3D seismic reflection imaging of volcanic-hosted massive sulfidedeposits: Insights from reprocessing Halfmile Lake data, New Brunswick,Canada

摘要

Three-dimensional seismic reflection data from the HalfmileLake area,NewBrunswick, Canada, was reprocessed over an 18-km~2 grid to improve the seismic signatures of a 5-million-ton volcanic-hosted massive sulfide VHMS deposit located at 1200-mdepth, known as the deep zone, as well as key host-rock structures.We chose a prestack dip moveout DMO and poststackmigration processing sequence to preserve the possible diffractionsignature of the deep VHMS zone. Despite the high level ofsource-generated noise and large statics caused by near-surfaceconditions, our processing results revealed improved 3D seismicimages for shallow and deep structures. Many of the imagedstructures were easily correlated with known lithological contactsconstrained by boreholes and petrophysical measurements.Ashort, flat-lying segment of high-amplitude reflection at about800-m depth in the unmigrated cube was interpreted to originatefrom a small portion of the lower VHMS zone. The DMO stackwas characterized by a large, high-amplitude asymmetric diffractionsignature originating from the deep VHMS zone. Theasymmetry of the diffraction hyperbola relative to the location ofthe deep zone was interpreted as resulting from a shape effectfrom the zone, with the strongest amplitudes along the diffractionhyperbola found north-northwest of the apex. This indicated thatthe deep VHMS zone dips in a similar direction. This diagnosticdiffraction signature was not preserved with the prestack migrationapproach previously implemented for processing HalfmileLake data.