Fire Assay — Gold (Gravimetric Finish)
High-precision gold determination designed for high-grade exploration intercepts, mine production ores, concentrates, and bullion samples using direct micro-gravimetric weighing.
Analytical Overview & Methodology
When gold concentrations exceed standard AAS linearity (>30 g/t Au), our Fire Assay with Gravimetric Finish (FA-GRAV-02) provides the definitive, absolute measurement required by mine operators, financial institutions, and commercial smelters. This classical method eliminates instrument dilution errors through direct micro-gravimetric determination.
The Gravimetric Protocol
Following high-temperature fusion and cupellation, the resulting gold-silver dore bead is inquarted with high-purity silver if necessary to achieve a 3:1 Ag-to-Au ratio. The bead is annealed and treated with heated dilute nitric acid in specialized porcelain parting cups. Nitric acid selectively dissolves all silver, leaving an intact sponge of pure metallic gold (the cornet).
The gold cornet is washed with deionized water, annealed at 800°C to consolidate the gold into a bright coherent bead, and weighed on an isolated anti-vibration micro-balance accurate to 0.001 mg. This direct physical weight gives the true gold grade with zero instrument drift.
| Method Code | FA-GRAV-02 |
|---|---|
| Element Coverage | Gold (Au) High Grade |
| Detection Range | 1.0 – 10,000.0 ppm Au (g/t) |
| Sample Requirement | 30g or 50g pulverized sample pulp |
| Instrumentation | Fire Assay Fusion + Cupellation + Ultra-Micro Balance (0.001 mg precision) |
| Standard Turnaround | Standard: 3-5 Working Days | Fast-Track Rush: 24 Hours |
Laboratory Protocols & Execution Specs
- Sample Charge: 30g / 50g pulp charge
- Fusion: Multi-element flux tailored for high-grade sulphides and concentrates
- Parting: Hot nitric acid parting of silver in platinum/porcelain crucibles
- Weighing: Mettler Toledo 6-decimal micro-balance (0.001 mg / 1 µg resolution)
- Applications: Grade control, mine reconciliation, high-grade vein intercepts, mill feed
- Quality Assurance: Certified pure gold (99.999%) synthetic calibration checks
JORC & NI 43-101 Data Integrity Guarantee
Every batch tested under method FA-GRAV-02 includes matrix-matched Certified Reference Materials (CRMs), analytical blanks, and duplicate splits at a minimum 20% insertion rate. Official digital Certificates of Analysis are digitally signed and traceable.