Gold Ore is a naturally occurring mineral material that contains gold in its raw, unrefined form. Gold occurs either as native metallic gold or in combination with other minerals such as quartz, sulfides, tellurides, and iron oxides. Gold ore is mined from the earth and processed through crushing, grinding, and extraction to obtain pure gold metal.
Gold is usually present as:
• Native gold (metallic Au)
• Microscopic particles dispersed in minerals
• Chemically bound forms, especially in sulfide ores
Types of Gold Ore
Free-Milling (Oxide) Gold Ore
Gold occurs as free particles and is easily recovered by gravity separation and
cyanidation.
Sulfide Gold Ore
Gold locked within pyrite or arsenopyrite; requires roasting or pressure oxidation.
Refractory Gold Ore
Gold encapsulated in sulfides or carbon; difficult and costly to process.
Placer Gold Ore
Weathered gold concentrated in sediments; processed mainly by gravity methods.
Typical Chemical Composition
| Component | Typical Content |
|---|---|
| Gold (Au) | 0.5 – 30 g/ton |
| Quartz (SiO₂) | Major gangue |
| Iron sulfides | Common |
| Silver (Ag) | Often present |
| Base metals (Cu, Pb, Zn) | Trace to moderate |
| Carbonaceous matter | Refractory ores |
Note: Ore grade, not purity, defines economic value.
Key Physical Properties
| Property | Typical Range |
|---|---|
| Bulk Density | 2.5 – 4.0 g/cm³ |
| Hardness (Mohs) | 5 – 7 |
| Porosity | Low – Moderate |
| Magnetic Behavior | Non-magnetic |
| Thermal Conductivity | Low (host rock dependent) |
Mechanical Properties of Ore Rock
| Property | Typical Value |
|---|---|
| Compressive Strength | 100 – 300 MPa |
| Tensile Strength | 5 – 25 MPa |
| Fracture Toughness | Moderate |
| Abrasiveness | Medium – High |
Metallurgical Behavior & Challenges
• Native gold is soft and ductile
• Encapsulated gold is inaccessible without liberation
• Fine gold particle size (<10 µm) complicates recovery
• Sulfide encapsulation and carbon preg-robbing increase complexity
Processing & Refining Stages
1. Comminution
Crushing and SAG / ball milling
2. Concentration
Gravity separation and flotation
3. Extraction
Cyanide leaching (CIP, CIL, Heap Leach)
4. Refractory Treatment
Roasting, pressure oxidation, bio-oxidation
5. Refining
Smelting to doré bars, electro-refining, chemical purification
Available Forms
✔ Run-of-mine (ROM) ore
✔ Crushed ore
✔ Concentrates
✔ Heap-leach material
✔ Doré bars (Au–Ag alloy)
Gold Ore vs Refined Gold
| Feature | Gold Ore | Refined Gold |
|---|---|---|
| Gold Content | Very low | Very high |
| Processing | Complex | None |
| Value Form | Latent | Immediate |
| Transport | Bulk | Compact |
| Environmental Impact | High | Minimal |
Why Gold Ore Matters
Gold ore is the fundamental natural source of gold, containing trace quantities of precious metal locked within complex mineral systems. Its value lies in recoverability, governed by geology, metallurgy, processing technology, and economics. From free-milling oxide ores to refractory sulfide ores, gold ore processing remains one of the most technically sophisticated and economically critical sectors in global mining.