(U-Th)/He-dating of Iron oxides: Towards establishing a temporal framework for landscape evolution and regolith development in Southwest Western Australia

Wells, MA1, González-Álvarez, I2,3 and Danišík, M4

1John de Laeter Centre (JdLC), Curtin University, Perth, WA 6102, Australia; 2CSIRO, Mineral Resources, Discovery Program, Perth, Australia; 3University of Western Australia, Centre for Exploration Targeting, Perth, Australia; 4John de Laeter Centre for Isotope Research, Applied Geology, Curtin University, Perth, Australia

Understanding the temporal formation of iron oxides can provide important clues for understanding landscape evolution, weathering processes and past climatic conditions. Recent application of (UTh)/He-dating to iron oxide assemblages in iron ore deposits1 and in weathering systems in Western Australia, analysed in the John de Laeter Center (JdLC) GeoHistory Facility, have demonstrated the efficacy of the technique for the geochronological analysis of iron oxide-rich systems. Hence, the iron oxide-rich duricrust, capping the deeply weathered regolith of the Darling Range in the south-west of Western Australia, provides a suitable geochronological proxy that provides a time-integrated record of the weathering processes that have shaped regolith formation.

Despite numerous studies focused on laterite formation in the Darling Range , there is a paucity of data pertaining to the age or timing of laterite formation. The exceptions are for exposures of lateritic duricrust at two sites along the Darling Scarp. Early work on lateritic duricrust near Toodyay (50 km northeast of Perth), yielded (U-Th)/He ages of 10.0–7.5 Ma (Late Miocene) and more recently, findings arising from a pathfinder JdL-GSWA project , measured comparable Late-Miocene/Early Pliocene, to possible Early-Pleistocene (U-Th)/He ages of 5.7–1.3 Ma for pisolitic and fragmental duricrust in lateritic profiles at the Boddington Gold Mine (100 km southeast of Perth).

Further east, in the central Yilgarn, a recent JdL-CSIRO pilot study also measured Late Miocene/Pliocene ages (7.9–3.5 Ma) for nodular duricrust exposed near the Blue Haze Au mine, Forrestania (120 km southeast of Southern Cross). An exception in this study was an Early Oligocene age (34.8 +/- 3.8 Ma) for one example of nodular duricrust. Given the small number of
samples examined in this study, an explanation for the much older age is currently open to interpretation. However, the generally comparable (U-Th)/He ages for lateritic duricrust across these
widely spread locations in southern WA, suggest that the processes of regolith formation and/or modification were, broadly, regionally synchronous. These initial findings help to underscore and
provide the impetus in establishing a temporal framework for duricrust formation, which may also provide a record of past processes that have helped in shaping landscape evolution in the broader, Southwest Western Australia.

Acknowledgements
The authors would like to thank Classic Minerals for their support and permission in publishing the Forrestania dating work. The Boddington dating results derive from a project funded by the Geological Survey of Western Australia (GSWA) from the Exploration Incentive Scheme. Martin Danišík acknowledges the support of a Curtin Senior Research Fellowship.


Biography

In 1997, Martin joined CSIRO to study WA’s Ni laterite and Pilbara iron ore deposits. In 2017, Martin joined the John de Laeter Centre to investigate (U-Th)/He-dating of WA regolith and characterize e-metal (Li,V) ores. Throughout his career, Martin has investigated the element and mineral distribution of these varied deposits.

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