Pegmatites revealed – A multi-method exploration case study from Northern Norway

Exploration for buried pegmatites presents a challenge, mainly caused by weak geophysical signals due to commonly low petrophysical contrasts between pegmatites and wall rocks. However, dedicated petrophysical studies and a better genetic, structural, and lithologic understanding of pegmatites motivate reassessment of the geophysical methods pool and open the door for refined pegmatite exploration workflows. The EU Horizon 2020 GREENPEG project developed a toolset for this purpose, including a comprehensive petrophysical database for European pegmatites, that is both cost-effective and promotes sustainable exploration, while combining geophysical and geochemical exploration methods.

The Jennyhaugen quarry close to Drag, Northern Norway, hosts N(iobium)-Y(ttrium)-F(lourine) pegmatites and served as one of the field labs for the development of the exploration toolset. We present here insights gained during comprehensive field tests for method selection and combinations, while we focus on the geophysical exploration tools.

NYF pegmatites often have a geochemical halo enriched in the radioelements thorium, uranium and potassium, highlighting gamma-ray spectrometry as a successful tool to be used in areas with no or little soil cover. When targeting hidden pegmatites, depth penetrating methods like ground penetrating radar and electrical resistivity tomography, in combination with legacy drill core lithology, ground magnetics, gravity and innovative piezoelectric sensing proved in part very successful. The combination of the individual methods closes interpretation gaps and besides identifying buried pegmatites, we also improved understanding of the settings and geometries of pegmatites.