Volcanic Rocks-Discrimination and Hydraulic Parameters by Spectral Induced Polarisation (SIP)

The increasing application of spectral induced polarisation (SIP) in hydrogeophysics is accompanied by petrophysical studies investigating the possibilities to derive the hydraulic conductivity from recorded complex electrical resistivity spectra. <br>The presented study concentrates on the volcanic rocks of Styria and their spectral behaviour. The Styrian basin in the south-eastern part of Austria is characterised by volcanic activity during Miocene and Pliocene, which can be discriminated by their SiO2-contents. Since especially pyroclastic rocks show large variations in grain size and porosity, we expected significant differences of electrical behaviours in the low frequency range (0.001-1000 Hz). For the laboratory studies seven sites were sampled including mainly basaltic and tuffitic rocks. <br>Concluding the results three groups can be classified by their electrical properties. This demanded further laboratory investigations showing that samples with a single phase peak are characterized by one single dominant pore throat size diameter. In contrast samples with constant phase angles throughout the spectra show an almost even distribution of pore throat sizes. <br>As these correlations had been observed in earlier SIP studies on sandstones the existing models relating permeability, pore-throat size and porosity present the possibility to evaluate all relevant hydraulic parameters by SIP.<br>