Hydrothermal mineral deposits are accumulations of valuable minerals which formed from hot waters circulating in Earth's crust through fractures. They eventually produce metallic-rich fluids concentrated in a selected volume of rock, which become supersaturated and then precipitate ore minerals. In some occurrences, minerals can be extracted for a profit by mining. Discovery of mineral deposits consumes considerable time and resources and only about one in every one thousand prospects explored by companies are eventually developed into a mine. [1] A mineral deposit is any geologically significant concentration of an economically useful rock or mineral present in a specified area. [2] The presence of a known but unexploited mineral deposit implies a lack of evidence for profitable extraction. [2]
Hydrothermal mineral deposits are divided into six main subcategories: porphyry, skarn, volcanogenic massive sulfide (VMS), sedimentary exhalative (SEDEX), and epithermal and Mississippi Valley-type (MVT) deposits. Each hydrothermal mineral deposit has different distinct structures, ages, sizes, grades, geological formation, characteristics and, most importantly, value. [3] Their names derive from their formation, geographical location or distinctive features. [3]
Generally, porphyry-type mineral deposits form in hydrothermal fluid circulation systems developed around felsic to intermediate magma chambers and/or cooling plutons. However, they did not precipitate directly from the magma. While, a skarn deposit is an assemblage of ore and calc-silicate minerals, formed by metasomatic replacement of carbonate rocks in the contact aureole of a pluton. [4] Volcanogenic massive sulfide deposits form when mafic magma at depth, (perhaps a few kilometers beneath the surface), acts as a heat source, causing convective circulation of seawater through the oceanic crust. [5] The hydrothermal fluid leaches metals as it descends and precipitates minerals as it rises. Sedimentary exhalative deposits, also called sedex deposits, are lead-zinc sulfide deposits formed in intracratonic sedimentary basins by the submarine venting of hydrothermal fluids. These deposits are typically hosted in shale. Hydrothermal epithermal deposits consist of geological veins or groups of closely spaced geological veins. Finally, Mississippi Valley-type (MVT) are hosted in limestone or dolomite that was deposited in a shallow marine environment in a tectonically stable intraplate environment. As expected in such an environment, volcanic rocks, folding and regional metamorphism are absent as a general rule. MVT deposits commonly lie in close proximity to evaporites. [6]
A mineral ore deposit is the volume of rock that can be mined at a profit. [7] Therefore, there are many variants that can define whether a mineral deposit is profitable or not, such as price, tonnage, or location. Mineral commodities can be classified as metals or non-metals. [2] Metals refer to elements of the periodic table which include base, ferrous, minor fissionable and precious metals. On the other hand, non-metals refer to industrial minerals such as gypsum, diamonds, oil, coal and aggregate. Hydrothermal deposits of economically valuable and recoverable minerals are generally considered scarce, meaning such deposits are very small relative to the total area of earth's surface. [2]
Each of these deposit types is usually considered to represent a distinctive deposit group with common features and in a similar four-dimensional geodynamic context. [8] The formation of deposits of a particular type can vary in time and location, but different deposit types may also form synchronously, but spatially separated within the same broad orogen. [9]
Hydrothermal mineral deposits play a key role in nearly all modern industrial activities.
