Saturday, August 6, 2022

How Is Gold Formed Geologically

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Why Do Gold Deposits Form Only In Certain Areas Of The Earth

Geology of Gold deposits – How Gold deposits form_Volcanoes, Yellowstone, sulfur and iron Epithermal

In the map above you can find that most elements are spread evenly throughout Earth’s crust and that they are available all around the Earth. However, gold can only be found in certain areas of the planet such as Australia and Canada. Is there a specific reason to why gold can only be mined at these locations or is it just a coincidence?

I’ll take the form of the question given by another person here and attempt to provide a different answer.

So what you are asking is: “How did gold become so concentrated in certain parts of the world?”

So yes, gold is all around but the concentration is too low to make extraction of it worthwhile. You need some process to take small amounts of gold from a large volume and turn it into large amounts of gold in a small volume where it is convenient to build a mining facility and get it from the Earth.

One of the most common process to concentrate gold is through the action of hydrothermal fluids. This is basically heated water flowing through the Earth’s crust. Heated water with certain properties such as acidity or dissolved anions can dissolve solid gold and put it into solution. Just like regular water can dissolve table-salt or sugar and put it into solution.

I made an example, that I hope will help you understand this in a clearer way:

I do agree with Gimelist how gold is accumulated through hydrothermal fluids, adding that the main driver is for this process is volcanism.

Geology Of Hard Rock Gold Deposits

Man knew more about gold itself and lusted for it much before he understood the geology of hard rock gold or its deposits. Man had to learn about hard rock extraction methods and how to locate those gold deposits just to satisfy the thirst for that yellow metal. Gold has been the most highly esteemed and sought after precious commodity since the times of antiquity It has spurred on numerous …

What Are Gold Deposits

Gold occurs in a wide range of ore deposit types, which can be roughly defined as either primary ore deposits or secondary ore deposits . Gold in all ore deposits is typical in the form of native gold and/or electrum , or within the crystal structure or as small nano-inclusions within other minerals .

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Gold Comes From Outer Space

Gold, the shiny yellow metal prized for its beauty and malleability and used in many different industries, is actually created inside massive stars when they explode into a supernova. Of course, after a star supernovas and forms gold, the precious metal has to travel to Earth in some way. By studying ancient rock samples with high-precision instruments, scientists have found evidence that accessible gold, or the gold that is technologically and economically feasible to reach on the surface of the planet, arrived via asteroids when the earth was still fairly young.

Heres another interesting fact: During the initial formation of the planet, heavy iron sank into the middle to form the planets core. This iron took other heavy elements, like gold, with it. Thats where most of the gold on the planet should be, rather than in the crust, which is where we find it. Because the gold is so near the earths surface, humans have been able to stumble across it aboveground and extract it through mining.

Scientists say gold is actually ten times more common in the planets crust than they would expect it to be if it came here when the earth was still forming and molten hot. This lends credence to their conclusion that gold must have arrived on earth later, and it is likely that asteroids carried it here. It is fair to conclude that gold comes from outer space.

Alluvial Gold Explained To Help You Find Gold

Gold

Fine gold and small nuggets Can be transported many kilometers from source of gold. Can be ancient alluvial gold deposits in ground lifted high above current stream levels. Large nuggets, may be closer to primary gold source. How is this type of gold transported. Moved by water through gullies, streams, creeks and rivers.

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How Do Gold Nuggets Form

Many Nuggets Gold formed as clusters of gold crystals from very hot water in cracks and fissures in hard-rocks, often with quartz. Later, weathering released the gold nuggets that end up in a stream due to gravity.

Nuggets are gold fragments weathered out of an original lode. They often show signs of abrasive polishing by stream action, and sometimes still contain inclusions of quartz or other lode matrix material. A 2007 study on Australian nuggets ruled out speculative theories of supergene formation via in-situ precipitation, cold welding of smaller particles, or bacterial concentration, since crystal structures of all of the nuggets examined proved they were originally formed at high temperature deep underground .

Other precious metals such as platinum form nuggets in the same way. A later study of native gold from Arizona, US, based on lead isotopes indicates that a significant part of the mass in alluvial gold nuggets in this area formed within the placer environment.

How Much Gold Is In The World

The amount of gold extracted from the Earth is a tiny fraction of its total mass. In 2016, the United States Geological Survey estimated 5,726,000,000 troy ounces or 196,320 U.S. tons had been produced since the dawn of civilization. About 85% of this gold remains in circulation. Because gold is so dense , it does not take up much space for its mass. In fact, if you melted all the gold mined to date, you’d wind up with a cube about 60 feet across!

Nevertheless, gold accounts for a few parts per billion of the mass of the Earth’s crust. While it’s not economically feasible to extract much gold, there are about 1 million tons of gold in the top kilometer of the Earth’s surface. The abundance of gold in the mantle and core is unknown, but it greatly exceeds the amount in the crust.

