\sout\sout Copper-Au magmatic-hydrothermal systems dominate in the Chibougamau area of the Neoarchean Abitibi Subprovince, whereas orogenic gold mineralization is more common in the rest of the Abitibi. Understanding differences in the metal endowment of parts of the Abitibi Subprovince requires insights into the geodynamic evolution of the Chibougamau area. This is addressed by imaging the crust using seismic reflection data acquired as part of the Metal Earth project. Seismic reflection imaged shallowly south-dipping structures in the upper-crust (e.g., deep extension of the Barlow fault) and a northward-dipping mid-crust region. The upper part of the mid-crust zone is characterized by multiple reflectors that are likely faults superimposed on a major lithological boundary. These structures were likely acquired at ca 2.70 Ga during terrane accretion prior to carbonization. Combining the seismic data with known stratigraphic, structural and magmatic records, we propose that the study area was initially a normal (i.e., thick) Archean oceanic crust that formed at or before 2.9 Ga and that evolved through terrane imbrication at 2.73 Ga or before. This caused rapid burial of mafic rocks followed by devolatilization and partial melting of hydrated mafic rocks to produce tonalite magmas that may have mixed with mantle-derived melts to produce the diorite-tonalite suite associated with Cu-Au magmatic-hydrothermal mineralization.

Passive seismic methods are considered as cost-effective and environmental-friendly alternatives to active (reflection) seismic methods. We have acquired co-located active and passive seismic surveys over a metal-endowed Archean granite-greenstone terrane in the Larder Lake area to investigate the reliability of the estimated elastic properties using the passive seismic methods. The passive seismic data was processed using two different data processing approaches, the ambient noise surface wave tomography (ANSWT) and receiver function analysis methods to generate shear-wave velocity and P- to S-wave (P-S) convertibility profiles of the subsurface, respectively. The Cadillac-Larder Lake Fault (CLLF) was imaged as a south-dipping sub-vertical zone of weak reflectivity in the reflection seismic profile. To the north of the CLLF, a package of north-dipping reflections in the upper-crust (at depths of 5-10 km) resides on the boundary of high (on the top) and low (on the bottom) shear-wave velocity zones estimated using the ANSWT method. This package of reflections is most likely caused by overlaying mafic volcanic and underlying felsic intrusive rocks. The P-S convertibility profile imaged the Moho boundary at ~40 km depth as well as a south-dipping slab that penetrates into the mantel which was interpreted to be either caused by the delamination of the lower crust or a possible deeper extension of the Porcupine-Destor Fault. Overall, the reflectivity, shear-wave velocity, and P-S convertibility profiles exhibited a good correlation and provided a detailed image of the subsurface lithological structure to a depth of 10 km.

Copper-Au magmatic-hydrothermal systems dominate in the Chibougamau area of the Neoarchean Abitibi subprovince (greenstone belt) of the Superior Province (craton), whereas orogenic gold mineralization is more common in the rest of the Abitibi. Understanding differences in metal endowment within the Abitibi greenstone belt requires insights into the geodynamic evolution of the Chibougamau area. This was addressed by imaging the crust using seismic reflection profiling acquired as part of the Metal Earth project. Seismic reflection sections display shallowly south-dipping reflectors located within the upper-crust (e.g., deep continuation of the Barlow fault) and a northward-dipping mid-crust imbricated with older crust (Opatica subprovince) to the north. Multiple reflectors characterize the upper part of the mid-crust, interpreted as faults superimposed on a major lithological boundary. These structures likely formed during terrane accretion prior to craton stabilization. Combining the new seismic data with known stratigraphic, structural and magmatic records, we propose that the study area was initially a normal (i.e., thick) Archean oceanic crust that formed at or before 2.80 Ga and that evolved through terrane imbrication at 2.73-2.70 Ga. Shortening caused rapid burial, devolatilization and partial melting of hydrated mafic rocks to produce tonalite magmas that may have mixed with mantle-derived melts to produce the diorite-tonalite suite associated with observed Cu-Au magmatic-hydrothermal mineralization.