Fire assay is the industry standard process for obtaining gold and platinum group element (PGE) concentrations from high-grade ores.
Lead collection gold fire assay is considered the most definitive technique for gold analysis. Platinum and palladium can also be determined by this method, but the full PGE six-element suite is best determined by nickel sulfide collection fire assay. SGS experts are always available to help you select the analytical technique that is fit for your purposes.
Most of the laboratories in the SGS global network offer fire assay gold determinations with an unparalleled level of analytical expertise.
Lead collection fire assay is used to determine gold in all sample types, including rocks, drill core, soil and chip samples. SGS can use various sample sizes (15, 30 and 50 g), depending on anticipated gold contents and degree of homogeneity expected. This time proven, industry standard method has several steps:
The pulverized sample is weighed and mixed with a fluxing agent. Lead is added as a collector. The sample is then heated in a furnace at about 1000 degrees. After about 20 minutes, the sample has fused and the precious metals and lead have separated from the silicate slag to form a ‘button’ in the bottom of the crucible. This button contains the precious minerals.
Precious Metal Extraction
Once the sample is removed from the furnace and cools, the lead button is separated from the silicate slag. The precious metals are then extracted by a process known as cupellation.
During cupellation, the lead in the button oxidizes and is absorbed into the cupel leaving a precious metal bead known as a prill. The gold content of the prill is determined either by weighing (gravimetrically) or it is dissolved in aqua regia.
Analysis and Detection
Once in solution, gold, platinum and palladium can be analyzed by several methods:
- Flame Atomic Absorption (AA)
- Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES)
- Inductively Coupled Plasma-Mass Spectrometry (ICP-MS)
- Instrumental Neutron Activation Analysis (INAA)
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