<p>Considering this again, from a slightly different perspective...</p>
<p>Minerals such as gold, for instance, are deposited along faults and fractures by super-saturated hydrothermal solutions emanating from a cooling and solidified magma source at depth.  As these <em>mother liquors</em> encounter cooler rock, they become the agent of deposition of metals such as gold or silver, which do not combine easily with other constituents in this super-heated water.  Consequently, the gold is deposited in its native form as a metal that is easily recognized. And silver may be deposited either as a native metal or as a metal sulfide.  Quartz, a silica mineral, is typically found in association with such gold and silver deposits.  Where these gold-laced quartz veins are discovered and accessible, they are mined – first by placement of an adit to determine the quality of the gold-rich vein, and second by expansion of the adit into a tunnel or shaft, to recover the gold ore.</p>
<p>As these mineral deposits become exposed at the surface, they are then subject to erosion and their source may remain undiscovered.  Gold, however, is a mineral known to be largely inert as it will not combine with carbonate or dissolve in atmospherically derived carbonic and nitric acid.  The other mineral constituents such as quartz will, however, ultimately break down in these atmospherically derived acids.  Hence, gold is thus left behind as elemental flakes and nuggets which are washed down slope by rainwater runoff, and ultimately into streams.  Eventually, this gold becomes transported to the sea.  <em>Placer deposit</em> is the term given to gold found as nuggets and flakes in association with stream gravels.  Gold is typically recovered from placers by sluicing and washing of the placer gravel to remove the lower density gravels and concentrate the higher density gold.  A metal of disdain in the sluicing process is <em>lead.</em>  Some silver sulfides are found in gold  placers and these will be concentrated along with lead sulfides in the sluicing process, but they are very difficult to distinguish and separate.  Gold, by virtue of its density and color, is easily separated.</p>
<p>The age of these deposits may be difficult to ascertain.  Some vein bodies may contain compounds that may be dated using <em>radiometric methods.</em> These methods assess the relative amounts of certain radioactive elements, or end constituents in the radioactive-decay process, to determine age.  Gold deposits in the Cripple Creek district, in Colorado (USA) are found in relation to Oligocene volcanics (approx. 34 to 23 million years old).  But in other instances, with placer deposits, there may be no readily apparent source and the placer has to be dated by other inferential means, if possible.  Such deposits may have ages of several hundred thousand to millions of years.  Of course, the age of the gold within the placer is much, much, older.</p>
<p>Nevertheless, many other metals in hydrothermal solutions will combine with sulfides to produce metal-sulfide ores which are deposited as the solution cools, or as the parent magma body cools.  These sulfide ores are mined at the earth's surface, or at limited depth.  In the American southwest, for instance, these sulfide ores are found in association with volcanic vents and pipes where the magma was sourced from a subducting plate during the Jurassic. The magma cooled to form a pipe or large body having a crystalline structure called <em>porphyry.</em> Copper is one such metal that is of principal importance found in volcanic porphyry. Other metals such as elemental gold, silver, and molybdenum may be bound or trapped as sulfide compounds within copper ore and these other metals are extracted when the ore is smelted or acid processed. However, some of these copper ore bodies have been found at depths inaccessible to surface mining.  In these instances, the ore body is penetrated by an array of injection and extraction wells, and an acid solution is circulated through the ore body.  The acid solvent is then processed to remove these trace metals that may be in solution. The copper is removed by electroplating in a process known as <em>solvent-extraction electro-winning,</em> or SX-EW.</p>
<p>What constitutes an ore, or an ore body?  Basically, this is a matter of economics.  If the cost of winning the metal from the ore is less than what can be made from the sale of the metal, the body of rock from which the metal was won is called an <em>ore.</em>  In other words, <em>ore is  profitable.</em> However, some trace metals, such as gold and silver, or molybdenum, which are found at very low concentrations in such rocks, are by themselves, too costly to recover on their own.  Nevertheless, when another principal constituent metal can be produced from the rock, such as copper, for instance, these trace metals can also be relatively inexpensively recovered as part of the ore refining process and stockpiled to be sold later, especially at a time when the market price for copper is down and copper is not being sold. The production and sale of such trace metals will, therefore, help maintain the mining and ore-processing operation as profitable.  Typically gold has a stable price and is saleable at any time, while molybdenum is an in-demand metal commodity, particularly in the production of steel.</p>

CC BY-SA 4.0
2024-09-23T09:09:38.707Z
Excellent answer, thank you
Peter A
CC BY-SA 4.0
2024-09-23T05:00:02.723Z
2024-09-23T05:00:02.723Z
Thomas Perry
<p>Different minerals have different melting points thus volcanic activity creates molten channels which can melt thru some strata and block others. These minerals leak and inevitable cool producing vein deposits.</p>

