Gold is one of the most sought-after precious metals, and exists in a variety of forms and geological settings, making its extraction and utilization a cornerstone of the global mining industry. Understanding gold minerals involves exploring their diverse types, physical and chemical characteristics, and industrial significance. From native gold to gold-bearing sulfides and tellurides, each mineral type presents unique properties and challenges. Furthermore, analyzing the phase distribution of gold in ores provides essential insights for optimizing extraction methods, ensuring maximum recovery, and addressing environmental concerns. Next, we will introduce some knowledge of gold minerals.
Gold and Gold-Bearing Minerals
There are about 250 identified gold-bearing minerals in the world. These include minerals where gold exists as a native element or is chemically bound within the mineral’s structure. The following are the main gold minerals.
1. Native Gold Minerals
- Native Gold (Au): The most important and widely distributed gold mineral is commonly found in primary and secondary deposits.
- Electrum (Au, Ag): A natural alloy of gold and silver with varying proportions, often associated with primary gold deposits.
- Porpezite and Rhodite: Gold alloys containing palladium are often found in ultramafic rocks or certain placer deposits.
2. Sulfide Gold-Bearing Minerals
Gold is often encapsulated in sulfide minerals, including:
- Pyrite (FeS₂): Commonly referred to as “fool’s gold,” it can contain submicroscopic gold inclusions.
- Arsenopyrite (FeAsS): A significant gold carrier in hydrothermal gold deposits.
- Chalcopyrite (CuFeS₂): Contains trace amounts of gold, particularly in porphyry copper-gold deposits.
3. Telluride Gold-Bearing Minerals
Gold often combines with tellurium to form tellurides:
- Calaverite (AuTe₂): A gold telluride mineral common in epithermal deposits.
- Sylvanite ((Au, Ag)Te₂): An important ore mineral in certain gold-tellurium deposits.
- Petzite (Ag₃AuTe₂): A rare silver-gold telluride found in specific hydrothermal systems.
4. Oxide and Halide Gold Minerals
- Aurostibite (AuSb₂): A rare mineral found in gold-antimony deposits.
- Gold Chlorides: Rare compounds that can occur in oxidized zones under extreme conditions.
5. Other Gold-Bearing Minerals
- Carbonaceous Materials: Gold can be adsorbed or bound within carbon-rich rocks (e.g., shales and coal seams).
- Silicates and Aluminosilicates: Gold may occur in trace amounts within silicate minerals in granitoid-hosted systems.
Major gold minerals and gold-bearing minerals
Gold occurs in various forms in nature, including as native gold and as a component of other minerals. At present, there are 250 kinds of gold minerals and gold-containing minerals discovered in the world, and there are only about 47 common ones, while there are only 20 kinds of industrial minerals of gold. The main industrial minerals of gold in China are natural gold and silver-gold ores. The below table shows the main gold minerals.
| Mineral Name | Mineral Molecular Formula | Au Content (%) | Ag Content (%) | Others |
| Native Gold | Au | 80~100 | 0~20 | |
| Silver-Gold Ore | (Au, Ag) | 50~80 | 20~50 | |
| Gold-Silver Ore | (Ag, Au) | 20~50 | 50~80 | |
| Mercurial Natural Gold | (Ag, Hg) | 73.38~88.23 | 0~13.56 | Hg 8.83~10.07 |
| Platinum Natural Gold | (Au, Pt) | 80.1 | 9.0 | Pt 8.7 |
| Palladium Natural Gold | (Au, Pd) | 87.6 | Pd 10.2 | |
| Bismuth Natural Gold | (Au, Bi) | 83.84~92.08 | Bi 5.69~13.00 | |
| Black Bismuth Gold Ore | Au2Bi | 63.55~66.85 | Bi 32.34~35.73 | |
| Tellurium-Gold Ore | AuTe2 | 37.32~45.84 | Te 54.16~58.32 | |
| Antimony-Gold Ore | AuSb2 | 41.80~47.86 | 0~7.55 | Sb 50.0~57.04 |
| Sulfur Gold-Silver Ore | Ag3AuS2 | 18.6~35.9 | 41.0~67.7 | S 10.7~11.7 |
| Selenium Gold-Silver Ore | Ag3AuSe2 | 28.02 | 48.0 | Se 23.98 |
Typical Features of Gold Minerals
- Chemical Stability: Gold is highly resistant to chemical reactions and corrosion.
- Physical Excellence: With exceptional ductility and conductivity, gold is ideal for industrial and jewelry applications.
- Economic Value: Gold is widely used in reserves, currency, electronics, and decoration.
