TRACKING GROWTH EVOLUTION IN CONTEMPORANEOUS HYDROTHERMAL QUARTZ: HIGH RESOLUTION FTIR CHARACTERIZATION OF CRYSTALS SAMPLED AT WINDGäLLENHüTTE, SWITZERLAND

The spatial distribution of chemical impurities in hydrothermal quartz crystals document the evolution of their host hydrothermal fluids and offer potential insights into their syn and post-crystallization thermal histories. Few specifics are known regarding the growth of hydrothermal quartz and its relation to external factors. Four distinct growth regimes have been identified across the central Swiss Alps by Mullis and colleagues (1994) and offer an ideal setting for examining the effect of external variables on the uptake of hydrous impurities in vein quartz. We present infrared spectroscopic analyses from seven crystals extracted from the classic alpine collecting locality at Windgällenhütte, Switzerland. The concentrations of hydroxyl-bearing species, including LiOH, AlOH, and molecular water, have been measured using micro-FTIR spectroscopy. Analyses utilize 100 µm spot sizes across polished 1-mm thick crystal wafers to obtain the high spatial resolution required for detailed crystal impurity mapping.

Our results show significant variations in impurity abundance across r and z growth sector zones and allow us to chart the morphologic evolution of individual crystals. Compared to quartz crystals from other localities in the Swiss Alps, Windgällenhütte crystals show elevated concentrations in AlOH, LiOH, and molecular water. LiOH and AlOH concentrations are generally twice that of molecular water, with LiOH/AlOH ratios decreasing from the base towards the terminus. Also evident in every crystal are pronounced diffusion profiles documenting syn and post-crystallization diffusive loss from the edges of crystals. These data offer quantitative insights into the timescales of growth and thermal exposure.