How is it determined that a mine has run out of gold?
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In large scale mining (not just for gold) core drilling is done to determine the size, concentration and extent of ore bodies underground. I used to work at what was the largest underground mine in North America, they had a very good idea of their target ore–the mine was on top of a large, roughly hemispherical ore body, the farther down they went the bigger it got.
It was a molybdenum mine high in the Rockies. They claimed that they were not in the gold business, though it was encountered from time to time–a well known historic gold mining area was just on the other side of the mountain ridge. Mine development was carefully planned by the engineers, where, when and how tunnels were drilled and shot, etc. Miners being miners, when they’d run across a gold vein, well, those carefully laid plans went out the window–the miners would start following the gold instead of the plans. Management teams would be brought in, concrete forms built to wall off the gold from access. For all that, though, rumors persisted that there was gold extraction going on behind locked doors up in the mill buildings.
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