Allanite geochronology in the Mount Isa Inlier.

Abstract\nKEY POINTSNew allanite geochronology is presented for four mineral deposits in the Mount Isa Inlier (SWAN, Mary Kathleen, Koppany and Elaine Dorothy). The data indicate the occurrence of multiple phases of allanite formation: one at 1732 ± 8 Ma at Koppany, one at <italic>ca</italic> 1520 Ma at Mary Kathleen, Koppany and SWAN, and one at <italic>ca</italic> 1473 Ma at Mary Kathleen and Elaine Dorothy associated with vein calcite. In the Mary Kathleen–Koppany–Elaine Dorothy skarn system, there are chemical and textural differences between the three allanite generations; the <italic>ca</italic> 1520 Ma generation formed by dissolution–reprecipitation of 1732 Ma allanite, with no addition of externally sourced rare earth elements, as shown by the identical Nd isotopic compositions of these two populations. Allanite at SWAN yielded a 207Pb/206Pb ID-TIMS age of 1519.6 ± 1.1 Ma; its homogeneity, low common Pb contents and near-concordance make it a suitable reference material. Repeated remobilisation of rare earth elements in the Mary Kathleen system is surprising, given the widely accepted low solubility of these elements, but may have been restricted in spatial extent.New ages for allanite formation at four REE-rich deposits near Mount Isa.Some localities show multiple generations of allanite with distinct compositions.Nd isotopes link these generations to each other and to the source of the ore-forming fluids. [ABSTRACT FROM AUTHOR]