Regional Diagenetic Trends and Uranium Mineralization in the Morrison Formation Across the Grants Uranium Region
Published:January 01, 1986
Paula L.. Hansley, 1986. "Regional Diagenetic Trends and Uranium Mineralization in the Morrison Formation Across the Grants Uranium Region", A Basin Analysis Case Study: The Morrison Formation, Grants Uranium Region, New Mexico, Christine E. Turner-Peterson, Elmer S. Santos, Neil S. Fishman
Download citation file:
Early diagenesis in the Morrison Formation resulted in the formation of the world’s largest sandstone-hosted uranium deposits. Distribution of diagenetic alterations in ore-bearing sandstones of the Westwater Canyon Member suggests that these alterations were strongly influenced by pore waters expelled from fine-grained units in the overlying Brushy Basin Member. A moderately high pH created by hydrolysis and dissolution of volcanic ash enabled these fluids to dissolve and mobilize humate in lower Brushy Basin and upper Westwater Canyon sediments. When these fluids mixed with connate water in sandstones of the middle to lower parts of the Westwater Canyon Member, tabular uranium orebodies were formed. A strong diagenetic overprint related to Laramide tectonism and late Tertiary oxidation obscured early alteration patterns and resulted in the local redistribution of primary uranium ore and dissolution of previously formed authigenic cements.
Similarities between ore mineralogy and postdepositional alterations in the Morrison Formation of the Grants uranium region and in the Morrison of the northern part of the Colorado Plateau suggest that these ore deposits have a common genesis. The apparent replacement of the organic matrix in the Grants region by chlorite and locally by a chlorite-coffinite mixture in ore zones suggests that, where a chlorite- dominated assemblage is now present, carbonaceous uranium ore once existed. This observation leads to the hypothesis that the organic-carbon-rich, locally chlorite- bearing Grants uranium ore and the organic-carbon-poor, chlorite-rich ore of the northern Colorado Plateau are end members of the same mineralization process.
Figures & Tables
A Basin Analysis Case Study: The Morrison Formation, Grants Uranium Region, New Mexico
This volume summarizes results of a U.S. Geological Survey multidisciplinary basin analysis research effort that encompasses all aspects of the geology of the Morrison Formation in the Grants uranium region, located in the San Juan basin of northwestern New Mexico, U.S.A. Tectonic, stratigraphic, sedimentologic, structural, petrographic, mineralogic, geochemical, and resource studies are drawn together to provide a geologic synthesis of the Jurassic Morrison Formation, the main uranium host rock in the region, and to provide background data for the formulation of genetic models for ore genesis. The result is a compendium of 21 papers that incorporates many recent and significant advances in our understanding of factors that favored uranium mineralization in the Morrison, and several new genetic models that incorporate these recent advances. The basin analysis approach used here has proved fruitful in that ore genesis can now be viewed in the context of the evolution of a sedimentary basin rather than as an isolated event. This approach to ore genesis has application not only to uranium deposits but also to all sediment-hosted ore deposits.