Abstract
Core samples of all members of the Elk Point evaporite sequence, Saskatchewan Subbasin, from basal shale to potash-rich and halite-rich members, have been analyzed for copper, lead, and zinc. The highest concentrations of all three metals are in the basal Ashern shale, the overlying Winnipegosis dolomite, and anhydrite layers in the Prairie Evaporite. Copper and lead contents are related to the contents of water-insoluble materials in various members of the sequence, whereas zinc shows no such relation.Total copper present in the evaporite sequence appears to be much less than would be supplied from sea water entering the basin, if the metal content of Devonian sea water were comparable to that of modern sea water. It is thus possible that copper was concentrated in residual brines. The contents of lead and zinc in the sequence, however, are such that concentration of the two metals in residual brines appears unlikely.The results indicate that an evaporating basin provides an effective mechanism for concentrating the three metals and that the amounts of metals present in a major evaporite sequence may be very large. Such a sequence could be an important source both of metals and of chloride-rich brines capable of transporting the metals to evaporite-associated deposits such as cupriferous shales and Mississippi Valley-type deposits. Chloride-rich brines could have been generated at three stages in the history of the Saskatchewan Subbasin: during compaction of the sediments; during diagenesis, when large volumes of water would be released by conversion of gypsum to anhydrite; and during postdepositional circulation of ground waters.
