Aquifer mineralogy and natural radionuclides in groundwater : the lower Paleozoic of central Texas /
Water-mineral interactions in an aquifer can give rise to high levels of radium and radon in ground water. An understanding of aquifer mineralogy is therefore essential to determine the sources of natural radionuclides and design possible means for improving water quality. Anomalous radium and rad...
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1995.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=742744811&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Water-mineral interactions in an aquifer can give rise to high levels of radium and radon in ground water. An understanding of aquifer mineralogy is therefore essential to determine the sources of natural radionuclides and design possible means for improving water quality. Anomalous radium and radon concentrations have been detected in ground water produced from the Cambrian Hickory and Cap Mountain aquifers in the Llano Uplift area, central Texas. This study examines cored aquifer rock samples, focusing on the abundance, distribution, and nature of occurrence of minerals containing uranium and thorium, parent nuclides of radium and radon. The Hickory consists of a coarse-grained sandstone lower submember, a calcareous sandstone interbedded with siltstone middle submember, and a fossiliferous and hematitic sandstone upper submember, with thin shale laminae throughout. The Cap Mountain is a sandy Limestone, containing shale laminae and intraclasts. From sediment textures, sedimentary structures, and bedding sequence, the Hickory and Cap Mountain were possibly deposited in fan-deltas to shallow marine environments. Detrital materials are composed of 77 % quartz, 19 % feldspars, and 4 % lithic fragments, and are classified as subarkose. Accessory minerals average less than I %. Authigenic minerals, primarily carbonate, clay, and Fe-oxide minerals, make up 18 % of the bulk rock. Porosity is of secondary origin. Analysis of uranium in 128 samples by delayed-neutron counting shows an average concentration of 3.8 ppm. Shaly samples generally contain significantly higher uranium. Gamma-ray analysis of thorium in 21 samples yields an average of 13.7 ppm. The concentrations of uranium and thorium are similar to those of the underlying Precambrian granites, from which much of the sediments were derived. Fission-track imaging shows that uranium occurs predominantly in: (1) phosphatic fossil fragments and intraclasts, especially in the Cap Mountain; (2) thin shaly laminae abundant in the Hickory; (3) authigenic minerals including hematite and clay minerals, also common in the Hickory; and (4) detrital accessory minerals. Mobilization of uranium and its decay products by ground water can account for the radium and radon in the produced water, particularly from intervals where there are high concentrations of shaly laminae, phosphatic materials, or hematitic cement. |
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| Item Description: | Vita. "Major Subject: Geology". |
| Physical Description: | xii, 126 leaves : illustrations, maps ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |