花岗岩－伟晶岩接触带元素地球化学迁移──高放废物地质处置库安全评价的天然类比研究

我国苏州花岗岩－伟晶岩接触带岩石中，与高放废物内某些长寿命超铀铜系元素和裂变产物化学性质相似的微量元素、同位素迁移行为天然类比研究表明，伟晶岩脉中的Ｕ、Ｌｉ、Ｓｒ、Ｂｅ、Ｍｏ、Ｎｂ、Ｅｒ、Ｙ和２３４Ｕ、２３８Ｕ在该岩脉形成后约１３０Ｍａ期间，在水－岩反应作用下，仅向花岗岩中迁移１０－３０ｃｍ，而Ｔｈ、Ｐｂ、２０６Ｐｂ、２０７Ｐｂ、２０８Ｐｂ、８７Ｒｂ、８７Ｓｒ、８６Ｓｒ则未发生明显迁移。这一研究结果为我国拟在花岗岩中处置高放废物提供了长期安全评价的依据。

GEOCHEMICAL MIGRATION OF ELEMENTS ACROSS CONTACT ZONE BETWEEN GRANITE AND PEGMATITE. A NATURAL ANALOGUE STUDY OF SAFETY ASSESSMENT ON GEOLOGICAL DISPOSAL REPOSITORY OF HIGHLEVEL RADIOACTIVE WASTE

The distribution of radioelements and other trace elements has been examined across the contact zone between granite and pegmatite dike in Suzhou, as a natural analogue to near-field conditions for high-level radioactive waste disposal repository.Such investigation is the first time in China. The granite and pegmatite in Suzhou have Rb-Sr isotopic ages of 140.9-132.5Ma, and are significantly enriched in such elements as REE,U, Th, Mo and Pb. The pressure and temperature conditions of the contact zone are similar to those expected in the near-field environment of a high-level radioactive waste disposal repository. It is showed that chemical gradients between the granite and the pegmatite dike are pronounced, making possible the assessment of elemental and isotopic migration related to the intrusion of the dike into the granite. The results show that the migration of elements U, Li, Sr, Be,Mo, Nb, Er, Yb and Y and isotopes 234U, 238U are restricted to within 30cm of the contact zone in the time gap of abount 130Ma. There is no evidence of redistribution of Pb, Th, 206Pb, 207Pb, 208Pb, 87Sr, 86Sr. The results also indicate that elemental migration is attributed to pore diffusion of groundwater, rather than to fracturewater flowing.