James Beresford Lee

Airborne TEM surveying with a SQUID magnetometer sensor

Traditionally airborne time-domain electromagnetic (AEM) survey systems use induction coils as the sensor (receiver). We have replaced the induction coil in a transient electromagnetic (TEM) system with a liquid-nitrogen cooled superconducting quantum interference device (SQUID) magnetometer sensor. Using this prototype system, we aimed to improve performance in detecting conductive mineralization, particularly where the conductive mineralization of interest is covered by a conductive regolith. We successfully demonstrated one- and three-component SQUID sensors in airborne TEM surveying, and achieved performance comparable to the induction-coil systems.Implementation of the SQUID system required development of devices capable of operating in magnetically unshielded environments with low noise, high slew rate, and wide bandwidth. Operation of the SQUID sensor in the highly dynamic environment of a towed bird was also necessary, and this implies a high dynamic range and high level of noise associated with t...

High resolution gravity surveys from a fixed wing aircraft

BHP has in operation two FALCON airborne gravity gradiometer (AGG) systems providing gravity surveys with sufficient sensitivity and resolution for mapping the gravity anomalies associated with mineral deposits. Their development was motivated by the need for greater selectivity in regional reconnaissance surveying. This is achieved through the addition of density information to magnetic susceptibility and electrical conductivity which are available from other airborne survey technologies. The capability of the FALCON AGG systems is demonstrated with three examples. The King George anomaly was identified as an isolated magnetic anomaly in government release regional magnetic survey data. A FALCON survey of 2500 line km over the anomaly was completed in 5 days and demonstrates a clearly defined gravity anomaly of 7 mGal coincident with the magnetic anomaly. This gravity information is sufficient to upgrade the significance of the magnetic anomaly as a potential iron-oxide-copper-gold (IOCG) target. The Middleback Ranges, South Australia are an iron ore province supplying the OneSteel steelworks at Whyalla. The survey area includes relief of 300 m and some sharp escarpments, requiring accurate topographic correction of the gravity data. The FALCON survey has been compared with the ground gravity data in both gravity and gravity gradient form.