ToF-SIMS as a Rapid Method for Mapping Rare Earth Elements and Anion Cluster Associations in Drill Core Samples

Rare‐earth elements (REE) in the drill core commonly occur at trace levels and within heterogeneous hosts, making rapid, phase‑aware mapping a bottleneck for exploration. We show that time‑of‑flight secondary ion mass spectrometry (ToF-SIMS) provides a fast, surface‑sensitive route for locating and characterizing REE enrichments and their anion cluster associations directly on polished core sections. Large‑area surveys (millimeter scale, ~30 min per field) quickly identify hotspots of Y and various light REEs; higher resolution imaging resolves colocalization with phosphate-derived groups (e.g., PO₂⁻) and discriminates REE occurrence in apatite versus xenotime within altered rhyolite from Yellowstone. These results highlight ToF-SIMS’s complementary strengths—very low detection limits, high mass resolution for elemental and molecular ions, and multiscale imaging—relative to SEM/EPMA and XRF methods that struggle with REE line overlaps or bulk averaging. These capabilities make ToF-SIMS a powerful complement to conventional techniques for investigating trace REE distributions in geological cores.