Evaluating the Surficial Geochemical Expressions in Soil, and Tree Cores Surrounding an LCT Pegmatite at Pakeagama Lake, Ontario
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Authors
Reith, Will
Date
Type
thesis
Language
eng
Keyword
Geology , Geochemistry , Pegmatite , Pakeagama Lake
Alternative Title
Abstract
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.
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This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.