CC BY-SA 4.0
2024-09-22T06:20:18.767Z
2024-09-22T06:20:18.767Z
LazyReader
<p>This happens because different element behave in different ways.</p>
<p>Just like salt (sodium chloride) is very soluble and can be transported by water from one place to another, or carbon tends to burn and end up as carbon dioxide in the atmosphere, all elements will move and tend to bond with other elements depending on the condition.</p>
<p>For example, when magma forms, some elements tend to end up in the magma preferentially to other elements that are left behind. By doing this, you are concentrating one set of elements in the residue, and another set of elements ends up in the lava. Some elements can be dissolved in water, and other elements can be dissolved in pressurised supercritical water (which exists in the deep earth). Once this water flows, it can pick up elements from one place and move them to another place. If this happens over very long time and volume of rock, you can move quite a lot of the same elements into one place, forming a deposit.</p>
<p>Tin, for example, tends to end up in magmas. Once the magmas crystallise into rock, the tin doesn't actually like to be in the rock, so it ends up in the volcanic gas that comes off the magma. If this is channeled through cracks in the rock, the tin gets deposited in veins.</p>
<p>Same for gold: There are special conditions that can dissolve gold and move it from one place to another. It turns out that gold in &quot;atomic dust&quot; form is picked up from a large volume of rock, and then being channeled into a much smaller volume.</p>

CC BY-SA 4.0
2024-09-20T22:28:39.323Z
There's a volcano in Antarctica that spews the gold out. There is no chance for a vein to form as it instantly freezes in the arctic air into a fine dust.
David S
CC BY-SA 4.0
2024-09-21T10:12:40.777Z
@DavidS many volcanoes have some gold in their emissions. Whakaari / White Island in New Zealand is a good examples. None of the volcanoes will form veins from the erupted material regardless of air temperature, and all will freeze to fine dust or end up in whatever volcanic stuff comes out. Veins form underground, within the Earth, where the air temperature has no influence.
Gimelist
CC BY-SA 4.0
2024-09-19T12:14:25.323Z
2024-09-19T12:14:25.323Z
Gimelist
<p>One would imagine that the various atoms of the periodic table would be well mixed in the earth's crust. Yet, certain locations on earth have large amounts of specific mineral deposits. Consider gold in South Africa, or tin in Cornwall, for example.</p>
<p>Why are specific minerals, like gold, found in veins or even nuggets rather than being dispersed evenly around the world in a fine atomic dust?</p>
<p>What process caused a nugget of gold to form, and when did it happen?</p>

<mineralogy><mining><economic-geology>
Why do mineral deposits exist in veins?
Peter A
# Why do mineral deposits exist in veins?

(Asked by: username_0 on 2024-09-18)

One would imagine that the various atoms of the periodic table would be well mixed in the earth's crust. Yet, certain locations on earth have large amounts of specific mineral deposits. Consider gold in South Africa, or tin in Cornwall, for example.

Why are specific minerals, like gold, found in veins or even nuggets rather than being dispersed evenly around the world in a fine atomic dust?

What process caused a nugget of gold to form, and when did it happen?

**Tags:** mineralogy, mining, economic-geology


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## 3 answers

### Answer by username_3 on 2024-09-19. Score: 8 | Accepted answer

This happens because different element behave in different ways.

Just like salt (sodium chloride) is very soluble and can be transported by water from one place to another, or carbon tends to burn and end up as carbon dioxide in the atmosphere, all elements will move and tend to bond with other elements depending on the condition.

For example, when magma forms, some elements tend to end up in the magma preferentially to other elements that are left behind. By doing this, you are concentrating one set of elements in the residue, and another set of elements ends up in the lava. Some elements can be dissolved in water, and other elements can be dissolved in pressurised supercritical water (which exists in the deep earth). Once this water flows, it can pick up elements from one place and move them to another place. If this happens over very long time and volume of rock, you can move quite a lot of the same elements into one place, forming a deposit.

Tin, for example, tends to end up in magmas. Once the magmas crystallise into rock, the tin doesn't actually like to be in the rock, so it ends up in the volcanic gas that comes off the magma. If this is channeled through cracks in the rock, the tin gets deposited in veins.

Same for gold: There are special conditions that can dissolve gold and move it from one place to another. It turns out that gold in "atomic dust" form is picked up from a large volume of rock, and then being channeled into a much smaller volume.

> **Comments:**
> **username_4**: There's a volcano in Antarctica that spews the gold out. There is no chance for a vein to form as it instantly freezes in the arctic air into a fine dust.  
> **username_3**: @username_4 many volcanoes have some gold in their emissions. Whakaari / White Island in New Zealand is a good examples. None of the volcanoes will form veins from the erupted material regardless of air temperature, and all will freeze to fine dust or end up in whatever volcanic stuff comes out. Veins form underground, within the Earth, where the air temperature has no influence.  

