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    The Origin and Formation of Gold: From Cosmic Events to Earth’s Crust

    Where Does Gold Come From?

    Ah, gold. The most popular precious metal in the world has held sway over civilizations for thousands of years. The first coins in recorded history were made from gold, and it’s certainly no less popular today.

    However, despite its familiarity across almost every human culture, there is still much we don’t know about how gold forms on earth or, for that matter, where it comes from. So, we present this page to you in order to explore the origin of the world’s favorite precious metal, along with the science behind its formation.

    The Cosmic Origin of Gold

    As integral as gold has proven to be to residents of Earth over millennia, its true origins are thought to be far more cosmic in nature. In fact, the two most-accepted theories for the primordial creation of gold are due to certain activities of the stars.

    Before we discuss the theories in question, we first need to discuss the rapid neutron-capture process. Better known as the r-process, it is a group of nuclear reactions that create heavy elements like gold. In essence, nuclei with atomic masses equal to or less than that of iron (56) capture neutrons and combine to form new, heavier nuclei. While lighter elements can be formed through the nuclear fusion found in stars, heavier atoms must begin as lighter ones and capture neutrons until they reach stability.

    Needless to say, the r-process requires incredible amounts of energy to proceed. So, it takes truly cataclysmic events to initiate the formation of gold and other heavy metals. In fact, the r-process is theorized to occur in two specific types of astrophysical events.

    The first of these events is a supernova. A supernova is the sudden and dramatic end of a star’s evolutionary process and takes place either when a star experiences accelerating and runaway nuclear fusion or the star collapses into itself.

    The incredible energy release present in a supernova thus creates a conducive environment for the r-process to take place. This process is known as supernova nucleosynthesis.

    The other primary way that gold likely came or comes into being is through the collision of two neutron stars. When two neutron stars get into the same orbit, they eventually collide. The collision generates sufficient energy and the proper conditions for the r-process to occur once again and create more gold nuclei.

    In either scenario, the resulting gold (and lots of other stuff) is flung out in infinite directions away from the supernova or neutron star collision. Some of the flung gold ended up in the precursors to our solar system.

    Gold’s Journey to Earth

    This cosmic flinging affected the formation of many systems, including the massive group of molecules that would eventually become our Sun and solar system. However, the methods by which gold came to Earth vary wildly according to the time when it came and the area of the planet involved – the crust, the mantle, or the core.

    Gold exists on Earth on all three of its layers. Gold first came to Earth during the early days of the planet’s formation. At the time, Earth was in a molten, rather than a solid state. As a result, any gold that entered its system sank to the core at the middle of the planet, rather than remaining on the crust (the surface) or within the mantle (the molten middle).

    However, as we are still finding plenty of gold on the surface, we are somewhat certain that the gold we find was not present during Earth’s formation. The “late veneer” theory aims to solve this quandary by suggesting that the terrestrial gold (and other heavy elements) came to the planet via comets and asteroids. As the theory goes, comets and asteroids picked up gold as they formed and, when they collided with earth, spread the gold into the crust and mantle.

    Some scientists have posited a different theory to the late veneer. The “mantle return” theory instead postulates that the gold found on the Earth’s surface is from the core and has migrated to the surface through mantle plumes.

    Whether either theory is correct or some other process is at work, there is no denying that Earth’s gold is the stuff of stars and is not a native product of our planet.

    Gold Formation in Earth’s Crust

    However, its presence doesn’t guarantee that it would end up accessible to us, regardless of where it is on Earth. It’s mostly still in the mantle, rather than lying around to be found. It is only through two geological processes that gold becomes a collectible commodity on the surface of the planet.

    Hydrothermal processes

    One mechanism to bring gold to the Earth’s surface is via one of two hydrothermal processes. Both of these processes involve superheated and molten fluids rising to the crust and cooling.

    In the first process, magma oozes up from the mantle and cools, usually during a volcanic eruption. Magma, of course, is molten rock and is composed of various elements and minerals. One of those elements is gold, and due to gold’s atomic weight (which exceeds most other common elements), the metal ends up settling out into a vein or deposit. These are known as intrusion-related deposits.

    Magma is not, however, the only fluid that exists in the mantle. There are water and noble gasses floating around that pick up gold as they flow through the middle layer. Sometimes, these fluids also make their way to the surface and – like magma – cool when they encounter colder air. The gold precipitates out of them and forms lode deposits.

    In either case, these processes create deposits of gold known as primary sources. A gold vein or deposit is almost always the product of one of these processes. Other minerals, such as quartz, also play a significant role in gold formation in hydrothermal deposits.

