Evaluation of the applicability of geophysical methods when characterizing mine waste in Yxsjöberg, Sweden

Abstract: Smaltjärnen tailings repository located in Yxsjöberg, Sweden, attracts researchers with questions regarding characterization and potential re-mining. This thesis continuous geophysical characterization done by researchers from the Exploration Geophysics department at Luleå University of Technology but using new data from 2019. Geophysical methods used were self potential (SP), direct current resistivity (DCR), induced polarization (IP), and ground-penetrating radar (GPR). SP data were collected using a fixed base procedure and equipment from EMIT. Data were processed in MATLAB and presented in Oasis Montaj/ Geosoft software, yielding results difficult to interpret. Similar pattern was seen in previous investigations from 2016. However, some discrepancies were noticed, and more work is needed in order to validate these data. Therefore, data is presented without any interpretation. RES2DINV inversion software by Geotomo Software (now maintained by Aarhus GeoSoftware) was used for inversion of DCR data to produce four 2D resistivity sections, and the 3D resistivity model was made by Jingyu Gao with his software. DCR data were acquired by using Terrameter LS by ABEM and measuring using a roll-along procedure and dipole-dipole configuration. Results show consistency between vertical variations at profile crossings from different profiles. Three layers are indicated from results, interpreted to contain mine tailings and quaternary deposits, at some locations interpreted to be water-saturated, and bedrock. No IP effect is seen at Smaltjärnen. GPR data were processed in GPRSoft® PRO produced by Geoscanners to understand internal structures and water table, by using zero-offset surveying with 250 MHz antenna from Malå Geoscience and 300 MHz antenna from Geoscanners. Since the tailings of Smaltjärnen consists of very thin layers, the results are complex to interpret. Hyperbolas and layers, along with other more uncertain patterns, are seen in radargrams, and further research is needed to fully understand the images.