Neutron activation analysis following fire-assay preconcentration in a nickel sulphide button allows processing of relatively large samples (25 g) for precision analysis of platinum group elements. Using this method, an iridium anomaly with maximum concentration of 3.36 ± 0.04 ppb has been located at the Cretaceous–Tertiary boundary at the base of the Nevis coal seam in the Red Deer Valley of Alberta. The iridium anomaly coincides with the disappearance of diagnostic late Cretaceous palynomorphs, including all but one species of Aquilapollenites.

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