Gold Dore Bars Assessment by Refineries and Refined Gold Bars: Measurements, Specifications & Calculations
This reference guide provides accurate, industry-standard technical details for gold dore (unrefined/semi-processed gold, typically 50–95% purity) assessment by refineries and specifications for refined gold bars. It is based on globally accepted methods (Fire Assay per ISO 11426:2014 / ASTM standards) and official specifications from the Bureau of Indian Standards (BIS) India Good Delivery Standards (IGDS) and London Bullion Market Association (LBMA) Good Delivery Rules (current as of 2026).
1. Gold Dore Bars: Assessment by Refineries
Gold dore is assessed primarily to determine the exact fine gold content for settlement, pricing, and refining charges. Refineries use destructive testing for the highest accuracy.
Key Measurements
- Gross Weight: Measured on calibrated precision scales (accuracy ±0.01 g or better) after melting the dore bar for homogeneity.
- Moisture / Impurities: Checked via drying and visual/chemical inspection.
- Purity (Fineness): Expressed as parts per thousand (‰) or percentage (%). Typical range: 500–950‰ (50–95% Au).
- Silver & Base Metals: Silver content (often 5–40%), plus traces of copper, lead, etc.
Primary Assessment Method: Fire Assay (Cupellation)
Fire Assay is the legal reference method worldwide for dore settlement due to its accuracy of 0.01% (1 part in 10,000). It is preferred by refineries, LBMA-accredited labs, and BIS-approved facilities in India.
Step-by-Step Fire Assay Process (for a representative sample, typically 0.25–0.5 g):
- Sampling & Melting: Dore bar is fully melted in an induction furnace. A homogeneous sample is taken.
- Fusion: Sample is mixed with lead oxide, fluxes, and silver (for inquartation) and fused in a crucible at ~1,200°C. Lead collects the precious metals.
- Cupellation: The lead button is placed in a porous cupel and heated at 900–1,100°C. Lead and base metals oxidize and are absorbed, leaving a small “doré bead” (gold + silver).
- Parting: The bead is weighed, then treated with nitric acid to dissolve silver. Pure gold remains.
- Weighing: Pure gold bead is weighed on a microbalance (accuracy to 0.001 mg or better).
Supporting Methods (used for screening only):
- X-Ray Fluorescence (XRF) — non-destructive, fast (±0.1–0.5% accuracy).
- ICP-OES / Potentiometric Titration — for trace impurities.
Key Calculations & Formulas (Gold Dore)
- Fine Gold Content (in grams): Fine Gold (g) = Gross Weight (g) × (Assay Fineness / 1,000)
- Fine Gold in Troy Ounces: Fine Gold (oz t) = Fine Gold (g) / 31.1035
- Net Payable Gold (after deductions): Net Payable = Fine Gold – Refining Loss (0.05–0.2%) – Penalty Elements (As, Sb, Hg) – Refining Charges
- Example Calculation (1 kg dore bar at 850‰ assay): Fine Gold = 1,000 g × (850 / 1,000) = 850 g (or ~27.33 troy oz).
Settlement is always based on the independent refinery assay report. In India, BIS-approved refineries must submit utilization reports to Customs/Central Excise.
2. Refined Gold Bars: Measurements & Specifications
Refined bars must meet strict physical, chemical, and marking standards for “Good Delivery” status on exchanges and international trade.
India Good Delivery Standards (IGDS) – BIS
Applicable for 1 kg bars traded on Indian exchanges (MCX, NSE, etc.).
| Parameter | Specification |
|---|---|
| Fineness | 995.0‰ or above (99.5%+). No negative tolerance on declared gold content. |
| Weight | 1,000 g (1 kg). Tolerance: –0 / +0.5 g |
| Dimensions | Length (top): 113–117 mm Width (top): 51–55 mm Height: 6.5–10.5 mm |
| Refining Process | Aqua regia or Electrolysis |
| Marks (must be stamped) | • “1 kg gold” or “1000 g gold” (prominently on top face) • Refiner identification • Serial number • Fineness (to 4 significant figures) • Year of manufacture • Weight |
LBMA Good Delivery Standards (International / Large Bars)
Used globally for 400 oz-class bars.
| Parameter | Specification |
|---|---|
| Fineness | Minimum 995.0‰ (99.5%) fine gold |
| Fine Gold Content | 350–430 troy ounces (~10.9–13.4 kg) |
| Gross Weight | Expressed in multiples of 0.025 troy oz (rounded down) |
| Dimensions (approx.) | Length (top): 250 mm ±40 mm Width (top): 70 mm ±15 mm Height: 35 mm ±10 mm Undercut: 5°–25° |
| Marks | Serial number, refiner assay stamp, fineness, year of manufacture |
Note: 1 kg refined bars in international trade are usually 999.9‰ (four-nines) with tighter weight tolerance (±0.1 g).
Verification & Calculations for Refined Bars
- Fineness Verification: Fire Assay or XRF (final certification by hallmarking lab in India).
- Fine Gold Content (in grams): Fine Gold (g) = Gross Weight (g) × (Fineness ‰ / 1,000)
- Fine Gold in Troy Ounces: Fine Gold (oz t) = Gross Weight (g) × (Fineness / 1,000) / 31.1035
- Example (1 kg bar at 999.9‰): Fine Gold = 1,000 g × (999.9 / 1,000) = 999.9 g (or 32.1507 troy oz).
Additional Checks:
- Density / Archimedes principle (for quick verification).
- Hallmarking (BIS in India) – mandatory for domestic bullion.
- No negative tolerance on declared fine gold content.
Important Notes:
- All measurements use troy ounces (1 oz t = 31.1034768 g) for international trade and grams/kilograms for India.
- Fire Assay remains the most accurate method for settlement (refineries and exchanges rely on it).
- Policies are subject to updates by DGFT, BIS, RBI, and LBMA. Always verify the latest notifications.
- For business use: Engage BIS/NABL-accredited labs and licensed Customs House Agents.
