An Examination of Metamorphic Uranium Occurrences in Coosa County, Alabama

Abstract

Coosa County, Alabama, is host to one or more presumably metamorphosed uranium occurrences of unknown size or grade. The exact location, size and mode of emplacement of each uranium occurrence is currently unknown. This thesis expands on existing knowledge of these occurrences through fieldwork, and geochemical and petrographic studies. Geochemical maps document that most of the anomalous uranium occurrences are within Section 30 T. 23 N, R. 18 E, overlapping with radiometric contour highs reported in surveys conducted during the 1970’s. Geochemical analyses document concentrations of barium and vanadium within anomalously green micas (mean values of 5,894.50 and 3,470.10 ppm respectively). Microprobe analyses indicate a decrease in uranium and vanadium in the micas with alteration (mean values of 1.50 to 1.07 and 0.92 to 0.27 weight percent, respectively). Uranium is present in small quantities within the anomalously green mica, but higher abundances are indicated by individual whole-rock samples (mean values of 7.51 and 4.89 ppm respectively). The likely prototype for the uranium occurrences is similar to the occurrences in the Colorado Plateau or the Mauch Chunk Formation in the eastern United States. Recrystallized micas and quartz indicate temperatures of ~400°C, and brittle fractures within quartz indicate temperatures >300°C suggesting two stages of metamorphism, the first of which was sillimanite grade and occurred during the Acadian Orogeny. The rocks underwent retrograde metamorphism occurring during the Alleghanian Orogeny at which time the uranium and vanadium moved from the muscovites and into other unidentified sites (such as minor shear zones) within the host rock.