A review of Australian experience in the evaluation of helium as a pathfinder in exploration

Abstract

Orientation surveys were conducted to test the potential of using 4He as a pathfinder in mineral and hydrocarbon exploration. Groundwaters were sampled from drill holes and stock wells. Overburden gas samples were collected via fixed tubes emplaced at 6 m depth in backfilled drill holes. While He concentrations in groundwaters associated with most U mineralization were far in excess of the atmospheric equilibrium value of 0.044 μL/L, equivalent, or higher, concentrations were found in groundwaters from unmineralized areas around the deposits. These latter concentrations appear to be due to accumulation of He in groundwaters with long residence times and by leakage from deep sources, particularly granitoid basement. Only at the Koongarra U deposit, where groundwaters are annually recharged, did anomalous He concentrations appear to indicate the presence of the deposit. No credible He anomaly was detected in overburden gas over any U deposit. However, a marked overburden gas He anomaly was detected over the Gingin gas field, although normalization to constant 20Ne suggested much of this to be a relative enrichment due to near‐surface biological activity related to the leakage of hydrocarbons altering the major gas composition, particularly the CO2/O2 ratio of the soil atmosphere. It is concluded that He, when used in conjunction with other gases, may be useful in near‐surface geochemical exploration for hydrocarbons but that it does not appear to be an effective pathfinder for U deposits.