Gold Doré Bars are semi-refined bullion products produced at mining sites as an intermediate stage between raw gold ore and fully refined gold bars. They consist primarily of gold alloyed with silver and small amounts of base metals.
Unlike investment-grade gold bars (99.9%+ purity), doré bars typically contain 50–95% gold and are supplied to refineries for further purification. They are a critical link in the global precious-metals supply chain.
Chemical Composition
Composition varies widely depending on ore type and processing route.
| Element | Typical Range |
|---|---|
| Gold (Au) | 50 – 95% |
| Silver (Ag) | 5 – 45% |
| Copper (Cu) | 0.1 – 5% |
| Zinc (Zn) | Trace |
| Lead (Pb) | Trace |
| Iron (Fe) | Trace |
| Platinum Group Metals | ppm – trace (occasionally) |
High-silver doré is common in epithermal and polymetallic deposits.
Key Physical Properties
| Property | Typical Value |
|---|---|
| Density | 14.0 – 18.5 g/cm³ (composition dependent) |
| Melting Range | 960 – 1050 °C |
| Thermal Conductivity | 250 – 320 W/m·K |
| Electrical Conductivity | High |
| Coefficient of Thermal Expansion | ~14 × 10⁻⁶ /K |
| Magnetic Behavior | Non-magnetic |
| Surface Appearance | Dull yellow to silvery-gold |
Mechanical Properties
Gold doré bars inherit properties from Au–Ag solid-solution alloys.
| Property | Typical Value |
|---|---|
| Hardness | 40 – 90 HV |
| Tensile Strength | 150 – 300 MPa |
| Elongation | 20 – 35% |
| Malleability | Very high |
| Brittleness | Low |
Higher silver content increases hardness while reducing density.
Strengthening & Metallurgical Behavior
Crystal Structure
Gold and silver both have FCC crystal structures with complete solid solubility.
Strengthening Mechanisms
✔ Solid-solution strengthening (Ag in Au lattice)
✔ Minor strengthening from Cu and base metals
✔ Work hardening during handling
❌ No heat-treatment strengthening possible
Metallurgical Nature of Doré Bars
Doré bars represent gold already liberated from ore and are the final product of mine-site metallurgy. They may contain inclusions, entrapped slag, and surface oxidation.
Refining & Processing
Production Route
Ore crushing & grinding → gravity recovery / cyanidation →
electrowinning → smelting with fluxes → doré bar casting
Secondary Refining
Miller process (≈99.5%)
Wohlwill electro-refining (99.99%)
Silver separation via nitric acid or electrolysis
Available Forms
✔ Cast doré bars (mine bars)
✔ Doré ingots (small or large)
✔ Anode bars for electro-refining
✔ Doré buttons (laboratory scale)
Typical weights: 5 – 25 kg (standard mine doré), with custom refinery formats available.
Typical Applications
Precious Metal Refining
Primary feedstock for gold refineries and electro-refining anodes
Bullion Production
Conversion into LBMA gold bars, coins, and jewelry-grade gold
International Trade
Export product from mines, traded under assay-based contracts
Advantages of Gold Doré Bars
✔ Much higher value density than ore
✔ Lower transport cost
✔ Easier storage & security
✔ Faster conversion to pure gold
✔ Reduced environmental footprint vs shipping ore
Gold Ore vs Doré vs Refined Gold
| Feature | Gold Ore | Gold Doré | Refined Gold |
|---|---|---|---|
| Gold Content | 0.5 – 30 g/t | 50 – 95% | 99.9 – 99.99% |
| Processing Stage | Raw | Semi-refined | Final |
| Transport Efficiency | Poor | Excellent | Excellent |
| Market Form | Resource | Refinery feed | Investment / industrial |
| Environmental Load | High | Moderate | Low |
| Usability | None | Limited | Immediate |
Why Choose Gold Doré Bars?
Gold doré bars are the critical bridge between mining and refining. They enable efficient monetization, secure transport, accurate accounting, and centralized refining of gold and silver in the global supply chain.