Page:Popular Science Monthly Volume 80.djvu/194

190 other conditions are constantly enabling the gold miner to treat ores of lower and lower grade. Ores that were once considered of too low grade to be of value are now treated at a large profit, and many a mine abandoned years ago as worked out has been reopened and has become very profitable; while the old waste dumps have been sorted over for ore that was thrown away as worthless in the early days.

In placer mining the same progress has taken place. The early work by hand with pans and cradles was replaced by sluices, then these by hydraulic machinery and sluices, while later the system of dredging the gravel was introduced. Each method marked a step in the economical evolution of gravel mining, and to-day in many parts of the west gravels are being worked which have already been handled several times over by older methods.

An important amount of gold comes as a by-product from the treatment of copper and lead ores, and to some extent zinc, iron and other ores, and as the amount of base metals mined is constantly increasing, the gold from this source will also probably increase.

When we consider the probability of new gold discoveries in the United States, the longer life of known mines under improved conditions, the increased production as a by-product from the base metals, the future of gold in the United States seems bright. For a long time to come the present production of approximately $100,000,000 yearly should easily be maintained and there is a strong probability that it may in time be greatly exceeded.