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 (pH) or dissolved anions (think chlorine-rich seawater is more corrosive than your tap water) can dissolve solid gold and put it into solution. Just like regular water can dissolve table-salt or sugar and put it into solution.
So you have this hydrothermal fluid flowing through huge masses of rock (mountain-like, but underground) for a very long time, and when it goes up to the surface, it is channelled into thin conduits of fluid flow. During their ascent the conditions change (be it temperature or pH, etc.) and the water are not capable of carrying gold with them anymore. This results in the deposition of gold in that specific region.
I made an example, that I hope will help you understand this in a clearer way:
So in here you have rain water, entering the Earth in a large area and getting hotter as they descend down. It becomes possible for them to dissolve the gold from the large volume of rock. But also, because the water (now steam or a supercritical fluid) are hot they start to ascend upwards, usually through a narrow zone. When they cool down again, gold forms as a solid. For example, gold associated with quartz veins commonly forms through this process.
Now, what happens if these gold-bearing quartz veins are exposed on the surface? They may erode by rain and snow and get concentrated in river beds. So you can either mine the original quartz vein or the nearby river bed.
Gold has primary origin in hydrothermal veins and contact metamorphic deposits and pegmatites. Also occurs in placer deposits of secondary origin.
It is more easily found in veins that is related to igneous rocks rich in silica.
The main sources of gold are in hydrothermal quartz veins with pyrite and other sulfides. Gold is mechanically mixed with sulfides and not by chemical substitution.
In most of the gold grain is so finely disseminated that its presence can only be detected with microscopic techniques. Plenty of 0.004 ppm in the Earth's crust.
I do agree with Gimelist how gold is accumulated through hydrothermal fluids, adding that the main driver is for this process is volcanism.
There is, however, something interesting to be noted. We can find very 'old' gold of the Archean, more than 2 billion years ago, and mainly during 2 periods of the Archean, mainly hydrothermal gold in very old greenstone belts of the type described by Gimelist. Think of Canada, South Africa and Australia.
However, there is also very 'young' gold, Tertiary/Quaternary, in the Andes, Rockies, and Philipines, Papua New Guinea and Indonesia. Those are along the 'ring of fire', and it seems you need, at least nowadays, subduction of an oceanic, and maybe old, crust, to form strong volcanism that creates the hydrothermal processes described by Gimelist.
There is some gold during a few other periods, one around the formation of Pangea. That is the gold we find for instance in Spain. But worldwide it is much less than the other 2 periods, the ones from the Archean and the Tertiary/Quaternary one.
It is at least very interesting that we find mainly gold from mainly 2 periods, old and young, and that there is substantially less found in rocks from other era's.
Gold is found all over the world. Where it happens to be most economic to mine depends on a range of random factors, including political factors.
One big factor in gold mining is the cost of labor. Places where labor rates are low are more likely to have people mining gold. There are places in Africa where people dig up gold with their bare hands.
There is probably plenty of gold left in California, but do you really want to restart hydraulic mining, washing entire mountains into mud to get that gold? Hydraulic mining was banned in California over a 100 years ago, but hey as long as you are willing to destroy every mountain in the Sacramento valley, we could start it up again and turn California into a gold mining district.
[Above] Hydraulic mining. We could make California a gold mining region again, but do we want to?
I must agree some countries seem to have more gold than others. Using Australia as an example; There is more east coast gold finds, yet the west coast has produced more gold. The east coast states are more populated, so it would make sense more gold deposits where found. I read theories that gold was formed from stars going nova after the big bang. Prior to Earth's final formation these now ancient meteors/asteroids deposited gold all over the world. Gold would be found closet to the Earth's core. As gold is a heavy element and Earth's early stages, naturally more gold would be found closer to the core. Confused as Uranium is also heavy but only found in the Earth's crust. Once again I looked to Australia for answers.
Australia recorded only 180 impacts, compared to other countries recording over 900. Both Western and Northern Australia record three times more impacts than the East coast. The west coast produced veins of gold while the east coast produced huge nuggets and flecks. The east coast of Australia suffered volcanic eruptions. While the western and northern have few if any inactive volcano's. The vast plans would explain the veins, spread of impact over distances. All confirming the theory but not why uranium is found in the crust in these areas. Perhaps uranium was formed over time from impact of these asteroids or took longer to cook than gold during the big bang. Its odd though that uranium is proficient in the same areas.
I'm just a backyard scrub but for my two bob answer to your question, I'd say gold is more evident on larger continents that are more accessible. Remember Australia is wide as the USA with fewer mountain ranges and a tenth of the population.
In the 1900 a man near death and surely out of his mind returned to town claiming to of found a reef of gold a mile long. Harold Bell Lasseter had rode west to find his fortune, on finding it he lost his way home and the location of his fortune. For 30yrs Lasseter insisted on continuing the trek looking for his goldern mile, until eventually he died of malnutrition and exhaustion. Kalgoorlie in Western Australia was dicovered soon after. Kalgoorlie mines produce 850,000 ounces (28 tonnes) of gold per year. Lasseter reef has never been found.
