International Journal of Earth Sciences

, Volume 103, Issue 8, pp 2273–2300

Hydrothermal alteration and zeolitization of the Fohberg phonolite, Kaiserstuhl Volcanic Complex, Germany

  • Tobias Björn Weisenberger
  • Simon Spürgin
  • Yann Lahaye
Original Paper

DOI: 10.1007/s00531-014-1046-1

Cite this article as:
Weisenberger, T.B., Spürgin, S. & Lahaye, Y. Int J Earth Sci (Geol Rundsch) (2014) 103: 2273. doi:10.1007/s00531-014-1046-1

Abstract

The subvolcanic Fohberg phonolite (Kaiserstuhl Volcanic Complex, Germany) is an economic zeolite deposit, formed by hydrothermal alteration of primary magmatic minerals. It is mined due to the high (>40 wt%) zeolite content, which accounts for the remarkable zeolitic physicochemical properties of the ground rock. New mineralogical and geochemical studies are carried out (a) to evaluate the manifestation of hydrothermal alteration, and (b) to constrain the physical and chemical properties of the fluids, which promoted hydrothermal replacement. The alkaline intrusion is characterized by the primary mineralogy: feldspathoid minerals, K-feldspar, aegirine–augite, wollastonite, and andradite. The rare-earth elements-phase götzenite is formed during the late-stage magmatic crystallization. Fluid-induced re-equilibration of feldspathoid minerals and wollastonite caused breakdown to a set of secondary phases. Feldspathoid minerals are totally replaced by various zeolite species, calcite, and barite. Wollastonite breakdown results in the formation of various zeolites, calcite, pectolite, sepiolite, and quartz. Zeolites are formed during subsolidus hydrothermal alteration (<150 °C) under alkaline conditions. A sequence of Ca–Na-dominated zeolite species (gonnardite, thomsonite, mesolite) is followed by natrolite. The sequence reflects an increase in \(\log [(a_{{{\text{Na}}^{ + } }} )/(a_{{{\text{H}}^{ + } }} )]\) and decrease in \(\log [(a_{{{\text{Ca}}^{2 + } }} )/(a_{{{\text{H}}^{ + } }}^{2} )]\) of the precipitating fluid. Low radiogenic 87Sr/86Sr values indicate a local origin of the elements necessary for secondary mineral formation from primary igneous phases. In addition, fractures cut the intrusive body, which contain zeolites, followed by calcite and a variety of other silicates, carbonates, and sulfates as younger generations. Stable isotope analysis of late-fracture calcite indicates very late circulation of meteoric fluids and mobilization of organic matter from surrounding sedimentary units.

Keywords

Zeolite Götzenite Pectolite Sepiolite Hydrothermal alteration Kaiserstuhl Volcanic Complex 

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Tobias Björn Weisenberger
    • 1
  • Simon Spürgin
    • 2
  • Yann Lahaye
    • 3
  1. 1.Department of GeosciencesUniversity of OuluOuluFinland
  2. 2.Hans G. Hauri MineralstoffwerkeBötzingenGermany
  3. 3.Geological Survey of FinlandEspooFinland

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