Abstract: Uranium Host Depositional Systems of Texas Gulf Coastal Plain--Influence of Genetic Facies on Mineralization Pattern
W. E. Galloway
Significant reserves of uranium have been delineated in the Jackson, Catahoula, and Oakville Formations of the south and central Texas coastal plain. The Jackson includes (1) a major barrier bar-lagoon system, consisting of strike-parallel barrier bar and associated small cuspate and bayhead delta sandstone units, which lies south of the San Marcos arch, and (2) a fluvial-dominated delta system consisting of dip-oriented fluvial and distributary channel, and delta-margin sands, which infilled the Houston embayment northeast of the arch. The overlying Catahoula and Oakville formations compose several major dip-oriented fluvial systems containing bed-load and mixed-load channel sandstones and associated crevasse splay, flood-plain, and lacustrine facies.
Uranium was introduced into the sediments by coastward migrating groundwater and concentrated along mobile, Eh-defined (oxidation potential) hydrochemical boundaries. The volume, direction, and downdip extent of oxidizing groundwater flux was directly affected by bulk permeability, facies heterogeneity, and trend and degree of vertical interconnection of permeable elements within each system. Consequently, the regional distribution, as well as local geometry, trend, internal complexity, and size of individual uranium deposits, reflects the genetic facies framework of the host depositional system. Depositional patterns, subsequent groundwater flow geometry, and cross-stratal flux of extrinsic reductants (hydrogen sulfide and hydrocarbon gasses) also were affected by major strike-parallel zones of faulting and by local piercement salt domes. Relatively shallow mineralization fronts, which have been the objective of exploration to date, oc ur predominantly at margins of major sandstone facies or along fault zones where flow patterns were disturbed and intrinsic or extrinsic reductants most available. Understanding of groundwater-flow patterns within major coastal-plain depositional systems will enhance predictive capability of both regional and local exploration programs.
AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas