Fig. 1: Neon isotope data.
Neon signatures confirm that fluids sampled at Moab Khotsong (blue stars) are the result of radiogenic (nucleogenic) production in the crust added to an initial, Air-Saturated Water (ASW) component recharged from the surface, but no discernible mantle contribution. These data are consistent with the elevated crustal 21Ne production observed to date only in samples collected from Precambrian cratons, e.g. Kidd Creek2,14 (Canadian Shield), fracture fluids from Driefontein, Evander, Kloof, and Mponeng mines in the Witwatersrand Basin17 (demonstrated here by the red triangles and dashed red line reproduced from Lippmann-Pipke et al.18), and fluid inclusions from both the St. Ives Goldfield in the Yilgarn Craton33 (grey diamonds), and the Mt. Isa inlier (green triangles)34. Prior to the discovery of these distinctive radiogenic 21Ne signatures, radiogenic neon addition to ASW in average continental crust globally fell along the lower trend represented here by the solid black line. Published data from Kidd Creek fracture fluids2,14 are plotted for context (black squares and red circles). Sample 090719MK95BHA (half-shaded star) reveals a lower radiogenic excess for all noble gases and is consistent with addition of a minor air component introduced during sampling (see Methods). Error bars represent analytical uncertainty of 1σ and are typically smaller than the plotted symbols.
