Metallic Ore Deposits and Formation Environments
Undoubtedly, the foundation of the mineral exploration strategy is laid by determining the appropriate mineralization environment for the targeted metal. It is difficult to imagine where and how the metal, which was enriched millions of years ago, is found today, but it is somehow possible. So how do geologists and mining professionals do this? Let’s examine this through models of the most important known mineralization types to strengthen this foundation. Plate tectonics and crustal movements at the plate scale contribute to mineral enrichments in specific regions. Paleontology and paleogeography have provided extensive data by tracing plate movements from the past to the present. Leveraging this data to meet the world’s metal needs, in this article, we will discuss various mineralization types including epithermal, volcanogenic massive sulphide (VMS), Mississippi Valley Type (MVT), Sedex, porphyry, skarn, Carlin type (CTDG), iron oxide copper-gold (IOCG), carbonate replacement (CRD), orogenic, and mesothermal deposits.
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1. Volcanogenic Massive Sulfide (VMS) Deposits
Volcanogenic massive sulfide (VMS) deposits represent a variety of mineral deposits formed in submarine volcanic environments through hydrothermal processes at temperatures below 400°C. Subtypes of these deposits include bimodal and felsic associated deposits. These deposits are often found in geological environments such as rift zones, oceanic spreading centers, and island arcs. The best examples in the world include the Skellefte District in Sweden and the Bathurst Mine in Canada. Their most important feature is that they generally have a stratiform layered structure and are often found in clusters, which increases their economic value and facilitates mineral exploration processes.
Zn, Pb, Cu, Au commodities are generally exploited in VMS deposits, important examples are:
- Rio Tinto, Spain: This supergiant mineralization contains around 1.5 billion tons of sulphide.
- Kholodrina, Russia: It is a deposit containing around 300 million tons of sulphide.
- Windy Craggy, Canada: Contains 300 million tons of sulphide.
- Brunswick, USA: Contains 230 million tons of sulfite.
- Ducktown, USA: Contains 163 million tons of sulfite.
2. Epithermal Deposits
Epithermal deposits are hydrothermal mineral deposits formed at temperatures between 50°C and 300°C (sometimes to 350). These deposits are divided into three different branches: high, low and intermediate sulphidation. Epithermal deposits generally contain quartz, adularia, native elements within carbonate minerals, and sulfides such as pyrite, galena, and sphalerite. Elements such as lead, zinc, copper, antimony, arsenic and mercury, especially gold and silver, are generally found in these deposits. Their formation is a scale that hovers between low and medium salinity. They occur in volcanic environments, especially volcanic calderas, hot springs and geothermal systems. The best examples in the world include Hishikari Gold Mine (Japan) and El Indio (Chile). Their most important characteristics are high efficiency and generally low sulfur content, making them economically valuable while reducing difficulties in operability.
Epithermal deposits are generally exploited for Au, Ag, Cu, Pb, Zn, Hg, Sb, As commodities, important examples are:
- Hishikari Mine, Japan
- Veladero Mine, Argentina
- El Indio, Chile and Argentina
- Round Mountain Mine, USA (Nevada)
- Waihi Mine, New Zealand
- Ovacık Mine, Türkiye
3. Sedimentary Exhalative (SedEx) & Mississippi Valley Type (MVT) Mineralizations
SEDEX (sedimentary exhalative) deposits are mineral deposits formed by the minerals of hydrothermal fluids precipitating on the sea floor, they form at temperatures less than 300°C. SEDEX deposits contain ore minerals such as galena, sphalerite and pyrite, as well as barite and fluorite. They are generally operated for Zn, Pb, Ag, Cu, Ba commodities. It is usually found in marine sediment basins as stratiform strutures where active tectonic processes occur. Sullivan Mine in Canada and Mt. Isa Mine in Australia are important examples.
Mississippi Valley Type (MVT) deposits are hydrothermal mineral deposits generally found in sedimentation basins. These deposits are formed by the circulation and settlement of low-temperature hydrothermal fluids, below 150°C (Less than 200), rich in lead-zinc, barite and fluorite, within structural elements such as faulting. MVT deposits are characterized by the presence of minerals such as galena, sphalerite and fluorite, often associated with barite. Pb, Zn, Ba, Sr, Cu are commonly found in MVT deposits. Notable examples include the Tri-State Area in the United States and the Pine Point Mine in Canada. Their most important feature is that they are stratiform or vein-like, making them economically valuable due to their high-quality ore deposits and relatively simple mining techniques.
4. Orogenic Mineralizations or Mesothermal Deposits
Orogenic gold deposits, also known as mesothermal gold deposits, are a type of gold mineralization formed during regional tectonic events often associated with mountain-building processes. It occurs in high-grade metamorphic rocks and is generally schistosity-controlled by fault-fractures due to compression or extension. The formation temperatures of such deposits can vary from high-temperature mineral paragenesis (mesothermal-hypothermal) to epithermal. These deposits encompass a variety of subtypes, including structurally controlled vein deposits, disseminated gold deposits, and placer deposits.
