| 1. |
- Bastani, M., et al.
(författare)
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Ground geophysical measurements made on mine-tailings in Sweden. Case studies and lessons learnt
- 2023
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Ingår i: 29th European Meeting of Environmental and Engineering Geophysics, Held at Near Surface Geoscience Conference and Exhibition 2023, NSG 2023. - 9789462824607
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Konferensbidrag (refereegranskat)abstract
- Ground-based geophysical surveys were conducted at eight mine-tailings repositories during 2021 and 2022 to help preparing an inventory of potential sources of critical raw materials in mine-waste. Geophysical methods included ERT, DCIP, RMT, and tTEM. In this study, we show results obtained on two of the sites as an example. Integration of models of electrical properties, geological observations, historical orthophotos, and drillhole samples provided estimations of the thickness of tailings. The interpretation was extended to construct 3D models of the deposits. Moreover, the modelled electrical properties helped to study the variations in the grain size, porewater content and mineral chemistry. The used geophysical methods resulted in consistent estimations of the geophysical properties and the depth to the more resistive material below the tailings could therefore be determined with higher confidence. Variations in chargeability and phase response from inversion of DCIP data are generally more strongly related to variations in mineral content and grain size. A strong correlation was observed at one of the sites. Spectral IP measurements on samples showed Cole-Cole like spectra and a clear relationship between the frequency of the maximum phase angle and the grain size.
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| 2. |
- Madsen, L. M., et al.
(författare)
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Comparison of tTEM-IP and ERT-IP : cases from mine tailing sites in Sweden
- 2023
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Ingår i: 29th European Meeting of Environmental and Engineering Geophysics, Held at Near Surface Geoscience Conference and Exhibition 2023, NSG 2023. - 9789462824607
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Konferensbidrag (refereegranskat)abstract
- The induced polarization (IP) effect can be studied using both galvanic and inductive methods. Here we study IP and its manifestation in transient electromagnetic (TEM) data from a tTEM system and in time-domain electric resistivity tomography (ERT) data. Since the two methods are sensitive to two different frequency ranges, a direct IP spectrum comparison is not possible. Instead, we assess the IP resolution and compare both resistivity and chargeability inversion results. We show that tTEM data recorded in highly resistive environments with high IP, suffer from fast-decaying transients and sign-changes, which makes it difficult to resolve the true resistivity and IP model due equivalences. A comparison of the maximum phase shifts from two mine tailing sites shows that the chargeability structures gained from the inversion of tTEM data to some degree follow the structures of the chargeability resolved from the ERT data. However, the magnitudes of the resolved phases are generally below 50 mRad for ERT, but up to 500 mRad for tTEM. This indicates that different polarization mechanisms are dominating within the different frequency ranges of the tTEM and ERT methods.
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