Hydrothermal alteration of pyrochlore and associated minerals of an alkali pegmatite from Zomba-Malosa (Malawi): A record f pyrochlore-fluid re-equilibration

• Applicant: Professor Dr. Thorsten Geisler-Wierwille
• Subject Area: Mineralogy, Petrology and Geochemistry
• Term: from 2007 to 2010
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 43577395

Pyrochlore has been suggested as a host phase for the safe immobilisation of high-level nuclear waste such as weapons-grade plutonium. Mineralogical studies on the alteration of natural pyrochlore-group minerals are important to gain an understanding of the long-term performance of a pyrochlore ceramic nuclear waste form in certain geological environments. In the project proposal we suggest integrating detailed mineralogical, geochemical, and geochronological investigations on complexly altered pyrochlore and associated minerals (potassium feldspar, aegirine, muscovite, and zircon) from an alkali pegmatite from Malawi to unravel the alteration history of the pyrochlore. The textural evolution and the chemical and structural changes during pyrochlore alteration will be investigated by SEM, EMP, TOFSIMS, micro-Raman spectroscopy, and TEM. To date the fluid events and to determine the cooling history of the pegmatite, U-Pb dating of altered and pristine pyrochlore by LA-ICPMS and TIMS, and K-Ar dating of aegirine, muscovite, feldspar will be carried out. Fluid inclusions found in altered potassium feldspar will be analysed by microthermometry and Raman spectroscopy. By linking the dating and fluid inclusion results, it should be possible to reconstruct the P-T-Xconditions that prevailed during the alteration event(s).

• DFG Programme: Research Grants
• Participating Person: Professor Dr. Andrew Putnis