Rapid, inexpensive evaluation of the potential of frontier areas for epigenetic uranium deposits can be conducted using functional source-rock analysis analogous to that employed in the petroleum industry. Association of uranium-rich volcanic glass with nearly all such deposits suggests that their uranium came from glass. Concentration of uranium in ores is about 10³ times that in glass-rich sources, so great volumes of depleted rock should mark favorable areas.

Fresh rhyolite glass contains uranium adsorbed on shard surfaces, soon washed off, and 5 to 10 ppm internal uranium, which is released when the glass converts to a crystalline assemblage. Only under certain circumstances does released uranium migrate. Studies conducted in south and west Texas and in Nevada on volcanic rocks and sediments that originally contained abundant volcanic glass lead to the following conclusions: conversion in soil or by very early diagenesis, and low temperature conversion of glassy ash flows to clay release uranium for migration; high temperature conversion by divitrification or vapor phase crystallization and diagenesis in open hydrologic systems trap uranium near its site of release. Structures and textures produced during each of these processes are disti ctive and can be recognized in the field or in thin section. Furthermore, the processes probably produce distinctive chemical effects other than depletion of uranium. Functional source rock exploration for uranium consists of field, petrographic, and geochemical detection of depleted rock that altered in a favorable fashion. Evaluation of likely migration routes; geologic, geochemical, and radiometric exploration for traps; and drilling programs can then be concentrated in the most favorable areas.

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