This study investigates Rb–Sr system behavior in hydrothermally altered muscovite using in-situ LA-ICP-MS/MS (Laser Ablation-Inductively Coupled Plasma-Tandem Mass Spectrometry) analyses from the Athabasca Basin. Unaltered muscovite records Paleoproterozoic crystallization ages, whereas muscovite altered to illite and sudoite yields a consistent age of ~1640 Ma, corresponding to alteration halos related to unconformity-type uranium deposits. These results highlight the potential of Rb–Sr dating to constrain hydrothermal processes and fluid–rock interactions.