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Gold-min′ing.

The different modes of collecting gold in the placers of California — and the same is true of some other places, Australia, for instance — are familiarly known as panning, winnowing, cradle-rocking, washing with the long-tom or the quicksilver-machine, jamming or turning the course of a river, burrowing or tunneling, ground-sluicing, sluiceboxes in connection with the hydraulic process, or water-jet. See list under metallurgy ; mining.

In panning, the operator takes his station by the edge of the water, dips his pan, which he holds by the rim, and then imparts to it a rotary and oscillatory motion, occasionally stirring up the earth and mashing the clods. The large stones are thrown out and the water caused to circulate around the inside circumference of the pan, the heavier portions, including the gold, collecting in the center, and the lighter matters being discharged over the edge. The residue, consisting of fine gold and black sand, is separated after being dried.

The winnowing operation is practiced where water is not available, and consists of tossing in a blanket the finely powdered and dry earth, depending upon the wind to blow away the lighter particles.

The cradle is a box about 3 1/2 feet long, 20 inches wide, and 18 inches deep. The top and one end are open. Upon the rear half of the top is fitted a box with a perforated sheet-iron bottom. This box receives the earth, which is disintegrated therein, and passes through the holes as the cradle is rocked to and fro. Water is bailed by hand from the stream, and the gold is arrested in its passage by wooden cleats placed on the inclined bottom of the cradle, while the lighter matters are carried out at the end by the stream of water. See cradle.

The long-tom consists of a shallow, inclined trough, from 10 to 20 feet long and perhaps 16 inches wide. At the lower end is an upwardly inclined perforated plate to arrest the gold which falls through the holes into a box below, while the tailings pass over the end by the force of the stream of water which is introduced into the upper end of the trough. The gold is collected by riffles in the box, and quicksilver is added to amalgamate the finer particles, if necessary.

The quicksilver-machine is somewhat similar to that last mentioned, but is intended to bring all the gold in contact with mercury, the amalgam being afterwards treated for the removal of the mercury. See amalgamator.

In jamining, the water of a river is turned into a temporary channel while the bed is explored for gold.

Burrouring or tunneling are adopted as a more economical means of reaching the lower strata or more valuable deposit upon the hard pan, or ancient river bottom, instead of digging away or working over the whole mass of superincumbent earth.

Ground-sluicing consists in turning a stream upon a bank of earth to remove it and uncover the more valuable strata below, the auriferous deposit in the upper portion being detained by its gravity to be washed with the lower denuded layer of pay dirt.

Hydraulic-mining by jet and sluice-boxes has given rise to some of the greatest engineering works of California. A series of boxes about 14 inches in length and 3 feet wide, called sluice-boxes, are fitted together at the ends so as to form a continuous trough, as long as may be desired, sometimes extending several thousand feet. The earth and stones are washed through this sluice by the force of a strong current of water, often brought from a great distance. The sluice has a flooring of wooden blocks which offer some impediment to the passage of the earth, and afford crannies for collecting the gold, and for holding the quicksilver by which the finer particles of gold are arrested and amalgamated. The bank of auriferous earth is washed into the sluice, thus prepared, by means of a powerful stream conducted through and directed by a pipe in the manner of a fire-engine. The water is brought to the scene of operations from immense distances, in some cases over one hundred miles, and the flumes and canals which form a network over the country are among the most remarkable local features (see flume). To quote from the description of “A miner of 1849,” Harper's Magazine, April, 1860: —

“To shovel a mass of several millions of tons of earth into this sluice for washing would be too expensive. By means of water directed through hose and pipe the labor of many men is cheaply performed, and the hill torn down to its base. The water is led through india-rubber or double canvas hose, and generally from a great hight above the scene of operations. It is consequently thrown with such force as to eat into the hillside as if the latter were sugar or salt. Several of these streams directed upon a hillside bring down more earth than could be thrown by one hundred men with picks and shovels. But the art of the miner does not rest here. He undermines as well as breaks down, working in a single cavern in the hillside with his water batteries until the earth topples over like an avalanche.” See hydraulic-nozzle.

By a combination of shovels and the current of [995] water the earth is then carried into the sluice in which it is disintegrated and washed down with great rapidity, the gold catching, as has been observed, in the interstices between the blocks which form the floor of the sluice. See amalgamator.

1877.

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