Effects of radon in drill holes on gamma-ray logs

Economic Geology
By:  and 



Drill holes in uranium deposits in the Todilto limestone of Late Jurassic age near Grants, New Mexico, do not yield duplicate gamma-ray logs when probed at different times; some logs show equivalent uranium greatly in excess, in thickness and grade, of the chemical and laboratory radiometric analyses. Radon and its daughter products principally cause the discrepancies. Experimental work was undertaken by the writers to learn the relations of the radon to the uranium deposits and its behavior under different physical conditions. The work is based on the interpretation of about 600 gamma-ray logs, taken from 480 drill holes.Abnormally high amounts of radon, referred to here as contamination, ranged from barely detectable amounts to amounts that emitted as much radiation as ore-grade material. Most contaminated holes were in the higher-grade ore, and the contamination increased with elapsed time after drilling. Geologic conditions favorable for contamination by radon and its daughter products in drill holes are: proximity to uranium deposits and fractured or highly permeable rocks above the water table. Most drill holes can be decontaminated by blowing them out with compressed air or filling them with water. Water, however, tends to reduce the thickness-times-grade figures below the amounts determined in air.

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Publication type Article
Publication Subtype Journal Article
Title Effects of radon in drill holes on gamma-ray logs
Series title Economic Geology
DOI 10.2113/gsecongeo.52.4.438
Volume 52
Issue 4
Year Published 1957
Language English
Publisher Society of Economic Geologist
Description 18 p.
First page 438
Last page 455
Country United States
State New Mexico
Other Geospatial Near Grants
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