The geophysical signature of the Teutonic Bore Cu?Zn?Ag massive sulphide deposit, Western Australia

Abstract

The Teutonic Bore deposit contains about 1.4 Mt of 4.2% Cu, 16.4% Zn, and 203 g t?1 Ag in a massive sulphide lens approximately 400 m in strike length with a maximum thickness of about 30 m. The massive sulphides did outcrop and extend to a depth of 250 m. The ore is oxidized to 85 m. Although no geophysical surveys were completed before discovery, the open pit presented a unique opportunity to measure the physical properties of a massive sulphide and its environment. Magnetic susceptibility, density, IP effect and resistivity were measured on wall rocks in the pit, on drill core, and from the surface. Magnetic susceptibilities were generally low. The density contrast between the ore and host was about 1.1 but the small size of the deposit made the gravity response barely detectable in the geological noise. Limited surface IP effect measurements were made. While the IP effect contrast between the ore and host should be large, the constraints Imposed by electrode arrays and conductive overburden make this contrast difficult to detect. Of all of the physical properties measured the conductivity contrast is the largest and easiest to detect. Between ore and host the measured contrast is at least 10000:l. Of all of the electrical methods run over the deposit the TEM method SIROTEM produced the most diagnostic response from the ore body. Once a drill hole was available applied potential methods helped define the limits of the deposit. The other methods tried showed responses in the area of the ore body that ranged from non-existent to possible.