Using lead isotopes and elemental abundances in till for mineral exploration in Cordillera
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New elemental abundances and Pb isotopic ratios for 2.5N HCl leachates from basal till samples (<0.063 mm fraction) are used to highlight down-ice glacial dispersal for volcanogenic massive sulphide (VMS) occurrences in the Chehalis valley, southwestern British Columbia. The middle Jurassic Seneca VMS deposit and surrounding volcanic-arc rocks show up to 9% lead isotopic difference, orders of magnitude above the state-of-the-art analytical uncertainties. The Pb abundances and isotopic compositions of the Chehalis tills are consistent with mixing of leads derived from the local bedrock sources and the isotopically distinct VMS mineralization. Pb, Zn, Cu, and Ba abundances show inconsistent till anomalies. In contrast, the Pb isotopes are effective indicators of down-ice glacial dispersal for the VMS deposits.
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