Combination of a new strato-tectonic model for the Olympic Metallogenic Event (OME) and a zircon-based geochemical tool offers a significant step-change for ore target vectoring for a spectrum of IOCG and coeval copper-gold deposit styles in the Gawler Craton. The model proposes the Paris-Nankivel epithermalporphyry belt formed at the same time as Olympic Dam on the margins of a super caldera filled with Gawler Range Volcanics (GRV). Prior subduction tectonics produced precursor conditions suitable for the formation of epithermal and porphyry copper deposits on the southern shoulder of the caldera, whereas IOCGs formed on the northern and eastern margins with haematite- or magnetite-dominated systems respectively formed on the shoulder or in hotter more reduced conditions within the caldera. A stratigraphic marker of the OME palaeosurface and caldera formation includes volcanogenic conglomeratic facies collapsed into the IOCG pipes. The marker provides a correlation and an upper strato-tectonic limit to the OME mineralization across the craton. The Zircon Alteration Index (ZAI = 40 - Zr/Hf) is a robust search tool that is universally applicable to the OME spectrum of deposit styles and hosts. The exclusive association of Hf with Zr in zircon enables wholerock analysis of the Zr/Hf ratio to measure the amount of hydrothermal overprinting of the inherited volcanic or detrital zircon in a host rock and hence proximity to a mineral target. ZAI targeting requires less drilling and assay samples. Comparison of downhole ZAI profiles and strato-tectonic lithologies often enables lateral or vertical target vectors to be estimated for single holes. Vectoring with ZAI has been validated in the Stuart Shelf with a comprehensive study of 35 holes in varying proximities to known IOCG systems. Preliminary target ranges are assigned to the ZAI values and 8 holes nominated for review as being proximal to new targets.

Open-Access Online Publication: March 01, 2023