This map of the first vertical derivative of the total magnetic field was derived from data acquired during a helicopter-borne aeromagnetic survey carried out by Fugro Airborne Surveys during the period between February 4 to March 15, 2010. The data were recorded using split-beam cesium vapour magnetometers (sensitivity = 0.005 nT) rigidly mounted on each of the two Astar 350B aircraft (C-FGSC and C-GAVO). The nominal traverse and control line spacings were, respectively, 400 m and 2 400 m, and the aircraft flew at a nominal terrain clearance of 100 m. Traverse lines were oriented N30?E with orthogonal control lines. The flight path was recovered following post-flight 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.