摘要：

In central Newfoundland (NTS 12A/10, 15, 16, 2H/1), As, Pb, and Zn concentrations in the clay-sized (1000ppm), exceeding levels commonly set for purposes of environmental protection. Near Pb-Zn mines at Buchans, geochemical variation with depth reflects the dispersal of detritus from mineralized bedrock, and differences in sediment type and provenance. There, surface sediments are rich in granitic debris derived from the Topsails igneous terrane 5km north of Buchans and contain low concentrations of trace metals. These sediments are compositionally unrelated to either Buchans Group volcanic rock or an underlying, older till enriched in sulphide minerals and trace metals. Metal-rich till extending up to 10km southwest of Buchans results from combined glacial and debris flow transport related to two distinct geological events. Trace metals are enriched (two- to fourfold) in the clay-sized fraction of till compared to the silt and clay-sized, and are associated with Al- and Mg-bearing minerals that preferentially concentrate in the clay fraction. The geochemistry of the silt and clay-sized fraction can approximate that of the <2-mm fraction. Background variations in till illustrate the important role of a geological framework to the interpretation of geochemical surveys and the origins of trace metals in the environment.

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