Impacts of environmental variables on biogeochemical results - orientation survey in the Peräpohja Belt, northern Finland


Impacts of environmental variables on biogeochemical results - orientation survey in the Peräpohja Belt, northern Finland

Middleton, M.; Pospiech, S.; Kinnunen, J.; Tolosana Delgado, R.

The potential of biogeochemistry, i.e. plant ionome, for mineral exploration has been previously demonstrated in case studies in Fennoscandia, where soils are formed on glacially transported sediments. Because plant element uptake is controlled by a variety of processes, anomalies can be weak and not necessarily caused by the underlying bedrock geochemistry. The goals of this study were: 1) to understand the effect of selected environmental variables on plant ionome and 2) to propose a compositional data analysis approach for selecting the most effective element log-ratios, plant species and their tissue types, and elementsfor a routine exploration survey in an orientation survey set-up.

The test site is located on Au-Co prospects at Rajapalot, northern Finland, stretching over highly variable metasedimentary bedrock in an undisturbed boreal forest. Sampling microsites included well-drained soils and edges of the peatlands over a variety of overburden thicknesses, which resulted in a broad spectrum of rootzone conditions. Based on existing geophysical data sets (magnetic, resistivity), used as proxies for lithological contrast, and nature type mapping, we set up a stratified random sampling design (n=98) to collect a multi-species dataset of conifer tree species and common juniper.

The compositional data analysis results show that soil moisture had a weak effect on the plant ionome. However, element log-ratios involving the target element Co in common juniper and Norway spruce were highly affected by the root zone bulk electrical conductivity. These findings highlight the importance of including the soil conditions in the sampling design and using soil electrical conductivity and dielectric permittivity measurements in the data interpretation. The response of plant ionome to bedrock was compared to the geophysical data as a coarse proxy for lithological contrasts between geological domains and to drill core lithogeochemical data as evidence for mineralization. The highly variable bedrock complicated interpretation of results in terms of relating plant ionome to geological domains. However, when compared to bedrock resistivity data, which roughly delineates the mineralized prospects, the plant ionome allowed prediction of sites with high probability for the concealed mineralized bodies at depths of several tens of meters.

Keywords: plant geochemistry; mineral exploration; anomaly; spatial pattern; environmentally friendly

  • Lecture (Conference)
    29th International Applied Geochemistry Symposium IAGS2022 - Facing the challenges of today using applied geochemistry, 23.-28.10.2022, Viña del Mar, Chile

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Publ.-Id: 34717