Nine cores from a sedimentary-type uranium orebody of the upper Jackson Formation, Karnes County, Texas, were studied to determine the stratigraphy and the mineralogy in relation to the uranium distribution, and to provide guidelines for further exploration and/or exploitation. The uranium concentration ranges from 1.4 to 6,000 ppm in approximately 200 samples, as determined by delay neutron counting.

The orebody is generally a fine-grained, gray, well-sorted, arkosic sandstone that is enclosed in finer grained, poorly sorted lagoonal or paludal mudstone or lignite. The depositional environment of the orebody is presumably a beach-barrier-bar sequence with its northeastern end delineated by a downward-cutting fluvial system.

The bulk mineralogy of the ores consists primarily of quartz and feldspar with minor amounts of biotite, muscovite, augite, clinoptilolite, and very minor amounts of hematite, pyrite, and coffinite. The clay analysis of the less than 2 µm fractions reveals a preponderance of smectite with very minor amounts of kaolinite and illite.

The high concentration of uranium in the cores is generally associated with a high concentration of clays, zeolites, and/or carbonaceous material. Additionally, uranium concentration usually increases with a decrease in size fraction. Since smectite dominates the clay mineral assemblage in the ore, the expandable and absorptive smectite could be a significant factor in uranium mineralization.

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