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### Answer by username_1 on 2024-09-23. Score: 3

Considering this again, from a slightly different perspective...

Minerals such as gold, for instance, are deposited along faults and fractures by super-saturated hydrothermal solutions emanating from a cooling and solidified magma source at depth. As these *mother liquors* encounter cooler rock, they become the agent of deposition of metals such as gold or silver, which do not combine easily with other constituents in this super-heated water. Consequently, the gold is deposited in its native form as a metal that is easily recognized. And silver may be deposited either as a native metal or as a metal sulfide. Quartz, a silica mineral, is typically found in association with such gold and silver deposits. Where these gold-laced quartz veins are discovered and accessible, they are mined – first by placement of an adit to determine the quality of the gold-rich vein, and second by expansion of the adit into a tunnel or shaft, to recover the gold ore.

As these mineral deposits become exposed at the surface, they are then subject to erosion and their source may remain undiscovered. Gold, however, is a mineral known to be largely inert as it will not combine with carbonate or dissolve in atmospherically derived carbonic and nitric acid. The other mineral constituents such as quartz will, however, ultimately break down in these atmospherically derived acids. Hence, gold is thus left behind as elemental flakes and nuggets which are washed down slope by rainwater runoff, and ultimately into streams. Eventually, this gold becomes transported to the sea. *Placer deposit* is the term given to gold found as nuggets and flakes in association with stream gravels. Gold is typically recovered from placers by sluicing and washing of the placer gravel to remove the lower density gravels and concentrate the higher density gold. A metal of disdain in the sluicing process is *lead.* Some silver sulfides are found in gold placers and these will be concentrated along with lead sulfides in the sluicing process, but they are very difficult to distinguish and separate. Gold, by virtue of its density and color, is easily separated.

The age of these deposits may be difficult to ascertain. Some vein bodies may contain compounds that may be dated using *radiometric methods.* These methods assess the relative amounts of certain radioactive elements, or end constituents in the radioactive-decay process, to determine age. Gold deposits in the Cripple Creek district, in Colorado (USA) are found in relation to Oligocene volcanics (approx. 34 to 23 million years old). But in other instances, with placer deposits, there may be no readily apparent source and the placer has to be dated by other inferential means, if possible. Such deposits may have ages of several hundred thousand to millions of years. Of course, the age of the gold within the placer is much, much, older.

Nevertheless, many other metals in hydrothermal solutions will combine with sulfides to produce metal-sulfide ores which are deposited as the solution cools, or as the parent magma body cools. These sulfide ores are mined at the earth's surface, or at limited depth. In the American southwest, for instance, these sulfide ores are found in association with volcanic vents and pipes where the magma was sourced from a subducting plate during the Jurassic. The magma cooled to form a pipe or large body having a crystalline structure called *porphyry.* Copper is one such metal that is of principal importance found in volcanic porphyry. Other metals such as elemental gold, silver, and molybdenum may be bound or trapped as sulfide compounds within copper ore and these other metals are extracted when the ore is smelted or acid processed. However, some of these copper ore bodies have been found at depths inaccessible to surface mining. In these instances, the ore body is penetrated by an array of injection and extraction wells, and an acid solution is circulated through the ore body. The acid solvent is then processed to remove these trace metals that may be in solution. The copper is removed by electroplating in a process known as *solvent-extraction electro-winning,* or SX-EW.

What constitutes an ore, or an ore body? Basically, this is a matter of economics. If the cost of winning the metal from the ore is less than what can be made from the sale of the metal, the body of rock from which the metal was won is called an *ore.* In other words, *ore is profitable.* However, some trace metals, such as gold and silver, or molybdenum, which are found at very low concentrations in such rocks, are by themselves, too costly to recover on their own. Nevertheless, when another principal constituent metal can be produced from the rock, such as copper, for instance, these trace metals can also be relatively inexpensively recovered as part of the ore refining process and stockpiled to be sold later, especially at a time when the market price for copper is down and copper is not being sold. The production and sale of such trace metals will, therefore, help maintain the mining and ore-processing operation as profitable. Typically gold has a stable price and is saleable at any time, while molybdenum is an in-demand metal commodity, particularly in the production of steel.

> **Comments:**
> **username_0**: Excellent answer, thank you  

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### Answer by username_2 on 2024-09-22. Score: 0

Different minerals have different melting points thus volcanic activity creates molten channels which can melt thru some strata and block others. These minerals leak and inevitable cool producing vein deposits.


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