Отправлено: 11.06.19 10:27. Заголовок: The role of smectites in the electrical conductivity of active hydrothermal systems

L. Levy,´ 1,2,3 B. Gibert,4 F. Sigmundsson,2 O.G. Fl´ ovenz,´ 3 G.P. Hersir,3 P. Briole1 and
P.A. Pezard4

The role of smectites in the electrical conductivity of active hydrothermal systems: electrical properties of cores amples from Krafla volcano, Iceland

Geophys. J. Int. (2018) 215, 1558–1582 doi: 10.1093/gji/ggy34

S U M M A R Y
The underground circulation of hot water, of interest for geothermal energy production, is
often indirectly inferred from the presence of minerals formed by hydrothermal alteration at
different temperatures.

Clay minerals, such as smectite and chlorite, can be mapped from the surface using electrical soundings
and give information about the structure of the geothermal system.

Here, we investigate the specific role of smectite in the electrical response of igneous basaltic rocks
and evaluate what physical processes make smectite a better electrical conductor
than surrounding minerals. Laboratory measurements of cation exchange capacity (CEC),
mineralogy, porosity and electrical conductivity are presented for 88 core samples from four
boreholes at the Krafla volcano, Northeast Iceland.

CEC is found to be a reliable measure of the smectite weight fraction in these volcanic samples, through
a comparison with an independent quantification of the smectite content using Rietveld refinements of X-ray diffraction patterns.

The bulk electrical conductivity, measured at fluid conductivities in the range 0.02–11.7 S m− 1 ,
increases non-linearly with the fluid conductivity for samples with high smectite content.

This non-linear variation is fitted with a function and a model for a conduction process through
connected interlayer spaces within smectite. The process differs from electrical double layer
conduction, which involves only cations on the crystal edges of smectite, not in the interlayer
spaces. The laboratory results can help refine interpretations of electrical soundings in the
context of geothermal exploration