This equipment is known as Cradle. After the gold pan, rockers have been employed to evaluated placers in order to obtained concentrates with free gold. The equipment is good to work in small scale and can be operated easily in the same place or any lab. A rocker needs water and is necessary to be sure about the water source. One to three cubic yards, can be processed in a rocker per man-shift, depending on the water source, the character of the sample, and the size of the equipment. Basically, rockers are considered a small sluice and can vary in shape and size. They are 60 to 150 cm in length and 30 to 60 cm in width. The height is variable ranging from 15 to 60 cm. At the top, a screen is installed in order to reject coarse particles.
The rocker has three parts, screen, apron and sluice. The main body contains riffles that retain heavy particles. Screens aperture is 12 mm. Fine particles pass the screen and go onto the apron that feeds the material to the inclined surface with riffles (sluice). The rocker must be operated carefully in order to avoid loss of fine gold. With this machine, the washing task is not very tedious. However, to remove material trapped by riffles can be a little annoying.
The material is fed into the screen; the operator sits by the side the equipment and shakes it, at the same time water is added in order to wash and disintegrate any lumps formed on the screen. All the material minus 12 mm is transported on the apron that is equipped with a blanket so that fine gold can be trapped, and the other particles are transported on the riffled section. Technically, coarse, free gold particles and heavy material are trapped. By the shaking motion, lumps are disintegrated and screen apertures are not blocked, otherwise gold and heavy particles would be lost.
Ideally, two operators are required to operate the equipment and the water addition must be continuous and the flow has to be appropriated in order to don’t have excessive turbulence. Approximately the amount of water to be required is three to five time the weight of material to be processed. In general, the water addition depends on the mineralogical properties of the material to be tested.
Schematic view of rocker