Tensor magnetotelluric (MT) soundings were carried out to delineate the geometry of an extended shallow conductor detected by airborne electromagnetic method in the mining camp of Chibougamau (Canada). Careful distortion analysis of the impedance tensors from eleven sites indicate that the subsurface is reasonably 2-D within the 0.0025–10s range. The recovered regional impedances are corrected for static shifts employing 2-D inversion for minimum structure. The modeled resistivity cross‐sections show a far more complex conductivity structure than anticipated. The sheet‐like shallow conductor lies near the boundary between the conductive southern section located in the Abitibi subprovince and the resistive northern section located in the Opatica subprovince. It extends to a depth of 250 m. Two other limited conductive zones are imaged respectively between 0.4 km and 3 km and between 1.5 km and 4 km. We propose that the conductors are associated with sulfide mineralization and graphite in shear zones. They are delimited by steeply south dipping thrust faults. The northern resistive section does not show clear resistivity changes up to a depth of 15 km. Gravity data collected along the MT profile have provided additional constraints. Both MT and gravity models are consistent with one another and with the known regional geologic structure. They indicate that the Abitibi greenstone belt is 3.5–4.4 km thick in the survey area and that the steeply dipping geology at the surface is flattening at depths of 4 km approximately.

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The authors present a residual gravity map for Gaspésie based on a separation of the regional and residual fields by a graphical method. This map results from the smoothing of 24 gravity profiles with lengths that far exceed the dimension of the zone of interest. The base value of the regional field has been estimated by taking into account surface data and by calculating the maximum gravity lows associated with relatively low-density Silurian-Devonian rocks. The residual gravity map includes all the gravity features that are clearly associated with shallow sources and shows a minimum distortion of the shape of the anomalies. Current Research 2006-D1 1 N. Pinet et al. Résumé : Nous présentons une carte de l'anomalie de Bouguer résiduelle de la péninsule de la Gaspésie basée sur une méthode graphique de séparation des composantes régionale et résiduelle du champ de gravité. Cette carte résulte du lissage de 24 profils de gravité dont la longueur excède grandement les dimensions de la zone d'intérêt. La valeur de base de la composante régionale a été estimée en prenant en compte les données de surface et en calculant les bas gravimétriques maximums associés aux roches siluriennes et dévoniennes de densité relativement faible. La carte de l'anomalie de Bouguer résiduelle comprend l'ensemble des anomalies clairement associées à des sources peu profondes et montre une distorsion minimale de la forme des anomalies gravimétriques.

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