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Geology; March 2006; v. 34; no. 3; p. 173-176; DOI: 10.1130/G22003.1
© 2006 Geological Society of America
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Dating paleochannel iron ore by (U-Th)/He analysis of supergene goethite, Hamersley province, Australia

Jonathan A. Heim1, Paulo M. Vasconcelos1, David L. Shuster*,2, Kenneth A. Farley2 and G. Broadbent4

1 Earth Sciences, University of Queensland, Brisbane, Queensland 4072, Australia
2 Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA
4 Rio Tinto Exploration—Australasia Region, 37 Belmont Avenue, Belmont, WA 6104, Australia

(U-Th)/He dating of late-stage authigenic goethite, combined with corrections for diffusive loss of 4He by the 4He/3He methodology, reveals strong correlation between a sample's age and its depth in ferruginized channel sediments from the Yandicoogina deposit, Western Australia. Corrected ages, ranging from ca. 18 Ma near the surface to ca. 5 Ma at the bottom of the profile, indicate that ferruginization of the aggraded channels becomes progressively younger with depth. This trend is consistent with goethite precipitation at the groundwater-atmosphere interface during water table drawdown driven by the aridification of Western Australia during the Neogene. The results demonstrate that the (U-Th)/He system is ideal for dating goethite if diffusive loss corrections are applied. The approach is suitable for dating weathering reactions on Earth and should also be suitable for dating Fe oxyhydroxides in the Martian regolith.

Key Words: (U-Th)/He dating • goethite • weathering geochronology • channel iron deposits • iron ore






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