Overview of potential isotopic techniques for dating groundwaters in crystalline rocks

摘要

The rate of groundwater flow through a particular rock formation is a major factor in determining whether it may be an acceptable geologic medium for the disposal of high-level nuclear fuel waste. This report reviews isotopic techniques that could be potentially useful for the dating of groundwaters in crystalline rocks of the Canadian Precambrian Shield and presents and discusses results that have been reported in the literature. Carbon-14 dating is the most widely used technique for dating groundwaters up to about 50,000 years old, but the method requires that the measured carbon-14 activity be corrected for subsurface contributions of 'dead' carbon to the dissolved inorganic carbon. Thus, the geochemical evolution of the groundwater flow system must be well understood. Moreover, there are practical limitations on applying this technique to deep, saline groundwaters because of their very low alkalinity concentrations. Nevertheless, existing isotopic data suggest that groundwaters at depths of 500 m or greater are generally at least 10,000 years old. Refinement of the krypton-81 technique offers the most promise in the future for being able to date deep saline groundwaters and brines that are present at depths of 1000 m or greater. (author) 92 refs., 1 tab., 3 figs. (Atomindex citation 27:055890)