Uranium geochemistry in geopressured-geothermal aquifers of the U.S. Gulf Coast

Formation water from U.S. Gulf Coast geopressured-geothermal sandstone aquifers has been analyzed to determine the geochemistry of uranium in these systems. Results of chemical analyses and chemical equilibrium modeling indicate the formation waters are in equilibrium with uraninite (UO2) and coffinite (USiO4). The 234U/238U activity ratios in the formation waters range from 1.06 to 1.69. These isotopic data suggest that at formation temperatures uranium is continually reequilibrating chemically and isotopically between water, a solid phase of either UO2 or USiO4 and a component of 234U supplied to solution from the aquifer matrix material by alpha recoil processes. (author)