Igneous | Ore minerals are precipitated directly from a magma. |
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Sedimentary | Ore minerals are concentrated or formed by sedimentary processes. |
Metamorphic | Ore minerals are formed during metamorphism. |
Hydrothermal | Ore minerals are precipitated by a hydrothermal solution percolating through intergranular spaces and along bedding planes and fractures in the host rocks. |
According to some authors, the hydrothermal solutions can have four origins, although any single volume of hydrothermal solution is commonly a mixture of two or more types: [11]
Ore minerals can form at the same time and from the same processes as the host rock, also termed as syngenetic, they can form slightly after the formation of the host rock, perhaps during weathering or compaction, also termed as diagenetic, or they can form much later than the host rock or epigenetic. [12] Host rock is the rock surrounding the ore deposit. [13] [6]
Hydrothermal deposit Subcategory | Known abbreviation | Formation | Principal metals | Host rocks |
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Porphyry | — | Epigenetic | Cu, Mo, Au | The ore is spatially associated with one or more high-level intrusions of felsic to intermediate composition such as granite, granodiorite or diorite. [14] |
Skarn | — | Epigenetic | Cu, Mo, Ag, Au | A skarn deposit is an assemblage of ore and calc-silicate minerals, formed by metasomatic replacement of carbonate rocks in the contact aureole of a pluton. [15] |
Volcanogenic massive sulphide | VMS | Syngenetic | Cu, Zn, Pb | The host rocks are mainly volcanic, with the felsic volcanic rocks pointing to a convergent setting (island arc or orogenic belt). [16] |
Sedimentary exhalative | SEDEX | Syngenetic | Zn, Pb | These deposits are commonly stratiform and are typically hosted in shale. [3] |
Epithermal | — | Epigenetic | Au, Ag | The host rocks can be sheared muscovite granite, small plutons. |
Mississippi Valley-type | MVT | Epigenetic | Pb, Zn | MVT deposits are hosted in carbonate rocks, whereas sedex deposits are found within marine shales |
Porphyry deposits account for most of the copper and molybdenum world production, 60 and 95 percent of its supply respectively. [1]
Porphyry-type ore deposits form in hydrothermal fluid circulation systems developed above and around high-level, subvolcanic felsic to intermediate magma chambers and/or cooling plutons. The ore is temporally and genetically related to the intrusions, but did not precipitate directly from the magma. [1]
Porphyry mineral deposits are formed when two plate tectonic plates collide in an advanced subduction zone, then cools off reacting with existing rocks and finally forming a copper deposit. The level of displacement is usually shallow at less than two kilometers below surface in an active volcanic area.
An example for a typical arc-island porphyry deposit is described as follows: [1]
Finally, volcanic activity ceased and erosion removed the upper portions of the volcano and exposed the intrusive rocks and stockwork mineralization that used to lie within. [17]
Age | Average age of 13 million years, continental and oceanic arcs of Tertiary and Quaternary age. [18] |
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Size | Amongst the largest in the world, especially porphyry-type deposits. [19] |
Location | The 25 biggest porphyry deposits are found in the southwest Pacific and South America. [20] |
Host rocks | Ore is associated with one or more subvolcanic intrusions of felsic to intermediate composition such as granite, granodiorite or diorite. [21] |
Economic metals | In island arc settings where the host plutons are typically andesitic in composition, the elements of economic interest are mainly copper and gold. In contrast, those that occur in continental orogenic belts are typically rhyolitic in composition and carry copper, molybdenum and gold, and in some cases tin and/or tungsten. [21] |
Grade | Commonly low in grade and have relatively low dollar value [21] |
Fractures | Ore minerals are generally confined to small veinlets and less common larger veins that formed as fracture fillings in the host rocks. [21] Hydrothermal breccia can often occur, sometimes in the form of pebble dikes. [22] |
Hydrothermal alteration | The wallrock on both sides of each veinlet is typically altered to varying degrees. The primary silicate minerals such as feldspar and amphibole are replaced by hydrothermal minerals stable at temperatures of about 400 °C or less such as chlorite, epidote, muscovite and quartz. [21] Alteration assemblages typically include proximal potassic, intermediate phyllic or QSP, and more distal propylitic and argillic alteration. [23] Where veinlets are close together, the zones of alteration around each veinlet overlap, making the whole rock hydrothermally altered. [24] |
Mining activity | Bingham Mine, The Chuquicamata deposit, El Teniente deposit, Henderson Mine |
Skarn Mineral Deposits tend to be small in size but high in mineral grade. Therefore, it is a balance and challenge to find a profitable skarn orebody.
