Data from: Complex conductivity of graphitic schists and sandstones

Spectral Induced Polarization spectra were carried out on 3 graphitic
schists and 2 graphitic sandstones. The microstructural arrangement of
graphite of two graphitic schists was studied with thin sections using
transmitted and reflected light optical and electron microscopic methods.
Chemical maps of selected areas confirm the presence of carbon. The
complex conductivity spectra were measured in the frequency range 10 mHz
to 45 kHz and in the temperature range +20°C down to -15°C. The measured
spectra are fitted with a double Cole Cole complex conductivity model with
one component associated with the polarization of graphite and the second
component associated with the Maxwell Wagner polarization. The Cole Cole
exponent and the chargeability are observed to be almost independent of
temperature including in freezing conditions. The conductivity and
relaxation time are dependent on the temperature in a predictable way. As
long as the temperature decreases, the electrical conductivity decreases
and the relaxation time increases. A finite element model is able to
reproduce the observed results. In this model, we consider an intra-grain
polarization mechanism for the graphite and a change of the conductivity
of the background material modeled with an exponential freezing curve. One
of the core sample (a black schist), very rich in graphite, appears to be
characterized by a very high conductivity (approximately 30 S m-1). Two
induced polarization profiles are discussed in the area of Thorens. The
model is applied to the chargeability data to map the volumetric content
of graphite.