For hundreds of years, mining operations processed high-grade gold from the richest mines in America and around the world. The valuable "mineral waste" that fell into the tailings, is the remainder from the mining and milling of only highly-concentrated ore, but - this is key - processing was limited to the techniques and technology of the 1940's and back into the 19th century.
Turn of the century mining operations used hundreds of shaker tables or sluice boxes that worked in harmony to process gold. The shaker tables, however, did not do a very thorough job of separating much of the fines and ultra-fines (-100 to -500 mesh), commonly referred to as fine gold, dust or flour. Much of this gold simply flowed off the tables and into the thousands of tailings, piled on the mines above-ground dumping sites.
The amount of gold remaining in these types of tailing piles can be very substantial. For example, a mine that operated from 1890 to 1910 that produced 10,000 ounces of gold would not be considered a particularly large mine. Yet, a loss rate of 20%, which is not extreme at all, could mean 2,000 ounces or more sitting in the above-ground tailing piles just waiting to be reclaimed, reworked and recovered using today's modern recovery systems.
The only thing that needs to be done to recover more gold from tailing piles is to run them once again. The real money here is in fine gold, but these old mining types of operations lost surprising amounts of large gold also, especially if the gold contained or is mostly composed of quartz or iron ores. Large gold-quartz /iron specimens just rolled through these systems along with the other rock and landed in the tailing piles.
When the term, "Tailings" is used, usually a picture comes to mind of heaps of useless waste dirt piles left over from digging out old mine shafts and tunnels to get to the vein of gold. In reality, mill and mine tailing piles can be highly valuable and a source of extreme profits.
Veins of gold run deep underground and usually found in about a 3-inch-wide seam; but a 6-foot wide tunnel or shaft was dug out, often hundreds of feet down to claim that 3-inch seam of gold.
However, ONLY the 3-inch-wide seam would have been transported to the PROCESSING MILL. The tailing piles at the dig-site contained the entire mine waste, left unprocessed and piled neatly above the ground.
THE VALUE OF A 3 MILLION TON, 50-FOOT-HIGH MOUND OF DIRT AND RUBBLE CAN QUICKLY TURN TO A GLIMMERING PILE OF TREASURE!
MW Mining and Inspections Gold