Airborne TDEM by He-filled Balloon

Performing Time Domain Electromagnetic surveys in rugged terrain is a challenging task and as an alternative to mundanely laying out loops or using a helicopter system, a central loop configuration Time Domain EM system has been fitted to a 5m diameter He–filled balloon with a capacity to lift a ~48kg payload. The transmitter and receiver loops have a diameter of 10 and 5m, respectively. The balloon is handled by an operator and 3 assistants and measures while drifting above the topography. The TDEM electronics was custom built by Elta-Geo in Novosibirsk, Russia and records the soundings to a HP IPAQ handheld PC via BlueTooth communication. A maximum transmitter current input of up to 20 Amp is possible using a conventional half sine waveform.<br>One of the areas where the balloon was employed was the N’teisha gold occurrence in Yemen where the gold is situated in narrow shear zones, between 0.5 and 2m wide. Although the shear zones are possibly too narrow to be detected by the TDEM system an interesting conductivity anomaly was detected in the vicinity of the shear zones that still has to be further investigated.