ZTEM (Z‐Tipper Axis Electromagnetic) surveys were conducted over the Mt‐Milligan Test Block, belonging to Terrane Metals Corp. (Vancouver, BC) and situated in the Mackenzie region of central British‐Columbia, from October 15TH to 22ND, 2008. The ZTEM survey comprised airborne Tipper AFMAG (audio frequency electromagnetics) measurements, as well as aeromagnetics using a caesium magnetometer. The survey consisted of twenty five (25) approx. 8.0 km long, EW oriented flight lines, totaling 200 line‐km, that were obtained at nominal 250m line spacings over an approximately 6 x 8 km area. The area was chosen because it hosts the Mt Milligan copper‐gold porphyry deposit, containing a Measured and Indicated Mineral Resource of 590.8 Mt at 0.193% Cu and 0.352 g/t Au, totaling 2.52 billion lb copper and 6.70 million oz gold (Terrane Metals Corp. 2008), that is not yet in production, and also because area's geology is well known and available in the public domain ‐ making it an ideal case‐history example.
The Z‐axis tipper measurements of the vertical (Z) component were obtained using Geotech's patented ZTEM induction aircoil system, suspended at approximately 110m elevation above ground level. The vertical component data (Hz) were then ratioed to fixed horizontal field measurements (Hx‐Hy) obtained using identical reference coils, that were oriented in the in‐line (X) and cross‐line (Y) directions, in order to obtain the tipper functions Z/X and Z/Y. The In‐Phase and Quadrature components ZTEM field ratio data were obtained, using Fourier‐based, digital signal processing analyses, at 5 frequencies, between 30Hz and 360Hz. The magnetometer was a Geometrics proton‐precession model towed at 130m above ground level.