Application of a new TEM data acquisition system based on a HTS SQUID magnetometer (SQUITEM) to metal exploration in Broken Hill area

Abstract

JOGMEC completed construction of the SQUITEM, a three-channel TEM data acquisition system based on the HTS SQUID magnetometer, in 2006. A HTS SQUID is a high-sensitivity magnetic sensor that has wide bandwidth, and offers high field sensitivity, even at low frequencies. The SQUID magnetometer offers advantages over an induction coil receiver in depth of investigation and detecting conductive targets especially in the presence of conductive overburden. The magnetic field resolution of the SQUITEM is 300 fT/vHz at 1 kHz as measured in the field. A Slew rate (6.8 mT/sec in maximum) is sufficient to respond to square-wave primary-field variation in metal exploration. Frequency bandwidth from DC to 100 kHz provides minimal distortion of the recorded signal. JOGMEC applied the SQUITEM to metal exploration at the White Roo Prospect in the Border Project, west of Broken Hill, a JOGMEC/Minotaur Joint Venture. The joint venture was targeting Broken Hill Type Pb-Zn-Ag mineralisation. Initial drilling had intersected pyrrhotite/chalcopyrite mineralization hosted within a mafic gneiss. A SQUITEM survey was conducted in October 2006 to investigate bedrock conductor highlighted by a conventional TEM survey. The SQUITEM data was superior to the conventional TEM system with respect to depth of investigation. The SQUITEM data profiles and inverted sections highlighted a conductive zone at depth that was not apparent in the conventional TEM data. Drilling of this bedrock conductor resulted in the intersection of pyrrhotite-chalcopyrite mineralisation.