Chaos and control: the interplay between discordant IOCG-related breccias and their bounding fault and shear arrays, Cloncurry District, northern Australia

In the Cloncurry District, several similar to 1530 Ma iron oxide-copper-gold (IOCG) deposits such as Ernest Henry, and the Merlin Mo-Re deposit, are hosted by polymictic hydrothermal breccias with textures implying fluidization. Similarly textured breccias, highly discordant yet barren, are found along fault arrays and junctions in specific corridors through the Cloncurry district. We generated geomechanical models of the stress and fluid pressure requirements for failure along the fault arrays thought to be active at the time of IOCG and Mo-Re mineralization. The richest mineralized breccias occur within corridors in areas of overlap of predicted highest rock failure potential for the two main structural events. Most barren breccias and some IOCGs without fluidized breccia occur in low to moderate failure potential sites of only one of the deformation events. We infer the mineralizing, high energy packages were structurally connected to mid-crustal metal + fluid sources (e.g. from intrusions) along deeper-penetrating and longer lived master structures. Barren, very high energy breccias, were connected, probably more transiently, to metal-poor fluid sources due to time/space differences in fluid release, or because more extreme overpressures failed to precipitate metals.