Age of Cu-Au mineralisation, Cloncurry district, eastern Mt Isa Inlier, Queensland, as determined by 40Ar/39Ar dating
Titel:
Age of Cu-Au mineralisation, Cloncurry district, eastern Mt Isa Inlier, Queensland, as determined by 40Ar/39Ar dating
Auteur:
Perkins, C. Wyborn, L. A. I.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 45 (1998) nr. 2 pagina's 233-246
Jaar:
1998-04
Inhoud:
The 40Ar/39Ar dating of alteration biotite, muscovite and amphibole from a number of post-peak metamorphic Cu-Au deposits and alteration systems in the Cloncurry district, north Queensland has determined the timing of mineralisation and hydrothermal activity. Alteration biotite from the Ernest Henry Cu-Au, Starra Au-Cu, and Mt Elliott Cu-Au deposits, sericite associated with hematite breccias in the Wimberu Granite, muscovite from an albitite pipe that intrudes the Gilded Rose Breccia, and sericite from a granitoid near the Osborne Cu-Au deposit, yield ages which are broadly contemporaneous with the late ca 1510-1485 Ma phases of the Williams and Naraku Batholiths. Hornblende and biotite alteration, which pre-date Cu-Au mineralisation at Osborne, give a maximum age of ca 1540 Ma for the deposit, which is also a probable minimum age for peak metamorphism. Metamorphic minerals from the vicinity of Osborne yield dates which are significantly older (ca 1590-1570 Ma) than those from the hydrothermal phases. Dating by the K-Ar method of red, hematitic K-feldspars which are regionally common in the Cloncurry district, was not effective, as the mineral yields ages up to 300 million years younger than coexisting alteration sericite. The 40Ar/39Ar age spectra obtained from most hydrothermal phases in the Eastern Fold Belt, Mt Isa Inlier, commonly contain flat parts which comprise a large proportion of the released gas, and are indicative of rapid cooling through the temperature of partial closure to Ar diffusion for the respective minerals.
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