The Electrical Properties of the Scuddles VHMS Deposit

Abstract

In-situ and laboratory measurements were used to characterise the electrical properties of the Scuddles VHMS deposit, Western Australia. A major emphasis of this investigation was to study the scale variation of electrical properties. Massive pyrite and pyrite-chalcopyrite ores were highly conductive and the underlying intense stringer mineralisation only slightly less conductive. Some sphalerite-rich ore zones were moderately resistive as expected but others with similar grade and mineralogy were highly conductive. Laboratory current mapping and connectivity measurements, together with petrographic investigation indicate that the high conductivity Zn-rich ores at Scuddles owe their unusual properties to very small amounts of well-connected pyrrhotite. At all measurement sites, irrespective of mineralogy, there was a clear trend of decreasing resistivity with increasing electrode spacing. At some sites resistivity variations of more than three orders of magnitude were apparent between small and large-scale measurements. Laboratory samples from most sites also display clear bimodal resistivity distributions. The most conductive laboratory samples have properties similar to in-situ measurements at large electrode spacings while the resistive end members have properties consistent with small-scale in-situ measurements. The connectivity of the conductive phases clearly increases with increasing measurement scale. In-situ and laboratory measurements at Scuddles demonstrate the difficulty of using traditional statistical approaches to estimate bulk electrical petrophysical properties from laboratory scale measurements.