Blakelock2The Horizontal Loop EM survey by HBED used a 100m separation. The rule of thumb for the depth of penetration for this system is generally half the Tx-Rx separation. Therefore, the depth of penetration would be about 50m. The depth of penetration for the GEOTEM EM system would average 400m, but could be deeper, depending on the conductance of the source.
Also, the HBED conductor is about 300m long (even though their grid was 800m long), while the GEOTEM airborne conductor is about 1000m long (eastern flank only). This would seem to suggest that the HBED conductor is near surface, and was easily picked up, while the ends of the conductor to the north, as well as to the south, were deeper (>50m) and therefore out of reach from the HLEM system.
One reasonable target would be near the apex of the Anticline, near the fault structure. This area also has chalcopyrite, which was intersected in TGS's DDH2. There were 5 sections of massive sulphides (py/po) in that hole that was intersected, which seems to convince me that the TGS DH 2 was drilled parallel, and along strike of the western flank conductor.