Gold deposits can be classified into several main types based on their geological characteristics and mode of formation:
Magmatic-Hydrothermal Deposits
- Porphyry Deposits: Hydrothermal deposits associated with felsic to intermediate intrusions, characterized by low to medium gold grades but very high tonnages. Mineralization occurs in stockworks, fractures, faults or disseminated in the host rock.
- Epithermal Deposits: Formed at shallow depths from boiling hydrothermal fluids, these deposits have a wide range of gold grades. They are often associated with volcanic rocks.
- Skarn Deposits: Formed by the interaction of hydrothermal fluids with carbonate-rich rocks, producing gold-bearing calc-silicate mineral assemblages.
- Iron Oxide-Copper-Gold (IOCG) Deposits: A diverse group of hydrothermal deposits with iron oxides as a major component, found in various tectonic settings.
Hydrothermal Deposits
- Orogenic Gold Deposits: Also known as mesothermal or greenstone-hosted quartz-carbonate vein deposits, these are associated with deformation in accretionary orogens. They are found in greenschist to amphibolite facies metamorphic belts.
- Volcanogenic Massive Sulfide (VMS) Deposits: Formed by submarine hydrothermal activity, these deposits contain gold along with copper, zinc, lead, silver and barite.
- Carlin-Type Deposits: Sediment-hosted disseminated gold deposits characterized by microscopic gold grains, found primarily in Nevada. Gold occurs in decalcified and silicified sedimentary rocks.
Placer Deposits
- Alluvial and Eluvial Placers: Gold concentrated by physical and chemical weathering processes in stream sediments, beach sands or residual soils.
The most productive gold deposits fall into six main categories: orogenic, reduced intrusion-related, oxidized intrusion-related, Carlin-type, low-sulfidation epithermal, and gold-rich VMS deposits. The Witwatersrand deposits in South Africa have produced the most gold historically.
Bibliography
Franck Wilfried, N., Bolarinwa, A., Yongue-Fouateu, R., Ndikumana, J. D. D., Olajide-Kayode, J., Olisa, G., Abdus-Salam, M., Kamga, M., & Ernest Serge, D. (2017). Diversity of Gold Deposits, Geodynamics and Conditions of Formation: A Perspective View. Open Journal of Geology, 07, 1690–1709. https://doi.org/10.4236/ojg.2017.711113
Sillitoe, R. (2020). Gold deposit types: An overview (pp. 1–28). https://doi.org/10.5382/SP.23.01
