Geothermal analyses of the breccia pipes (Arizona) - Organic matter, fluid inclusions, fission tracks and computerized modeling

Geothermal characterization of sedimentary uranium deposits has frequently been carried out using geological data (burial, erosion, faulting...). Organic matter has also been used as a geothermometer but, considering its involvement in oxidation, the chemical composition of oils, coals or kerogens is not always representative of the thermal maturation. More recently fluid inclusions have been analyzed by microthermometry in several sedimentary deposits. Nevertheless, problems concerning leakage, necking or reequilibration phenomena can disturb the geothermal diagnosis. Furthermore organic matter gives an integration of the time-temperature effects while fluid inclusions represent temperature peaks. This is why a complete geothermal study including the analyses of fission tracks in apatite has been carried out on the Arizona pipes of the Grand Canyon region (Arizona). Results have been compared to geological data and computerized on two thermal modeling programs at the Institut Francais du Petrole (organic matter) and at the C.R.E.G.U. (fission track). Brecciated rocks inside the pipe throat and samples from undisturbed formations have been analyzed. Interpretations give important data on the maximum temperatures, thermal history, time of erosion in this uraniferous area. (author)