Migration of mantle-derived uranium and thorium within the crust
The three most readily apparent media for the transport of mantle-derived thorium and uranium to the crust are ultramafic and mafic magmas, alkaline undersaturated magmas, and volatiles. Each type constitutes a distinctive geologic and geochemical environment for the radioelements.
Mantle-derived magma has penetrated ocean basins along spreading ridges (Figs. 3, 5) and in plumes. Although irregularly distributed outwardly, the plumes appear to be controlled by regional tectonic features including lineaments and intersections. Along ocean ridges, mantle material intrudes more or less passively in a rising medium. Ocean-ridge magmas range widely in composition from olivine tholeiite to alkali basalt (Aumento, 1967), depending on the degree of partial melting of peridotitic or eclogitic mantle material rising beneath the ridge (Wyllie, 1971, p. 357-359). Most commonly, however, these magmas are tholeiites with very low uranium and thorium contents.
Figures & Tables
The uranium resource industry since the late 1960s has presented a paradox to those concerned with the growing energy shortage and the relative ability of uranium resources to respond to the need on a timely basis. This publication reviews the possible ways that uranium in the earth might be concentrated into economic deposits, and considers what industry should be able to expect from an exploration effort. Some of the chapters in this volume include: Fundamental sources of uranium and thorium; Mechanisms of uranium and thorium transfer to the crust; Shallow uranium mobilization processes; Geochemical distinction of uranium moneralization processes; and Oceanic migration history of uranium and thorium.