Exploring the invisible: Multi-scale geophysical studies to delineate granite-hosted Li-bearing pegmatites of the Seixo Amarelo-Gonçalo region, Portugal

A holistic geophysical approach was conducted to assess the effectiveness of electromagnetic, direct current resistivity, induced polarization, magnetic and Ground Penetrating Radar (GPR) methods for exploration of pegmatite sills in the Seixo Amarelo-Gonçalo region of central eastern Portugal. While electromagnetic data provided rapid coverage, low signal/noise ratio and noise rendered the survey method less impactful. Resistivity results from direct current surveys were characterized by higher values for pegmatites (1500–3500 Ωm) that presented alteration halos of higher conductivity. Considering a relatively greater penetration depth from resistivity surveys compared to e.g. GPR methods and their relatively high resolution, it should be considered as one of the main tools for exploration of deeper pegmatite sills. Induced polarization data failed to provide significant insight for differentiation of the main lithologies, primarily due to noise and weak polarization effect in studied rocks. Magnetic data, after processing, was able to successfully locate mafic dikes and fault zones within the deposit and distinguish shallow pegmatite sills from biotite-rich granites. GPR surveys only indicated major contacts within the top ~4 m of the subsurface. The study results demonstrate that integration of various geophysical methods can provide significant information for pegmatite exploration in the Seixo Amarelo-Gonçalo region, which can be applied to pegmatite exploration in similarly complex environments.