THE ROLE OF BASAL FREEZE ON AND SECONDARY MINERAL PRECIPITATION IN GLACIER MELTWATER CHEMISTRY

Within the glacier geochemistry literature, there is considerable debate as to whether the proglacial water chemistry is dominated by the quickflow or delayed drainage system, the amount of mixing between the two, and the importance of post mixing weathering reactions. Regardless, the water chemistry is often explained solely by dissolution reactions. Alternatively, we present data to show the importance of secondary mineral precipitation in the delayed drainage system as a means of controlling the observed proglacial water composition.

Hydrochemical investigations were carried out for a polythermal surge-type glacier on granodiorite bedrock situated in the Donjek Range of the St. Elias Mountains, YT. In borehole and proglacial waters, we observe a substantial enrichment of Cl^-, indicative of either meltwater refreezing, or mixing of dilute water with a water source that has undergone substantial refreezing. This is supported by field evidence of debris rich basal ice at the terminus, resulting from either regelation or basal freeze on processes. Data for the chemical composition of the meltwaters are presented on log activity plots to show the possibility of stable secondary minerals and precipitates such as laumontite, illite/muscovite, and calcite. These minerals are present in significant quantities in the borehole and proglacial waters, along with trace amounts of montmorillonite, and ankerite/dolomite. No secondary minerals or precipitates were observed in the bedrock samples. Together, the mineralogy and water chemistry data show the importance of meltwater refreezing as a driver of precipitation reactions.