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Exploring For Gold: From Ancient Peoples To Modern Mines

Finding sources of metals can be done in a number of ways. Geologists can recognise minerals or specific rock types they know contain the metal or element they are looking for. This can involve many weeks or months of studying aerial or satellite photographs and then going out into the countryside , to hunt for evidence and collect rock samples. These are then brought back to the laboratory for analysis and the percentage of different elements can be worked out.

But normally it’s a combination of methods. There are more indirect routes that dont look at the elements in the rocks themselves but measure them in the water of streams and rivers.

The concentration of metals that are found dissolved in stream and river water will increase as you get closer to the source rock which contains them. This means geologists can plot maps showing these concentrations that tell us where the best places might be to find metals. Metal concentrations can also be measured from soil samples and used to track sources. The ultimate aim is to find the source of the gold or other metal of interest.

How Do You Find Gold Deposits

How gold is formed on earth.

Well, that is essentially what exploration geologists and prospectors do, we try and locate where the gold deposits might be, whether it is gold in primary ore deposits , or gold in secondary ore deposits . There are lots of things to consider, from the global scale to the local scale . I wont go into detail about this as it is quite a rabbit hole , but the process typically involves applying a combination of new and old techniques and technologies, and a consideration and application of many branches of geosciences .

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What Is The Composition Of Gold Nuggets

Nuggets are usually 20.5K to 22K purity . Gold nuggets in Australia often are 23K or slightly higher, while Alaskan nuggets are usually at the lower end of the spectrum. Purity can be roughly assessed by the nugget color, the richer and deeper the orange-yellow the higher the gold content.

How Gold Is Formed In Quartz

How gold is formed geologically? Lode- gold deposits are intimately associated with orogeny and other plate collision events within geologic history. Most lode gold deposits sourced from metamorphic rocks because it is thought that the majority are formed by dehydration of basalt during metamorphism.

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How Is Gold Formed Origins And Process

    • Ph.D., Biomedical Sciences, University of Tennessee at Knoxville
    • B.A., Physics and Mathematics, Hastings College

    Gold is a chemical element easily recognized by its yellow metallic color. It is valuable because of its rarity, resistance to corrosion, electrical conductivity, malleability, ductility, and beauty. If you ask people where gold comes from, most will say you obtain it from a mine, pan for flakes in a stream, or extract it from seawater. However, the true origin of the element predates the formation of the Earth.

    Under Ancient Seas Another Location For Metal Deposits

    Gold

    The second main type of ore for copper, is a submarine sulphide deposit, such as that exposed at Parys Mountain in Wales. Gold is also associated with this mine.

    The Parys Mountain metal deposits on Anglesey in North Wales have been mined for almost 4,000 years, but the formation of the deposits dates back much further, to the Ordovician, over 443 million years ago. At that time, the area that we now call Anglesey, was underwater and part of an ancient ocean called Iapetus located south of the equator.

    The deposits that now make up the ores at Parys Mountain and at many copper deposits worldwide, were produced in volcanoes. But not the sort of volcano you might automatically think of these are subsea volcanoes. Most of the worlds volcanoes arent the cone shaped mountains with lava bursting out of them that you might imagine. Most volcanoes are found under the oceans, in long ridges which span the globe.

    These volcanoes make new oceanic crust at spreading centres distributed from the centre of the world oceans. These are the constructive plate margins and where all new sea floor is made.

    The Parys Mountain mine is actually divided into multiple zones, which have very different amounts of copper in each zone and not just copper, but other useful elements too.

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    Synthesizing The Element Gold

    Attempts by alchemists to turn lead into gold were unsuccessful because no chemical reaction can change one element into another. Chemical reactions involve a transfer of electrons between elements, which may produce different ions of an element, but the number of protons in the nucleus of an atom is what defines its element. All atoms of gold contain 79 protons, so the atomic number of gold is 79.

    Making gold isn’t as simple as directly adding or subtracting protons from other elements. The most common method of changing one element into another is to add neutrons to another element. Neutrons change the isotope of an element, potentially making the atoms unstable enough to break apart via radioactive decay.

    Japanese physicist Hantaro Nagaoka first synthesized gold by bombarding mercury with neutrons in 1924. While transmuting mercury into gold is easiest, gold can be made from other elementsâeven lead! Soviet scientists accidentally turned the lead shielding of a nuclear reactor into gold in 1972 and Glenn Seabord transmuted a trace of gold from lead in 1980.

    Thermonuclear weapon explosions produce neutron captures similar to the r-process in stars. While such events are not a practical way to synthesize gold, nuclear testing did lead to the discovery of the heavy elements einsteinium and fermium .

    How Does Gold Naturally Form On Earth’s Crust

    Gold is not formed on the Earth like diamonds and many other gems and minerals. Instead, most scientists now believe that gold actually came to earth from outer space in large meteorites that have struck the planet over billions of years. … geologically speaking. Most of the original discoveries of gold were made by accident around stream …

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    Bendigo: New Chum Line Of Reef Lazarus Co Cross

    This plan by GSV geologist E.J. Dunn illustrates the repetition at depth of the distinctive boomerang-shaped masses of quartz known as saddle reefs. Early miners at Bendigo discovered that a saddle reef at the surface indicated another such reef at depth. It was this predictability that led to successful deep sinking on the Bendigo goldfield.

