In situ U-Pb geochronology, Hf and Sm-Nd isotopic characteristics of zircon, titanite, apatite and monazite from the Hoidas Lake REE mineralization, northern Saskatchewan, Canada

English Abstract:

The diopside-allanite veins and apatite breccia veins of the Hoidas Lake rare earth element (REE) deposit were emplaced along the Hoidas-Nisikkatch Fault, an inferred subsidiary of the regional Black Bay Fault, and cross-cut the strongly deformed Archaean and Paleoproterozoic granitoid gneisses of the Rae Province. We report on the results of laser-ablation ICP-MS U-Pb geochronology of zircon and titanite from the diopside-allanite veins and green apatite and monazite from the apatite breccia veins, Hf isotopic data of zircon and Sm-Nd isotopic compositions of titanite, apatite and monazite, in an attempt to constrain the age of the REE mineralization, and to provide implications on its magmatic source.

Geological relationships and in situ U-Pb data indicates that the REE veins formed during and after peak metamorphism, which occurred at ca. 1.9 Ga. However, there are zircon crystals in the diopside-allanite veins with concordant U-Pb ages of ~2350 Ma which are interpreted to be inherited from granitoids that formed during the Arrowsmith Orogeny. Zircon rims with concordant U-Pb ages around 1906 Ma are inferred to represent zircon growth during the emplacement of the REE veins, based on textural features and the difference in Hf isotopic composition of rims vs. cores (ɛHf(t) of approximately -5 vs. 30, respectively). Titanite and monazite yielded concordant U-Pb ages ranging from ca. 1931 to 1825 Ma, whereas green apatite defined a discordant array with an upper intercept of ~1814 Ma. The calculated ɛNd(t) values of titanite, green apatite and monazite (-15.3 to -10.9) are comparable to ɛNd(t) values reported for the Martin Group alkali basalts in the Beaverlodge Domain and the Christopher Island Formation in the Baker Lake Basin, both of which also yielded similar U-Pb ages, suggesting that these alkali units originated from a similar source, most probably an ancient and compositionally complex lithospheric mantle reservoir.