The working over of old dumps has become quite a feature of the mining business. It is due to two things; one, the carelessness and extravagance of the old operators and the improvement in the treatment of low grade ores.
In old days when railroad accessibility was scarce and - smelters far distant, and when only high grade ores could be shipped or treated with profit, any ore below a certain standard went over the dump.
Again, on a fairly rich surface property the hasty eagerness to get rich quick caused a somewhat indiscriminate system of sorting, if sorting was done at all. Instead of ore or rock being broken on the sorting table to the size of a walnut before being done with, big chunks that looked poor were thrown into the waste bin.
Again, when we consider how hard it is often to see and recognize free gold at sight, or to detect it from pyrite, especially where, as in some cases, it is rusted and coated over till it is as brown as an autumn leaf, what possibilities there are for much of such hard to see, or invisible gold, going over the dump.
When sorting has been careless or ignorant, or the early management of a mine extravagant and wasteful, there may be a rich harvest for the modern man who comes later with his cyanide process to work over the old dump to his profit.
In the case of Cripple Creek ores the chances of rich tellurlde ores going over the dump, unless there is the closest kind of sorting, are remarkably good. Anyone acquainted with those ores knows how minute generally are the little blades of rich gold-bearing telluride, how readily they, as also the brown, rusty, free gold might be overlooked or mistaken for something else.
Moreover, it is quite possible for a grain of free gold or a crystal of rich telluride to be enclosed in a fragment of rock no larger than a pea, and to be quite invisible and easily discarded.
What to do with the dump of mines is often a serious problem. In locating a mine or mining prospect, one of the first things to see to is its facilities for dumping. In the case of a vast undertaking, like the Newhouse tunnel, for example, projected to run with a broad gauge for several miles into the mountain, it was necessary to take up quite a large acreage of land in the river bottom on which to deposit the waste that would come out from the tunnel.
Sometimes a mine is located near the bottom of a valley and for some time there is sufficient dumping room. By and by the prosperity of the locality causes a town to grow around the mine, whose streets and houses congregate around the dump.
By degrees the dump keeps growing and advancing, like the snout of a glacier, and threatens to overwhelm houses and streets. As mines cannot consume their own dump, they sometimes get over the difficulty by carting it away and filling up ravines or leveling up town lots or building roadways.
Some mines have actually been discovered in the heart of a town, and houses and lots have been bought up at great expense on which to deposit the dump.
On the sloping side of a hill the dump of the mine above is apt to encroach on and threaten the works and dump of the mine lower down. In this case for a time cribbing by square sets is resorted to and dumps may be cribbed back, tier upon tier, above one another. Some of these cribbed back dumps are 50 to 100 feet high. In time the timbers may rot and the dump pour down like an avalanche on cottages built below it in supposed safety.
At Cripple Creek railroad tunnels pass clear through dumps, the sides of the tunnel being securely timbered.