The downhole EM response of the Hellyer ore deposit

Abstract

Following the discovery of the Hellyer base metal deposit in Tasmania, test drillhole electromagnetic (DHEM) surveys were conducted in order to determine their effectiveness and to compare several field systems. The DHEM profiles reflect both the variation in size of the ore body along strike and the approximately equidimensional cross-section of the ore zone. At the small southern end of the deposit, results from a drillhole illustrate that the surface transmitter loop has generated a rapidly decaying local eddy current system as well as a more slowly decaying current system in the main part of the conductor to the north. In the central part of the deposit, DHEM results show clearly that in a thick conductor, currents are not restricted to flowing in a particular orientation. Comparison of all the currently available impulse response DHEM systems shows that all are very effective exploration tools if the field work is conducted properly.