Geochemical distinction of uranium mineralization processes
The trace-element content of host sandstones and uranium orebodies has been investigated (Shoemaker, 1959), but their relative abundance was not found to be unusually high. Elements abundant enough to suggest a distinctive family of elements preferentially associated with low-temperature uranium mineralization of sandstones were usually attributed to sedimentation. However, the writer early recognized that, if specific uranium mineralization processes were to be proved fundamentally sedimentary, tectonic, magmatic, or secretionary, the relationship would have to be established through the associated elements, many of which, unlike uranium, cannot exist easily in the great variety of environments. By establishing empirically the families of elements that characterize the alteration and metallization phases of mineralization by fluids of different and less questionable origins, the one or more mechanisms specifically responsible for a deposit or district may be identified. Such identification would be an invaluable aid to exploration, which to date has been based largely on genetic models.
The element suite of high-temperature epigenetic uranium mineralization is only beginning to be studied because of the emerging importance of economic deposits of this type (e.g., Rössing), but some elements which are mobile only at high temperature are readily recognizable, including thorium, rare earths, and zircon. The intermediate-temperature suite was long ago established to include Co, Ni, Ag, and As and has not been questioned since the 1940s. However, recently the possibility that uranium was unusual among Co-Ni-Ag deposits on a worldwide basis was recognized (Badham et al, 1972), and the writer (Gabelman, 1974) advanced the possibility that two independent suites may be represented.
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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.