锆石自辐射损伤对晶格破坏与元素运移的影响

Effect of Zircon Self-radiation Damage on Lattice Destruction and Elements Migration

锆石富U和Th并具有极高稳定性,通常用于地质测年。岩浆锆石晶体具有典型的振荡环带结构,其核部的振荡环带常受到局部改造而形成杂乱不规则的区域,此类锆石的结构可分为外部振荡环带区域和核部孔隙区域。由放射性元素衰变所产生的自身辐射损伤会导致锆石的晶格破坏(锆石蜕晶化),从而使振荡环带区域形成小型指状交互断裂结构,这为元素交换提供了“运移通道”。本文结合锆石的微观结构,探讨自辐射损伤对锆石内部元素运移的影响,以及砂岩型铀矿中铀源与铀的迁移。砂岩型铀矿床中的锆石晶体在表生含铀氧化流体和铀矿物辐射双重作用下,使U迁入导致锆石U含量增加;另一方面,造山带中的锆石蜕晶化作用释放出的铀,运移至沉积盆地可为砂岩型铀矿提供微弱“铀源”。

Zircon is rich in U and Th with high stability,which are usually used for geological dating.Magmatic zircons crystals commonly have typical oscillatory zoned structure.The oscillatory zones in the core of zircon crysals are often partially modified to form disordered and irregular regions.Therefore,the structure of this kind of zircon can be divided into external“oscillatory zone”and the internal“pore zone”.The self-radiation damage caused by the decay of radioactive elements leads to the lattice damage of zircon(zircon metamictization),thus finger-like interactive fracture structures form in the oscillatory zones,which provides a“migration channel”for elements exchange.Based on the microstructure of zircon,this paper discusses the influence of self-radiation damage on the elements migration in zircon,the migration of uranium as well as uranium source in sandstone-type uranium deposits.It is considered that under the double effects of supergene uranium-containing oxidation fluids and uranium mineral radiation,uranium migrates and the uranium content of zircon increases in sandstone-type uranium deposit.On the other hand,uranium released by zircon metamictization in the orogenic belt can provide a weak uranium sources for sandstone-type uranium deposit.