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Qualitative Uranium Analysis of Mississippian-Age High Gamma Carbonate, Bend Arch Region, Texas

Brian Crass
Dept. of Geosciences, Texas Tech University, Lubbock, Texas 79415, USA

Fifty-six (56) feet of core from a productive carbonate interval of Mississippian age in the Bend Arch region of north-central Texas has occasionally higher than expected gamma ray values. Interpretation of the full spectrum gamma-ray log would be attributed to significant shale components in some intervals. However, assaying of spectral gamma-ray logs suggests that the peaks in the gamma-ray values are caused by higher than expected uranium/potassium ratios. Ten core plugs were taken from throughout the core at the approximate intervals that coincide with highest and lowest gamma-ray activity. Aliquots from the core-plugs have been prepared for a sequential leeching procedure (Tessier et al, 1979) that is designed to strip heavy metals, including uranium, from a variety of mineralogical hosts. The initial leach will liberate exchangeable metals from clay and other secondary minerals. A second leaching step will quantify any role between gamma-ray activity and metals bound to carbonates. A third step will release metals associated with iron and manganese sulfides and oxides. Finally, metals that are bound to organic matter will be brought into solution, leaving a residual portion of silicates and other stable minerals. After each leaching step the concentration of uranium dissolved in solution will be measured by ICP-AES to qualitatively assess the portion of gamma-ray activity represented by each mineralogical category. Results from the Tessier procedure will be compared to whole-rock uranium abundances determined for individual samples by X-ray fluorescence spectrometry. This study will determine if a relationship between high uranium/potassium ratios, mineralogical species, and portion of gamma-ray activity not associated with shale minerals exists and may help guide future field development.


AAPG Search and Discovery Article #90164©2013 AAPG Southwest Section Meeting, Fredericksburg, Texas, April 6-10, 2013