    When gold mining faltered with the onset of the 1890s depression, the GSV launched an extensive underground mapping program to gauge the future prospects for mining at Bendigo. The findings of E.J. Dunn and his team were lauded by Bendigo miners and the press:

    ‘The general opinion for many years has been that the Bendigo goldfield is practically inexhaustible. That was the opinion of experienced miners. And now after careful survey and a collation of facts, a scientific opinion is given, which bears this out to the very letter Mr Dunn expresses the firm opinion thatvast deposits of gold remain to be won compared with which the gold hitherto yielded by the field is trifling. ‘

    Nor could the Advertiser resist from adding – It is a pity Sir Roderick Murchison is not alive to read these eloquent facts. Gold in abundance continues to be found in the reefs more than a kilometre under Bendigo up to the present day.

    Where Does Gold Come From

    Geology of coarse crystalline gold – Big Gold nugget geology – Formation of large gold nuggets

    Gold is heavenly, in every sense of the word. Most people dont know this but, while we mine for gold here on earth, all of the gold thats deposited in our planet was formed during the explosions of stars and collisions of asteroids, and eventually found its way to earth over time.On earth, gold is one of the most valuable precious metals and rarest natural minerals. It is also one of the 118 elements so far discovered and classified by humans.Pure gold is a bright warm yellow, malleable and soft substance. Its so soft that, in its purest form, it cant really be used for everyday wear. To harden it, it is alloyed with a mixture of metals like silver, copper, platinum, palladium and zinc.Its primary use is in jewellery, but its also used in finance, electronics, computers, dentistry, medicine, aerospace, glassmaking, and as awards and status symbols.Its clearly present in the formation and upkeep of many of our innovations, but how is gold made?

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    How Is Gold Formed And Where Does It Come From

    Where does gold come from? Sadly, leprechauns dont exist, so we wont be finding any gold pots at the ends of rainbows. Similarly, alchemists never managed to turn base metals into gold. How is gold actually formed? If we can recall back to our high school chemistry classes, we might remember that in its purest form gold is actually an element, notated by the symbol AU on the periodic table of elements. Gold isnt truly formedat least, not on Earth.

    Where Are Gold Nuggets Found

    It found in residual deposits where the gold-bearing veins or lodes are weathered. Nuggets are also found in the tailings piles of previous mining operations, especially those left by gold mining dredges.

    The best areas for finding gold nuggets are those which are known for producing coarse gold. The term coarse is used to describe gold pieces which range in size from a wheat grain to many grams. Scanning with a metal detector is the most common, practical method for finding gold nuggets and other forms of gold.

    Coarse gold did not occur in all gold fields, even when some were considered especially rich. In some areas of Australia the gold is fine and concentrated in crevices in bedrock and any gravel wash overlying this. A metal detector cannot pick up this fine gold sprinkled through sand and gravel, nor can it detect minute traces of gold still enclosed in quartz reef material.

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    Goldfields Mapping: Shallow Versus Deep Sinking

    No less an authority than Sir Roderick Murchison – then the worlds foremost geologist – doubted that payable gold would be found below water level in Victoria.

    The mass of the public in Victoria, Murchison wrote in a letter published by the Bendigo Advertiser, will gladly believe that auriferous treasures really extend from the surface to such vast depths in the solid interior of the earth. But, he cautioned, such a result be at variance with dear-bought experience in many other countries.

    An 1857 Royal Commission into the progress of the Victorian goldfields supported Murchisons view that mining of the Bendigo quartz reefs would be shallow and shortlived. Miners on the ground, however, were disdainful of the views dispensed by scientific mining men on the other side of the world. They were sinking ever deeper and still finding abundant gold.

    Bursting Balloons Of Copper Mineralisation

    Mesothermal and Greenstone Gold Deposits AKA Orogenic Geology Formation

    Porphyry copper deposits are usually formed by small igneous intrusions formed by hot, molten rock forcing their way through existing rocks. The ore minerals that contain the copper are mainly copper sulphides like chalcopyrite and bornite , and theyre found in networks of veins called stockwork. Each of the veins are only a few millimetres across, so you can imagine why it isnt efficient to try to remove just the copper minerals. In porphyry copper deposits, gold often occurs as either precipitated grains or in composite with copper-iron or copper sulphides. Gold would typically be in the order of a few several thousand parts per million in gold bearing minerals such as bornite or chalcopyrite.

    The minerals in the veins are deposited by water being forced through the rocks. As the magma rises through the earth, it cools and solidifies first at the edges, where the hot magma is in contact with the cold rock which it is being forced through. It rises up like a balloon, because it’s hotter and less dense than the rocks that surround it – just like a hot air balloon.

    Thinking back to locations, porphyry ore bodies tend to be either copper rich or gold rich, with some of the latter being clearly related to post subduction or post collision magmatic settings .

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