You need to know what gold ore is
Gold ore refers to a mineral aggregate containing gold elements formed under natural conditions. Its gold content reaches a certain economic mining value and can be extracted from it by industrial methods. Gold ore not only includes gold itself, but also contains other minerals and rock components that coexist with gold.
Formation of gold ore
The formation of gold ore is a complex geological process, which is usually related to the following factors:
| Geological structure | Gold ores are mostly formed in specific geological structural environments, such as fault zones, fold zones, etc. These structural zones provide favorable space for gold enrichment. |
| Hydrothermal activity | Hydrothermal activity is one of the important mechanisms for the formation of gold ore. Hydrothermal fluids carry gold elements from deep to shallow, and precipitate and enrich under appropriate conditions. |
| Magmatic activity | Magmatic activity can provide a source of gold and enrich gold in the surrounding rock through intrusion. |
| Sedimentation | In some cases, gold can be enriched in river, lake or marine sediments through sedimentation to form placer gold. |
15 Types Of Gold Ores
1. Native gold
Native gold is a naturally formed gold mineral in nature and is one of the main sources of gold extraction. It usually exists in a single substance. Native gold is a natural gold nugget produced from vein or placer. Because its shape resembles a dog’s head, it is commonly known as “dog head gold”.
The main component of native gold is gold (Au), but it usually contains a small amount of silver (Ag), copper (Cu), palladium (Pd), platinum (Pt), bismuth (Bi), tellurium (Te), selenium (Se) and other elements.
According to the different silver content, native gold can be divided into the following types:
| Native gold: silver content is less than 15%. | Silver-gold ore: silver content is between 16% and 50%. |
| Gold-silver ore: silver content is between 51% and 85%. | Natural silver: silver content is greater than 85%. |
2.Gold-bearing pyrite
Auriferous pyrite refers to pyrite ore containing gold. Auriferous Pyrite Ore is an important type of gold ore. Its main component is pyrite (FeS₂), and it also contains a certain amount of gold (Au) and other associated elements. Pyrite itself is a common sulfide mineral with a chemical formula of FeS₂. Under certain geological conditions, pyrite can be enriched with gold to form gold-bearing pyrite.
Gold-bearing pyrite is usually light copper-yellow or bluish-yellow. Gold is often present in the pyrite lattice or on the surface of the grains in the form of fine particles, and can also coexist with pyrite in the form of mechanical admixtures.
3.Gold-bearing arsenopyrite
Gold-bearing arsenopyrite refers to an ore type formed by arsenopyrite (FeAsS) as the main carrier mineral, and gold is wrapped or impregnated in fine particles (usually <10 microns). Gold-bearing arsenopyrite is an important subtype of hydrothermal gold deposits. Gold and arsenic-sulfur minerals are closely associated and need to be extracted through complex processes.
Arsenopyrite crystals are columnar or plate-shaped, often in dense blocks or impregnated aggregates.
Gold exists in the arsenopyrite lattice in the form of solid solution (isomorphic substitution of As or S), or in fine vein-like inclusions.
4.Iron Oxide-Copper-Gold Ore
Iron Oxide-Copper-Gold, referred to as IOCG, is an important ore type with unique geological characteristics and economic value. Iron Oxide-Copper-Gold Ore refers to copper and gold deposits containing a large amount of primary iron oxides (such as magnetite and hematite), usually accompanied by other metal elements such as silver, uranium, rare earth elements, etc.
This type of deposit is distinguished from other types of deposits by its significant geochemical characteristics and diverse mineralogy, ore-bearing rocks and local geological background. Gold is often present in the form of fine particles in the pyrite lattice or on the surface of the grains, and can also coexist with pyrite in the form of mechanical admixtures.
5.Gold-Bearing Quartz Vein Deposits
Gold-Bearing Quartz Vein Deposits are one of the most important forms of gold resources. They are typical representatives of hydrothermal deposits and are widely distributed in major mineralization belts around the world. Their formation is closely related to the tectonic-magmatic activities deep in the crust. Gold-Bearing Quartz Vein Deposits refer to quartz veins formed by the filling and replacement of hydrothermal fluids in the crustal fissures, in which gold elements are present in the form of natural gold or gold-silver minerals in the quartz matrix or paragenetic minerals.
This type of deposit usually occurs in vein, stockwork or lens shapes, is significantly controlled by structural faults, and is the main industrial type of rock gold deposits. The particle size of gold occurrence is >0.1mm, which can be directly observed by naked eye or microscope. Microscopic gold exists in the form of inclusions in pyrite or quartz lattices and needs to be analyzed by electron probe.
6.Oxidized gold ore
Oxidized gold ore is formed by the long-term exposure of gold-bearing ore to the surface or near the surface, and the long-term weathering and oxidation of natural factors such as the atmosphere, water and organisms, which causes the sulfides (such as pyrite) in the ore to be oxidized into oxides (such as limonite), and the gold minerals also undergo a certain degree of oxidation and enrichment. Common minerals in oxidized gold ore include limonite, hematite, native gold, silver-gold ore, gold-silver ore, etc.
Gold minerals are mainly found in the crystal gaps or cracks of limonite, and a few are distributed in the crystal gaps of quartz. The ore bodies are diverse in shape, and the common ones are lens-shaped, lenticular, cystic, etc., and are often found in the lower part of the iron cap.
Gold usually exists in the form of fine particles in oxidized ore, with a finer particle size, generally 0.0024~0.036mm. The gold fineness is high, generally 700‰~900‰.
