In New Zealand, the gold fields formed in the southern alpine regions, due to geothermal activity that lifted gold from the crust and precipitated it out into quartz veins of ore. Glaciation then ground rock and ore, and post-glacial weathering washed the gold down the rivers of both the eastern and western catchments of the southern parts of Te Waka a Māui (the South Island).
As such, I would expect there to be significant levels of gold in the sediments of the cold glacial lakes (Wakatipu, Wanaka, Te Anau, Tekapo, and others). However, at up to 300+ meters depth and almost certainly covered in glacial silt, there would be no reasonable way to recover any of it without destroying the lake environment. The spoil from dredging in the surrounding rivers is enough of a blot on the landscape.
The process described by @si_blakely above covers both of the most important mechanisms for gold deposits. You get either gold deposited in mineralised veins or alluvial deposits. One of the more impressively astounding things I learnt about geophysics is just how potent water is. At geological depths the pressures are so large that water can achieve very high temperatures. It is astoundingly active in this state and will dissolve almost anything. Including, in the right circumstances, gold. So highly mineralised water can percolate up and eventually deposit its load into the building geology at shallow depths. This is why geologists get really excited by complex deep faults. Gold is found intermixed with quartz, as both have been deposited from the same source. But alluvial gold is important as alluvial processes act to concentrate the gold in the alluvial deposits. Even the huge deposits in the deep South African mines is of ancient alluvial origin. Sourced from long gone mountain ranges ground away in ancient geological times. The Olympic Dam mine deposit in Australia is of hydrothermal breccias, where mineralisation of copper, gold, silver and uranium are found in the fissures between the breccias as deposited by hydrothermal processes. IMHO there is more than one as yet undiscovered Olympic Dam sized deposit in the same geological region. But that isn’t the USA. But you get the idea.
Like oil, the easy alluvial gold is probably gone. Making your fortune with nothing more than hard work and a pan isn’t going to happen. But industrial level extraction of lower quality ores, especially when the prices are high, is another matter. Higher prices mean there is much more economically recoverable gold, so estimates of reserves can be fluid. Once shuttered low grade mines have re-opened worldwide as the prices increased.
The trouble is that once you get past easily accessible alluvial deposits discovery gets vastly harder. Deposits may be hundreds of metres underground. You need expensive technological exploration, and deep pockets to get into the game. Even when found, economic viability remains difficult. Olympic Dam gets 0.5 grams per tonne of gold. It is only viable because of the copper. But there are 600 million tons of ore down there. So how you measure reserves remains difficult.
Thanks, F_V. That answers my question. The chances of someone going to some remote area in the US and finding a stream filled with gold flakes and nuggets like they did in 1848 in California is not plausible. Such surface gold has already been discovered and removed. You need high-tech and very expensive machinery, along with high gold prices, in order to process enough low-grade ore to make your fortune. That’s still possible, but out of reach for almost everyone except the already wealthy risk takers.
A majority of the gold is mined in Nevada, especially the northeast, there’s lodes left. Alaska likely has tons, the matter is how environmentally and politically certain this is. The on-again and off-again Pebble mine appears to be off now.
It probably never was (as your smiley indicates you know).
I recall reading in a geology book that “lost mine” legends are common wherever gold was found - but they are almost always bogus. The purpose of these legends was simply to provide a plausible way of “laundering” stolen ore.
So, with a looming global copper shortage for EVs and green grid components, the EPA just closed off one of the largest untapped copper deposits. That’ll make the transition more expensive and harder to push.
Working over the tailings of a previously worked-out gold mine is certainly a thing, if the price of gold rises to the point where it is economically worth it.
