Gold has always been one of the most popular metals in the world. The crazy gold rush makes it sought after by various gold mining companies, mineral experts, and amateur gold prospectors.
About 70%-75% of the gold deposits are natural gold, and 20% are Au-Ag telluride. The remaining 5% -10% is "invisible" gold ore, symbiotic in quartz ore, silver ore, pyrite, pyrrhotite, sphalerite, gangue, arsenopyrite, gangue, and other minerals.
In South Africa, Witwatersrand Basin has the world's largest placer gold deposit. Brazil's gold ores exist with diamonds. In Australia, gold is present wherever pyrites can be found. So how to extract gold from different types of gold ore?
1. Quartz gold ore
Quartz gold ore properties
Gold has long been found in the fractures and cracks of quartz stone and can occur in large veins during hard rock mining. Gold from quartz veins is one of the rarest natural gold.
Quartz appears as small stones in large cracks in riverbeds or mountain slopes and has crystals in different colors such as white, yellow, pink, purple, gray, or black.
The most common types of gold quartz ore are rose quartz gold ore and rainbow gold ore. A high gold-quartz ore contains 25% gold by mass, and it occurs in areas where the bedrock is fractured by tectonic and volcanic activity.
Gold from quartz ore
Once you find gold in quartz ore, you can extract gold by the flowing steps:
- 1Use a gold ore crusher to break the raw gold ore into smaller pieces.
- 2The rock is ground in water using a wet pan mill and sieved to collect and extract the gold.
- 3Adopt standard placer gold washing methods and then separate small gold nuggets and powder from the ground rock with a gold shaker table.
- 4Recover the gold from tailings with a flotation machine so as to obtain high-grade gold ore concentrate.
2. Silver-gold ore
Silver gold ore properties
Gold silver ore is rich in silver sulfide and free gold. High-grade silver ore usually has a much lower base metal content. Volcanic activity accompanied by plate subduction will form superheated gold and silver deposits.
For example, most superheated gold and silver deposits in Japan form through the precipitation of gold from fountains.
Extraction method of silver gold ore
- 1Grind bulk silver-rich gold ore to a finer size by using a ball mill.
- 2Leach the flotation tailings.
- 3Use cyanidation to extract gold and silver.
3. Iron oxide copper gold ore
Properties of iron oxide copper gold ore
Iron oxide copper gold ore refers to the symbiosis of copper ore and gold ore in gold ore in some form. Its amount is about 10 million to 4 billion tons. IOCG ore contains copper with a grade of 0.2% to 5% and gold with a content of 0.1 to 1.41 grams per ton.
Iron oxide copper gold ore tends to be conical on the edge of granite or appears as long banded breccia or massive iron oxide ore in faults or shears.
Extraction of gold from copper ore
- 1Crush, grind, and classify the raw oxidized gold ore (containing copper).
- 2Give the ore an alkaline treatment.
- 3Add certain proportion of chelating agent and sodium cyanide to inhibit the leaching of copper and the selective leaching of gold.
- 4Use conventional activated carbon in the leachate to adsorb gold.
4. Gold sulfide ore
Properties of gold sulfide ore
Gold sulfide ore is a rock gold ore with a chemical formula of Au2S. It is the principal sulfide of gold (usually pyrite) and decomposes to gold metal and elemental sulfur, illustrating the "nobility" of gold.
In nature, the covalent radii of gold sulfide and silver are similar, and the two will form a solid solution.
Extraction method of gold sulfide ore
- 1Grind large pieces of gold sulfide ore to a certain particle size.
- 2Use a jig to recover the coarse and fine free gold.
- 3Separate the ore in a flotation plant, and then send it to a cyanidation plant to recover gold.
5. Blue clay gold ore
Properties of blue clay gold ore
Blue clay gold ore generally contains a small amount of quartz, a large amount of gold, and a lot of black sand, and this type of gold ore is easy to identify.
