216 Geochronology of Critical Mineral Deposits with Special Reference to U-Th-Pb Dating of Common-Pb-Rich Minerals

Radiometric dating of ore deposits containing critical minerals. Studies discussing analytical aspects of methods such as U-Th-Pb, Ar-Ar, Rb-Sr, Sm-Nd, Re-Os and/or using radiometric ages for ore genesis research or critical mineral resource evaluation.

Tuesday, 21 October 2025
1:30 PM - 5:30 PM
HBGCC, 304C

Mica Rb-Sr dating by laser ablation ICP-MS/MS using an isochronous calibration material and application to the REE-mineralized Twihinate carbonatite complex

Paper number: 216-1
Program: Technical Sessions
Time: 1:35 PM – 1:55 PM

Authors

  • Lucas Tatnell
    Centre for Exploration Targeting and ARC Centre in Critical Resources for the Future, School of Earth and Oceans, The University of Western Australia, Perth
  • Andrea Giuliani Presenting Author
    Carnegie Institution for Science, Washington, DC
  • Marco Fiorentini
    Centre for Exploration Targeting and ARC Centre in Critical Resources for the Future, School of Earth and Oceans, The University of Western Australia, Perth
  • Mohammed Bouabdellah
    Département de Géologie, Faculté des Sciences, Université Mohammed Premier, Oujda
  • Wissale Boukirou
    Département de Géologie, Faculté des Sciences, Université Mohammed Premier, Oujda
  • Chris Fisher
    Centre for Exploration Targeting and ARC Centre in Critical Resources for the Future, School of Earth and Oceans, The University of Western Australia, Perth
  • Isra ezad
    Centre for Exploration Targeting and ARC Centre in Critical Resources for the Future, School of Earth and Oceans, The University of Western Australia, Perth
  • Laurent Sapor
    Groupe Managem, Casablanca

Abstract

In-situ Rb-Sr dating of mica by laser ablation ICP-MS/MS is increasingly employed to date several geological processes including magmatic intrusions and hydrothermal mineralization. This analytical method overcomes the isobaric interference of 87Rb on 87Sr by reaction of Sr+ ions with a gas reagent (SF6 or N2O) in a collision cell. Rb+ ions are not affected by this reaction while the isotopes of Sr are quantified as reacted species (e.g., SrO+). The majority of available age results are based on Rb/Sr calibration using the MicaMG pressed-powder pellet. Strontium isotope ratios are calibrated using the synthetic glass NIST610. However, various studies have reported low accuracy associated with mica Rb-Sr ages using this method or large variations in calculated Rb/Sr for the same mica attributed to the different ablation properties of MicaMG and natural mica. In this presentation we first show the results of a recently developed strategy to obtain in-situ mica Rb/Sr ages where NIST610 is initially employed to estimate both 87Sr/86Sr and 87Rb/86Sr, thus producing very stable splines for drift correction. 87Rb/86Sr in the mica unknowns is then corrected based on the age of an isochronous in-house mica standard. Comparison of in-situ Rb/Sr ages with those obtained by isotope dilution for the same micas from kimberlites in southern and western Africa testifies to the improved accuracy of this procedure compared to those utilizing MicaMG. In-situ mica Rb/Sr dating is then combined with U/Pb dating of perovskite and apatite to constrain the emplacement ages of multiple lithological units (carbonatites, syenites, ultramafic lamprophyres) within the REE-endowed Twihinate complex in Morocco. Age variations between 89.0±1.3 Ma and 82.6±3.1 Ma (2s) indicate a protracted history of magma emplacement including an apparent inward younging which has not been previously inferred in carbonatite complexes elsewhere. This pattern probably resulted from repeated pulses of melt injected into the same lithospheric pathway over ~7 million years, and implies melt channeling towards the center of annular carbonatite structures. This process can foster the re-dissolution, extraction and concentration of critical elements including REE in late-stage melts and fluids hence explaining why REE are distributed in the center of the complex at Twihinate and in other major carbonatite complexes such as Mt Weld in Australia.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-411946

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