Abstract: Helium Detection in Uranium Exploration

R. H. De Voto, R. H. Mead, L. E. Berquist, J. P. Martin

Extensive test work over known uranium deposits in the Powder River basin, Wyoming, with a portable helium-detector mass spectrometer has observed the following general facts about helium in soil gas and the atmosphere: (a) the helium content in the atmosphere (at ground level) is not constant, and ranges from 5.04 to 5.30 ppm over short periods of time and from spot to spot; (b) helium in soil-gas measurements is influenced strongly by temperature and soil-moisture variations; (c) a diurnal variation of helium content in the soil gas of 100 to 250 ppb occurs at every location. During the daylight hours (8 A.M. to 9 P.M.), the helium content of soil gas is lower (often 100 to 200 ppb lower) than the helium content in the atmosphere; during the night, the helium content in soil gas is equal to or slightly higher than in the atmosphere.

Thus, in an exploration survey, soil-gas samples should be collected as near to the same time as possible over an area, to eliminate the changing environmental conditions.

Instantaneously collected soil-gas samples along traverses and in a grid pattern over known uranium deposits of different depths show (a) broad, umbrella-helium anomalies in soil gas of up to 60 ppb (1% above background) over areas of uranium mineralization; (b) the "detectability" and level of the anomalies apparently decreased with the decrease in soil moisture as the summer progressed; (c) reproducible, 60-ppb helium-in-soil-gas anomalies are present over uranium deposits buried at 30, 100, and 260-m depths beneath intervening mudstones, lignites, and sandstones.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC