Uranium is found in widespread occurrences and several commercial concentrations in volcanic rocks of western North America. Mineral exploration and estimates of potential resources in this frontier geologic environment have been hampered by the lack of a viable genetic model. Geologic, geophysical, and geochemical aspects of numerous deposits are compared and synthesized, and a genetic model is presented that integrates these features. The model includes uranium migration during caldera evolution, and subsequent ground water and diagenetic effects. The comparison and model are enhanced by the availability of large chemical data sets for several example areas, and statistical properties are discussed.

Exploration for these deposits should involve close attention to detailed volcanic geology, rock permeability, and trace element chemistry. Significant deposits exist in the intrusive, intra-caldera, outflow, and volcaniclastic environments. The variety of potential host environments is large, and this has presented a bewildering array to the explorationist and to the commodity specialist. Lithogeochemical exploration proves to be more successful than stream sediment studies.

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