Paragon Geochemical provides quality assay lab services in Northern Nevada. Please read below for a detailed description of our Fire Assay process.
Once preparation is complete, samples can be analyzed for metals content. Most samples will follow one of two analytical processes: wet geochemistry for a broad spectrum of elements, or fire assay for precious metals, both of which are described here.
Combines pulps with a lead flux mixture and fuse at ~1150 C to break down the chemical bonds within the sample, collecting the precious metals and allowing their quantification.
Fusion furnace can fire 84 pots at a time. Lead fumes from the process are captured within the baghouse filter. Cupellation takes place at ~1000 C where fused buttons oxidize and are absorbed into cupels leaving behind the precious metals.
From the fire assay process, the resultant precious metal beads are quantified by one of two ways: gravimetrically or through AA/ICP. The gravimetric process involves parting away any silver and weighing the resultant gold flake. AA/ICP involves digesting the bead in aqua regia and analyzing the solution by an AA or ICP instrument.
Reagents, fluxes, crucibles and cupels: Vendor prepared flux batches are tested for gold before client samples are analyzed. Results from 6 tests are determined with method Au-OES30 that has a detection limit of 0.001 ppm. Tests also confirm crucible and cupel cleanliness. Reused crucibles are either cleaned by firing them with a cleaning mixture, or by classifying them per their prior assay’s gold concentration.
Equipment: Fusion furnaces are made by Furnace Industries and the cupellation furnaces are made by Pyradia. All furnaces utilized by Paragon have dual pyrometers that must remain within tolerance or will indicate a problem code. Pyrometers must be replaced every 12 months.
Samples are visually and chemically prescreened for flux suitability. Before adding flux to samples, sample color and chemical reactivity is evaluated. Reactivity is measured with a droplet of nitric acid on the sample which will indicate which flux amendment to add.
A furnace load is 84 samples or two racks of 42. Furnace temperatures are examined 15 minutes after sample loading—the fusion time upon which the furnaces’ temperature should recover to its maximum temp.
Post-fusion indicators are many, and often visually apparent. Fusion slag clarity, color and brittleness is evaluated, along with the lead buttons’ weights and malleableness.
Post cupellation indicators are found in the residue left on the cupels from the flux lead or other metals, cupel color, and prill weight, color and shininess.
A cyanide solution or a heated acid solution is used to dissolve metals and minerals for analysis.
Dissolved minerals and metals have their concentrations quantified by either: ICP-OES, ICP-MS or AAS. Using calibration blanks and standards instrument’s readings are indexed in order to provide accurate results.