Geologically speaking, a skarn deposit is an assemblage of ore and calc-silicate minerals, formed by metasomatic replacement of carbonate rocks in the contact aureole of a pluton. Typical calc-silicate minerals are garnet, epidote, pyroxene, chlorite, amphibole and quartz – magnesian minerals dominate if dolomite is replaced whereas calcic minerals dominate where limestone is replaced. [25]
Skarn deposits are of economic interest, since they are the source of numerous metals as well as minerals of industrial application. [25]
Skarn formation, as illustrated in the figure on the right, can be explained in three stages: [26]
There is a very close spatial association with the granite, the skarn occurs only within marble which is known to be a very reactive rock type, and the skarn has a chemical composition that is unlike any known igneous or sedimentary rock type. Furthermore, various structures such as flexures in the contact or impermeable hornfels beds affected the distribution and ore grade of the skarn zones. [27]
Size | Relatively small, they tend to be less than 10 million tonnes, although a few large ones exist such as the Mission mine in Arizona, 320 million tonnes. [28] |
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Economic Metals | Tungsten, tin, molybdenum, copper, iron, lead-zinc and gold ores. [28] |
Geologic Features | Nonfoliate rock textures formed by contact metamorphism such as hornfels and marble [28] |
Level of Emplacement | Close proximity to a felsic to intermediate pluton of relatively large size. Therefore, shallow depths. [28] |
Grade | Ore zones may grade laterally into calcic or dolomitic marble. [28] |
Geometry | Equidimensional geometries are most common. Many orebodies are elongate along structural weaknesses such as faults and bedding planes The largest and thickest orebodies tend to occur where carbonate beds lie immediately above gently inclined pluton contacts. [28] |
Mining activity | Grasberg and Ertsberg Mines are part of a single mining complex in the glacier-capped mountains of Irian Jaya, Indonesia. Together, they comprise the single largest copper-gold mine in the world, with reserves of 2.8 billion tonnes grading 1.1% Cu and 1.1 g/t Au. [29] |
Hydrothermal vein ore deposits consist of discrete veins or groups of closely spaced veins. Veins are believed to be precipitated by hydrothermal solutions travelling along discontinuities in a rockmass. [10] They are commonly epithermal in origin, that is to say they form at relatively high crustal levels and moderate to low temperatures. They are epigenetic since they form after their host rocks. [10]
Hydrothermal vein deposits fall into three main categories:
There are two main possibilities for the origin of the ore, both of which are hydrothermal: [30]
One possibility, the rise of a small body of felsic magma may have led to either the:
Elements were leached from the already solidified portions of the pluton. The fluids would have migrated upward and outward, following fractures in the solidified part of the granite pluton, precipitating ore minerals in veins and altering the wallrocks.
The other possibility, a regional shearing event developed in the crust. Shearing take place at temperatures on the order of 300–400 °C. Thus, the shearing event may have been accompanied by the generation and movement of hydrothermal fluid as the crust was subjected to prograde devolatilization. [31] This fluid might have leached the ore elements from one part of the granite pluton and reprecipitated them in veins in another part of the same pluton, effectively concentrating them. [31]
Epithermal ore deposits form at shallow depth [32] and are typically tabular (two-dimensional) in geometry. [33]
Good examples are the gold-silver veins in northwestern Nevada and large ion veins such as the fluorspar veins in the St. Lawrence mine in Newfoundland [34] and the tin-bearing veins that made up the East Kemptville Mine in southwestern Nova Scotia. [35]
Volcanogenic massive sulfide (VMS) are responsible for almost a quarter of the world's zinc production while contributing for lead, silver and copper as well. VMS deposits tend to be of great size since they form over a long period of time and have a relatively high grade in valuable minerals. The main minerals in this deposit are sulphide minerals such as pyrite, sphalerite, chalcopyrite and galena.
The term “massive sulfide” deposit refers to any deposit containing more than 50% sulfide minerals. The modifier “volcanogenic” indicates that the massive sulfides are believed to be genetically related to volcanism that was ongoing at the time of sulfide deposition. Thus, VMS deposits are believed to be syngenetic or perhaps slightly diagenetic in age relative to their host volcanic rocks.
Deposition of VMS is due to mainly two reasons: [36]
VMS deposits form in zones of extension and active volcanism. The original fluid is mainly cold, alkaline, deficient-in-metals sea water and in some cases it can include a lesser proportion of magmatic fluid.
The main source of the minerals comes from the volcanic rocks through which the sea water flows, taking with it the minerals of the volcanic rock.
The sea water is heated, convection currents are formed and they ascend carrying the minerals which are discharged at the bottom of the sea or immediately below the surface in the form of black smokers. [37]
Magma rises up from the mantle and then cools off in the crust and then releases volatile fluids that contain metals that are eventually transported up to the surface and over time these accumulations become mineral deposits.
As the high-temperature volatile fluids from the magma make contact with low-temperature liquids such as seawater that travel downwards via cracks and faults, producing, due to the large difference in temperature and chemical properties, mineral precipitation, yielding the black colour in the black smokers that end up showing up in the seafloor.
