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Gold is one of the most popular materials in the world.
It's used to make jewelry, coins, and electronics. People have mined for gold for thousands of years.
But where does it come from?
In this blog post, learn about the different types of gold deposits found in ancient history and how they form.
Gold is a chemical element. Its atomic number on the periodic table is 79. It has a very high density, and it's usually found in nature as gold (III) sulfide, also known as "native gold." Native gold is quite rare. Most of the time, you'll find metallic gold attached to another mineral.
To get pure native gold, we have to smelt elements together at extremely hot temperatures. This process can be done with other metals and sulphur (S).
How is gold formed?
Gold deposits are formed through a few different geological processes, which are usually found in association with quartz, pyrite, and sulfide minerals- this become clear ever since gold was discovered.
Geologists have five primary theories of how gold forms: hydrothermal replacement, magmatic replacement, metamorphic replacement, seafloor hydrothermal fluids, massive seafloor sulfides.
Hydrothermal veins are created when hot water circulates through cracks in the Earth's crust.
As this water becomes heated by the surrounding rock, it begins to circulate back towards the Earth's surface, where it cools down and heats up again, over and over again.
Gold is soluble in water, so it will dissolve into these waters while they're moving.
These waters pick up a lot of different minerals as they move through the Earth's crust, and many of these minerals become part of the hydrothermal vein.
If these hot waters come in contact with rocks that aren't very stable, they might form gold deposits when they cool down and leave behind evidence such as quartz or pyrite.
Gold can also be created during the cooling process of magma (melted rock).
When magma is lower than the Earth's surface, it tends to release its dissolved minerals, including gold.
That means that if you see veins or pockets of quartz, that could mean that there once was magma present, and it's likely that this area has some amount of gold.
Gold can also form when minerals are changed by the pressure and heat in the Earth's crust.
For this to happen, you need increased temperature and increased pressure.
This type of deposit is called a metamorphic hydrothermal deposit because it forms in the same way as hydrothermal deposits do.
4.Seafloor Hydrothermal Fluids
When gold is in a rock with a lot of heat and water present, it can be pushed towards the surface through hydrothermal vents, which can eventually collect as placer deposits.
The original deposit will stay deep in the Earth's crust, but over time, when erosion breaks down these rocks, the ore minerals will become much more concentrated in riverbeds.
These are often found to contain large amounts of gold because they traveled so far from their original source. Some deposits may also form alluvial fans.
These look like big fluffy piles of sand which accumulate around rivers and streams. When there's a sudden drop (a waterfall) near these rivers and streams, this area becomes very concentrated with minerals.
Gold will mostly be found in these areas starting at the top of this alluvial fan because it was the first area to form and collect gold.
Where is gold found?
The history of gold points to the formation starting with igneous (granite), metamorphic, and sedimentary rocks.
The locations on Earth where gold is most commonly found are called "gold belts."
These locations are generally long but mostly narrow strips that follow structures like mountain ranges or fault lines.
Gold belts can be found all over the world, but there are a few places that have a lot of gold.
The largest deposit is in South Africa, and this deposit is called Witwatersrand Basin.
You'll also find significant deposits in Australia, Russia, China, Canada, the United States, Mexico, Peru, Central Europe, Scandinavia, Germany, Spain, Portugal, Great Britain, and Ireland.
How is gold processed?
In order to turn gold into bullion, it needs to be smelted from its ore which creates jobs in its process.
There are a few different ways that this can happen:
This is a method of producing gold by smelting copper and silver together in a furnace at very high temperatures. The metal gets separated from the mixture when it comes out of the furnace and is placed in a crucible. This process almost always creates silver dendrites that look like branching veins or tree branches. These are rarer than pure silver but still valuable. Once you get rid of these, you'll have pure gold bars.
Carat Process is an older way of turning smaller gold (less than 50 pieces) into gold bars. It's done by mixing all the different pieces of gold together and then heating it until the smaller pieces melt and runoff, leaving behind only larger gold nuggets. This would leave you with a smelted lump at the end that you could then pour into molds to make your gold bars or ingots.
Gold Dust Process
This method will work if you've got small pieces (smaller than 1/4 ounce) of gold. It involves dissolving loose bits of ore in concentrated acids like sulfuric acid. Once there is no more visible chemical reaction, the solution can be boiled away, which leaves behind nothing but a fine powder that can be poured into a mold for bullion bars.