Sources of sediment in the Eocene Garford paleovalley, South Australia, from detrital-zircon geochronology

Abstract

Detrital zircons from the Eocene Garford paleovalley, central South Australia, were derived from two main sources: (i) local Archean–Mesoproterozoic rocks of the Gawler Craton exposed in the paleocatchment, including the 2525–2440 Ma Mulgathing Complex and 1595–1575 Ma Gawler Range Volcanics–Hiltaba Suite; and (ii) Phanerozoic sedimentary rocks in the catchment that contribute a Late Mesoproterozoic to Cretaceous component of recycled zircons from a variety of primary sources. These sources include: the 1190–1120 Ma Pitjantjatjara Supersuite and 1080–1040 Ma Giles Complex, in the Musgrave Province; ca 510 Ma syn-Delamerian magmatism possibly derived from the Adelaide Rift Complex; and Jurassic–Cretaceous zircons ranging from ca 220 Ma to ca 100 Ma, with a prominent population at 122 ± 3 Ma. It is likely that zircons from these sources outside the paleocatchment were transported into the Mesozoic rocks of the Eromanga Basin within the catchments, before being re-eroded into the Garford paleovalley. Given the presence of significant gold mineralisation in the Neoarchean rocks of the Gawler Craton, the abundance of locally derived Archean zircons suggests potential for paleoplacer gold deposits in the Eocene paleodrainage system. Likewise, the abundance of zircons derived from the Gawler Range Volcanics–Hiltaba Suite supports the potential for secondary uranium mineralisation in the paleovalleys derived from Mesoproterozoic volcanics and granites, some of which are known to be uranium-enriched. Finally, these data suggest that the Garford paleovalley was not a major contributor to the zircon budget of the heavy-mineral sands province of the adjacent Eucla Basin.

Key Words:

• detrital zircon
• Eocene
• Eucla Basin
• Garford paleovalley
• geochronology
• provenance
• South Australia

Acknowledgements

This study has benefited from discussions with colleagues including John Keeling and Wenlong Zang. Reviews by Natalie Kositcin and Geoff Fraser along with two anonymous journal reviewers improved the paper. We thank Chris Foudoulis for his help with SHRIMP zircon analyses. Published with permission of the Manager, Geological Survey, PIRSA and CEO, Geoscience Australia.