Hydrothermal origin of the Paleoproterozoic xenotime from the King Leopold Sandstone of the Kimberley Group, Kimberley, NW Australia: Implications for a ca 1.7 Ga far-field hydrothermal event

A mineral chemical study by electron microprobe microanalyser was carried out to decipher the origin of xenotime overgrowths from the King Leopold Sandstone, the Kimberley Group, NW Australia. Results show that the King Leopold Sandstone xenotime overgrowths are characterised by LREE depletion and MREE-HREE enrichment. The King Leopold Sandstone xenotime overgrowths also show higher Zr content and lower U, Fe, and Lu contents, suggestive of hydrothermal origin rather than diagenetic origin, as previously claimed. The intrusive contact relationships between the Hart Dolerite and King Leopold, Warton and Pentecost sandstones suggest that xenotime overgrowths from the latter two units should also be hydrothermal in origin. The differing U and Th concentrations suggest a different chemical pore fluid would have been responsible for the formation of xenotime overgrowths from the King Leopold, Warton and Pentecost sandstones as the depth of siliciclastic sediments reached the zone of xenotime precipitation. The ca 1.7 Ga ages of xenotime overgrowths from the King Leopold Sandstone can be equated with the ca 1.7 Ga xenotime overgrowth ages obtained from the Warton and Pentecost sandstones of the same group and the ca 1.7 Ga zircon U-Pb ages from the Dingo Granite in northern Australia, and together they are consistent with the age of Capricorn orogeny. As such, the ca 1.7 Ga ages point to a common hydrothermal event possibly associated with the low temperature far-field Dingo Granite intrusion during Capricorn orogeny in the Paleoproterozoic Australia. The Paleozoic Alice Springs Orogeny resulted in radiogenic lead loss and thus is likely responsible for the 1.6-1.3 Ga discordant ages from the King Leopold, Warton and Pentecost sandstones.