Scanning electron microscopy (SEM) study of authigenic minerals in the Westwater Canyon Member of the Morrison Formation (Late Jurassic) indicates that mineral compositions vary within and adjacent to sandstone-type uranium deposits. Montmorillonite is the dominant clay mineral in the reduced ground downdip of the orebody; chlorite is enriched in the ore zones; and kaolinite and altered montmorillonite dominate in the "oxidized" ground updip of the ore. Our data also suggest that clay minerals, not pyrite or hematite, may locally be the iron-bearing species of importance.

Although it is not possible to make positive identification of organic materials in SEM photomicrographs, materials deduced to be organic in nature postdate the beginning of authigenic clay formation. This implies that these materials may be carriers of uranium in the groundwater system from which the ore deposits precipitated.

Identification of these patterns of clay-mineral alteration and the role that organic materials may play as transporting media may significantly alter our exploration techniques. These patterns may be especially useful tools in areas where the orebodies are known to be removed from the iron species redox interface.

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