The uranium-silica-fluorine relation

Intimate association of pitchblende, coffinite and amorphous silica, with the absence of commonly recognized uranium reductants such as carbonaceous matter, clay or pyrite are being noted increasingly in micro-textural analytical investigations. Some occurences involve fluorite or fluorine. Recalling chalcedonic caps of fluorite deposits and recognizing the mobility of uranium halides, samples and descriptions of the uranium and thorium deposits were interrogated for the silica-fluorine association. Deposits ranged from high-temperature replacement disseminations, through veins and breccia pipes, to low-temperature impregnations of sandstone, and hot spring silica. The association was recognized in sufficient occurences to justify consideration of halogen transport as one possibility significant mechanism of uranium mineralization, particularly the mobility of uranous ions for which adequate mechanisms in the shallow environment have been wanting. Halogen transport is a possible mechanism for the original transfer of thorium and uranium from the mantle to become litophile. Once in shallow environment uranyl halogen transport appears simpler than uranous halogen transport. Silica need not have been derived from depth, but could have been leached from conduit walls by excess fluorine and carried as SiF4 gas along with UF4 or UF6. The referenced association could form by release of fluorine at deposition sites. Excellent adsorbing quality may make amorphous silica a significant fixant for later vagrant uranyl ions, but a reductant other than silica may be needed for uranous ions. (orig.)