Magma sources and gold mineralisation in the Mount Leyshon and Tuckers Igneous Complexes, Queensland, Australia: U-Pb and Hf isotope evidence

Valeria Murgulov*, Suzanne Y. O'Reilly, William L. Griffin, Phillip L. Blevin

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    20 Citations (Scopus)

    Abstract

    In situ LAM-ICPMS U-Pb, Hf-isotope and trace-element analyses of zircon have been used to evaluate the relative contributions of juvenile mantle and crustal sources to the intrusive rocks of the mafic to intermediate, gold-poor Tuckers Igneous Complex (TIC), and the spatially and temporally related, felsic Mount Leyshon Igneous Complex (MLIC), which hosts a gold-rich porphyry system.The TIC intrusions range in age from 304.2. ±. 9.1Ma to 288.5. ±. 6.4Ma, and the MLIC intrusions from 291.0. ±. 4.8Ma to 288. ±. 6Ma. Cross-cutting relationships define the intrusion sequence from oldest to youngest; Diorite, Monzodiorite, Mafic Granodiorite and Biotite Microgranite within the TIC; Early Dyke, Southern Porphyry and Late Dyke within the MLIC.Zircons from the earliest rock type within each complex have a wide range in eHf (5.2 to 14.8 for the TIC Diorite, 2.0 to 12.4 for the MLIC Early Dykes) suggesting the mixing of juvenile and crustal magmas. This interpretation is supported by trace-element data that show the presence of two distinct zircon populations in the MLIC Early Dyke. The later intrusive rocks have narrower ranges in eHf (typically <4 eHf units) and trace-element patterns of zircon. This homogeneity suggests derivation from magmas produced by further mixing and fractional crystallisation of the TIC Diorite and the MLIC Early Dyke magmas respectively. A greater crustal contribution to the gold-rich MLIC is inferred from the range of median eHf (3.2 to 4.5 for the MLIC, 5.4 to 8.7 for the TIC). We suggest that the MLIC was derived by melting of more felsic crustal rocks, and with less input from juvenile mantle, then the TIC; it was not derived by fractional crystallisation of an intermediate to mafic TIC-like magma. Modelling of Hf isotope data yields a mean model age of 1040±10Ma (at 176Lu/177Hf=0.015) for the crustal component in both complexes.Gold was precipitated in the MLIC Breccia during the emplacement of the Late Dykes. The isotopically homogenous nature of the Late Dykes suggests that no additional juvenile-mantle input was involved at the mineralisation stage. This supports a model in which gold and other metals were indigenous to the Late Dykes magma and were concentrated by magma differentiation and fluid-evolution processes.

    Original languageEnglish
    Pages (from-to)281-307
    Number of pages27
    JournalLithos
    Volume101
    Issue number3-4
    DOIs
    Publication statusPublished - 1 Mar 2008

    Keywords

    • granitic magma sources
    • granite genesis
    • gold mineralisation sources
    • zircon geochronology
    • zircon Hf isotopes
    • crustal reservoirs

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