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Alaska Gold Prospecting

METHODS OF MINING

I will now describe the methods of mining in vogue in the early days, and compare them with those of more recent date. We have already seen that the first mining done in the territory was confined to the bars and banks of the streams, for the reason that it was considered impossible to reach bed-rock as in other regions, where less frost prevailed. In those days the principal means of separating the fine gold from the sand and gravel was the rocker. In all the methods used a common principle existed ; that is, the principle of gravity. Gold is nineteen times heavier than water, and seven to eight times heavier than rock, and although native gold is never pure, consequently lighter than pure, the difference does not affect the principle of extraction. Generally, then, the practical application of the principle to the separation of the precious metal from the dirt holding it, is an inclined plane, over which a stream of water is made to flow. The gold-bearing dirt is shovelled into the fast-flowing stream, which carries along the lighter material and leaves the heavy gold behind.

To aid in arresting and holding the gold, barriers are put in the bottom of the trough. Where there is plenty of water, and a head can be had, that is, if the water can be taken from a higher level to a lower one, a series of troughs are made of plank, as wide as possible consistent with the supply of water. These are elevated on trestles or other appliances, so that the water enters the high end and flows through them. They are fitted into each other at the joints, so that the strearn is continuous, and the line of three or more " sluice boxes," as they are termed, is sloped, to give the water momentum enough to carry down the gravel and sand, yet hardly move the gold. The progress of the metal is finally stopped by the barriers, called " riffles." These are in up-to-date gold-saving plants made of angle iron, cut into lengths the width of the sluice box, and bolted together at a constant distance from each other, in groups resembling a large gridiron. The groups are, of course, limited in size for convenience in handling. Sometimes, especially when the gold is fine, expanded metal and coco-matting are associated with the riffles. The metal is laid on top of the matting, so that its bars throw down the fine material and the gold is entrapped in the matting. The bars of angle iron in the riffles are set about an inch apart. The spaces soon fill with sand and fine gravel, but the small cataract formed by the water falling over each bar keeps a basin between them in which the gold and heavy material remains, the heavier bits at the top, and the lighter scattered along in proportion to their size and weight ; and the very lightest in the coco matting. In the early days the riffles were made of bars of wood, generally sections of small trees, cut in convenient lengths, placed parallel to each other, and held in that position by a section of plank nailed on to their ends. These sections of riffles, unlike those made of angle iron, were placed longitudinally with the sluice box, instead of transversely.

That system is all right where the gold is very coarse, but with fine gold a lot of it escapes. Small stones soon got wedged between the wooden bars, and pits in the sand were formed between them, as in the case of the angle-iron bars. Variations of the sluice box and riffles constitute all the methods of washing gold. Where the sluice box could be used, it always was, but it is obvious that on bar and bank mining there would be but few places where the miner could avail himself of it, and those only where a stream joining the main one came in with a rapid descent.