216-10 Mesoproterozoic Lithium-Cesium-Tantalum Pegmatite Mineralization Constrained by U-Pb Titanite and Apatite Geochronology

Session: Geochronology of Critical Mineral Deposits with Special Reference to U-Th-Pb Dating of Common-Pb-Rich Minerals

Presenting Author:

Authors:

Abstract:

The demand for lithium, which is mainly sourced from lithium-cesium-tantalum (LCT) pegmatites, brines, and volcanic clays, is projected to continue increasing as global investment in electric vehicles and battery storage continues to expand. Exploration strategies for LCT pegmatites rely on the prevailing models that these pegmatites form as late-stage fractionation products of nearby peraluminous granites or through partial melting of Li-bearing high-grade metamorphic rocks, yet many LCT pegmatite localities lack the precise age estimates to discriminate between these competing mineralization models. Building on the petrologic and geochemical foundation from previous research on the King’s X and Animikie Red Ace pegmatites in Florence County, WI, USA, we used LA-ICP-MS U-Pb geochronology and trace-element analysis of magmatic apatite within the pegmatites and neocrystallized titanite in the proximal ~1866 Ma Quinnesec Fm. amphibolite-facies wall rock to date LCT pegmatite formation. The dominant field-geochemical models suggest pegmatite emplacement occurred between the end of the Penokean orogeny (~1835 Ma) and Yavapai arc accretion (~1750–1700 Ma), based on outcrops within the Pembine-Wausau terrane, with pegmatites sourcing from the nearby (presumed 1835 Ma) Bush Lake granite or from Quinnesec Fm. partial melts. Apatite grains that nucleated in the chilled margin of the pegmatites, adjacent to the wall rock contact, have rare earth element (REE) profiles and oscillatory cathodoluminescence zoning suggestive of igneous crystallization within an LCT pegmatite and give U-Pb dates of 1444 ± 6 [29] Ma and 1432 ± 5 [29] Ma, respectively, for the King’s X and Animikie pegmatites. Xenoblastic, light REE-depleted titanite from the Quinnesec Fm., sampled at distances <1 cm to ~150 m from the pegmatites, have U-Pb ages ranging from 1473 ± 7 [29] Ma to 1438 ± 13 [29] Ma, whereas euhedral titanite grains from a non-mineralized granitic dike (>1.8 km away) have a U-Pb age of 1806 ± 10 [36] Ma. These ages reveal a previously unrecognized Mesoproterozoic thermal and fluid overprint in the region, though the exact source of the pegmatites is yet to be determined. As the Florence pegmatites significantly postdate the Penokean and Yavapai orogenies, we are currently developing geochemical fractionation/melting models that take into consideration the role that the ~1476 Ma Wolf River batholith (exposed ≥24 km south) and/or the Mesoproterozoic Pinware-Baraboo-Picuris orogeny played in LCT pegmatite petrogenesis.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9557

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