7.Gossan-Type Gold Deposit
Gossan-Type Gold Deposit is a special type of surface oxidation deposit in gold resources. After the primary sulfide deposit (such as pyrite, arsenopyrite and other gold-bearing sulfides) is exposed to the surface, the sulfide decomposes into a residue mainly composed of iron oxides (limonite, hematite) after long-term oxidation and leaching. In this process, the gold element is reprecipitated through secondary enrichment to form a gold deposit, which is a secondary product of sulfide deposit weathering on the surface.
The formation of gossan-type gold deposit is directly related to the oxidation and leaching process of the primary sulfide ore body. It is often used as an important surface mark for finding deep primary ore, and it may also have independent mining value.
Gold is present in iron/manganese oxides or clay minerals in the form of natural gold or adsorbed state.
8.Orogenic gold deposits
Orogenic gold deposits are formed by deformation and metamorphism of pre-existing rocks such as sedimentary or volcanic rocks, often associated with quartz veins or shear zones.
The processing of orogenic gold ore involves crushing the ore into a fine powder and then mixing it with water to form a slurry. The slurry then passes through a series of gravity separation equipment such as sluices, jigs or shaking tables, which use the density differences of the gold particles to separate the ore. The concentrate is then smelted into gold bars.
9.Porphyry copper-gold deposit
Porphyry copper-gold deposit refers to a copper-gold deposit associated with intermediate-acidic intrusive rocks with porphyritic structures. The alteration and mineralization of this type of deposit are controlled by fluids and structures. The ore is mainly impregnated with fine veins, and has the characteristics of low grade and large reserves.
The ore is mainly impregnated with fine veins. The average copper content is low in primary ore (0.3%-0.8%), but high in oxidized ore (1%-1.5%).
Porphyry copper-gold ore bodies are often developed in areas where hydrothermal altered rocks are widely present. The altered rocks include sericite-quartz, biotite-potassium feldspar, argillaceous, and greenstone-type metasomatic rocks.
10.Epithermal gold ore
Epithermal gold ore is gold ore that is formed near the surface by hot fluids, usually associated with volcanic rocks or geothermal systems.
The processing of epithermal gold ore involves crushing the ore into a fine powder and then mixing it with water to form a slurry. The slurry is then concentrated to produce gold particles through gravity separation or flotation. The final concentrate is smelted and made into gold bars.
11.Magmatic Gold Deposit
Magmatic gold deposit is a special type of gold deposit, which refers to the deposit formed by the enrichment of gold element directly through magma differentiation, melting or crystallization.
The formation of magmatic gold deposit is closely related to magmatic activity.
Gold is usually found in the rich ore melt or sulfide melting phase in the late stage of magmatic evolution. Gold exists in the form of natural gold or alloy minerals (such as gold and silver ore) in sulfide droplets (such as pyrrhotite), oxides or silicate mineral lattices.
12.Definition of volcanic gold deposit
Volcanic gold deposit refers to gold deposits that are found in volcanic rocks or their surrounding rocks and are closely related to volcanic activities (such as magmatic eruptions and hydrothermal activities).
The gold in volcanic gold deposits is mostly wrapped in fine particles in the cracks or veins of volcanic rocks, or coexists with sulfides (such as pyrite) formed by volcanic hydrothermal activities. It is an important subtype of hydrothermal gold deposits. It is mainly produced in volcanic rock areas, such as basalt, rhyolite, andesite and other extrusive rocks or intrusive rocks nearby. It is commonly found in structural fissures or subvolcanic rocks (such as cryptoexplosive breccia) after volcanic eruptions.
13. Carbonaceous gold ores
Carbonaceous gold ores are ores that contain organic carbon (such as graphite or asphaltenes) that can bind gold particles, making them difficult to recover by conventional methods. Carbonaceous gold ores are often associated with sedimentary rocks or coal seams.
The processing of carbonaceous gold ores involves pretreatment to remove organic carbon by roasting or autoclaving, followed by cyanide leaching to dissolve the gold particles. Alternatively, other leaching agents such as thiosulfate, iodine or bromine can be used to dissolve the gold particles.
14.Modern placer gold mines
Modern placer gold mines refer to deposits formed in water environments such as rivers, lakes, and oceans, where gold particles in primary gold ores are transported and enriched in specific sedimentary environments due to weathering, erosion, and hydraulic transport. Modern placer gold deposits are secondary gold deposits. Gold particles usually exist in a single form, with high density and good weathering resistance.
After the primary gold deposits are exposed to the surface, they are weathered and eroded, and gold particles are separated from the ore. Due to their high density, gold particles are transported to low-lying areas such as river valleys, lakes, and oceans under the action of water flow. Placer gold mining is relatively simple, and water washing is usually used to extract gold, which is relatively low in cost.
15.Paleoplacer gold deposits
Paleoplacer gold deposits refer to deposits formed by long-term sorting and enrichment of gold elements in ancient river sedimentary layers. This type of gold deposit was formed in a river alluvial environment millions to hundreds of millions of years ago. Gold is present in the form of placer gold or fine particles in conglomerate, sandstone or gravel-bearing sandstone layers. It is a typical surface accumulation gold deposit.
Paleoplacer gold deposits are mainly produced in ancient river sedimentary rock systems, such as conglomerate, sandstone, gravel-bearing sandstone, and are common in stable sedimentary basins in the craton area.
Gold morphology particles are large (0.1-5 mm), often in the form of round particles, flakes or dendrites, and are partially wrapped in quartz or agate.