The biogeochemical expression of deeply buried uranium mineralization in Saskatchewan, Canada

Abstract

Ten kilometres from the eastern edge of the Athabasca Sandstone, near McClean Lake, uranium mineralization (locally up to 27% U 3O 8) lies 150 m beneath the surface at the unconformity between the Athabasca and crystalline basement. A biogeochemical survey of the area sampled A H and B F soil horizons, peat moss, and plant organs from the dominant species, viz. black spruce ( Picea mariana), jack pine ( Pinus banksiana), labrador tea ( Ledum groenlandicum), and leather leaf ( Chamaedaphne calyculata). Uranium concentrations in the ash of various media are surprisingly high: spruce twigs up to 154 ppm U; labrador tea and leather leaf stems around 100 ppm U. Conversely, labrador tea roots yield < 5 ppm U and spruce trunk wood usually < 1 ppm U. Soils give values of 1–3 ppm U. Contoured U values reveal that highest concentrations occur in plants growing above, but laterally displaced from the mineralization. Track-Etch data show a similar pattern. Upward migration of ions along steeply inclined fractures is invoked to explain the phenomenon. Other elements are present in varying concentrations, depending upon the plant species and the plant organ. High concentrations of several elements are recorded, most notably Cd and Ag in the conifers.