The GOLDFINGER Project: Imaging a Late-Variscan gneissic dome. Preliminary results.

The late Variscan gravitational collapse and coeval magmatism are getting the attention of the community due to their role in the generation of strategic mineral resources. In this regard, the GOLDFINGER project’s main scope is to study how the Variscan orogenic architecture controls the generation of strategic ore deposits (i.e. Sn, W, Nb, Ta, Sc, Au, Sb). With this goal, a 3D model of a gneissic dome with several mineral deposits will be constructed based on high-resolution geophysics (Seismic/Gravity/Magnetism), and regional geology. The study area encompasses the Martinamor gneiss dome which represents a Late-Variscan syn-collisional extensional system with a well-preserved architecture. This gneiss dome structure presents low topography, relatively flat structural geometry in-depth, and contrasting lithotypes regarding seismic, gravity, and magnetic properties. As part of the project, in spring 2022 the area was covered by 30 low-period seismic recorders with 2Hz sensors in a regular grid. The 35x40 km grid consisted of 60 nodes, separated by approximately 4.5 km. To achieve the final node number, the stations were deployed twice, first in a regular grid with nodes each 6 km, and then the grid was moved 3 km to the west and to the south for a second deployment. The seismic stations were continuously recording in the field for up to 40 days in each deployment. We are using a state-of-the-art technique to retrieve high-resolution seismic images of the Martinamor gneiss dome using seismic interferometry applied to seismic background noise (SBN). The preliminary results show that SBN interferometry allows us to 1) detect and track discontinuities that can be related to the structures that control the ore deposits, and 2) identify the location of deep intrusions that are inferred as sources of metallogenic fluids. In this contribution, we present the GOLDFINGER geophysical experiment and the preliminary results.

Funding: grant PID2020-117332GB-C21 funded by MCIN/ AEI /10.13039/501100011033; EIT-Raw Materials project 17024 (SIT4ME: Seismic Imaging Techniques for Mineral Exploration); SA085P20 from the JCYL government, and TED2021-130440B-I00 by MCIN. IP is funded by MCIU and USal (BEAGAL18/00090).