Abstract：
Accessory minerals in granitic rocks are unlikely significant radionuclide contributions to groundwater due to their remarkable durability. However, accessory minerals incorporating U and Th may suffer structural damages due to the radioactivity and become highly susceptible to alteration. This study investigates geochemistry coupled with textural analysis of the U-Th bearing accessory minerals using a field emission scanning electron microscope and an electron probe micro-analyzer. Altered zircons with numerous open structures related to the radioactive decay show higher contents of U and Th and low analytical totals. Some thorites show high contents of U and non-formula elements due to the hydrothermal alteration in the metamicted thorite. The cerianite including U occurs as micro-veinlet in fracture with trace of Fe and Mn oxides, which indicates secondary phase formation from the decomposed accessory minerals in an oxidizing environment. Some accessory minerals with the high content of U and Th have been found in Mesozoic granite terrain in South Korea, where high concentration levels of radionuclide in groundwater were also reported. The leaching of U may be more likely when the accessory minerals are highly metamicted or altered as found in our samples. The altered zircon and thorite of the study area could be major carriers of radioelement in Mesozoic granitic aquifers where the occurrence of soluble U-minerals has not been reported.
摘要：
花岗岩岩石中的副矿物由于其显着的耐久性，不太可能对地下水产生重要的放射性核素贡献。然而,含有U和Th的辅助矿物可能由于放射性而遭受结构破坏，并变得非常容易改变。本研究使用场发射扫描电子显微镜和电子探针微分析仪对含U-Th的副矿物进行了地球化学和纹理分析。具有许多与放射性衰变有关的开放结构的锆石显示出更高的U和Th含量以及较低的分析总量。由于变质的thorite中的热液蚀变，一些thorite显示出大量的U和非配方元素。含U的铈铁矿作为微细脉出现在裂缝中，有痕量的铁和锰氧化物，这表明在氧化环境中从分解的辅助矿物形成第二相。在韩国中生代花岗岩地形中发现了一些U和Th含量高的副矿物，据报道，地下水中放射性核素的浓度也很高。当我们的样品中发现的辅助矿物被高度分解或改变时，U的浸出可能更有可能。研究区的改变的锆石和透辉石可能是中生代花岗岩含水层中放射性元素的主要载体，这些含水层尚未报道过可溶性铀矿物的存在。
