Zeolites in volcanic-igneous hydrothermal systems: a case study of Pauzhetka geothermal field (Kamchatka) and Oligocene Smrekovec volcanic complex (Slovenia) |
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Authors: | Polona Kralj Sergei Rychagov Peter Kralj |
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Institution: | (1) Geological Survey of Slovenia, Dimiceva 14, 1000 Ljubljana, Slovenia;(2) Institute of Volcanology and Seismology, Piip Blv 9, 63008 Petropavlovsk-Kamchatsky, Russia;(3) Gejzir Consulting, Turnerjeva 17, 1000 Ljubljana, Slovenia |
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Abstract: | Production from geothermal reservoirs in volcanic-igneous hydrothermal systems may be disturbed owing to the formation of
authigenic minerals that reduce primary porosity and infill fissure systems. Crystallization may be induced by natural processes
or human activity related to the reservoir exploitation. In volcanic and volcaniclastic rocks, zeolites and related authigenic
silicate minerals commonly develop. Two selected study sites—Pauzhetka geothermal field in Russia and Smrekovec volcanic complex
in Slovenia are characterized by extensive development of progressive stage medium- and low-temperature propylitization and
zeolitization with similar mineral assemblages that reduced original reservoir rock porosity and permeability. Retrograde
and overprinting reactions of argillitization commonly enhance porosity and permeability of rocks, but some other reactions,
like from prehnite to laumontite, from laumontite to heulandite, and from laumontite to analcime, encountered in the Smrekovec
volcanic complex reduced it appreciably. Retrograde reactions recognized in the study sites were not induced by the temperature
drop only, but were accompanied by the change in chemical composition of reacting fluids. Chemical composition of interstitial
waters produced from exploitation wells in the Pauzhetka geothermal field indicate that propylitic and zeolite facies alteration
is related to Na–Cl, slightly alkaline waters, while argillitization involved acidic thermal waters with more complex ion
composition. |
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