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

烧绿石已被建议作为安全固定高级别核废料（如武器级钚）的主相。对天然烧绿石族矿物蚀变的矿物学研究对于了解烧绿石陶瓷核废料形式在某些地质环境中的长期性能非常重要。在项目建议书中，我们建议结合详细的矿物学，地球化学和地质年代学调查复杂的蚀变烧绿石和伴生矿物（钾长石，霓石，白云母，锆石）从碱性伟晶岩从马拉维解开烧绿石的蚀变历史。利用SEM、EMP、TOFSIMS、显微拉曼光谱和TEM等手段研究了烧绿石蚀变过程中的结构演化和化学结构变化。为了确定伟晶岩的流体事件和冷却历史，将进行蚀变和原始烧绿石的LA-ICPMS和TIMS U-Pb年龄和霓石、白云母、长石的K-Ar年龄。对蚀变钾长石中的流体包裹体进行显微测温和拉曼光谱分析。通过将测年和流体包裹体结果联系起来，应该可以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).