Papers by Michel Chouteau
Geophysics, Feb 15, 2022
Detection and assessment of the deeply buried high-grade uranium deposits in the Athabasca Basin ... more Detection and assessment of the deeply buried high-grade uranium deposits in the Athabasca Basin rely on geophysical methods to map conductive rocks. Variable Quaternary surface cover can mask the anomalous signals from depth and affect the interpretation of inverted conductivity models. We present the analysis of several electromagnetic (EM) modeling studies and two field data sets to demonstrate the effects of varying Quaternary cover resistivity and thickness, on the ability to resolve the parameters of underlying sandstone, alteration, and basement conductors. Synthetic data, assuming a typical shallow EM sounding system and realistic resistivities found in the Athabasca Basin, indicate that resistivity and thickness parameters of the Quaternary cover can be separately recovered in cases in which this cover is more conductive than the underlying sandstone, but not when the cover is significantly more resistive. A 3D modeling study indicates that by using airborne EM data, it is possible to detect a basement conductor of 20 S at a depth of at least 600 m below the surface, even in the presence of Quaternary cover thickness variations of the up to 20% (40-60 m). Furthermore, although Quaternary cover variations and deeper sandstone alteration can produce comparable anomalous signal amplitudes in a time-domain EM response, their effects are most visible in distinctly separate time windows. Ground-penetrating radar and other data to characterize the Quaternary cover in the McArthur River area indicate that this cover consists mostly of sandy tills ranging in thickness from 0 to 117 m. Constrained 3D inversion of an airborne EM data set from the same area indicates basement conductors consistent with the depth and location of a known fault. Elevated conductivity in the sandstone by up to a factor of two over the background values could indicate possible alteration.
... The HydroGeophysics Group, Department of Earth Sciences, University of Aarhus ... With the re... more ... The HydroGeophysics Group, Department of Earth Sciences, University of Aarhus ... With the resolution capabilities and the equivalence problem of resistivity data in mind it is important to know not only the geological/hydrogeophysical model but also the probability of the model. ...
Echos du monde classique: Classical views, 1989
Tunisie, entre Mahdia et La Chebba, a proximite de Ksour-Essaf| c'est l'antique Sullecthu... more Tunisie, entre Mahdia et La Chebba, a proximite de Ksour-Essaf| c'est l'antique Sullecthum. Les AA. renvoient a la presentation exhaustive qu'ils publieront dans le volume " Sullecthum I ", Cahiers des Etudes Anciennes, fasc. XXII, a paraitre prochainement. Ces catacombes chretiennes sont exceptionnellement bien conservees| l'article ne donne pas encore de donnees chronologiques
Geophysics, Mar 1, 2017
Processing of potential field data is commonly done by spectral methods because of their low comp... more Processing of potential field data is commonly done by spectral methods because of their low computational complexity. However, we have studied some geostatistical methods to process the potential field data, and we find the advantages of using these spatial methods. First, we investigate transformation of data by kriging using a gravimetric model of covariance, we compare this approach with the spectral method, and we find its advantage when the data were sparse and not on a regular grid using a synthetic example as well as a field data example. Then, we use factorial kriging for noise reduction and separation of the regional and residual components. This method does not have some of the practical limitations that the spectral-based methods encounter. Finally, we determine the flexibility of interpolation using nonstationary covariances.
Geophysics, Jul 1, 2016
In geophysical inverse problems, an a priori structured mesh is often used for inversion and mesh... more In geophysical inverse problems, an a priori structured mesh is often used for inversion and mesh refinement is applied if needed by the user after observation of inversion results. We have developed a new intelligent self-adaptive unstructured finite-element meshing technique for electrical resistivity tomography inverse problems. This new approach uses Harris corner-and-edge detectors that are based on the local autocorrelation function of 2D distribution of pixels. This meshing technique optimizes the size of the inverse problem by refining areas where variations in the physical property structure are sensed to be important. The meshing technique also generates a more appropriate and optimum mesh for the inverse problem that is dependent on the problem itself. Tests on modeled data have demonstrated that the proposed intelligent meshing technique can reduce data misfit, produce a better reconstruction of the true physical properties, and minimize the size of the inverse problem. The synthetic model consists of a conductive dike in a resistive medium. By applying the proposed intelligent meshing technique, the inverse model of the dike is very similar to the inverse model produced using fine meshes, and it is also better reconstructed than the inverse model produced using conventional meshes. We have also applied the intelligent meshing technique to survey data collected for groundwater-saltwater mapping and characterizing the subsurface conductive structure with topography included. Our results indicate that the new meshing technique can produce solutions that are comparable with standard meshing and fine meshing techniques, while optimizing the size of the inverse problem.
