Are precious metals, such as gold, continuing to be produced naturally or was the gold found during the 1800’s the result of processes during early Earth formation that are no longer occurring?
All the gold atoms were created before the formation of the earth (claims of alchemists not withstanding)
The element gold is not “produced” on the Earth. All of it that we have was gathered up during the formation of the Earth.
That having been said, the same geologic processes that produce gold deposits are still going on today - for the most part.
The American Museum of Natural History has a good page about How Gold Deposits are Formed.
Does that mean that we could have gold rushes in 100,000 years similar to what we saw 200 years ago, at least theoretically?
OK, let’s break this down into two bits:
-
Gold, itself, the element, as it exists in the crust and upper mantle, is mostly of extra-terrestrial origin (the gold that was originally in the pre-Earth nebula is in the core and never coming out.) This meteorite gold was emplaced during the Late Heavy Bombardment, and that’s not happening again, so what we have is mostly what we’ll always have - any asteroid impact after now is not going to have a significant effect).
-
Ore deposits of crustal gold are still being created, especially the hydrothermal ones. BUT some of the processes that created the biggest gold deposit in the world, the Witwatersrand Basin (50% of ALL gold ever mined comes from the Wits), *aren’t *still possible - large-scale placer deposits of that order of magnitude don’t occur anymore on an Earth that has stabilizing vascular plant life. and there’s some evidence the gold deposition had a biogenic component that would involve bacterial mats that wouldn’t survive in those environments today, amongst other factors. The Archaean Earth was a very different place.
In a similar vein, large igneous provinces of the kind that gave rise to the biggest platinum deposits are also likely characteristic of a particular set of events, so something like the Bushveldis unlikely to happen again in the same way, but similar processes could still lead to viable ore bodies in the future. But likely not on that scale, IMO.
Definitely not.
In 100 million years? Maybe.
I don’t think people really understand the timescales involved - 100, 000 years is an eyeblink in geological time. It can take 100s of kiloyears or more for the largest ore bodies to form - there’s a considerable amount of reworking and/or concentration that has to happen, whether that be placer processes or fractional crystallization in a layered intrusion.
The Wits basin, for instance, is 6 km thick, and was laid down over 260 million years. And that’s ignoring the original emplacement of that gold in the placer’s source rocks.
Magmatic processes are a lot faster - only 200 000 years for the 7-8km thick Bushveld Igneous Complex (the source ofmost of the world’s Platinumand other PGEs) to solidify.
Hydrothermal deposits are faster, but remember that they’re just moving and concentrating metals that had to be deposited as primary ores somewhere else, so that needs factoring in.
Looks like gold can be produced through nuclear transmutation from a few isotopes of other elements.
Whether such transmutations continue to happen naturally isn’t so clear. But with significant energy input we can make it happen in a particle accelerator. Not cost effective though.
To be completely accurate, very very very tiny amounts (like, one at a time) of gold atoms are going to be formed on Earth occasionally, as something radioactive decides to decay on a path that leads to gold, or a stray alpha particle hits an Iridium atom in just the right way or what not. A few gold atoms are also being destroyed, too.
My random guess – not really being up on nuclear reactions and whether there are any common decay paths to gold-- is that gold is stable but moderately heavy, so probably there’s a rough balance between creation and destruction. But again, we’re talking about individual atoms, which don’t matter on human scales.
If they’re left alone, some placer deposits (gold in stream beds) will gradually replenish themselves as the stream churns sediment around and moves it downstream from the source. The “if they’re left alone” caveat is a big one because historic mining operations usually involved dredging and processing the majority of the sediments in a stream system, and often working upstream to the source of the gold (the “mother lode”) and mining that too. However, hobbyist gold miners often work placer deposits that weren’t rich enough to attract intensive historic development but which produce enough to pay for the equipment and beer. With those deposits, the weekend miners can work a section of stream and then work it again the next year after the spring runoff has cycled the sediments around.