| Abstract: | Losses in the complete fire assay for gold were found to be less than 1% under ideal conditions. The use of polythene bags for mixing each sample was shown to improve both the accuracy and the precision of the assay. Fusion temperatures of 1900°–2300°F and times from 0.5–3.5 h showed only small variations in gold recovery. The optimal conditions were fusion for 1.5–2 h at 2100°F, with a button weight of 18 g, and cupellation at 1800°F. However, the overall assay proved remarkably insensitive to variation in conditions. The need to determine the silver retained in the parted gold beads is emphasized. Gold losses in the procedural stages were established with tracers; the loss to the crucible was most significant. The use of lead foil as a simulated button gives misleading results. For synthetic samples containing 24.5–490 μg of gold, average recoveries were 100% (s=0.6–1.8). Application to two gold ores is discussed. |
