U-Pb and reconnaissance Lu-Hf isotope analysis of cassiterite and columbite group minerals from Archean Li-Cs-Ta type pegmatites of Western Australia

Abstract

Lithium–Cesium–Tantalum pegmatites represent a valuable global source of rare metals, however the crustal processes that facilitate the generation of Li-Cs-Ta pegmatite melts are not fully understood. Knowledge of the timing, melt sources and tectonic setting of this class of rare element pegmatite is limited in particular by the availability of geochronological and other isotopic data. This study presents new geochronological data from Li-Cs-Ta pegmatites across Western Australia, that vary in age, host lithology and geodynamic setting, by applying in situ LA-ICPMS U-Pb methods to date columbite group minerals and cassiterite samples. In a novel approach, reconnaissance Lu-Hf isotope data obtained from cassiterite samples by LA-MC-ICPMS are also reported providing insights into the source of Li-Cs-Ta pegmatite melts. The crystallisation ages and Lu-Hf isotopic data collected from the Li-Cs-Ta type pegmatites are interpreted within the existing magmatic and tectonic framework of their host terranes, and commonalities are identified. Li-Cs-Ta pegmatites are found to have been emplaced late in regional tectonic history and to follow periods of extended crustal reworking.