Successive zoning of Al and H in hydrothermal vein quartz

Abstract

Electron microprobe and micro-FTIR (mFTIR) analyses of a quartz crystal from a hydrothermal vein reveal zoning in Al and H concentrations. The Al concentration ranges from 27 to 468 Al/10 6 Si, and the H concentration ranges correspondingly from 49 to 266 H/10 6 Si. The zoning profile reveals a positive correlation between Al and H concentrations. At low Al concentration ( 6 Si), the H/Al ratio is ~1.0 and the infrared spectra show strong bands due to Al-OH and very weak bands due to Li-OH. These results indicate that most of the charge imbalance resulting from Al 3+ substituting for Si 4+ is compensated by H. At an Al concentration >100 Al/10 6 Si, the ratio of H/Al drops to ~0.5 and the infrared spectra show absorption bands due to both Al-OH and Li-OH species. No other alkali ions were detected by microprobe analysis. These results suggest that a combination of H and Li are providing charge compensation in the more Al-rich zones. Replacement of Si 4+ by Al 3+ + H + ± Li + is the principal mechanism for the incorporation of these trace elements into the quartz structure.