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1A3 - (1A3-30 or 50) - Au 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) and with Ag added as a collector 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.      

Au is separated from the Ag in the doré bead by parting with nitric acid. The resulting gold flake is annealed using a torch.  The gold flake remaining is weighed gravimetrically on a microbalance.


Code 1A3 (Fire Assay-Gravimetric) Detection Limits (g/T)







0.03 (30 g)

0.02 (50 g)





Hoffman, E.L., Clark, J.R. and Yeager, J.R. 1998.  Gold analysis - Fire Assaying and alternative methods. Exploration and Mining Geology, Volume 7, p.155-160.


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