Integrating 3D geological modelling and seismic imaging methods at the Lalor VMS deposit, Manitoba
CIM Vancouver 2016
Mr Bellefleur Gilles (Natural Resources Canada), Mr Ernst Schetselaar (Natural Resources Canada), Mr Jim Craven (Natural Resources Canada)
Active and passive 3D seismic data sets were acquired over the Lalor volcanogenic massive sulfide deposit near Snow Lake, Manitoba, Canada, to assess the reflectivity of the ore and further validate the potential of 3D reflection seismic methods for deep mineral exploration. The Lalor Lake deposit was chosen as a test site as it provided an intact, well-characterized 25 Mt deep ore deposit with a rich catalog of geological and geophysical data, as well as extensive drill-core, and drillhole geophysical and geological logs.
The interpretation of the seismic data (active-source and passive) is constrained with a detailed 3D lithofacies model constructed from the categorical kriging of 15 lithological units identified in borehole intersections. Final seismic images obtained from the active-source seismic data reveal some strong reflections associated with the zinc-rich massive sulfide zones. The most prominent reflection results from the constructive interference of thin and closely-spaced massive sulfide zones and felsic-mafic volcanic rock contacts above and below the mineralization. Contacts between felsic and mafic volcanic rocks, including those either weakly altered or metamorphosed, produced prominent and continuous reflections that are used to map the main architecture of the footwall rocks.
Approximately 300 hours of ambient noise data (passive seismic method) were also recorded on a grid of receivers over the Lalor deposit to test the capability of seismic interferometry to image ore deposits in the crystalline rock environment. The larger 3D active-source seismic survey was used to evaluate the interferometry results. Virtual shot gathers retrieved by cross-correlating ambient noise at all receivers were processed using a sequence similar to the one applied to the active source seismic data. Passive seismic stacked sections reveal a number of events similar to those observed on the processed active seismic sections. In particular, the passive seismic interferometry method is capable to partly image shallowly-dipping reflections but did not produce convincing images of steeply-dipping reflections. The passive seismic interferometry results over the Lalor mining area are encouraging, but image quality of the passive survey is lower than image quality obtained for the active seismic data.
Future ambient noise surveys with longer offsets, shorter receiver spacing, and wider azimuth distribution are needed in crystalline rock environment to address further the potential of the method for mineral exploration.