The Spectrem airborne electromagnetic system—Further developments

The Spectrem airborne electromagnetic (AEM) system has been in full production in Canada and Africa since 1989. The prototype, built by A‐cubed of Mississauga, Canada, was subject to two major upgrades by Anglo American Corp. staff to produce the Spectrem II instrument that located the Photo Lake and Konuto Lake orebodies in Manitoba, Canada. Subsequent work in tropical Africa has made it desirable to further increase the transmitter power and use greater available computer power in the aircraft to substantially improve the ability of the system to reject sferic noise, although there appears to be a limiting sferic level above which current filtering methods are ineffective. Although designed to detect massive sulfide bodies deep below conductive overburden, techniques have been developed to map the regolith—in particular, to compute resistivity‐depth sections using an approximate but fast method. A comparison is presented of such a section with the same section flown and processed using a frequency‐domain helicopter AEM system. The latest upgrade of the system, Spectrem 2000, with a 50% increase in transmitter power, was completed in October 1999 and is currently at work in northern Canada.