Petrogenesis of the North Harper Creek uranium prospect

The North Harper Creek uranium prospect, Avery County, North Carolina, is located in the late Precambrian Wilson Creek Gneiss within the Grandfather Mountain window of the Blue Ridge province.

Host rocks consist of orthogneisses that have suffered both dynamothermal metamorphism and cataclastic deformation probably during the Taconic orogeny. The protolith consisted of quartz-rich granites, alkali-feldspar granites, and tonalites. Prograde metamorphism, coupled with the onset of cataclastic deformation, reached a maximum of . almandine grade producing cataclasites and cataclastic gneisses. Subsequent lowering of temperatures and continued cataclastic deformation under high fluid pressure retrograded the sequence forming chlorite at the expense of mica.

Previous authors have described two types of uranium emplacement; first as substitution within crystals of feldspars, micas, titanite, and zircon, and second as veins within the rock sequence. This study has shown that vein-type uranium mineralization is directly related to the deformation that produced the cataclasites. Uranium was probably transported as complexes from a deeper metamorphic source and deposited as uraninite. Upward movement of fluids enriched in U, CO. through zones of permeability produced by the cataclasis was responsible for uraninite deposition. It is suggested that as liquids migrated upward, gases were boiled off thus decreasing the stability of the uranyl-complexes. Uraninite was subsequently precipitated in veins with calcite, pyrite, pyrrhotite, and chalcopyrite. · Chlorite, or more probably, a pre-metamorphic precursor of chlorite was co-precipitated with the uraninite.