt and sand, lodgment till, deltaic recessional outwash, and colluvial fans were deposited during the last 25 000 radiocarbon years. Ice movement followed the classical alpine glaciation model. Tributary lobes advanced downvalley and merged (without mixing) to form a main trunk Buttle lobe, which advanced northward, truncating some of the tributary valleys. At the Fraser maximum, glacier ice had built up to cover all but the highest peaks; drumlinoids imply southwestward flow over the highest glaciated ridges. During deglaciation, the Buttle lobe probably retreated rapidly, depositing recessional outwash and glaciolacustrine diamictons.

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