A Pb isotope model for the Proterozoic of northern Australia with a focus on the McArthur Basin

Abstract

The Pb isotopic composition of mineral exploration samples can be used to help determine their metallogenic association and hence to assess prospectivity in geological provinces where there is an established Pb isotope database. We have developed such a database, available online, and models that relate Pb isotopic signatures to known metallogenic events in Proterozoic terrains in northern Australia. Two terrain-specific Pb isotope model curves, the Western Fold Belt curve and the Eastern Fold Belt curve, were developed based on major ore systems in the Mount Isa and McArthur terrains. The Western Fold Belt curve was optimised to give an age of 1640 Ma for the McArthur Formation HYC deposit. This is the well-constrained age of the Barney Creek Formation, host of the mineralisation. To validate the accuracy of the models, we attempted to determine the initial Pb isotope ratios of granitic rocks from across the Proterozoic terrains with ages varying from 1870 to 1550 Ma. The curves give model ages for major ore systems including Mount Isa, George Fisher Zn–Pb, Century and Cannington that are consistent with their stratigraphic locations and accepted metallogenesis. Focusing on the McArthur Basin, a database of 59 deposits and prospects was developed. In addition to the 1640 Ma HYC event, an older event at ca 1700 Ma has been fingerprinted, a younger Upper McArthur event at ca 1570 Ma, an event coeval with the Mount Isa Orogeny at ca 1550–1500 Ma and a late Roper event younger than 1500 Ma. There is also evidence of hydrothermal activity of Cambrian age and recent weathering-related metal concentration.