Open Session - SWISS GEOSCIENCE MEETINGs

Statistical analysis of the composition data shows that Ca-HCO 3 -SO 4 and Na-K-Cl are strongly correlated. Three chemical types
of water can be distinguished: Mg-HCO 3 , Ca-SO 4 and Ca-HCO 3 . The calculation of saturation states with phreeqc shows that
all surface waters are undersaturated with respect to all relevant minerals.
A model for the hydrogeochemical evolution has been set up to estimate the contributions of the various rock-forming minerals
to the composition of the waters. It shows that: A) The dominant source of solutes is the dissolution of carbonate
minerals. B) Sulfate originates mostly from oxidation of sulfide minerals (pyrite and others). C) Two reaction equations relate
the dissolution of the most reactive minerals to the observed water compositions. These are (1) Cal + Py + Chl + Pl + Ms + Qtz
= Kao + Hem + Water and Cal + Sd + Py + Ab + Chl + Ms + Qtz = Kao + Hem + Water. D) Water compositions can be represented
and characterized by the proportion of the minerals that are needed to be dissolved to create the observed water composition.
The computed models are shown as pie charts in Fig. 1 and they are related to the background geology of the sampling
area.
Fig.1: Hydrogeochemical models and background geology of the Zermatt-Matterhorn area. The models show that the composition of the
surface waters is controlled by the geology (dominant lithology) of the catchment.
REFERENCE:
Brown G. H., 2002: Glacier meltwater hydrochemistry, Applied Geochemistry, 17, 855-883.
Collins, D. N.,1979: Quantitative determination of the subglacial hydrology of two alpine glacials, Journal of glaciology, 23,
347-361
Drever, J.I., & Zobrist, J., 1992: Chemical weathering of silicate rocks as a function of elevation in the southern Swiss Alps,
Geochimica et Cosmochimica Acta, 56, 3209-3216.
Tranter M., Brown, G.H., Hodson, A., & Gurnell, A.M., 1996: Hydrochemistry as an indicator of subglacial drainage system
structure: a comparison of Alpine and Sub-Polar environments, Hydrological Processes, 10, 541-556.
White, A.F., & Blum, A.E., 1995: Effects of climate on chemical, weathering in watersheds, Geochimica et Cosmochimica
Acta 59(9), 1729-1747.
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Symposium 2: Mineralogy-Petrology-Geochemistry