The host rocks are mainly volcanic, with the felsic volcanic rocks pointing to a convergent setting such as an island arc or orogenic belt. Minor sedimentary beds such as chert and slate are found in VMS deposits and they indicate marine deposition, below the wave base.
VMS deposits formed on the seafloor, in the same way that modern seafloor smokers are forming today. The most recent compilations of VMS deposits on land include about 1,100 deposits in more than 50 countries and 150 different mining camps or districts. [38]
Age | Almost any age can potentially host a VMS deposit, the oldest VMS deposits are 3.4 billion years old. [39] |
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Size | Individual lenses that are a hundred meters thick and extend hundred meters along strike. The median deposit size is only about 70,000 tonnes. [36] |
Types | There are three of types of sulfide ore that can be found in these mineral deposits. [40]
|
Geometry | Typically tabular to lensoid, and range from less than 1 to more than 150 million tonnes. They often occur in clusters. |
Economic minerals | Chalcopyrite (Cu), sphalerite (Zn), galena (Pb), silver and gold. The dominant gangue minerals are quartz, pyrite and pyrrhotite. Lenses of barite (BaSO4), gypsum or anhydrite are associated with the sulfides in some deposits. [39] |
Mining activity | Flin Flon, Manitoba, Canada, Kidd Creek Mine, Ontario, Canada |
Sedimentary exhalative (SEDEX) deposits account for 40% of total world zinc production, 60% of lead and a significant proportion of silver. Despite their economic importance however, sedex deposits are relatively rare. A worldwide compilation of sedex deposits indicates that about 70 are known, of which 24 have been or are being mined. The majority is uneconomic to mine because of relatively low grade or unusually fine grain size, making mill recovery rather low. [41]
SEDEX deposits are lead-zinc sulfide deposits formed in intracratonic rift basins by the submarine venting of hydrothermal fluids. These deposits are commonly stratiform, tabular - lenticular and are typically hosted in shale however, sedimentary rocks detrictics or even carbonates could be the host.
SEDEX deposits form in sedimentary basins under a regional tectonic extensional environment, under the ocean where cold seawater (blue arrows) is mixed with basin water and through sinsedimentary faults flow towards the bottom of the basin, which are heated by the geothermal gradient, and later ascends by convective currents (red arrows). [42]
Model for the origin of the Red Sea sulfide deposits. Cold seawater (blue arrows) enters the seafloor via deep-seated fractures. As it descends, it heats up and leaches silicon, metals and other solutes from the seafloor basalts.
The source of sulfur can be by bacterial reduction of marine sulfate a process that takes place at the bottom of the basin. It can also come from the washing of the underlying series or by the thermochemical reduction of the marine sulfate. Precipitation of sulfide minerals could be triggered by inorganic precipitation and/or bacterial precipitation.
Size | Average 41 million tonnes Generally take the form of stratiform lenses with maximum thicknesses in the range of just 5 to 20 m.. In contrast, sphalerite tends to be concentrated in the lower grade outer portions of the ore bodies. [43] |
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Grade | 6.8% Zn, 3.5% Pb and 50 g/t Ag [43] |
Ore minerals | Zinc, lead, silver, copper, tin and tungsten [43] |
Geometry | Form of stratiform lenses with maximum thicknesses in the range of just 5 to 20 meters. |
Mining activity | Mt Isa, Australia, Red Dog, USA, Sullivan Mine |
The deposits are hosted in limestone or dolomite that was deposited on shallow marine platforms in a tectonically stable intraplate environment. As expected in such an environment, volcanic rocks, folding and regional metamorphism are absent as a general rule. MVT deposits commonly lie in close proximity to evaporites and/or beneath unconformities. [43]
Deposits are discordant to bedding on a deposit scale, and are confined to specific stratigraphic horizons. Ore-hosting structures are most commonly zones of highly brecciated dolomite – these structures may be more or less vertical, crossing bedding at high angles, or they may be lensoid in shape extending in the same direction as bedding.
A petrogenetic model to explain MVT deposits in general:
Deposits are discordant to bedding on a deposit scale.
Ore-hosting structures are most commonly zolinknes [ clarification needed ] of highly brecciated dolomite.
These structures may be more or less vertical, crossing bedding at high angles, or they may be lensoid in shape extending in the same direction as bedding.
