Isotope and geochemical fingerprinting of placer gold: insights into the provenance and age

Characterisation of the source of hydrothermal gold deposits typically relies on isotopic composition and textural interpretations of co-precipitating minerals. However, native gold contains trace elements and mineral inclusions of value to source characterisation. In this work, we studied several small gold nuggets from placer occurences in the Kurnalpi Terrane, Yilgarn Craton, Western Australia for their geochemical and isotopic characteristics using thermal ionisation mass spectrometry (TIMS) and secondary ion mass spectrometry (SIMS) methods. One of the most important findings of this study was the establishment of reliable Pb-Pb model ages for some gold samples, as well as the characterisation of the source of Pb prior to mineralisation. We establish that galena inclusions in native gold preserve Pb-isotope compositions compatible with known Archean deposits in the Kurnalpi Terrane, and that some native gold grains contain <10 ppm Pb and virtually exclude U, allowing initial Pb-isotope compositions to be measured. This study demonstrates that the geochemical and isotopic fingerprints of native gold could be used for exploration of primary gold sources, and potentially identify transport corridors.