Mesoproterozoic rift sedimentation, fluid events and uranium prospectivity in the Cariewerloo Basin, Gawler Craton, South Australia

ABSTRACT

The Cariewerloo Basin formed in the Mesoproterozoic following assembly of the Gawler Craton, South Australia, and was filled by arenaceous redbeds of the Pandurra Formation. While previous regional-scale work reveals a basin with similar size and sedimentary fill to the Proterozoic Athabasca and Kombolgie basins that host unconformity-related uranium deposits, few details of the Cariewerloo Basin are known. In this study, stratigraphy, petrography, lithogeochemistry, stable isotope geochemistry and ⁴⁰Ar/³⁹Ar geochronology are integrated to clarify the depositional history of the Pandurra Formation, and to assess fluid events in the basin that could be linked to the formation of uranium deposits. In the study area, the Pandurra Formation was deposited in two eastward-thickening packages that terminate at faulted basement uplifts, interpreted as half-grabens that formed in a continental rift system as the eastern Gawler Craton underwent extension. Deposition occurred between 1575 Ma (latest Hiltaba Suite age) and ca 1490 Ma, the ⁴⁰Ar/³⁹Ar age of diagenetic illite in the basal Pandurra. Diagenesis involving fluids having δ¹⁸O and δ²H values between –2.1 and 3.6‰, and between –66 and –8‰, respectively, occurred at around 150°C. Protracted diagenesis preferentially occurred in the upper Pandurra Formation based on petrography and Pearce Element Ratios that show complete replacement of detrital lithic and feldspathic grains by diagenetic phyllosilicates, and younger ⁴⁰Ar/³⁹Ar ages between ca 1330 and 1200 Ma that record fluid events later into basin history. Conversely, the basal Pandurra Formation shows better preservation of detrital grains, and older ⁴⁰Ar/³⁹Ar ages around 1450 Ma that suggest these strata became closed to fluid flow earlier in basin history. Although, based on O-isotope ratios, fluid–rock interaction did not occur in the Cariewerloo Basin to the same extent as that in the Athabasca or Kombolgie basins, it is possible that a uranium deposit formed where the upper Pandurra Formation was in contact with metasedimentary basement units outside the present basin margins.

KEYWORDS:

• unconformity-related uranium
• Pandurra Formation
• Cariewerloo Basin
• stratigraphy
• isotope geochemistry
• geochronology

Acknowledgements

We remember our co-author Kurt Kyser, who died far too soon in August 2017, and venerate his many contributions to geochemistry. Special thanks to James Marlatt and Garth Drever for the intellectual impetus to study the Pandurra and for sharing their valuable knowledge of worldwide Proterozoic basins. We thank April Vuletich, Kristen Gault, Evelyne Leduc, Sandeep Banerjee, Don Chipley, Marissa Valentino, Rachel Schwartz-Narbonne and Jordan Rouse at QFIR for technical assistance and sample preparation. Bill MacFarlane is thanked for lithogeochemistry analytical assistance. Scientific discussion and logistical assistance by Tania Wilson, Wayne Cowley and others at PIRSA were much appreciated. The manuscript was greatly improved thanks to the constructive reviews by David Quirt and an anonymous reviewer.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary papers

Appendix 1 Lithogeochemistry data

Appendix 2 ⁴⁰Ar/³⁹Ar analytical data

Additional information

Funding

This research was funded by a Natural Sciences and Engineering Research Council Collaborative Research and Development (NSERC-CRD) grant and Raven Minerals Corporation.