Precipitation sequence of fracture-filling calcite in fractured granite and changes in the fractionation process of rare earth elements and yttrium

Mizuno, Takashi; Milodowski, Antoni E.; Iwatsuki, Teruki

doi:10.1016/j.chemgeo.2022.120880

Cited by 7 publications

(1 citation statement)

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“…Trace element (TE) incorporation in carbonate fracture fillings is highly sensitive to changes of the precipitation environment, e.g., pH value, oxidation state, TE speciation, temperature, salinity, precipitation rate, pressure and characteristics of the precipitation solution, e.g., aqueous TE/ Ca ratio, adsorption-desorption equilibrium of TE at the crystal surface and microbial activity (Lorens 1981;Zhong and Mucci 1989;Rouff et al 2005;Tang et al 2008;Day and Henderson 2013;Füger et al 2019;Smrzka et al 2019). Hence, the study of the spatial trace element distribution within the fracture filling minerals can help to reconstruct the paleo-hydrogeological evolution of the site (Tullborg et al 2008;Milodowski et al 2018;Mizuno et al 2022). In the context of SNF storage, these findings allow us to estimate the potential TE retention under prospective hydrogeologic and climatic changes.…”

Section: Introductionmentioning

confidence: 99%

LA-ICP-MS analysis of trace and rare-earth element distribution in calcite fracture fillings from Forsmark, Simpevarp and Laxemar (Sweden)

et al. 2022

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Concentrations and spatial distribution of trace elements in secondary minerals provide valuable information about mobility controlling processes in natural fractures. Important examples include rare-earth element contents that act as analogues for the retention of trivalent actinides such as Am/Cm or Pu(III). The secondary phases (carbonates) investigated in this study originate from exploration drilling bore cores of the Swedish Nuclear Fuel and Waste Management Company SKB (Forsmark, Simpevarp and Laxemar, Sweden).Here, high-resolution element analysis (Micro-X-ray Fluorescence-Spectrometry (µXRF) and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)) is applied to scan for Na and the trace elements Mn, Fe, Sr, Pb, Th and U as well as the rare-earth elements Y, La, Ce and Yb associated with carbonate fracture fillings. High resolution element maps highlight growth zones and microstructures within the samples, which are not detected by the usual point and line measurements. Evidence of phase-dependent partitioning is observed.The partition coefficients, D, determined from formation water and carbonate data were compared to experimentally generated coefficients and values derived from a 17-year precipitation experiment carried out at the Äspö Hard Rock Laboratory (HRL).Distribution coefficients of the light rare-earth elements La and Ce have been found to be relatively high in the studied samples, whereas the coefficients of distribution of Sr and U are remarkably low.Overall, the results of this work show that the secondary calcite formed in deep granitic fractures coprecipitated periodically with significant amounts of radionuclide analogues (i.e., rare-earth elements).

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