Current mapping on the Mingary 1:100 000 map area has been investigating the nature of the boundary between the Olary Domain and Broken Hill Domain, both of which are subdivisions of the Curnamona Province. Earlier work had settled on a prominent north-northeast-trending TMI feature, which coincides roughly with an equally prominent change in regional gravity, as the boundary. The geological mapping, however, shows no major changes across this zone. A different domain boundary based on the regional influence of a 1690 Ma thermal event is supportable by the mapping. Alternatively, metamorphic-grade zonation established at 1590 Ma could also be used to define a domain boundary. Since these two events are 100 Ma years apart, they define two separate domain boundary conditions. Neither of these possible domain boundaries correlates with the TMI feature.