Petrology of Clay Minerals in the Subsurface Morrison Formation Near Crownpoint, Southern San Juan Basin, New Mexico: An Interim Report
Published:January 01, 1986
C. Gene Whitney, 1986. "Petrology of Clay Minerals in the Subsurface Morrison Formation Near Crownpoint, Southern San Juan Basin, New Mexico: An Interim Report", A Basin Analysis Case Study: The Morrison Formation, Grants Uranium Region, New Mexico, Christine E. Turner-Peterson, Elmer S. Santos, Neil S. Fishman
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Preliminary examination of the distribution, texture, and chemical composition of clay minerals in the Morrison Formation suggests that the sandstone of the Westwater Canyon served as a conduit for potassium- and aluminum-rich, possibly warm, fluids that moved updip from the center of the basin toward the basin margin, giving rise to mineral zonation within the sandstone over a lateral distance of approximately 35 km.
The observed patterns include: (1) Pure smectite occurs as grain coatings in the Westwater Canyon Member in the shallowest core; this smectite is texturally similar to mixed-layer illite-smectite found in the deeper cores. (2) Expandability of the illite-smectite decreases toward the center of the basin and is more expandable near the upper and lower sandstone-mudstone contacts than at the center of the sandstone. This illite-smectite is generally highly ordered and frequently exhibits well-defined superlattice peaks. (3) Iron-rich chlorite occurs texturally on top of the smectite and illite-smectite and therefore must be later. (4) Smectite in the overlying Brushy Basin Member and in the underlying Recapture Member remains 100% expandable through the area analyzed. (5) Kaolinite, the latest clay mineral to form, is most abundant in the middle cores, decreasing in the shallow cores and in the deeper cores.
The fluid movement event probably occurred subsequent to the basin formation during Laramide time. Diagenetic reactions are more extensive in the deeper sections, near the basin center, and have obliterated some chemical and mineralogical relationships which are still observable in the shallower cores.
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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.