Radionuclide (Ή, ,4 C, 36 C1, ,29 I), noble gas isotopes ( 4 He, 20 -21 ' 22 Ne), stable isotope (Ο, H) and hydrochemical analyses have been carried out on fracture-hosted, brackish to saline groundwaters from a well-characterised hydrogeologic system in the Archean Lac du Bonnet Batholith, Manitoba, Canada.He and Ne isotope systematics of saline groundwaters in deeper fractures are dominated by α,η and η,α reactions with 18 0, 25 Mg, 19 F in the rock matrix. With depth, the groundwaters have increasing concentrations of CI", 36 C1, radiogenic "He ( 4 He r ) and nucleogenic 2, Ne and 22 Ne. 36 C1/C1 ratios in the groundwaters are comparable to measured and calculated in situ 36 C1/C1 production ratios for the granites indicating the Cr ions have likely been dissolved from the rock matrix. Concentrations of 129 I are not correlatable with I" and only broadly correlate with 36 C1 and "He, concentrations, suggesting that the observed l29 I is not due to water/rock interactions, but to the accumulation of fissiogenic 129 I with time.The correlations amongst 36 C1, ,29 I, noble gases and hydrochemical systematics suggest the chemical compositions of the groundwaters have been modified by interactions with silicate and oxide minerals and dissolution of matrix Cl~. Modelling of accumulation of fissiogenic 129 I suggests these processes have occurred over at least several million years for the most-evolved groundwaters.