Gold Phase Analysis
Phase analysis of gold is an important method for studying the occurrence and distribution of gold in ores. Its purpose is to determine the existence of gold and its relationship with other minerals and to provide a basis for mineral processing and metallurgical processes.
Importance of physical phase analysis of gold
- Determine the form of gold
Determine the distribution of gold in the ore, and clarify the degree of difficulty in recovering gold.
Provide a scientific basis for ore dressing and smelting, and optimize the process flow. - Identify the minerals associated with gold
Understand the minerals coexisting with gold (e.g. sulfides, oxides, carbonaceous materials). And provide references for improving the beneficiation process. - Predict metallurgical recoveries
Determine whether the gold needs special treatment (e.g. roasting or fine grinding) to reduce loss and improve metallurgical efficiency.
The main physical phases of gold and beneficiation methods
- Bare and semi-bare native gold
- Carbonate-coated gold
- Sulfide-coated gold(lead-zinc-copper sulfide-coated gold, pyrite)
- Limonite-coatedgold
- Quartz, silicate-encrusted gold
Native gold is mainly recovered directly by physical beneficiation techniques such as gravity separation and flotation. Inclusion gold requires treatments such as roasting, oxidative leaching, ultrafine grinding or bio-oxidation. Microscopic gold needs to be extracted in combination with chemical processes such as cyanidation, leaching, etc. Adsorbed gold is often extracted by cyanide leaching or carbon adsorption techniques. The chemical gold needs to be converted to a recoverable form utilizing roasting and oxidizing.
Gold Ore Industrial Grade
Rock gold
Boundary grade: 1~2 g/t
Industrial grade: 3~5 g/t
Average grade of deposit: 5~ 8g/t
Alluvial gold
| Item | open-pit mining | underground mining | |||||
| surface mining | Separate mining | ||||||
| Gold mining ship mining | Water gun mining | ||||||
| South | North | ||||||
50~ 100L | 150~ 300L | 50~ 100L | 150~ 300L | ||||
| Mixed sand boundary grade（g/m3） | 0.05~0.07 | 0.04~0.06 | 0.06~0.08 | 0.05~0.07 | 0.1 | 0.3~0.5 | |
| Mixed sand block section industrial grade（g/m3） | 0.16~0.18 | 0.14~0.16 | 0.18~0.20 | 0.16~0.18 | 0.3 | 0.6~1.0 | |
| Small recoverable thickness（m） | 30~50 | 40~60 | 30~35 | 40~60 | 20 | ||
| Rejection width of non-mineralized section (entrapment stone) （m） | 30~35 | 40~60 | 30~35 | 40~60 | |||
| Mineable sand volume of ore body（Ten thousand m3） | 150~450 | 900~2000 | 100~300 | 600~1400 | |||
| Boundary grade of mineral sand layer（g/m3） | 1 | ||||||
| Industrial grade of ore layer block section（g/m3） | 3 | ||||||
| Height of mining width of mineral sand layer（m） | 1.3~1.5 | ||||||
Comprehensive Evaluation of Gold Ore
| Element or component | Cu | Pb | Zn | WO3 | Sb | Mo | S |
| Content（%） | 0.1 | 0.2 | 0.4 | 0.05 | 0.4 | 0.01 | 2.0 |
| Notes: 1. Copper, lead, zinc, antimony, and molybdenum content all refer to the content in sulfide. 2. Sulfur refers to the sulfur in sulfide iron ore. 3. Silver is commonly found in gold deposits, and the evaluation of the content of associated silver depends on its recovery. | |||||||
Gold Concentrate Quality Standards
| Deposit Type | Grade | Au(not less) /g.t-1 | Impurity(not more) /% |
| As | |||
| Single metal mine | Special Grade | 160 | 0.1 |
| Grade 1 | 140 | 0.1 | |
| Second Grade | 120 | 0.2 | |
| Third Grade | 100 | 0.2 | |
| Fourth Grade | 80 | 0.3 | |
| Fifth Grade | 70 | 0.3 | |
| Polymetallic mine | Special Grade | 100 | 0.1 |
| Grade 1 | 80 | 0.2 | |
| Second Grade | 60 | 0.3 | |
| Third Grade | 40 | 0.3 | |
| Fourth Grade | 30 | 0.3 |
In summary, comprehensive knowledge of gold minerals, including their types, features, and phase distribution, plays a critical role in efficient mining and metallurgical practices. By combining advanced analytical techniques with a deep understanding of gold’s occurrence and associations, industries can improve recovery rates, reduce environmental impact, and maximize the economic potential of this precious resource. As gold remains indispensable in fields ranging from finance to technology, continued research into its mineralogical behavior will further enhance its utility and sustainability.