A new study published online in advance of coming out in the July-August GSA Bulletin that examined the groundwater system in the southern Colorado Plateau-Arizona Transition Zone region found that "groundwaters are a complex mixture of 'upper world' waters derived from rain and snowmelt with a newly recognized 'lower world' component. Helium isotope measurements of gases dissolved in spring waters indicate that a significant component of the lower world fluid comes up more than 30 miles along faults from the Earth's mantle to the surface. Also, about one third of the CO2 emitted from the springs is from deep sources."
This is an astounding relation linking mantle degassing and neotectonics to the geochemistry of groundwaters.
Ref: Plateau region -- Neotectonic connections and implications for groundwater systems, Laura J. Crossey et al., Dept. of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131, USA. GSA Bulletin, Pages 1034-1053, doi: 10.1130/B26394.1