    Placer deposits

    The other areas where gold collects are known as placer deposits. Once gold has settled on the surface, it may migrate from its source and collect elsewhere.

    The first migration method is via an alluvial deposit, which occurs when water or another liquid picks up particles of gold from a primary source. Because gold is so heavy, it can only travel this way for a time, either through a river or stream. It tends to hang up and collect in certain areas where the water’s flow enters a bottleneck or bend.

    The other secondary deposit method is known as an eluvial deposit. In this case, the gold doesn’t so much travel as get exposed via erosion or other weathering that reveals the gold-bearing portions of a rock.

    These areas are known as placer deposits. They are secondary sources, and cannot form without a primary deposit of gold relatively nearby.

    Factors Influencing Gold Formation

    Both of the primary methods of gold deposit mentioned above are geologic processes. Naturally, gold forms near areas where other geologic processes are also evident.

    The first type of area where gold forms is within extremely old geologic formations. These formations are commonly known as greenstone belts due to the presence of low-silica metamorphic rocks and several associated minerals, which happen to be green. Since these arise from ancient ocean formations (which involve magma), gold deposits often occur.

    The second type of area is anywhere where earthquakes and/or volcanoes occur. The movement of tectonic plates allows plumes of magma and other bits of mantle to rise to the surface. With those plumes comes gold.

    Finally, gold is often found near veins of quartz, as these minerals are old and capture gold over scales of geologic time. In other words, we take gold from these areas as the final act of a process millions of years in the making.

    Modern Gold Production and Extraction

    There are several ways that we humans can secure gold in our possession. The most productive of these processes is through the purposeful mining of gold by cracking open larger rocks in order to extract the gold within. Getting gold in this manner is usually performed in major operations with large equipment and great amounts of ground or material.

    Gold may also be mined as a by-product of mining for other metals, too. In particular, gold is often found as a side benefit of mining for copper.

    Finally, panning for gold or prospecting is a form of gold mining. It’s the one most accessible to the average person, but it is also the least productive.

    Gold that comes out of the ground is not necessarily the purest, however. In fact, it rarely is, and it must be refined in order to reach the appropriate levels of purity for jewelry-making or other purposes.

    The most common ways to refine gold ore usually involve subjecting the ore to various elemental gasses or fields, which bind to the various non-gold portions of the sample and are made easier to sift out. Usually, chlorine is the gas of choice for this endeavor, but there are also some occasions where mercury is used to refine.

    The other type of refining is similar, but involves using electric current to separate the atoms of a sample. However, it is also more costly, so the chemical method is more popular.

    With either mining or refining, there are significant environmental concerns at play. Mining can disrupt the integrity of the grounds used, the groundwater, or create artificial tectonic situations. Refining uses chemicals or processes that can be dangerous to the public if not used or practiced responsibly.

    So, although it’s great that we can get nice gold in hand, it takes quite a bit of work and at least some risk to the environment to gather.

    The Ongoing Mystery of Gold

    Gold’s story is not over by any means. There are undoubtedly veins and deposits that remain undiscovered on the surface of the earth – particularly underwater.

    It is also possible that more gold may come to Earth the old-fashioned way, so to speak. If the late veneer theory is true, then there’s no reason to assume that more asteroids and comets will bombard us with more gold. Of course, that bombardment may come with other problems for us, but there might be fresh gold.

    It’s also possible that we might invent a technology to capture some of the gold dust that continues to float around near space in the future. However, we’re not there yet, and it’s hard to see how such an operation – even if feasible – would be financially viable.

    What’s more likely is that we will figure out a way to synthesize gold. To do so requires creating many of the same pressures and processes associated with the r-process. At this point, scientists have created small quantities of gold in the lab, but the samples aren’t stable or of appreciable size.

    The clearest thing, though, is that the human demand for gold is not stopping anytime soon. So, with the future may come innovations for gold that we haven’t even conceived.

    Conclusion

    Gold is literal star dust. It comes from the remnants of stars, either in the form of supernovae or when two neutron stars (themselves the products of supernovae). It came to Earth before the planet cooled to a solid state, and it will be here long after we’re all gone.

    However, the search for new gold continues. More mines will open, better refining methods will arise, and new sources of the metal – either natural or synthetic – will be discovered.

    The future looks bright for gold. From gold’s perspective, the future is indistinguishable from the time before time, anyway.

    All Market Updates are provided as a third party analysis and do not necessarily reflect the explicit views of JM Bullion Inc. and should not be construed as financial advice.