The 87Sr/86Sr ratio has been extensively used in groundwater studies for several reasons. While classified geochemically as a trace element, Sr is found in easily measurable quantities in a wide variety of rocks. It is soluble in aqueous solution as the +2 ion and is geochemically very similar to Ca, the latter a major alkaline-earth constituent of rocks. The half-life of 87Rb, which decays to 87Sr, is such that considerable variations exist in the present-day 87Sr/86Sr ratio in minerals. Finally, Sr isotopes are not measurably fractionated by geological processes, unlike the isotopes of the light elements. All these characteristics potentially make Sr a good tracer of the source rock(s) of the chemical constituents in water. The isotopic value provides an added insight to that achieved by analysing elemental abundances, and this is especially the case when there is precipitation of new mineral phases because this process changes the chemistry of the water, but not the isotopic composition.
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- Strontium Isotopes
Robert H. McNutt
- Springer US