PRECIPITATION OF MINERALS BETWEEN DETRITAL QUARTZ AND QUARTZ OVERGROWTHS IN SANDSTONES

In the uranium-vanadium bearing sandstones from the Morrison Formation (Colorado Plateau, U.S.A.), coffinite and vanadium clays are located at the interface between detrital quartz grains and quartz overgrowths. Tyuyamunite, which results from recent alteration of uranium-vanadium minerals, also occurs below the quartz overgrowths. Effective porosity at the core-overgrowth interface is demonstrated by resin impregnation. Etching experiments using dilute HF indicate that the detrital grain-quartz overgrowth interface is preferentially corroded. Coffinite and vanadium clays may have precipitated by dissolution/replacement along the detrital grain-overgrowth interface. The interface between detrital grain and overgrowths may therefore be a site for the creation or destruction of microporosity in sandstone.