Trace elements in cretaceous rocks of Manitoba

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Oddy, Richard William
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Trace quantities of copper, zinc, and molybdenum have been determined in the Cretaceous beds of Manitoba. The contents of the metals are in the ranges: copper, 2 to 78 p.p.m.; zinc 5 to over 400 p.p.m.; and molybdenum, less than 2.5 to 180 p.p.m. The results indicate an enrichment of molybdenum in the Cretaceous beds and it is suggested that adsorption of molybdenum from sea water by clay minerals and organic matter in the shales, and by clay minerals in the bentonites is responsible for the enrichment. In order for such extensive enrichment the sea water must have contained an abundance of available molybdenum and the likely source of the excessive molybdenum in the sea water is Precambrian rocks in the shield area to the east. The Cretaceous beds contain normal concentrations of copper and zinc but the bentonite layers contain much lower concentrations of copper and zinc than the interbedded shales. Molybdenum poisoning of cattle in Swan River Valley is the result of the abundance of molybdenum in the Favel beds from which the soils in the valley were derived.