Seismic imaging of the Noranda Formation in the Amulet and Ribago areas: signature of structures and geology associated with VMS mineralization, TGI-3 Abitibi Project
Gilles Bellefleur, Eric de Kemp (GSC), Jean Goutier (MRNF), Michel Allard (Xstrata Copper), and Erick Adam (SeisServ)

Within the framework of the Targeted Geoscience Initiative (TGI-3), the Geological Survey of Canada obtained access to industry-acquired seismic reflection data along two profiles in the Noranda camp. The two seismic lines (Amulet and Ribago) pass through the mine sequence from east to west. The Amulet profile extends between the Flavrian and Dufault plutons at the level of the Amulet mine. The Ribago profile is located just north of the Powell pluton.

Xstrata Copper Canada also contributed a 3D geological model of the Noranda central camp to the TGI-3 Abitibi Project. The model, constructed using exploration drill holes, is an essential tool for interpreting seismic profiles. The model allows for the precise correlation between reflections and known geology at depth. The seismic data provide an additional control for regions that have not been drilled.

Exhalite horizons in the Noranda Formation are particularly important for guiding VMS exploration. Studies of physical properties reveal that the interface between mafic and felsic volcanic rocks where these horizons are found should produce good reflections. However, in the area of the Amulet profile, exhalite horizons do not coincide with continuous or clear reflections. It is likely that the geological contacts, which are commonly faulted near the profile, do not present a sufficiently large enough surface at the scale of the seismic waves to generate good reflections. One of the most significant reflections along the Amulet profile crosscuts part of the volcanic sequence almost perpendicularly. Its orientation and position could indicate the presence of a conduit that focused hydrothermal fluids. Several dykes of this nature were observed under deposits in the mine sequence. The generally felsic composition of these dykes could produce a reflection at their contacts with mafic volcanic rocks.

On the Ribago profile, the C contact exhalite horizon is represented by a strong reflector. The greater continuity of lithological contacts in this part of the Noranda Formation probably explains why this exhalite horizon is observable on the section. An unmigrated version of the profile reveals two diffractions near the C contact. These diffractions correspond to small, known mineralized zones that were intersected by drill holes. The integration of the two seismic profiles with the 3D geological model allowed us to determine the nature of specific reflections and to identify structures associated with VMS-type mineralization.