Size | Tend to be less than 10 million tonnes each, and they tend to occur in clusters. As many as 400 individual deposits occur within the upper Mississippi Valley mining district alone. [44] |
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Grade | Generally fall between 5% and 15% combined Pb plus Zn. Iron sulfides are commonly minor, although pyrite and chalcopyrite can be present and are even abundant in a few deposits. [43] |
Host rocks | Limestones and dolomite, deposited on shallow marine platforms in a tectonically stable intraplate environment |
Ore minerals | Sphalerite and galena |
Mining activity | Pine Point Mine, NWT |
Mississippi Valley-type deposits can be compared with the Red Sea deposits, which are modern analogues of ancient sedex deposits, some differences can be made: [44]
Ore is natural rock or sediment that contains one or more valuable minerals concentrated above background levels, typically containing metals, that can be mined, treated and sold at a profit. The grade of ore refers to the concentration of the desired material it contains. The value of the metals or minerals a rock contains must be weighed against the cost of extraction to determine whether it is of sufficiently high grade to be worth mining and is therefore considered an ore. A complex ore is one containing more than one valuable mineral.
Breccia is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix.
Sphalerite is a sulfide mineral with the chemical formula (Zn,Fe)S. It is the most important ore of zinc. Sphalerite is found in a variety of deposit types, but it is primarily in sedimentary exhalative, Mississippi-Valley type, and volcanogenic massive sulfide deposits. It is found in association with galena, chalcopyrite, pyrite, calcite, dolomite, quartz, rhodochrosite, and fluorite.
Hydrothermal circulation in its most general sense is the circulation of hot water. Hydrothermal circulation occurs most often in the vicinity of sources of heat within the Earth's crust. In general, this occurs near volcanic activity, but can occur in the shallow to mid crust along deeply penetrating fault irregularities or in the deep crust related to the intrusion of granite, or as the result of orogeny or metamorphism. Hydrothermal circulation often results in hydrothermal mineral deposits.
Skarns or tactites are coarse-grained metamorphic rocks that form by replacement of carbonate-bearing rocks during regional or contact metamorphism and metasomatism. Skarns may form by metamorphic recrystallization of impure carbonate protoliths, bimetasomatic reaction of different lithologies, and infiltration metasomatism by magmatic-hydrothermal fluids. Skarns tend to be rich in calcium-magnesium-iron-manganese-aluminium silicate minerals, which are also referred to as calc-silicate minerals. These minerals form as a result of alteration which occurs when hydrothermal fluids interact with a protolith of either igneous or sedimentary origin. In many cases, skarns are associated with the intrusion of a granitic pluton found in and around faults or shear zones that commonly intrude into a carbonate layer composed of either dolomite or limestone. Skarns can form by regional or contact metamorphism and therefore form in relatively high temperature environments. The hydrothermal fluids associated with the metasomatic processes can originate from a variety of sources; magmatic, metamorphic, meteoric, marine, or even a mix of these. The resulting skarn may consist of a variety of different minerals which are highly dependent on both the original composition of the hydrothermal fluid and the original composition of the protolith.
Metasomatism is the chemical alteration of a rock by hydrothermal and other fluids. It is traditionally defined as metamorphism which involves a change in the chemical composition, excluding volatile components. It is the replacement of one rock by another of different mineralogical and chemical composition. The minerals which compose the rocks are dissolved and new mineral formations are deposited in their place. Dissolution and deposition occur simultaneously and the rock remains solid.
Volcanogenic massive sulfide ore deposits, also known as VMS ore deposits, are a type of metal sulfide ore deposit, mainly copper-zinc which are associated with and created by volcanic-associated hydrothermal events in submarine environments.
Greisen is a highly altered granitic rock or pegmatite, usually composed predominantly of quartz and micas. Greisen is formed by self-generated alteration of a granite and is a class of moderate- to high-temperature magmatic-hydrothermal alteration related to the late-stage release of volatiles dissolved in a magma during the solidification of that magma.
Porphyry copper deposits are copper ore bodies that are formed from hydrothermal fluids that originate from a voluminous magma chamber several kilometers below the deposit itself. Predating or associated with those fluids are vertical dikes of porphyritic intrusive rocks from which this deposit type derives its name. In later stages, circulating meteoric fluids may interact with the magmatic fluids. Successive envelopes of hydrothermal alteration typically enclose a core of disseminated ore minerals in often stockwork-forming hairline fractures and veins. Because of their large volume, porphyry orebodies can be economic from copper concentrations as low as 0.15% copper and can have economic amounts of by-products such as molybdenum, silver, and gold. In some mines, those metals are the main product.
