As-rich florencite-(La) inclusions in euclase and quartz from hydrothermal veins in Abaíra, Bahia, Brazil: evidence from EPMA, single-crystal X-ray diffraction and Raman spectroscopy

As-rich florencite-(La) occurs as microscopic inclusions within pink-orange euclase and quartz from auriferous hydrothermal veins in Abara, Bahia State, Brazil.Electron probe microanalysis indicates a predominance of phosphate over arsenate at the tetrahedral site.Single-crystal X-ray diffraction reveals slight unit-cell expansion in the As-rich variety.Raman spectroscopy detects both phosphate-and arsenate-related vibrational modes, along with weak OH-stretching and diffuse bands attributable to hydrogen-bonded species, indicating mainly structural hydroxyl with possible contributions from weakly bound HO.The mineral likely formed during a late hydrothermal stage involving progressive REE enrichment and oxidising, acidic fluid conditions.These findings emphasise the structural sensitivity of florencite-(La) to tetrahedral-site substitutions and hydrogen bonding, and its potential as a sensitive tracer of REE-enriched hydrothermal systems.