Geophysics, Jun 1, 1988
Field distortions caused by topography hamper the interpretation of magnetotelluric (MT) data. To... more Field distortions caused by topography hamper the interpretation of magnetotelluric (MT) data. Topographic features that can be simulated by two‐dimensional models seriously affect the H-polarization results. A technique to reduce those effects in MT data uses a finite‐element program to compute correction coefficients. After correction, the resulting data can be interpreted as if they were obtained over a flat surface and depended only on the subsurface structure. The technique is applied to four examples representative of MT survey targets in high‐relief terrain. Results indicate that terrain correction removes the misleading topographic anomalies and improves the quality of subsurface interpretation in regions where the surface relief is two‐dimensional. The correction technique yields some geometrical distortion of the original subsurface structure, but the distortion is usually of small importance. In practice, telluric dipoles of realistic length do not smooth out topographic effects having wavelengths longer than the telluric dipole. A practical procedure derived from the proposed technique allows terrain correction when the relief is approximately two‐dimensional.
Construction and Building Materials, Mar 1, 2020
The distress caused by alkali-silica reaction (ASR) to concrete structures can occur long time af... more The distress caused by alkali-silica reaction (ASR) to concrete structures can occur long time after the reaction has been triggered. We propose to use spectral induced polarization (SIP) as a non-destructive method for early detection of ASR reaction before the damage is apparent. Our research deals with monitoring the difference between the electrical behaviour (phase lag, bulk resistivity, relaxation time, total chargeability) of non-reactive (NR) and reactive (RC) concrete samples affected by ASR. Laboratory measurements of complex resistivity were done in the frequency range 1.43 mHz-20 kHz. A Debye decomposition (DD) model was used to determine the DC bulk resistivity (q 0), and the distribution of the chargeability as a function of the relaxation time. The total chargeability (R m) and the mean relaxation time (s mean) were computed as DD parameters to characterize the ASR development. While q 0 was strongly dependent on the electrical conductivity of the solution (water, NaOH) with a constant change with time, both concrete mixtures saturated with the same solution showed an increase q 0 due to the development of the matrix skeleton over time. In this work, q 0 did not play a significant role to characterize the ASR development. For the samples affected by ASR, a significant evolution of R m and s mean was found compared to the non-affected mixtures (RC, NRC-H 2 O), specially over the low frequency range [1.48 mHz < f < 5.86 Hz]. The RC-NaOH samples displayed a strong linear correlation between normalized chargeabilty and imaginary conductivity. This observation could be associated with an increase in surface conductivity of the Stern layer at reactive grain surface or the evolution of specific surface area due to production of ASR silica gel, or both. Based on our conceptual electrochemical model of RTD presented in this work, an evolution of chargeability peak was observed at relatively long relaxation time s > 10 2 s that could be associated with the polarization of aggregates affected by ASR.
Engineering Geology, Jul 1, 2023
Construction and Building Materials, Jun 1, 2019
Electrical impedance spectroscopy (EIS), also known as Spectral Induced Polarization (SIP) has pr... more Electrical impedance spectroscopy (EIS), also known as Spectral Induced Polarization (SIP) has proven to be a successful non-destructive technique able to characterize the chemical and physical properties of a complex structure (concrete, rocks, and soil) under various environmental conditions. Because this technique aims to measure small amplitude signals, it can easily be influenced by parasitic effects which are not representative of the intrinsic properties of the investigated material. The purpose of this paper is to validate the resolution of our experimental methodology as a preliminary step to ensure an accurate measurement of the bulk complex resistivity response of concrete samples within a wide frequency range (1.43 mHz-20 kHz). A cement mortar sample is first used as a homogeneous (isotropic) material to improve the sample holder design for reducing the errors and controlling the external parameters (such as coupling effect, geometric factor, contact impedance, electrode polarization) during the laboratory measurements. Also, the performance and installation of the measuring components such as the electrodes (current and potential) and the sample holder design are assessed. The specimen dimensions and designs are selected based on a sample standard size that will be used to determine the physicomechanical properties of concrete (compressive strength, modulus of elasticity, ultrasonic pulse velocity, length variation). The examinations are performed in parallel with the SIP measurement on the same sample. The accuracy of our measurement setup is then validated using aluminum-bronze plates bonded to the sample using a conductive gel to transmit electric current with a density less than 10 À3 A m À2. The results showed that by controlling the sponge moisture in the Ag/AgCl non-polarizable voltage electrodes, our SIP measurement system is able to measure the phase lag with an error smaller than 1 mrad over a frequency range from 1.43 mHz to 20 kHz.
