Like so many other topics, people’s understanding of gold formation is incomplete. Gold is frequently associated with volcanic systems, not the volcanoes themselves. Rather than actually creating that precious substance, a volcanic system allows the gold to be transported by water through cracks in the underground rock layers while it comes towards the surface.
Liquid gold is not what moves through the earth. It is not actually inside the magma, either. The volcanic system may properly be described as a method of transportation. As the water cools, the gold which it was carrying will become solid and drop out of the water, usually becoming imbedded in white silicon dioxide, which becomes quartz. This is why gold is so often found associated with quartz.
Since the water which contains dissolved gold must follow these fractures up through the bedrock, quartz can be found in nearby concentrations. These become gold veins or lodes. These veins are where hard rock gold mines follow and remove the gold bearing quartz.
Usually, the ground where gold lodes are now used to be near volcanoes that perished many millions of years ago. To get an idea of the time span involved, some major gold-bearing quartz finds which are considered “younger” are about 400 million years old. A number of such deposits are estimated to be as much as 2.4 billion years old.
So, the volcanoes themselves didn’t bring the gold to the surface – they just formed in the same place as gold. This is because the magma which creates volcanoes had to follow the same cracks through the earth from deep below the surface as water which carried gold. The conditions which are needed for volcanoes to be created and gold being brought near the surface are the same. The gold may be found near volcanoes because those are the places it is most likely to reach the surface.
The crevices in underground rock formation which allow the metal-bearing water to be transported from deep beneath the earth are not the only reasons why volcanic systems may be home to gold deposits. Sometimes gold which moves toward the surface will become embedded in rocks underground. However, this may be just a stop during the gold’s journey.
Extreme heat from the magma beneath volcanoes can heat water which produces very hot acidic underground springs. These can dissolve surrounding rocks. Gold which was embedded in these rocks may then be released into the water. Because gold is so heavy, it will fall to the bottom of these reservoirs which are located near volcanoes. Over time, significantly large concentrations of this valuable material may accumulate.
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Unlike the gold which has been transported by water from deep underground until it cooled, gold which had been released by melted rocks into the reservoirs may still be superheated. Although a number of superheated reservoirs have been discovered beneath volcanoes, unless you have very advanced equipment, the gold will remain in those underground reservoirs. A conversation with a geologist today might go something like “Yes, we know there is a fortune down there, No, we don’t have a practical way to recover more than trace amounts.”
Why, one might ask, if gold was frequently brought to the surface near volcanoes, is it often found so far away from them? Given hundreds of millions of years, anything erodes, so some of the gold which was contained in lodes will be transported to other parts of the earth. The surrounding rock eventually is worn down into gravel containing gold or ultimately the gold flakes will be released and drift to the bottom of streams. It can then be recovered using placer mining methods.
Given millions of years, material doesn’t have to move very fast to travel great distances.
Next: Types of Placer Gold Deposits