Non-destructive characterization of variously colored gypsum and aragonite/calcite speleothems from the Cigalère Cave (Ariège, France)

Authors

Martin Vlieghe, Department of Geology, University of Namur, BelgiumFollow
Johan Wouters, Department of Chemistry, University of Namur, BelgiumFollow
Gérald Fanuel, Association de Recherche Souterraine du Haut Lez, BelgiumFollow
Jean-François Drion du Chapois, Association de Recherche Souterraine du Haut Lez, BelgiumFollow
Anne Gallez, Association de Recherche Souterraine du Haut Lez, BelgiumFollow
Stéphane Pire-Stevenne, Groupe de Recherches et Photographie en SpéléologieFollow
Gaëtan Rochez, Department of Geology, University of Namur, BelgiumFollow
Johan Yans, Department of Geology, University of Namur, BelgiumFollow

Highlights

• Portable X-ray fluorescence allows non-destructive elemental analysis in the field
• Designated calibration greatly increases accuracy and reproducibility
• Detection of Fe, Mn, Zn, Pb, and Cu, responsible for the various colorations
• Metals and sulphate ions likely originate from the overlying Pb-Zn sulfide ores

Abstract

The Cigalère Cave is a 21 km-long karstic cave located in the Ariège Department, in the French Pyrenees, and underlies directly the Bentaillou Pb-Zn-Fe sulfide ores. The cave hosts abundant gypsum mineralizations, some of them exhibiting various colorations including blue, yellow, purple, orange and black. Due to strict preservation policies, these colored mineralizations have not been studied much. Here we propose a non-destructive characterization of five distinct gypsum or carbonate speleothem structures from the Cigalère, exhibiting different colorations. To comply with the preservation policies, no sample was taken from the cave, and all speleothems were analyzed in situ using portable X-Ray fluorescence spectrometry (pXRF), with two custom-made calibrations respectively adapted to carbonate and sulfate speleothems. The “Cascade Noire” is suggested to be colored black and orange by coatings composed respectively of hematite/goethite and jarosite. The “Chapelle de Donnea” speleothems are likely colored black by different Mn oxides (likely birnessite) covered by a thin gypsum or calcite layer. The cores of gypsum speleothems are colored blue by Cu²⁺ substitution, which may be influenced by the presence of blue Zn-bearing phases. Yellow carbonate speleothems from the “Gino affluent” may be colored by the presence of humic substances, which could not be detected by pXRF. Field observations and comparison of the speleothems’ composition with ores from the overlying Bentaillou mine suggest that all the metallic elements and sulfate ions originate from the weathering of sulfide ores by groundwater and subsequent transportation through joints and fractures. This work also show the capabilities and limitations of pXRF analysis and its potential application in other preserved caves.

DOI

https://doi.org/10.5038/1827-806X.ijs2564

Creative Commons License

This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 4.0 License.

Recommended Citation

Vlieghe, M., Wouters, J., Fanuel, G., Drion du Chapois, J.-F., Gallez, A., Pire-Stevenne S., Rochez, G., Yans, J., 2026. Non-destructive characterization of variously colored gypsum and aragonite/calcite speleothems from the Cigalère Cave (Ariège, France). International Journal of Speleology, 55(1), ijs2564. https://doi.org/10.5038/1827-806X.ijs2564