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Investigation of Regional Geohydrology South of Great Slave Lake, Canada, Utilizing Natural Sulphur and Hydrogen Isotope Variations

K.U. Weyer, H.R. Krouse and W.C. Horwood
Paper from "Isotope Hydrology 1978", Vol. I.
International Atomic Energy Agency, 1979

1979, K.U. Weyer, H.R. Krouse and W.C. Horwood



Abstract

The well-defined topographic, geological, and orographic setting in the area south of Great Slave Lake, in Canada's North-West Territory (N.W.T.), is favourable for a meaningful investigation of the local and regional groundwater flow systems in the area of the Mississippi Valley type lead-zinc deposits at Pine Point. Chemical and isotope (δ34S, δD) investigations have provided supporting evidence for conceptual models of groundwater flow. The range of the SD values encountered (-111 to -205 SMOW) indicates that the hydrodynamic systems convey meteoric waters. Differences in δD values of water samples were used to elucidate the hydrological relationship between groundwater and a major river in a karst area. The ore bodies at Pine Point are engulfed in a reducing hydrosphere. Sulphur species, derived from gypsum layers by regional groundwater flow, are instrumental in maintaining the reducing conditions. There is evidence that the reduction of sulphate to sulphide is caused by bacteria. Microbiological sulphate reduction, rather than isotopic exchange processes, is also responsible for shifts of measured δ34S values in dissolved sulphates. After correction for those shifts, four different sources for dissolved sulphate were identified. In addition to supporting the conceptual model of regional groundwater flow in this area, the isotopic data also help to delineate hydrological features on a more local scale.

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