Recent research by the U.S. Geological Survey demonstrates that helium-gas analysis of waters and soils holds great promise as a cost-effective exploration technique for uranium, oil and gas, and geothermal energy sources. The technologic advances include assembling a helium analyzer, almost entirely from commercially available equipment, and packaging the equipment into a mobile laboratory capable of performing as many as 100 analyses a day at a field location. Helium is an attractive indicator element for many exploration programs because of its unique properties: it is highly diffusive, chemically inert, radioactively stable, and not produced or affected by biologic activity. Many associations of helium with uranium have been observed, in which helium is produced by na ural radioactive disintegration; with oil and gas, where helium is trapped by structural and stratigraphic features; and with hot-water geothermal systems, in which the cooling and reduced pressure of rising water causes dissolved helium to be released. The following are examples of distinctive helium anomalies found associated with energy "deposits": for uranium, the Ambrosia Lake district, New Mexico; for oil and gas, the Cement oil field, Oklahoma, and the Cliffside gas field, Texas; and for geothermal, the East Mesa known geothermal resource area in the Imperial Valley, California. With respect to an ambient air background of 5.24 ppm helium, the highest observed concentrations of excess helium in soil and soil gas were typically 0.5 ppm for uranium, 10 ppm for oil and gas, and 100 p m for geothermal; water samples usually had several hundred parts per million helium for all types of energy deposits. Helium analysis can be used as a rapid and inexpensive reconnaissance tool and as complementary support for other geophysical and geochemical prospecting techniques.

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