Regional geochemistry of uranium as a guide to deposit formation

Abstract

Geochemical maps of northern Scotland prepared by the Institute of Geological Sciences show the distribution of uranium based on the analysis of stream sediment and water samples by the delayed neutron method. These maps not only indicate the relative concentration of the element in the principal tectonic units but also identify areas of uranium mineralization in the bedrock. Evaluation of the geochemical maps in the light of known geophysical and geological data suggests that both the Caledonides of northern Scotland and the Hebridian craton to the west of the Caledonian orogenic front are underlain by a thick layer of basement depleted in uranium and other incompatible elements. Enrichment of uranium has occurred only where the basement has been disrupted either as a result of magmatism or by deep faulting. Thus, most granites in the area surveyed contain only average abundances of U, but large values characterize certain early Proterozoic and Caledonian granites which appear to have derived at least part of their substance from the mantle. Uranium enrichment in the non-marine Old Red Sandstone overlying the metamorphic Caledonides is most marked in the vicinity of deep faults which are thought to have separated areas of emergence from subsiding sedimentary basins in Old Red Sandstone times. The style of mineralization thus reflects both regional and local factors.