So If you find blue clay contains a lot of black sand, this may be a very good sign that gold is also nearby. Alluvial gold is mostly found in blue clay and is in clay-laden gravel or between thin layers of rock.
Extraction of gold from blue clay gold ore
It is easy to extract gold from alluvial gold/placer gold, and 95% of gold can be recovered.
- 1Mix evenly the blue clay, mud, or silt containing gold with enough water.
- 2Make this diluted clay flow through a sieve with a diameter of about 120 microns to separate larger particles to avoid affecting the work behind it.
- 3The separation of large gold particles can be carried out by cyclone method, shaking table, or vibrating screen according to different situations.
6. Tellurium gold ore
Properties of tellurium gold ore
Tellurite has high economic value and is the most important in metallurgy. Tellurium–gold deposits differ from normal gold mineralization in their significant content of tellurium‐bearing minerals with a close relation between Au and Te.
Gold-bearing minerals containing tellurium are called "tellurides". Tellurides contain calaverite, mayenite (AuTe2), potash-zinc ore (AuAgTe4), and green feldspar. They often appear in Australia’s Kalgoorlie and America's California and Colorado.
Extraction of gold from tellurium gold ore
Telluride ore is not suitable for direct cyanidation, because it dissolves very slowly in cyanide solutions. Therefore, it is usually roasted to decompose gold telluride compounds. After calcination, gold is recovered from the telluride ore with the aid of a copper cyanide solution.
7. Gold in arsenopyrite
Properties of gold in arsenopyrite
Arsenopyrite is also the main gold-bearing mineral, which is closely related to gold. The distribution of gold in arsenopyrite is similar to that in pyrite. Most of the fine-grained gold having a particle size of less than 10 μm is highly dispersed in arsenopyrite.
When the arsenopyrite ore is crushed and ground, it occurs that the pores of the ore have been cracked and the gold has been dissociated.
In the arsenopyrite gold mine, the Au content is 72.27%, the Ag content is 27.73%, the As content is 38.79%, the S content is 24.29%, and the Fe content is 36.92%.
The extraction method of gold in arsenopyrite
- 1A common practice in processing pyrite gold ore is to remove as much gold and sulfide as possible by gravity treatment and/or flotation.
- 2Generally, arsenopyrite concentrate is contacted with mercury to recover the free gold content.
- 3The mercury and amalgam are recovered by washing on the amalgam plate, and then the resulting product is evaporated to recover the mercury and produce gold sponge residue.
- 4The gold sponge is fire-refined to produce gold ingots.
- 5Tailings often contain large amounts of residual gold and need to be transported to a smelter for further processing.
8. Granite gold ore
Granite gold ore properties
Granite and plutonic rocks belong to crystalline rock and ore veins, which are also the main source of gold. The muscovite granite also contains gold, which has formed relatively black iron due to the intrusion of gold deposits into the rock mass.
Gold is also scattered on the top area of granite containing magnetite and ilmenite. For example, in Timbala, the entire gold resources are distributed in a wide range of muscovite granite mines and are composed of medium-grained to coarse-grained rocks.
The scattered gold ores are present in all five deposits, accounting for more than 95% of the total resources of Timbala. Granite gold ores mainly appear in the form of light immersion, in the shape of plates and columns, and are limited to fine-grained mica under the carapace and inner mica layer.
Extraction of gold from granite gold ore
- 1Wash, filter, and grind the granite ore into smaller pieces.
- 2Put the ground ore into a tank containing a dilute cyanide solution and add zinc. The chemical reaction between a dilute cyanide solution and zinc will separate the gold from the ore.
- 3Use a filter press to remove the gold from the solution.
- 4Use the pulp-in-carbon method by which you should combine carbon with gold to get carbon gold particles.
- 5Put the carbon gold particles into the caustic carbon solution to separate the gold.
If you want to obtain high-grade gold concentrate, you must know the types of gold rocks you have. The extracted gold can be made into alloy products such as platinum, black gold, and blue gold.
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