Soil and overburden gas surveys

Other surveys have tended to show only small areas with elevated He concentrations. Thus, over the Lamprecht ore body in Texas, USA, where mineralisation is at 70-90 m beneath clays and cemented sandstones, soil gas He contents have a total range of 5.20-5.34 ppm He (Reimer et al., 1979a). The few values over 5.27 ppm He occur over part of one mineralised zone and sporadically elsewhere, but another zone has background to negative values. 

When the results of these and other surveys are considered, it is apparent that the observed concentration ranges may be due to background variations plus the sampling and analytical errors discussed previously. Pogorski and Quirt (1979) suggest that the errors 

Similarly, there is probably little significance in the difference of 0.02 ppm He noted for soil gases over two lithological units at the Aurora uranium deposit, Oregon, USA (Reimer, 1986). Although a higher He flux over the prospective units is a possible explanation, so too are background variations related to the influence of soil type on interaction with the atmosphere, major gas composition and analytical performance. 

The highest He concentrations reported for probe sampling were found at the Ambrosia Lake district. New Mexico, USA, in a restricted survey of 46 samples from a 1.2 x 3.2 km area over mineralisation 300-400 m deep (Reimer et al., 1979b). The mean soil-gas concentration was 5.30 ppm He, with three samples containing 5.47-5.65 ppm He. The distribution pattern has some coherence but is not readily related to the location of the mines and has probably been affected by the mining operations. 

Butt and Gole (1985) also found no He anomaly over shallow (15-20 m) zircon- and monazite-rich mineral sands at Eneabba, Western Australia. These contain 300-500 ppm U + Th and thus represent a moderate source of He. However, the He contents of overburden gases were the same over the mineral sands (5.24-5.31 ppm) and a background site 5 km distant (5.21-5.30 ppm). Any He must either be retained within the minerals or lost to the 

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