The approach for reconstructing palaeo-fluid flow is based on the investigation of mineralised structures by 1) thin-section petrography to identify the inventory of different types of minerali­sation, different mineral growth generations and paragenetic sequences and 2) using a set of selected isotope tracers (δ ¹⁸O, δ¹³C, δ³⁴S^SO4, δ¹⁸O^SO4, ⁸⁷Sr/⁸⁶Sr) and clumped isotope thermometry (Meckler et al. 2014, Müller et al. 2017) of secondary minerals. Thus, knowing the δ¹⁸O value of the mineral and the temperature of precipitation allows the calculation of δ¹⁸O of the mineral-forming fluid. These results are then combined with information on the timing of mineral precipitation obtained from U-Pb and U-Th geochronology for reconstructing their evolution with time. The respective analytical protocols and methods are described by Dold & Spangenberg (2005), Waber (2020) and Looser (2022).

Challenges related to reconstructing palaeo-fluid flow in sedimentary sequences relate to the different behaviour of solutes/isotopes while interacting with the rock. In the case of carbon and strontium, the rock is the dominant reservoir and thus generally buffers the isotope composition of the fluid. This means that external fluid signals will be obliterated during migration, especially when fluid/rock ratios and fluid fluxes are low. In contrast, the oxygen isotope system is more robust to rock buffering as the water constitutes a very large reservoir for oxygen. Apart from concentration differences between rock and fluid, concentration differences between different fluids also have to be considered. For example, an infiltrating meteoric water with low strontium concentrations has a limited potential to change the Sr isotope signal of a local marine porewater showing high strontium concentrations (i.e. lever rule).

Ultimately, it has to be noted that geochemical data do not provide direct information on the transport mechanisms. These have to be deduced in the context of the regional hydrogeological evolution and be verified by transport simulations. Thus, for the remainder of this section, the term "migration" is used for solute movement in the underground by either advection or diffusion.