ABSTRACT

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/lagoon system, consisting of strike-parallel barrier bar and associated small cuspate and bayhead delta sand 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 comprise several major dip-oriented fluvial systems containing bedload and mixed-load channel sands and assocaited crevasse splay, floodplain, and lacustrine facies.

Uranium was introduced into the sediments by coastward-migrating ground water and concentrated along mobile, Eh-defined hydrochemical boundaries. The volume, direction, and downdip extent of oxidizing ground-water 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 reflect the genetic facies framework of the host depositional system. Depositional patterns, subsequent ground-water flow geometry, and cross-stratal flux of extrinsic reductants (H2S and hydrocarbon gases) were also 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, dominantly occur at margins of major sand facies or along fault zones where flow patterns were disturbed and intrinsic or extrinsic reductants were most available. Understanding ground-water flow patterns within major coastal plain depositional systems will enhance predictive capability of both regional and local exploration programs.

1. Publication authorized by Director, Bureau of Economic Geology, The University of Texas at Austin

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