Open AccessModification of streaming potential by precipitation of calcite in a sand–water system: laboratory measurements in the pH range from 4 to 12
Author(s) -
Guichet Xavier,
Jouniaux Laurence,
Catel Nicole
Publication year - 2006
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2006.02922.x
Subject(s) - calcite , electrokinetic phenomena , zeta potential , quartz , mineralogy , streaming current , geology , precipitation , saturation (graph theory) , mineral , permeability (electromagnetism) , hydrothermal circulation , chemistry , materials science , membrane , nanotechnology , biochemistry , physics , paleontology , mathematics , organic chemistry , combinatorics , seismology , meteorology , nanoparticle
SUMMARY Spontaneous potentials associated with volcanic activity are often interpreted by means of the electrokinetic potential, which is usually positive in the flow direction (i.e. Zeta potential of the rock is negative). The water–rock interactions in hydrothermal zones alter the primary minerals leading to the formation of secondary minerals. This work addresses the study of calcite precipitation in a sand composed of 98 per cent quartz and 2 per cent calcite using streaming potential measurements. The precipitation of calcite as a secondary mineral phase, inferred by high calcite saturation indices and by a fall in permeability, has a significant effect on the electrokinetic behaviour, leading to a significant reduction in the Zeta potential (in absolute value) and even a change in sign. The measured decrease in Zeta potential from −16 mV to −27 ± 4 mV takes place as the pH rises from 4 to 7, while it remains constant at −25 ± 1 mV as the pH increases from 8 to 10.5. For pH higher than 10.5, calcite precipitates and is expected to coat the quartz surface. The measured Zeta potential vary from −17 to +8 mV for pH ranging from 10.6 to 11.7 depending on the amount of precipitated calcite indicated by the decrease in permeability. The observed change in sign of the electrical surface potential rules out the usual qualitative interpretation of SP anomalies in order to determine fluid circulations, even at pH lower than 9 if calcite is widely present as a secondary mineral phase, since the electrical surface potential of calcite depends also on CO 2 partial pressure and [Ca 2+ ]. Therefore, SP anomalies as measured in hydrothermal field, without mineralogical analyses of hydrothermal deposits, and without geochemical fluid survey, should be interpreted with caution.