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This paper focusses on obtaining a better understanding of the subsurface geology of the Chibougamau area, in the northeast of the Abitibi greenstone belt (Superior craton), using geophysical data collected along a 128 km long traverse with a rough southwest--northeast orientation. We have constructed two-dimensional (2D) models of the study area that are consistent with newly collected gravity data and high-resolution magnetic data sets. The initial models were constrained at depth by an interpretation of a new seismic section and at surface by the bedrock geology and known geometry of lithological units. The attributes of the model were constrained using petrophysical measurements so that the final model is compatible with all available geological and geophysical data. The potential-field data modelling resolved the geometry of plutons and magnetic bodies that are transparent on seismic sections. The new model is consistent with the known structural geology, such as open folding, and provides an improvement in estimating the size, shape, and depth of the Barlow and Chibougamau plutons. The Chibougamau pluton is known to be associated with Cu--Au magmatic-hydrothermal mineralisation and, as the volume and geometry of intrusive bodies is paramount to the exploration of such mineralisation, the modelling presented here provides a scientific foundation to exploration models focused on such mineralisation. Key words: geophysics, potential-field modelling, 2.5D modelling, geological modelling, geological, seismic and petrophysical constraints, gravity and magnetic. L'article est axe sur l'etablissement d'une meilleure comprehension de la geologie du sous-sol de la region de Chibougamau, dans le nord-est de la ceinture de roches vertes de l'Abitibi (craton du Superieur), a la lumiere de donnees geophysiques recueillies le long d'une traverse de 128 km d'orientation approximativement sud-ouest--nord-est. Nous avons construit des modeles bidimensionnels (2D) de la region a l'etude qui concordent avec des donnees gravimetriques et des ensembles de donnees magnetiques de haute resolution nouvellement acquis. Les modeles initiaux ont ete delimites en profondeur par l'interpretation d'une nouvelle coupe sismique et en surface par la geologie du substrat rocheux et la geometrie connue des unites lithologiques. Les attributs du modele ont ete etablis en utilisant des mesures petrophysiques, le modele final etant ainsi compatible avec toutes les donnees geologiques et geophysiques disponibles. La modelisation des donnees de champ de potentiel a permis de cerner la geometrie de plutons et de corps magnetiques qui sont transparents sur les coupes sismiques. Le nouveau modele s'accorde avec les elements connus de la geologie structurale, comme un plissement ouvert, et ameliore l'estimation de la taille, de la forme et de la profondeur des plutons de Barlow et de Chibougamau. Il est etabli que ce dernier est associe a une mineralisation magmatique-hydrothermale a Cu--Au et, comme le volume et la geometrie des corps intrusifs revetent une importance capitale dans l'exploration pour ce type de mineralisation, la modelisation presentee constitue un fondement scientifique pour les modeles d'exploration axes sur ce type de mineralisation. [Traduit par la Redaction] Mots-cles : geophysique, modelisation du champ de potentiel, modelisation en 2,5D, modelisation geologique, contraintes geologiques, sismiques et petrophysiques, gravite et magnetisme., Introduction The Metal Earth project aims to better understand the differences between greenstone belts in the Abitibi and Wabigoon belts of the Superior craton of Canada that are well endowed [...]

A high‐resolution seismic reflection transect was acquired over a hard‐rock geological setting along an existing roadway in the Larder Lake area of the Superior Craton of Canada for the Metal Earth project in 2017. This profile, as well as other Metal earth transects, primarily aims to enhance the knowledge and to better understand the subsurface geology of the Abitibi Greenstone Belt within the Canadian Shield. The complex geological settings of the study area as well as the tribulations caused by the survey geometry have made the imaging and velocity field estimation more challenging. A recently introduced 2.5D multifocusing stacking method is one potential solution for processing crooked‐line seismic data with a poor signal‐to‐noise ratio. The 2.5D multifocusing approach offers more realistic modelling of the zero‐offset wavefield by explicitly accounting for the midpoint dispersion and cross‐dip effects. The main practical problem of the 2.5D multifocusing implementation is the simultaneous determination of the optimal wavefield parameters for each image point and time location. We address this optimization problem using a multidimensional constrained differential evolution global optimization algorithm, as this improves the efficiency and accuracy of the estimation. We have also designed an efficient processing sequence for multifocusing seismic imaging. The performance of the 2.5D multifocusing procedure has been examined on a synthetic model, generated using the same real acquisition geometry. Numerical tests demonstrate that the 2.5D multifocusing technique can produce a more focused stack with the primary reflections appearing at their poststack correct locations, and the procedure can also provide reliable estimates of interface dips. Due to the importance and difficulty of imaging the data, several conventional and advanced processing strategies have been attempted on the transect, specifically: 2D phase‐shift time migration of a dip moveout corrected stack; 2D prestack Kirchhoff time migration; swath 3D poststack migration; and our 2.5D multifocusing imaging algorithm. We found that applying the 2.5D multifocusing stacking algorithm followed by a poststack time migration approach improved the resolution of the image significantly compared to all the conventional and advanced methods and identified new reflections. The 2.5D multifocusing method also focused the steeply dipping reflections more coherently, which resolved ambiguities in geological architecture by understanding the location and continuity of structures. The method also accurately extracts 3D structural information and results in an improved signal‐to‐noise ratio. [ABSTRACT FROM AUTHOR]

In 2017, the Metal Earth multi‐disciplinary exploration project acquired a total of 921 km of regional deep seismic reflection profiles and 184 km of high‐resolution seismic reflection profiles in the Abitibi and Wabigoon greenstone belts of the Superior province of Canada. The Abitibi belt hosts several world‐class mineral deposits, whereas the Wabigoon has sparse economic mineral deposits. Two high‐resolution surveys in the Swayze area, a poorly endowed part of the western Abitibi greenstone belt, served as pioneer surveys with which to better understand subsurface geology and design a strategy to process other surveys in the near future. Swayze seismic data were acquired with crooked survey geometries along roads. Designing an effective seismic processing flow to address these geometries and complex geology required straight common midpoint lines along which both two‐dimensional prestack dip‐moveout correction and poststack migration processing were applied. The resulting seismic sections revealed steeply dipping and subhorizontal reflections; some correlate with folded surface rocks. An interpreted fault/deformation zone imaged in Swayze north would be a target for metal endowment if it extends the Porcupine–Destor structure. Because of the crooked line geometry of the surveys, two‐dimensional /three‐dimensional prestack time migration and swath three‐dimensional processing were tested. The prestack time migration algorithm confirmed reflections at the interpreted base of the Abitibi greenstone belt. The swath three‐dimensional images provided additional spatial details about the geometries of some reflections, but also had less resolution and did not detect many reflectors observed in two dimensions. Geological contacts between felsic, mafic and ultramafic greenstone rock layers are thought the main cause of reflectivity in the Swayze area. [ABSTRACT FROM AUTHOR]