Feasibility of virtual source reflection seismology using interferometry for mineral exploration: A test study in the Lalor Lake volcanogenic massive sulphide mining area, Manitoba, Canada

Approximately 300 hours of ambient noise data were recorded on a grid of receivers covering an area of 4 km(2) over the Lalor Mine, Canada, to test the capability of seismic interferometry to image ore deposits in the crystalline rock environment. Underground mining activities create the main source of ambient noise in the area. Alongside the ambient noise survey, a larger three-dimensional active-source seismic survey was also acquired and used to evaluate the interferometry results. Power spectral density calculations show random ambient noise with a frequency range of 2 Hz-35 Hz. A beamforming analysis identified body waves arriving from the west-northwest ( pointing towards the mine) and surface waves propagating from the northeast. The calculated virtual shot gathers retrieved by cross-correlating ambient noise at all receivers were processed following both two-dimensional and three-dimensional approaches using a sequence similar to the one applied to the active-source three-dimensional data. The dip-moveout stacked section reveals 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. Dip-moveout stacked sections obtained with different cross-correlation time windows indicate that the strength and number of reflections generally increase with longer noise records. However, a few reflections at depth show reduced coherency with longer noise time windows. The passive seismic interferometry results over the Lalor mining area are encouraging, but image quality of the passive survey is lower than the acquired active three-dimensional survey at the area. Future ambient noise surveys with longer offsets, shorter receiver spacing, and wider azimuth distribution are needed in crystalline rock environment to address the potential of the method for mineral exploration.