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

有人建议将焦绿石作为安全固定高水平核废料（如武器级钚）的宿主相。对天然焦绿石群矿物的蚀变进行矿物学研究对于了解焦绿石陶瓷核废料形式在某些地质环境中的长期性能具有重要意义。在项目建议书中，我们建议综合对马拉维碱伟晶岩中复杂蚀变的焦绿石及其伴生矿物（钾长石、绿石、白云母和锆石）进行详细的矿物学、地球化学和年代学调查，以揭示该焦绿石的蚀变历史。利用SEM、EMP、TOFSIMS、微拉曼光谱和TEM等研究了焦绿石蚀变过程中的结构演变和化学结构变化。为了确定流体事件的年代并确定伟晶岩的冷却历史，将利用LA-ICPMS和TIMS对蚀变和原始焦绿石进行U-Pb测年，并对绿石、白云母和长石进行K-Ar测年。在蚀变钾长石中发现的流体包裹体将通过显微测温和拉曼光谱进行分析。通过将测年和流体包裹体结果联系起来，应该有可能重建蚀变事件期间普遍存在的p - t - x条件。

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).