Abstract: Measurement of Rn222 and He4/Ar36 Ratios in Soil Gas Overlying Two Uranium Ore Deposits
Donald F. Schutz
Soil-gas sampling has been performed under sponsorship of the Energy Research & Development Administration (ERDA) at two sites of known uranium mineralization in Wyoming, the World nuclear site 140 mi (220 km) southwest of Casper and the Irigaray Ranch 100 mi (160 km) north of Casper. Samples were taken from drill holes 10 ft (3 m) deep using a pneumatic packer sealed with drilling mud. A vacuum/compressor was used to take 25 100-1 STP samples at each site. Five locations at each site were resampled to determine reproducibility of the sampling technique. Rn222 concentrations were measured in a field laboratory and verified by recounting samples at the home laboratory. Values range from < 1 to 607 pCi/l at the Irigaray Ranch site and from 89 to 25,400 pCi l at Wold nuclear site.
The Rn222 concentrations at Irigaray Ranch do not correlate well with the orebody position. At the Wold nuclear site there is some tendency toward higher values above the ore deposit but the variability precludes a clear distinction.
He4/Ar36 ratios are being measured to test the hypothesis that He4 emanation from uranium mineralization can be an important diagnostic tracer in soil gas overlying prospective deposits. The He4 is referenced to Ar36 to eliminate apparent He4 concentration variations which result from soil-gas changes not related to He4 production. Measured He4/Ar36 ratios do not show any significant difference from atmospheric ratios. As indicated by calculations, the residence time of soil gas at the sampling depth of 10 ft (3 m) is too short to allow accumulation of He4 sufficient to modify the He4/Ar36 ratio for the areas studied.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC