Compilation and Review of ⁸⁷Sr/⁸⁶Sr and Stable Isotopes from Groundwater, Calcite Fracture Fillings, Mineral, and Whole‐Rock Sampling at Äspö, Sweden

Abstract

Integrated isotopic and hydrochemical studies of groundwater at Äspö, Sweden, support mixing models involving deep saline water, low-solute infiltration, and Baltic Sea water. Carbon, oxygen, and strontium isotope analyses of calcite fracture fillings indicate that paleohydrologic conditions were different than those of today in terms of the isotopic composition of water flowing through fractures. Sr isotopes of whole-rock and mineral (plagioclase, microcline, biotite, and epidote) samples are used to assess the effects of water-rock interaction. Biotite is a major reactant in the early stages of water-rock interaction. Strontium isotope systematics of groundwater from deep in the Hard Rock Laboratory, and underground research facility, and from low conductivity zones revealed a first order mixing line defined by a high-chloride saline component with 66 mg/L Sr and an ancient sea water component with approximately 4.5 mg/L. Dilution with low salinity recharge has produced groundwater with variable Sr contents and 87Sr/86Sr values between 0.7186 and 0.7160. Differences between Äspö and Laxemar groundwater are shown by trends in Sr concentrations plotted against 87Sr/86Sr. The Äspö trend shows increasing 87Sr/86Sr values with increasing concentrations of Sr, whereas the Laxemar groundwater trend shows little variability in 87Sr/86Sr with increasing Sr concentrations. These trends are controlled by the differences in 87Sr/86Sr composition of the saline end members in the two areas.

Geochemical processes controlling the groundwater chemistry and fluoride contamination in the Yuncheng Basin, China—An area with complex hydrogeochemical conditions

“…The mechanisms by which evaporation increases the fluoride concentration may include the following: 1) Evaporation could directly remove water from shallow aquifers [ 74 ], [ 75 ], elevating the fluoride concentration in groundwater [ 16 ]. 2) Evaporation could increase ion concentrations, leading to the precipitation of some major minerals [ 33 ], [ 76 ], [ 77 ], e.g., calcite and dolomite, reducing the Ca concentration and favoring the dissolution of fluorite and the enrichment of fluoride in groundwater. Deep groundwater is not affected by evaporation due to the great burial depth; therefore, the appearance of three deep groundwater samples in subgroup D group is perhaps due to the leakage of shallow groundwater, irrigation return water and/or surface water that had been subjected to evaporation.…”

Origin of 87Sr enrichment in calcite cements in Jurassic limestones (Eastern Paris Basin, France)

“…When preserved, the chemical and isotopic compositions of authigenic carbonates provide information regarding the nature, origin, and timing of mineralizing fluid flows Beaudoin et al, 2020). Such information is required in the geological characterization of underground nuclear waste storage (Mazurek, 1999;Blyth et al, 2000;Sandström and Tullborg, 2009;Dublyansky and Spötl, 2010;de Haller et al, 2011;Drake et al, 2012;Wallin and Peterman, 2015;Drake et al, 2020). The geochemistry of calcite cements also helps to unravel tectonic evolution (André et al, 2010), and in certain cases, to date brittle deformation (Goodfellow et al, 2017;Pagel et al, 2018;Mazurek et al, 2018;Sutcliffe et al, 2020;Davis et al, 2020).…”