It's geology, but a lot of locations have small amounts of gold if you pan them. I had a friend who hung out with a prospector who had a lot of his fellow prospectors over for supper while my friend was their. They went and got a pan full of gravel from the river and dumped it on the table and the prospectors all sorted it out. There were garnets, gold, etc. The results were worth a few dollars, but the amount of work vs the value was such that you could make a little money every day if you wanted to do the work, but you could find a job and make more. One of the prospectors had a silver mine with a vein in it and he was following the vein through hard rock and would go work in it whenever he needed a little cash. Places with gold will probably ALWAYS have some gold there. It's just less and less as people work them. But sometimes the amount gets refreshed by more soil getting washed out by a good rain. Very few have enough to make a living, but some do. My location there really isn't any because of the geology again. What you find here is a lot of limestone and some very nice flint nodules. The American Indians were quarrying the flint for the last few millennia. The guy who built my house was in California during the gold rush and he and his friends were making about $200 a day sluicing all the dirt in the area. Most of the work was digging ditches to move the water and shoveling dirt. They never completely ran out of gold in any given spot, but it would reach the point where it was more profitable to move somewhere else.