Various theories of ore genesis explain how the various types of mineral deposits form within Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined.
Sedimentary exhalative deposits are zinc-lead deposits originally interpreted to have been formed by discharge of metal-bearing basinal fluids onto the seafloor resulting in the precipitation of mainly stratiform ore, often with thin laminations of sulfide minerals. SEDEX deposits are hosted largely by clastic rocks deposited in intracontinental rifts or failed rift basins and passive continental margins. Since these ore deposits frequently form massive sulfide lenses, they are also named sediment-hosted massive sulfide (SHMS) deposits, as opposed to volcanic-hosted massive sulfide (VHMS) deposits. The sedimentary appearance of the thin laminations led to early interpretations that the deposits formed exclusively or mainly by exhalative processes onto the seafloor, hence the term SEDEX. However, recent study of numerous deposits indicates that shallow subsurface replacement is also an important process, in several deposits the predominant one, with only local if any exhalations onto the seafloor. For this reason, some authors prefer the term clastic-dominated zinc-lead deposits. As used today, therefore, the term SEDEX is not to be taken to mean that hydrothermal fluids actually vented into the overlying water column, although this may have occurred in some cases.
Seafloor massive sulfide deposits or SMS deposits, are modern equivalents of ancient volcanogenic massive sulfide ore deposits or VMS deposits. The term has been coined by mineral explorers to differentiate the modern deposit from the ancient.
Carbonate-hosted lead-zinc ore deposits are important and highly valuable concentrations of lead and zinc sulfide ores hosted within carbonate formations and which share a common genetic origin.
Partial melting is the phenomenon that occurs when a rock is subjected to temperatures high enough to cause certain minerals to melt, but not all of them. Partial melting is an important part of the formation of all igneous rocks and some metamorphic rocks, as evidenced by a multitude of geochemical, geophysical and petrological studies.
Iron oxide copper gold ore deposits (IOCG) are important and highly valuable concentrations of copper, gold and uranium ores hosted within iron oxide dominant gangue assemblages which share a common genetic origin.
The Kiruna mine is the largest and most modern underground iron ore mine in the world. The mine is located in Kiruna in Norrbotten County, Lapland, Sweden. The mine is owned by Luossavaara-Kiirunavaara AB (LKAB), a large Swedish mining company. In 2018 the mine produced 26.9 million tonnes of iron ore. The Kiruna mine has an ore body which is 4 km (2.5 mi) long, 80 metres (260 ft) to 120 metres (390 ft) thick and reaching a depth of up to 2 km (1.2 mi). Since mining began at the site in 1898, the mine has produced over 950 million tonnes of ore. As of 2020 the main haulage level is 1365 m below the ore outcrop at Kiirunavaara that existed prior to mining.
El Laco is a volcanic complex in the Antofagasta Region of Chile. It is directly south of the Cordón de Puntas Negras volcanic chain. Part of the Central Volcanic Zone of the Andes, it is a group of seven stratovolcanoes and a caldera. It is about two million years old. The main summit of the volcano is a lava dome called Pico Laco, which is variously reported to be 5,325 metres (17,470 ft) or 5,472 metres (17,953 ft) high. The edifice has been affected by glaciation, and some reports indicate that it is still fumarolically active.
Farallon Negro is a volcano in the Catamarca province of Argentina. Active between about 9-8 million years ago, it was formerly a stratovolcano or a multi vent volcano. Eventually, erosion removed most of the volcano and exposed the underlying structure including subvolcanic intrusions.
An orogenic gold deposit is a type of hydrothermal mineral deposit. More than 75% of the gold recovered by humans through history belongs to the class of orogenic gold deposits. Rock structure is the primary control of orogenic gold mineralization at all scales, as it controls both the transport and deposition processes of the mineralized fluids, creating structural pathways of high permeability and focusing deposition to structurally controlled locations.
Massive sulfide deposits are ore deposits that have significant stratiform ore bodies consisting mainly of sulfide minerals. Most massive sulfide ore deposits have other portions that are not massive, including stringer or feeder zones beneath the massive parts that mostly consist of crosscutting veins and veinlets of sulfides in a matrix of pervasively altered host rock and gangue.
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