Minerals such as gold, quartz, pyrite, arsenopyrite and rarely sulphides such as chalcopyrite and galena containing elements commonly found in these deposits include gold, silver, arsenic and antimony. Orogenic gold deposits are generally clustered in areas of intense tectonic activity, often associated with major fault lines and shear zones in metamorphic areas. Notable examples of orogenic gold deposits (As, Ag, As, Sb, Bi) include the Witwatersrand Basin in South Africa and the Bendigo Gold Field in Australia. Their most important characteristics are their association with major tectonic events and the presence of significant gold mineralization, making them economically important targets for gold exploration and mining.
5. Porphyry Deposits
The formation temperature of porphyritic copper-gold-molybdenum deposits is generally between 200 and 700 degrees Celsius, and they are generally the product of waters of medium and high salinity. These deposits are formed when circulating hydrothermal activity carries precious metals such as copper, gold and molybdenum to the fractures at certain stages, as a result of cracks occurring during the cooling and solidification of magmatic rocks, which are generally associated with volcanic activities. Porphyry deposits are characterized by mineralization and alteration zones spread over a wide area. They are generally found in tectonically active regions such as subduction zones and continental collision zones. The best-known examples include the Bingham Canyon Mine in Utah and the Grasberg Mine in Indonesia. Their most important characteristics are their large size and often serve as important sources of more than one precious metal.
6. Skarn Mineralizations
Skarn deposits are hydrothermal mineral deposits formed in the contact zone between intrusions and carbonate or calcareous sedimentary rocks. These deposits include various subtypes such as calcareous, magnesic and exoskarn. They are generally formed as a result of thermal metamorphosis of surrounding rocks by convex magmatic fluids, and their temperatures generally vary between 200°C and 700°C, and are the product of moderate to high salinity waters. Skarn deposits generally contain minerals such as garnet, pyroxene and vesuvianite, and sulfides such as chalcopyrite and pyrite. Elements commonly found in these deposits include copper, gold, silver, zinc and tungsten.
Skarn deposits are generally placed in areas where contact metamorphosis occurs, especially at the edges of intrusive magmatic bodies, Fe, Cu, Zn, Pb, Au, W, Ti, Mo, REEs, Sn deposits are observed quite frequently. Notable examples of skarn deposits include the Greens Creek Mine in Alaska and the El Indio Mine in Chile. Their most important feature is that they contain valuable concentrations of multiple metals and are therefore economically important targets for mining.
7. Carlin Type Gold Deposits (CTGD) & Carbonate Replacement (CRD) Mineralizations
Carlin Type Gold deposits are deposited following layering or faulting in sedimentary rocks caused by the circulation of hydrothermal fluids at 150°C to 250°C. It is generally characterized by the distribution of microscopic gold particles along thin bands within pyrite and arsenopyrite. In addition to the eponymous Carlin Mine in Nevada, Goldstrike, Cortez and many other examples are located on 4 major trends. Carbonate displacement deposits, more similar to distal skarn deposits than the Carlin type, are known for hydrothermal activity progressing through layers of sedimentary rocks and structural elements perpendicular to them.
Carlin-type deposits are a subtype of sediment-hosting disseminated gold deposits and are specific to Nevada, USA. These deposits are associated with the Carlin Trend, a linear clustering of gold mineralizations located in north-central Nevada. Carlin-type deposits consist of fine dispersion of microscopic gold particles usually associated with arsenic sulphides such as arsenopyrite and realgar, occasionally they may contain pyrite and stibnite. Elements commonly found in these deposits include Au, Ag, As, Sb, Hg, Tl. Salinity changes in hydrothermal fluids play an important role in their formation. Carlin-type deposits are generally hosted in carbonate rocks, especially limestone, in areas of complex faulting and folding associated with ancient tectonic events. The Carlin Trend in Nevada is home to some of the world’s most significant Carlin-type deposits, including the Goldstrike Mine and the Carlin Mine. Their most important characteristics are their high gold grades and large areas of mineralization, making them deposits that play an important role in gold production in the United States.
8. Iron Oxide Copper - Gold (IOCG) Deposits
Iron Oxide Copper-Gold (IOCG) deposits represent a type of mineral deposits that contain significant amounts of iron oxide along with copper and gold mineralization. These deposits include several subtypes, including IOCG deposits dominated by magnetite and hematite. It typically forms at temperate temperatures between 200°C and 400°C, formed by the interaction of hydrothermal fluids with rocks in the Earth’s crust. IOCG deposits contain minerals such as magnetite, hematite, chalcopyrite and bornite, and contain significant concentrations of elements such as copper, gold and sometimes uranium.
These deposits are often associated with major tectonic features at crustal extension or junctional zones, notable examples include the Olympic Dam mine in Australia and the Candelaria mine in Chile. Their most important feature is that they contain valuable concentrations of copper, gold and other elements, making them economically important targets for mining.
Subjects discussed in this article may overlap with your mineral exploration, modeling, mining operation and business development issues and may provide solutions for those. However, remember that various factors specific to your business may bring about different challenges. Therefore, seek support from expert consultants to evaluate all data together in order to convert potential into profit most efficiently.
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