Geochronological and microstructural constraints on deformation events in the Olympic Dam Cu-U-Au-Ag deposit, South Australia

The integration of electron backscatter diffraction (EBSD) with targeted geochronology provides a powerful tool for direct dating of deformation events preserved within mineral microstructures. EBSD analysis of mechanically robust minerals with well-characterised deformation behaviours such as pyrite, can reveal deformation characteristics which can be dated by targeting texturally associated geochronometers. This study combines microstructural analysis of pyrite with sericite and K-feldspar Rb-Sr geochronology to resolve the early (1590–1000 Ma) tectonothermal evolution of Olympic Dam. Initial deformation (∼1590–1500 Ma) is recorded by subgrain rotation dynamic recrystallisation textures in pyrite, indicative of temperatures above 400 °C, followed by pyrite dislocation creep (∼260 °C) dated at 1537 ± 42 Ma. Reactivation of pyrite dislocation creep at ∼1410 Ma corresponds with oblique, crosscutting shear-dominated veins, interpreted to represent large-scale reactivation of the Masher’s Fault zone and incorporation of bedded clastic units into the orebody. This is correlated with the trans -Laurentian Pinware–Baraboo–Picuris orogenic belt (∼1520–1340 Ma) and is among the first evidence for the influence of this planetary-scale orogeny in Australia. Careful EBSD analysis used in parallel with other complementary techniques can effectively distinguish microstructural types. When integrated with targeted geochronology of well understood isotopic systems, this can be used across diverse geological settings, for example, to reveal sequences of metasomatism and ore deposition in skarn systems, or track deformation and fluid infiltration in pegmatites or shear zone-hosted (orogenic) gold systems. It also holds great promise for planetary geology by allowing determination of the conditions and timing of thermal/impact events.