Abstract: Abstract: Helium Detection in Uranium Exploration
Richard H. De Voto, Richard H. Mead, L. E. Bergquist, Joseph P. Martin
Extensive test work over known uranium deposits in the Powder River basin, Wyoming, and in the Ambrosia Lake district, New Mexico, with a portable helium-detector mass spectrometer has obtained 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 varies 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; and (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 (commonly 100 to 200 ppb lower) than the helium content in t e atmosphere; during the night, the helium content in soil gas is equal to or slightly higher than that in the atmosphere.
Thus, in an exploration survey over an area, soil-gas samples should be collected as near to the same time as possible to eliminate changing environmental conditions.
Instantaneously collected soil-gas samples, collected 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; and (c) reproducible, 60 ppb helium-in-soil-gas anomalies over uranium deposits buried at 30, 100, and 260-m depths beneath intervening mudstones, lignites, and sandstones.
AAPG Search and Discovery Article #90969©1977 AAPG-SEPM Rocky Mountain Sections Meeting, Denver, Colorado