Small Mining

Rocker

At least double volume of gravel can be worked per day with the rocker as with the batea (pan). The rocker or cradle, as it is sometimes called, must be manipulated carefully to prevent loss of fine gold. With the rocker, the manual labour of washing is less strenuous, but whether panning or rocking, the same method is used for excavating the gravel.

The rocker, like the pan, is used extensively in small-scale placer work, in sampling, and for washing sluice concentrates and material cleaned by hand from bedrock in other placer operations. One to three cubic yards, bank measure, can be dug and washed in a rocker per man-shift, depending upon the distance the gravel or water has to be carried, the character of the gravel, and the size of the rocker. Rockers are usually homemade and display a variety of designs. A favourite design consists essentially of a combination washing box and screen, a canvas or carpet apron under the screen, a short sluice with two or more riffles, and rockers under the sluice. The bottom of the washing box consists of sheet metal with holes about 1/2 inch in diameter punched in it, or a l/2-inch-mesh screen can be used. Dimensions shown are satisfactory but variations are possible. The bottom of the rocker should be made of a single wide, smooth board, which will greatly facilitate cleanups. The materials for building a rocker cost only a few dollars, depending mainly upon the source of lumber.

After being dampened, the gravel is placed in the box, one or two shovelfuls at a time. Water is then poured on the gravel while the rocker is swayed back and forth. The water usually is dipped up in a simple long-handled dipper made by nailing a tin can to the end of a stick. A small stream from a pipe or hose may be used if available. The gravel is washed clean in the box, and the oversize material is inspected for nuggets, then dumped out. The undersize material goes over the apron, where most of the gold is caught. Care should be taken that not too much water is poured on at one time, as some of the gold may be flushed out. The riffles stop any gold that gets over the apron. In regular mining work, the rocker is cleaned up after every 2 to 3 hours, or oftener when rich ground is worked and gold begins to show on the apron or in the riffles. In cleaning up after a run, water is poured through while the washer is gently rocked, and the top surface sand and dirt are washed away.

Then the apron is dumped into a pan. The material back of the riffles in the sluice is taken up by a flat scoop, placed at the head of the sluice, and washed down gently once or twice with clear water. The gold remains behind on the boards, from which it is scraped up and put into the pan with the concentrate from the apron. The few colors left in the sluice will be caught with the next run. The concentrate is cleaned in the pan.

Skilful manipulation of the rocker and a careful cleanup permit recovery of nearly all the gold. Violent rocking should be avoided, so that gold will not splash out of the apron or over the riffles. The sand behind the riffles should be stirred occasionally, if it shows a tendency to pack hard, to prevent loss of gold. If the gravel is very clayey it may be necessary to soak it for some hours in a tub of water before rocking it.

Where water is scarce, two small reservoirs are constructed, one in front and the other to the rear of the rocker. The reservoir at the front serves as a settling basin. The overflow drains back to the one at the rear, and the water is used over again.

The capacity of rockers may be increased by using power drives. Such a device might be rocked by an eccentric arm at the rate of approximately forty 6-inch strokes per minute. The capacity of the typical machine with two men working is 1 cubic yard per hour. Where gravel is free from clay, the capacity may be as great as 3 cubic yards per hour.

[ Small Mining - Rocker Dip box Long tom Sluice Surf washer Dreging Dry washer ]

From: Bureau of Mines Information Circular 8517 by J.M. West, released in 1971.

Rafal Swiecki, geological engineer email contact
January, 2007

This document is in the public domain.