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Understanding the variation and correlation between physical properties of ore bodies of interest is vital for every exploration project. Therefore comprehensive petrophysical laboratory measurements on representative sample material from two dispersemineralized greisen bodies of the Southern Bohemian Batholith (Austria) and the Eastern Erzgebirge Vulcano-Plutonic Complex (Germany), respectively, are presented in this study. As many greisen bodies host mineral deposits of economic interest, the aim of the study was to identify petrophysical properties which are suitable for distinguishing greisen bodies from the surrounding rocks. The gathered physical information (density, porosity, velocity, magnetic susceptibility, gamma spectroscopy, electrical resistivity, spectral induced polarization (SIP)) indicates that a differentiation of mineralized greisen zones of interest from the surrounding rocks is only possible based on a combined investigation of several parameters. Elevated grain and bulk densities (mean: 3 2.75 g/cm and 2.67 g/cm , respectively) are indicative of the Erzgebirge low-porosity (mostly < 3%) mineralized greisen rocks in comparison to the lower densities of the surrounding Teplice rhyolite and albite granite. Bulk density, however, is critically influenced by porosity and is therefore not suitable to distinguish the Austrian greisen rocks from the surrounding two-mica granites, 3 despite the greisens' comparably high grain density (mean: 2.74 g/cm ). Their higher porosity (mean: 5.7%) also results in lower elastic wave velocities (mostly < 2900 m/s) and lower electrical resistivities (mostly < 2100 Ohmm) than the surrounding rocks. The electrical resistivities and elastic wave velocities of the German greisen samples are, in contrast, rather variable with no distinct level above or below the neighboring rocks. Magnetic susceptibility also delivers a good contrast between the greisens and their surrounding rocks as it is highly responsive to elevated mica contents or the presence of oxidic ore minerals. If quartz content predominates or oxidic ores are absent, however, there is no contrast in the magnetic susceptibility of the greisens and the surrounding rocks. With regard to natural gamma radiation, the greisens are characterized by generally low absolute readings as well as low U counts, while K and Th counts seem to be dependent on mica type. Results from SIP measurements suggest that especially phase information can be used to adequately differentiate greisen zones associated with Li-mineralization from country rocks in the Erzgebirge. In Austrian greisen rocks, however, the characteristics of the SIP spectra are less distinct. A crossplot of the real vs. the imaginary part of complex conductivity, however, is suitable for identification of rocks with high mica content. Based on these results a combined investigation of density, magnetic susceptibility, and spectral gamma seems to be most promising for identification of greisen bodies. und dem Auftreten von oxidischen Erzmineralen ko...

Pore space properties of sedimentary rocks are of fundamental importance with regard to reservoir evaluation and fluid flow modelling or special geotechnical applications such as stability considerations for reservoirs, dams, or embankments. Processes such as compaction due to pressure drawdown in weakly consolidated reservoirs, effects caused by stimulation of reservoirs with decreasing productivity, or the compaction of building ground can be effectively studied by verifying and monitoring changes in porosity. The close connections between electrical resistivity or conductivity and pore space geometry as well as a high sensitivity to even slight changes in pore space characterising parameters are well-established.Therefore, the results of complex electrical conductivity measurements in the frequency range from 0.05 Hz to 1 kHz on a set of heterogeneous shaly sand samples during increasing compaction are presented in this study. The major objective of these investigations was to quantify the porosity reduction in shaly sands during the step-wise compaction of the samples in a specially designed measurement cell. Overall, ten unconsolidated shaly sand samples with varying grain size distribution were analysed. In addition, selected shaly sandstone data are presented to enhance the observations made for the sand samples with regard to the potential influence of cementation as expressed by the cementation exponent.With increasing compaction, the measured complex conductivity data of the fully water-saturated samples show two co-occurring effects. On the one hand, the real part decreases due to the dominating effect of Archie's law. On the other hand, the imaginary part increases due to the increasing contribution of interface conductivity. This effect is due to an increase in the internal surface-area-to-porosity ratio. Cementation exponent and the considered porosity range seem to be controlling the magnitude of this effect. These observations may be explained by using a simple complex conductivity model that relates conductivity components to porosity, specific surface area, and cementation exponent. An interpretation algorithm is proposed that allows determining relative porosity variations based on a baseline and a single repeat measurement without prior knowledge of further rock characteristics.To demonstrate the applicability of the algorithm on field measurements, data from spectral induced polarization soundings obtained at a test site for compaction techniques were interpreted. It could be shown that these observations bear further potential for enhancing the prediction of porosity, changes of compaction, and, hence, changes in hydraulic permeability. determination of naturally or artificially induced porosity changes and accompanied changes in permeability or compaction in very heterogeneous sedimentary rocks.Electrical resistivity measurements are frequently used to predict hydraulic conductivity (e.g., Slater and Lesmes 2001) because the transport of charge carriers and mass in the pore space are couple...