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Geochronology Advances in geochronological science
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https://doi.org/10.5194/gchron-2020-7
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/gchron-2020-7
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 31 Mar 2020

Submitted as: research article | 31 Mar 2020

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This preprint is currently under review for the journal GChron.

Resolving multiple geological events using in situ Rb-Sr geochronology: implications for metallogenesis at Tropicana, Western Australia

Hugo K. H. Olierook1,2,3, Kai Rankenburg1,3, Stanislav Ulrich4, Christopher L. Kirkland1,2, Noreen Evans1,3, Stephen Brown4, Brent I. McInnes3, Alexander Prent1,3, Jack Gillespie1, Bradley McDonald1, and Miles Darragh4 Hugo K. H. Olierook et al.
  • 1School of Earth and Planetary Sciences, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
  • 2Centre for Exploration Targeting – Curtin Node, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
  • 3John de Laeter Centre, Curtin University, GPO Box U1987, Perth, WA 6845, Australia
  • 4AngloGold Ashanti Australia Ltd., 140 St. Georges Terrace, Perth, WA 6000, Australia

Abstract. Dating multiple geological events in single samples using thermochronology and geochronology is relatively common but it is only with the recent advent of triple quadrupole LA-ICP-MS that in situ Rb-Sr dating has become a more commonly applied and powerful tool to date K- and Rb-bearing minerals. Here, we date, for the first time, two generations of mineral assemblages in individual thin sections using the in situ Rb-Sr method. Two distinct mineral assemblages, both probably associated with Au mineralization, are identified in samples from the Tropicana gold mine in the Albany–Fraser Orogen, Western Australia. For Rb-Sr purposes, the key dateable minerals are two generations of biotite, and additional phengite associated with the second assemblage. Our results reveal that the first, coarse-grained generation of biotite grains records a minimum age of 2535 ± 18 Ma, coeval with previous 40Ar/39Ar biotite, Re-Os pyrite and U-Pb rutile results. The second, fine-grained and recrystallized generation of biotite grains record an age of 1207 ± 12 Ma across all samples. Phengite and muscovite yielded broadly similar results at ca. 1.2 Ga but data is overdispersed for a single coeval population of phengite and shows elevated age uncertainties for muscovite. We propose that the ca. 2530 Ma age recorded by various geochronometers represents cooling and exhumation, and that the age of ca. 1210 Ma is related to major shearing associated with the regional deformation associated with Stage II of the Albany–Fraser Orogeny. This is the first time that an age of ca. 1210 Ma has been identified in the Tropicana Zone, which may have ramifications for constraining the timing of mineralization in the region. The in situ Rb-Sr technique is currently the only tool capable of resolving both geological events in these rocks.

Hugo K. H. Olierook et al.

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Hugo K. H. Olierook et al.

Hugo K. H. Olierook et al.

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Latest update: 11 Jul 2020
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Short summary
Using a relatively new dating technique, in situ Rb-Sr geochronology, we constrain the ages of two generations of mineral assemblages from the Tropicana Zone, Western Australia. The first dated at ca. 2535 Ma is associated with exhumation of an Archean craton margin and gold mineralization. The second, dated at ca. 1210 Ma, has not been previously documented in the Tropicana Zone. It is probably associated with Stage II of the Albany-Fraser Orogeny and additional gold mineralization.
Using a relatively new dating technique, in situ Rb-Sr geochronology, we constrain the ages of...
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