Chemical Weathering of Smectitic Sulphide-Mineral- Bearing Unconsolidated Surficial Sediments in South- Central Alberta, Canada

摘要

This study used a mass-balance simulation approach in conjunction with geochemical, mineralogical, thermodynamic and isotopic constraints, to assess the origins of NaSO_4(±HCO_3) type groundwater and springwater associated with smectitic sulphidemineral- bearing unconsolidated surficial sediments and the underlying Paskapoo Formation in south-central Alberta. Results indicate that alteration of albite to kaolinite and alteration of kaolinite to Na-smectite are the primary controls on dissolved Na and SiO_2 concentrations in groundwater and springwater. Concentrations of dissolved Ca and Mg are controlled by reactions involving carbonate minerals and possibly cation exchange. Dissolved SO_4 is generated primarily through oxidation of pyrite. Most H~+ generated by oxidation of pyrite is consumed in aluminosilicate alteration reactions. The carbon isotopic composition of CO_2 gas required in mass-balance simulations suggests the presence of an isotopically heterogeneous environment with respect to ~(13)C. This apparent isotopic heterogeneity may result from the presence of varying fractions of atmospheric and microbially respired CO_2.