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1A3 - Ag (Au, Ag) - Fire Assay-Gravimetric

Fire Assay

A sample size of 5 to 50 grams can be used but the routine size is 30 g for rock pulps, soils or sediments (exploration samples). The sample is mixed with fire assay fluxes (borax, soda ash, silica, litharge), which contain no silver, and the mixture is placed in a fire clay crucible. The mixture is then preheated at 850°C, intermediate 950°C and finish 1060°C with the entire fusion process lasting 60 minutes. The crucibles are then removed from the assay furnace and the molten slag (lighter material) is carefully poured from the crucible into a mould, leaving a lead button at the base of the mould. The lead button is then placed in a preheated cupel which absorbs the lead when cupelled at 950°C to recover the Ag (doré bead) + Au.

The cupellation of the bead is controlled by the volatility of the silver. The Ag bead is weighed and Ag value calculated from the weight. Au is separated from the Ag in the doré bead by parting with nitric acid. The gold (roasting) flake remaining is weighed gravimetrically on a micro balance for Au.




Code 1A3-Ag (Au, Ag) (Fire Assay-Gravimetric) Elements and Detection Limits (g/tonne)












Activation Laboratories Ltd. | 41 Bittern Street, Ancaster, Ontario, L9G 4V5, Canada | TF: +1.888.228.5227
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