Electrical properties of zeolitized volcaniclastic materials

Abstract

[1] The interpretation of electromagnetic anomalies associated with volcanic activity requires a good understanding of two rock properties, the electrical conductivity and the streaming potential coupling coefficient. We measured these properties on 22 consolidated tuff samples containing clays and zeolites typically found in hydrothermal systems or in other areas of high water-rock interactions associated with active volcanic areas. These rocks exhibit unusually high surface conductivity and electrical cementation exponent (2.5-3.3). These features are explained by the highly complex texture of these rocks due to hydration/dissolution processes of the volcanic glass and the formation of clay minerals and zeolites as alteration products. At a pore fluid conductivity of 1.0 ± 0.2 S m À1 , the streaming potential coupling coefficient ranges from À3.55 to À10.7 mV MPa À1 . The zeta potential (a key electrochemical property of the pore water/mineral interface) determined from these measurements at T 0 = 20°C and pH $6-7 and corrected for surface conductivity is $À28 ± 8 mV at 0.1 M NaCl. Two clay-free samples exhibit a zeta potential $À16 ± 5 mV, a value associated with zeolites (clinoptilolite). The temperature dependence of the z potential is rather strong with z(T ) = z(T 0 ) [1 + n z (T À T 0 )], where n z % 4.2 Â 10 À2 C À1 in the temperature range 20-60°C. These data are applied to the understanding of large-scale self-potential anomalies located at the ground surface of Miyake-Jima volcano.

Dependence of spectral‐induced polarization response of sandstone on temperature and its relevance to permeability estimation

“…For the calculation of h(T) we use the formulation given by Patek et al [26] The DC conductivity of rocks does not depend exclusively on ionic mobility, as the second term in equation (27) also contributes to s 0 . Various studies concerning the temperature dependence of shaly rocks report an increase in DC surface conductivity stronger than that of s f with increasing temperature [e.g., Waxman and Thomas, 1974;Sen and Goode, 1992;Revil et al, , 2002Rabaute et al, 2003]. As we assume b + d (T) ≈ b + f (T), this implies an increase of surface site density in the diffuse layer with increasing temperature (see equation (27)).…”

“…[6] The effect of temperature on DC conductivity is fairly well investigated [e.g., Waxman and Thomas, 1974;Johnston, 1987;Llera et al, 1990;Sen and Goode, 1992;Revil et al, , 2002Roberts, 2002;Hayley et al, 2007], but there are only a few published studies that deal with the temperature dependence of SIP response. Vinegar and Waxman [1984] measured the SIP response of a 'clean' and a shaly sandstone in the temperature range of 25°C to 90°C.…”

The volcano‐electric effect

“…For an unconfined aquifer, the electrical potential distribution associated with the contribution j 0 can be represented as a double layer of charge (electrical dipoles) lying on the piezometric surface [Fournier, 1989]. Revil et al [2002aRevil et al [ , 2002b demonstrate that this double layer is simply related to the volume density of current dipole moment (current polarization) resulting from groundwater flow associated with piezometric head variations.…”

“…The data are interpreted with the model developed by Revil et al [2002b]. The samples are crushed basalts (primarily composed of plagioclase, feldspar, and pyroxene), scoria (from Stromboli), and two crushed tuff samples.…”

“…The samples are crushed basalts (primarily composed of plagioclase, feldspar, and pyroxene), scoria (from Stromboli), and two crushed tuff samples. Sample Bu-96-8 is a clay-free zeolite-rich sample, whereas Bu-96-7 is a smectite-rich zeolite-rich sample (sample Bu-96-7: 61.0% clinoptilolite, 11% smectite, 18.5% feldspar, 7.6% quartz; sample Bu-96-8: 62.0% clinoptilolite, 8.5% feldspar, 14.9% quartz, and 9.4% plagioclase, determined from semiquantitative XRD analysis [see Revil et al, 2002b]). …”