Platinum group elements and Au in arctic vegetation growing on gossans, Keewatin District, Canada

Abstract

The concentration and distribution of Au and the platinum group elements (PGEs) Pd, Pt and Rh were studied in two arctic shrub species, Labrador tea and dwarf birch, growing in the vicinity of PGE bearing NiCu mineralisation at Ferguson and Townsend Lakes, NWT. Abundance of these elements in ashed vegetation from the gossan was several orders of magnitude above background with values ranging up to 4014 ppb Pd, 275 ppb Pt, 223 ppb Rh and 387 ppb Au. Enrichment of the elements in a direction down-ice from the gossan varied depending on the element; however distances were generally less than 450 m. There were concentration differences between tissue types for Pd, with generally higher levels in twigs; however the concentration of Pt, Rh and Au were similar between tissues. This study demonstrates the applicability of a recently developed analytical method to determine Au, Pt and Pd in ashed vegetation samples, weighing only 0.3 to 1 g, to detection limits of 0.5–1 ppb. The sample is ashed at 870°C, digested in HF-aqua regia, the analytes separated by co-precipitation on Te and re-dissolved in a solution ideal for analysis by inductively coupled plasma mass spectroscopy (ICP-MS). Precision obtained is dominated by the homogeneity of each 0.3–1 g sub-sample, Pt showing the greatest degree of heterogeneity as demonstrated by duplicated analysis of 10 Labrador tea samples. Results given for Rh are tentative as synthetic standard evaporates show some volatilisation losses upon ashing at 870°C; however the spatial pattern for Rh in both species at Ferguson Lake demonstrated patterns similar to the other elements.