3D seismic imaging of the Lalor volcanogenic massive sulphide deposit, Manitoba, Canada

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A three-component three-dimensional seismic data set was acquired over the Lalor volcanogenic massive sulphide deposit near Snow Lake, Manitoba, Canada, to assess the reflectivity of the ore and further validate the potential of three-dimensional reflection seismic methods for deep mineral exploration. The Lalor deposit was chosen as a test site as it provided an intact, well-characterized 25-Mt-deep ore deposit with a rich catalogue of geological and geophysical data, as well as extensive drill-core and drill-hole geophysical and geological logs. An analysis of physical rock properties from borehole logging data indicates that massive sulphides associated with the zinc-rich zones could produce prominent reflections, whereas acoustic impedances of zones with disseminated gold do not sufficiently differ from the impedances of the host rocks to produce reflections. The interpretation of the seismic data is constrained with a detailed three-dimensional lithofacies model constructed from the categorical kriging of 15 lithological units identified in borehole intersections. Processing of the seismic data included prestack dip-moveout and poststack time migration. Final images reveal some strong reflections associated with the zinc-rich massive sulphide zones. The most prominent reflection results from the constructive interference of thin and closely spaced massive sulphide zones and felsic–mafic volcanic rock contacts above and below the mineralization. Contacts between felsic and mafic volcanic rocks, including those that were hydrothermally altered and subsequently metamorphosed, produced prominent and continuous reflections that are used to map the main architecture of the footwall rocks. At depth, a series of continuous and conformable reflections indicate the general geometry of the volcanic sequences in the area of the three-dimensional seismic survey.

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