LA-ICP-MS analysis of trace and rare earth elements in carbonate fracture fillings from Granitoid Rocks (Sweden)

Abstract

Trace elements (TE) and rare earth elements (REE) commonly
coprecipitate in secondary carbonates and provide valuable
information about the fluid chemistry and system parameters at
the times of their formation. REE share similar chemical
properties with trivalent actinides and are therefore used as
analogues to estimate the retention potential of crystalline host
rock fractures.
Here we apply high-resolution 2D element analysis (µXRF
and LA-ICP-MS) to scan for the trace elements Na, Mn, Fe, Sr,
Y, La, Ce, Yb, Pb, Th and U coprecipitated in low-temperature
calcite fracture fillings originating from exploration drill cores
from the sites Simpevarp, Laxemar and Forsmark (Sweden) [1].
The generated element maps highlight microstructures and
growth zones within the fracture fillings. Conclusions on the
palaeohydrological evolution of the fracture network can be
drawn by them. Evidence of face dependent partitioning within
the same concentric growth zones shows that sector related
preferential coprecipitation of the measured trace elements
occurs in three clusters with major enrichment in Mn-Fe-Sr, YYb-U and Na-La-Ce-Pb-Th.
The calculation of the partition coefficient DTE is
based on the trace and rare earth element assemblage of the most
recent growth zone and associated formation waters. Compared
to experimentally generated coefficients [2] (and references
mentioned therein) and values derived from a 17-year
precipitation experiment carried out at the Äspö Hard Rock
Laboratory [3], DTE ratios of the light REE La and Ce are
relatively high, whereas for Sr and U DTE ratios are remarkably
low.
References
[1] Tullborg, Drake & Sandström (2008), Applied
Geochemistry 23, 1881-1897.
[2] Curti (1999), Applied Geochemistry 14, 433–445.
[3] Drake, Mathurin, Zack, Schäfer, Roberts, Whitehouse et al.
(2018), Environmental Science & Technology 52, 493–502.