Brotodewo, Adrienne1,2,, Tiddy, Caroline1,2, Zivak, Diana3, Fabris, Adrian4, Giles, David1,2
1Future Industries Institute, University of South Australia, Adelaide, Australia, 2Mineral Exploration Cooperative Research Centre (MinEx CRC), Adelaide, Australia, 3Department of Earth and Environmental Sciences, The University of Adelaide, Adelaide, Australia, 4Geological Survey of South Australia, Adelaide, Australia
Zircon preserves chemical signatures that reflect crystallisation environments and post-crystallisation modification (e.g. Belousova et al., 2002). Typically, zircon is used to study petrogenesis and evolution of rocks due to its robustness during surficial, metamorphic and igneous processes, as well as its affinity for rare earth elements (REE), U and Th. Recent research has focused on understanding and characterising the geochemical composition of zircon. However, this has been met with many challenges as REE and trace element compositions can be highly variable in zircon from the same lithological unit, and within a single grain itself as a result of micro inclusions, metamictisation, strong differences in compositional zoning and recrystallisation (Nardi et al., 2003). Despite this, zircon has successfully been used as a provenance tool to discriminate between igneous, metamorphic and sedimentary source rocks (Belousova et al., 2002). Zircon has also been demonstrated to preserve a geochemical signature that can be related to porphyry Cu mineralisation (Lu et al., 2016). However, the use of zircon as a pathfinder for other commodities, such as iron oxide-copper-gold (IOCG) deposits, is limited (Courtney-Davies et al., 2019).
The Gawler Craton, South Australia, preserves a complex geological history dating back to the late Archean. The craton preserves multiple igneous units that each have their own unique geochemical characteristics and some of which are associated with IOCG mineralisation. IOCG mineralisation occurred during a major period of mineral genesis, magmatism, deformation and metamorphism at ca. 1600-1580 Ma (e.g. Tiddy & Giles, 2020) and includes the Olympic Dam, Prominent Hill and Carrapateena deposits along the eastern Gawler Craton. Within the Gawler Craton, zircon has commonly been used for dating or isotopic purposes. However, limited research has focused on the geochemistry of zircon, its variability between igneous suites and its use as a pathfinder mineral towards IOCG deposits.
In this study, new zircon geochemical data is presented on samples from the ca. 1850 Ma Donington Suite, ca. 1600-1575 Ma Hiltaba Suite and ca. 1594-1587 Ma Gawler Range Volcanics. Samples from all three suites preserve evidence of variable potassic and hematite alteration associated with hydrothermal activity during IOCG mineralisation at ca. 1600-1580 Ma. Assessment of zircon chemistry within each of the three igneous units shows that there are characteristic enrichments and depletions in trace and REE chemistry in samples that have undergone variable degrees of alteration. The variations in zircon chemistry between unaltered and altered samples is attributed to chemical modification by F-rich hydrothermal fluids that altered the host rocks and was associated with IOCG mineralisation. These distinct geochemical characteristics recognized in zircon suggests the potential of zircon as a pathfinder for IOCG deposits in the Gawler Craton.
Belousova et al. 2002: Contrib. Min. Pet. 143, 602-622
Courtney-Davies et al. 2019: Min. 2019, 9, 364
Lu et al. 2016: Soc. Eco. Geo. Vol 19
Nardi et al. 2013: Chem. Geo. 335, 1-7
Tiddy & Giles, 2020: Ore Geo. Rev. 122, 103-483.
Adrienne Brotodewo is a PhD candidate at the Future Industries Institute, University of South Australia, and is undertaking her research as part of MinEx CRC.
Adrienne is focusing on establishing a geochemical exploration criteria using zircon within basement and cover sequences in the Gawler Craton, South Australia.