An isotope ratio mid-infrared laser spectrometer (Delta Ray, Thermo Scientific, Bremen, Germany) for measurement of CO2 concentrations and its stable isotope ratios of 13C/12C as well as 18O/16O was placed in a salt mine at a depth of approximately 600 m below ground. A location, where diffusive contributions of mantle CO2 were suspected and historically evident, was chosen for long-term measurements over several weeks from September, 24 to October, 26 of 2019.