Geophysics, Mar 1, 2003
In the spring of 1996, a direct current (dc) resistivity and induced polarization (IP) borehole s... more In the spring of 1996, a direct current (dc) resistivity and induced polarization (IP) borehole survey was carried out at the Casa Berardi gold mine in northwestern Quebec to study the spatial extent of the economic disseminated zone of an auriferous quartz vein type orebody. Crosshole pole‐pole and single‐hole pole‐dipole configurations were used to delineate the geometry of the body associated with the Casa Berardi fault system. Since the spatial data sampling was insufficient for 3D inversion, the interpretation has been done using 3D dc and IP forward modeling. Model changes were applied iteratively to match synthetic with field data. Sensitivities provide information on how to alter the models efficiently. Furthermore, they indicate the significant regions of the model, giving evidence on where the model is meaningful. A model study using a simple prismatic block structure is shown to enhance understanding of the physical response associated with the two types of borehole survey. The algorithms used for the interpretation offer a so‐called grid‐independent electrode positioning technique, which is a helpful modus operandi to significantly facilitate the simulation process. The result is a resistivity and chargeability model that produces the observed physical response and incorporates all known geological a priori information. Particularly, the IP response carries detailed information on the appearance of the orebody, whereas the potential response reflects the resistivity contrast between metavolcanic and metasedimentary rocks at the Casa Berardi fault.
EGU General Assembly Conference Abstracts, Apr 1, 2016
Exploration Geophysics, 2019
We evaluated imaging alteration associated with porphyry copper style mineralisation using aeroma... more We evaluated imaging alteration associated with porphyry copper style mineralisation using aeromagnetic data in the Highland Valley Copper (HVC) district as part of the Natural Sciences and Engineering Research Council of Canada (NSERC) and Canada Mining Innovation Council (CMIC) Footprints project. The first step of the investigation involved construction of a 3D geological model based on surface and regional information, and petrophysical data of the host rocks. From the petrophysics, it was observed that hydrothermal alteration affected the magnetic susceptibility of some batholithic host rocks at HVC, and low susceptibility values were associated with the altered rocks. From this observation, an alteration index was devised, differencing, based on the magnetic susceptibility, between unaltered and altered batholith host rocks. Threedimensional inversions were conducted using geological constraints obtained from surface and borehole geology as well as physical property data. Then the alteration index methodology was tested using 3D inversions and residual models within five overlapping blocks covering portions of the batholith. The indices inferred from inverted susceptibility were compared to surface mapped alteration. For some felsic facies of the batholith, the alteration index derived from inverted magnetic susceptibility corresponds to the mapped alteration and delineates the known porphyry Cu system district. However, it is not true for others where alteration was less magnetite-destructive and more focused in structures.
Vadose Zone Journal, 2019
Core Ideas 3D time‐lapse ERT is used to monitor water infiltration for mining environmental issue... more Core Ideas 3D time‐lapse ERT is used to monitor water infiltration for mining environmental issues. Geoelectrical images provide information where no hydrogeological data is available. Water resistivity must be taken into account to understand bulk resistivity variations. Electrical resistivity of water is used as a tracer to reconstruct water infiltration. Infiltration model integrating both hydrogeological and geophysical data is proposed. Open‐pit mines often generate large quantities of waste rocks that are usually stored in waste rock piles (WRPs). When the waste rocks contain reactive minerals (mainly sulfides), water and air circulation can lead to the generation of contaminated drainage. An experimental WRP was built at the Lac Tio mine (Canada) to validate a new disposal method that aims to limit water infiltration into reactive waste rocks. More specifically, a flow control layer was placed on top of the pile, which represents a typical bench level, to divert water toward ...
Ore Geology Reviews, 2018
Predicting rock type and detecting hydrothermal alteration using machine learning and petrophysic... more Predicting rock type and detecting hydrothermal alteration using machine learning and petrophysical properties of the Canadian Malartic ore and host rocks,
GEOPHYSICS, 2018
Applications of the spectral induced polarization (SIP) method to mineral exploration are limited... more Applications of the spectral induced polarization (SIP) method to mineral exploration are limited by our knowledge of the relationships among rock texture, mineral composition, and electrical properties. Laboratory SIP responses were measured on rock samples from the Canadian Malartic gold deposit. Field SIP responses were also measured at the outcrop scale, along a profile that intersects a well-studied mineralized zone. The mineralogy and the texture of sedimentary rocks from this deposit were quantitatively determined with mineral liberation analysis. A systematic decrease (Pearson [Formula: see text]) in total chargeability with increasing fraction of the sulfide mineral interfaces associated with feldspar minerals (namely, K-feldspar and albite) was observed. On the other hand, total chargeability increased with the fraction of sulfide mineral interfaces associated with carbonates and micas (Pearson [Formula: see text]). At Canadian Malartic, proximal alteration in the minerali...
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Papers by Michel Chouteau