Petrophysical Characterization of the Rabenwald Talc Deposit

This study presents a petrophysical characterization of the Talc-schist deposit Rabenwald in Eastern Styria, with the aim to evaluate the potential of geophysical exploration methods to distinguish the host rock from the talc deposit. For this purpose drill core samples, hand specimens as well as water samples were collected at the mine site and areas targeted for future exploration Laboratory measurements were conducted to determine the following petrophysical properties: density, porosity, magnetic susceptibility, dry and saturated ultrasonic P- and S-wave velocities as well as electrical resistivities. The measured petrophysical properties show that Talc-schist can be partially distinguished from the host rock lithologies. The highest contrasts was observed for unsaturated resistivity and density. Contrary to other talc deposits the magnetic susceptibility of the Talc-schist was found to be three to four orders of magnitudes lower than reported for other deposits with little difference to the host rock. This likely reflects the genetic history of the deposit, associated with syn-metamorphic hydrothermal alteration. Seismic velocities display significant variation and are likely of limited use in lithological differentiation in the field. The velocities in-situ are more likely to be controlled by fractures than by lithology. The same is most likely true for resistivity measurements if the deposit is fully water saturated. This is supported by laboratory results. Even though, the measured porosities are relatively small at the sample scale, the measured sample resistivities show a strong dependence on saturation and fluid conductivity.