Mining gold is a dirty business. Refining gold is a dirty business.
Surprise, surprise.....recycling gold is a dirty business.
...While working on a project on problems with a heap-leach operation here in Nevada I was lucky enough to get to watch a "pour". Don't remember what the approximate net value was, but there was about a 1/2 dozen solid gold ingots at least. It's something to see.
They would't let me keep the booties I had to put on when I went in. Darn.
When I was out there it was cost effective to mine as long as the gold price was over $250/oz, and their nominal grade of ore was .08oz gold per ton of ore. A ton is about 3 55gal barrels of dirt, and as I recall, the gold, at that grade, is about a 3/16" cube. Pretty impressive technology when you think about it.
(heap-leaching is where they mill the ore, often in the range of .1ozgold/ton ore, pile it up 10-20ft deep over a rubber liner spanning an acre or more..then drip cyanide through to gather up the gold. The cyanide collects in a pond. Then they filter or electroplate the gold out)