Gold values in the surveyed sulfide-poor rock units proved to be generally even lower than those in sulfidic sandstone. As a further check on this survey of mineralization, silver values began to be measured by NAA on the silver-gold beads. Radioactivity induced in silver by neutron bombardment is long-lived. The half-life of 110mAg is 253 days, as opposed to a half-life of 2.7 days for 198Au (Aliev et al., 1970). It was therefore possible to retrieve silver-gold beads previously analyzed only for gold and measure silver, without reinsertion into the nuclear reactor. A delay of a few months had little effect on the accuracy of silver measurements.
Silver concentrations of several p.p.m. were found in the fire-assay beads, but it was initially unclear what proportion of the silver had been introduced with PbO flux. Variation among batches of Purified-grade PbO resulted in erratic silver values ranging as widely as 0.4 p.p.m. to 37 p.p.m. Ag for different portions of a homogenized rock sample. Multiple 45 g portions of homogenized Sunedco samples displayed much less variability when fluxed with Certified-grade PbO. Deviations from the means of these multiple analyses were within 15% of the means, on the average. Although Certified-grade flux proved ….Read more