Evaluating the Surficial Geochemical Expressions in Soil, and Tree Cores Surrounding an LCT Pegmatite at Pakeagama Lake, Ontario
The Pakeagama Lake Pegmatite is a complex type, petalite subtype Li-Cs-Ta (LCT) pegmatite, located in Northwestern Ontario, Canada, at the border of the Berens River and Sachigo subprovinces of the Archean Superior Province. In order to quantify the surface expression produced by the pegmatite, A and B horizon soils and tree cores of black spruce (Picea mariana) and jack pine (Pinus banksiana) were collected throughout the Pakeagama Lake property. The < 63 μm fraction of the soils were separated, digested, and measured using two different methods, a near total digest using HCl, HF, HNO3, and H2O2 (3-acid digest) and a weak acid leach (WAL) technique designed to leach adsorbed ions. For A and B horizon soils that have undergone the 3-acid digest, there is a poor relationship between the chemistry of the underlying lithologies, and the chemistry of the soil, indicating that the soil is primarily sourced from till. Locations with greater concentrations of Li and Cs, two pathfinder elements associated with LCT pegmatites, are correlated with greater Fe and Mg concentrations and lower Na and K concentrations. This suggests that Li and Cs concentrations are also controlled by the dominate clay mineral and will be greatest in areas with the most illite or vermiculite. Concentrations of pathfinder elements (Li, Rb, Cs, Nb) in B horizon samples that underwent a WAL are not significantly elevated in samples taken adjacent to the pegmatite relative to background values. Both black spruce and jack pine were sampled during the survey, based on availability. At nine sites, both species were sampled for comparison. In all elements but Cs and Nb, the chemistry of the two species were poorly correlated, even when Ca normalized, so tree species were considered as independent media for analysis. No relationships between the chemistry of the underlying bedrock and either of the tree species is noted, and Li/Ca, Rb/Ca, and K/Ca do not exceed background values, even when taken directly adjacent to the pegmatite.