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Ministry of Energy Mines and Responsible for Core Review

BCGS Geoscience Map 2017-4

Aeromagnetic survey of the Llewellyn area, NTS 104-M/9,10,15,16 and parts of 104-M/11,14, British Columbia

Also published as Geological Survey of Canada Open Files 8288 and 8291

O. Boulanger and F. Kiss

These maps were derived from data acquired during an aeromagnetic survey carried out by Goldak Airborne Surveys from March 10, 2017 to July 6, 2017. The nominal traverse and control line spacings were, respectively, 400 m and 2400 m, and the airplane flew at a nominal terrain clearance of 150 m. Traverse lines were oriented N45°E with orthogonal control lines. The flight path was recovered following postflight differential corrections to the raw Global Positioning System (GPS) data and inspection of ground images recorded by a vertically-mounted video camera. The survey was flown on a pre-determined flight surface to minimize differences in magnetic values at the intersections of control and traverse lines. These differences were computer-analysed to obtain a mutually levelled set of flight-line magnetic data. The levelled values were then interpolated to a 100 m grid. The International Geomagnetic Reference Field (IGRF) defined at the average GPS altitude of 1950 m for the current mid-survey date of 2017/06/08 was removed. Removal of the IGRF, representing the magnetic field of the Earth's core, produces a residual component related almost entirely to magnetizations within the Earth's crust.

The first vertical derivative of the magnetic field is the rate of change of the magnetic field in the vertical direction. Computation of the first vertical derivative removes long-wavelength features of the magnetic field and significantly improves the resolution of closely spaced and superposed anomalies. A property of first vertical derivative maps is the coincidence of the zero-value contour with vertical contacts at high magnetic latitudes (Hood, 1965).


For data along strike to the south, see BCGS Geoscience Map 2017-2


Data coverage extends from northwestern British Columbia into Yukon as Geological Survey of Canada Open File 8289 and Yukon Geological Survey Open File 2017-61. These publications are available for free download through GEOSCAN ( and from the Yukon Geological Survey (, P.O. Box 2703 (K-102), Whitehorse, Yukon Y1A 2C6. Telephone (867) 667-3201, email:

Corresponding digital profiles and gridded data and similar data for adjacent airborne geophysical surveys are available from Natural Resources Canada's Geoscience Data Repository for Geophysical Data at


The same products are also available, for a fee, from the Geophysical Data Centre, Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8. Telephone: (613) 947-3337, email:


Download readme (PDF, 0.8 MB)


Download sheet 1 residual total magnetic field (PDF, 17.3 MB)


Download sheet 2 first vertical derivative (PDF, 19.4 MB)


Download GDB (Zip, 731 MB)


Download GRD (Zip, 18.3 MB)


Download GEOTIFFS (Zip, 13.6 MB)



For further information:

email BCGS Mailbox

call toll free (British Columbia residents only)