Pedro Castiñeiras

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).

This study aims to use geochemical, mineralogical, ecotoxicological and biological indicators for a comprehensive assessment of the ecological risks related to the mobility, ecotoxicity and bioavailability of potentially harmful elements in the Lousal mining district. Particularly, toxicity was evaluated using four assays: algae, cytotoxicity assays with HaCaT cell line (dermal), earthworms and Daphnia magna. The geochemical and mineralogical characterization of the studied area shows that the mine wastes underwent intense weathering processes, producing important contamination of the adjacent soils, which also led to the release and mobilization of PHEs into nearby water courses. Total PTE results indicate that the soils affected by mining activities were highly contaminated with As and Cu, while Zn and Pb content ranged from low to very high, depending on the analyzed samples. Cadmium levels were found to be very low in most of the soil samples. The test using Daphnia magna was the most sensitive bioassay, while the Eisenia foetida test was the least sensitive. Except for the LOS07 soil sample, the rest of the soils were classified as “High acute toxicity” and “Very high acute toxicity” for aquatic systems. The results in HACaT cells showed results similar to the ecotoxicological bioassays. The application of biotests, together with geochemical and mineralogical characterization, is a very useful tool to establish the degree of contamination and the environmental risk of potentially harmful elements.

Abandoned mine wastes, containing high sulfide contents, are of particular concern because of the formation of acid mine drainage (AMD), becoming an active and harmful point source of potentially toxic elements (PTEs) to the environment. A detailed evaluation of the chemical and mineralogical composition of mining wastes is necessary to determine effective remediation actions. Due to the high amount of generated wastes as a result of mining and processing activities, the cost and time consumed for this characterization are limiting. Hence, efficient tools could be applied to predict the composition of these wastes and their spatial distribution. This study aims to determine the physico-chemical characterization of wastes from mining activities using geochemical and geophysical techniques. The obtained results, both geochemical and geophysical, allow us to locate areas with a high potential risk of contamination by As in an economic and simple way, and enable us to design detailed geochemical sampling campaigns. In addition, the fact that there are conductive fractures in depth suggests the possible circulation of contaminants through them as well as the preferential lines of circulation.

Zircon crystal texture and Th / U ratio have been used as a watertight argument when interpreting U-Pb ages. The wide, and sometimes indiscriminate, use of those gauges could result into misinterpretation of the geological meaning of U-Pb data. A case study is presented here where zircons from a controversial polymetamorphic eclogite unit were analyzed with SHRIMP. Both U-Pb and trace element (TE) data were collected for each point. The combination of TE and structural arguments indicates that zircon was part of the eclogite facies mineral assemblage at 390 Ma. However, using Th / U ratio and CL textures lead to a different interpretation. Our results suggest that in complex orogenic scenarios and extreme environments well-known techniques (CL) and geochemical relationships (Th / U) must be used in combination with TE data and structural relationships as provenance/process gauges. While geochronology provides accurate isotope relationships, their temporal dimension must rely on structural and petrological evidence.

The Sobrado unit, within the upper part of the Órdenes complex (NW Iberia) represents an allochthonous tectonic slice of exhumed high grade metamorphic rocks formed during a complex sequence of orogenic processes in the middle to lower crust. In order to constrain those processes, U-Pb geochronology and REE analyses of accessory minerals in migmatitic paragneisses (monazite, zircon), and mylonitic amphibolites (titanite) were conducted using LASS-ICP-MS. The youngest metamorphic zircon age obtained co-incides with a Middle Devonian concordia monazite age (~ 385 Ma) and is interpreted to represent the minimum age of the Sobrado high-P granulite-facies metamorphism that occurred during the early stages of the Variscan Orogeny. Metamorphic titanites from the mylonitic amphibolites yield a Late Devonian age (~ 365 Ma), and track the progressive exhumation of the Sobrado unit. In zircon, cathodoluminescence images and REE analyses allow two aliquots with different origins in the paragneiss to be distinguished. An Early Ordovician age (~ 490 Ma) was obtained for metamorphic zircons, employing the TuffZirc algorithm, although with a large analytical dispersion. This age is considered to mark the onset of granulite-facies metamorphism in the Sobrado unit under intermediate-P conditions, and related to intrusive magmatism and coeval burial in a magmatic arc setting. A maximum depositional age for the Sobrado unit is established in the late Cambrian (~ 503 Ma). The zircon dataset also record several inherited populations. The youngest cogenetic set of zircons yield a crystallization age from TuffZirc algorithm of ~ 530 Ma and are thought to be related to the peri-Gondwana magmatic arc. The additional presence of inherited zircons older than ~ 530 Ma is interpreted as suggesting a West African Craton provenance.

A comprehensive study of the serpentinite and associated veins belonging to the Frido Unit in the Pollino Massif (southern Italy) is presented here with the aim to provide new constraints about the hydrothermal system hosted by the accretionary wedge of the southern Apennines. The studied serpentinites are from two different sites: Fosso Arcangelo and Pietrapica. In both sites, the rocks show mylonitic-cataclastic structures and pseudomorphic and patch textures and are traversing by pervasive carbonate and quartz-carbonate veins. The mineralogical assemblage of serpentinites consists of serpentine group minerals (with a predominance of lizardite), amphiboles, pyroxene, chlorite, titanite, magnetite, and talc. In some samples, hydro-garnet was also detected and documented here for the first time. As for cutting veins, different mineralogical compositions were observed in the two sites: calcite characterizes the veins from Fosso Arcangelo, whereas quartz and dolomite are the principal minerals of the Pietrapica veins infill, suggesting a different composition of mineralizing fluids. Stable isotopes of C and O also indicate such a different chemistry. In detail, samples from the Pietrapica site are characterized by δ¹³C fluctuations coupled with a δ¹⁸O shift documenting calcite formation in an open-system where mixing between deep and shallow fluids occurred. Conversely, δ¹³C and δ¹⁸O of the Fosso Arcangelo veins show a decarbonation trend, suggesting their developing in a closed-system at deeper crustal conditions. Precipitation temperature calculated for both sites indicates a similar range (80 °C to 120 °C), thus suggesting carbonate precipitation within the same thermal system.

Las capas de rodadura son las más expuestas al clima y al efecto del tráfico, especialmente en carreteras sometidas a mantenimiento invernal. Por este motivo, es importante conocer mejor los mecanismos de deterioro de dichas capas a la hora de mejorar su diseño, construcción y uso a largo plazo. Con este fin, dos tipos de mezclas asfálticas utilizadas en el NO de España fueron expuestas a ensayos de durabilidad (heladicidad y choque térmico) con una solución saturada de NaCl. Después, se realizó el ensayo de pista y el material deteriorado y deformado resultante fue analizado mediante microscopia óptica de luz polarizada y de fluorescencia. Dicho análisis mostró que el principal responsable de la degradación de la mezcla fue la baja adhesión árido-betún. Esta degradación se concentró en el árido debido a que el ligante actuó como una pared impermeable. En consecuencia, la solución de NaCl pudo penetrar y degradar rápida e intensamente el árido.