Abstract: Abstract: Relations Among Depositional System, Groundwater-Flow History, and Origin, Migration, and Concentration of Uranium--Catahoula Formation, Texas Coastal Plain

William E. Galloway

The Catahoula Formation is a host for major known reserves of uranium ore and is the target of extensive exploration in the Texas coastal plain. Regional genetic facies analysis shows the Catahoula to consist of two principal fluvial systems. The Gueydan fluvial system of South Texas consists of low sinuosity, bed-load to mixed-load, channel sandstones and gravelly sandstones interbedded with ash-rich crevasse and flood-plain facies. Coarse material was derived from erosion of volcanic debris in Trans-Pecos Texas; ash was derived from explosive eruptive centers in western Mexico. The Chita-Corrigan fluvial system of East Texas contains deposits of several sinuous to meandering, mixed-load, channel complexes surrounded by extensive crevasse splay, flood-plain, and lacustri e facies. Sands were derived from nonvolcanic sources, but airfall ash is abundant.

Analysis of trace-uranium content of ash-derived mudstones indicates early mobilization of uranium in depositional environments characterized by subaerial leaching and soil formation. Solubilized uranium entered a well-integrated, semiconfined groundwater flow system in areas of groundwater recharge and moved coastward down the regional hydrodynamic gradient. Primary controls on the geometry of groundwater flow and total flux through a particular area include (1) the aggregate permeability, degree of interconnection, and orientation of aquifer sandstones (determined by the depositional system); (2) the distribution of syndepositional fault zones (which affect both facies distribution and later groundwater flow geometry); and (3) the geographic position of recharge and discharge areas. The areal extent, geometry, and uranium content of alteration fronts, in turn, reflect the geometry and flux of the groundwater flow system at the time of mineralization. Postmineralization diagenetic alteration of host sandstones and geologic relations suggest that Catahoula mineralization patterns were established soon after deposition in a semiconfined aquifer; subsequent remobilization and migration of uranium have been limited.

AAPG Search and Discovery Article #90969©1977 AAPG-SEPM Rocky Mountain Sections Meeting, Denver, Colorado