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TitleVertical seismic profiling using distributed acoustic sensing with scatter-enhanced fibre-optic cable at the Cu-Au New Afton porphyry deposit, British Columbia, Canada
AuthorBellefleur, G; Schetselaar, E; Wade, D; White, D; Enkin, R; Schmitt, D R
SourceGeophysical Prospecting 2019 p. 1-21, (Open Access)
Alt SeriesNatural Resources Canada, Contribution Series 20180255
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®); html
ProvinceBritish Columbia
NTS92I/09; 92I/10
Lat/Long WENS-120.5500 -120.4833 50.6833 50.6333
Subjectseconomic geology; geophysics; Science and Technology; mineral deposits; porphyry deposits; porphyry copper; copper; gold; geophysical surveys; seismic surveys, ground; seismic reflection surveys; seismic profiles; seismic waves; s waves; p waves; seismic velocities; acoustic surveys; boreholes; geophysical logging; caliper logging; bedrock geology; lithology; igneous rocks; volcanic rocks; basalts; picrites; intrusive rocks; monzonites; diorites; latites; structural features; fault zones; faults; mineralization; ore mineral genesis; alteration; structural controls; in-field instrumentation; densities; New Afton Porphyry Deposit; vertical seismic profiles; geological mapping techniques; wireline logs; fibre optics; distributed acoustic sensing; acoustic impedance; data processing; depth imaging; cave-ins; tomography
Illustrationslocation maps; lithologic sections; profiles; geophysical logs; schematic diagrams; geophysical profiles; seismic profiles; spectra; graphs; geophysical images; tables
ProgramTargeted Geoscience Initiative (TGI-5), Porphyry systems
Released2019 06 21
AbstractWireline logs and vertical seismic profile data were acquired in two boreholes intersecting the main mineralized zone at the Cu-Au New Afton porphyry deposit, Canada, with the objectives of imaging lithological contacts, fault zones that may have acted as conduits that channelled the mineralization, and alteration zones. Log data provide physical rock properties for the main lithologies and alteration zones. Calliper logs reveal many faults and caved-in zones generally indicating rocks with low integrity at the borehole wall. The preponderance of these zones, as indicated by the logs, suggests that their response may dominate the seismic-reflection wavefield. Outside fault zones, compressional and shear-wave velocities exhibit significant variability due to porosity, the heterogeneity of volcanic fragmental rocks and alteration. Distributed acoustic sensing was used to acquire vertical seismic profiling data in the two boreholes surveyed with wireline logs. Straight and helically wound fibre-optic cables housed standard fibres and a fibre engineered to increase the intensity of backscattering at the distributed acoustic sensing interrogator. Standard and engineered optical fibres placed in the two boreholes were daisy-chained together to form two 5-km-long continuous fibres that were interrogated at once with two interrogators. A new generation of interrogator connected to the engineered fibres provided field data with lower noise level and higher signal-to-noise ratio. These data with higher signal-to-noise ratio from straight fibre-optic cable were processed and used for depth imaging. Depth images benefitted from new migration weights that account for the directional sensitivity of the straight fibre-optic cable and limit the extent of migration artefacts. Migration results show several reflectors with shallow dips to the northwest, some explained by faults intersecting the surveyed boreholes. The main sub-vertical lithological and alteration contacts at New Afton generated downgoing reflections that were not considered in the migration.
Summary(Plain Language Summary, not published)
Geophysical logs and seismic data were acquired in two boreholes intersecting the main mineralized zone and host rocks at the Cu-Au New Afton porphyry deposit, BC. A novel technology utilizing fibre-optic cables was used to record seismic data in boreholes. This survey at New Afton is one of the first applications of this technology for mineral exploration. Advantages includes cost-effectiveness and simpler logistics during field work. Results reveal several fault zones, some possibly associated with the conduits that channeled mineralized fluids that led to the formation of this porphyry deposit.