Three‐Dimensional Electrical Conductivity and Induced Polarization Tomography of a Rock Glacier

Abstract

Three‐dimensional electrical resistivity and induced polarization data were collected on an unstable Alpine rock glacier in Val Thorens (Vanoise massif, France). In addition to these field data, we also performed induced polarization measurements during freeze and thaw using a soil sample and the poorly mineralized water, both from this site. In the tomograms, the electrical conductivity and the normalized chargeability show very distinctly the presence of the rock ice mixture. The chargeability itself is however quite constant over the entire investigated area with the exception of a small area associated with the presence of carboniferous rocks rich in graphite. The background chargeability is close to the dimensionless number R = 8 × 10−2, which is consistent with the prediction of the dynamic Stern layer model for the polarization of porous media. The theory implies that this dimensionless number R is independent on saturation and temperature in agreement with field observations. A main implication of this observation is that the classical Archie's law cannot be applied to describe the electrical conductivity in this type of environments with poorly mineralized pore water. Surface conductivity dominates the measured conductivity of the materials implying in turn that the electrical conductivity is related to both the water content and cation exchange capacity of the material. We propose new equations for both the electric conductivity and the normalized chargeability in this type of environments.

Complex Conductivity of Graphitic Schists and Sandstones

“…Above the value of M = R = 0.08 (highest value reached for nonmetallic rocks), the data can only be explained by the presence of graphite. In absence of graphite, we observe that the chargeability (i.e., the ratio between the normalized chargeability and the conductivity) is close to R indicating the strong role of surface (double layer) conductivity on the overall conductivity response as discussed in Duvillard et al (). The background is characterized by a chargeability of 0.03.…”

“…Below freezing conditions, the water content of the liquid water is changing with the temperature according to a freezing curve. Duvillard et al () and Coperey et al () used an exponential freezing curve for the volumetric water content θ ( T ) written as which has the advantage to only require three parameters, T F (the liquidus or freezing point), T C (a characteristic temperature), and θ r (the residual water content).…”

Electrical Conductivity Versus Temperature in Freezing Conditions: A Field Experiment Using a Basket Geothermal Heat Exchanger

“…Below the freezing temperature, we need to consider the change in the liquid water content θ (dimensionless) with temperature T and the segregation of the salt in the liquid pore water. The following freezing curve can be used to describe the dependence between θ and T (in °C) (see Duvillard et al, ): where T F (in °C) denotes the freezing temperature, T C (in °C) denotes a characteristic temperature associated to the pore size distribution, θ r denotes the residual liquid water content at low temperatures, and ϕ (dimensionless) denotes the (connected) porosity. The soil freezing curve can be related to the characteristics of the pore size distribution like the capillary pressure curve (Spans & Baker, ).…”

“…Electrical conductivity tomography has been recently used to image permafrost in the shallow subsurface (e.g., Scott et al, 1990;Kneisel, 2006;Magnin et al, 2015). This has prompted the recent development of an improved physics-based petrophysical model, beyond the classical Archie's law, to connect electrical conductivity to temperature (e.g., Coperey et al, 2019;Duvillard et al, 2018). Such model needs to be further tested.…”

Investigating the applicability of induced polarization method in ore modelling and drilling optimization: a case study from Abassabad, Iran

“…IP and ER methods are among the most applicable geophysical methods used in subsurface studies notably for selection of the best drilling points for exploration purposes (Bishop and Emerson 1999;Wynn and Grosz 2000;Ferdows and Ramazi 2015b;Hope and Andersson 2016). Some examples of their increased usage include copper exploration using 3D IP modelling in NSW, Australia (Whaite et al 2001), using combination of ER and IP in polymetal deposit in China (Yang, Liu and Wang 2008), gold exploration at the eastern desert of Egypt by IP measurement (Taha et al 2018), combination of ER, IP and microgravity to detect buried caves in Spain (Martínez-Moreno et al 2013), copper exploration using IP and ER in Iran (Ramazi and Jalali 2014), gold-silver deposit exploration by IP method in Russia (Gurin et al 2015), detection of the uranium mineralization zone in India (Biswas and Sharma 2016), integration of geophysical methods including IP and ER methods for massive sulphide exploration in Sweden (Tavakoli et al 2016), bitumen mineralization exploration in the west of Iran (Mashhadi, Mostafaei and Ramazi 2017), gold deposit exploration by 3D-induced polarization modelling in Indonesia (Halim et al 2017), 3D tomography of induced polarization and its application in polymetallic mine (Jun-Lu et al 2017), copper mineral exploration using 3D model of IP and resistivity in Brazil (Morriera et al 2018), investigation of a rock glacier by 3D tomography of IP and ER in France (Duvillard et al 2018) and urban area investigation by 3D IP and ER in Stockholm (Pazzi et al 2018;Rossi et al 2017Rossi et al , 2018.…”