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Page:Popular Science Monthly Volume 72.djvu/76

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72
POPULAR SCIENCE MONTHLY

alone for use in this branch of business, and more than 200,000 miles in all the gold-producing states of America.

Placer gravel varies in value. The unit of quantity is a cubic yard. In the early days of a new field the ground must carry at least $1 per cubic yard to be attractive to the individual miner or small capitalist. Later, under consolidation and extensive operation, plenty of money can be made out of material carrying fifteen cents per yard, if the physical conditions surrounding the operation are good; that is, plenty of water available and a good dump. At a number of places in the west and in New Zealand good profits are being made from ground carrying much less than fifteen cents per yard.

The business of vein or reef mining is a very much more elaborate and complicated affair. The lodes or veins of gold-bearing quartz that nature has distributed in certain localities in the rocky crust of the earth are from a few hundred to a few thousand feet in length, so far as their outcrop at the surface is concerned, and from a few inches to a dozen feet or more in width. They extend downward no one knows how far, for as yet the deepest explorations made on any one of them have revealed no termination, though at several shafts in America, Australia and South Africa explorations have been pushed to depths of over 3,000 feet.

But the quartz of the vein changes continually in value. Here there may be but a trace of the precious metal, while a few feet or yards away a ton may contain as much as $50 worth. Generally, however, the gold is dispersed throughout the vein in patches called "ore shoots," so that certain areas are clearly payable and others not. This is wholly a relative term, depending upon the width of the quartz, its hardness, the nature and condition of the walls, the presence or absence of water, the price of labor, of explosives and of supplies in general, the cost of power for hoisting, pumping and milling, etc. In Mexico, America and Canada money can generally be made on a vein of a width of five feet, that will yield gold to the extent of $5 per ton, and in a number of instances, where the vein is larger, ore worth much less is yielding handsome dividends. Thus, the Homestake mine in South Dakota is paying magnificently on ore that produces on an average about $3.50 per ton, while the Treadwell mine at Juneau, Alaska, is doing finely on $1.50 rock. On the other hand, in Kalgoorlie, the great Australian gold district, where the veins are comparatively narrow but rich, and all working expenses high by reason of the desert character of the country, the costs connected with mining and milling rarely are less than $7.50 per ton, and in South Africa, where labor has been poor, company management expenses abnormally large, and the payable reef less than twenty inches thick, costs will average even a little more than in Australia.

Now that, at last, after centuries of irregular and haphazard pro-