Experimental hydrothermal alteration of crystalline and radiation-damaged pyrochlore

Thorsten Geisler (1) , Anne-Magali Seydoux-Guillaume (1, 2) , Philip Poeml (1) , Ute Golla-Schindler (1) , Jasper Berndt (1) , Richard Wirth (3) , Kilian Pollok (1) , Arne Janssen (1) , Andrew Putnis (1)

1 Institut für Mineralogie-Münster
2 LMTG - Laboratoire des Mécanismes et Transfert en Géologie
3 GFZ - German Research Centre for Geosciences - Helmholtz-Centre Potsdam

We have performed hydrothermal experiments with a crystalline microlite and a heavily self-irradiation-damaged (i.e., X-ray amorphous) betafite in a solution containing 1 mol/l HCl and 1 mol/l CaCl2 at 175 °C for 14 days. The well-crystalline microlite grains were partly (?5 10 ?m rim) replaced by a Ca and Na-poorer, defect pyrochlore phase with a larger unit-cell and a sharp chemical gradient at the interface (on a nm scale) to the unreacted core. The amorphous betafite grains (up to ?2 mm in diameter), on the other hand, were completely transformed into an intergrowth of different crystalline phases (polycrystalline anatase and rutile, a yet unidentified Nb Ta oxide, and a Y REE phase), showing complex non-equilibrium structures. Our experimental observations bear a remarkable resemblance to those made on natural samples. They indicate that the processes of the fluid pyrochlore interaction are influenced by self-irradiation structural damage and that thermodynamic equilibrium models can hardly be applied to adequately describe such systems.

Domaines: Minéralogie

Thorsten Geisler, Anne-Magali Seydoux-Guillaume, Philip Poeml, Ute Golla-Schindler, Jasper Berndt, et al.. Experimental hydrothermal alteration of crystalline and radiation-damaged pyrochlore. Journal of Nuclear Materials, 2005, 344 (1-3), pp.17-23. ⟨10.1016/j.jnucmat.2005.04.009⟩. ⟨hal-00607316⟩