Journal of Radioanalytical and Nuclear Chemistry

, Volume 298, Issue 3, pp 1567–1585 | Cite as

Leaching of uranyl–silica complexes from the host metapelite rock favoring high radon activity of subsoil air: case of Castañar cave (Spain)

  • J. Garcia-Guinea
  • A. Fernandez-Cortes
  • M. Alvarez-Gallego
  • E. Garcia-Antón
  • M. Casas-Ruiz
  • D. Blázquez-Pérez
  • O. Teijón
  • S. Cuezva
  • V. Correcher
  • S. Sanchez-Moral


Castañar cave is a subterranean site with an outstanding natural environmental radioactivity. The maintaining of high radon activity of cave air and the detection of spatially anomalies of this gas in some cave emplacements, suggests that some natural geochemical processes are involved on the mobilization of radioactivity sources to cave environment, other than a simple exhalation of radon from the host-rock. The host rocks are interlaid dolostone–metapelite beds with radioactive nuclides of the three actinium, thorium and uranium decay series. In situ measurements on the spatial distribution of radioactivity, uranyl group’s luminescence and radon gas concentrations inside cave were main focus of this work to model lixiviation and deposition mechanisms of radioactive elements from the host rock to the karstic system. In addition, collected micro-samples were also analyzed by a multi-approach suite of analytical techniques: inductively coupled plasma mass spectrometry, environmental scanning electron microscopy with an attached X-ray energy dispersive system and spectral cathodoluminescence detector, thermoluminescence, Raman spectroscopy, X-ray diffraction, differential-thermal and thermogravimetry analysis, Alpha-spectrometry and Gamma-spectrometry techniques. The host metapelitic beds contain Zr(Hf)–Th(U)–Ti–P–REE phases such as zircon, xenotime-(Y), monazite-(Ce, La) and poly-metallic mineralization veins of hydrothermal origin. Carbonated host beds and speleothems show frequently chemical elements leaked from the upper host rock masses. The weathering leakage processes are favored by the existence of pyrite and limonite in the dolostone masses. The cave exhibits under UV lamps abundant hydrous silica–uranyl coatings covering carbonated speleothems with radionuclides of 238U natural decay series. The long-lived radio-nuclides of the radium radioactive decay chain are responsible of the continuous regeneration of radon gas inside cave. The experimental work was focused to identify origin and remobilization processes of radio-nuclides and their latte settlement into the cave environment associated to mineral phases of speleothems and cave deposits.


Uranyl–silica Luminescence Radionuclide Uranium Radon Leaching Speleothem Cave 



This research was supported by the Spanish Ministry of Science and Innovation; project CGL2010-17108/BTE. M.A-G is supported by a MEC FPI-Predoctoral. A. F.-C. was funded by a postdoctoral fellowship the JAE-Doc Program (CSIC). S.C. benefits of a postdoctoral fellowship from the Spanish Ministry of Science and Innovation, research program Juan de la Cierva. We are sincerely grateful for all the help given by the cave guide Ana Blazquez and the cave managers from the Regional Government of Extremadura (Spain) for their valuable collaboration throughout the entire investigation.


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Copyright information

© Akadémiai Kiadó, Budapest, Hungary 2013

Authors and Affiliations

  • J. Garcia-Guinea
    • 1
  • A. Fernandez-Cortes
    • 1
  • M. Alvarez-Gallego
    • 1
  • E. Garcia-Antón
    • 1
  • M. Casas-Ruiz
    • 3
  • D. Blázquez-Pérez
    • 4
  • O. Teijón
    • 4
  • S. Cuezva
    • 1
    • 5
  • V. Correcher
    • 2
  • S. Sanchez-Moral
    • 1
  1. 1.Museo Nacional de Ciencias Naturales (MNCN-CSIC)MadridSpain
  2. 2.Department Dosimetría de RadiacionesCIEMATMadridSpain
  3. 3.Department Física AplicadaUniversidad de CádizPuerto RealSpain
  4. 4.Fabrica de Elementos CombustiblesENUSAJuzbadoSpain
  5. 5.Departmento Ciencias de la Tierra y del Medio Ambiente Unidad Asociada UA-CSICUniversidad de AlicanteSant Vicent del RaspeigSpain

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