Compositional Evolution of Tourmalines and Exploration Implications in the Petalite Subtype Prof Pegmatite, Revelstoke, British Columbia, Canada

Abstract Tourmaline geochemistry provides insights into pegmatite evolution by recording changing geochemical conditions during crystallization, which help to understand magmatic differentiation and mineralization processes due to tourmaline’s ability to accommodate diverse elemental substitutions, making it a valuable tool. The Prof pegmatite is a zoned petalite subtype pegmatite located in southeastern British Columbia, near Revelstoke. It is part of the Boulder Mountain Pegmatite Group, an underexplored, extensive group of pegmatites which are interpreted to extend across the valley 15 km to the south to the Mount Begbie pegmatites. The tourmalines in the Prof pegmatite exhibit significant color, geochemical, and textural variability, reflecting the evolving melt and fluid chemistry from early crystallization to late-stage metasomatism. Tourmalines from the pegmatite’s border and intermediate zones are brown-green and show strong concentric zoning, transitioning from dravite to schorl compositions (locally feruvite). Intermediate zone tourmalines commonly develop colorless, Li-rich elbaite to fluor-elbaite rims. The quartz zone is characterized by the presence of deep blue tourmalines with schorl to fluor-schorl compositions. In the central “distal tourmaline” subzone, tourmaline shows diverse blue and green colors with elbaite to fluor-elbaite compositions, whereas in the core subzone tourmaline is pink with elbaite to fluor-elbaite composition and quartz inclusions. Early tourmaline crystallization incorporated Ca, Mg, Ti, and Fe from calc-silicate wall rock contamination and has dravite-schorl compositions. Fractional crystallization subsequently enriched the melt in Mn, Li, F, and Al, which promoted elbaite and fluor-elbaite growth. Tourmaline compositions were further controlled by mineral buffering, with plagioclase regulating Na, garnet influencing Mg and Mn, and petalite buffering Li availability. The dominant exchange vector in the border and intermediate zone tourmalines is Fe(Mg)−1, controlling the dravite–schorl compositions. The elbaite–fluor-elbaites of the intermediate zone are primarily influenced by the AlLi(Fe2+)−2 vector, which also plays a role in the central zone alongside the (Al◻)(R2+Na)−1 vector. Tourmaline geochemistry at the Prof pegmatite offers valuable exploration insights for lithium-bearing pegmatites within the Boulder Mountain Pegmatite Group. The presence of colorless, Li-rich elbaite rims in the intermediate zones of other pegmatites in the region suggests that lithium mineralization may be present at depth, even when surficial expressions appear barren. Given the limitations of visual identification due to the colorless appearance of the tourmaline, handheld analytical tools such as Raman spectroscopy, X-ray fluorescence, and laser induced breakdown spectroscopy provide rapid geochemical analysis, enhancing the effectiveness of lithium exploration. This study highlights the importance of understanding pegmatite mineralogy in refining efficient lithium exploration.