Analysis of Gold and Platinum Group Elements by Fire Assay

The methodology we use to analyse precious metals is called Fire Assay. Fire Assay is a concentration technique for precious metals (gold, platinum palladium, silver, ruthenium, rhodium, iridium, osmium). The minerals containing precious metals are considered as viable ore resource even at the levels of 1ppm whereas other metals are viable when they are in % levels. In Fire Assay technique we extract the pure metal from the sample and determine either weighing it as it is or by dissolving it in acids and then estimating its weight using instruments like ICP OES and ICP MS. 

We melt a 50g sample with 150g of flux. The flux contains surrogate metals like lead and silver. When we melt the gold and silver get coextracted with lead and silver. Other gang materials are removed by breaking form lead bead. Lead is evaporated at higher temperature and pure gold and silver as a small shining bead form is available in the crucible. This bead is either weighed using a highly sensitive 6 decimal balance and reporting the gold content. Other precious metals are dissolved in acids and determined by instruments like ICP OES and ICP MS in the solution.

Shiva Analyticals, a Cotecna Group Laboratory in Bangalore, has mastered both the art and science of Fire Assay and has been serving the geochemical exploration and mining industry by providing the accurate and reliable assay of gold and precious metals for the last 3 decades. Shiva Analyticals has one of the largest sample preparation facilities in Asia using 50 pot capacity LPG fired fire assay and cupellation furnaces as a global standard and provides 2000 assays a day including ~ 15% of QA/QC samples. Gas fired furnaces are preferred for the fusion process as LPG flame facilitates reducing environment required for converting oxides to metal.

The sample preparation facility includes global benchmark equipment like ESSA 2000 Jaw Crushers, Boyd Crushers, Rotary Sample Dividers and LM2 Pulverisers. The process of sample drying, crushing, division and pulverisation ensures the true representation of the analysis sample. Considering the heterogeneity of gold resources, the homogenised reduced sample of ~1000g is pulverised to <75 microns by using LM2 Pulverisers. The repeatability is verified by running 10% of replicate samples.

Screen Fire Assay & Cyanide Leach Methods:

The presence of nugget gold or metallic gold results in the flaking and heterogeneity of gold within the sample. The screen fire assay and cyanide leach methodologies are used for gold extraction by using about 2kg of sample wherever the nugget effect is suspected.

The following analysis method packages are offered for Gold and Precious Elements:

To learn more about gold testing and other Shiva Analyticals services, please contact us.